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   4215篇
  免费   143篇
  国内免费   23篇
化学   2859篇
晶体学   35篇
力学   157篇
数学   401篇
物理学   929篇
  2024年   18篇
  2023年   36篇
  2022年   255篇
  2021年   197篇
  2020年   145篇
  2019年   133篇
  2018年   162篇
  2017年   115篇
  2016年   162篇
  2015年   156篇
  2014年   167篇
  2013年   309篇
  2012年   254篇
  2011年   283篇
  2010年   158篇
  2009年   141篇
  2008年   149篇
  2007年   169篇
  2006年   127篇
  2005年   133篇
  2004年   84篇
  2003年   78篇
  2002年   70篇
  2001年   72篇
  2000年   52篇
  1999年   58篇
  1998年   27篇
  1997年   27篇
  1996年   44篇
  1995年   40篇
  1994年   27篇
  1993年   32篇
  1992年   33篇
  1991年   40篇
  1990年   19篇
  1989年   20篇
  1988年   28篇
  1987年   26篇
  1986年   26篇
  1985年   38篇
  1984年   23篇
  1983年   23篇
  1982年   22篇
  1981年   11篇
  1980年   28篇
  1979年   21篇
  1978年   27篇
  1977年   27篇
  1976年   18篇
  1968年   10篇
排序方式: 共有4381条查询结果,搜索用时 15 毫秒
51.
Riju Khandaker  M.  Kamruzzaman  M.  Afrose  R.  Rahman  M.  Khan  M. K. R.  Liton  M. N. H.  Helal  M. A.  Anam  T. K.  Rahman  M. M. 《Crystallography Reports》2020,65(6):968-979
Crystallography Reports - Transition metals doped FeS2 thin films are promising materials for optoelectronics, energy saving and storage applications. This is a first time report on the...  相似文献   
52.
53.
Dysfunction of the blood–brain barrier (BBB) is involved in the pathogenesis of many cerebral diseases. Oxidative stress and inflammation are contributing factors for BBB injury. Piceatannol, a natural ingredient found in various plants, such as grapes, white tea, and passion fruit, plays an important role in antioxidant and anti-inflammatory responses. In this study, we examined the protective effects of piceatannol on lipopolysaccharide (LPS) insult in mouse brain endothelial cell line (bEnd.3) cells and the underlying mechanisms. The results showed that piceatannol mitigated the upregulated expression of adhesion molecules (ICAM-1 and VCAM-1) and iNOS in LPS-treated bEnd.3 cells. Moreover, piceatannol prevented the generation of reactive oxygen species in bEnd.3 cells stimulated with LPS. Mechanism investigations suggested that piceatannol inhibited NF-κB and MAPK activation. Taken together, these observations suggest that piceatannol reduces inflammation and oxidative stress through inactivating the NF-κB and MAPK signaling pathways on cerebral endothelial cells in vitro.  相似文献   
54.
55.
An infinitely extending homogenous partially ionized plasma endowed with several physical mechanisms and permeated by a variable magnetic field is considered. The combined effect of these parameters, namely, Hall currents, finite conductivity, ion viscosity, collision with neutrals and thermal conductivity on the gravitational instability of the plasma is studied. It is found that the several mechanisms play different physical roles in the perturbed problem. Jeans' Criterion is analyzed in the framework of Tsallis' statistics for possible modifications due to the presence of nonextensive effects. A simple generalization of the Jeans' criterion is obtained and the standard values are obtained in the limiting case q = 1, q being the nonextensive parameter. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
56.
Interaction of three waves in a beam-plasma system in a circular cylindrical waveguide is studied. The dispersion relation and the axial growth rate have been obtained.  相似文献   
57.
This paper deals with exact solutions for some oscillating motions of a generalized Oldroyd-B fluid. The fractional calculus approach is used in the constitutive relationship of fluid model. Analytical expressions for the velocity field and the corresponding shear stress for flows due to oscillations of an infinite flat plate as well as those induced by an oscillating pressure gradient are determined using Fourier sine and Laplace transforms. The obtained solutions are presented under integral and series forms in terms of the Mittag–Leffler functions. For α = β = 1, our solutions tend to the similar solutions for ordinary Oldroyd-B fluid. A comparison between generalized and ordinary Oldroyd-B fluids is shown by means of graphical illustrations.  相似文献   
58.
This paper deals with exact solutions for some oscillating motions of a generalized Oldroyd-B fluid. The fractional calculus approach is used in the constitutive relationship of fluid model. Analytical expressions for the velocity field and the corresponding shear stress for flows due to oscillations of an infinite flat plate as well as those induced by an oscillating pressure gradient are determined using Fourier sine and Laplace transforms. The obtained solutions are presented under integral and series forms in terms of the Mittag–Leffler functions. For α = β = 1, our solutions tend to the similar solutions for ordinary Oldroyd-B fluid. A comparison between generalized and ordinary Oldroyd-B fluids is shown by means of graphical illustrations.  相似文献   
59.
Suppose that p(XY) = A − BX − X(∗)B(∗) − CYC(∗) and q(XY) = A − BX + X(∗)B(∗) − CYC(∗) are quaternion matrix expressions, where A is persymmetric or perskew-symmetric. We in this paper derive the minimal rank formula of p(XY) with respect to pair of matrices X and Y = Y(∗), and the minimal rank formula of q(XY) with respect to pair of matrices X and Y = −Y(∗). As applications, we establish some necessary and sufficient conditions for the existence of the general (persymmetric or perskew-symmetric) solutions to some well-known linear quaternion matrix equations. The expressions are also given for the corresponding general solutions of the matrix equations when the solvability conditions are satisfied. At the same time, some useful consequences are also developed.  相似文献   
60.
Using a sample of 152 x 10(6) BB pairs accumulated with the Belle detector at the KEKB e+e- collider, we study the decay mechanism of three-body charmed decay B- --> Lambdac+ ppi-. The intermediate two-body decay B--->Sigmac (2455)0 p is observed for the first time with a branching fraction of (3.7 +/- 0.7 +/- 0.4 +/- 1.0) x 10(-5) and a statistical significance of 8.4sigma. We also observe a low-mass enhancement in the (Lambdac+p) system, which can be parametrized as a Breit-Wigner function with a mass of (3.35(-0.02)(+0.01) +/-0.02) GeV/c2 and a width of (0.07(-0.03)(+0.04) +/-0.04) GeV/c2. We measure its branching fraction to be (3.9(-0.7)(+0.8) +/- 0.4 +/- 1.0) x 10(-5) with a statistical significance of 6.2sigma. The errors are statistical, systematic, and that of the Lambdac+-->pK- pi+ decay branching fraction.  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