全文获取类型
收费全文 | 5059篇 |
免费 | 261篇 |
国内免费 | 22篇 |
专业分类
化学 | 3889篇 |
晶体学 | 13篇 |
力学 | 111篇 |
数学 | 665篇 |
物理学 | 664篇 |
出版年
2023年 | 55篇 |
2022年 | 57篇 |
2021年 | 89篇 |
2020年 | 110篇 |
2019年 | 112篇 |
2018年 | 68篇 |
2017年 | 62篇 |
2016年 | 225篇 |
2015年 | 196篇 |
2014年 | 191篇 |
2013年 | 286篇 |
2012年 | 367篇 |
2011年 | 387篇 |
2010年 | 241篇 |
2009年 | 217篇 |
2008年 | 313篇 |
2007年 | 267篇 |
2006年 | 280篇 |
2005年 | 278篇 |
2004年 | 242篇 |
2003年 | 173篇 |
2002年 | 188篇 |
2001年 | 95篇 |
2000年 | 82篇 |
1999年 | 77篇 |
1998年 | 62篇 |
1997年 | 87篇 |
1996年 | 69篇 |
1995年 | 66篇 |
1994年 | 45篇 |
1993年 | 50篇 |
1992年 | 32篇 |
1991年 | 25篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有5342条查询结果,搜索用时 15 毫秒
31.
In this contribution we consider a port-Hamiltonian setting for partial differential equations. A crucial property of this system class is the property to be able to link a power balance relation to the structure of the equations. However, one has to take into account also the effects of energy flows via the boundary. This is straightforward when the Hamiltonian depends on derivative variables of first order, e.g. by using integration by parts. If second-order derivatives appear then integration by parts cannot be used without due care, thus we suggest an approach by using the so-called Cartan-form. We visualize the derivation of a power balance relation by using the Kirchhoff plate as an example. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
32.
A small-deformation strain gradient plasticity (GP) model for single-crystals has been proposed in [1], including a grain boundary (GB) yield condition without hardening. It has been extended by a hardening term for the GBs after a comparison to discrete dislocation dynamics (DDD) results in [2]. Differences between the strain gradients of the GP results and the DDD results motivate the consideration of a non-quadratic defect energy [3] in the GP model. It is shown that the gradients in the GP model can be improved using an exponent different from two. Remaining discrepancies in the strain profiles, compared to the DDD results, are attributed to the neglect of the individual gradients of plastic slip and due to the lack of a mechanism for the misorientation-dependent elastic interactions of dislocations across GBs [4] in the GP model. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
33.
34.
The new ternary carbodiimide LiY(CN2)2 was synthesized by solid state metathesis reaction between YF3 and Li2(CN2) in a silica tube at 550 °C. The X‐ray single‐crystal structure determination yielded an orthorhombic crystal system (Pbcn, Z = 4, a = 982.0(3), b = 698.5(2), c = 613.4(2) pm). The crystal structure can be considered related to the NiAs structure. The carbodiimide ions are arranged in layers following the motif of a hexagonal closest packing of sticks. Lithium and yttrium cations occupy all octahedral voids in an ordered fashion, alternating on top of each other along the hcp stacking direction. 相似文献
35.
36.
Li Luo Kathrin Häfliger Dan Xie Markus Niederberger 《Journal of Sol-Gel Science and Technology》2013,65(1):28-35
Homogeneous transparent conducting Sn:ZnO films on fused silica substrates were prepared by dip-coating from nanoparticle dispersions, while the nanocrystalline Sn:ZnO particles with different dopant concentrations were synthesized by microwave-assisted non-aqueous sol–gel process using Sn(IV) tert-butoxide and Zn(II) acetate as precursors and benzyl alcohol as solvent. The dopant concentration had a great impact on the electrical properties of the films. A minimum resistivity of 20.3 Ω cm was obtained for a porous Sn:ZnO film with initial Sn concentration of 7.5 mol% after annealing in air and post-annealing in N2 at 600 °C. The resistivity of this porous film could further be reduced to 2.6 and 0.6 Ω cm after densified in Sn:ZnO and Al:ZnO reaction solution, respectively. The average optical transmittance of a 400-nm-thick Sn:ZnO film densified with Sn:ZnO after the two annealing steps was 91%. 相似文献
37.
38.
The self-reproduction ability of mitotic cells results in an increase of the number of cells with the same characteristics in living bodies. While cells grow in volume and divide themselves, the living body consequently grows in mass and volume. Further, if the factors which regulate the growth process are inhomogeneously distributed, growth takes place at different rates and directions. In this work we aim to provide a new continuum model for growing tissues. More specifically, the model considers the reorientation of the cell-division plane in mitotic cells depending on the stress field of the growing body. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
39.
The complexity of technical products increases significantly, due to an increasing number of interacting design variables of many components and subsystems. At the same time, the need for separated development processes is increasing due to specialization and outsourcing. Solution space methods are designed to solve this conflict. The requirements from an upper level, e.g. performance measures of the whole system, can be cascaded down to requirements on a lower level, e.g. performance measures of the subsystems or components, as it is done in the V-model approach. The method does not only take the numerous interactions into account but also guarantees the resulting intervals of different parameters to be independent of each other. Unfortunately, the computational cost of the state-of-the-art stochastic approach is high. The approach in this paper shows that the computational effort can be reduced considerably using a gradient based optimization approach for constraint problems. We demonstrate that the approach reduces the required number of function evaluations for a chassis design problem by a factor of 30, but more important, the CPU time for solving the problem by a factor of 20. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
40.
Fracture experiments of single silicon crystals reveal that after the critical fracture load is reached, the crack speed jumps from zero to approximately 2 km/sec, indicating that crack motion at lower speeds is forbidden. This contradicts classical continuum fracture theories predicting a continuously increasing crack speed with increasing load. Here we show that this threshold crack speed may be due to a localized phase transformation of the silicon lattice from 6-membered rings to a 5-7 double ring at the crack tip. 相似文献