首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22108篇
  免费   1152篇
  国内免费   1437篇
化学   16829篇
晶体学   189篇
力学   466篇
综合类   10篇
数学   2960篇
物理学   4243篇
  2023年   154篇
  2022年   106篇
  2021年   428篇
  2020年   382篇
  2019年   415篇
  2018年   386篇
  2017年   366篇
  2016年   826篇
  2015年   675篇
  2014年   729篇
  2013年   1633篇
  2012年   1725篇
  2011年   1895篇
  2010年   1026篇
  2009年   1226篇
  2008年   1417篇
  2007年   1383篇
  2006年   1156篇
  2005年   1194篇
  2004年   1375篇
  2003年   1024篇
  2002年   916篇
  2001年   486篇
  2000年   388篇
  1999年   288篇
  1998年   255篇
  1997年   229篇
  1996年   251篇
  1995年   195篇
  1994年   168篇
  1993年   208篇
  1992年   171篇
  1991年   111篇
  1990年   107篇
  1989年   88篇
  1988年   90篇
  1987年   81篇
  1986年   85篇
  1985年   138篇
  1984年   144篇
  1983年   91篇
  1982年   83篇
  1981年   83篇
  1980年   65篇
  1979年   37篇
  1978年   54篇
  1977年   51篇
  1976年   39篇
  1975年   43篇
  1974年   40篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
In this article, a way to employ the diffusion approximation to model interplay between TCP and UDP flows is presented. In order to control traffic congestion, an environment of IP routers applying AQM (Active Queue Management) algorithms has been introduced. Furthermore, the impact of the fractional controller PIγ and its parameters on the transport protocols is investigated. The controller has been elaborated in accordance with the control theory. The TCP and UDP flows are transmitted simultaneously and are mutually independent. Only the TCP is controlled by the AQM algorithm. Our diffusion model allows a single TCP or UDP flow to start or end at any time, which distinguishes it from those previously described in the literature.  相似文献   
2.
Archiv der Mathematik - In this note, we introduce a criterion to detect vanishing of essential algebras of a Green biset functor by means of morphisms. We introduce the inflation morphism and...  相似文献   
3.
During the past two decades, single-atom-centered medium-sized germanium clusters [M@Gen] (M=transition metals, n>12) have been extensively explored, both from theoretical perspectives and experimental gas-phase syntheses. However, the actual structural arrangements of the Ge13 and Ge14 endohedral cages are still ambiguous and have long remained an unresolved problem for experimental implementation. In this work, we successfully synthesize 13-/14-vertex Ge clusters [Nb@Ge13]3− ( 1 ) and [Nb@Ge14]3− ( 2 ), which are structurally characterized and exhibit unprecedented topologies, neither classical deltahedra nor 3-connected polyhedral structures. Theoretical analysis indicates that the major stabilization of the Ge backbones arises due to the substantial interaction of Ge 4p-AOs with the endohedral Nb 4d-AOs through three/four-center two-electron bonds with an enhanced electron density accumulated over the shortest Nb−Ge13 contact in 1 . Low occupancies of the direct two-center two-electron (2c–2e) Nb−Ge and Ge−Ge σ bonds point to a considerable degree of electron delocalization over the Ge cages revealing their electron deficiency.  相似文献   
4.
CRANAD-2 is a fluorogenic curcumin derivative used for near-infrared detection and imaging in vivo of amyloid aggregates, which are involved in neurodegenerative diseases. We explore the performance of CRANAD-2 in two super-resolution imaging techniques, namely stimulated emission depletion (STED) and single-molecule localization microscopy (SMLM), with markedly different fluorophore requirements. By conveniently adapting the concentration of CRANAD-2, which transiently binds to amyloid fibrils, we show that it performs well in both techniques, achieving a resolution in the range of 45–55 nm. Correlation of SMLM with atomic force microscopy (AFM) validates the resolution of fine features in the reconstructed super-resolved image. The good performance and versatility of CRANAD-2 provides a powerful tool for near-infrared nanoscopic imaging of amyloids in vitro and in vivo.  相似文献   
5.
Central European Journal of Operations Research - This paper presents a discrete event simulation model to support decision-making for the short-term planning of hospital resource needs, especially...  相似文献   
6.
Algebras and Representation Theory - Let A and B be two Morita equivalent finite dimensional associative algebras over a field ��. It is well known that Hochschild cohomology is...  相似文献   
7.
Journal of Solid State Electrochemistry - The addition of nanocrystalline titanium dioxide (P90) to a cathode of Li/S cell enhances its voltammetric charge capacity by 19%, from which only a small...  相似文献   
8.
9.
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号