全文获取类型
收费全文 | 11145篇 |
免费 | 893篇 |
国内免费 | 847篇 |
专业分类
化学 | 8369篇 |
晶体学 | 122篇 |
力学 | 314篇 |
综合类 | 66篇 |
数学 | 1898篇 |
物理学 | 2116篇 |
出版年
2024年 | 9篇 |
2023年 | 108篇 |
2022年 | 207篇 |
2021年 | 323篇 |
2020年 | 337篇 |
2019年 | 311篇 |
2018年 | 265篇 |
2017年 | 266篇 |
2016年 | 518篇 |
2015年 | 475篇 |
2014年 | 529篇 |
2013年 | 767篇 |
2012年 | 960篇 |
2011年 | 1037篇 |
2010年 | 735篇 |
2009年 | 649篇 |
2008年 | 818篇 |
2007年 | 793篇 |
2006年 | 722篇 |
2005年 | 611篇 |
2004年 | 534篇 |
2003年 | 350篇 |
2002年 | 296篇 |
2001年 | 147篇 |
2000年 | 119篇 |
1999年 | 131篇 |
1998年 | 78篇 |
1997年 | 78篇 |
1996年 | 80篇 |
1995年 | 60篇 |
1994年 | 50篇 |
1993年 | 49篇 |
1992年 | 45篇 |
1991年 | 37篇 |
1990年 | 39篇 |
1989年 | 25篇 |
1988年 | 24篇 |
1987年 | 34篇 |
1986年 | 22篇 |
1985年 | 36篇 |
1984年 | 26篇 |
1983年 | 19篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 21篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1975年 | 7篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
81.
Guo Hua GAO Jin Bao GAO Wen Juan ZHOU Liang LU Ming Yuan HE 《中国化学快报》2006,17(10):1293-1296
Since much more attention has been paid to the sustainable development, many researchers try to improve conventional chemical process and find new and more, environmentally friendly routes1. Aqueous-phase reactions are of interest as environ- mentally ben… 相似文献
82.
DFT computational study of the mechanism of allyl halides carbonylation catalyzed by nickel tetracarbonyl 总被引:1,自引:0,他引:1
Bottoni A Miscione GP Novoa JJ Prat-Resina X 《Journal of the American Chemical Society》2003,125(34):10412-10419
A theoretical investigation at the DFT(B3LYP) level on the carbonylation reaction of allyl bromide catalyzed by nickel tetra-carbonyl Ni(CO)(4) is discussed. The computational results show the following: (i) Three main steps characterize the catalytic cycle: (a) an oxidative addition step, (b) a carbonylation step, and (c) a reductive elimination step where the acyl product is obtained and the catalyst is regenerated. (ii) Both Ni(CO)(3) and Ni(CO)(4) complexes can behave as "active" catalytic species. (iii) The oxidative addition leads to the formation of either eta(3) or eta(1)-allyl nickel complexes, which are involved in a fast equilibrium. (iv) The carbonylation occurs much more easily on the eta(1) than on the eta(3) intermediates. 相似文献
83.
84.
Paital AR Mitra T Ray D Wong WT Ribas-Ariño J Novoa JJ Ribas J Aromí G 《Chemical communications (Cambridge, England)》2005,(41):5172-5174
Based on a combined theoretical-experimental study, we propose that substituted m-phenylene ligands (m-N-Phi-N) can act as tuneable strong ferromagnetic couplers connecting Cu(II) ions; a new complex presenting that bridge with J close to +15 cm(-1) has been suggested and synthesized. 相似文献
85.
86.
87.
