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   146848篇
  免费   1464篇
  国内免费   394篇
化学   80208篇
晶体学   2387篇
力学   6063篇
综合类   3篇
数学   13569篇
物理学   46476篇
  2021年   1030篇
  2020年   1182篇
  2019年   1251篇
  2018年   1644篇
  2017年   1689篇
  2016年   2541篇
  2015年   1559篇
  2014年   2350篇
  2013年   6037篇
  2012年   4846篇
  2011年   5938篇
  2010年   4181篇
  2009年   4206篇
  2008年   5723篇
  2007年   5510篇
  2006年   5381篇
  2005年   4942篇
  2004年   4449篇
  2003年   4120篇
  2002年   4008篇
  2001年   5541篇
  2000年   3971篇
  1999年   3075篇
  1998年   2110篇
  1997年   2207篇
  1996年   2071篇
  1995年   1915篇
  1994年   1914篇
  1993年   1726篇
  1992年   2215篇
  1991年   2300篇
  1990年   2134篇
  1989年   2099篇
  1988年   2078篇
  1987年   2086篇
  1986年   1909篇
  1985年   2373篇
  1984年   2391篇
  1983年   1909篇
  1982年   1913篇
  1981年   1751篇
  1980年   1737篇
  1979年   2026篇
  1978年   2100篇
  1977年   2046篇
  1976年   1976篇
  1975年   1859篇
  1974年   1844篇
  1973年   1874篇
  1972年   1235篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The satellite structure of 1s2p 1,3 P 1-1s 21 S 0 lines of the He-like argon ion in plasma produced by a 45-fs laser pulse in a gas-jet cluster target is measured with a high spectral resolution. Radiation transitions 2p → 1s from autoionizing states (AISs) are detected for ions ranging from Li-like to F-like. The spectrum observed is theoretically simulated with the use of the spectroscopic data for the AISs of multicharged ions obtained within the multiconfiguration relativistic Hartree-Fock method. Good agreement with experimental data is obtained when the main population channels of these states are taken into account for typical values of cluster-target plasma parameters.  相似文献   
92.
Nonlinear optical parameters (nonlinear refractive indices and nonlinear absorption coefficients) of solutions of polyvinylpyrrolidone doped by cobalt to various concentrations are measured at the lasing and second-harmonic wavelengths of a picosecond Nd:YAG laser (λ=1064 and 532 nm, respectively, and τ=35 ps). Data on optical limitation in these solutions are presented. The absence of nonlinear absorption in the IR spectral range and its significant effect in the visible range are demonstrated. Optical limitation at a wavelength of 1064 nm is related to defocusing, whereas at 532 nm, this effect is caused by two-photon absorption and partially by inverse saturated absorption and defocusing. Nonlinear optical parameters of metal-polymer complexes are reported.  相似文献   
93.
Analytical formulas are derived that describe the dependences of the transition probabilities in vibrational-rotational spectra of XY3-type molecules with C 3v symmetry on the rotational quantum numbers.  相似文献   
94.
95.
A three-dimensional molecular dynamics (MD) model is utilized to investigate the effect of tool geometry on the deformation process of the workpiece and the nature of deformation process at the atomic-scale. Results show that different states exist between the atomic force microscope (AFM) pin tool and the workpiece surface, i.e. the non-wear state, the ploughing state, the state in which ploughing is dominant and the state in which cutting plays a key role. A relationship between the deformation process of the workpiece and the potential energy variation is presented. The potential energy variation of atoms in different deformed regions in the workpiece such as plastically deformed region, elastically deformed region and the mixed deformation region is different. The features of variations of potential energy are discussed.  相似文献   
96.
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   
97.
98.
 The development of a tool for calculating resonances and bound states in three-body systems described by a single-potential energy surface is reported. The method has been applied to the antiprotonic helium, doubly excited states in helium, the 11Li nuclear halo, the NeICl van der Waals molecule, and the recently found FHD reaction complex. Received November 26, 2001; accepted for publication November 28, 2001  相似文献   
99.
The buffer extracts (3S) of sclerotia of Sclerotinia sclerotiorum IFO 9395 contained mitogenic substance(s) to murine splenocytes (Shinohara et al. Chem. Pharm. Bull., 38, 2219 (1990)). Although the native 3S was slightly mitogenic, heating of 3S induced significant mitogenic activity. To isolate the mitogen, we separated 3S by ion-exchange and gel filtration chromatographies. The isolated mitogen, named sclerogen, has a molecular mass of 32 kilodaltons (kDa) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the isoelectric point (pI) of 5.9 by chromatofocusing. Sclerogen was significantly mitogenic in vitro against murine splenocytes after heat denaturation, and also showed the augmentation of the primary mixed lymphocyte reaction (MLR) in vitro. However, sclerogen did not show the activation of an alternative pathway of complement and hemagglutination activity. These results suggest that sclerogen is a unique mitogen which differs from lectins and shows mitogenicity after heat denaturation.  相似文献   
100.
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