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   444432篇
  免费   6301篇
  国内免费   1489篇
化学   244360篇
晶体学   6029篇
力学   18699篇
综合类   13篇
数学   52390篇
物理学   130731篇
  2020年   3288篇
  2019年   3344篇
  2018年   3471篇
  2017年   3375篇
  2016年   6487篇
  2015年   4982篇
  2014年   7003篇
  2013年   19885篇
  2012年   15438篇
  2011年   19014篇
  2010年   12158篇
  2009年   12107篇
  2008年   17399篇
  2007年   17701篇
  2006年   16945篇
  2005年   15416篇
  2004年   13816篇
  2003年   12229篇
  2002年   12062篇
  2001年   13201篇
  2000年   10197篇
  1999年   8096篇
  1998年   6703篇
  1997年   6531篇
  1996年   6463篇
  1995年   5954篇
  1994年   5643篇
  1993年   5382篇
  1992年   6026篇
  1991年   5885篇
  1990年   5569篇
  1989年   5380篇
  1988年   5595篇
  1987年   5160篇
  1986年   5013篇
  1985年   7017篇
  1984年   7166篇
  1983年   5875篇
  1982年   6351篇
  1981年   6338篇
  1980年   6045篇
  1979年   6317篇
  1978年   6435篇
  1977年   6311篇
  1976年   6258篇
  1975年   6118篇
  1974年   6010篇
  1973年   6145篇
  1972年   3711篇
  1971年   2947篇
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
971.
We compare the efficiency of two Faddeev-type approaches for the nuclear three-body Coulomb problem. The first one is a modification of Noble’s approach, the second one is due to Sasakawa and Sawada. In an integral-equation formulation both of these methods rely on the same Green’s operators and driving terms. The differences lie in the treatment of the long-range Coulomb potentials. Numerical examples show that the modified Faddeev-Noble approach provides for faster convergence.  相似文献   
972.
X-ray diffraction (XRD), Mössbauer spectrometry (MS), secondary ions mass spectroscopy (SIMS) and laser-ablation microprobe–inductively coupled plasma–mass spectrometry (LAM–ICP–MS) were used to study mineral samples of Colombian auriferous ores collected from the “El Diamante” mine, located in the municipality of Guachavez-Nariño, in Colombia. The samples were prepared as polished thin sections and polished sections. From XRD data, quartz, sphalerite and pyrite were detected and their respective cell parameters were estimated. From MS analyses, pyrite, arsenopyrite and chalcopyrite were identified; their respective hyperfine parameters and respective texture were deduced. Multiple regions of approximately 200 × 200 μm in each sample were analyzed with SIMS; the occurrence of “invisible gold” associated mainly with pyrite and secondarily with arsenopyrite could thus be assigned. It was also found that pyrite is of the arsenious type. Spots from 30 to 40 μm in diameter were analyzed with LAM–ICP–MS for pyrite, arsenopyrite and sphalerite; Au is “homogeneously” distributed inside the structure of the arsenious pyrite and the arsenopyrite (not as inclusions); the chemical composition indicates similarities of this “invisible gold”, forming a solid solution with arsenious pyrite and arsenopyrite. One hundred nineteen and 62 ppm of ‘invisible gold’ was quantified in 21 spots analyzed on pyrite and in 14 spots on arsenopyrite, respectively.  相似文献   
973.
A tin(IV) porphyrin was combined with two axial NCN‐pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN‐pincer platinum derived benzoic acid. The solid‐state structure determined by X‐ray crystallography revealed some close contacts between the pincer complexes and the mesop‐tolyl subsitutents of the porphyrin. It was shown by 1H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures.  相似文献   
974.
Palladium(II) complexes with N,N‐bis(diphenylphosphino)aniline ligands catalyse the Heck reaction between styrene and aryl bromides, affording stilbenes in good yield. The structures of two of the complexes used as pre‐catalysts have been determined by single‐crystal X‐ray diffraction. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
975.
Let T be a bounded linear operator in a Banach space, with σ(T)={1}. In 1983, Esterle-Berkani' s conjecture was proposed for the decay of differences (I - T) T^n as follows: Eitheror lim inf (n→∞(n+1)||(I-T)T^n||≥1/e or T = I. We prove this claim and discuss some of its consequences.  相似文献   
976.
Analysis of stochastic processes governed by the Langevin equation is discussed. The analysis is based on a general method for non-parametric estimation of deterministic and random terms of the Langevin equation directly from given data. Separate estimation of the terms corresponds to the decomposition of process dynamics into deterministic and random components. Part I of the paper presented several possibilities for qualitative and quantitative analysis of process dynamics based on such decomposition. In Part II, some of these analysis possibilities are applied to experimental datasets from metal cutting and laser-beam welding.  相似文献   
977.
Methods of silicon planar technology and pulsed laser deposition were applied to fabricate fully solid-state chemical sensors for determining ions of copper, lead, cadmium, thallium, and also sulfide and chloride ions on the basis of thin chalcogenide films as ion-sensitive membranes.  相似文献   
978.
979.
This work deals with the polymer latexes synthesized using zinc-containing monomers. The effect of the ligand environment of the zinc-containing monomers on the colloidal and rheological properties of the latexes, as well as on mechanical properties of their films is studied. Mixed zinc salts containing the residues of saturated and unsaturated carboxylic acids are shown to be more efficient cross-linking agents than the symmetric salts of this metal.  相似文献   
980.
Recently, the theory of sortability of partition property has been shown to be an effective tool to prove the existence of an optimal partition with that property. In this paper, we extend the theory to multi-partition where the partition is on t types of components. We apply our results to settle an optimal assignment problem whose proof was incomplete as given in the literature.  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