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   29801篇
  免费   780篇
  国内免费   237篇
化学   19284篇
晶体学   128篇
力学   648篇
综合类   1篇
数学   5385篇
物理学   3889篇
无线电   1483篇
  2022年   186篇
  2021年   322篇
  2020年   376篇
  2019年   342篇
  2018年   303篇
  2017年   312篇
  2016年   643篇
  2015年   667篇
  2014年   707篇
  2013年   1468篇
  2012年   1491篇
  2011年   1777篇
  2010年   1004篇
  2009年   883篇
  2008年   1548篇
  2007年   1547篇
  2006年   1644篇
  2005年   1456篇
  2004年   1390篇
  2003年   1135篇
  2002年   1105篇
  2001年   471篇
  2000年   437篇
  1999年   421篇
  1998年   406篇
  1997年   455篇
  1996年   413篇
  1995年   371篇
  1994年   409篇
  1993年   355篇
  1992年   327篇
  1991年   327篇
  1990年   282篇
  1989年   287篇
  1988年   263篇
  1987年   225篇
  1986年   253篇
  1985年   374篇
  1984年   379篇
  1983年   329篇
  1982年   358篇
  1981年   324篇
  1980年   350篇
  1979年   283篇
  1978年   306篇
  1977年   283篇
  1976年   229篇
  1975年   197篇
  1974年   208篇
  1973年   169篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Gallin Peter Prof. Dr. 《ZDM》2003,35(3):110-119
In order to emphasize functional thinking in mathematical education, arguments are brought forward for an early and frequent use of tree diagrams in teaching stochastics. Since set and tree diagrams can be regarded as two sides of the same matter, Bayes’ theorem, which is strongly associated with predicative set diagrams, need not be dealt with explicitly any longer. Set diagrams are replaced by tree diagrams that are labelled in detail and by tree inversion as a functional instrument of dealing with conditioned probabilities. This technique is demonstrated by three typical problems in the context of conditioned probability. Finally, two letters by Pascal to Fermat are analysed in order to illustrate that predicative and functional approaches were already pursued in the early stages of probability calculus in the 17th century.  相似文献   
32.
3rd International Conference on Trace Element Speciation in Biomedical, Nutritional and Environmental Sciences  相似文献   
33.
34.
研制成用LD泵浦的声光调Q的Nd:YVO4-KTP腔内倍频激光器,得到了TEM00模、频率高达100kHz的稳定的532um绿激光脉冲系列输出,阈值泵浦功率为27mW;在连续570mW的泵浦功率下,绿激光脉冲的峰值功率达1100W,脉宽为4.6us;输出功率稳定,在±5℃的工作温度变化下,输出功率变化小于±2%。此种器件可望得到广泛的应用。  相似文献   
35.
It is shown that any local quantum field theory admits thermodynamical equilibrium states (KMS-states) for all positive temperatures provided it satisfies a nuclearity condition, proposed by Wichmann and one of the authors, which restricts the admissible number of local degrees of freedom.Dedicated to E. H. Wichmann on the occasion of his 60th birthday  相似文献   
36.
The concept of smoothing noisy data using appropriate polynomials turns out to be equivalent to the application of suitable nonrecursive digital filters having the following properties: They process the data in such a way that the moments are conserved up to a desired order while the energy of their impulse response is minimum. Flatness constraints of their frequency response at =0 are equivalent to the moment condition. By using orthogonal polynomials, an explicit solution is known from the literature. A second approach which uses a special decomposition also yields closed form solutions. The realization is simplified, especially in the case where a large number of moments is supposed to be conserved.  相似文献   
37.
Six different hierarchal clustering algorithms were used to cluster eleven sets of compounds for which associated property data were available. The effectiveness of the clustering in each case was assessed by inspection of the resulting tree diagram representing the classification and by the utility of the classification for molecular property prediction. The best predictions were generally obtained by using the algorithm proposed by Ward while the widely-used nearest neighbour algorithm performed very badly. Unstandardised data gave better results than standardised data although the difference was less when structurally related, rather than structurally disparate, groups of compounds were tested.  相似文献   
38.
A new approach to the evaluation of two-electron repulsion integrals over contracted Gaussian basis functions is developed. The new scheme encompasses 20 distinct, but interrelated, paths from simple shell-quartet parameters to the target integrals, and, for any given integral class, the path requiring the fewest floating-point operations (FLOPS ) is that used. Both theoretical (FLOP counting) and practical (CPU timing) measures indicate that the method represents a substantial improvement over the HGP algorithm.  相似文献   
39.
Sodium hexafluoromanganate(III) has been synthesized by heating equimolecular quantities of Na2MnF5 and NaF in argon atmosphere. The compound is monoclinic witha=5.56 (1) Å,b=5.84 (1) Å,c=8.10 (2) Å, =90.7 (2) andZ=2. It is a high spin complex with eff and the deformation of the octahedra is evident from its IR-spectra. Two enantiotropic transitions (at 562 and 653°C) and the melting point at 800°C have been observed.

8. Mitt.: Mh. Chem.106, 483 (1975).  相似文献   
40.
Pyrolysis of homoadamant-3-ene (5), generated from 1-adamantylcarbene (7), leads to the same three olefins (2, 3, and 4) that are produced from pyrolysis of 3-homoadamantyl acetate (1).  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