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   1549篇
  免费   46篇
  国内免费   2篇
化学   1142篇
晶体学   19篇
力学   31篇
数学   149篇
物理学   256篇
  2023年   8篇
  2022年   33篇
  2021年   50篇
  2020年   42篇
  2019年   37篇
  2018年   21篇
  2017年   18篇
  2016年   37篇
  2015年   56篇
  2014年   46篇
  2013年   102篇
  2012年   113篇
  2011年   108篇
  2010年   58篇
  2009年   76篇
  2008年   111篇
  2007年   85篇
  2006年   70篇
  2005年   50篇
  2004年   68篇
  2003年   53篇
  2002年   43篇
  2001年   30篇
  2000年   31篇
  1999年   23篇
  1998年   17篇
  1997年   28篇
  1996年   16篇
  1995年   16篇
  1994年   11篇
  1993年   10篇
  1991年   5篇
  1990年   15篇
  1989年   10篇
  1988年   6篇
  1987年   6篇
  1985年   8篇
  1983年   7篇
  1982年   3篇
  1981年   7篇
  1980年   12篇
  1979年   4篇
  1978年   5篇
  1977年   7篇
  1976年   3篇
  1975年   6篇
  1974年   3篇
  1973年   6篇
  1924年   2篇
  1918年   2篇
排序方式: 共有1597条查询结果,搜索用时 46 毫秒
121.
The main difficulty with the characterization of thin coatings using depth-sensing indentation tests is related to the determination of the contributions of the substrate and the film to the measured properties. In this study, three-dimensional numerical simulations of the Vickers hardness test are used in order to examine the influence of the elastic and plastic properties of the substrate and the film on the composite’s Young’s modulus results. The hardness of the film is equal to or higher than the substrate hardness. A study of the stress distributions and the indentation geometry of composites, film/substrate, was performed, taking into account the relative mechanical properties of the film and substrate. In addition, stress evolution during indentation was studied, in order to quantify the critical indentation depth under which the substrate is not elastically deformed. The accurate evaluation of the Young’s modulus of the films using weight functions is also examined: some of these have previously been proposed and one was introduced for this study. Two different fitting procedures were used to compare the results obtained from eight fictive film/substrate combinations using six weight functions. The first procedure, commonly used, considers the substrate’s modulus as a known parameter in the fitting process. In the second, the film and the substrate’s modulus are considered as unknown variables that are calculated simultaneously during the fitting process. The validity of the conclusions obtained using the fictive materials was checked by applying the weight functions to four real composites.  相似文献   
122.
A kinetic theory is developed for rarefied polyatomic gases of spherical and rough molecules with rotational energy in the presence of an external constant magnetic field. A method of solution of Boltzmann equation that combines features of the methods of Chapman-Enskog and Grad is used to determine transport coefficients that depend on the external magnetic field (Senftleben-Beenakker effect). Received August 4, 1997  相似文献   
123.
Biological self‐assembly is very complex and results in highly functional materials. In effect, it takes a bottom‐up approach using biomolecular building blocks of precisely defined shape, size, hydrophobicity, and spatial distribution of functionality. Inspired by, and drawing lessons from self‐assembly processes in nature, scientists are learning how to control the balance of many small forces to increase the complexity and functionality of self‐assembled nanomaterials. The coiled‐coil motif, a multipurpose building block commonly found in nature, has great potential in synthetic biology. In this review we examine the roles that the coiled‐coil peptide motif plays in self‐assembly in nature, and then summarize the advances that this has inspired in the creation of functional units, assemblies, and systems.  相似文献   
124.
125.
Reaction of (2,4,5-trimethoxyphenyl)(2-hydroxyphenyl)methanone with ceric ammonium nitrate furnished the xanthone, 2,3-dimethoxy-9H-xanthen-9-one. Under the same conditions the related (1,4-dimethoxynaphthalen-2-yl)(2-hydroxyphenyl)methanone resulted in the formation of 12a-methoxy-5H-benzo[c]xanthenes 5,7(12aH)-dione. Other examples of this novel transformation are also outlined.  相似文献   
126.
We experimentally demonstrate the first integrated temporal Fourier transformer based on a linearly chirped Bragg grating waveguide written in silica glass with a femtosecond laser. The operation is based on mapping the energy spectrum of the input optical signal to the output temporal waveform by making use of first-order chromatic dispersion. The device operates in reflection, has a bandwidth of 10 nm, and can be used for incident temporal waveforms as long as 20 ps. Experimental results, obtained through both temporal oscilloscope traces and Fourier transform spectral interferometry, display a successful Fourier transformation of in-phase and out-of-phase pairs of input optical pulses, and demonstrate the correct functionality of the device for both amplitude and phase of the temporal output.  相似文献   
127.
We study complete noncompact spacelike hypersurfaces immersed into conformally stationary spacetimes, that is, Lorentzian manifolds endowed with a timelike conformal vector field V. In this setting, by using as main analytical tool a suitable maximum principle for complete noncompact Riemannian manifolds, we establish new characterizations of totally umbilical hypersurfaces in terms of their higher order mean curvatures. For instance, supposing an appropriated restriction on the norm of the tangential component of the vector field V, we are able to show that such hypersurfaces must be totally umbilical provided that either some of their higher order mean curvatures are linearly related or one of them is constant. Applications to the so‐called generalized Robertson‐Walker spacetimes are given. In particular, we extend to the Lorentzian context a classical result due to Jellett  29 .  相似文献   
128.
In this paper, a parametric algorithm is introduced for computing all eigenvalues for two Eigenvalue Complementarity Problems discussed in the literature. The algorithm searches a finite number of nested intervals \([\bar{l}, \bar{u}]\) in such a way that, in each iteration, either an eigenvalue is computed in \([\bar{l}, \bar{u}]\) or a certificate of nonexistence of an eigenvalue in \([\bar{l}, \bar{u}]\) is provided. A hybrid method that combines an enumerative method [1] and a semi-smooth algorithm [2] is discussed for dealing with the Eigenvalue Complementarity Problem over an interval \([\bar{l}, \bar{u}]\) . Computational experience is presented to illustrate the efficacy and efficiency of the proposed techniques.  相似文献   
129.
130.
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