全文获取类型
收费全文 | 426661篇 |
免费 | 3643篇 |
国内免费 | 1247篇 |
专业分类
化学 | 205728篇 |
晶体学 | 6976篇 |
力学 | 21301篇 |
综合类 | 6篇 |
数学 | 59580篇 |
物理学 | 137960篇 |
出版年
2019年 | 2597篇 |
2018年 | 11296篇 |
2017年 | 12011篇 |
2016年 | 8672篇 |
2015年 | 4061篇 |
2014年 | 5226篇 |
2013年 | 14323篇 |
2012年 | 14364篇 |
2011年 | 24379篇 |
2010年 | 15567篇 |
2009年 | 15414篇 |
2008年 | 21545篇 |
2007年 | 24814篇 |
2006年 | 11730篇 |
2005年 | 16860篇 |
2004年 | 12766篇 |
2003年 | 11783篇 |
2002年 | 9823篇 |
2001年 | 9968篇 |
2000年 | 7793篇 |
1999年 | 6064篇 |
1998年 | 5176篇 |
1997年 | 5037篇 |
1996年 | 4949篇 |
1995年 | 4615篇 |
1994年 | 4324篇 |
1993年 | 4381篇 |
1992年 | 4660篇 |
1991年 | 4781篇 |
1990年 | 4509篇 |
1989年 | 4505篇 |
1988年 | 4538篇 |
1987年 | 4447篇 |
1986年 | 4177篇 |
1985年 | 5662篇 |
1984年 | 5997篇 |
1983年 | 4887篇 |
1982年 | 5327篇 |
1981年 | 5091篇 |
1980年 | 5056篇 |
1979年 | 5175篇 |
1978年 | 5369篇 |
1977年 | 5154篇 |
1976年 | 5290篇 |
1975年 | 4933篇 |
1974年 | 4803篇 |
1973年 | 5097篇 |
1972年 | 3389篇 |
1971年 | 2715篇 |
1968年 | 2596篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
P. Paasche T. Valenzuela D. Biswas C. Angelescu G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):295-300
We have examined experimentally the motional spectrum of an electron cloud confined in a Penning trap. When the axial oscillation
is excited by a radio frequency field the resonance exhibits a double structure. Both components depend differently on the
number of trapped electrons and have different shape and width. We conclude that one of them corresponds to the excitation
of the individual electrons while the other is the center-of-mass mode of the cloud. The threshold behaviour of the center-of-mass
resonance suggests that it is a parametric instability of a Mathieu type equation of motion.
Received 11 July 2001 and Received in final form 12 November 2001 相似文献
992.
Several variations of two-dimensional (workers x jobs) and three-dimensional (workers x jobs x machines) time- as well as cost-minimizing assignment problems, which arise owing to (i) precedence relations of some form among the jobs or (ii) capacity restrictions on workers/machines imposed by the requirement that the surplus resources have to be fully employed, have been considered in the literature. In this paper, an algorithm is presented for time-cost trade-off analysis which is applicable to any general pair of such constrained problems. The algorithm is also illustrated by a numerical example. 相似文献
993.
This note discusses the need to use various data-compaction schemes in the implementation of sophisticated large-scale linear programming codes on modest personal computers. It demonstrates a method whereby the overhead of using these schemes is significantly reduced on Intel 80 x 86 processors. 相似文献
994.
995.
The optimal return function for a Borel measurable gambling problem with a bounded utility function was shown by Strauch (1967)
to be universally measurable when the problem is leavable in the sense that the gambler may terminate play at any time. The
same is shown here for the more general class of nonleavable problems.
Research supported by National Science Foundation Grant DMS-8801085. 相似文献
996.
Results of acoustic measurements in skeletal muscle are generalized. It is shown that assessment of the pathologies and functional condition of the muscular system is possible with the use of shear waves. The velocity of these waves in muscles is much smaller than the velocity of sound; therefore, a higher symmetry type is formed for them. In the presence of a preferential direction (along muscle fibers), it is characterized by only two rather than five (as in usual media with the same anisotropy) moduli of elasticity. A covariant form of the corresponding wave equation is presented. It is shown that dissipation properties of skeletal muscles can be controlled by contracting them isometrically. Pulsed loads (shocks) and vibrations are damped differently, depending on their frequency spectrum. Characteristic frequencies on the order of tens and hundreds of hertz are attenuated due to actin-myosin bridges association/dissociation dynamics in the contracted muscle. At higher (kilohertz) frequencies, when the muscle is tensed, viscosity of the tissue increases by a factor of several tens because of the increase in friction experienced by fibrillar structures as they move relative to the surrounding liquid; the tension of the fibers changes the hydrodynamic conditions of the flow around them. Finally, at higher frequencies, the attenuation is associated with the rheological properties of biological molecules, in particular, with their conformational dynamics in the wave field. Models that describe the controlled shock dissipation mechanisms are proposed. Corresponding solutions are found, including those that allow for nonlinear effects. 相似文献
997.
998.
Yu You George W. Kattawar Ping Yang Yong X. Hu Bryan A. Baum 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,100(1-3):470-482
Measurements from depolarized lidars provide a promising method to retrieve both cloud and aerosol properties and a versatile complement to passive satellite-based sensors. For lidar observations of clouds and aerosols, multiple scattering plays an important role in the scattering process. Monte Carlo simulations are carried out to investigate the sensitivity of lidar backscattering depolarization to cloud and aerosol properties. Lidar parameters are chosen to be similar to those of the upcoming space-based CALIPSO lidar. Cases are considered that consist of a single cloud or aerosol layer, as well as a case in which cirrus clouds overlay different types of aerosols. It is demonstrated that besides thermodynamic cloud phase, the depolarized lidar signal may provide additional information on ice or aerosol particle shapes. However, our results show little sensitivity to ice or aerosol particle sizes. Additionally, for the case of multiple but overlapping layers involving both clouds and aerosols, the depolarized lidar contains information that can help identify the particle properties of each layer. 相似文献
999.
W. Hufenbach R. Böhm A. Langkamp L. Kroll T. Ritschel 《Mechanics of Composite Materials》2006,42(2):151-162
The basic damage and failure models of multiaxially reinforced composites with a thermoplastic matrix are presented and verified.
Within the framework of continuum damage mechanics, a phenomenological model is introduced, where the damage is defined as
a change in the elasticity tensor. For damage identification, a specific ultrasonic device was developed. A combination of
an immersion set-up and a contact coupling device formed a system for an efficient determination of stiffness-tensor components
from convenient sets of velocity measurements. Linked to a tensile machine, it allowed us to measure the anisotropic damage
of the new materials group caused by tensile loading.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 221–234, March–April, 2006. 相似文献
1000.