全文获取类型
收费全文 | 11138篇 |
免费 | 407篇 |
国内免费 | 299篇 |
专业分类
化学 | 4797篇 |
晶体学 | 249篇 |
力学 | 808篇 |
综合类 | 5篇 |
数学 | 1329篇 |
物理学 | 4656篇 |
出版年
2023年 | 87篇 |
2022年 | 184篇 |
2021年 | 194篇 |
2020年 | 180篇 |
2019年 | 178篇 |
2018年 | 200篇 |
2017年 | 168篇 |
2016年 | 259篇 |
2015年 | 214篇 |
2014年 | 321篇 |
2013年 | 538篇 |
2012年 | 724篇 |
2011年 | 832篇 |
2010年 | 617篇 |
2009年 | 636篇 |
2008年 | 663篇 |
2007年 | 600篇 |
2006年 | 593篇 |
2005年 | 454篇 |
2004年 | 396篇 |
2003年 | 317篇 |
2002年 | 269篇 |
2001年 | 485篇 |
2000年 | 400篇 |
1999年 | 272篇 |
1998年 | 208篇 |
1997年 | 188篇 |
1996年 | 207篇 |
1995年 | 161篇 |
1994年 | 150篇 |
1993年 | 111篇 |
1992年 | 116篇 |
1991年 | 132篇 |
1990年 | 112篇 |
1989年 | 85篇 |
1988年 | 68篇 |
1987年 | 49篇 |
1986年 | 43篇 |
1985年 | 52篇 |
1984年 | 46篇 |
1983年 | 25篇 |
1982年 | 39篇 |
1981年 | 35篇 |
1980年 | 29篇 |
1979年 | 25篇 |
1978年 | 26篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 21篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
A domain partitioning algorithm for minimizing or maximizing a Lipschitz continuous function is enhanced to yield two new, more efficient algorithms. The use of interval arithmetic in the case of rational functions and the estimates of Lipschitz constants valid in subsets of the domain in the case of others and the addition of local optimization have resulted in an algorithm which, in tests on standard functions, performs well. 相似文献
42.
We describe the formation of a narrow beam for intensity-modulated electromagnetic radiation propagating through highly scattering materials. We propose to use this beam to reconstruct images, similar to X-ray back-projection techniques. For sufficiently high modulation frequency, the photon density wave is primarily carried by photons that suffer small or no large-angle scattering, which gives rise to the beam’s narrow divergence. The beam-narrowing concept is supported by large-scale numerical simulations to examine the quality of the imaging. 相似文献
43.
D. Liu Y. Li R. An Y. Dou H. Yang Q. Gong 《Applied Physics A: Materials Science & Processing》2006,84(3):257-260
We studied the influence of focusing depth on the index change threshold and damage threshold of silica glass irradiated by a focused 120 fs laser beam. Both thresholds increased with the focusing depth. The aspect ratio of the waveguide cross section can be selected by changing the focusing depth. A 5 mm long waveguide was written at the depth of 2100 μm, which was single mode at 632.8 nm and exhibited propagation loss of 0.56 dB/cm. The refractive index change was calculated to be ∼2.47×10-3. The influence of the focusing depth should be considered in multi-layer devices as shown in the fabrication of a 3×3 waveguide array. PACS 42.62.-b; 42.82.Et; 81.05.Kf 相似文献
44.
Organically modified solid-state silicates (ORMOSILS) doped with a new laser dye 1,3,5,7,8-pentamethylpyrromethene-2,6-disulfonate-BF2 complex (pyrromethene 556) have been synthesized by a sol-gel method and the compositional effects on pore characteristics, fluorescence and lasing properties have been investigated. It is found that the use of dimethylsulfoxide and γ-glycidoxypropyltrimethoxysilane could greatly change the structure properties of sol-gel derived ORMOSILS cage, and thus the fluorescence and lasing properties of the materials could improve significantly. A successful laser oscillation from this dye-doped ORMOSILS sample has been achieved upon pumping with a Q-switched frequency-doubled Nd:YAG laser at 532 nm. A slope efficiency of 54% with a useful lifetime greater than 10,000 shots has been demonstrated at a pump repetition rate of 1 Hz and a pump intensity of 1 J/cm2 by using the new ORMOSILS cage on our newly designed laser system. Our results have shown that it is possible to obtain a high-efficiency with a long-lifetime for a compact new laser device by low cost dye-doped solid-state ORMOSILS. 相似文献
45.
Inexact Newton methods for the nonlinear complementarity problem 总被引:2,自引:0,他引:2
Jong-Shi Pang 《Mathematical Programming》1986,36(1):54-71
An exact Newton method for solving a nonlinear complementarity problem consists of solving a sequence of linear complementarity
subproblems. For problems of large size, solving the subproblems exactly can be very expensive. In this paper we study inexact
Newton methods for solving the nonlinear, complementarity problem. In such an inexact method, the subproblems are solved only
up to a certain degree of accuracy. The necessary accuracies that are needed to preserve the nice features of the exact Newton
method are established and analyzed. We also discuss some extensions as well as an application.
This research was based on work supported by the National Science Foundation under grant ECS-8407240. 相似文献
46.
Introduction and Applications of a Generalized Intermediate Entangled State Representation 下载免费PDF全文
We introduce a generalized intermediate entangled state representation |β〉Λ to study the energy spectrum of an electron in a uniform magnetic field and a harmonic potential through algebraic calculatiOn. We find that the degeneracy of the energy levels is disappeared due to the existence of the additional potential. We make it clear that the eigenfunction is just the expression of eigenvector, defined in n Fock space, in |β〉Λ representation. 相似文献
47.
Invex-convexlike functions and duality 总被引:4,自引:0,他引:4
P. Q. Khanh 《Journal of Optimization Theory and Applications》1995,87(1):141-165
We define a class of invex-convexlike functions, which contains all convex, pseudoconvex, invex, and convexlike functions, and prove that the Kuhn-Tucker sufficient optimality condition and the Wolfe duality hold for problems involving such functions. Applications in control theory are given.The author is grateful to Professor W. Stadler and the referees for many valuable remarks and suggestions, which have enabled him to improve considerably the paper. 相似文献
48.
Cory J. Hill Baohua Yang Rui Q. Yang 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):486
Mid-IR type-II interband cascade lasers were demonstrated in pulsed mode at temperatures up to 325 K and in continuous mode up to 200 K. At 80 K, the threshold current density was 8.9 A/cm2 and a continuous wave output power of 140 mW/facet was obtained. 相似文献
49.
By means of a new force sensor based on optical beam deflection (OBD), the mechanical effects of laser-matter interaction underwater at different incident laser energy are investigated in detail. The experimental results show that a target underwater is impacted in turn by laser-plasma ablation force and high-speed liquid-jet impulse induced by bubbles collapse in the vicinity of a solid boundary. Furthermore, the amplitudes of the two forces increase monotonously with laser energy. According to the ablation force detected by the experiment and the theoretical relationship between laser intensity and ablation pressure, the value of liquid-jet impact against a solid boundary can be easily obtained. In addition, based on the model of a collapsing bubble, some characteristic parameters, such as the liquid-jet impact velocity, the maximum bubble radius, the bubble energy can also be obtained at different laser energy, which are valuable in the corresponding research fields. 相似文献
50.
In this paper we consider an obstacle control problem where the state satisfies a quasilinear elliptic variational inequality and the control function is the obstacle. The state is chosen to be close to the desire profile while the H2 norms of the obstacle is not too large. Existence and necessary conditions for the optimal control are established. 相似文献