全文获取类型
收费全文 | 2397篇 |
免费 | 39篇 |
国内免费 | 14篇 |
专业分类
化学 | 1443篇 |
晶体学 | 31篇 |
力学 | 83篇 |
数学 | 420篇 |
物理学 | 473篇 |
出版年
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 19篇 |
2017年 | 22篇 |
2016年 | 34篇 |
2015年 | 30篇 |
2014年 | 29篇 |
2013年 | 113篇 |
2012年 | 94篇 |
2011年 | 95篇 |
2010年 | 57篇 |
2009年 | 67篇 |
2008年 | 101篇 |
2007年 | 109篇 |
2006年 | 105篇 |
2005年 | 109篇 |
2004年 | 113篇 |
2003年 | 80篇 |
2002年 | 77篇 |
2001年 | 48篇 |
2000年 | 45篇 |
1999年 | 56篇 |
1998年 | 32篇 |
1997年 | 32篇 |
1996年 | 34篇 |
1995年 | 23篇 |
1994年 | 25篇 |
1993年 | 22篇 |
1992年 | 32篇 |
1991年 | 21篇 |
1990年 | 25篇 |
1989年 | 37篇 |
1988年 | 14篇 |
1987年 | 24篇 |
1986年 | 29篇 |
1985年 | 45篇 |
1984年 | 50篇 |
1983年 | 40篇 |
1982年 | 41篇 |
1981年 | 58篇 |
1980年 | 39篇 |
1979年 | 43篇 |
1978年 | 39篇 |
1977年 | 44篇 |
1976年 | 25篇 |
1975年 | 33篇 |
1974年 | 35篇 |
1973年 | 37篇 |
1972年 | 26篇 |
1970年 | 18篇 |
排序方式: 共有2450条查询结果,搜索用时 15 毫秒
971.
K Fucke MJ Peach JA Howard JW Steed 《Chemical communications (Cambridge, England)》2012,48(79):9822-9824
The disodium salt of diatrizoic acid crystallises as a tetragonal channel hydrate structure. One of the incorporated water molecules is coordinated to three individual sodium cations in a unique geometry. 相似文献
972.
McCann LC Hunter HN Clyburne JA Organ MG 《Angewandte Chemie (International ed. in English)》2012,51(28):7024-7027
Negishi revisited: higher-order alkyl zincates have been subjected to Negishi coupling with alkyl bromides. For the first time, coupling takes place in straight THF, i.e., without a salt additive and a high dielectric co-solvent. This provides evidence that it is the higher-order zincate that undergoes transmetalation to Pd, and not mono-anionic zincates or any of the other species present in the Schlenk equilibrium. 相似文献
973.
Ionic diamine rhodium complexes catalyze the reductive N-heterocyclization of N-(2-nitroarylidene)amines under carbon monoxide to afford the corresponding 2H-indazoles in up to 75% yields. 相似文献
974.
Kiran B Kandalam AK Rallabandi R Koirala P Li X Tang X Wang Y Fairbrother H Gantefoer G Bowen K 《The Journal of chemical physics》2012,136(2):024317
Theoretical calculations based on density functional theory have found (PbS)(32) to be the smallest cubic cluster for which its inner (PbS)(4) core enjoys bulk-like coordination. Cubic (PbS)(32) is thus a "baby crystal," i.e., the smallest cluster, exhibiting sixfold coordination, that can be replicated to obtain the bulk crystal. The calculated dimensions of the (PbS)(32) cluster further provide a rubric for understanding the pattern of aggregation when (PbS)(32) clusters are deposited on a suitable surface, i.e., the formation of square and rectangular, crystalline nano-blocks with predictable dimensions. Experiments in which mass-selected (PbS)(32) clusters were soft-landed onto a highly ordered pyrolytic graphite surface and the resulting aggregates imaged by scanning tunneling microscopy provide evidence in direct support of the computational results. 相似文献
975.
