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   1025篇
  免费   167篇
  国内免费   148篇
化学   761篇
晶体学   13篇
力学   57篇
综合类   3篇
数学   104篇
物理学   402篇
  2024年   3篇
  2023年   38篇
  2022年   34篇
  2021年   44篇
  2020年   60篇
  2019年   37篇
  2018年   35篇
  2017年   33篇
  2016年   56篇
  2015年   57篇
  2014年   52篇
  2013年   75篇
  2012年   87篇
  2011年   111篇
  2010年   64篇
  2009年   66篇
  2008年   67篇
  2007年   56篇
  2006年   53篇
  2005年   38篇
  2004年   27篇
  2003年   12篇
  2002年   14篇
  2001年   17篇
  2000年   18篇
  1999年   18篇
  1998年   20篇
  1997年   15篇
  1996年   13篇
  1995年   17篇
  1994年   11篇
  1993年   20篇
  1992年   14篇
  1991年   12篇
  1990年   5篇
  1989年   8篇
  1988年   7篇
  1987年   4篇
  1985年   4篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1980年   4篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1968年   2篇
排序方式: 共有1340条查询结果,搜索用时 0 毫秒
951.
952.
A diode-end-pumped electro-optic (EO) Q-switched Nd:YVO4 laser operating at repetition rate of 10 kpps (pulses per second) was reported. A block of La3Ga5SiO14 (LGS) single crystal was used as a Q-switch and the driver was a metal oxide semiconductor field effect transistor (MOS-FET) pulser of high repetition rate and high voltage. At continuous wave (CW) operation, the slope efficiency of the laser was 46%, and maximum optical-to-optical efficiency was 38.5%. Using an output coupler with transmission of 70%, a 10-kpps Q-switched pulse train with 0.4-mJ monopulse energy and 8.2-ns pulse width was achieved, the optical conversion efficiency was around 15%, and the beam quality M2 factor was less than 1.2.  相似文献   
953.
Using 1,9-salicylamide bissubstituted oxadecane ligand, 1,9-bis [2-(2′-picolylaminoformyl)-1,4,7,9-tetraoxadecane (L), two novel lanthanide complexes have been prepared and well characterized by means of elemental analysis, IR spectroscopy, UV-vis spectroscopy, TGA analysis and single-crystal X-ray diffraction. {[PrL(NO3)3(H2O)2]·CH3OH}n is a 1D zigzag polymer with three-dimensional supramolecular structure formed by hydrogen bonds, while [EuL(NO3)3(H2O)]n is a linear coordination polymer and present an interesting supramolecular double chain, which are very different from the structure of terbium complex reported before. The result reported herein demonstrated that steric crowding associated with the decreasing lanthanide ion radius causes changes of the conformation of the ligand as well as structures. Luminescence studies for the Eu(III) complexes demonstrated that the salicylamide ligand also exhibits a good antennae effect for the Eu(III) ion due to efficient intersystem crossing and ligand-to-metal energy transfer and the Eu(III) ion is well shielded from the surrounding environment.  相似文献   
954.
955.
956.
957.
958.
This paper addresses an integrated inventory and routing problem in a three-echelon logistics system, which consists of a supplier, a central warehouse and a group of retailers. The inventory decision of each member and the routing decision among members of the system are made simultaneously, with the objective of minimizing the overall average cost of the system. A strategy named fixed partition and power-of-two (FP–POT) is proposed for the considered problem and a variable large neighborhood search (VLNS) algorithm, which is a special case of variable neighborhood search (VNS) algorithm, is developed. The efficiency of the strategy as well as the algorithm is illustrated by comparing computational results with a lower bound. The advantage of the proposed VLNS algorithm is further shown by getting better results for the problems in a two-echelon logistics system, which have been solved by a Tabu Search algorithm recently.  相似文献   
959.
We report mode-hopping-free tuning (MHF) over 2 THz (6 nm) of a Littman-Metcalf-type external-cavity diode laser by means of quasi-synchronous tuning, wherein the pivot point is displaced 65 mm away from the conventional rigorous synchronous rotation center. An experimental method for judging the relative position between actual pivot location and the quasi-synchronous tuning line is developed. An adjustment structure with only one freedom of movement is enough to accurately locate the pivot point, and the precise requirement is relaxed to more than 300 μm for achieving a MHF tuning range of over 1THz in our configuration.  相似文献   
960.
This paper concerns with limit cycles through Hopf and homoclinic bifurcations for near-Hamiltonian systems. By using the coefficients appeared in Melnikov functions at the centers and homoclinic loops, some sufficient conditions are obtained to find limit cycles.  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