全文获取类型
收费全文 | 20884篇 |
免费 | 685篇 |
国内免费 | 48篇 |
专业分类
系统科学 | 1137篇 |
丛书文集 | 181篇 |
教育与普及 | 32篇 |
理论与方法论 | 346篇 |
现状及发展 | 7355篇 |
研究方法 | 791篇 |
综合类 | 11489篇 |
自然研究 | 286篇 |
出版年
2018年 | 749篇 |
2017年 | 770篇 |
2016年 | 480篇 |
2012年 | 527篇 |
2011年 | 1501篇 |
2010年 | 923篇 |
2009年 | 515篇 |
2008年 | 829篇 |
2007年 | 1238篇 |
2006年 | 327篇 |
2005年 | 372篇 |
2004年 | 445篇 |
2003年 | 505篇 |
2002年 | 375篇 |
2001年 | 459篇 |
2000年 | 446篇 |
1999年 | 313篇 |
1992年 | 267篇 |
1991年 | 200篇 |
1990年 | 224篇 |
1989年 | 219篇 |
1988年 | 223篇 |
1987年 | 218篇 |
1986年 | 205篇 |
1985年 | 293篇 |
1984年 | 229篇 |
1983年 | 158篇 |
1982年 | 167篇 |
1981年 | 152篇 |
1980年 | 181篇 |
1979年 | 418篇 |
1978年 | 309篇 |
1977年 | 307篇 |
1976年 | 289篇 |
1975年 | 324篇 |
1974年 | 385篇 |
1973年 | 363篇 |
1972年 | 381篇 |
1971年 | 436篇 |
1970年 | 551篇 |
1969年 | 462篇 |
1968年 | 469篇 |
1967年 | 432篇 |
1966年 | 383篇 |
1965年 | 285篇 |
1959年 | 169篇 |
1958年 | 297篇 |
1957年 | 199篇 |
1956年 | 185篇 |
1954年 | 185篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
31.
32.
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
33.
The exponential Radon transform, a generalization of the Radon transform, is defined and studied as a mapping of function
spaces. It is represented in terms of Fourier transform of its domain and range, and this leads to the harmonic decomposition
reconstruction. The results are similar results of Tretiak and Metz.
Foundation item: Supported by the National Natural Science Foundation of China (No. 19971064), Key Project of Science and
Technology of Hubei Province Education Committee.
Biography: Wang Jin-ping (1963-), male, Ph.D. candidate, research direction: numberical solution of singular integral equation
and integral transformation etc. 相似文献
34.
YU Jianqiao LIAO Jianwei 《武汉大学学报:自然科学英文版》2007,12(5):887-892
We propose a multiple-tree overlay structure for resource discovery in unstructured P2P systems. Peers that have similar interests or hold similar type of resources will be grouped into a tree-like cluster. We exploit the heterogeneity of peers in each cluster by connecting peers with more capacities closer to the root of the tree. The capacity of a peer can be defined in different ways (e.g. higher network bandwidth, larger disk space, more data items of a certain type etc.) according to different needs of users or applications. 相似文献
35.
In October 1924, The Physical Review, a relatively minor journal at the time, published a remarkable two-part paper by John H. Van Vleck, working in virtual isolation
at the University of Minnesota. Using Bohr’s correspondence principle and Einstein’s quantum theory of radiation along with
advanced techniques from classical mechanics, Van Vleck showed that quantum formulae for emission, absorption, and dispersion
of radiation merge with their classical counterparts in the limit of high quantum numbers. For modern readers Van Vleck’s
paper is much easier to follow than the famous paper by Kramers and Heisenberg on dispersion theory, which covers similar
terrain and is widely credited to have led directly to Heisenberg’s Umdeutung paper. This makes Van Vleck’s paper extremely valuable for the reconstruction of the genesis of matrix mechanics. It also
makes it tempting to ask why Van Vleck did not take the next step and develop matrix mechanics himself.
This paper was written as part of a joint project in the history of quantum physics of the Max Planck Institut für Wissenschaftsgeschichte and the Fritz-Haber-Institut in Berlin. 相似文献
36.
DING Mingtao WEI Fangqiang ZHANG Jinghong WANG Hongjuan 《武汉大学学报:自然科学英文版》2007,12(4):599-604
By analyzing the observation data from Dongchuan Debris Flow Observation and Research Station and historical data from year 1965 to 1990 gotten from National Astronomical Ob-servatories/Yunnan Observatory,the responding of debris flow in Jiangjia Ravine to Solar Proton Flare is studied. The following conclusion can be drawn. Solar Proton Flare,as one of most im-portant astronomical factors,affects the activity of debris flow in Yunnan. Generally,from 1965 to1990,the more active Solar Pro-ton Flare is,the greater the probability of high frequency and large runoff of debris flow is. On the contrary,the less active Solar Pro-ton Flare is,the greater the probability of low frequency,small runoff,and low sediment transport of debris flow is. 相似文献
37.
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
38.
39.
The unified chaotic system contains the Lorenz system and the Chen system as two dual systems at the two extremes of its parameter
spectrum. This paper presents the design of bang bang controller for unified system and multitude of numerical experiments
under various control parameters. Numerical experiments meet the theoretic proof perfectly and convincingly demonstrated the
controller can be effectively used for unified systems with uncertainty of the equilibrium points. The method enriches the
applications of chaotic control.
Foundation item: Supported by the National Natural Science Foundation of China(50209012)
Biography: Deng Xiao-ming (1980-), male, Master candidate, research direction: chaos control. 相似文献
40.
Human cytomegalovirus UL97 open reading frame encodes a protein that phosphorylates the antiviral nucleoside analogue ganciclovir. 总被引:32,自引:0,他引:32
Human cytomegalovirus (HCMV, a betaherpes virus) is the cause of serious disease in immunologically compromised individuals, including those with acquired immunodeficiency syndrome. One of the compounds used in the chemotherapy of HCMV infections is the nucleoside analogue 9-(1,3-dihydroxy-2-propoxymethyl)-guanine (ganciclovir). The mechanism of action of this drug is dependent on the formation of the nucleoside triphosphate, which is a strong inhibitor of the viral DNA polymerase. Thymidine kinase, which is encoded by many of the herpesviruses, catalyses the initial phosphorylation of ganciclovir. But there is no evidence for the coding of this enzyme by HCMV, and DNA sequence analysis of the HCMV genome has shown that there is no open reading frame characteristic of a herpesvirus thymidine kinase. Here we present biochemical and immunological evidence that the HCMV UL97 open reading frame codes for a protein capable of phosphorylating ganciclovir. This protein seems to be responsible for the selectivity of ganciclovir and will be useful tool in the understanding and refinement of the antiviral activity of new selective anti-HCMV compounds. 相似文献