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   37386篇
  免费   5507篇
  国内免费   3656篇
化学   25770篇
晶体学   359篇
力学   2233篇
综合类   241篇
数学   4393篇
物理学   13553篇
  2024年   111篇
  2023年   759篇
  2022年   1224篇
  2021年   1378篇
  2020年   1446篇
  2019年   1332篇
  2018年   1156篇
  2017年   1076篇
  2016年   1614篇
  2015年   1649篇
  2014年   2019篇
  2013年   2600篇
  2012年   3262篇
  2011年   3235篇
  2010年   2189篇
  2009年   2057篇
  2008年   2211篇
  2007年   1967篇
  2006年   1843篇
  2005年   1541篇
  2004年   1302篇
  2003年   984篇
  2002年   894篇
  2001年   738篇
  2000年   691篇
  1999年   830篇
  1998年   694篇
  1997年   636篇
  1996年   705篇
  1995年   603篇
  1994年   550篇
  1993年   470篇
  1992年   449篇
  1991年   364篇
  1990年   324篇
  1989年   237篇
  1988年   216篇
  1987年   198篇
  1986年   141篇
  1985年   156篇
  1984年   135篇
  1983年   116篇
  1982年   80篇
  1981年   59篇
  1980年   49篇
  1979年   33篇
  1978年   26篇
  1976年   27篇
  1975年   31篇
  1974年   23篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
The article referenced above was first published online on 7 August 2007 with incorrect pagination; the pagination has now been corrected online and in print. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
122.
Tumor cells transduced with herpes simplex virus thymidine kinase gene have been intensively applied to the field of positron emission tomography via imaging of its substrate. As a pilot synthesis approach, a facile preparation of 5‐[125I] iodoarabinosyl uridine starting from commercially available uridine is reported herein.  相似文献   
123.
It is shown that for a large collection of independent martingales, the martingale property is preserved on the empirical processes. Under the assumptions of independence and identical finite-dimensional distributions, it is proved that a large collection of stochastic processes are martingales essentially if and only if the empirical processes are also martingales. These two results have implications on the testability of the martingale property in scientific modeling. Extensions to submartingales and supermartingales are given.

  相似文献   

124.
125.
An interval-parameter fuzzy linear programming method (IFMOLP) is proposed in this study for multiple objective decision-making under uncertainty. As a hybrid of interval-parameter and fuzzy methodologies, the IFMOLP incorporates interval-parameter linear programming and fuzzy multiobjective programming approaches to form an integrated optimization system. The method inherits advantages of interval-parameter programming, and allows uncertainties and decision-makers’ aspirations to be effectively communicated into its programming processes and resulting solutions. Membership functions for both objectives and constraints are formulated to reflect uncertainties in different system components and their interrelationships. An interactive solution procedure has been developed based on solution approaches of the interval-parameter and fuzzy programming techniques, plus necessary measures for handling the multiobjective feature. A didactic example is provided in the paper to illustrate the detailed solution process. Possibilities of further improvements by seeking Pareto optimum and incorporating flexible preference within constraints are also discussed.  相似文献   
126.
Ab initio energetic calculations based on the density functional theory (DFT) and projector augmented wave (PAW) pseudo-potentials method were performanced to determine the crystal structural parameters and phase transition data of the polymorphic rare-earth sesquioxides Ln2O3 (where Ln=La-Lu, Y, and Sc) with A-type (hexagonal) and B-type (monoclinic) configurations at ground state. The calculated results agree well with the limited experimental data and the critically assessed results. A set of systematic and self-consistent crystal structural parameters, energies and pressures of the phase transition were established for the whole series of the A- and B-type rare-earth sesquioxides Ln2O3. With the increase of the atomic number, the ionic radii of rare-earth elements Ln and the volumes of the sesquioxides Ln2O3 reflect the so-called “lanthanide contraction”. With the increase of the Ln3+-cation radius, the bulk modulus of Ln2O3 decreases and the polymorphic structures show a degenerative tendency.  相似文献   
127.
Single-crystal magnetite nanowires with average diameter of ca. 20 nm and length of up to several micrometers were prepared by a simple alkaline surfactant-free hydrothermal process. The crystallinity, purity, morphology, and structural features of the as-prepared magnetite nanowires were investigated by powder X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction. The composition and length of nanowires depends on the pH, with higher pH favoring longer nanowires composed entirely of Fe3O4. A mechanism for nanowire growth is proposed.  相似文献   
128.
该文对一般的随机变量序列及相当弱的系数条件研究了随机级数定义的整函数的奈望里纳特征函数,并证明了它是几乎必然无有限例外值的.  相似文献   
129.
针对重力输水管道设计中存在的问题,文章以管道造价最小为目标,应用动态规划,提出了一种新的重力输水管道优化设计方法,对输水管的当量管径、流量分配、连接管设置与可靠性校核计算等问题作了探讨。该方法可用于沿线有节点流量流出的并联输水管道优化设计,能明显节省投资,有良好的实用性  相似文献   
130.
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