全文获取类型
收费全文 | 62041篇 |
免费 | 274篇 |
国内免费 | 551篇 |
专业分类
系统科学 | 1246篇 |
丛书文集 | 370篇 |
教育与普及 | 290篇 |
理论与方法论 | 536篇 |
现状及发展 | 33310篇 |
研究方法 | 1066篇 |
综合类 | 23856篇 |
自然研究 | 2192篇 |
出版年
2013年 | 802篇 |
2012年 | 689篇 |
2011年 | 2762篇 |
2009年 | 615篇 |
2008年 | 894篇 |
2007年 | 1041篇 |
2006年 | 1081篇 |
2005年 | 1270篇 |
2004年 | 2372篇 |
2003年 | 1993篇 |
2002年 | 1696篇 |
2001年 | 1706篇 |
2000年 | 1237篇 |
1999年 | 1087篇 |
1998年 | 646篇 |
1997年 | 775篇 |
1996年 | 538篇 |
1994年 | 685篇 |
1993年 | 693篇 |
1992年 | 1030篇 |
1991年 | 878篇 |
1990年 | 970篇 |
1989年 | 809篇 |
1988年 | 765篇 |
1987年 | 751篇 |
1986年 | 829篇 |
1985年 | 986篇 |
1984年 | 856篇 |
1983年 | 754篇 |
1982年 | 845篇 |
1981年 | 880篇 |
1980年 | 983篇 |
1979年 | 1609篇 |
1978年 | 1401篇 |
1977年 | 1394篇 |
1976年 | 1194篇 |
1975年 | 1210篇 |
1974年 | 1250篇 |
1973年 | 1343篇 |
1972年 | 1440篇 |
1971年 | 1517篇 |
1970年 | 1712篇 |
1969年 | 1447篇 |
1968年 | 1446篇 |
1967年 | 1253篇 |
1966年 | 1116篇 |
1965年 | 863篇 |
1959年 | 497篇 |
1958年 | 676篇 |
1957年 | 566篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
In this paper two alternative loss criteria for the least squares Procrustes problem are studied. These alternative criteria
are based on the Huber function and on the more radical biweight function, which are designed to be resistant to outliers.
Using iterative majorization it is shown how a convergent reweighted least squares algorithm can be developed. In asimulation
study it turns out that the proposed methods perform well over a specific range of contamination. When a uniform dilation
factor is included, mixed results are obtained. The methods also yield a set of weights that can be used for diagnostic purposes. 相似文献
52.
Studies of intracellular traffic in yeast and mammalian systems have implicated members of the Rab family of small GTP-binding proteins as regulators of membrane fusion. We have used the patch clamp technique to measure exocytotic fusion events directly and investigate the role of GTP-binding proteins in regulating exocytosis in mast cells. Intracellular perfusion of mast cells with GTP-gamma S is sufficient to trigger complete exocytotic degranulation in the absence of other intracellular messengers. Here we show that GTP is a potent inhibitor of GTP-gamma S-induced degranulation, indicating that sustained activation of a GTP-binding protein is sufficient for membrane fusion. We have found that synthetic oligopeptides, corresponding to part of the effector domain of Rab3a, stimulate complete exocytotic degranulation, similar to that induced by GTP-gamma S. The response is selective for Rab3a sequence and is strictly dependent on Mg2+ and ATP. This suggests that sustained activation of a Rab3 protein causes exocytotic fusion. The peptide response can be accelerated by GDP-beta S, suggesting that Rab3a peptides compete with endogenous Rab3 proteins for a binding site on a target effector protein, which causes fusion on activation. 相似文献
53.
54.
55.
通过对“洋务运动博物馆”东立面形象的反思 ,讨论了建筑形态设计中隐喻手法的运用 ;就此引申 ,探讨传统问题 ,指出正确理解传统与创新的四个方面。 相似文献
56.
R. Poggioli A. V. Vergoni A. Bertolini 《Cellular and molecular life sciences : CMLS》1985,41(2):265-266
Summary Hydrochlorothiazide, acutely injected in rats, has a weak analgesic activity per se and potentiates and prolongs the antinociceptive effect of morphine.This work was supported in part by grants from Consiglio Nazionale delle Ricerche, and by Ministero della Pubblica Istruzione, Roma. 相似文献
57.
David H. Hubel 《自然科学进展(英文版)》2007,17(13):1-3
The visual field is topographically mapped onto the primary visual cortex (V1), forming a retinotopic map which is far more detailed for the foveal regions than for the periphery. We found that receptive field (RF) size in monkey V1 increases with eccentricity, and that a 1—2 m2 V1 region contains roughly a complete set of machinery necessary to analyze a visual-field area whose size is about that of the RFs of the cells. This allows V1 to be anatomically uniform, and is in sharp contrast with the retina. 相似文献
58.
1 Results This paper presents the development of platinum nanocomposites structures based on organically modified c.a.2 nm core platinum nanoparticles.The chemical modification of the 4-mercaptoaniline functionalized particles by various in coming molecules is evidenced and precisely quantified.The particles can be dissolved like molecules in various solvents depending on the features of the new crown and X-rays shows that the interparticle distance is affected by the crown modification.These platinum n... 相似文献
59.
60.
1 Results The development of the concepts of nanotechnology has given an important impact on the design of new polymer based materials which are in most cases characterized by a multiphase morphology. When at least one phase has nanometric dimension(s) the system can be considered as a nanocomposite where the interface is not only determining for the adhesion but also may play a role in some bulk properties. Indeed in nanostructured multiphase solids the interface is significant as a bulk component. The... 相似文献