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   34533篇
  免费   1271篇
  国内免费   255篇
化学   24393篇
晶体学   275篇
力学   684篇
综合类   1篇
数学   5941篇
物理学   4765篇
  2023年   161篇
  2022年   160篇
  2021年   429篇
  2020年   611篇
  2019年   600篇
  2018年   417篇
  2017年   389篇
  2016年   941篇
  2015年   827篇
  2014年   1006篇
  2013年   1719篇
  2012年   2186篇
  2011年   2467篇
  2010年   1330篇
  2009年   1182篇
  2008年   2275篇
  2007年   2095篇
  2006年   2118篇
  2005年   1972篇
  2004年   1689篇
  2003年   1383篇
  2002年   1336篇
  2001年   486篇
  2000年   472篇
  1999年   409篇
  1998年   397篇
  1997年   406篇
  1996年   387篇
  1995年   291篇
  1994年   359篇
  1993年   324篇
  1992年   290篇
  1991年   269篇
  1990年   238篇
  1989年   207篇
  1988年   206篇
  1987年   219篇
  1986年   172篇
  1985年   374篇
  1984年   329篇
  1983年   276篇
  1982年   339篇
  1981年   277篇
  1980年   289篇
  1979年   241篇
  1978年   229篇
  1977年   218篇
  1976年   211篇
  1975年   186篇
  1974年   160篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The synthesis of chiral oxazolidinedione derived bicalutamide analogs has been discussed.  相似文献   
132.
The volume integral equation formalism is used to prove the scale invariance rule for an arbitrarily sized scatterer with an arbitrary shape, morphology, and orientation. The only assumptions are that the scatterer is made of optically isotropic linear materials and is embedded in a homogeneous, linear, isotropic, and nonabsorbing infinite medium.  相似文献   
133.
134.
We give general conditions on a generator of a C0-semigroup (resp. of a C0-resolvent) on Lp(E,μ), p ≥ 1, where E is an arbitrary (Lusin) topological space and μ a σ-finite measure on its Borel σ-algebra, so that it generates a sufficiently regular Markov process on E. We present a general method how these conditions can be checked in many situations. Applications to solve stochastic differential equations on Hilbert space in the sense of a martingale problem are given. Dedicated to Giuseppe Da Prato on the occasion of his 70th birthday  相似文献   
135.
136.
Cluster ions have been recognized as a superb primary species in time of flight secondary ion mass spectroscopy (ToF-SIMS) compared with monatomic primary ions, as they significantly enhance the secondary ion yields from bulk samples. Self-assembled monolayers provide an important system for studying the fundamental mechanism involved in the yield enhancement.We used a gold cluster ion source to analyze a new type of self-assembled monolayer: a fluorocarbon-grafted polyethylene terephthalate. In addition to the structure details, which helped to understand the grafting mechanism, ToF-SIMS analysis revealed that fluorocarbon secondary ion yield enhancements by cluster ions were due to the enhanced sputter efficiency. A larger information depth may also be expected from the enhancement. Both mathematical definitions of damage cross-section and disappearance cross-section were revisited under a new context. Another cross-section parameter, sputter cross-section, was introduced to differentiate the beam induced sputter process from damage process.  相似文献   
137.
In this paper, we generalize a theorem of Kallman [2, Theorem 1.1] and we resolve the unsettled case there.  相似文献   
138.
The synthesis of tris-allyl-DOTA starting from cyclen and its application in the preparation of DOTA-peptide conjugates is reported. Clinically important conjugates such as DOTA-Tyr3-octreotide (DOTA-TOC), DOTA-Tyr3-octreotate (DOTA-TATE) as well as a DOTA-RGD peptide were synthesized in high yields with Fmoc solid phase peptide synthesis. The final, extremely reliable de-allylation was achieved on solid phase by different methods identifying morpholine/Pd(0) as the most suitable one obtaining all DOTA peptide conjugates in high yields. All DOTA-peptides were purified by reversed phase HPLC and structural identity was proved using MALDI-TOF mass spectrometry.  相似文献   
139.
We describe a procedure for determining a few of the largest singular values of a large sparse matrix. The method by Golub and Kent which uses the method of modified moments for estimating the eigenvalues of operators used in iterative methods for the solution of linear systems of equations is appropriately modified in order to generate a sequence of bidiagonal matrices whose singular values approximate those of the original sparse matrix. A simple Lanczos recursion is proposed for determining the corresponding left and right singular vectors. The potential asynchronous computation of the bidiagonal matrices using modified moments with the iterations of an adapted Chebyshev semi-iterative (CSI) method is an attractive feature for parallel computers. Comparisons in efficiency and accuracy with an appropriate Lanczos algorithm (with selective re-orthogonalization) are presented on large sparse (rectangular) matrices arising from applications such as information retrieval and seismic reflection tomography. This procedure is essentially motivated by the theory of moments and Gauss quadrature.This author's work was supported by the National Science Foundation under grants NSF CCR-8717492 and CCR-910000N (NCSA), the U.S. Department of Energy under grant DOE DE-FG02-85ER25001, and the Air Force Office of Scientific Research under grant AFOSR-90-0044 while at the University of Illinois at Urbana-Champaign Center for Supercomputing Research and Development.This author's work was supported by the U.S. Army Research Office under grant DAAL03-90-G-0105, and the National Science Foundation under grant NSF DCR-8412314.  相似文献   
140.
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