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   7229篇
  免费   314篇
  国内免费   208篇
化学   3892篇
晶体学   178篇
力学   306篇
综合类   26篇
数学   990篇
物理学   2359篇
  2023年   71篇
  2022年   122篇
  2021年   133篇
  2020年   145篇
  2019年   152篇
  2018年   134篇
  2017年   150篇
  2016年   212篇
  2015年   174篇
  2014年   223篇
  2013年   474篇
  2012年   394篇
  2011年   410篇
  2010年   279篇
  2009年   289篇
  2008年   334篇
  2007年   328篇
  2006年   259篇
  2005年   261篇
  2004年   203篇
  2003年   162篇
  2002年   155篇
  2001年   106篇
  2000年   79篇
  1999年   81篇
  1998年   69篇
  1996年   84篇
  1995年   79篇
  1994年   80篇
  1993年   103篇
  1992年   105篇
  1991年   74篇
  1990年   84篇
  1989年   78篇
  1988年   76篇
  1987年   71篇
  1986年   53篇
  1985年   101篇
  1984年   118篇
  1983年   74篇
  1982年   72篇
  1981年   81篇
  1980年   83篇
  1979年   91篇
  1978年   77篇
  1977年   74篇
  1976年   69篇
  1975年   55篇
  1974年   60篇
  1973年   75篇
排序方式: 共有7751条查询结果,搜索用时 0 毫秒
21.
In the present paper, we study the rate of convergence in simultaneous approximation for the Bézier variant of the Baskakov-Beta operators by using the decomposition technique of functions of bounded variation.  相似文献   
22.
Reactions between polypyromellitamido acid and component materials of microelectronic articles were examined by thermogravimetric analysis. Modes of modification of the surfaces of semiconductor structures to be used in formation of a system of interconnections with polyimide as interlayer insulator to obtain a high adhesion between the layers via their chemical reactions.  相似文献   
23.
JPC – Journal of Planar Chromatography – Modern TLC - A high-performance thin-layer chromatographic (HPTLC) method has been established for simple and rapid quantification of two...  相似文献   
24.
用干涉方法测量薄膜应力   总被引:2,自引:2,他引:0  
基于基片弯曲法和牛顿环的基本原理,使用He-Ne激光器、扩束镜、凸透镜和带分光镜的移测显微镜,搭建了薄膜应力测量装置.采用直流溅射法制备了厚度为30~144 nm的银薄膜,衬底采用厚度为0.15 mm、直径为18 mm的圆形玻璃片.实验发现,薄膜厚度对银薄膜的内应力有显著的影响,在薄膜厚度很小时,随着薄膜厚度的增加,应力迅速增大,达到最大值后,随着厚度的继续增加,薄膜应力下降较快并趋于稳定值.  相似文献   
25.
The asymptotic null distribution of the likelihood ratio test for two cases of ordered hypotheses in a particular genetic model is considered. A simple iterative process is proposed in order to get the restricted estimates. It is shown that both tests have asymptotically a chi-bar squared distribution and the same size. A simulation study is also conducted in order to compare the usual unrestricted test with the corresponding one of ordered hypotheses. Finally, the results are extended to some special cases.  相似文献   
26.
M B Pande  S Dutta Gupta 《Pramana》1991,37(4):357-362
We present exact numerical results for a symmetric layered medium (prism/Ag film/nonlinear dielectric/Ag film/prism) where the middle dielectric slab is assumed to have a saturation-type nonlinearity. We show bistable behaviour in the power dependence of the reflectivity ofp-polarized light under the condition when coupled surface modes are excited in the structure. Moreover, we study the effect of saturation on the bistable behaviour to show that multivalued character is inhibited by saturation effects. The field distributions corresponding to the minimum reflectivity states of the nonlinear structure are also presented.  相似文献   
27.
Surajit Sen 《Physica A》2006,360(2):304-324
There are very few formalisms available to solve the Liouville equation for energy-conserved systems. The continued fraction formalism, introduced through the works of Zwanzig, Mori, Kubo, Lee, Grigolini and others is described here. A detailed discussion is presented on ways to apply the continued fraction formalism to solve for relaxation functions and for the dynamical variable itself for a simple and exactly solvable quantum spin system.  相似文献   
28.
Gamma ray bursts (GRBs) have been proposed as one possible class of sources of the ultrahigh energy cosmic ray (UHECR) events observed up to energies ≳ 1020 eV. The synchrotron radiation of the highest energy protons accelerated within the GRB source should produce gamma rays up to TeV energies. Here we briefly discuss the implications on the energetics of the GRB from the point of view of the detectability of the prompt TeV γ-rays of proton-synchrotron origin in GRBs in the up-coming ICECUBE muon detector in the south pole.  相似文献   
29.
    
From flash photolysis data of benzil and 2,2′-dichlorobenzil, the role of conformeric triplets in the formation of hydrogen adduct radicals has been discussed. The planar relaxed triplet absorbing at 470 nm is less efficient in forming a hydrogen adduct radical as compared to its puckered conformeric partner. Among the hydrogen donors, triethyl amine and isopropanol, the former is more efficient in converting puckered triplets and less efficient in the case of planar conformers. Absorptions of radicals and radical anions of 2,2′-dichlorobenzil appear at 355 nm and 460 nm respectively. These are blue-shifted as compared to those of the parent compound benzil appearing at 370 nm and 540 nm, respectively. This blue-shift has been discussed in terms of steric hindrance due to ortho-substitution.  相似文献   
30.
In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Whereas the failure rate can be expressed quite simply in terms of the mean residual life and its derivative, the inverse problem—namely that of expressing the mean residual life in terms of the failure rate—typically involves an integral of a complicated expression. In this paper, we obtain simple expressions for the mean residual life in terms of the failure rate for certain classes of distributions which subsume many of the standard cases. Several results in the literature can be obtained using our approach. Additionally, we develop an expansion for the mean residual life in terms of Gaussian probability functions for a broad class of ultimately increasing failure rate distributions. Some examples are provided to illustrate the procedure.  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