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   1942篇
  免费   109篇
  国内免费   16篇
化学   1317篇
晶体学   5篇
力学   70篇
数学   251篇
物理学   424篇
  2024年   3篇
  2023年   18篇
  2022年   29篇
  2021年   60篇
  2020年   72篇
  2019年   64篇
  2018年   41篇
  2017年   37篇
  2016年   97篇
  2015年   72篇
  2014年   75篇
  2013年   121篇
  2012年   130篇
  2011年   164篇
  2010年   73篇
  2009年   100篇
  2008年   130篇
  2007年   129篇
  2006年   128篇
  2005年   105篇
  2004年   74篇
  2003年   51篇
  2002年   62篇
  2001年   15篇
  2000年   33篇
  1999年   17篇
  1998年   11篇
  1997年   19篇
  1996年   18篇
  1995年   12篇
  1994年   11篇
  1993年   15篇
  1992年   5篇
  1991年   6篇
  1990年   9篇
  1989年   8篇
  1988年   8篇
  1987年   7篇
  1986年   2篇
  1985年   6篇
  1984年   5篇
  1982年   2篇
  1981年   6篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1977年   2篇
  1976年   3篇
  1944年   1篇
  1923年   2篇
排序方式: 共有2067条查询结果,搜索用时 31 毫秒
1.
Enhancement of axial magnetic anisotropy is the central objective to push forward the performance of Single-Molecule Magnet (SMM) complexes. In the case of mononuclear lanthanide complexes, the chemical environment around the paramagnetic ion must be tuned to place strongly interacting ligands along either the axial positions or the equatorial plane, depending on the oblate or prolate preference of the selected lanthanide. One classical strategy to achieve a precise chemical environment for a metal centre is using highly structured, chelating ligands. A natural approach for axial-equatorial control is the employment of macrocycles acting in a belt conformation, providing the equatorial coordination environment, and leaving room for axial ligands. In this review, we present a survey of SMMs based on the macrocycle belt motif. Literature systems are divided in three families (crown ether, Schiff-base and metallacrown) and their general properties in terms of structural stability and SMM performance are briefly discussed.  相似文献   
2.
Molecular Diversity - Hypertension is a medical condition that affects millions of people worldwide. Despite the high efficacy of the current antihypertensive drugs, they are associated with...  相似文献   
3.
4.
Nonlinear Dynamics - Introduction of stiffness nonlinearities to broaden the frequency bandwidth of vibratory energy harvesters has the adverse influence of complicating the response behavior of...  相似文献   
5.
In this paper we study the room temperature ferromagnetism reported on Mn-doped ZnO and ascribed to spin polarization of conduction electrons. We experimentally show that the ferromagnetic behaviour is associated to the coexistence of Mn3+ and Mn+4 in MnO2 grains where diffusion of Zn promotes the Mn4+→Mn3+ reduction. Potential uses of this material in spintronic devices are analysed.  相似文献   
6.
It is proved that both the prediction problem and the problem of reconstructing the state from the observations in quantum mechanics are NP-hard.  相似文献   
7.
In this paper we make use of the Pol-Šapirovski?'s technique to prove several cardinal inequalities, which generalize other well-known inequalities.  相似文献   
8.
The first Fundamental Theorem of Asset Pricing establishes the equivalence between the absence of arbitrage in financial markets and the existence of Equivalent Martingale Measures, if appropriate conditions hold. Since the theorem may fail when dealing with infinitely many trading dates, this paper draws on the A.A. Lyapunov Theorem in order to retrieve the equivalence for complete markets such that the Sharpe Ratio is adequately bounded.  相似文献   
9.
Consider an infinite dimensional diffusion process with state space TZd, where T is the circle, and defined by an infinitesimal generator L which acts on local functions f as Lf(η)=∑i∈Zd(ai2i)2?2fi2+bi(η)?fi). Suppose that the coefficients ai and bi are smooth, bounded, of finite range, have uniformly bounded second order partial derivatives, that ai are uniformly bounded from below by some strictly positive constant, and that ai is a function only of ηi. Suppose that there is a product measure ν which is invariant. Then if ν is the Lebesgue measure or if d=1,2, it is the unique invariant measure. Furthermore, if ν is translation invariant, it is the unique invariant, translation invariant measure. The proofs are elementary. Similar results can be proved in the context of an interacting particle system with state space {0,1}Zd, with uniformly positive bounded flip rates which are finite range. To cite this article: A.F. Ram??rez, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 139–144  相似文献   
10.
In this paper we present the application of a direct demodulation method for the measurement of surface topography by means of Shadow-Moiré. In our set-up, we use three LEDs (with green, red and blue peak wavelengths) to illuminate the grating. Due to the different position of these light sources, a polychromatic Shadow-Moiré fringe pattern is produced, which can be described as the superposition of three monochromatic (red, green and blue) fringe patterns. Taking the image of this polychromatic fringe pattern with a RGB CCD camera, we get a monochromatic fringe pattern stored at each RGB channel of the CCD. The direct demodulation algorithm employed uses these fringe patterns to calculate the wrapped phase map. After unwrapping the phase map using a standard multi-grid technique, we implemented an automatic procedure to detect the area of interest of the phase map by removing low modulation zones and to calculate the absolute value of the phase. In this way it is possible to determine the topography of a surface with a single RGB snapshot maintaining a simple experimental set-up, which is an important feature, especially for the study of dynamic phenomena such as deformations. We present the experimental results obtained after measuring different objects with both smooth and rough surface textures.  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