全文获取类型
收费全文 | 7804篇 |
免费 | 426篇 |
国内免费 | 16篇 |
专业分类
化学 | 5830篇 |
晶体学 | 43篇 |
力学 | 86篇 |
数学 | 880篇 |
物理学 | 1407篇 |
出版年
2023年 | 62篇 |
2022年 | 92篇 |
2021年 | 116篇 |
2020年 | 230篇 |
2019年 | 206篇 |
2018年 | 86篇 |
2017年 | 106篇 |
2016年 | 295篇 |
2015年 | 287篇 |
2014年 | 317篇 |
2013年 | 358篇 |
2012年 | 537篇 |
2011年 | 576篇 |
2010年 | 329篇 |
2009年 | 278篇 |
2008年 | 433篇 |
2007年 | 420篇 |
2006年 | 379篇 |
2005年 | 296篇 |
2004年 | 287篇 |
2003年 | 234篇 |
2002年 | 227篇 |
2001年 | 157篇 |
2000年 | 123篇 |
1999年 | 119篇 |
1998年 | 93篇 |
1997年 | 111篇 |
1996年 | 83篇 |
1995年 | 97篇 |
1994年 | 128篇 |
1993年 | 87篇 |
1992年 | 82篇 |
1991年 | 67篇 |
1990年 | 60篇 |
1989年 | 68篇 |
1988年 | 59篇 |
1987年 | 60篇 |
1986年 | 49篇 |
1985年 | 45篇 |
1984年 | 46篇 |
1983年 | 30篇 |
1982年 | 36篇 |
1981年 | 43篇 |
1980年 | 45篇 |
1979年 | 41篇 |
1978年 | 41篇 |
1977年 | 33篇 |
1976年 | 45篇 |
1975年 | 24篇 |
1973年 | 23篇 |
排序方式: 共有8246条查询结果,搜索用时 15 毫秒
61.
62.
63.
Martina Dotzler Astrid Schmidt Jochen Ellermann Falk A. Knoch Matthias Moll Walter Bauer 《Polyhedron》1996,15(24):4425-4433
BiBr3 or SbI3 react at 20°C with LiN(PPh2)2 (1) to give elementary Bi or Sb and the P---P coupled phosphazene ligand Ph2P---N=PPh2---PPh2=N---PPh2 (2). The reaction of AsI3 with 1 at room temperature formed yellow needles of the eight-membered heterocycle
(3), whereas AsI3 interacted at 80°C with 1 in the molar ratio of 1:3 to give elementary arsenic and 2. Treatment of AsI3 and 1 at 20°C in a 1:2 stoichiometry yielded the seven-membered, cyclic arsenium(I) salt I·4THF (5·4THF), which was characterized by elemental analysis, conductivity, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis. 相似文献
64.
65.
Matthias Deppner 《Journal of organometallic chemistry》2005,690(12):2861-2871
The synthesis is described of symmetric alkylidene bridged dinuclear zirconocene complexes. The influence of structural parameters and different cocatalysts such as methylaluminoxane (MAO), triphenyl tetrakis(pentafluorophenyl)borate- or tris(pentafluorophenyl)borane has been investigated for homogeneous propylene polymerization. The dinuclear catalysts show highest polymerization activities by activation with MAO. Activation with triphenyl tetrakis(pentafluorophenyl)borate results in polypropylenes with the highest degree of isotacticity. Compared to the mononuclear reference catalyst the dinuclear MAO activated complex achieved higher propylene polymerization activity and the polypropylene obtained from the dinuclear complex has a higher molecular weight than that one that was produced with the mononuclear complex. 相似文献
66.
A total synthesis of the optically active tetrahydroesterastin β -lactam analogue 2 using Miller's hydroxamate approach is described (Scheme 2). Significant modification of published procedures has resulted in a short and facile stereospecific preparation of the N-[(benzyloxycarbonyl)methyl]-β -lactam 17 starting from the readily available D -serine. This material served as intermediate for the preparation of a variety of N-[(benzyloxycarbonyl)methyl]tetrahydroesterastin β-lactam analogues (Scheme 5). 相似文献
67.
The source of the effect of N-alkylation on the redox properties of Ni(II/I) and Cr(III/II) cyclam complexes has been investigated using DFT calculations. The structures of the anhydrous and hydrated complexes were optimized in the gas phase, and single point calculations were performed in a polarized continuum. The main results are the following: the decrease in outer sphere solvation upon N-alkylation is the major source of the relative stabilization of the lower oxidation state complexes by the tertiary amine ligands; tertiary amine nitrogen donors are stronger sigma-donors than the secondary amines, as predicted from the inductive effect of alkyls; steric strain elongates the metal-nitrogen bonds in the tertiary complexes and decreases the ligand strain energies; and the site of water binding to the complexes differs because of their different electronic structures (i.e., in the Ni complexes, the water molecules bind to the M[bond]N[bond]H sites, whereas in the Cr complexes they bind to the central metal cation). Outer sphere hydrogen bonding of water to the ligands in the coordination sphere lowers the ionization potentials by charge delocalization. 相似文献
68.
Annals of Global Analysis and Geometry - In the present paper, we consider star-shaped mean convex hypersurfaces of the real, complex and quaternionic hyperbolic space evolving by a class of... 相似文献
69.
70.
Roland Huber 《Geometriae Dedicata》1995,58(3):291-311
We show some topological properties of semianalytic subsets of rigid analytic varieties: curve selection lemma, the closure
of a semianalytic subsetS is semianalytic,
for every quasi-compact morphismf. As an application we show that a morphismf: X Y of rigid analytic varieties is open at a pointx X if and only if SpecO
X,x SpecO
Y,f(x) is surjective. 相似文献