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   610540篇
  免费   4642篇
  国内免费   1479篇
化学   307139篇
晶体学   8731篇
力学   31531篇
综合类   24篇
数学   81703篇
物理学   187533篇
  2021年   5644篇
  2020年   6102篇
  2019年   6969篇
  2018年   9450篇
  2017年   9604篇
  2016年   13050篇
  2015年   6945篇
  2014年   11783篇
  2013年   26607篇
  2012年   20658篇
  2011年   24662篇
  2010年   18655篇
  2009年   18655篇
  2008年   23401篇
  2007年   23185篇
  2006年   21059篇
  2005年   18802篇
  2004年   17629篇
  2003年   15900篇
  2002年   15886篇
  2001年   17105篇
  2000年   13141篇
  1999年   10150篇
  1998年   8844篇
  1997年   8664篇
  1996年   8057篇
  1995年   7291篇
  1994年   7250篇
  1993年   7056篇
  1992年   7433篇
  1991年   8031篇
  1990年   7659篇
  1989年   7626篇
  1988年   7392篇
  1987年   7205篇
  1986年   6887篇
  1985年   8798篇
  1984年   9109篇
  1983年   7716篇
  1982年   8001篇
  1981年   7511篇
  1980年   7073篇
  1979年   7733篇
  1978年   8044篇
  1977年   7971篇
  1976年   7958篇
  1975年   7636篇
  1974年   7429篇
  1973年   7785篇
  1972年   5805篇
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
11.
12.
V. A. Steklov Mathematics Institute, USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 79, No. 3, pp. 347–358, June, 1989.  相似文献   
13.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 1, pp. 46–50, January, 1991.  相似文献   
14.
15.
A systematic study on the electrochemical behavior of diosmin in Britton-Robinson buffer (pH 2.0-10.0) at a glassy carbon electrode (GCE) was made. The oxidation process of the drug was found to be quasi-reversible with an adsorption-controlled step. The adsorption stripping response was evaluated with respect to various experimental conditions, such as the pH of the supporting electrolyte, the accumulation potential and the accumulation time. The observed anodic peak current at +0.73 V vs. Ag/AgCl reference electrode increased linearly over two orders of magnitude from 5.0x10(-8) M to 9.0x10(-6) M. A limit of detection down to 3.5x10(-8) M of diosmin at the GCE was achieved with a mean recovery of 97+/-2.1%. Based on the electrochemical data, an open-circuit accumulation step in a stirred sample solution of BR at pH 3.0 was developed. The proposed method was successfully applied to the determination of the drug in pharmaceutical formulations. The results compared favorably with the data obtained via spectrophotometric and HPLC methods.  相似文献   
16.
Ionic conductivity of dry quaternary ammonium polymer, polydiallyldimethylammonium with Cl and H2PO4 counter ions was studied in a wide range of frequencies (10−2-107 Hz) and temperatures (300-470 K). The data were analysed within the formalism of permittivity. WAXS, and thermal properties of this polymer were investigated prior to conductivity measurements.  相似文献   
17.
18.
Systems for automatic detection and correction of spelling errors in natural language texts are considered. The development of such systems for both English and Russian (and for inflected languages in general, including all Slavic languages) is discussed. An approach associated with morphological analysis of the wordforms in the given text is described. The topics considered in the paper include the main methods of automatic spelling correction, levels of automation of the spelling error correction process, the effect of the type of computer used, the use of spelling error correctors in a stand-alone mode and in combination with word-processing software, and the maintenance of auxiliary dictionaries.Translated from Itogi Nauki i Tekhniki, Seriya Teoriya Veroyatnostei, Matematicheskaya Statistika, Teoreticheskaya Kibernetika, Vol. 28, pp. 111–139, 1988.  相似文献   
19.
Consider a projective algebraic variety W which is an irreducible component of the set of all common zeros of a family of homogeneous polynomials of degrees less than d in n + 1 variables over a field of zero characteristic. Consider a dominant rational morphism from W to W′ given by homogeneous polynomials of degree d′. We suggest algorithms for constructing objects in general position related to this morphism. They generalize some algorithms from the first part of the paper to the case dim W > dim W′. These algorithms are deterministic and polynomial in (dd′)n and the size of the input. Bibliography: 12 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 325, 2005, pp. 181–224.  相似文献   
20.
The semi‐analytical integration of an 8‐node plane strain finite element stiffness matrix is presented in this work. The element is assumed to be super‐parametric, having straight sides. Before carrying out the integration, the integral expressions are classified into several groups, thus avoiding duplication of calculations. Symbolic manipulation and integration is used to obtain the basic formulae to evaluate the stiffness matrix. Then, the resulting expressions are postprocessed, optimized, and simplified in order to reduce the computation time. Maple symbolic‐manipulation software was used to generate the closed expressions and to develop the corresponding Fortran code. Comparisons between semi‐analytical integration and numerical integration were made. It was demonstrated that semi‐analytical integration required less CPU time than conventional numerical integration (using Gaussian‐Legendre quadrature) to obtain the stiffness matrix. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006  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