全文获取类型
收费全文 | 299篇 |
免费 | 3篇 |
国内免费 | 7篇 |
专业分类
教育 | 197篇 |
科学研究 | 30篇 |
体育 | 52篇 |
综合类 | 28篇 |
信息传播 | 2篇 |
出版年
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 1篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 10篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 15篇 |
2012年 | 8篇 |
2011年 | 19篇 |
2010年 | 13篇 |
2009年 | 17篇 |
2008年 | 17篇 |
2007年 | 28篇 |
2006年 | 19篇 |
2005年 | 24篇 |
2004年 | 17篇 |
2003年 | 19篇 |
2002年 | 10篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有309条查询结果,搜索用时 93 毫秒
41.
以饲料为原料筛选出一株既产乳酸又产芽孢的益生菌,经过分子生物学鉴定为凝结芽孢杆菌(Bacillus coagulans),命名为T-8。从培养基碳源、氮源、有机物浸出液、培养基pH、培养温度、培养时间等方面对菌株T-8展开发酵特性研究,结果表明,最优培养基配方为:玉米粉6 g/L、豆粕粉15 g/L、小麦麸皮浸出液60%、酵母粉5 g/L、蛋白胨10 g/L、氯化钠10 g/L,pH 5.0。以5%的接种量将种子液转接至最优培养基,在47℃的摇床中以200 r/min的转速振荡培养28 h,菌株T-8的细胞密度达到4.8×109 CFU/mL,芽孢率达到95.2%。本试验可为益生菌凝结芽孢杆菌应用于饲用微生物菌剂的工业化生产提供参考。 相似文献
42.
魏瑞演 《福建工程学院学报》2002,(1)
从基本的钢结构材料在高温下的力学性能着手 ,进行高温条件下钢结构材料的性能试验 ,建立高温下钢材的屈服强度、极限强度、弹性模量和极限应变随温度变化的力学模型 ,为高温 (火灾 )条件下钢结构的结构分析提供依据。 相似文献
43.
The endochronic equations proposed by Valanis (1980) were extended to a finite deformation range. Jaumann's rate,Fu's rate and Wu's rate were incorporated into the endochronic equations to analyze simple shear finite deformation. Incremental equations and numerical solutions are deduced for three endochronic objective models. The results show that an oscillatory shear stress response to a monotonically increasing shear strain occurs when the Jaumann's rate objective model is employed for endochronic materials. The oscillatory response is dependent on the adopted objective rate. Compared with the Jaumann's rate, the Fu's rate and the Wu's rate satisfy the restrictions to elastic-plastic constitutive relations and are in agreement with the experimental results. 相似文献
44.
To study the dynamic properties of the concrete subjected to impulsive loading,stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the concrete were analyzed.The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature.But with temperature increasing,the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect.So,strain rate effect,strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively corn plex. 相似文献
45.
刘一 《广东技术师范学院学报》2007,(3):16-18
基于光束传播法(beam propagation method,BPM),提出了聚合物光纤在受到拉力和压力产生形变的情况下的光传输的理论分析模型,模拟计算了光纤受拉力作用时形变区域的光强传输情况. 相似文献
46.
通过对芜湖市部分高校排球爱好者发放问卷以及对国内相关文献资料的综合分析,了解高校排球爱好者在排球运动中髌骨劳损的状况,分析损伤原因和机制,并提出具体的预防措施.所以,髌骨劳损是影响排球爱好者进行锻炼的主要原因之一,应加以预防并在伤后采取适当的处理措施. 相似文献
47.
针对应变片工作时易受环境温度影响产生温漂,导致测量的准确度下降,提出了一种基于递归神经网络的应变片温度误差的补偿方法,利用神经网络良好的非线性映射能力,根据实际工作参数训练网络,从而实现应变片温度误差的智能补偿。结果表明:当环境温度从20℃~60℃变化时,应变片的温度漂移可从补偿前的0.23%下降到补偿后的0.02%,能有效地解决温度漂移现象。 相似文献
48.
49.
Rocks are heterogeneous from the point of microstructure which is of significance to their dynamic failure behavior. Both the compressive and tensile strength of rock-like materials is regarded different from the static strength. The present study adopts smoothed particle hydrodynamics (SPH) which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials. The SPH method is capable of simulating rock fracture, free of the mesh constraint of the traditional FEM and FDM models. A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling. The results show the compressive strength increases with the increase of strain rate as well as the tensile strength, which is important to the engineering design. 相似文献
50.
Eddy H. de Bruyn 《Educational studies》2005,31(1):15-27
The present study was designed to investigate the relationships between role strains following the transition to secondary school and academic achievement. Academic engagement was hypothesized to mediate between role strain and achievement. The sample consisted of 749 students in their first year of secondary school. Four types of role strain were investigated: parent, teacher, school and peer. Parent and teacher role strains appeared to be negatively associated with academic achievement, as mediated through academic engagement. Parent and school role strain were directly and negatively associated with achievement. Results are discussed in the light of parenting practices and the developmental mismatch hypothesis. 相似文献