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   1393篇
  免费   28篇
  国内免费   9篇
化学   742篇
晶体学   3篇
力学   34篇
数学   365篇
物理学   286篇
  2023年   7篇
  2022年   21篇
  2021年   14篇
  2020年   19篇
  2019年   26篇
  2018年   28篇
  2017年   26篇
  2016年   39篇
  2015年   37篇
  2014年   37篇
  2013年   98篇
  2012年   106篇
  2011年   76篇
  2010年   44篇
  2009年   47篇
  2008年   84篇
  2007年   73篇
  2006年   70篇
  2005年   68篇
  2004年   73篇
  2003年   51篇
  2002年   31篇
  2001年   31篇
  2000年   32篇
  1999年   29篇
  1998年   13篇
  1997年   12篇
  1996年   9篇
  1995年   16篇
  1994年   13篇
  1993年   13篇
  1992年   14篇
  1991年   8篇
  1990年   8篇
  1989年   5篇
  1988年   7篇
  1985年   11篇
  1984年   10篇
  1983年   6篇
  1982年   13篇
  1981年   12篇
  1980年   5篇
  1979年   8篇
  1978年   9篇
  1977年   10篇
  1976年   10篇
  1975年   9篇
  1974年   13篇
  1973年   6篇
  1960年   3篇
排序方式: 共有1430条查询结果,搜索用时 15 毫秒
71.
免受温度影响的光纤光栅位移传感器   总被引:14,自引:0,他引:14  
将一定长度、均匀周期的光纤光栅沿轴向刚性粘贴于厚度呈阶跃分布的等腰三角状悬臂梁界线附近的表面上 ,通过观测该光栅反射谱中两个峰值的间距来监测梁自由端在垂直于表面方向上的位移。实验表明该无源温漂位移线性传感装置的传感灵敏度达 9.2 4× 10 -2 nm/ mm,与理论值 9.4× 10 -2 nm/ mm非常接近。  相似文献   
72.
73.
Formation of back corona and its effect on the voltage–current characteristics, etc., have been analysed by several authors. It has also been examined how the harmful effect of back corona can be reduced, for example by the application of pulse energisation. However, to find an optimal solution, modelling of the back corona effect is necessary. Different back corona models were created to estimate the time of its development, the change in current–voltage characteristics, the decrease in particle charge and finally, the collection efficiency of the ESP with back corona. In this paper the authors present an improved numerical ESP model that is capable of determining the parameters of back corona in such cases, when pulse energisation is applied for the power supply of the electrostatic precipitator. Based on the modular structure of the model, different modules calculate the distribution of gas velocity, electric field intensity, particle charging and particle movement. All these parameters are important to determine the properties of back corona while it feeds back on these parameters; therefore iteration is necessary to obtain reliable result. The harmful effects of back corona can be characterised with the help of the evaluation of calculated results.  相似文献   
74.
For any , let be the following subset of :

We show that if , then is always convex. When , it is an ellipsoid, probably degenerate. The convexity result is best possible in the sense that if we have defined similarly, then there are examples which fail to be convex when and .

The set is also symmetric about the origin for all , and contains the origin when . Equivalent statements of this result are given. The convexity result for is similar to Au-Yeung and Tsing's extension of Westwick's convexity result for .

  相似文献   

75.
In this note, we will prove that under certain conditions, the space of polynomial growth harmonic functions and harmonic forms with a fixed growth rate on manifolds which are asymptotically nonnegatively curved is finite dimensional. This is a partial generalization of the works of Li and Colding-Minicozzi. We will also give an explicit estimate for the dimension in case the manifold is a complete surface of finite total curvature. This is a generalization to harmonic forms of the work of Li and the author.

  相似文献   

76.
77.
78.
Building on a recent paper [8], here we argue that the combinatorics of matroids are intimately related to the geometry and topology of toric hyperkähler varieties. We show that just like toric varieties occupy a central role in Stanley’s proof for the necessity of McMullen’s conjecture (or g-inequalities) about the classification of face vectors of simplicial polytopes, the topology of toric hyperkähler varieties leads to new restrictions on face vectors of matroid complexes. Namely in this paper we will give two proofs that the injectivity part of the Hard Lefschetz theorem survives for toric hyperkähler varieties. We explain how this implies the g-inequalities for rationally representable matroids. We show how the geometrical intuition in the first proof, coupled with results of Chari [3], leads to a proof of the g-inequalities for general matroid complexes, which is a recent result of Swartz [20]. The geometrical idea in the second proof will show that a pure O-sequence should satisfy the g-inequalities, thus showing that our result is in fact a consequence of a long-standing conjecture of Stanley.  相似文献   
79.
Wai PK  Xu L  Lui LF  Chan LY  Lee CC  Tam HY  Demokan MS 《Optics letters》2005,30(12):1515-1517
We have demonstrated all-optical packet add-drop for all-optical packet-switched networks. Intelligent all-optical add-drop of packets is performed, based on all-optical processing of packet headers. The header and payload rates are 5 and 10 Gbits/s, respectively.  相似文献   
80.
A bridging chemistry process was developed to form an ether bridge between 6-O and 11-O of erythromycin A via a tandem or stepwise palladium-catalyzed bis-pi-allylation. By applying this bridging process, new 6,11-O-bridged bicyclic ketolides (BBKs) were synthesized. These BBKs showed good antibacterial activities against the macrolide-susceptible strains as well as mef-resistant strains and served as a good core for further modifications to study the structure-activity relationship (SAR) and to overcome bacterial resistance. [reaction: see text]  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