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   473574篇
  免费   6880篇
  国内免费   1330篇
化学   255951篇
晶体学   5760篇
力学   19523篇
综合类   16篇
数学   59415篇
物理学   141119篇
  2021年   4308篇
  2020年   4858篇
  2019年   5148篇
  2018年   7043篇
  2017年   6700篇
  2016年   10362篇
  2015年   6801篇
  2014年   9759篇
  2013年   22870篇
  2012年   18066篇
  2011年   21653篇
  2010年   15102篇
  2009年   14772篇
  2008年   19742篇
  2007年   19491篇
  2006年   18025篇
  2005年   16305篇
  2004年   14939篇
  2003年   13127篇
  2002年   12748篇
  2001年   14085篇
  2000年   10825篇
  1999年   8448篇
  1998年   6985篇
  1997年   6711篇
  1996年   6584篇
  1995年   5833篇
  1994年   5848篇
  1993年   5468篇
  1992年   6125篇
  1991年   6108篇
  1990年   5915篇
  1989年   5674篇
  1988年   5666篇
  1987年   5545篇
  1986年   5235篇
  1985年   6847篇
  1984年   6954篇
  1983年   5505篇
  1982年   5609篇
  1981年   5603篇
  1980年   5115篇
  1979年   5534篇
  1978年   5675篇
  1977年   5563篇
  1976年   5532篇
  1975年   5095篇
  1974年   5038篇
  1973年   5072篇
  1972年   3555篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Cavitation erosion is caused in solids exposed to strong pressure waves developing in an adjacent fluid field. The knowledge of the transient distribution of stresses in the solid is important to understand the cause of damaging by comparisons with breaking points of the material. The modeling of this problem requires the coupling of the models for the fluid and the solid. For this purpose, we use a strategy based on the solution of coupled Riemann problems that has been originally developed for the coupling of 2 fluids. This concept is exemplified for the coupling of a linear elastic structure with an ideal gas. The coupling procedure relies on the solution of a nonlinear equation. Existence and uniqueness of the solution is proven. The coupling conditions are validated by means of quasi‐1D problems for which an explicit solution can be determined. For a more realistic scenario, a 2D application is considered where in a compressible single fluid, a hot gas bubble at low pressure collapses in a cold gas at high pressure near an adjacent structure.  相似文献   
62.
63.
64.
Russian Journal of General Chemistry - Hybrid liquid crystal systems with different ratios of the components have been prepared on the basis of 5,5′-di(heptadecyl)-2,2′-bipyridine...  相似文献   
65.
66.
Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
67.
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   
68.
69.
Nanocomposites based on poly-N-vinylcaprolactam (PVC), characterized by different drying temperatures of aqueous PVC solution at 25°С (PVC25) and 40°С (PVC40), with titanium(IV) oxide nanoparticles (TONs) (η-phase (TP: TiO2 – x · mH2O) with a superstructure to the anatase structure and ordered solid solution with partial replacement of oxygen atoms in the η-phase with peroxo group O 2 2– (PP: TiO x (O2)2 – x · nH2O)) have been obtained for the first time and characterized by X-ray diffraction and IR spectroscopy. It is found that a common feature of TP/PVC and PP/PVC obtained by dry mixing and grinding is the decrease in the number of water molecules for TP and PP in the interlayer space of the structure and their attachment to the PVC amide groups; the differences are related to the specificity of PVC behavior in these systems: mechanodestruction of PVC in PP/PVC40 and different numbers of water molecules in PVC25 and PVC40.  相似文献   
70.
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