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   119867篇
  免费   590篇
  国内免费   654篇
化学   35618篇
晶体学   1088篇
力学   8161篇
综合类   13篇
数学   41334篇
物理学   23683篇
无线电   11214篇
  2021年   79篇
  2020年   74篇
  2019年   79篇
  2018年   13070篇
  2017年   12994篇
  2016年   7817篇
  2015年   1616篇
  2014年   972篇
  2013年   1293篇
  2012年   7572篇
  2011年   14191篇
  2010年   8732篇
  2009年   8412篇
  2008年   7833篇
  2007年   10301篇
  2006年   883篇
  2005年   6363篇
  2004年   5721篇
  2003年   4522篇
  2002年   1625篇
  2001年   630篇
  2000年   427篇
  1999年   355篇
  1998年   345篇
  1997年   238篇
  1996年   267篇
  1995年   184篇
  1994年   150篇
  1993年   135篇
  1992年   254篇
  1991年   238篇
  1990年   235篇
  1989年   215篇
  1988年   203篇
  1987年   167篇
  1986年   147篇
  1985年   145篇
  1984年   123篇
  1983年   111篇
  1982年   105篇
  1981年   84篇
  1980年   92篇
  1979年   111篇
  1978年   92篇
  1976年   137篇
  1975年   80篇
  1974年   88篇
  1973年   107篇
  1972年   76篇
  1966年   74篇
排序方式: 共有10000条查询结果,搜索用时 62 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.
In this paper, we present a novel memory access reduction scheme (MARS) for two-dimension fast cosine transform (2-D FCT). It targets programmable DSPs with high memory-access latency. It reduces the number of memory accesses by: 1) reducing the number of weighting factors and 2) combining butterflies in vector-radix 2-D FCT pruning diagram from two stages to one stage with an efficient structure. Hardware platform based on general purpose processor is used to verify the effectiveness of the proposed method for vector-radix 2-D FCT pruning implementation. Experimental results validate the benefits of the proposed method with reduced memory access, less clock cycle and fewer memory space compared with the conventional implementation.  相似文献   
3.
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   
4.
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   
5.
6.
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   
7.
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