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   44014篇
  免费   1729篇
  国内免费   1801篇
化学   13199篇
晶体学   1111篇
力学   599篇
综合类   106篇
数学   20742篇
物理学   6108篇
无线电   5679篇
  2024年   52篇
  2023年   468篇
  2022年   463篇
  2021年   496篇
  2020年   662篇
  2019年   926篇
  2018年   888篇
  2017年   723篇
  2016年   830篇
  2015年   978篇
  2014年   1519篇
  2013年   2777篇
  2012年   1731篇
  2011年   3226篇
  2010年   2683篇
  2009年   3006篇
  2008年   3211篇
  2007年   3042篇
  2006年   2445篇
  2005年   1960篇
  2004年   1803篇
  2003年   1584篇
  2002年   1716篇
  2001年   993篇
  2000年   901篇
  1999年   927篇
  1998年   784篇
  1997年   625篇
  1996年   699篇
  1995年   671篇
  1994年   597篇
  1993年   466篇
  1992年   442篇
  1991年   333篇
  1990年   304篇
  1989年   303篇
  1988年   198篇
  1987年   213篇
  1986年   172篇
  1985年   257篇
  1984年   195篇
  1983年   120篇
  1982年   170篇
  1981年   196篇
  1980年   142篇
  1979年   92篇
  1978年   128篇
  1977年   119篇
  1976年   111篇
  1974年   52篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
101.
An effective residual interaction between particles and holes for shell model calculations around 208Pb, derived from the interaction between free nucleons, is compared with the measured properties of proton-hole neutron states in 208Tl and the interaction between proton holes is adjusted to newly measured level energies in 206Hg. These interaction elements are particularly relevant for neutron-rich nuclei. The adjustment of two mixing elements reproduces the known γ-decay data in 208Tl. Received: 2 April 2002 / Accepted: 2 May 2002  相似文献   
102.
本对PN结反向物理特性,应用电子技术和计算机技术实现了对实验过程的控制和效据处理。  相似文献   
103.
Oleg Borodin 《Combinatorica》1993,13(1):121-125
The weight of an edge in a graph is the sum of the degrees of its end-vertices. It is proved that in each 3-polytope there exists either an edge of weight at most 13 for which both incident faces are triangles, or an edge of weight at most 10 which is incident with a triangle, or else an edge of weight at most 8. All the bounds 13, 10, and 8 are sharp and attained independently of each other.  相似文献   
104.
105.
本文通过对大量的黄酮类化合物13C NMR图谱的分析和研究,总结了不同类型的黄酮类化合物的13C NMR图谱特征及化学位移规律.对影响黄酮类化合物结构骨架上不同位置碳原子化学位移的因素进行了分析,建立了用于黄酮类天然产物13C NMR图谱智能解析的知识库.  相似文献   
106.
Summary We prove convergence and error estimates in Sobolev spaces for the collocation method with tensor product splines for strongly elliptic pseudodifferential equations on the torus. Examples of applications include elliptic partial differential equations with periodic boundary conditions but also the classical boundary integral operators of potential theory on torus-shaped domains in three or more dimensions. For odd-degree splines, we prove convergence of nodal collocation for any strongly elliptic operator. For even-degree splines and midpoint collocation, we find an additional condition for the convergence which is satisfied for the classical boundary integral operators. Our analysis is a generalization to higher dimensions of the corresponding analysis of Arnold and Wendland [4].  相似文献   
107.
The main aim of this paper is the calculation of the dimension of certain atomic amalgams. These consist of finite Boolean algebras (blocks) pasted together in such a way that a pair of blocks intersects either trivially in the bounds, or the intersection consists of the bounds, an atom, and its complement.  相似文献   
108.
By means of a direct and constructive method based on the theory of semi‐global C2 solution, the local exact boundary observability and an implicit duality between the exact boundary controllability and the exact boundary observability are shown for 1‐D quasilinear wave equations with various boundary conditions. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
109.
Ali Liazid  Jamal Brigui 《Talanta》2007,71(2):976-980
The stability of Ochratoxin A during its extraction using different extraction techniques has been evaluated. Microwave-assisted extraction and pressurised liquid extraction, in addition to two other reference methods of extraction, i.e. ultrasound-assisted and magnetic stirring-assisted extraction, were evaluated. The effect of extraction temperature using the cited techniques was checked.The results show that Ochratoxin A can be extracted using microwave-assisted extraction at temperatures up to 150 °C without degradation. Pressurised liquid extraction can be used at temperatures up to 100 °C, for extraction times of less than 30 min. Further, both ultrasound-assisted extraction and magnetic stirring extraction can be applied at temperatures up to 65 °C.High-performance liquid chromatography combined with fluorescence detection using a Chromolith RP-18e column at a flow rate of 5 mL min−1 was used to quantify the Ochratoxin A. The retention time for the Ochratoxin A was 1.3 min. The limits of detection (LOD) and of quantification (LOQ) were 0.03 and 0.10 μg L−1, respectively.  相似文献   
110.
Let Λ be a smooth Lagrangian submanifold of a complex symplectic manifold X. We construct twisted simple holonomic modules along Λ in the stack of deformation-quantization modules on X.  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