共查询到20条相似文献，搜索用时 78 毫秒
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《淮北师范大学学报》2016,(4)
研究一类带有Holling III型反应函数的捕食-食饵模型{ì?dx(t)t?)[r1(t)-a(t)x(t-τ1(t))-b(t)íd=xt(∫t-∞k(t-s)x(s)d]c-1(t)x(t)y2(ts)m2y2τ(t)+x2(t),?dy(t)d=y2(t))y(t-τt(t)[-r2(t)c+2(t)x(t-))2(t?))m2y2(t-τ2(t+x2(t-τ2(t))].运用重合度拓展定理,证明其存在2个正周期解.并举一个实例验证结论的可行性. 相似文献
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在正规线性空间上讨论微分方程系统X′(t)=F(t,x,y)X′(t)=ε.G(t,x,y),这里参数ε很小。证明了如果F和G满足Lipschitz条件,F(t,x,y)对y的小的值是指数稳定的,系统在x和y对1/ε阶时间周期的持久扰动是稳定的。考虑扰动系统X′(t)=F(t,x,y) J(t),X′(t)=ε.G(t,x,y) K(t),这里J(t)和K(t)从S到S 1的积分值很小。从而得到存在仅依赖于F和G的常数A,B,C和λ,使对σ≤λ,如果初始值和持久扰动比σ小,且ε≤σ,则解X(t)和Y(t)对一切时间t有界σAeBtε,使得σeBtε≤C。 相似文献
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研究了具无界时滞多滞量的非自治Logistic方程X′(t) +∑mi=1ai(t)〔1+x(t)〕x(t-τi(t) =0的零解的全局渐近稳定性 ,获得了方程的零解为全局渐近稳定的充分条件 ,所得结果推广并改进了许多熟知的结论 相似文献
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古伟清 《韩山师范学院学报》1993,(3)
本文讨论了线性非自治时滞微分方程 x′(t)+sum from i=1 to n p_i(t)x(t-τ_i(t))=0的解的振动性,给出所有解振动的充分条件,改进了文[1,2]的结果. 相似文献
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研究了一类具非线性扩散系数和阻尼项的双曲型偏微分方程系统(a)2u1(x,t)/(a)t2+m(t)(a)u1(x,t)/(a)t=ai(t)hi(ui)△ui+n∑j=1aij(t)hij(u1(x,t-τj(t)))△ui(x,t-τj(t))-m∑k=1bik(x,t)uk(x,t-σ(t)) (x,t)∈Ω×R+≡G,i=1,2,…m,获得了该方程组在Robin边值条件下解振动的充分条件. 相似文献
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利用重合度理论研究了在脉冲条件下二阶非线性脉冲中立型泛函微分方程[x(t) cx(t-τ)]″=f(t,x(t-σ)),t>t0,t≠tkΔx(tk)=gk(x(tk)),Δx′(tk)=hk(x′(tk)),k=1,2…的周期解的存在性,得出了该周期解存在的充分条件。 相似文献
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题目:在图1中,平面镜MN竖直放置,发光点经平面镜所成的像为S′.保持S不动,使MN在竖直面内绕O点按顺时针方向转过α的过程中,试确定S的虚像S′的运动轨迹.图1图2解:建立如图2所示的坐标系.各位置坐标为O(0,0),S(m,0),S′(x,y).MN与x轴的夹角为θ.所以,镜MN的方程为y=xtanθ.S与S′关于MN对称,所以直线SS′的斜率为k=-ta1nθ.(1)设SS′的中点为C,所以,C(x 2m,2y).因为C∈MN,所以y2=x 2mtanθ.(2)tanθ=-x-ym.(3)代入(2)式得y=-(x m)y(x-m).化简得x2 y2=m2.所以S′(x,y)的轨迹为以O为圆心,m为半径的一段圆弧.用数学方法解一道竞赛… 相似文献
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1 设元代数 ,化已知为未知例 1 若x =12 2 0 0 2 - 12 0 0 2 ,求x2 1 x的值 .分析 2 0 0 2是一个较大、带根号的无理数 ,直接代入较复杂 ,尝试用字母换元代入 .解 设 y=2 0 0 2 ,则x =12 y - 1y ,x2 1=14 y 1y2 ,因为 y 1y >0 .所以原式 =14 y 1y2 12 y- 1y =12 y 1y 12 y- 1y =y =2 0 0 2 .例 2 计算36 33× 36 35 × 36 39× 36 41 36 -36 36 × 36 38.解 设 36 37=t,则原式 =(t - 4) (t- 2 ) (t 2 ) (t 4) 36- (t - 1) (t 1)=(t2 - 10 ) 2 - (t2 - 1)=t2 - 10 -t2 1=- 9.2 设元代式 ,无理变有理有些题目的… 相似文献
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罗艳萍 《读与写:教育教学刊》2008,5(6)
The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity. 相似文献
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邱崇丙 《唐山师范学院学报》2014,(1):21-23
汉字的六书,《说文》对“转注”一类,语焉不详。后世学者提及转注,也仅限于许慎所举出的例字。《汉字例说》一文,作者从转注的角度综合考虑,对部分现代常用字作了分析,跟传统的解释有所不同。希望能抛砖引玉,互相切磋,以推进学术研究。 相似文献
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Richard Denner 《海外英语》2007,(4):14-15
Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose. 相似文献
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Given a graph G,a subgraph C is called a clique of G if C is a complete subgraph of G maximal under inclusion and |C|≥2. A clique-transversal set S of G is a set of vertices of G such that S meets all cliques of G. The clique-transversal number, denoted as TC (G), is the minimum cardinality of a clique-transversal set in G. The clique-graph of G, denoted as K (G), is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques in G have nonempty intersection. Let F be a class of graphs G such that F={G|K(G) is a tree}. In this paper the graphs in F having independent clique-transversal sets are shown and thus TC (G)/|G|≤1/2 for all G ∈ F. 相似文献
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《海外英语》2007,(5):10-11
Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help? 相似文献
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陈美曦 《山东教育学院学报》2008,23(2):103-107
Different nations have different social cultures, and the social culture of every nation is developing with the development of the nation, language is greatly influenced by social culture, which enables language to possess national and historical characteristics. Word is the smallest, independent, meaningful linguistic unit of language. It can well reflect the national and historical characteristics. From synchronic aspect, the social and cultural influence on word meaning is mainly embodied in conceptual and associative meanings of word. The incorrespondence of word meaning is a phenomenon that exists in both conceptual and associative meanings of word among different languages. From diachronic aspect, the development of social culture causes some changes of word meaning to some extent. Therefore, social culture plays a key role in vocabulary learning and mastery of a language. 相似文献
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Rachel Zupek 《海外英语》2007,(11):40-41
我们绝大部分人都同意一件事情——我们喜欢金钱。但是你对金钱的喜欢之情足够到让你创立一份事业么?.财富通常被人忽视,主要在于人们不能真正了 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献