Reinoso S Vitoria P Gutiérrez-Zorrilla JM Lezama L San Felices L Beitia JI 《Inorganic chemistry》2005,44(26):9731-9742
Reaction of in situ generated copper(II)-monosubstituted Keggin polyoxometalates and copper(II)-bipyridine-oxalate complexes in the corresponding alkaline acetate buffer led to the formation of hybrid metal organic-inorganic compounds K(2)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(H(2)O)(2)(mu-ox)}(2)].14H(2)O (1), K(14)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}](2)[SiW(11)O(39)Cu(H(2)O)].55H(2)O (2), (NH(4))(4)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}].10H(2)O (3), and Rb(4)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}].10H(2)O (4). Their structures have been established by single-crystal X-ray diffraction. The main structural feature of these compounds is the presence of copper(II)-monosubstituted alpha-Keggin polyoxoanions as inorganic building blocks, on which the mu-oxalatodicopper metalorganic blocks are supported. Compound 1contains the discrete hybrid polyanion [{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(H(2)O)(2)(mu-ox)}(2)](2)(-), whereas the polymeric hybrid polyanion [{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}(2)](n)(4)(n)(-) gives a monodimensional character to compounds 2-4. Magnetic and EPR results are discussed with respect to the crystal structure of the compounds. DFT calculations on both the [Cu(2)(bpy)(2)(H(2)O)(4)(mu-ox)](2+) cationic complex and the metalorganic blocks have been performed in order to determine the optimized geometry and the magnetic coupling constants, respectively. 相似文献
88.
Let G be a non-compact connected semisimple Lie group with finite center and let GK denote the centralizer of a maximal compact subgroup K of G inG, the universal enveloping algebra over of the Lie algebra of G. In [4] Lepowsky defines an injective anti-homo morphism P:G
KK
MA, where M is the centralizer in K of a Cartan subalgebraa of the symmetric pair (G,K),K andA are the universal enveloping algebras over corresponding to K anda, respectively, andK
M is the centralizer of M inK. The subalgebra P(G
K) ofK
MA has considerable significance in the infinite dimensional representation theory of G. In this paper we explicitly compute P(G
K) when G=S0o(4,1), and show how this result leads to the determination of all irreducible representations of G and its universal covering group Spin(4,1).Partially supported by CONICET (Argentina) grants. 相似文献
89.
Serrano MC Portolés MT Vallet-Regí M Izquierdo I Galletti L Comas JV Pagani R 《Macromolecular bioscience》2005,5(5):415-423
Tissue engineering offers the potential of providing vessels that can be used to replace diseased and damaged native blood vessels. The endothelization of a synthetic vascular graft minimizes the failures associated with blood clotting and platelet activation. The aim of this study was to culture vascular-derived endothelial and smooth muscle cells on both untreated and NaOH-treated poly(epsilon-caprolactone) (PCL) films, a biocompatible and bio-resorbable polymer, and to evaluate the behavior of both cell types as a preliminary study for vascular graft development. PCL films were prepared by hot pressing; characterized by DSC, IR, SEM, and scanning force microscopy; and treated with NaOH to increase the surface hydrophilicity before cell culture. Endothelial and smooth muscle cells, isolated from pig cava vein, were characterized by immunofluorescence and confocal microscopy studies of endothelial nitric oxide synthase and alpha-smooth muscle actin. Good adhesion, growth, viability and morphology of both the endothelial and smooth muscle cells on PCL films were obtained, but a light stimulation of mitochondrial activity was observed during short culture times. NaOH treatment improved the adhesion and enhanced the proliferation in both cell types. This verified the possible use of this modified polymer as a support in the preparation of a synthetic vascular graft. [Diagram: see text] SEM micrograph of smooth muscle cells cultured on NaOH-treated PCL film. (Original magnification: 1000x). 相似文献
90.
Eugenio?Garcia-Pa?eda Pilar?Guardado Alfredo?MaestreEmail author 《Journal of solution chemistry》2004,33(10):1277-1293
Partial molar volumes at infinite dilution, V02, of alkali–metal halides (LiCl, NaCl KCl RbCl CsCl, NaBr, KBr, KI), tetra-n-alkylammonium bromides, R4NBr (R=Me, Et, n-Pr, n-Bu, n-Pen), NaBPh4, and Ph4PCl have been determined in binary solvent mixtures of water with 2-methyl-2-butanol covering the water-rich region and the alcohol-rich region at 298.15 K. V02 for alkali–metal halides show relatively little dependence on the solvent composition. However, in the case of hydrophobic electrolytes the observed effects are more pronounced. A good linear dependence between V02(R4NBr) and the molecular weight of the tetra-n-alkylammonium cation is found. Limiting single-ion volumes have been obtained using the assumption that V0(Ph4P+)–V0(BPh–4)=2.0 cm3-mol–1. The trends in the single-ion volumes are discussed in both solvent regions. 相似文献