全文获取类型
收费全文 | 2643篇 |
免费 | 89篇 |
国内免费 | 9篇 |
专业分类
化学 | 1943篇 |
晶体学 | 7篇 |
力学 | 33篇 |
数学 | 411篇 |
物理学 | 347篇 |
出版年
2021年 | 22篇 |
2020年 | 41篇 |
2019年 | 44篇 |
2018年 | 21篇 |
2017年 | 17篇 |
2016年 | 62篇 |
2015年 | 63篇 |
2014年 | 75篇 |
2013年 | 91篇 |
2012年 | 123篇 |
2011年 | 138篇 |
2010年 | 90篇 |
2009年 | 62篇 |
2008年 | 102篇 |
2007年 | 128篇 |
2006年 | 136篇 |
2005年 | 119篇 |
2004年 | 84篇 |
2003年 | 81篇 |
2002年 | 86篇 |
2001年 | 59篇 |
2000年 | 38篇 |
1999年 | 40篇 |
1998年 | 38篇 |
1997年 | 28篇 |
1996年 | 26篇 |
1995年 | 32篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 45篇 |
1991年 | 27篇 |
1990年 | 26篇 |
1989年 | 30篇 |
1988年 | 37篇 |
1987年 | 39篇 |
1986年 | 31篇 |
1985年 | 43篇 |
1984年 | 31篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 30篇 |
1980年 | 33篇 |
1979年 | 23篇 |
1978年 | 30篇 |
1977年 | 26篇 |
1976年 | 30篇 |
1975年 | 32篇 |
1974年 | 34篇 |
1973年 | 32篇 |
1971年 | 20篇 |
排序方式: 共有2741条查询结果,搜索用时 31 毫秒
101.
Stereochemical effects in supramolecular self-assembly at surfaces: 1-D versus 2-D enantiomorphic ordering for PVBA and PEBA on Ag(111) 总被引:2,自引:0,他引:2
Barth JV Weckesser J Trimarchi G Vladimirova M De Vita A Cai C Brune H Günter P Kern K 《Journal of the American Chemical Society》2002,124(27):7991-8000
We present investigations on noncovalent bonding and supramolecular self-assembly of two related molecular building blocks at a noble metal surface: 4-[trans-2-(pyrid-4-yl-vinyl)]benzoic acid (PVBA) and 4-[(pyrid-4-yl-ethynyl)]benzoic acid (PEBA). These rigid, rodlike molecules comprising the same complementary moieties for hydrogen bond formation are comparable in shape and size. For PVBA, the ethenylene moiety accounts for two-dimensional (2-D) chirality upon confinement to a surface; PEBA is linear and thus 2-D achiral. Molecular films were deposited on a Ag(111) surface by organic molecular beam epitaxy and characterized by scanning tunneling microscopy. At low temperatures (around 150 K), both species form irregular networks of flat lying molecules linked via their endgroups in a diffusion-limited aggregation process. In the absence of kinetic limitations (adsorption or annealing at room temperature), hydrogen-bonded supramolecular assemblies form which are markedly different. With PVBA, enantiomorphic twin chains in two mirror-symmetric species running along a high-symmetry direction of the substrate lattice form by diastereoselective self-assembly of one enantiomer. The chirality signature is strictly correlated between neighboring twin chains. Enantiopure one-dimensional (1-D) supramolecular nanogratings with tunable periodicity evolve at intermediate coverages, reflecting chiral resolution in micrometer domains. In contrast, PEBA assembles in 2-D hydrogen-bonded islands, which are enantiomorphic because of the orientation of the supramolecular arrangements along low-symmetry directions of the substrate. Thus, for PVBA, chiral molecules form 1-D enantiomorphic supramolecular structures because of mesoscopic resolution of a 2-D chiral species, whereas with PEBA, the packing of an achiral species causes 2-D enantiomorphic arrangements. Model simulations of supramolecular ordering provide a deeper understanding of the stability of these systems. 相似文献
102.
The First Polyiodo Complex – Triethylsulfoniumtriiodomercurate(II)-tris(diiodine), (Et3S)[Hg2I6]1/2 · 3 I2 After Raman spectroscopic investigation of the system HgI2/Et3SIx, x = 3, 5, 7, triethylsulfoniumtriiodomercuratetris(diiodine), (Et3S)[Hg2I6]1/2 · 3 I2 was synthesized by reacting of HgI2 and liquid Et3SI7. The compound crystallizes at room temperature triclinically in the space group P1 with a = 879.4(7), b = 1 209.1(5), c = 1 291.5(5) pm, α = 96.16(3)°, β = 103.82(6)°, γ = 99.05(5)° and Z = 2. The crystal structure is composed of disordered Et3S+ cations, the centrosymmetric complex anion [HgI2/2I2]22? and three connecting iodine molecules I2. 相似文献
103.
Marcel Sickert Harald Weinstabl Brendan Peters Xiao Hou Mark Lautens 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(20):5247-5251
A palladium‐catalyzed intermolecular cross‐coupling of two aryl iodides is reported, giving polycyclic ring systems with a high level of convergence and efficiency. 相似文献
104.
105.
106.
107.
108.
Elvira Welzig Harald Pichler Rudolf Krska Dietmar Knopp Reinhard Niessner 《International journal of environmental analytical chemistry》2013,93(3-4):279-288
Abstract The development of an indirect competitive enzyme immunoassay for the sulfonylurea herbicide metsulfuron-methyl (MSM) is described. In contrast to traditional antibody generation in mammals, this extremely sensitive method is based on chicken egg yolk antibodies (IgY). They were raised in laying hens using an MSM-derivative-BSA hapten as immunogen. With a 1:10000 dilution of the antibody solution and a coating antigen (MSM-derivative-KLH) concentration of 10 μg L?1 the IC50 value achieved for the target analyte was 0.4 μg L?1. The least detectable dose was established at 13 ng L?1. Cross-reactivity was tested with 5 structurally related compounds, where only sulfometuron showed a significant binding. The ELISA was tested with spiked tap and surface water samples. This paper, for the first time, demonstrates the production of high-affinity IgY antibodies for a herbicide compound. 相似文献
109.
Abstract The synthesis of a new disc-like mesogenic compound permitted, for the first time, ferroelectric electrooptical switching in a tilted columnar liquid crystal. The spontaneous molecular dipole moment is induced by the bend between the dibenzopyrene core and part of the eight O-hexyllactic acid chains attached to it. Two similar new compounds displayed a weak electrooptical effect in the columnar phase. 相似文献
110.
Bernd Tieke Volker Enkelmann Harald Kapp Günter Lieser Gerhard Wegner 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(5):1045-1058
Abstract The topochemical polymerization of diacetylenes and.the dimerization of cinnamic acid derivatives have been studied in Langmuir-Blodgett-multilayers. The resulting polymer films are of controlled thickness and morphology and exhibit excellent stability. Structure, morphology and phase changes occuring in monomer and polymer films have been investigated using spectroscopic methods, electron and x-ray diffraction. Possible applications of the polymer films are discussed. 相似文献