全文获取类型
收费全文 | 12482篇 |
免费 | 65篇 |
国内免费 | 103篇 |
专业分类
系统科学 | 95篇 |
丛书文集 | 256篇 |
教育与普及 | 60篇 |
理论与方法论 | 62篇 |
现状及发展 | 5395篇 |
研究方法 | 530篇 |
综合类 | 6118篇 |
自然研究 | 134篇 |
出版年
2013年 | 173篇 |
2012年 | 253篇 |
2011年 | 385篇 |
2010年 | 148篇 |
2009年 | 123篇 |
2008年 | 271篇 |
2007年 | 303篇 |
2006年 | 261篇 |
2005年 | 264篇 |
2004年 | 220篇 |
2003年 | 227篇 |
2002年 | 238篇 |
2001年 | 323篇 |
2000年 | 329篇 |
1999年 | 210篇 |
1992年 | 183篇 |
1991年 | 154篇 |
1990年 | 166篇 |
1989年 | 167篇 |
1988年 | 171篇 |
1987年 | 165篇 |
1986年 | 171篇 |
1985年 | 232篇 |
1984年 | 143篇 |
1983年 | 143篇 |
1982年 | 99篇 |
1981年 | 120篇 |
1980年 | 157篇 |
1979年 | 389篇 |
1978年 | 287篇 |
1977年 | 316篇 |
1976年 | 219篇 |
1975年 | 223篇 |
1974年 | 354篇 |
1973年 | 291篇 |
1972年 | 314篇 |
1971年 | 333篇 |
1970年 | 430篇 |
1969年 | 380篇 |
1968年 | 384篇 |
1967年 | 347篇 |
1966年 | 303篇 |
1965年 | 222篇 |
1959年 | 117篇 |
1958年 | 211篇 |
1957年 | 169篇 |
1956年 | 160篇 |
1955年 | 133篇 |
1954年 | 133篇 |
1948年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
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
22.
23.
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
24.
1 Results Pyrimidinones (PMs) are a class of important heterocycles which have been well documented throughout the literature due to their biological importance. They exhibit a wide range of pharmaceutical and therapeutic properties[1].A rapid and efficient one-pot method for the synthesis of 4,6-diarylpyrimidin-2(1H)- ones and related heterocycles is described.The condensation of acetophenone derivatives,aldehydes and urea in the presence of sulfamic acid was employed to synthesize a variety of pyrimid... 相似文献
25.
Summary The application of diphenylilacetic acid has shown favorable effects on the growth of tobacco plants. Solutions containing 10 p.p.m. and 20 p.p.m. produce, in weight, an almost double growth in treated plants in comparison with the controls. Diphenylilacetic acid can be considered as a growth-promoting substance. The data are not definite. 相似文献
26.
Kang J.Y. Xu F.C. 《中国科学基金(英文版)》2004,(2):57-58,64
1 Introduction
Nanoscale science and technology have attracted greatattention since the novel properties become dominant for well-known materials as their sizes reduced to some critical dimension. These properties frequently originate in lattice distortions, structure transformations etc[1]. The variations of size and structure ofnanocrystals lead to the change of their electronic structures. Very recently, nanoscale materials with different electronic structures were utilized in fabricating nanoscale junctions[2].
…… 相似文献
27.
IPv4向IPv6过渡的机制 总被引:1,自引:0,他引:1
IPv4在Internet的高速发展中出现了许多急待解决的问题,如地址不足,路由表膨胀,安全性不高及移动性不够灵活等。新一代IPv6协议则提供了一些新的机制来解决这些问题。本文主要讨论了IPv6的特性以及IPv4向IPv6过渡的方法。 相似文献
28.
A. F. McDonagh Y. -M. Pu D. A. Lightner 《Cellular and molecular life sciences : CMLS》1992,48(3):246-248
The characteristic circular dichroism of bilirubin bound to human serum albumin undergoes a remarkable sign inversion on addition of halothane, chloroform and other volatile anesthetics. This sign inversion, which is completely reversed by removal of the anesthetic, reflects a pronounced conformational change of the bound ligand; probably a complete inversion of chirality. The observation suggests that association of volatile anesthetics with proteins can markedly alter the internal topography of receptor sites and potentially influence the stereoselectivity of ligand binding. 相似文献
29.
30.
A. Gutnisky P. Glikman M. F. Gimeno A. L. Gimeno 《Cellular and molecular life sciences : CMLS》1982,38(1):116-117
Summary The administration of 15(R)-15-methyl prostaglandin E2 (15(R)-15-M-PGE2) in vivo significantly diminished the uptake of59Fe into blood, spleen, liver, femur and dried intestine of rats, whereas acetylsalicylic acid (ASA) increased the counts significantly. This effect of ASA was counteracted by 15(R)-15-M-PGE2. It is suggested that prostaglandins (PGs) might play an important role in inhibiting iron absorption at the intestinal level.This work was supported by grant No.6638 from CONICET (Argentina). The technical assistance of Mrs María E. Castro and Norma Rizzo is gratefully acknowleged. 相似文献