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   528800篇
  免费   4158篇
  国内免费   1282篇
化学   269156篇
晶体学   7647篇
力学   25992篇
综合类   17篇
数学   67810篇
物理学   163618篇
  2021年   5038篇
  2020年   5478篇
  2019年   6222篇
  2018年   8413篇
  2017年   8561篇
  2016年   11631篇
  2015年   6177篇
  2014年   10443篇
  2013年   23496篇
  2012年   18341篇
  2011年   21798篇
  2010年   16425篇
  2009年   16284篇
  2008年   20663篇
  2007年   20511篇
  2006年   18617篇
  2005年   16625篇
  2004年   15478篇
  2003年   13963篇
  2002年   13854篇
  2001年   14733篇
  2000年   11350篇
  1999年   8755篇
  1998年   7603篇
  1997年   7473篇
  1996年   6938篇
  1995年   6272篇
  1994年   6269篇
  1993年   6019篇
  1992年   6378篇
  1991年   6867篇
  1990年   6580篇
  1989年   6486篇
  1988年   6321篇
  1987年   6132篇
  1986年   5872篇
  1985年   7409篇
  1984年   7770篇
  1983年   6533篇
  1982年   6820篇
  1981年   6327篇
  1980年   6003篇
  1979年   6504篇
  1978年   6741篇
  1977年   6630篇
  1976年   6587篇
  1975年   6302篇
  1974年   6129篇
  1973年   6424篇
  1972年   4706篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
11.
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   
12.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 1, pp. 46–50, January, 1991.  相似文献   
13.
14.
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   
15.
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   
16.
17.
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   
18.
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   
19.
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field.  相似文献   
20.
The conformational properties of polymers derived from isocyanodipeptides have been investigated with a combination of model calculations, X‐ray diffraction, and circular dichroism spectroscopy. Depending on the configuration of the side chains, defined arrays of hydrogen bonds along the polymeric backbone are formed. This leads to a well‐defined conformation as, for example, expressed in the formation of lyotropic liquid‐crystalline phases and increased helical stability. Upon the disruption of the hydrogen bonds by a strong acid, a less well‐defined macromolecular conformation is observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1725–1736, 2003  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