全文获取类型
收费全文 | 511篇 |
免费 | 4篇 |
国内免费 | 4篇 |
专业分类
化学 | 262篇 |
力学 | 30篇 |
数学 | 73篇 |
物理学 | 154篇 |
出版年
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 6篇 |
2013年 | 26篇 |
2012年 | 19篇 |
2011年 | 19篇 |
2010年 | 9篇 |
2009年 | 7篇 |
2008年 | 28篇 |
2007年 | 19篇 |
2006年 | 13篇 |
2005年 | 17篇 |
2004年 | 19篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 14篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1974年 | 10篇 |
1973年 | 8篇 |
1930年 | 4篇 |
1881年 | 2篇 |
排序方式: 共有519条查询结果,搜索用时 15 毫秒
101.
102.
Abdou O. Abdelhamid Cyril Prknyi S. M. Khaledur Rashid Winston D. Lloyd 《Journal of heterocyclic chemistry》1988,25(2):403-405
Substituted 2-arylbenzimidazoles, 2-arylbenzoxazoles and 2-arylbenzothiazoles were obtained in good yield by the reaction of hydroximoyl chlorides with ortho-substituted aromatic amines. The benzo moiety of the benzimidazoles was shown by nmr to be symmetrical, indicating that the N-H group proton of the imidazole ring is exchanging with the water protons in the DMSO-d6 solvent. 相似文献
103.
Summary: High temperature semibatch free radical copolymerizations of dodecyl methacrylate (DMA) and styrene (ST) were carried out. A mechanistic model including depropagation and penultimate chain growth was built in Predici®. The comparison between the simulated and the experimental final polymer molecular weights indicates that the initiator efficiency decreases when DMA is used as a comonomer. Using estimated initiator efficiencies and termination coefficients, the model provides good fits to the complete set of experimental data. 相似文献
104.
Zhenyu Xue Jonas Faleskog John W. Hutchinson 《International Journal of Solids and Structures》2013,50(25-26):4258-4269
An extension of the Gurson model that incorporates damage development in shear is used to simulate the tension–torsion test fracture data presented in Faleskog and Barsoum (2013) (Part I) for two steels, Weldox 420 and 960. Two parameters characterize damage in the constitutive model: the effective void volume fraction and a shear damage coefficient. For each of the steels, the initial effective void volume fraction is calibrated against data for fracture of notched round tensile bars and the shear damage coefficient is calibrated against fracture in shear. The calibrated constitutive model reproduces the full range of data in the tension–torsion tests thereby providing a convincing demonstration of the effectiveness of the extended Gurson model. The model reinforces the experiments by highlighting that for ductile alloys the effective plastic strain at fracture cannot be based solely on stress triaxiality. For nominally isotropic alloys, a ductile fracture criterion is proposed for engineering purposes that depends on stress triaxiality and a second stress invariant that discriminates between axisymmetric stressing and shear dominated stressing. 相似文献
105.
State of polarization (SOP) and polarization mode dispersion (PMD) are stochastic in nature due to changes in the properties of the optical fibres and its positions because of both intrinsic and extrinsic perturbations. With 184 PMD values obtained by use of the FTB-5700 single-ended dispersion analyzer, the predicted theoretical Gaussian fit was obtained with a mean of 0.47 ps and standard deviation of 0.08 ps. This small standard deviation was justification for its accuracy in measuring PMD of aerial optical fibres. A comparison is also made on the accuracy of the GINTY and the FTB-5700 on measurement of PMD of aerial optical fibres with results showing that the latter is more accurate compared to the former. The time scale over which to compensate PMD in aerial optical fibres was determined and it is slightly higher than 400 s; the decorrelation time obtained for SOPs on a particular windy and hot day. This is because the changes of the PMD vector are known to be slower than SOP changes. 相似文献
106.
Viggo Tvergaard John W. Hutchinson 《Journal of the mechanics and physics of solids》2008,56(1):215-229
For crack growth along an interface between dissimilar materials the effect of combined modes I, II and III at the crack-tip is investigated. First, in order to highlight situations where crack growth is affected by a mode III contribution, examples of material configurations are discussed where mode III has an effect. Subsequently, the focus is on crack growth along an interface between an elastic-plastic solid and an elastic substrate. The analyses are carried out for conditions of small-scale yielding, with the fracture process at the interface represented by a cohesive zone model. Due to the mismatch of elastic properties across the interface the corresponding elastic solution has an oscillating stress singularity, and this solution is applied as boundary conditions on the outer edge of the region analyzed. For several combinations of modes I, II and III crack growth resistance curves are calculated numerically in order to determine the steady-state fracture toughness. For given values of KI and KII the minimum fracture toughness corresponds to KIII=0 in most of the range analyzed, but there is a range where the minimum occurs for a nonzero value of KIII. 相似文献
107.
We study expectation values of observables in three-dimensional spinfoam quantum gravity coupled to Dirac fermions. We revisit the model introduced by one of the authors and extend it to the case of massless fermionic fields. We introduce observables, analyse their symmetries and the corresponding proper gauge fixing. The Berezin integral over the fermionic fields is performed and the fermionic observables are expanded in open paths and closed loops associated to pure quantum gravity observables. We obtain the vertex amplitudes for gauge-invariant observables, while the expectation values of gauge-variant observables, such as the fermion propagator, are given by the evaluation of particular spin networks. 相似文献
108.
109.
T. Ditmire J.W.G. Tisch E.T. Gumbrell R.A. Smith D.D. Meyerhofer M.H.R. Hutchinson 《Applied physics. B, Lasers and optics》1997,65(3):313-328
Received: 12 May 1997 相似文献
110.
We give an algorithm for finding finite element approximations to surfaces of prescribed variable mean curvature, which span
a given boundary curve. We work in the parametric setting and prove optimal estimates in the H1 norm. The estimates are verified computationally. 相似文献