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   586529篇
  免费   22935篇
  国内免费   13969篇
化学   335338篇
晶体学   7983篇
力学   26425篇
综合类   732篇
数学   72047篇
物理学   180908篇
  2022年   4606篇
  2021年   6348篇
  2020年   7394篇
  2019年   7324篇
  2018年   8396篇
  2017年   8145篇
  2016年   11943篇
  2015年   9974篇
  2014年   13008篇
  2013年   28362篇
  2012年   25577篇
  2011年   29437篇
  2010年   19874篇
  2009年   19536篇
  2008年   25191篇
  2007年   24791篇
  2006年   23668篇
  2005年   23180篇
  2004年   20516篇
  2003年   17159篇
  2002年   15731篇
  2001年   16554篇
  2000年   12972篇
  1999年   10660篇
  1998年   8739篇
  1997年   8403篇
  1996年   8538篇
  1995年   7629篇
  1994年   7347篇
  1993年   6865篇
  1992年   7400篇
  1991年   7205篇
  1990年   6675篇
  1989年   6331篇
  1988年   6385篇
  1987年   6074篇
  1986年   5945篇
  1985年   8088篇
  1984年   8170篇
  1983年   6733篇
  1982年   7264篇
  1981年   7024篇
  1980年   6634篇
  1979年   6876篇
  1978年   7032篇
  1977年   7084篇
  1976年   7084篇
  1975年   6746篇
  1974年   6688篇
  1973年   6873篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
We establish conditions for survival and extinction of types of one-dimensional voter models, and show that increasing the flip rates at a finite number of sites typically does not affect survival, unless the flipping mechanism is altered. We provide an example of a modified voter model that does not survive but can be made to survive simply by altering the flip mechanism at one site. We also show that a rather general class of such models have clustering behavior.  相似文献   
962.
Organometallic compounds Cp2TiCl2, (EtC5H4)2NbCl2, and (PriC5H4)2WCl2 were assessed as additives that control polymer chain growth in the polymerization of methyl methacrylate. In the presence of compounds mentioned in amounts comparable with that of the initiator, a uniform process with no gel-effect occured and respective linear increase in the molecular weight of the polymer up to high degrees of the monomer conversion was observed.  相似文献   
963.
The sample average approximation (SAA) method is an approach for solving stochastic optimization problems by using Monte Carlo simulation. In this technique the expected objective function of the stochastic problem is approximated by a sample average estimate derived from a random sample. The resulting sample average approximating problem is then solved by deterministic optimization techniques. The process is repeated with different samples to obtain candidate solutions along with statistical estimates of their optimality gaps.We present a detailed computational study of the application of the SAA method to solve three classes of stochastic routing problems. These stochastic problems involve an extremely large number of scenarios and first-stage integer variables. For each of the three problem classes, we use decomposition and branch-and-cut to solve the approximating problem within the SAA scheme. Our computational results indicate that the proposed method is successful in solving problems with up to 21694 scenarios to within an estimated 1.0% of optimality. Furthermore, a surprising observation is that the number of optimality cuts required to solve the approximating problem to optimality does not significantly increase with the size of the sample. Therefore, the observed computation times needed to find optimal solutions to the approximating problems grow only linearly with the sample size. As a result, we are able to find provably near-optimal solutions to these difficult stochastic programs using only a moderate amount of computation time.  相似文献   
964.
我们给出了德摩根一致代数可伪度量化的一个充分必要条件。  相似文献   
965.
The PARRNe facility has been used to produce neutron-rich isotopes 83,84Gaby the ISOL method. Their decay has been studied, and β-γ coincidence and γ-γ coincidence data were collected as a function of time. The first two excited levels in 83Ge and the first excited level in 84Ge have been measured for the first time.  相似文献   
966.
Journal of Experimental and Theoretical Physics - The magnetoresistance effect in the SmCu3Mn4O12 compound with a perovskite-like structure is investigated for the first time. It is found that an...  相似文献   
967.
新型菲涅尔线聚光太阳电池组件特性分析   总被引:3,自引:1,他引:2  
以PMMA为材料,采用热压成型工艺加工线聚焦菲涅尔聚光棱镜,对在其聚光条件下不同入射角度情况下太阳电池的电流电压特性进行测试,结果表明:该菲涅尔线聚焦棱镜能有效提高太阳电池的单位输出功率,而且具有比较宽泛的集光角的特性,基本满足实际应用的要求.  相似文献   
968.
969.
Two quantities ηrel and are applied to study the nonideal acetone–water association mixture. An all-atom acetone model and a TIP5P water model have been adopted for molecular dynamics simulation. We study the transport properties of the system comparing the 's of strong hydrogen bond and weak contact based on transport properties, MD simulations together with NMR experimental data and find good agreement of concentration dependence, which exhibits the cooperation effect.  相似文献   
970.
An experiment was designed to determine whether normally sighted human subjects would be able to adapt to the handicapping effects of sudden deprivation of visual cues on horizontal plane sound localization. Two groups of sighted normal-hearing young adults participated. One group was allowed the benefit of sight. The other group was blindfolded. Measurements of accuracy and the time to respond were made daily over the course of five consecutive days, in a semi-reverberant sound proof booth that modeled listening in a small office. Sound localization was assessed using an array of eight speakers that surrounded the subject in space. Each day, one block of 120 trials was presented for each of three stimuli, two one-third octave noise bands, centred at 0.5 and 4 kHz, and broadband noise, to assess the utilization of interaural temporal difference cues, interaural level difference cues and binaural and spectral cues in combination. Blindfolded subjects were relatively less accurate than sighted subjects. Both groups showed gains with practice, the blindfolded group to a greater degree, largely due to improvements in the use of spectral cues. The blindfolded group took longer to respond than the sighted group, but showed greater decrements in response time with practice.  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