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   38023篇
  免费   1087篇
  国内免费   6篇
化学   21417篇
晶体学   166篇
力学   780篇
数学   6198篇
物理学   10555篇
  2023年   200篇
  2021年   292篇
  2020年   483篇
  2019年   320篇
  2018年   429篇
  2017年   404篇
  2016年   962篇
  2015年   814篇
  2014年   919篇
  2013年   2025篇
  2012年   1560篇
  2011年   1900篇
  2010年   960篇
  2009年   793篇
  2008年   1829篇
  2007年   1803篇
  2006年   1592篇
  2005年   1398篇
  2004年   1105篇
  2003年   954篇
  2002年   913篇
  2001年   753篇
  2000年   672篇
  1999年   455篇
  1998年   411篇
  1997年   421篇
  1996年   531篇
  1995年   465篇
  1994年   494篇
  1993年   566篇
  1992年   459篇
  1991年   359篇
  1990年   403篇
  1989年   329篇
  1988年   346篇
  1987年   344篇
  1986年   319篇
  1985年   499篇
  1984年   473篇
  1983年   431篇
  1982年   459篇
  1981年   469篇
  1980年   428篇
  1979年   383篇
  1978年   427篇
  1977年   406篇
  1976年   345篇
  1975年   330篇
  1974年   308篇
  1973年   318篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
In [8] the author gave a report on some properties of flag space motions, especially of the composition of screw motions or rotations in flag space. Planet motions more generally are motions which can be composed by two one-parameter-groups. These motions are investigated with respect to their orbits, their multiple ways of construction and the tubular surfaces they can determine. Some of them yield tubular screw surfaces, some others move every sphere the way that it again envellopes a sphere. These motions, which have no Euclidean counterpart, determine non-trivial, kinematically generated LIE-transformations in flag space.  相似文献   
72.
We develop an interactive approach for multiobjective decision-making problems, where the solution space is defined by a set of constraints. We first reduce the solution space by eliminating some undesirable regions. We generate solutions (partition ideals) that dominate portions of the efficient frontier and the decision maker (DM) compares these with feasible solutions. Whenever the decision maker prefers a feasible solution, we eliminate the region dominated by the partition ideal. We then employ an interactive search method on the reduced solution space to help the DM further converge toward a highly preferred solution. We demonstrate our approach and discuss some variations.  相似文献   
73.
74.
75.
The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 A GeV In–In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size close to 400000 events and the good mass resolution of about 2% made it possible to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum shows some non-trivial centrality dependence, but is largely consistent with a dominant contribution from π+π-→ϱ→μ+μ- annihilation. The associated ϱ spectral function exhibits considerable broadening, but essentially no shift in mass. The pT-differential mass spectra show the excess to be much stronger at low pT than at high pT. The results are compared to theoretical model predictions; they tend to rule out models linking hadron masses directly to the chiral condensate. PACS 25.75.-q; 12.38.Mh; 13.85.Qk  相似文献   
76.
An optical parametric oscillator using a periodically poled LiNbO3 crystal and a volume Bragg grating output coupler is presented. Signal and idler wavelengths of 2008 and 2264 nm were generated from the 1064 nm Nd:YVO4 pump laser. The Bragg grating was reflecting in a narrow band around 2008 nm, creating a purely singly resonant cavity. Signal and idler linewidths of approximately 0.44 and 0.72 nm, respectively, were measured. This is a reduction of 80 and 60 times compared to when using a mirror as output coupler. A total output energy of 156 μJ was measured with 47% slope efficiency. PACS 42.65.Yj; 42.72.Ai; 42.40.Eq  相似文献   
77.
In this paper we raise a question about the boundary of the crown domain of a Riemannian symmetric space X. In case X is of Hermitian type we give an affirmative answer.  相似文献   
78.
A series of nucleon–nucleon bremsstrahlung (NNγ) experiments at 190 MeV incident beam energy have been performed at KVI in order to gain more insight into the dynamics governing the bremsstrahlung reaction. After initial measurements wherein the bremsstrahlung process was studied far away from the elastic limit, a new study was used to probe the process nearer to the elastic limit by measuring at lower photon energies. Measured cross sections and analyzing powers are compared with the predictions of a microscopic model and those of two soft-photon models. The theoretical calculations overestimate the data by up to ≈30%, for some kinematics.  相似文献   
79.
We present a method to create at the same time trenches and ordered macropore arrays during photo-electrochemical etching of n-type silicon. This novel method allows in situ separation of single devices with a submicrometer precision. It also enables new device structures in macroporous silicon in the areas of photonics, sensing and electronics. The limits of this new process are simulated using electrostatic models and are verified experimentally. PACS 82.45.Yz; 81.16.-c  相似文献   
80.
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