全文获取类型
收费全文 | 971篇 |
免费 | 16篇 |
国内免费 | 8篇 |
专业分类
化学 | 716篇 |
晶体学 | 12篇 |
力学 | 14篇 |
数学 | 135篇 |
物理学 | 118篇 |
出版年
2020年 | 12篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 6篇 |
2013年 | 33篇 |
2012年 | 36篇 |
2011年 | 58篇 |
2010年 | 17篇 |
2009年 | 18篇 |
2008年 | 39篇 |
2007年 | 49篇 |
2006年 | 75篇 |
2005年 | 52篇 |
2004年 | 64篇 |
2003年 | 42篇 |
2002年 | 53篇 |
2001年 | 11篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 9篇 |
1994年 | 19篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 15篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 15篇 |
1974年 | 15篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1966年 | 5篇 |
排序方式: 共有995条查询结果,搜索用时 15 毫秒
71.
The dimerization of methyl acrylate to the head-to-tail 2-methylene-pentanedioic acid dimethyl ester product was realized in 82 and 85% yield in only 4 h at room temperature in THF in the presence of catalytic amounts of P(RNCH2CH2)3N (R = i-Bu and Bn, respectively). These phosphines are to our knowledge the best nonmetallic catalysts so far reported for this reaction. In contrast, less sterically hindered P(MeNCH2CH2)3N failed to catalyze this dimerization, giving oligomer or polymer instead. 相似文献
72.
The synthesis of the alkylating subunit of the DNA cross-linking agent, isochrysohermidin (2), and its subsequent incorporation into conjugates with distamycin A (1) are described. The DNA binding properties of these agents were compared to that of distamycin A, using a fluorescence intercalator displacement (FID) assay. 相似文献
73.
Macrocyclic inhibitors of the NS3 protease as potential therapeutic agents of hepatitis C virus infection 总被引:3,自引:0,他引:3
74.
Huang JH Luci JJ Lee TY Swenson DC Jensen JH Messerle L 《Journal of the American Chemical Society》2003,125(7):1688-1689
Reduction of the organoditantalum allene complex (eta-C5Me4R)2Ta2(mu-X)X3(mu-eta1,eta3-C3H4) (R = Me (Cp*), Et; X = Cl, Br) with sodium amalgam leads to the propynylidene complex (eta-C5Me4R)2Ta2(mu-H)2X2(mu-HCCCH) by a formal double 1,3-C-H activation of the allene ligand. The solid-state molecular structure contains a planar HCCCH ligand bridging, in parallel coordination mode, the two tantalum atoms, with the HCCCH and Ta atoms coplanar. Key structural features are a Ta-Ta distance of 2.8817(7) A, propynylidene C-C-C angle of 153.7(13) degrees , C-C distance of 1.370(8) A, Ta-C(central) distance of 2.194(9) A, and Ta-C(terminal) distance of 1.970(9) A. Molecular orbital calculations on the complex at the RHF/SBK(d) and B3LYP/LanL2dz levels of theory demonstrate that the propynylidene ligand is best viewed formally as an allenediylidene(4-) ligand bonded to two d0 tantalum atoms via two Ta=C(terminal) double bonds and an unusual three-center, two-electron bridge bond involving both tantalum atoms and a lone pair on the planar, tetracoordinate central carbon. There is no net Ta-Ta bonding based on the orbital analysis. 相似文献
75.
Dale N. Skinner 《Proceedings of the American Mathematical Society》2001,129(10):3069-3077
We show that any compact 3-manifold carrying a metric with sufficiently pinched negative Ricci curvature admits a hyperbolic metric. This proof is a corrected version of the proof first suggested by Maung Min-Oo. The key insight in this new proof is that the error in Min-Oo's paper does not occur if the type curvature is considered instead of the type curvature.
76.
Xu W Dutta D Xiong F Anderson B Auberbach L Averett T Bertozzi W Black T Calarco J Cardman L Cates GD Chai ZW Chen JP Choi S Chudakov E Churchwell S Corrado GS Crawford C Dale D Deur A Djawotho P Filippone BW Finn JM Gao H Gilman R Glamazdin AV Glashausser C Glöckle W Golak J Gomez J Gorbenko VG Hansen JO Hersman FW Higinbotham DW Holmes R Howell CR Hughes E Humensky B Incerti S de Jager CW Jensen JS Jiang X Jones CE Jones M Kahl R Kamada H Kievsky A Kominis I Korsch W Kramer K Kumbartzki G 《Physical review letters》2000,85(14):2900-2904
We have measured the transverse asymmetry A(T') in 3He(e,e(')) quasielastic scattering in Hall A at Jefferson Laboratory with high precision for Q2 values from 0.1 to 0.6 (GeV/c)(2). The neutron magnetic form factor G(n)(M) was extracted based on Faddeev calculations for Q2 = 0.1 and 0.2 (GeV/c)(2) with an experimental uncertainty of less than 2%. 相似文献
77.
Xianglei Mao Alexander A. Bol'shakov Inhee Choi Christopher P. McKay Dale L. Perry Osman Sorkhabi Richard E. Russo 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(11-12):767-775
The experimental details are reported of Laser Ablation Molecular Isotopic Spectrometry (LAMIS) and its application for performing optical isotopic analysis of solid strontium-containing samples in ambient atmospheric air at normal pressure. The LAMIS detection method is described for strontium isotopes from samples of various chemical and isotopic compositions. The results demonstrate spectrally resolved measurements of the three individual 86Sr, 87Sr, and 88Sr isotopes that are quantified using multivariate calibration of spectra. The observed isotopic shifts are consistent with those calculated theoretically. The measured spectra of diatomic oxide and halides of strontium generated in laser ablation plasmas demonstrate the isotopic resolution and capability of LAMIS. In particular, emission spectra of SrO and SrF molecular radicals provided clean and well resolved spectral signatures for the naturally occurring strontium isotopes. A possibility is discussed of using LAMIS of strontium isotopes for radiogenic age determination. 相似文献
78.
79.
Dale R. Harshman 《Hyperfine Interactions》1986,32(1-4):847-863
The interactions of muonium (μ
+
e
−, Mu) with the surfaces of fine silica powders have been extensively studied using zero, longitudinal and transverse field
μSR techniques. These studies indicate diffusion and trapping behavior of the Mu atoms on the silica surface, which is strongly
influenced by the surface hydroxyl (OH) concentration. Specifically, the presence of the surface OH groups is observed to
inhibit the surface mobility of the Mu atoms at low temperatures. Information provided by zero and longitudinal field data
suggest a random anisotropic distortion of the Mu hyperfine interaction (RAHD) as the principal relaxation mechanism. A recently
developed RAHD spin relaxation theory is used to interpret these data. Additional investigations, using platinum loaded silica,
have yielded the first observed surface reaction of Mu.
Studies of the interactions of positive muons with surfaces have been also extended to single crystals, where low energy (<10
eV)μ
+ andMu
− ions are observed to be reemitted from some materials (e.g., the <100> surface of lithium fluoride). Future applications
of these emission phenomena toward the development of a slow847-3 (or Mu−) beam are considered. 相似文献
80.