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   265256篇
  免费   890篇
  国内免费   285篇
化学   116443篇
晶体学   3763篇
力学   15983篇
综合类   7篇
数学   43898篇
物理学   86337篇
  2019年   2290篇
  2018年   10871篇
  2017年   11629篇
  2016年   7730篇
  2015年   2552篇
  2014年   3695篇
  2013年   7145篇
  2012年   9361篇
  2011年   17668篇
  2010年   11666篇
  2009年   12018篇
  2008年   15704篇
  2007年   18940篇
  2006年   5795篇
  2005年   10449篇
  2004年   7576篇
  2003年   7447篇
  2002年   5840篇
  2001年   5142篇
  2000年   4008篇
  1999年   2865篇
  1998年   2646篇
  1997年   2476篇
  1996年   2444篇
  1995年   2157篇
  1994年   2102篇
  1993年   2122篇
  1992年   2146篇
  1991年   2457篇
  1990年   2387篇
  1989年   2473篇
  1988年   2361篇
  1987年   2388篇
  1986年   2208篇
  1985年   2756篇
  1984年   2784篇
  1983年   2416篇
  1982年   2464篇
  1981年   2369篇
  1980年   2171篇
  1979年   2506篇
  1978年   2670篇
  1977年   2673篇
  1976年   2803篇
  1975年   2593篇
  1974年   2521篇
  1973年   2728篇
  1972年   2192篇
  1971年   2001篇
  1970年   1880篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
Epithio-substituted primary-tertiary dialkyl peroxides were prepared by treatment of tert-alkyl oxiranylmethyl peroxides with potassium thiocyanate and were tested as polymerization initiators in synthesis of light-resistant polystyrene.  相似文献   
952.
Surface morphology and catalytic properties of electrolytic silver crystals in partial oxidation of ethylene glycol into glyoxal were studied.  相似文献   
953.
The Diels-Alder reaction of 1-methylcycloprop-2-ene-1-carbonitrile and coumalic acid methyl ester (methyl 2-oxo-2H-pyran-5-carboxylate) gave a 2:1 adduct with endo-syn configuration of both cyclopropane fragments, which was established by X-ray analysis. According to the 1H NMR data, the reaction involves intermediate formation of decarboxylated 1:1 adduct having a cycloheptatriene structure; its isomerization into the corresponding caradiene, followed by addition of the second dienophile molecule, was confirmed by quantum-chemical calculations.  相似文献   
954.
The process of preservation of newspaper with aqueous solutions and dispersions of acrylic copolymers is considered from the instant of impregnation till removal of the polymeric preservative from paper.  相似文献   
955.
The objective of this paper is to analyze under what well-known operations the class of quasipolyhedral convex functions, which can be regarded as an extension of that of polyhedral convex functions, is closed. The operations that will be considered are those that preserve polyhedral convexity, such that the image and the inverse image under linear transformations, right scalar multiplication (including the case where λ=0+) and pointwise addition.   相似文献   
956.
Correlation between the particles from the proton-nucleus interactions in emulsion at 70 GeV/c is presented through the study of the rapidity gap analysis and compared with the two-particle rapidity correlations. It is observed that the strength of correlation decreases as the size of cluster increases. Asymmetry between the forward and backward components were also studied.Authors are thankful to Prof. K. D. Tolstov, JINR, Dubna, USSR for sending the exposed emulsion plates. Thanks are also due to UGC for financial assistance. We sincerely acknowledge the encouragement from Prof. T. Roy.  相似文献   
957.
This paper presents results of studies on dc electrical conductivity and transference number measurements on potassium bromate (KBrO3) complexed polyvinyl chloride (PVC) films prepared by solution cast technique. Temperature dependence of dc electrical conductivity and transference number data indicated the dominance of ion type charge transport in these specimens. The magnitude of conductivity increased with increase in concentration of the salt and temperature. Using this (PVC + KBrO3) electrolyte, solid-state electrochemical cells were fabricated, and their discharge profiles were studied under a constant load of 100 kΩ. Several cell profiles such as open circuit voltage, short circuit current, power density, and energy density associated with these cells were evaluated and were reported. The features of complexation of the electrolytes were studied by X-ray diffraction and Fourier transform infrared spectroscopy. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006  相似文献   
958.
The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the “hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode. The text was submitted by the authors in English.  相似文献   
959.
A convenient procedure was developed for preparation of thiazolo[5,4-b]pyridine-2-carboxamides by oxidation of monothiooxamides synthesized from 3-aminopyridine.  相似文献   
960.
Mechanisms of orientation for the solutions of polyacrylonitrile synthesized under conditions of radical and anionic polymerization were studied. The effect of the fractal-matrix structuring agent developed by the AIRES foundation on the correlation parameters of the solution density and average squared fluctuation polarizability, which can be used to determine how the supramolecular structure changes by “self-orientation” and “induced orientation” mechanisms, was analyzed.  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