Roberts RJ Li X Lacey TF Pan Z Patterson HH Leznoff DB 《Dalton transactions (Cambridge, England : 2003)》2012,41(23):6992-6997
A new series of lanthanide-containing dicyanoaurate coordination polymers, [(n)Bu(4)N](2)[Ln(NO(3))(4)Au(CN)(2)] (Ln = Nd, Eu, Gd or Tb), were synthesized and structurally characterized. They form an isomorphous series, crystallizing in the space group I2(1)2(1)2(1). The structure is composed of a one dimensional zigzag of Ln-N-C-Au-C-N-Ln chains with no intra- or inter-chain aurophilic interactions. The series is related to and can be described as a reduced dimensionality analogue of the previously studied Ln[Au(CN)(2)](3)·3H(2)O. Unlike the Ln[Au(CN)(2)](3)·3H(2)O series, there is no efficient energy transfer between dicyanoaurate and the lanthanide metal centers in the complexes and they essentially act as two separate emissive chromophores. 相似文献
976.
Abstract Examination of the Infrare and Raman spectra of cis, cis-dipropenyl ether (which was produced by isomerization of diallyl ether) has produced evidence for strong vibrational coupling between the two double-bonds. This ether has strong bands it 1655 cm?1 in the infrared and at 1691 cm?1 in the Raman. The 1658 cm?1 band in the Raman is about 10 fold less intense than the strong polarised band. Thus it appears reasonable to associate the strong IR and Raman bands with the asymmetric and symmetric vibrations shown. 相似文献
977.
A. Q. Howard Jr 《Fiber and Integrated Optics》2013,32(2):181-196
Abstract A new, relatively simple way of calculating bend radiation is developed. As is often done in propagation over gently curved surfaces, the fiber curvature is accounted for by placing a straight fiber in a fictitious medium that is inhomogeneous in the plane of the bend. For a gently curved fiber, the medium is slowly varying and the WKB method is used to approximate the radial field dependence. This solution is related to the unperturbed straight fiber solution through an ansatz consistent with the WKB solution. The propagating modes in this approximation remain orthogonal, allowing an immediate generalization to the multimoded case. The radiation loss per unit length is calculated two ways and is consistent with results in the literature. 相似文献
978.
In any probabilistic theory, we say that a bipartite state ω on a composite system AB steers its marginal state ω B if, for any decomposition of ω B as a mixture ω B =∑ i p i β i of states β i on B, there exists an observable {a i } on A such that the conditional states $\omega_{B|a_{i}}$ are exactly the states β i . This is always so for pure bipartite states in quantum mechanics, a fact first observed by Schrödinger in 1935. Here, we show that, for weakly self-dual state spaces (those isomorphic, but perhaps not canonically isomorphic, to their dual spaces), the assumption that every state of a system A is steered by some bipartite state of a composite AA consisting of two copies of A, amounts to the homogeneity of the state cone. If the state space is actually self-dual, and not just weakly so, this implies (via the Koecher-Vinberg Theorem) that it is the self-adjoint part of a formally real Jordan algebra, and hence, quite close to being quantum mechanical. 相似文献
979.
Peter Howard 《偏微分方程通讯》2013,38(4):590-612
We consider the spectrum associated with three types of bounded stationary solutions for the Cahn–Hilliard equation on ? d , d ≥ 2: radial solutions, saddle solutions (only for d = 2), and planar periodic solutions. In particular, we establish spectral instability for each type of solution. The important case of multiply periodic solutions does not fit into the framework of our approach, and we do not consider it here. 相似文献
980.
Peter Howard 《偏微分方程通讯》2013,38(1):73-121
ABSTRACT We consider degenerate viscous shock waves arising in systems of two conservation laws, where degeneracy describes viscous shock waves for which the asymptotic endstates are sonic to the hyperbolic system (the shock speed is equal to one of the characteristic speeds). In particular, we develop detailed pointwise estimates on the Green's function associated with the linearized perturbation equation, sufficient for establishing that spectral stability implies nonlinear stability. The analysis of degenerate viscous shock waves involves several new features, such as algebraic (nonintegrable) convection coefficients, loss of analyticity of the Evans function at the leading eigenvalue, and asymptotic time decay of perturbations intermediate between that of the Lax case and that of the undercompressive case. 相似文献