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   7434篇
  免费   245篇
  国内免费   30篇
化学   5679篇
晶体学   78篇
力学   100篇
数学   419篇
物理学   1433篇
  2023年   37篇
  2022年   61篇
  2021年   70篇
  2020年   86篇
  2019年   120篇
  2018年   70篇
  2017年   62篇
  2016年   147篇
  2015年   132篇
  2014年   167篇
  2013年   370篇
  2012年   383篇
  2011年   461篇
  2010年   252篇
  2009年   286篇
  2008年   473篇
  2007年   455篇
  2006年   497篇
  2005年   446篇
  2004年   425篇
  2003年   343篇
  2002年   346篇
  2001年   149篇
  2000年   109篇
  1999年   82篇
  1998年   91篇
  1997年   84篇
  1996年   94篇
  1995年   63篇
  1994年   54篇
  1993年   60篇
  1992年   53篇
  1991年   64篇
  1990年   44篇
  1989年   42篇
  1988年   52篇
  1987年   54篇
  1986年   64篇
  1985年   102篇
  1984年   81篇
  1983年   51篇
  1982年   77篇
  1981年   85篇
  1980年   66篇
  1979年   76篇
  1978年   61篇
  1977年   41篇
  1976年   51篇
  1975年   33篇
  1973年   30篇
排序方式: 共有7709条查询结果,搜索用时 31 毫秒
21.
Frequency dependence of ac conductivity from 1 to 105 Hz and time series of the conductivity at 2 kHz were measured along c-axis of thulium nitrate crystal, Tm(NO3)36H2O at temperatures from 203.15 to 293.15 K. The meta-stability was observed. The frequency spectra of the conductivity were similar to those in disorder system. Aging effect was observed. Non-periodic instability (burst) was found. Non-linear dynamical property was characterized by 1/f noise spectrum, limit cycle in return map and dependence of correlation exponent on embedding dimension.  相似文献   
22.
23.
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   
24.
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   
25.
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   
26.
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   
27.
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   
28.
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   
29.
30.
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   
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