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   508篇
  免费   17篇
化学   291篇
晶体学   3篇
力学   22篇
数学   119篇
物理学   90篇
  2022年   9篇
  2021年   18篇
  2020年   3篇
  2019年   9篇
  2018年   5篇
  2017年   3篇
  2016年   15篇
  2015年   10篇
  2014年   18篇
  2013年   40篇
  2012年   31篇
  2011年   35篇
  2010年   17篇
  2009年   29篇
  2008年   27篇
  2007年   25篇
  2006年   16篇
  2005年   20篇
  2004年   24篇
  2003年   13篇
  2002年   9篇
  2001年   5篇
  2000年   3篇
  1999年   10篇
  1998年   5篇
  1997年   4篇
  1996年   6篇
  1993年   2篇
  1992年   6篇
  1991年   4篇
  1990年   3篇
  1989年   2篇
  1988年   2篇
  1987年   4篇
  1986年   4篇
  1985年   7篇
  1984年   8篇
  1983年   4篇
  1982年   3篇
  1981年   2篇
  1980年   5篇
  1979年   5篇
  1976年   4篇
  1974年   4篇
  1929年   2篇
  1921年   4篇
  1911年   3篇
  1907年   2篇
  1906年   3篇
  1875年   2篇
排序方式: 共有525条查询结果,搜索用时 0 毫秒
1.
2.
The preparation of the nucleophile trans-[RuCl(NO)( 1 )], where 1 is the bidentate ligand Ph2PCH2C18CH2PPh2, and of the five-coordinate species [RuCl(CO)(NO)( 1 )], [RuCl(CO)(NO)(Ph2PCH2Ph)2] and [RuCl(NO)( 2 )( 1 )] are reported. The crystal structure of [RuCl(CO)(NO)( 1 )] shows that the coordination around the metal atom is distorted trigonal bipyramidal with the phosphorus atoms in axial positions. The Ru? N? O bond angle is 142.8°. 1H- and 31P-NMR. and \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \nu $\end{document}NO IR.-data for the above complexes are reported and related to the coordination geometry.  相似文献   
3.
(B)-Geometries are incidence structures arising from permutation sets. The present paper studies the automorphism groups of (B)-Geometries. In certain cases these automorphisms yield examples of inversive planes and of subplanes which are embedded in Minkowski planes (chapter 2). In chapter 3 we describe the automorphism groups of the (B)-Geometries arising from the groups PL(2, pn) and AL(1, pn) in their natural representations on the points of the projective and affine line.Dedicated to Prof.Dr. Walter Benz on his 60th birthdayWork done within the activity of G.N.S.A.G.A. of C.N.R. and supported by the 40% grants of M.U.R.S.T.  相似文献   
4.
Water decontamination is an important challenge resulting from the incorrect disposal of heavy metal waste into the environment. Among the different available techniques (e.g., filtration, coagulation, precipitation, and ion-exchange), adsorption is considered the cheapest and most effective procedure for the removal of water pollutants. In the last years, several materials have been tested for the removal of heavy metals from water, including metal-organic frameworks (MOFs), single-walled carbon nanotubes (SWCNTs), and graphene oxide (GO). Nevertheless, their powder consistency, which makes the recovery and reuse after adsorption difficult, is the main drawback for these materials. More recently, SWCNT buckypapers (SWCNT BPs) have been proposed as self-standing porous membranes for filtration and adsorption processes. In this paper, the adsorption capacity and selectivity of Pb2+ (both from neat solutions and in the presence of other interferents) by SWCNT BPs were evaluated as a function of the increasing amount of GO used in their preparation (GO-SWCNT buckypapers). The highest adsorption capacity, 479 ± 25 mg g−1, achieved for GO-SWCNT buckypapers with 75 wt.% of graphene oxide confirmed the effective application of such materials for cheap and fast water decontamination from lead.  相似文献   
5.
Abstract

Time-resolved emissions of Csl:T1 are investigated. The system is laser-excited in the A-band at 308 nm and the emissions are observed in the range 370–650 nm, from 30 K to 300 K. Their analysis by means of a deconvolution permits the valuation of decay-times down to 1 ns. At every temperature many bands are observed and some of them show slow and fast components. The decay-times of the fast components are in the range 1–10 ns while the slow ones are even longer than 1 μs. In many cases intermediate decay-times of the order of 100 ns exist. The competition among the bands interests the application of this system as active material for tunable solid-state laser.  相似文献   
6.
7.
8.
Sushko  Iryna  Commendatore  Pasquale  Kubin  Ingrid 《Nonlinear dynamics》2020,102(2):1071-1095
Nonlinear Dynamics - We consider a two-class growth model with optimal saving and switch in behavior. The dynamics of this model is described by a two-dimensional (2D) discontinuous map. We obtain...  相似文献   
9.
This work introduces channel-supermodular entropies, a subset of quasi-concave entropies. Channel-supermodularity is a property shared by some of the most commonly used entropies in the literature, including Arimoto–Rényi conditional entropies (which include Shannon and min-entropy as special cases), k-tries entropies, and guessing entropy. Based on channel-supermodularity, new preorders for channels that strictly include degradedness and inclusion (or Shannon ordering) are defined, and these preorders are shown to provide a sufficient condition for the more-capable and capacity ordering, not only for Shannon entropy but also regarding analogous concepts for other entropy measures. The theory developed is then applied in the context of query anonymization. We introduce a greedy algorithm based on channel-supermodularity for query anonymization and prove its optimality, in terms of information leakage, for all symmetric channel-supermodular entropies.  相似文献   
10.
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