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   1228篇
  免费   56篇
  国内免费   61篇
化学   627篇
力学   36篇
综合类   4篇
数学   300篇
物理学   378篇
  2024年   2篇
  2023年   40篇
  2022年   34篇
  2021年   32篇
  2020年   26篇
  2019年   39篇
  2018年   27篇
  2017年   48篇
  2016年   53篇
  2015年   40篇
  2014年   42篇
  2013年   87篇
  2012年   74篇
  2011年   53篇
  2010年   52篇
  2009年   67篇
  2008年   80篇
  2007年   66篇
  2006年   47篇
  2005年   48篇
  2004年   54篇
  2003年   41篇
  2002年   33篇
  2001年   23篇
  2000年   18篇
  1999年   18篇
  1998年   20篇
  1997年   27篇
  1996年   21篇
  1995年   15篇
  1994年   12篇
  1993年   9篇
  1992年   13篇
  1991年   8篇
  1990年   10篇
  1989年   10篇
  1988年   8篇
  1987年   4篇
  1986年   4篇
  1985年   2篇
  1984年   8篇
  1983年   4篇
  1982年   5篇
  1981年   3篇
  1979年   9篇
  1977年   1篇
  1976年   2篇
  1974年   3篇
  1973年   2篇
  1969年   1篇
排序方式: 共有1345条查询结果,搜索用时 125 毫秒
1.
2.
高效液相色谱切换波长法测定油菜内源激素   总被引:1,自引:0,他引:1  
采用反相高效液相色谱法(HPLC)切换波长法同时测定油菜中的内源激素赤霉素(GA3)、3-吲哚乙酸(IAA)和脱落酸(ABA),以甲醇:水:乙腈(20:60:20)为流动相,结果显示其检出限分别为GA3:0.08mg/L;IAA:0.015mg/L;ABA:0.025mg/L,比单波长检测的检出限提高了4-10倍;相对标准偏差(RSD)分别为GA3:6.3%,IAA:4.34%,ABA:7.95%.本实验采用切换波长法,显著减低了各组分的检出限,建立了一种以高灵敏度对多组分体系同时进行检测的方法.同时为快速、准确测定油菜内源激素提供了可靠方法.  相似文献   
3.
Gauss Algebras     
A special class of associative algebras is introduced and studied. A criteria of semisimplicity for suitable category of modules is obtained.  相似文献   
4.
The first aim in the present paper is to give an integral representation for Beppo Levi functions on R n. Our integral representation is an extension of Sobolev's integral representation given for infinitely differentiable functions with compact support. As applications, continuity and differentiability properties of Beppo Levi functions are studied.Our second aim in this paper is to study the existence of limits at infinity for Beppo Levi functions. We also consider the existence of fine-type limits at infinity with respect to Bessel capacities, which yields the radial limit result at infinity.  相似文献   
5.
We provide an approximate analysis of the transient sojourn time for a processor sharing queue with time varying arrival and service rates, where the load can vary over time, including periods of overload. Using the same asymptotic technique as uniform acceleration as demonstrated in [12] and [13], we obtain fluid and diffusion limits for the sojourn time of the Mt/Mt/1 processor-sharing queue. Our analysis is enabled by the introduction of a “virtual customer” which differs from the notion of a “tagged customer” in that the former has no effect on the processing time of the other customers in the system. Our analysis generalizes to non-exponential service and interarrival times, when the fluid and diffusion limits for the queueing process are known.  相似文献   
6.
Optical images can be used to transport, store and process information in a parallel way. We discuss different results obtained in the domain of ‘quantum imaging’, aiming at exploiting at the same time the quantum properties of optical images and their intrinsic parallelism. We define the notion of standard quantum limit (SQL) in optical resolution, set by the quantum noise of usual coherent light, and show that it can be much lower than the diffraction limit. We also prove that this limit can be circumvented by especially designed nonclassical and multimode light. We present an experiment showing that OPOs oscillating inside an exactly confocal cavity actually produce such transverse multimode nonclassical light. We finally describe another experiment which has surpassed the SQL in the case of beam positioning, both in the 1D and 2D cases.  相似文献   
7.
8.
本文分析了利用散斑斑纹检测大输液药品杂质含量的机理,报道了检测大输液药品杂质的实例.  相似文献   
9.
10.
Girish  Muckai K.  Hu  Jian-Qiang 《Queueing Systems》1997,26(3-4):269-284
The performance evaluation of many complex manufacturing, communication and computer systems has been made possible by modeling them as queueing systems. Many approximations used in queueing theory have been drawn from the behavior of queues in light and heavy traffic conditions. In this paper, we propose a new approximation technique, which combines the light and heavy traffic characteristics. This interpolation approximation is based on the theory of multipoint Padé approximation which is applied at two points: light and heavy traffic. We show how this can be applied for estimating the waiting time moments of the GI/G/1 queue. The light traffic derivatives of any order can be evaluated using the MacLaurin series analysis procedure. The heavy traffic limits of the GI/G/1 queue are well known in the literature. Our technique generalizes the previously developed interpolation approximations and can be used to approximate any order of the waiting time moments. Through numerical examples, we show that the moments of the steady state waiting time can be estimated with extremely high accuracy under all ranges of traffic intensities using low orders of the approximant. We also present a framework for the development of simple analytical approximation formulas. This revised version was published online in June 2006 with corrections to the Cover Date.  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