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   39356篇
  免费   6497篇
  国内免费   5213篇
化学   27845篇
晶体学   517篇
力学   2541篇
综合类   360篇
数学   4534篇
物理学   15269篇
  2024年   158篇
  2023年   832篇
  2022年   1565篇
  2021年   1585篇
  2020年   1652篇
  2019年   1653篇
  2018年   1476篇
  2017年   1429篇
  2016年   1927篇
  2015年   1907篇
  2014年   2286篇
  2013年   2982篇
  2012年   3422篇
  2011年   3453篇
  2010年   2452篇
  2009年   2341篇
  2008年   2512篇
  2007年   2136篇
  2006年   2019篇
  2005年   1773篇
  2004年   1371篇
  2003年   1131篇
  2002年   1093篇
  2001年   963篇
  2000年   820篇
  1999年   861篇
  1998年   679篇
  1997年   614篇
  1996年   602篇
  1995年   546篇
  1994年   476篇
  1993年   428篇
  1992年   337篇
  1991年   319篇
  1990年   275篇
  1989年   216篇
  1988年   166篇
  1987年   142篇
  1986年   114篇
  1985年   109篇
  1984年   70篇
  1983年   60篇
  1982年   53篇
  1981年   23篇
  1980年   14篇
  1979年   6篇
  1971年   1篇
  1959年   4篇
  1957年   8篇
  1936年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Zhou  Jiuru 《Archiv der Mathematik》2021,116(6):693-706

In this paper, we study vanishing and splitting results on a complete smooth metric measure space \((M^n,g,\mathrm {e}^{-f}\mathrm {d}v)\) with various negative m-Bakry-Émery Ricci curvature lower bounds in terms of the first eigenvalue \(\lambda _1(\Delta _f)\) of the weighted Laplacian \(\Delta _f\), i.e., \(\mathrm {Ric}_{m,n}\ge -a\lambda _1(\Delta _f)-b\) for \(0<a\le \dfrac{m}{m-1}, b\ge 0\). In particular, we consider three main cases for different a and b with or without conditions on \(\lambda _1(\Delta _f)\). These results are extensions of Dung and Vieira, and weighted generalizations of Li-Wang, Dung-Sung, and Vieira.

  相似文献   
2.
3.
建立了一套基于刀口灰度图红外探测的实验装置,对红外场景生成器的空间分辨率进行了测试。首先通过被测红外场景生成器产生带有刀口标志的红外图像,然后利用红外热像仪采集红外场景生成器所成的红外图像,通过对采集到的红外热图的数据处理,实现了对红外场景生成器空间分辨率的测量。测得的红外场景生成器的空间分辨率为5lp/mm,标准误差为0.04。  相似文献   
4.
Terahertz(THz) wave emission from argon atom in a two-color laser pulses is studied numerically by solving the one-dimensional(1D) time-dependent Schr ¨odinger equation. The THz spectra we obtained include both discontinuous and continuum ones. By using the special basis functions that we previously proposed, our analysis points out that the discontinuous and continuum parts are contributed by bound–bound and continuum–continuum transition of atomic energy levels. Although the atomic wave function is strongly dressed during the interaction with laser fields, our identification for the discontinuous part of the THz wave shows that the transition between highly excited bound states can still be well described by the field-free basis function in the tunneling ionization regime.  相似文献   
5.
6.
7.
A new approach has been developed to improve SO2 sorption by cyano‐containing ionic liquids (ILs) through tuning the basicity of ILs and cyano–sulfur interaction. Several kinds of cyano‐containing ILs with different basicity were designed, prepared, and used for SO2 capture. The interaction between these cyano‐containing ILs and SO2 was investigated by FTIR and NMR methods. Spectroscopic investigations and quantum chemical calculations showed that dramatic effects on SO2 capacity originate from the basicity of the ILs and enhanced cyano–sulfur interaction. Furthermore, the captured SO2 was easy to release by heating or bubbling N2 through the ILs. This efficient and reversible process, achieved by tuning the basicity of ILs, is an excellent alternative to current technologies for SO2 capture.  相似文献   
8.
9.
Ni–Co alloys have a wide range of applications in various fields owning to their excellent physical, chemical, and mechanical properties. In this paper, we prepare Ni–Co alloy coatings on 316L stain steel surfaces by electroplating. We present a novel approach utilizing a nanosecond laser to induce microtextures on Ni–Co alloy coatings. We study experimentally the effects of laser power and scanning rate on the surface morphologies of Ni–Co alloy coatings. The results indicate that the shape and size of induced microtextures can be controlled by the laser power and scanning rate. The size of grains increases with increase in the work current of the laser (WCL) at a certain scanning rate. With the WCL constant, the size of grains decreases with increase in scanning rate while their average height increases. It is a simple and easily-controlled method for the fabrication of microstructures on Ni–Co alloy coatings, which has promising applications in investigations of the properties of microtextured surfaces, such as friction, adhesion, and wetting.  相似文献   
10.
A high‐throughout bioanalytical method based on salting‐out‐assisted liquid/liquid extraction (SALLE) method with acetonitrile and mass spectrometry‐compatible salts followed by LC‐MS/MS analysis of trimetazidine in rat plasma is presented. It required only 50 μL of plasma and allows the use of minimal volumes of organic solvents. The seamless interface of SALLE and LC‐MS eliminated the drying‐down step and the extract was diluted and injected into an LC‐MS/MS system with a cycle time of 2.5 min/sample. The retention times of trimetazidine and IS were approximately 1.1 and 1.7 min, respectively. Calibration curves were linear over the concentration range of 0.1–100 ng/mL, which can be extended to 500 ng/mL by dilution. The intra‐ and inter‐batch precision, accuracy and the relative standard deviation were all <15%. This method was successfully applied to determine trimetazidine concentrations in rat plasma. Copyright © 2014 John Wiley & Sons, Ltd.  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