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   6182篇
  免费   216篇
  国内免费   34篇
化学   4822篇
晶体学   58篇
力学   84篇
数学   415篇
物理学   1053篇
  2023年   23篇
  2022年   23篇
  2021年   57篇
  2020年   74篇
  2019年   100篇
  2018年   58篇
  2017年   48篇
  2016年   121篇
  2015年   111篇
  2014年   146篇
  2013年   314篇
  2012年   348篇
  2011年   429篇
  2010年   231篇
  2009年   268篇
  2008年   441篇
  2007年   429篇
  2006年   454篇
  2005年   394篇
  2004年   370篇
  2003年   304篇
  2002年   302篇
  2001年   108篇
  2000年   88篇
  1999年   65篇
  1998年   76篇
  1997年   70篇
  1996年   62篇
  1995年   46篇
  1994年   36篇
  1993年   46篇
  1992年   38篇
  1991年   44篇
  1990年   22篇
  1989年   29篇
  1988年   33篇
  1987年   30篇
  1986年   43篇
  1985年   57篇
  1984年   55篇
  1983年   31篇
  1982年   54篇
  1981年   58篇
  1980年   43篇
  1979年   40篇
  1978年   42篇
  1977年   35篇
  1976年   28篇
  1975年   24篇
  1973年   23篇
排序方式: 共有6432条查询结果,搜索用时 31 毫秒
21.
Let X?(T,D) be a compactification of an affine 3-fold X into a smooth projective 3-fold T such that the (reduced) boundary divisor D is SNC. In this paper, as an affine counterpart to the work due to S. Mori (cf. [S. Mori, Threefolds whose canonical bundles are not numerically effective, Ann. of Math. 116 (1982) 133-176]), we shall classify (K+D)-negative extremal rays on T. In particular, if such an extremal ray R=R+[C] intersects K non-negatively, we shall describe the log flips and divisorial contractions appearing explicitly.  相似文献   
22.
Selective oxidation of an AlInAs layer was investigated for enhancement of magneto-optic effect in an optical isolator. Twelve times nonreciprocal phase shift enhancement was estimated from a measured AlInAs-oxide refractive index.  相似文献   
23.
Endoscopic Observation of Tissue by Narrowband Illumination   总被引:6,自引:0,他引:6  
We propose a new illumination method for a medical endoscope: narrow band imaging (NBI), in which the spectral bandwidth of the filtered light is narrowed. To confirm how the spectral specifications of the filtered light influence a reproduced image, an experiment was conducted observing the endoscopic images of the back mucosa of a human tongue. In addition, the effect of NBI on endoscopic images was investigated through preliminary clinical tests in colonoscopy and upper gastrointestinal endoscopy. It has been shown that NBI can enhance the capillary pattern and the crypt pattern on the mucosa. These patterns are useful features for diagnosing an early cancer.  相似文献   
24.
25.
Spacetime correlation functions of the time-varying speckle intensity have been evaluated for the case where speckle patterns are produced in the Fresnel diffraction region by light propagating through a series of moving random-phase screens. The correlation functions are given by a set of recursion formulae which are useful for numerical computations. Three statistical quantities relating to the motion of speckle patterns are derived to examine the relationship between the velocity distribution of the phase screens and the temporal behaviour of resultant speckle patterns. It is found that the velocity differences between the phase screens have a strong effect on both the decorrelation of speckle patterns and the fluctuating speed of the speckle intensity.  相似文献   
26.
In this paper, we define λ-joint, a-joint, (λ,λ)-joint, (λ,a)-joint and (a,a)-joint t-universality of Lerch zeta functions and consider the relations among those. Next we show the existence of (λ,λ)-joint t-universality. Finally, we also show the existence of λ-joint, a-joint, (λ,a)-joint and (a,a)-joint t-universality by using inversion formulas.  相似文献   
27.
In this article a stability result for the Falk model system is proven. The Falk model system describes the martensitic phase transitions in shape memory alloys. In our setting, the steady state is a nonlocal elliptic problem. We show the dynamical stability for the linearized stable critical point of the corresponding functional. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
28.
29.
A convergent synthesis of the key synthetic intermediate of hemibrevetoxin B was achieved via the intramolecular allylation of an α-chloroacetoxy ether and subsequent ring-closing metathesis.  相似文献   
30.
In this paper, we consider simultaneous confidence intervals for all contrasts in the means when the observations are missing at random in the intraclass correlation model. An exact test statistic for the equality of the means and Scheffé, Bonferroni and Tukey types of simultaneous confidence intervals are given by an extension of Bhargava and Srivastava [On Tukey's confidence intervals for the contrasts in the means of the intraclass correlation model, J. Royal Statist. Soc. B35 (1973) 147-152] when the missing observations are of the monotone type. Finally, numerical results of simultaneous confidence intervals are presented.  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