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   71806篇
  免费   1223篇
  国内免费   348篇
化学   35307篇
晶体学   1066篇
力学   3509篇
综合类   9篇
数学   6966篇
物理学   26520篇
  2022年   492篇
  2021年   645篇
  2020年   625篇
  2019年   614篇
  2018年   837篇
  2017年   752篇
  2016年   1319篇
  2015年   981篇
  2014年   1392篇
  2013年   3318篇
  2012年   3092篇
  2011年   3839篇
  2010年   2657篇
  2009年   2670篇
  2008年   3460篇
  2007年   3294篇
  2006年   3096篇
  2005年   2774篇
  2004年   2501篇
  2003年   2136篇
  2002年   1999篇
  2001年   3230篇
  2000年   2364篇
  1999年   1714篇
  1998年   1231篇
  1997年   1195篇
  1996年   1048篇
  1995年   883篇
  1994年   805篇
  1993年   703篇
  1992年   1044篇
  1991年   1028篇
  1990年   925篇
  1989年   839篇
  1988年   813篇
  1987年   868篇
  1986年   733篇
  1985年   975篇
  1984年   927篇
  1983年   634篇
  1982年   645篇
  1981年   623篇
  1980年   577篇
  1979年   699篇
  1978年   736篇
  1977年   726篇
  1976年   659篇
  1975年   544篇
  1974年   581篇
  1973年   517篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
Porous coordination polymers are molecule-based materials presenting a high degree of tunability, which offer many advantages for targeted applications over conventional inorganic materials. This work demonstrates that the hydrophilic/hydrophobic character of Prussian blue analogues having a lipophilic feature may be tuned to optimize the gas adsorption properties. The role of the coordinatively unsaturated metal sites is emphasized through a combination of theoretical and experimental study of water, ethanol, and n-hexane adsorption.  相似文献   
33.
34.
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar...  相似文献   
35.
36.
A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data  相似文献   
37.
In a previous paper (Ref. 1), an exact solution of the optimal planar interception with fixed end conditions was derived in closed form. The optimal control was expressed as an explicit function of the state variables and two fixed parameters, obtained by solving a set of nonlinear algebraic equations involving elliptic integrals. In order to facilitate the optimal control implementation, the present paper derives a highly accurate simplified solution assuming that the ratio of the pursuer turning radius to the initial range is small. An asymptotic expansion further reduces the computational workload. Construction of a near-optimal open-loop control, based on the approximations, completes the present paper.  相似文献   
38.
The coordination chemistry of beryllium with particular emphasis on chelates under physiological or near physiological conditions is surveyed. Hard donors such as oxygen are emphasized; equilibrium data and formation constants are reported as an indication of the strength of the complex.  相似文献   
39.
40.
Lanosterol derivatives with a functional group at C-32 have been synthesized from 3 beta-acetoxylanostan-7 alpha-ol. The key reaction of the synthesis is the hypoiodite reaction of 3 beta-acetoxylanostan-7 alpha-ol. In vitro antitumor activity testing of the lanosterol derivatives revealed that 3 beta-hydroxylanost-7-en-32-oic acid has antineoplastic activity.  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