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   107228篇
  免费   6537篇
  国内免费   5221篇
化学   62347篇
晶体学   1444篇
力学   5993篇
综合类   374篇
数学   12689篇
物理学   36139篇
  2023年   828篇
  2022年   1687篇
  2021年   2272篇
  2020年   2582篇
  2019年   2777篇
  2018年   3080篇
  2017年   3012篇
  2016年   3813篇
  2015年   2676篇
  2014年   3854篇
  2013年   5510篇
  2012年   5833篇
  2011年   6180篇
  2010年   4834篇
  2009年   4754篇
  2008年   5096篇
  2007年   4721篇
  2006年   4347篇
  2005年   3813篇
  2004年   3409篇
  2003年   3007篇
  2002年   3124篇
  2001年   2727篇
  2000年   2126篇
  1999年   1747篇
  1998年   1649篇
  1997年   1427篇
  1996年   1402篇
  1995年   1156篇
  1994年   1211篇
  1993年   1156篇
  1992年   1122篇
  1991年   1184篇
  1990年   1153篇
  1989年   1068篇
  1988年   948篇
  1987年   942篇
  1986年   896篇
  1985年   943篇
  1984年   935篇
  1983年   833篇
  1982年   811篇
  1979年   806篇
  1978年   818篇
  1977年   812篇
  1976年   923篇
  1975年   815篇
  1974年   848篇
  1973年   852篇
  1972年   755篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Laser welding is one of the most precise welding processes in joining sheet metals. In laser welding, performing real time evaluation of the welding quality is very important to enhance the efficiency of the welding process. In this study, the plasma and spatter, which are generated during laser welding, are measured using UV and IR photodiodes. The factors that influence weld quality are classified into five categories; optimal heat input, slightly low heat input, low heat input, partial joining due to gap mismatch, and nozzle deviation. The data number deviated from reference signals and their standard deviations were also considered to evaluate the qualities. A system was also formulated to perform real time evaluations of the weld quality using a fuzzy multi-feature pattern recognition with the measured signals.  相似文献   
102.
Some corollaries of the Hirzebruch-Thom signature theorem are discussed. The multiplicativity of the signature and the naturalness of the Pontryagin classes for coverings in the case of ℚ-homology manifolds is proved. A geometric proof of Hirzebruch’s well-known “functional equation” for the virtual signature is outlined. Bibliography: 25 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 231, 1995, pp. 197–209. Translated by N. Yu. Netsvetaev.  相似文献   
103.
The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material.  相似文献   
104.
对由一类非线性抛物型变分不等方程所描述的无穷维动力系统,给出了存在全局吸引子及弱近似惯性流形的充分条件.  相似文献   
105.
106.
Alkylation of 2 furanyl- and 2-thienylalkyl ketoximes with alkyl, allyl, and propargyl halides in the two phase catalytic system sol. K2CO3/C6H6/18-crown-6 at room temperature causes the formation of mixtures of E- and Z-isomers of the corresponding O-ethers with yields of 32–74%. Partial E/Z-isomerization takes place during the reaction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 18–23, January, 1994.  相似文献   
107.
The characterization of the clusters formed on alkaline hydrolysis of [PdCl4]2– was performed using17O,23Na,35Cl,133Cs NMR and UV spectroscopy. The chemical composition of the clusters was found to be [Pd(OH)2] n ·nNaCl. No mononuclear oxo- or hydroxocomplexes were detected. The spatial structure of the clusters is stabilized by alkali metal cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 675–679, April, 1993.  相似文献   
108.
We consider the inverse problem for the identification of the coefficient in a parabolic equation. The model is applied to describe the functioning of a hierarchical structure [1]; it is also relevant for heat-conduction theory [2]. Unique solvability of the inverse problem is proved.  相似文献   
109.
Mathematical Notes -  相似文献   
110.
This paper reports on the first experimental observation of quantum-well states and sp-type resonances in thin single-crystal gold, silver, and copper layers formed on single-crystal W(110) surfaces, which result from spatial localization of Bloch-type electronic wave functions in a quantum well with potential barriers at the vacuum/metal and metal/W(110) interfaces. The quantization of the valence-band electronic structure in Au/W(110), Ag/W(110), and Cu/W(110) systems was studied experimentally using angle-resolved photoelectron spectroscopy.  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