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   286500篇
  免费   3591篇
  国内免费   891篇
化学   136413篇
晶体学   3957篇
力学   14383篇
综合类   4篇
数学   57964篇
物理学   78261篇
  2021年   1644篇
  2020年   2014篇
  2019年   2128篇
  2018年   12729篇
  2017年   12557篇
  2016年   10472篇
  2015年   3966篇
  2014年   4635篇
  2013年   10793篇
  2012年   11872篇
  2011年   19180篇
  2010年   11888篇
  2009年   12022篇
  2008年   14863篇
  2007年   16661篇
  2006年   8046篇
  2005年   8497篇
  2004年   8077篇
  2003年   7738篇
  2002年   6530篇
  2001年   6268篇
  2000年   4979篇
  1999年   3692篇
  1998年   3122篇
  1997年   2909篇
  1996年   2957篇
  1995年   2597篇
  1994年   2619篇
  1993年   2504篇
  1992年   2786篇
  1991年   2673篇
  1990年   2648篇
  1989年   2505篇
  1988年   2509篇
  1987年   2475篇
  1986年   2368篇
  1985年   3079篇
  1984年   3105篇
  1983年   2705篇
  1982年   2833篇
  1981年   2656篇
  1980年   2580篇
  1979年   2720篇
  1978年   2739篇
  1977年   2652篇
  1976年   2696篇
  1975年   2598篇
  1974年   2575篇
  1973年   2763篇
  1972年   1768篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Lanthanide dinitrogen complexes, Ln(N2) x (x = 1-8), were investigated by Density Functional Theory computations using the B3LYP exchange-correlation functional in conjunction with quasirelativistic pseudopotentials for Ln. After a recent study on the lanthanum complexes (A. Kovács, Structural Chemistry 2018 , 29, 1825), the present study aimed to probe the changes upon variously filled 4f subshells of Ln on the structures, stabilities, and bonding properties in related complexes of Nd, Ho, and Lu. The bonding properties were assessed on the basis of natural atomic charges, Ln valence orbital populations, and analysis of bonding molecular orbitals.  相似文献   
22.
The design of new solid-state proton-conducting materials is a great challenge for chemistry and materials science. Herein, a new anionic porphyrinylphosphonate-based MOF ( IPCE-1Ni ), which involves dimethylammonium (DMA) cations for charge compensation, is reported. As a result of its unique structure, IPCE-1Ni exhibits one of the highest value of the proton conductivity among reported proton-conducting MOF materials based on porphyrins (1.55×10−3 S cm−1 at 75 °C and 80 % relative humidity).  相似文献   
23.
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   
24.
25.
26.
We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling.  相似文献   
27.
28.
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   
29.
30.
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   
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