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   1462535篇
  免费   29433篇
  国内免费   7833篇
化学   743554篇
晶体学   21181篇
力学   77843篇
综合类   107篇
数学   253009篇
物理学   404107篇
  2021年   13643篇
  2020年   16061篇
  2019年   16185篇
  2018年   17266篇
  2017年   15938篇
  2016年   30113篇
  2015年   21445篇
  2014年   30771篇
  2013年   74975篇
  2012年   44560篇
  2011年   47388篇
  2010年   42010篇
  2009年   43435篇
  2008年   44789篇
  2007年   42151篇
  2006年   42524篇
  2005年   38102篇
  2004年   36723篇
  2003年   33485篇
  2002年   33289篇
  2001年   33529篇
  2000年   27952篇
  1999年   24063篇
  1998年   21634篇
  1997年   21484篇
  1996年   21442篇
  1995年   19429篇
  1994年   18930篇
  1993年   18529篇
  1992年   19069篇
  1991年   19238篇
  1990年   18447篇
  1989年   18479篇
  1988年   18067篇
  1987年   17950篇
  1986年   16887篇
  1985年   23262篇
  1984年   24260篇
  1983年   20312篇
  1982年   21894篇
  1981年   21104篇
  1980年   20444篇
  1979年   20908篇
  1978年   22022篇
  1977年   21680篇
  1976年   21472篇
  1975年   20172篇
  1974年   19899篇
  1973年   20321篇
  1972年   14761篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
963.
The miscibility of bisphenol-A polycarbonate (PC) with poly(methyl methacrylate) (PMMA) has been reexamined using differential scanning calorimetry (DSC) and optical indications for phase separation on heating, i.e., lower critical solution temperature (LCST) behavior. Various methods have been used to prepare the blends including methylene chloride (CH2Cl2) and tetrahydrofuran (THF) solution casting, melt mixing, and precipitation of PC and PMMA simultaneously from THF solution by using the nonsolvents methanol and heptane. It is shown that the resulting phase behavior for PC/PMMA blends is strongly affected by the blend preparation method. However, these blends are miscible over the whole blend composition range (unambiguous single composition-dependent Tg's and LCST behavior) when prepared by precipitation from solution using heptane as the nonsolvent. To the contrary, solution-cast and melt-mixed PC/PMMA blends were all phase separated, which may be attributed to the “solvent” effect and LCST behavior, respectively, not discovered in previous reports. Methanol precipitation does not lead to fully mixed blends, which demonstrates the importance of the choice of nonsolvent when using the precipitation method.  相似文献   
964.
965.
High-temperature series expansions of the susceptibility and second moment to 15th order are calculated for zero external field on the linear chain (LC), plane square (PSQ), simple cubic (SC), and body-centered cubic (BCC) lattices. Checks for specific models against pertinent work in the literature are detailed.  相似文献   
966.
Copper bromide was used as a catalyst for the addition of pyrroles to enones. When both the reactants were used in equimolar amounts, mono and dialkylated products were obtained. However, the use of excess enone furnished only dialkylated products. Thus, copper bromide was shown to be an efficient catalyst for the dialkylation of pyrroles.  相似文献   
967.
A general nonlinear programming problem with interval functions is considered. Two reductions of this problem to the deterministic nonlinear programming problem are proposed, and illustrative examples are discussed.  相似文献   
968.
An implicit quasi-monotone second-order accurate method is proposed for analyzing the spiral Couette flow of a rarefied gas between coaxial cylinders. The basic advantages of the method over the conventional method of stationry iterations are that the former is conservative with respect to the collision integral, has a simple software implementation for any types of boundary conditions, and applies to a wide range of Knudsen numbers.  相似文献   
969.
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December 9–11, 2004  相似文献   
970.
We investigate the conjecture that every circulant graph X admits a k‐isofactorization for every k dividing |E(X)|. We obtain partial results with an emphasis on small values of k. © 2006 Wiley Periodicals, Inc. J Combin Designs 14: 406–414, 2006  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