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   10472篇
  免费   1147篇
  国内免费   775篇
化学   6595篇
晶体学   77篇
力学   718篇
综合类   33篇
数学   1569篇
物理学   3402篇
  2024年   66篇
  2023年   182篇
  2022年   292篇
  2021年   313篇
  2020年   365篇
  2019年   393篇
  2018年   234篇
  2017年   244篇
  2016年   420篇
  2015年   412篇
  2014年   410篇
  2013年   592篇
  2012年   782篇
  2011年   829篇
  2010年   555篇
  2009年   454篇
  2008年   643篇
  2007年   602篇
  2006年   545篇
  2005年   501篇
  2004年   479篇
  2003年   341篇
  2002年   322篇
  2001年   198篇
  2000年   143篇
  1999年   189篇
  1998年   149篇
  1997年   163篇
  1996年   179篇
  1995年   162篇
  1994年   127篇
  1993年   101篇
  1992年   94篇
  1991年   97篇
  1990年   96篇
  1989年   74篇
  1988年   75篇
  1987年   57篇
  1986年   55篇
  1985年   74篇
  1984年   49篇
  1983年   49篇
  1982年   47篇
  1981年   36篇
  1980年   31篇
  1979年   34篇
  1978年   22篇
  1977年   16篇
  1976年   18篇
  1974年   19篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Self-assembling and self-organizing methodologies are powerful tools for the "bottom-up" approach for the realization of complex structure with functional properties. Recently, this concept has been extended to the design of fluorescent chemosensors providing new exciting potentialities for the development of innovative sensing systems. This Concept Article deals mainly with this new approach and discusses its evolution, applications, and limitations.  相似文献   
152.
Dai Q  Xie X  Xu S  Ma D  Tang S  She X 《Organic letters》2011,13(9):2302-2305
First total syntheses of the isoechinulin-type alkaloids: Tardioxopiperazine A, Isoechinulin A, and Variecolorin C have been achieved from a common key intermediate 5, which was derived from a regiocontrolled Stille cross-coupling reaction of an allylindium reagent.  相似文献   
153.
Fu H  Li J  Meng W  Dong R  Dai R  Deng Y 《Electrophoresis》2011,32(6-7):749-751
This short communication describes the interaction between toll-like receptor 4 (TLR4) and lipopolysaccharide (LPS, its specific ligand) using analytical methods. Their interaction has been evidenced in many reports. Nevertheless, there are few reports focused on their binding constant. In this research, the interaction between TLR4 and LPS is investigated using mobility shift method by CZE. To optimize the electrophoresis conditions, the effecting factors, running buffer, sample concentration, injection duration, and operation voltage of electrophoretic on the mobility shift are studied in detail. Electrophoresis conditions were described as follows: borate buffer (pH 7.4, 20 mM), 5 s for 50 mbar pressure injection duration, and 13 kV of separation voltage in 41.5 cm fused silica capillary with 75 μm id and 375?μm od. The combination constant of TLR4 and LPS is calculated using Scatchard methods. The Scatchard liner correlation is y=-0.0165x+0.1456, binding constant is K=1.65 x 10? (g/mL)?1.  相似文献   
154.
A novel nickel beta-diketonate adduct, Ni(tta)2.tmeda, has been synthesized using 2-thenoyltrifluoroacetone as the beta-diketonate and N,N,N,'N'-tetramethylethylendiamine as the Lewis base. It has been characterized by elemental analyses, IR, 1H NMR, 13C NMR spectroscopy and single-crystal X-ray diffraction studies. Physical and thermal properties of Ni(tta)2.tmeda precursor have been also extensively investigated. Its efficacy as a metal-organic chemical vapour deposition (MOCVD) precursor for the growth of nickel oxide films has been fully tested by applying it to the deposition of NiO films on quartz substrate. NiO thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy and UV spectroscopy.  相似文献   
155.
The synthesis, structure, and bonding of BaTl(4) are described [C2/m, Z = 4, a = 12.408(3), b = 5.351(1), c = 10.383(2) ?, β = 116.00(3)°]. Pairs of edge-sharing Tl pentagons are condensed to generate a network of pentagonal biprisms along b that encapsulate Ba atoms. Alternating levels of prisms along c afford six more bifunctional Tl atoms about the waists of the biprisms, giving Ba a coordination number of 16. Each Tl atom is bonded to five to seven other Tl atoms and to three to five Ba atoms. There is also strong evidence that Hg substitutes preferentially in the shared edges of the Tl biprisms in BaHg(0.80)Tl(3.20) to generate more strongly bound Hg(2) dimers. Cations that are too small relative to the dimensions of the surrounding polyanionic network make this BaTl(4) structure (and for SrIn(4) and perhaps EuIn(4) as well) one stable alternative to tetragonal BaAl(4)-type structures in which cations are bound in larger hexagon-faced nets, as for BaIn(4) and SrGa(4). Characteristic condensation and augmentation of cation-centered prismatic units is common among many relatively cation- and electron-poor, polar derivatives of Zintl phases gain stability. At the other extreme, the large family of Frank-Kasper phases in which the elements exhibit larger numbers of bonded neighbors are sometimes referred to as orbitally rich.  相似文献   
156.
Diastereoisomeric D,L-N-Cbz-imino glycal-derived allyl epoxides 5 and 6 have been synthesized, and their addition reactions with alcohols examined. The reactions lead to the corresponding 2,3-unsaturated-aza-O-glycosides through a new, completely regioselective 1,4-addition process which proceeds with complete substrate-dependent stereoselectivity.  相似文献   
157.
The metadynamics method, recently proposed by Laio and Parrinello as a general tool to map multidimensional free-energy landscapes [A. Laio and M. Parrinello, Proc. Natl. Acad. Sci. U.S.A. 99, 12562 (2002)], has been exploited with the aim of illustrating the properties of generalized thermodynamic potentials across a discontinuous phase transition. Virtues and limitations of the method are discussed in the exemplifying case of the freezing of a Lennard-Jones fluid in two dimensions.  相似文献   
158.
159.
160.
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