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   2847篇
  免费   120篇
  国内免费   14篇
化学   2325篇
晶体学   18篇
力学   48篇
数学   194篇
物理学   396篇
  2023年   14篇
  2021年   26篇
  2020年   32篇
  2019年   58篇
  2018年   25篇
  2017年   31篇
  2016年   67篇
  2015年   51篇
  2014年   59篇
  2013年   117篇
  2012年   182篇
  2011年   226篇
  2010年   88篇
  2009年   89篇
  2008年   180篇
  2007年   220篇
  2006年   185篇
  2005年   188篇
  2004年   171篇
  2003年   141篇
  2002年   124篇
  2001年   57篇
  2000年   42篇
  1999年   26篇
  1998年   29篇
  1997年   21篇
  1996年   34篇
  1995年   17篇
  1994年   37篇
  1993年   31篇
  1992年   22篇
  1991年   23篇
  1990年   8篇
  1989年   22篇
  1988年   19篇
  1987年   23篇
  1986年   13篇
  1985年   24篇
  1984年   23篇
  1983年   23篇
  1982年   16篇
  1981年   23篇
  1980年   14篇
  1979年   8篇
  1978年   14篇
  1977年   16篇
  1976年   14篇
  1974年   15篇
  1973年   11篇
  1969年   8篇
排序方式: 共有2981条查询结果,搜索用时 31 毫秒
11.
The European Physical Journal E - The flow of Newtonian fluids was studied by directly measuring the hydrodynamic drainage force acting on a sphere approaching a flat surface. Our force...  相似文献   
12.
A modular approach has been developed for the synthesis of rod–coil block copolymers involving the initial preparation of a macroinitiator based on the rod block followed by the growth of the coil segment with living free-radical procedures. The key feature of this strategy is the utilization of an alkoxyamine group from the beginning of the synthesis, which serves as a solubilizing group and ensures that each rod block contains a single initiating fragment. Using this approach permits block copolymers based on insoluble biphenyl ester oligomers to be conveniently prepared with coil segments that range from styrenes to acrylates to 1,3-dienes. The tendency of the rod segments to crystallize is strongly dependent on the weight fraction of the rod segment and the chemical nature of the coil segment. Rod–coil molecules containing at least 25–35 wt % polystyrene or poly(n-butyl acrylate) coil segments show a two-dimensional hexagonal arrangement of rod aggregates, as characterized by transmission electron microscopy and small-angle X-ray scattering. Polyisoprene block copolymers exhibit a lamellar microstructure with short rigid domains in which the rod units lie in an interdigitated smectic C arrangement. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3640–3656, 2003  相似文献   
13.
14.
In this paper we prove for several classes of ideals in regular local rings of equicharacteristic 0 that the symbolic square of the ideal contains no minimal generator of the ideal. Our techniques come from residual intersections, integral closures of ideals, and differentials. Received January 14, 1997; in final form March 20, 1997  相似文献   
15.
The title compound (H2DTMSP[EBP]), C14H36O6P2Si2, was crystallized by the slow evaporation of a solution in a 20:1 mixture of pentane and acetone. The H2DTMSP[EBP] mole­cule lies about an inversion center. In the solid state, the mol­ecule exists in an anti configuration, with the mol­ecular backbone C—C bond located on an inversion center. The compound exists in the solid state as hydrogen‐bonded infinite sheets in the ab plane, unlike the methyl­ene analogue, which exists as hydrogen‐bonded infinite chains, demonstrating an `even–odd' effect of the length of the backbone alkyl chain.  相似文献   
16.
Block copolymer micelles and shell cross-linked nanoparticles (SCKs) presenting Click-reactive functional groups on their surfaces were prepared using two separate synthetic strategies, each employing functionalized initiators for the controlled radical polymerization of acrylate and styrenic monomers to afford amphiphilic block copolymers bearing an alkynyl or azido group at the α-terminus. The first route for the synthesis of the azide-functionalized nanostructures was achieved via sequential nitroxide-mediated radical polymerization (NMP) of tert-butyl acrylate and styrene, originating from a benzylic chloride-functionalized initiator, followed by deprotection of the acrylic acids, supramolecular assembly of the block copolymer in water and conversion of the benzylic chloride to a benzylic azide. In contrast, the second strategy utilized an alkynyl-functionalized reversible addition fragmentation transfer (RAFT) agent directly for the RAFT-based sequential polymerization of tetrahydropyran acrylate and styrene, followed by selective cleavage of the tetrahydropyran esters to give the α-alkynyl-functionalized block copolymers. These Click-functionalized polymers, with the functionality located at the hydrophilic polymer termini, were then self-assembled using a mixed-micelle methodology to afford surface-functionalized “Clickable” micelles in aqueous solutions. The optimum degree of incorporation of the Click-functionalized polymers was investigated and determined to be ca. 25%, which allowed for the synthesis of well-defined surface-functionalized nanoparticles after cross-linking selectively throughout the shell layer using established amidation chemistry. Functionalization of the chain ends was shown to be an efficient process under standard Click conditions and the resulting functional groups revealed a more “solution-like” environment when compared to the functional group randomly inserted into the hydrophilic shell layer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5203–5217, 2006  相似文献   
17.
Gold ultra-microelectrode arrays are used to explore the electrochemical oxidation of hydroxide ions and are shown to be analytical useful. Two types of ultra-microelectrode arrays are used; the first consist of 256 individual electrodes of 5 microm in radius, 170 of which are electrochemically active in a cubic arrangement which are separated from their nearest neighbour by a distance of 100 microm. The second array compromises 2597 electrodes of 2.5 microm in radius and of which 1550 of which are electrochemically active in a hexagonal arrangement separated by the nearest neighbour by 55 microm. Well defined voltammetric waves are found with peak currents proportional to the concentration of hydroxide ions in the range 50 microM to 1 mM. Detection limits of 20 microM using the 170 ultra-microelectrode and 10 microM with the 1550 ultra-microelectrode array are shown to be possible but with a higher sensitivity of 4 mA M(-1) observed using the 1550 ultra-microelectrode array compared to 1.2 mA M(-1) with the 170 ultra-microelectrode array.  相似文献   
18.
An enantioselective approach to the spiroimine fragment of pinnatoxins is described. The strategy is based on a recently developed diastereoselective Ireland-Claisen rearrangement to establish the challenging congested quaternary and tertiary stereocenters within the cyclohexene ring.  相似文献   
19.
20.
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