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   100861篇
  免费   1465篇
  国内免费   1809篇
化学   40355篇
晶体学   977篇
力学   7184篇
综合类   10篇
数学   35478篇
物理学   20131篇
  2023年   158篇
  2022年   289篇
  2021年   498篇
  2020年   385篇
  2019年   423篇
  2018年   10658篇
  2017年   10509篇
  2016年   6830篇
  2015年   1579篇
  2014年   1139篇
  2013年   2065篇
  2012年   5412篇
  2011年   12171篇
  2010年   6599篇
  2009年   7213篇
  2008年   7723篇
  2007年   9826篇
  2006年   1217篇
  2005年   2236篇
  2004年   2764篇
  2003年   2882篇
  2002年   1868篇
  2001年   722篇
  2000年   707篇
  1999年   492篇
  1998年   509篇
  1997年   430篇
  1996年   474篇
  1995年   352篇
  1994年   269篇
  1993年   306篇
  1992年   247篇
  1991年   207篇
  1990年   211篇
  1989年   195篇
  1988年   197篇
  1987年   181篇
  1986年   188篇
  1985年   226篇
  1984年   237篇
  1983年   173篇
  1982年   185篇
  1981年   188篇
  1980年   174篇
  1979年   167篇
  1978年   146篇
  1977年   127篇
  1976年   138篇
  1975年   133篇
  1974年   127篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Reactivity studies of the GeII→B complex L(Cl)Ge⋅BH3 ( 1 ; L=2-Et2NCH2-4,6-tBu2-C6H2) were performed to determine the effect on the GeII→B donation. N-coordinated compounds L(OtBu)Ge⋅BH3 ( 2 ) and [LGe⋅BH3]2 ( 3 ) were prepared. The possible tuning of the GeII→B interaction was proved experimentally, yielding compounds 1-PPh2-8-(LGe)-C10H6 ( 4 ) and L(Cl)Ge⋅GaCl3 ( 5 ) without a GeII→B interaction. In 5 , an unprecedented GeII→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1 − 5 . The different strength of the GeII→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed.  相似文献   
2.
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   
3.
Central European Journal of Operations Research - Digital competences are among the most important competences in modern society, with the education system playing a key role in the acquisition of...  相似文献   
4.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers.  相似文献   
5.
6.
7.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
8.
9.
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser.  相似文献   
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