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   536771篇
  免费   4041篇
  国内免费   1195篇
化学   256478篇
晶体学   8263篇
力学   28884篇
综合类   10篇
数学   73665篇
物理学   174707篇
  2021年   5079篇
  2020年   5402篇
  2019年   6314篇
  2018年   9008篇
  2017年   9292篇
  2016年   12322篇
  2015年   6446篇
  2014年   11446篇
  2013年   24046篇
  2012年   19109篇
  2011年   22612篇
  2010年   17578篇
  2009年   17858篇
  2008年   21014篇
  2007年   20766篇
  2006年   18949篇
  2005年   16486篇
  2004年   15608篇
  2003年   14082篇
  2002年   14204篇
  2001年   15636篇
  2000年   11926篇
  1999年   9145篇
  1998年   8039篇
  1997年   7722篇
  1996年   7160篇
  1995年   6321篇
  1994年   6295篇
  1993年   6177篇
  1992年   6518篇
  1991年   7049篇
  1990年   6761篇
  1989年   6696篇
  1988年   6321篇
  1987年   6501篇
  1986年   6073篇
  1985年   7391篇
  1984年   7671篇
  1983年   6468篇
  1982年   6637篇
  1981年   6212篇
  1980年   6001篇
  1979年   6624篇
  1978年   6661篇
  1977年   6806篇
  1976年   6818篇
  1975年   6383篇
  1974年   6199篇
  1973年   6383篇
  1972年   4988篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
A standard model Lagrangian is constructed making the pseudo-Finsleroid generalization of the Yang-Mills field equation by the conformal method. The Higgs field potential is suggested that ensures generation of particle masses caused by the spontaneous symmetry breaking. After transition to the conformal coordinates, the expressions obtained assume the standard form that in many cases allows the results of pseudo-Euclidean theory to be used in calculations of the Feynman diagrams. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 44–51, April, 2006.  相似文献   
122.
123.
The calcium salt of mono(hydroxyethoxyethyl)phthalate [Ca(HEEP)2] was synthesized by the reaction of diethylene glycol, phthalic anhydride, and calcium acetate. Calcium‐containing poly(urethane ether)s (PUEs) were synthesized by the reaction of hexamethylene diisocyanate (HMDI) or tolylene 2,4‐diisocyanate (TDI) with a mixture of Ca(HEEP)2 and poly(ethylene glycol) (PEG300 or PEG400) with di‐n‐butyltin dilaurate as a catalyst. A series of calcium‐containing PUEs of different compositions were synthesized with Ca(HEEP)2/PEG300 (or PEG400)/diisocyanate (HMDI or TDI) molar ratios of 2:2:4, 3:1:4, and 1:3:4 so that the coating properties of the PUEs could be studied. Blank PUEs without calcium‐containing ionic diols were also prepared by the reaction of PEG300 or PEG400 with HMDI or TDI. The PUEs were well characterized by Fourier transform infrared, 1H and 13C NMR, solid‐state cross‐polarity/magic‐angle‐spinning 13C NMR, viscosity, solubility, and X‐ray diffraction studies. The thermal properties of the polymers were also studied with thermogravimetric analysis and differential scanning calorimetry. The PUEs were applied as top coats on acrylic‐coated leather, and their physicomechanical properties were also studied. The coating properties of PUEs, such as the tensile strength, elongation at break, tear strength, water vapor permeability, flexing endurance, cold crack resistance, abrasion resistance, color fastness, and adhesive strength, were better than the standard values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2865–2878, 2003  相似文献   
124.
A method for suppressing self-modulation in backward-wave tubes is proposed. Additional delay is introduced into the feedback circuit, owing to which the output signal amplitude affects the electron beam current that enters into the interaction space. Numerical simulations demonstrate that the operating current in the single-frequency oscillation mode may be increased roughly twofold.  相似文献   
125.
The luminescence and scintillation properties of poly(methyl methacrylate) containing 1,1,3-trimethyl-3-phenylindan were studied.  相似文献   
126.
The structural change in the depth direction of a polyimide (UPILEX‐S) film treated in alkaline solution, which was a representative surface treatment used to form a seed layer for plating and to improve the adhesive strength, was analyzed by means of micro Fourier transform infrared attenuated total reflection (FTIR‐ATR) line analysis with gradient shaving preparation. The polyimide film was treated with KOH. The imide ring opened through the alkaline treatment, and the amide structure and carboxylic acid salt were formed. The attainment depth of this structural change was almost proportional to the treatment time, and it reached about 8 μm after a 30‐min treatment. The degree of structural change through the alkaline treatment was almost constant after it reached a considerably degraded stage, and the chemically changed region penetrated into the inner part of the film from the surface. An intermediate layer before the final degraded stage appeared in the treated layer, and its thickness increased with the treatment time. The region that was changed chemically by the alkaline treatment progressed to the inner part simultaneously and continuously as the treatment time increased. The combined use of gradient shaving preparation and micro FTIR‐ATR line analysis was found to be extremely effective for the depth profiling of organic materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2071–2078, 2003  相似文献   
127.
It is proved that a Galois extension of a field of characteristic p is completely determined by its Galois group and the endomorphism of the additive group of the group algebra that corresponds to the raising to the power p.  相似文献   
128.
An arbitrary operator-valued function from the generalized Shur class is realized as the transfer function of a minimal optimal and minimal *-optimal dissipative scattering system with the Pontryagin state space. These results generalize Arov's results for the case of the Hilbert state space. Bibliography: 11 titles.  相似文献   
129.
130.
For a planar convex set K with C 2-smooth boundary, the area of the set of the points lying on a given number of affine diameters of K is estimated. As a corollary, it is proved that the area of K is at most pM2 /4\pi M^2 /4 , where M is the largest length of a chord of K halving the area of K. Bibliography: 2 titles.  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