全文获取类型
收费全文 | 506252篇 |
免费 | 4707篇 |
国内免费 | 1573篇 |
专业分类
化学 | 258149篇 |
晶体学 | 7543篇 |
力学 | 25360篇 |
综合类 | 13篇 |
数学 | 76808篇 |
物理学 | 144659篇 |
出版年
2018年 | 14146篇 |
2017年 | 13953篇 |
2016年 | 12236篇 |
2015年 | 4989篇 |
2014年 | 6657篇 |
2013年 | 17825篇 |
2012年 | 16084篇 |
2011年 | 25293篇 |
2010年 | 16195篇 |
2009年 | 16327篇 |
2008年 | 20502篇 |
2007年 | 22831篇 |
2006年 | 14089篇 |
2005年 | 13738篇 |
2004年 | 12910篇 |
2003年 | 12271篇 |
2002年 | 11192篇 |
2001年 | 12291篇 |
2000年 | 9578篇 |
1999年 | 7438篇 |
1998年 | 6299篇 |
1997年 | 6301篇 |
1996年 | 6095篇 |
1995年 | 5596篇 |
1994年 | 5590篇 |
1993年 | 5281篇 |
1992年 | 6115篇 |
1991年 | 5971篇 |
1990年 | 5860篇 |
1989年 | 5763篇 |
1988年 | 5825篇 |
1987年 | 5713篇 |
1986年 | 5383篇 |
1985年 | 7152篇 |
1984年 | 7397篇 |
1983年 | 6154篇 |
1982年 | 6463篇 |
1981年 | 6349篇 |
1980年 | 6220篇 |
1979年 | 6401篇 |
1978年 | 6849篇 |
1977年 | 6591篇 |
1976年 | 6597篇 |
1975年 | 6179篇 |
1974年 | 6206篇 |
1973年 | 6349篇 |
1972年 | 4410篇 |
1971年 | 3669篇 |
1968年 | 3799篇 |
1967年 | 3995篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
With the use of an analytical approach developed, the influence of distribution of a tangential load on the stress concentration
in uniaxially tensioned flat specimens of high-strength unidirectional composites near the grips of a testing machine is evaluated.
In view of singularity of the analytical solution derived at the points of discontinuity of boundary conditions, for estimating
the stress concentration, it is suggested to employ the averaged value of longitudinal stresses, which is calculated by means
of an improper integral across the thickness of a near-surface layer.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 787–796, November–December, 2006. 相似文献
992.
Multinomial permutations on a circle are considered in the framework of combinatorics. Different cases are presented and shown to agree with previously derived formula for the number of cyclic necklaces. Two applied examples are discussed with a view to illustrate the implications of derived formulas. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
993.
Mathematical models with stage structures are proposed to describe the process of awareness, evaluation and decision-making. First, a system of ordinary differential equations is presented that incorporates the awareness stage and the decision-making stage. If the adoption rate is bilinear and imitations are dominant, we find a threshold above which innovation diffusion is successful. Further, if the adoption rate has a higher nonlinearity, it is shown that there exist bistable equilibria and a region such that an innovation diffusion is successful inside and is unsuccessful outside. Secondly, a model with a time delay is proposed that includes an evaluation stage of a product. It is proved that the system exhibits stability switches. The bifurcation direction of equilibria is also discussed. 相似文献
994.
Jean-Marc Hérard 《Comptes Rendus Mathematique》2006,342(10):779-784
We introduce a hyperbolic entropy-consistent model to describe three-phase flows, which ensures that void fractions, mass fractions and pressures remain positive through single waves occurring in the one dimensional solution of the Riemann problem. To cite this article: J.-M. Hérard, C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
995.
The gedanken experiment of the clock paradox is solved exactly using the general relativistic equations for a static homogeneous gravitational
field. We demonstrate that the general and special relativistic clock paradox solutions are identical and in particular that
they are identical for finite acceleration. Practical expressions are obtained for proper time and coordinate time by using the destination distance as
the key observable parameter. This solution provides a formal demonstration of the identity between the special and general
relativistic clock paradox with finite acceleration and where proper time is assumed to be the same in both formalisms. By
solving the equations of motion for a freely falling clock in a static homogeneous field elapsed times are calculated for
realistic journeys to the stars.
1 Both authors contributed equally to this paper. 相似文献
996.
J.H. Sung J.Y. Park T. Imran Y.S. Lee C.H. Nam 《Applied physics. B, Lasers and optics》2006,82(1):5-8
Optical pulses with 1.1-mJ energy and 5.5-fs duration have been generated at 1-kHz repetition rate from a chirped pulse amplification
Ti:Sapphire laser incorporating a differentially pumped hollow-fiber chirped-mirror compressor. The effects of self-focusing
and multi-photon ionization during the beam propagation were minimized by differentially pumping the hollow fiber filled with
neon. The spectral broadening at the hollow-fiber compressor was optimized by adjusting gas pressure, laser intensity, and
laser chirp, covering from 540 nm to 950 nm.
PACS 42.65.Jx; 42.65.Re 相似文献
997.
Christopher Batchelor-McAuley Craig E Banks Andrew O Simm Timothy G J Jones Richard G Compton 《Chemphyschem》2006,7(5):1081-1085
The benefits of using nanoparticle-modified electrodes are exemplified through the electrochemical detection of protons and/or hydrogen. It is shown that a palladium-nanoparticle-modified boron-doped diamond allows voltammetric information relating to the relative roles played by the surface and the bulk metal to be obtained for the proton-hydrogen system at palladium surfaces which is not accessible using palladium macroelectrodes or microelectrodes. 相似文献
998.
Forecasting electricity prices in presentday competitive electricity markets is a must for both producers and consumers because both need price estimates to develop their respective market bidding strategies. This paper proposes a transfer function model to predict electricity prices based on both past electricity prices and demands, and discuss the rationale to build it. The importance of electricity demand information is assessed. Appropriate metrics to appraise prediction quality are identified and used. Realistic and extensive simulations based on data from the PJM Interconnection for year 2003 are conducted. The proposed model is compared with naïve and other techniques. 相似文献
999.
We fabricated high-quality InAlN/GaN heterostructures by metal–organic vapor phase epitaxy (MOVPE). X-ray diffraction measurements revealed that InAlN/GaN heterostructures grown under optimal conditions have flat surfaces and abrupt heterointerfaces. Electron mobility from 1200 to 2000 cm2/V s was obtained at room temperature. To our knowledge, this mobility is the highest ever reported for InAlN/GaN heterostructures. We also investigated the relationship between the Al composition and sheet electron density (Ns) for the first time. Ns increased from 1.0×1012 to 2.7×1013 cm−2 when the Al composition increased from 0.78 to 0.89. 相似文献
1000.