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   11613篇
  免费   959篇
  国内免费   582篇
化学   7572篇
晶体学   116篇
力学   486篇
综合类   70篇
数学   1712篇
物理学   3198篇
  2023年   148篇
  2022年   265篇
  2021年   333篇
  2020年   352篇
  2019年   377篇
  2018年   346篇
  2017年   299篇
  2016年   453篇
  2015年   432篇
  2014年   532篇
  2013年   811篇
  2012年   803篇
  2011年   855篇
  2010年   569篇
  2009年   514篇
  2008年   638篇
  2007年   522篇
  2006年   538篇
  2005年   454篇
  2004年   354篇
  2003年   337篇
  2002年   325篇
  2001年   287篇
  2000年   210篇
  1999年   181篇
  1998年   128篇
  1997年   106篇
  1996年   112篇
  1995年   95篇
  1994年   143篇
  1993年   102篇
  1992年   113篇
  1991年   105篇
  1990年   92篇
  1989年   67篇
  1988年   64篇
  1987年   57篇
  1986年   58篇
  1985年   82篇
  1984年   75篇
  1983年   44篇
  1982年   71篇
  1981年   65篇
  1980年   70篇
  1979年   60篇
  1978年   64篇
  1977年   57篇
  1976年   51篇
  1975年   40篇
  1973年   41篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
Synthetic pathways to a range of novel semi-rigid tetradentate ligands, with sulfur, amido or amino donor groups, designed to coordinate technetium 99m have been developed. The technetium-99m complexes have been prepared and their stabilities in serum and by metathesis reaction via cysteine exchange reactions were compared. HPLC comparison of two (99m)Tc-complexes and their rhenium analogues led to the first proof of the nature of our radioactive complexes.  相似文献   
882.
We introduce the notion of unlinked invariant set for a diffeomorphism of the 2-torus or the closed annulus and we look at the properties of these sets which generalize the Aubry-Mather sets. We prove that for any irrational number in the rotation set of an area-preserving diffeomorphism of the annulus, there exists an unliked invariant set whose rotation set is reduced to . In the same way we prove that any minimal diffeomorphism of the 2-torus homotopic to the identity may be approximated in the C0-topology by a periodic diffeomorphism.

Mathematics Subject Classification (2000) 37E30, 37E45, 37J10  相似文献   
883.
This paper gives a construction of sticky flows on the circle. Sticky flows give examples of stochastic flows of kernels that interpolates between Arratias coalescing flow and the deterministic diffusion flow. They are associated with systems of sticky independent Brownian particles on the circle, for some fixed parameter of stickyness. It is proved that the noise generated by Brownian sticky flows is black. A new proof of the fact that the noise of Arratias coalescing flow is black is given.  相似文献   
884.
Let T B(X) be a hypercyclic operator and a complex number of modulus 1. Then T is hypercyclic and has the same set of hypercyclic vectors as T. A version of this results gives for a wide class of supercyclic operators that x X is supercyclic for T if and only if the set {tTn x : t > 0, n = 0, 1, ...} is dense in X. This gives answers to several questions studied in the literature.  相似文献   
885.
A geometrical interpretation of the G-structures associated to elastic material bodies is given. In addition, characterizations of their integrability are obtained. Since the lack of integrability is a geometrical measure of the lack of homogeneity, the corresponding inhomogeneity conditions are obtained.  相似文献   
886.
An H  Ashton B  Fleming S 《Optics letters》2004,29(4):343-345
A noninterferometric optical fiber add-drop channel filter based on a mismatched twin-core photosensitive-cladding fiber and long-period fiber grating is demonstrated. With assistance from the fiber grating, co-directional spectrally selective cross coupling between the two cores can be realized with an efficiency of 90%.  相似文献   
887.
The bonding and self-assembly of a chirally organized monolayer of alanine on the Cu(110) surface has been investigated using reflection-absorption infrared spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). This multitechnique approach has enabled an in-depth understanding of the hierarchy of chirality transfer: from a single adsorbed molecule, to size-defined chiral clusters, and then to an overall chiral assembly. The data have indicated that the alanine is in its anionic form, bound to the copper surface through the oxygens of the ionized carboxylate group and the nitrogen of the neutral amino group. Importantly, the methyl group is held away from the surface, resulting in direct chirality transfer into the footprint of the adsorbed alanine molecules, with the local adsorption motif for S-alanine being the mirror image of that created for R-alanine. STM has shown that S-alanine molecules self-organize to form size-defined chiral clusters of six or eight molecules at the surface, interspersed with chiral channels of bare metal. Together, these clusters and channels further self-assemble into a chiral array with one unique chiral domain sustained across the entire surface. A similar chiral assembly, but with the mirror organization, has been observed for R-alanine. Structural models for the individual clusters are proposed, and in conjunction with LEED data, overall models for these chiral phases of both S- and R-alanine have been constructed. Overall, this adsorption system has been found to be both strongly chemisorbed and capable of extensive intermolecular H-bonding, causing stresses that lead not only to the chiral self-organization of molecules but also to a specific self-organization of the empty chiral channels and spaces that intersperse the structure which, in turn, chirally assemble across macroscopic length scales to give a surface with global organizational chirality.  相似文献   
888.
889.
A critical interplay of two correlated noises in a nonlinear symmetrical two-well potential system is experimentally demonstrated. One state can become completely noise free, leading to an infinite Kramers time. If an independent lever breaks the potential symmetry, stochastic resonance is recovered. In this new regime, we obtain a plateau, i.e., a high signal-to-noise ratio even for vanishing forcing signals.  相似文献   
890.
In this paper, te edge mode variation is studied with three different methods: the reciprocal work method, already used by Torvik [J. Acoust. Soc. Am. 41 (1967) 346] to model this phenomenon, the S-parameter method and a finite element model that are applied for the first time to the study of the edge resonance. Moreover, laser probe measurements of the edge mode have also been performed and compared to the numerical predictions. The good agreement between the numerical predictions and the experimental data allows full understanding of the resonant phenomenon. The edge resonance is linked to the strong increase in amplitude of two complex Lamb waves, and the edge mode is proved to radiate into the plate as the first symmetrical Lamb mode S(0). Displacements at the edge and away from the edge have been computed and measured to evaluate the spatial and temporal behaviour of the edge mode. The dependence of the edge resonance frequency and amplitude on the Poisson coefficient has also been studied.  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