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   147692篇
  免费   1541篇
  国内免费   396篇
化学   81078篇
晶体学   2087篇
力学   6089篇
综合类   3篇
数学   13620篇
物理学   46752篇
  2021年   1038篇
  2020年   1220篇
  2019年   1291篇
  2018年   1668篇
  2017年   1701篇
  2016年   2579篇
  2015年   1593篇
  2014年   2378篇
  2013年   6117篇
  2012年   4947篇
  2011年   6035篇
  2010年   4216篇
  2009年   4272篇
  2008年   5833篇
  2007年   5606篇
  2006年   5499篇
  2005年   5028篇
  2004年   4530篇
  2003年   4187篇
  2002年   4067篇
  2001年   5579篇
  2000年   4008篇
  1999年   3090篇
  1998年   2119篇
  1997年   2222篇
  1996年   1931篇
  1995年   1891篇
  1994年   1884篇
  1993年   1694篇
  1992年   2209篇
  1991年   2267篇
  1990年   2124篇
  1989年   2099篇
  1988年   2082篇
  1987年   2083篇
  1986年   1901篇
  1985年   2376篇
  1984年   2406篇
  1983年   1893篇
  1982年   1919篇
  1981年   1746篇
  1980年   1734篇
  1979年   2026篇
  1978年   2104篇
  1977年   2054篇
  1976年   1991篇
  1975年   1866篇
  1974年   1845篇
  1973年   1876篇
  1972年   1231篇
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
81.
82.
Thetrans-[Pt(NC5H4C(O)NHC2H4ONO2)2Cl2] complex (2) was prepared by the reaction of nicorandyl (N-nitroethoxynicotinamide), which is widely used in cardiology, with K2PtCl4 in water. The structure of2 was established by X-ray structural analysis. It was found that complex2 exhibits high antitumor activity, in particular, antimetastatic activity, unlike the analogous CuII complex with bromine atoms. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1672–1675, September, 1997.  相似文献   
83.
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   
84.
The first results regarding the formation of a two-dimensional periodic structure of local melting regions on a silicon surface upon pulsed light irradiation are presented. The conditions are established, and the mechanism of the formation of such structures is discussed. Zh. Tekh. Fiz. 67, 97–99 (December 1997)  相似文献   
85.
Studies of microwave amplification with an in-focused electron beam drawn from an induction injector are reported. A free-electron laser (FEL) operating at 9.4 GHz and employing ion-focusing within the interaction region has achieved power in excess of 30 MW at 9.4 GHz, with a beam energy of 0.8 MeV and current of 0.7 kA. Peak gain is 20 dB/m, with no saturation after 15 wiggler periods. Also reported are the first evolution and detuning data for an ion-channel laser/maser (ICL). Two shortcomings of the prematurely halted ICL studies are poor frequency discrimination and a large axial plasma gradient. Prospects for operation with an upgraded 1.6 MeV accelerator are discussed  相似文献   
86.
87.
Halogen in positions 3 and 5 of the furan ring in ftirfurylidenedioxanediones is readily replaced by dithiocarbonate, dithiocarbatnate, dithiophosphate, thiocyanate, and azide anions, and by thiourea, and secondary and tertiary amines. The conformation of the initial halogen derivative is retained in the substitution products.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 327–334, March, 1994.  相似文献   
88.
We have synthesized 5-alkyl(alkoxy)-2-(o-lzydroxy-p-alkoxyphenyl)pyrimidines and considered the effect of the OH group on the inesomorphism. We have found that in binuclear o-hydroxyarylpyrimidines, an ortho OH group forming an intramolecular hydrogen bond increases Tmp, inhibits the appearance of nematic properties, and promotes the appearance of a smectic A.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 1, pp. 90–92, January, 1994.  相似文献   
89.
The yields and fatty acid compositions of the free lipids and lipids weakly and strongly bound to proteins from seeds of cottonplant varieties resistant and susceptible to verticillium wilt have been determined and the changes in these indices in the seeds of the infected plants have been measured. It has been established that the seeds of healthy plants of the two varieties are similar in the qualitative compositions of the lipids and fatty acids but differ with respect the amounts of lipids in them bound with protein in different ways and with respect to the amounts of the individual fatty acids. The observed changes in the lipid and fatty-acid compositions depend on the degree of resistance of the variety to wilt.  相似文献   
90.
State Scientific Center for Drugs, Khar'kov. Ukrainian Pharmaceutical Academy, Khar'kov. Botanical Gardem, Russian Academy of Sciences, St. Petersburg. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 564–565, July–August, 1994.  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