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   694437篇
  免费   5839篇
  国内免费   1884篇
化学   352416篇
晶体学   10187篇
力学   34514篇
综合类   33篇
数学   92137篇
物理学   212873篇
  2021年   6207篇
  2020年   6728篇
  2019年   7601篇
  2018年   10227篇
  2017年   10331篇
  2016年   14500篇
  2015年   8150篇
  2014年   13310篇
  2013年   30979篇
  2012年   24201篇
  2011年   28696篇
  2010年   21181篇
  2009年   21029篇
  2008年   26939篇
  2007年   26789篇
  2006年   24648篇
  2005年   22012篇
  2004年   20494篇
  2003年   18425篇
  2002年   18194篇
  2001年   19512篇
  2000年   15245篇
  1999年   11798篇
  1998年   10188篇
  1997年   9998篇
  1996年   9276篇
  1995年   8406篇
  1994年   8275篇
  1993年   8024篇
  1992年   8613篇
  1991年   8984篇
  1990年   8634篇
  1989年   8441篇
  1988年   8273篇
  1987年   8061篇
  1986年   7689篇
  1985年   9767篇
  1984年   10448篇
  1983年   8716篇
  1982年   9141篇
  1981年   8682篇
  1980年   8244篇
  1979年   8724篇
  1978年   9154篇
  1977年   9025篇
  1976年   8988篇
  1975年   8541篇
  1974年   8396篇
  1973年   8734篇
  1972年   6264篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
61.
The phsicochemical indices and the fatty-acid and triacylglycerol compositions of cottonseed and palm oils, of cottonseed oil hydrogenate, and of compositions based on them have been determined with the aid of IR and UV spectroscopies, GLC analysis, and chemical transformations. The compositions and amounts of the main classes of lipids in the initial oils and the hydrogenate have been studied. It has been found that in the process of hydrogenation the amount of oxygenated components falls. The work was conducted with the financial support of the Uzbek Fund for Fundamental Investigations.  相似文献   
62.
Institute of Botany, Academy of Sciences of the Republic of Azerbaidzhan, Baku. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 291–292, March–April, 1994.  相似文献   
63.
64.
It has been shown by the ESR of spin probes that thionin initially interacts with with negatively charged membranes electrostatically and then passes into the membranes to a depth comparable with the length of the hydrophobic sections of the protein loops.Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Brigham Young University, Provo, Utah, USA. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 594–597, July–August, 1993.  相似文献   
65.
66.
Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram.A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well.  相似文献   
67.
The synthesis of benzazepine analogues of the opium alkaloid noscapine ( 1 ) is described. The benzazepines 2 and 3 were prepared starting from nornarceine ethyl ester ( 4 ; readily available from 1 ) in several steps. X-Ray analysis of compound 2 revealed that it is not a diastereosisomer mixture but a racemate of the threo-form and thus has the same configuration as 1 .  相似文献   
68.
The applicability of differential electrolytic potentiometry as a detection system in flow injection analysis is investigated. A computer-controlled injector which delivers precise volumes of sample solutions in a reproducible manner was developed. Conditions such as current density employed, the concentrations of the solutions used and the flow rate were optimized. Chloride in water was determined by means of this system. The relation between chloride concentration and the measured signal was found to be Nernstian for solutions of concentrations above 6 μg ml−1 chloride. For solutions below this concentration, the relation is linear.  相似文献   
69.
An estimate of the factors which influence the rate of growth of filamentary silicon crystals in a standard chloride system using a quartz reactor with hot walls is given. It is shown that a diffusion form of crystallization is observed under the conditions investigated.Voronezh State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 22–26, October, 1995.  相似文献   
70.
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   
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