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   77627篇
  免费   17645篇
  国内免费   287篇
化学   78962篇
晶体学   177篇
力学   2936篇
综合类   1篇
数学   8441篇
物理学   5042篇
  2024年   465篇
  2023年   4794篇
  2022年   1753篇
  2021年   2987篇
  2020年   5355篇
  2019年   2819篇
  2018年   2762篇
  2017年   923篇
  2016年   6549篇
  2015年   6554篇
  2014年   6024篇
  2013年   6914篇
  2012年   4755篇
  2011年   2783篇
  2010年   4554篇
  2009年   4384篇
  2008年   2536篇
  2007年   2228篇
  2006年   1664篇
  2005年   1466篇
  2004年   1377篇
  2003年   1144篇
  2002年   1087篇
  2001年   504篇
  2000年   435篇
  1999年   425篇
  1997年   521篇
  1996年   493篇
  1995年   540篇
  1994年   502篇
  1993年   580篇
  1992年   444篇
  1985年   469篇
  1984年   486篇
  1983年   433篇
  1982年   490篇
  1981年   484篇
  1980年   543篇
  1979年   475篇
  1978年   516篇
  1977年   603篇
  1976年   609篇
  1975年   662篇
  1974年   687篇
  1973年   482篇
  1972年   557篇
  1971年   502篇
  1970年   710篇
  1969年   512篇
  1968年   542篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
Near Hartree-Fock level ab initio molecular orbital calculations on H3O+ and a minimum energy structure with θ(HOH) = 112.5° and r(OH) = 0.963 Å and an inversion barrier of 1.9 kcal/mole. By comparing these results to calculations on NH3 and H2O, where precise experimental geometries are known, we estimate the “true” geometry of isolated H3O+ to have a structure with θ(HOH) = 110-112°, r(OH) = 0.97–0.98 Å and an inversion barrier of 2–3 kcal/mole. Our prediction for the proton affinity of water is ≈ 170 kcal/mole, which is somewhat smaller than the currently accepted value.  相似文献   
212.
    
Summary It is outlined how the determination of Ca in food-stuffs by means of the oxalate method and potassium permanganate titration can be performed with sufficient accuracy. The influence of variable concentrations of the matrix elements P, Mg and Fe on the results is investigated.The relative standard deviation is of the order of ±0.3%. The given concentration of Ca in the presence of matrix elements is determined with an accuracy of ±0.5%.Zusammenfassung Es wird beschrieben, wie mit Hilfe des Oxalatverfahrens und anschließender Permanganat-Titration der Ca-Nachweis in Lebensmitteln mit ausreichender Genauigkeit durchgeführt werden kann. Der Einfluß verschiedener Konzentrationen der Matrixelemente P, Mg und Fe wird untersucht. Die relative Standardabweichung der gefundenen Resultate beträgt 0,3%. Die vorgegebene Konzentration des untersuchten Elements in Gegenwart von P, Mg und Fe wird mit einer Bestimmungsgenauigkeit von ±0,5% wiedergefunden.  相似文献   
213.
The color bond structure of a quark-antiquark system is extended, in the long-range approximation, self-consistently to the baryonic three-quark bond structure for SU(3)c and generally to the N-quark bond structure for SU(N)c. The universal (N-independent) mass square eigenvalues for massless quarks are
M2=(HN)2?2mρ2α=13N?3να+constant, να=0,1,2,…
.  相似文献   
214.
A new proof of a theorem of W. Neiss is given that the rays of the Quadratwurzelschnecke are uniformly distributed mod 2 . The exact order of the discrepancy of the sequence is determined. Multidimensional generalizations of this sequence are also considered. It is shown that the Quadratwurzelschnecke is something like a roulette.

Mit 2 Abbildungen

Herrn Prof. R. M. Redheffer in Freundschaft zum 60. Geburtstag gewidmet  相似文献   
215.
Motivated by an investigation ofKuz'min [2], in this note we introduce a topology on the set of nonassociative algebras of a fixed dimensionr< over a local fieldF. We obtain a space, which is notT 1. If the trivial algebra is removed, the remaining subspace is quasicompact. The space is homeomoprhic to the group of square classes ofF *; forr3 the space is notT 1. The set of division algebras is open in.  相似文献   
216.
We continue our investigations started in a paper with the same title. The -length of a curve defined in this paper can be written as an integral along the curve. Furthermore, we determine necessary and sufficient conditions for the existence of a measure of orientated lines which generates a given non-symmetric pseudo-metric.

Herrn Prof. Dr. H.-J. Kanold zum 65. Geburtstag gewidmet  相似文献   
217.
In this paper a new notion of uniform distribution of double sequences is introduced. In the most elementary case a double sequence (xmn)m, nN is called uniformly distributed in this sense if all finite matrices of equal size appear with the same frequency as submatrices of the infinite matrix (xmn). Some special double sequences with such a distribution property are studied and metric theorems are proved.  相似文献   
218.
Arithmetic formulae and an asymptotic expression for the order of magnitude of the arithmetic function ged (s, n) and of a generalisation of it are derived.  相似文献   
219.
It is shown by a simple induction that any square-free natural number is the square-free kernel of Euler's -function of infinitely many natural numbers. Furthermore every square-free natural number >1 is the square-free kernel of Euler's -function of infinitely many square-numbers.  相似文献   
220.
The classical Gauss-Bonnet formula has the form I(gij)=2, where I(gij) represents a sum of three terms each of which depends on the metric tensor gij. It is shown that the first variation I of I(gij) with respect to the metric gij vanishes and that for the Euclidean metric ij we have I(ij)=2. From this the formula I(gij)=2 follows. In the process, explicit expressions are obtained for the first variation of each of the three terms which comprise I(gij). Furthermore, a general expression for the first variation of a multiple integral whose integrand is a scalar density depending on the metric tensor gij and its derivatives up to the second order is obtained with the aid of results of Rund [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