全文获取类型
收费全文 | 9023篇 |
免费 | 107篇 |
国内免费 | 18篇 |
专业分类
教育 | 6075篇 |
科学研究 | 1028篇 |
各国文化 | 90篇 |
体育 | 992篇 |
综合类 | 6篇 |
文化理论 | 96篇 |
信息传播 | 861篇 |
出版年
2021年 | 69篇 |
2020年 | 122篇 |
2019年 | 175篇 |
2018年 | 237篇 |
2017年 | 252篇 |
2016年 | 218篇 |
2015年 | 153篇 |
2014年 | 216篇 |
2013年 | 1689篇 |
2012年 | 199篇 |
2011年 | 196篇 |
2010年 | 169篇 |
2009年 | 152篇 |
2008年 | 169篇 |
2007年 | 193篇 |
2006年 | 160篇 |
2005年 | 150篇 |
2004年 | 141篇 |
2003年 | 168篇 |
2002年 | 138篇 |
2001年 | 157篇 |
2000年 | 157篇 |
1999年 | 155篇 |
1998年 | 72篇 |
1997年 | 70篇 |
1996年 | 106篇 |
1995年 | 76篇 |
1994年 | 92篇 |
1993年 | 82篇 |
1992年 | 149篇 |
1991年 | 140篇 |
1990年 | 135篇 |
1989年 | 127篇 |
1988年 | 104篇 |
1987年 | 106篇 |
1986年 | 129篇 |
1985年 | 123篇 |
1984年 | 102篇 |
1983年 | 124篇 |
1982年 | 102篇 |
1981年 | 97篇 |
1980年 | 80篇 |
1979年 | 154篇 |
1978年 | 103篇 |
1977年 | 93篇 |
1976年 | 97篇 |
1975年 | 68篇 |
1974年 | 86篇 |
1972年 | 68篇 |
1971年 | 64篇 |
排序方式: 共有9148条查询结果,搜索用时 31 毫秒
991.
G. H. Lander Ph.D 《Endeavour》1990,14(4)
This year marks the 50th anniversary of the preparation of the first transuranium elements, neptunium and plutonium though thus losing pride of place in the Periodic Table, uranium still has secrets to reveal. This article describes efforts to characterize the extremely subtle series of distortions that appears at low temperature in the element. Our understanding of these distortions require some of the latest ideas in diffraction physics, so that the story is a continuously evolving one. Uranium is the only element (so far) that has been found to have a spontaneous charge-density wave. 相似文献
992.
Syed Shamil B.Sc. Ph.D. C.Chem. M.R.S.C. M.I.F.S.T. Gordon G. Birch B.Sc. Ph.D. D.Sc. F.R.C.S. F.I.F.S.T. 《Endeavour》1990,14(4)
Of all the senses, that of taste is perhaps the hardest to define and quantify and elucidation of the underlying mechanisms is unrespondingly difficult. This article describes a conceptual model — at the molecular level — for the four basic taste modalities, using apparent specific volume as a fundamental parameter. It also considers possible practical applications. 相似文献
993.
Optimization of grid configurations decreases the discretization error in the numerical solution of field problems. In this paper, the theoretical and algorithmic aspects of optimizing configurations of grids used in equilibrium, potential-type field problems is presented. The criterion for establishing the optimum grid and the steps required to move to the optimum grid are given. Sensitivity network modelling is invoked to systematically form matrices required in the algorithm. One-dimensional examples are presented to illustrate the validity of the approach. 相似文献
994.
Robert G. Crawford 《Information processing & management》1977,13(4):235-245
A method for updating the dictionary in a dynamic information retrieval system is presented. It is shown that as a collection changes through addition and deletion of documents, the appropriate set of index terms may be determined without complete periodic regeneration of the dictionary. Results are presented for experiments involving a complete change in collection membership, with the dynamic dictionary updating methods shown to be effective. 相似文献
995.
The level of sialic acid in the obese polymorphonuclear leukocytes (PMNL) was found to be significantly reduced as compared to normal. Activity of sialic acid degrading enzyme, sialidase, was found to be increased in the obese state. Restoration in both sialic acid content and sialidase activity was also evidenced in the PMNL of treated obese patients. 相似文献
996.
997.
G.L. Wise 《Journal of The Franklin Institute》1977,303(2):201-207
Mean square continuity of a random process is of considerable theoretical and practical importance. Mean square continuous random processes passed through zero memory non-linearities are considered. Several conditions are given relating to mean square continuity of the output. Bounded zero memory non-linearities are considered with arbitrary random processes as inputs, and conditions on both the zero memory non-linearity and on the random process are examined. Also, general zero memory non-linearities are considered with Gaussian random processes as inputs. 相似文献
998.
Warranting scientific belief 总被引:1,自引:0,他引:1
999.
Design of detectors for strong mixing signals in strong mixing noise is considered, where a large degree of dependency may occur between the signal and noise. Under the criterion of asymptotic relative efficiency, it is shown that this design reduces to determining the solution of an integral equation, where only knowledge of the second order statistics of the randon processes involved is required. In particular, if the signal is independent of the noise and has nonzero mean, the optimal detector is the same as in the known constant signal case. It is also shown that it is possible to delete several regularity conditions which may be difficult to check in practice in the slightly more restrictive case where the maximal correlation coefficients of the signal and noise tend to zero. 相似文献
1000.
Varinder Saini Narinder Saini Jasbinder Kaur G. P. Singh 《Indian journal of clinical biochemistry : IJCB》1993,8(1):36-38
348 patients of chronic obstructive pulmonary diseases (COPD) were studied for their acid base profile using ABL-3 blood gas
analyser (Radiometer, copenhagan). 185 patients (53.1%) had simple disorders (respiratory acidosis—53%, respiratory alkalosis—25.4%,
metabolic acidosis—11.3%, metabolic alkalosis—10.2%). Mixed disorders were present in 131 patients (34.9%) (respiratory acidosis
and metabolic acidosis—75.2%, respiratory acidosis and metabolic acidosis—14%, metabolic acidosis and metabolic alkalosis—5.7%,
metabolic alkalosis and respiratory alkalosis—4.9%). Hypoxemia without other acid base abnormalities was observed in early
patients of GOPD (42 patients—12%). Chronic respiratory acidosis was the most common finding in advanced cases of COPD (98%).
An almost equal number of such patients had a mixed disorder of respiratory acidosis with metabolic alkalosis (91%). Salt
restriction, prolonged use of steriods and hypokalemia were often related to metabolic alkalosis in such patients. 相似文献