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   232780篇
  免费   2244篇
  国内免费   800篇
化学   116841篇
晶体学   3996篇
力学   10757篇
综合类   1篇
数学   25503篇
物理学   78726篇
  2020年   1787篇
  2019年   2043篇
  2018年   2719篇
  2017年   2651篇
  2016年   3913篇
  2015年   2389篇
  2014年   3967篇
  2013年   10072篇
  2012年   7534篇
  2011年   9396篇
  2010年   6685篇
  2009年   6628篇
  2008年   8705篇
  2007年   8736篇
  2006年   8277篇
  2005年   7492篇
  2004年   6920篇
  2003年   6111篇
  2002年   6060篇
  2001年   7090篇
  2000年   5372篇
  1999年   4235篇
  1998年   3563篇
  1997年   3472篇
  1996年   3293篇
  1995年   3008篇
  1994年   2951篇
  1993年   3042篇
  1992年   3151篇
  1991年   3332篇
  1990年   3084篇
  1989年   3027篇
  1988年   3066篇
  1987年   2955篇
  1986年   2800篇
  1985年   3808篇
  1984年   4005篇
  1983年   3198篇
  1982年   3410篇
  1981年   3336篇
  1980年   3230篇
  1979年   3335篇
  1978年   3422篇
  1977年   3350篇
  1976年   3448篇
  1975年   3141篇
  1974年   3150篇
  1973年   3194篇
  1972年   2235篇
  1971年   1849篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
This paper deals mainly with generalizations of results in finitary combinatorics to infinite ordinals. It is well-known that for finite ordinals ∑bT<αβ is the number of 2-element subsets of an α-element set. It is shown here that for any well-ordered set of arbitrary infinite order type α, ∑bT<αβ is the ordinal of the set M of 2-element subsets, where M is ordered in some natural way. The result is then extended to evaluating the ordinal of the set of all n-element subsets for each natural number n ≥ 2. Moreover, series ∑β<αf(β) are investigated and evaluated, where α is a limit ordinal and the function f belongs to a certain class of functions containing polynomials with natural number coefficients. The tools developed for this result can be extended to cover all infinite α, but the case of finite α appears to be quite problematic.  相似文献   
62.
63.
64.
Results are reported for measurements of the spin-lattice relaxation times of E1 centers in quartz glass, produced by neutron irradiation, with the measurements made at two frequencies 9.25 and 24.0 GHz over a wide temperature interval 1.5–300 K. The experimental data are interpreted on the basis of interaction mechanisms of the spins with two-level systems with excitation energies ∼6, ∼26, and ∼420 cm−1. A small modification of the existing theory allows us to explain a number of features of the observed temperature and frequency dependence of the relaxation rate. The results are compared with the data available in the literature on spin-lattice relaxation of irradiation centers in crystalline quartz and quartz glass. Fiz. Tverd. Tela (St. Petersburg) 39, 1335–1337 (August 1997)  相似文献   
65.
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy.  相似文献   
66.
Molecular n-v complexes of quinoline N-oxides with BF3 have been studied by electronic and IR spectroscopy. In most case the donor centre is the oxygen atom of the N-oxide group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1087–1092, August, 1994.  相似文献   
67.
The influence of sunflowerseed and cottonseed oils and also of fractions of normal and oxidized triacylglycerols isolated from them on cytochrome P-450 from rat liver microsomes has been investigated.  相似文献   
68.
6-Halogeno-1,3-benzodioxane analogs of chalcones have been synthesized by various methods. Flavanone and flavone analogs of silandrin and hydnocarpin have been obtained from them. The structures of the new flavonoids have been shown by their PMR spectra.  相似文献   
69.
Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 891475. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 679–680, September–October, 1994.  相似文献   
70.
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