全文获取类型
收费全文 | 1147篇 |
免费 | 38篇 |
国内免费 | 9篇 |
专业分类
化学 | 655篇 |
晶体学 | 7篇 |
力学 | 36篇 |
数学 | 87篇 |
物理学 | 409篇 |
出版年
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 22篇 |
2019年 | 21篇 |
2018年 | 25篇 |
2017年 | 24篇 |
2016年 | 28篇 |
2015年 | 30篇 |
2014年 | 38篇 |
2013年 | 63篇 |
2012年 | 35篇 |
2011年 | 51篇 |
2010年 | 37篇 |
2009年 | 33篇 |
2008年 | 43篇 |
2007年 | 49篇 |
2006年 | 45篇 |
2005年 | 58篇 |
2004年 | 45篇 |
2003年 | 39篇 |
2002年 | 46篇 |
2001年 | 46篇 |
2000年 | 28篇 |
1999年 | 34篇 |
1998年 | 22篇 |
1997年 | 20篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 10篇 |
1989年 | 17篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1979年 | 9篇 |
1976年 | 7篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1972年 | 7篇 |
1971年 | 14篇 |
1970年 | 12篇 |
1968年 | 6篇 |
1967年 | 7篇 |
排序方式: 共有1194条查询结果,搜索用时 15 毫秒
1.
Journal of Experimental and Theoretical Physics - The nature of the training effect in exchange-biased compounds is studied. This effect consists in a decrease in the exchange bias field (HEB)... 相似文献
2.
Physics of Atomic Nuclei - The article presents the concept of a channel-type reactor with a combined cooled moderator. The moderator consists of ceramic beryllium oxide and a liquid... 相似文献
3.
4.
N. V. Vysotina A. S. Naumov N. N. Rozanov R. L. Sabirov V. E. Semenov V. A. Smirnov T. V. Starchikova S. V. Fedorov S. A. Chizhov V. E. Yashin 《Optics and Spectroscopy》2004,97(3):411-415
The final stage of self-focusing of 500-ps pulses of a neodymium laser in silicate and phosphate glasses and in the nonlinear liquids perfluorooctane, benzene, and toluene is studied theoretically and experimentally. The formation of spatial solitons, which are stable due to the nonlinearity saturation, is demonstrated. It is found that the intensity of the nonlinearity saturation is close to that of the threshold breakdown for glasses and the role of stimulated Raman scattering is significant for liquids. 相似文献
5.
Danny E. Akin W. Herbert Morrison III Luanne L. Rigsby Franklin E. Barton II David S. Himmelsbach Kevin B. Hicks 《Applied biochemistry and biotechnology》2006,129(1-3):104-116
Information is presented on structure, composition, and response to enzymes of corn stover related to barriers for bioconversion
to ethanol. Aromatic compounds occurred in most tissue cell walls. Ferulic acid esterase treatment before cellulase treatment
significantly improved dry weight loss and release of phenolic acids and sugars in most fractions over cellulase alone. Leaf
fractions were considerably higher in dry weight loss and released sugars with esterase treatment, but stem pith cells gave
up the most phenolic acids. Results help identify plant fractions more appropriate for coproducts and bioconversion and those
more suitable as residues for soil erosion control. 相似文献
6.
7.
A computer simulation of the kinetics of free-radical oxidation of lipids in the presence of tocopherol was performed. The induction periods and initial rates of oxidation as functions of initial tocopherol concentrations were found to exhibit extremums. The extended kinetic scheme used in this study describes all types of observed relationships and eliminates illusory contradictions between two groups of experiments in which the antioxidant and prooxidant effects of tocopherol were found. The model can form a basis for the prediction of the effects of tocopherol and its analogs under real conditions. 相似文献
8.
S. D. Gunapala S. V. Bandara J. K. Liu S. B. Rafol J. M. Mumolo C. A. Shott R. Jones J. Woolaway II J. M. Fastenau A. K. Liu M. Jhabvala K. K. Choi 《Infrared Physics & Technology》2003,44(5-6):411-425
A 9 μm cutoff 640 × 512 pixel hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated with excellent imagery. A noise equivalent differential temperature (NEDT) of 10.6 mK is expected at a 65 K operating temperature with f/2 optics at a 300 K background. This focal plane array has shown background limited performance at a 72 K operating temperature with the same optics and background conditions. In this paper, we discuss the development of this very sensitive long-wavelength infrared camera based on a GaAs/AlGaAs QWIP focal plane array and its performance in quantum efficiency, NEDT, uniformity, and operability. In the second section of this paper, we discuss the first demonstration of a monolithic spatially separated four-band 640 × 512 pixel QWIP focal plane array and its performance. The four spectral bands cover 4–5.5, 8.5–10, 10–12, and 13.5–15 μm spectral regions with 640 × 128 pixels in each band. In the last section, we discuss the array performance of a 640 × 512 pixel broad-band (10–16 μm full-width at half-maximum) QWIP focal plane. 相似文献
9.
We estimate the possible influence of spectral line profile (Lorentz profile, Van Vleck–Weisskopf profile, and profile obtained by solving kinetic equation) on the rotation part of the dielectric permittivity of water-vapor monomers. Spectral regions corresponding to long-wavelength (static) and high-frequency (optical) limiting cases as well as regions in close proximity to resonances of various intensities are considered. The studied effects are compared with the corresponding effects on water-vapor absorption coefficient, which are related to factors determining the line-shape structure. 相似文献
10.
Optimization theory provides a framework for determining the best decisions or actions with respect to some mathematical model of a process. This paper focuses on learning to act in a near-optimal manner through reinforcement learning for problems that either have no model or the model is too complex. One approach to solving this class of problems is via approximate dynamic programming. The application of these methods are established primarily for the case of discrete state and action spaces. In this paper we develop efficient methods of learning which act in complex systems with continuous state and action spaces. Monte-Carlo approaches are employed to estimate function values in an iterative, incremental procedure. Derivative-free line search methods are used to obtain a near-optimal action in the continuous action space for a discrete subset of the state space. This near-optimal control policy is then extended to the entire continuous state space via a fuzzy additive model. To compensate for approximation errors, a modified procedure for perturbing the generated control policy is developed. Convergence results under moderate assumptions and stopping criteria are established. 相似文献