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   22616篇
  免费   845篇
  国内免费   12篇
化学   14947篇
晶体学   169篇
力学   390篇
数学   3826篇
物理学   4141篇
  2023年   151篇
  2022年   165篇
  2021年   255篇
  2020年   351篇
  2019年   341篇
  2018年   472篇
  2017年   432篇
  2016年   866篇
  2015年   678篇
  2014年   701篇
  2013年   1492篇
  2012年   1452篇
  2011年   1460篇
  2010年   865篇
  2009年   808篇
  2008年   1267篇
  2007年   1315篇
  2006年   1164篇
  2005年   1076篇
  2004年   973篇
  2003年   747篇
  2002年   663篇
  2001年   500篇
  2000年   451篇
  1999年   338篇
  1998年   233篇
  1997年   216篇
  1996年   296篇
  1995年   209篇
  1994年   232篇
  1993年   191篇
  1992年   191篇
  1991年   176篇
  1990年   170篇
  1989年   150篇
  1988年   139篇
  1987年   133篇
  1986年   133篇
  1985年   194篇
  1984年   198篇
  1983年   123篇
  1982年   129篇
  1981年   140篇
  1980年   138篇
  1979年   96篇
  1978年   95篇
  1977年   103篇
  1976年   82篇
  1975年   86篇
  1973年   71篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Sauer, Shelah, Vapnik and Chervonenkis proved that if a set system on n vertices contains many sets, then the set system has full trace on a large set. Although the restriction on the size of the groundset cannot be lifted, Frankl and Pach found a trace structure that is guaranteed to occur in uniform set systems even if we do not bound the size of the groundset. In this note we shall give three sequences of structures such that every set system consisting of sufficiently many sets contains at least one of these structures with many sets.  相似文献   
32.
The distribution of mono- poly- and unlabelled protein molecules in the radiolabelling mixture was calculated from probability point of view as a function of the radioiodine/protein ratio.  相似文献   
33.
In order to study the influence of seeded impurities on ITER like reactor operation the COREDIV code has been extended to include the transport of several sputtered and/or injected impurities. In the COREDIV code the core plasma is treated in the frame of 1D radial transport model whereas in the edge the 2D multifluid code EPIT is used. The EPIT code solves in the slab geometry the MHD equations for densities and velocities for all ions species as well as for electron and ion temperatures. The iteration scheme in the code leads to steady state solution of coupled core and SOL system. The numerical results for Carbon and Nickel plate and seeded impurities Silicon and Neon are presented.  相似文献   
34.
Summary This article provides a glimpse of some of the highlights of the joint work of Endre Csáki and Pál Révész since 1979. The topics of this short exploration of the rich stochastic milieu of this inspiring collaboration revolve around Brownian motion, random walks and their long excursions, local times and additive functionals, iterated processes, almost sure local and global central limit theorems, integral functionals of geometric stochastic processes, favourite sites--favourite values and jump sizes for random walk and Brownian motion, random walking in a random scenery, and large void zones and occupation times for coalescing random walks.  相似文献   
35.
This article compares the performance of WDM lightpath protection and IP LSP protection schemes for IP-over-WDM networks. A mathematical formulation of the maximum throughput problem is presented and analytical expressions for recovery time are derived for both schemes. The throughputs and recovery times are analyzed and compared. Results show that the IP LSP protection scheme presents higher throughputs then WDM lightpath protection. The IP LSP protection scheme, providing individual IP LSP protection has, however, scalability problems. This scheme presents high recovery times when a failure affects many lightpaths and many hops are allowed for the primary routes of IP LSPs.  相似文献   
36.
37.
We studied the effectiveness of potable water treatment processes that consist of the stages of coagulation-flocculation-decantation, using iron-based coagulants, in eliminating gamma-emitting man-made radioisotopes of cesium, strontium, and americium from two natural waters with different degrees of mineralization. The resulting decontamination was found to depend on the chemical behavior of each of the radionuclides considered, on the pH at which the process of coagulation is carried out, and on the concentration of the other stable cations present. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
38.
JPC – Journal of Planar Chromatography – Modern TLC - Flavonoid glycosides are much more polar than their aglycones and the two groups of compounds are difficult to separate by planar...  相似文献   
39.
A sequential injection methodology for the spectrophotometric determination of calcium, magnesium and alkalinity in water samples is proposed. A single manifold is used for the determination of the three analytes, and the same protocol sequence allows the sequential determination of calcium and magnesium (the sum corresponds to the water hardness). The determination of both metals is based on their reaction with cresolphtalein complexone; mutual interference is minimized by using 8-hydroxyquinoline for the determination of calcium and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) for the determination of magnesium. Alkalinity determination is based on a reaction with acetic acid, and corresponding color change of Bromcresol Green. Working ranges of 0.5 - 5 mg dm(-3) for Ca, 0.5 - 10 mg dm(-3) for Mg, and 10 - 100 mg HCO3- dm(-3), for alkalinity have been achieved. The results for water samples were comparable to those of the reference methods and to a certified reference water sample. RSDs lower than 5% were obtained, a low reagent consumption and a reduced volume of effluent have been accomplished. The determination rate for calcium and magnesium is 80 h(-1), corresponding to 40 h(-1) per element, while 65 determinations of alkalinity per hour could be carried out.  相似文献   
40.
A note on a generalized Douglas space   总被引:1,自引:0,他引:1  
Periodica Mathematica Hungarica -  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