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   879489篇
  免费   9155篇
  国内免费   3891篇
化学   461148篇
晶体学   12178篇
力学   42227篇
综合类   40篇
数学   117450篇
物理学   259492篇
  2021年   7796篇
  2020年   8391篇
  2019年   9344篇
  2018年   12063篇
  2017年   11964篇
  2016年   17833篇
  2015年   10708篇
  2014年   16763篇
  2013年   40017篇
  2012年   30877篇
  2011年   37304篇
  2010年   26808篇
  2009年   26686篇
  2008年   34557篇
  2007年   34252篇
  2006年   31724篇
  2005年   28583篇
  2004年   26729篇
  2003年   23545篇
  2002年   23336篇
  2001年   24504篇
  2000年   19048篇
  1999年   14894篇
  1998年   12700篇
  1997年   12349篇
  1996年   11872篇
  1995年   10728篇
  1994年   10624篇
  1993年   10289篇
  1992年   11162篇
  1991年   11422篇
  1990年   11009篇
  1989年   10718篇
  1988年   10600篇
  1987年   10394篇
  1986年   9874篇
  1985年   12800篇
  1984年   13277篇
  1983年   10946篇
  1982年   11427篇
  1981年   10905篇
  1980年   10323篇
  1979年   11093篇
  1978年   11454篇
  1977年   11232篇
  1976年   11208篇
  1975年   10642篇
  1974年   10572篇
  1973年   10678篇
  1972年   7659篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Simulation of evaporation in operation area of an evaporator is considered. We obtained a formalized model of this process and optimum conditions of an engineering system on the basis on the analysis.  相似文献   
993.
994.
The complexity measure of the infinite set of self-similar hierarchically constrained ensembles is determined in the framework of the generalized combinatory approach. It is shown that, as the hierarchical coupling increases, the complexity increases to a value that decreases with increasing the dispersion of this coupling and with decreasing the branching degree of the hierarchical tree.  相似文献   
995.
Dynamics of the elementary photoelectric conversion upon interaction of a single-photon mode with a bound electron in a one-dimensional rectangular potential well is considered. The spatial and temporal dynamics of the wave packet corresponding to a free photoelectron is investigated.  相似文献   
996.
The thermoelastoplastic fracture mechanics problem of a thick-walled cylinder subjected to internal pressure and a nonuniform temperature field is solved by the method of elastic solutions combined with the finite-element method. The correctness of the solution is provided by using the Barenblatt crack model, in which the stress and strain fields are regular. The elastoplastic problem of a cracked cylinder subjected to internal pressure and a nonuniform temperature field are solved. The calculation results are compared with available data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 173–183, May–June, 2008.  相似文献   
997.
Bis(dialkylamide)hydrogen dibromobromates were synthesized and their reactivity was investigated in decomposition of diethylphosphonic, diethylphosphoric, and 4-toluenesulfonic acids 4-nitrophenyl esters. The nucleophilic reactivity of a typical α-nucleophile, hypobromite ion, is independent of the source of the active bromine. The cetyltrimethylammonium dibromobromate is a unique reagent for destruction of ecotoxicants. In weakly alkaline media the half-life of 4-nitrophenyl diethylphosphonate did not exceed 6 s at [BrO?] 0.02 mol l?1, and the apparent reaction rate compared to water increased ~40-fold. The main factor governing the micellar effects of surfactants is concentrating the substrate in the micellar pseudophase.  相似文献   
998.
A reaction of 2,2-disubstituted 1,1-dicyanoethenes with β-dimethylaminoacrolein aminal and 3-dimethylamino-1,1,3-trimethoxypropane leads to substituted 6,6-dicyano-1-dimethyl-aminohexatrienes and an organic salt containing 1,1,9,9-tetracyano-2,8-diphenylnona-2,4,6,8-tetraenide as the anion and (dimethylaminopropenylidene)dimethylammonium as the cation, on the basis of which new cation-anionic polymethine dyes were obtained. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1639–1643, August, 2008.  相似文献   
999.
Rare-earth metal 8-hydroxyquinolinates (q) were studied as emission layers for organic light-emitting diodes. Compounds Dyq3, Tbq3, and Smq3 possess weak electroluminescence due to the emission of the ligand, and the electroluminescence of Hoq3, Tmq3, and Ybq3 is due to electronic transitions of the lanthanide ion. The best electroluminescence characteristics were demonstrated by Scq3 and Yq3. The power efficiency of the organic light emitter based on ITO/TPD/Scq3/Yb (ITO is tin-alloyed indium oxide, TPD is N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine) is 2.6 lm W−1 at a luminance of the device of 300 cd m−2.  相似文献   
1000.
Effect of conditions of hydrothermal and microwave synthesis of supported vanadium-phosphorus oxide catalysts in an aqueous medium on the physicochemical properties of the vanadyl hydrophosphate obtained was studied. The transformations occurring in the system were examined using X-ray phase and differential-thermal analyses, adsorption-structural method, and scanning electron microscopy.  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