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   441522篇
  免费   5630篇
  国内免费   1315篇
化学   237470篇
晶体学   6562篇
力学   18904篇
综合类   13篇
数学   51537篇
物理学   133981篇
  2021年   3798篇
  2020年   4237篇
  2019年   4568篇
  2018年   5920篇
  2017年   5787篇
  2016年   8941篇
  2015年   5651篇
  2014年   8641篇
  2013年   20530篇
  2012年   15901篇
  2011年   19548篇
  2010年   13690篇
  2009年   13523篇
  2008年   17906篇
  2007年   17797篇
  2006年   16536篇
  2005年   14832篇
  2004年   13766篇
  2003年   12105篇
  2002年   11950篇
  2001年   13504篇
  2000年   10153篇
  1999年   7991篇
  1998年   6661篇
  1997年   6402篇
  1996年   6210篇
  1995年   5546篇
  1994年   5467篇
  1993年   5268篇
  1992年   5902篇
  1991年   5994篇
  1990年   5724篇
  1989年   5529篇
  1988年   5546篇
  1987年   5438篇
  1986年   5142篇
  1985年   6659篇
  1984年   6797篇
  1983年   5374篇
  1982年   5468篇
  1981年   5471篇
  1980年   5073篇
  1979年   5444篇
  1978年   5589篇
  1977年   5460篇
  1976年   5407篇
  1975年   5001篇
  1974年   4969篇
  1973年   4967篇
  1972年   3499篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
In the present paper we introduce a new family of linear positive operators and study some direct and inverse results in simultaneous approximation.  相似文献   
982.
983.
The conditions of compatibility of the magnetic sublattice hypothesis with the requirements of quantum theory have been derived. These conditions imply the presence of (even weak) magnetic anisotropy and a macroscopic number of spins in the sublattice.  相似文献   
984.
985.
Jeong  M. T. 《Hyperfine Interactions》2004,156(1-4):165-168
Hyperfine Interactions - The decay constants of nuclei are calculated based on the Cheon's idea, namely, the population of nuclear excited state can be modified by the mechanism that the...  相似文献   
986.
Zboril  R.  Mashlan  M.  Machala  L.  Walla  J.  Barcova  K.  Martinec  P. 《Hyperfine Interactions》2004,156(1-4):403-410
Hyperfine Interactions - The natural garnets from almandine (Fe3Al2Si3O12)–pyrope (Mg3Al2Si3O12) series with the iron to magnesium atomic ratio ranging from 0.2 to 1 were characterised and...  相似文献   
987.
A number of phenomena connected with the formation of electrode jets in discharges in hydrogen at a current of 10/sup 5/-10/sup 6/ A, a current growth rate of 10/sup 10/ A/s, an initial pressure 0.1-4.0 MPa, and a discharge gap length of 5-40 mm were studied. After the secondary breakdown, the jets are observed through a discharge semitransparent channel, widening with velocity (4-7) /spl middot/ 10/sup 2/ m/s. Shockwave formation was detected at the interaction of jets with the surrounding gas and the opposite electrode. Plasma vapor pressure of metal near the end of the tungsten cathode 70 /spl mu/s after initiation of a discharge was 180 MPa. Thus, magnitude of brightness temperature was 59 /spl middot/ 10/sup 3/ K, with an average charge of ions-m~=3.1, and a concentration of metal vapors n=5.3/spl middot/10/sup 19/ cm/sup -3/. While those at the end of the anode 90 /spl mu/s after initiation of discharge: m~=2.6, n=7.4/spl middot/10/sup 19/ cm/sup -3/. Probable reasons of high-voltage drops near the electrodes (the summarized magnitude of which is /spl sim/1 kV) are discussed on the basis of experimental data. For the first time, the shadow method registered symmetric ejection of material from the all-cathode surface the maximum discharge current was observed.  相似文献   
988.
989.
For any two points p and q in the Euclidean plane, define LUNpq = { v | vR2, dpv < dpq and dqv < dpq}, where duv is the Euclidean distance between two points u and v . Given a set of points V in the plane, let LUNpq(V) = V ∩ LUNpq. Toussaint defined the relative neighborhood graph of V, denoted by RNG(V) or simply RNG, to be the undirected graph with vertices V such that for each pair p,qV, (p,q) is an edge of RNG(V) if and only if LUNpq (V) = ?. The relative neighborhood graph has several applications in pattern recognition that have been studied by Toussaint. We shall generalize the idea of RNG to define the k-relative neighborhood graph of V, denoted by kRNG(V) or simply kRNG, to be the undirected graph with vertices V such that for each pair p,qV, (p,q) is an edge of kRNG(V) if and only if | LUNpq(V) | < k, for some fixed positive number k. It can be shown that the number of edges of a kRNG is less than O(kn). Also, a kRNG can be constructed in O(kn2) time. Let Ec = {epq| pV and qV}. Then Gc = (V,Ec) is a complete graph. For any subset F of Ec, define the maximum distance of F as maxepqFdpq. A Euclidean bottleneck Hamiltonian cycle is a Hamiltonian cycle in graph Gc whose maximum distance is the minimum among all Hamiltonian cycles in graph Gc. We shall prove that there exists a Euclidean bottleneck Hamiltonian cycle which is a subgraph of 20RNG(V). Hence, 20RNGs are Hamiltonian.  相似文献   
990.
Avian myosin light-chain kinase from smooth muscle of the gizzard and its catalytic domain, derived from the intact enzyme by trypsin digestion, was purified within 30-40 min by both analytical and preparative anion-exchange high-performance liquid chromatography. The proteins obtained were more than 95% pure and retained their biological activity. The high-performance anion-exchange chromatography protocols represent a significant decrease in purification time when compared with conventional ion-exchange chromatography.  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