全文获取类型
收费全文 | 222280篇 |
免费 | 2553篇 |
国内免费 | 791篇 |
专业分类
化学 | 112959篇 |
晶体学 | 3878篇 |
力学 | 10045篇 |
综合类 | 11篇 |
数学 | 23871篇 |
物理学 | 74860篇 |
出版年
2021年 | 1648篇 |
2020年 | 1789篇 |
2019年 | 1929篇 |
2018年 | 2472篇 |
2017年 | 2490篇 |
2016年 | 3947篇 |
2015年 | 2444篇 |
2014年 | 3959篇 |
2013年 | 9860篇 |
2012年 | 7677篇 |
2011年 | 9410篇 |
2010年 | 6818篇 |
2009年 | 6827篇 |
2008年 | 8837篇 |
2007年 | 8575篇 |
2006年 | 8111篇 |
2005年 | 7288篇 |
2004年 | 6729篇 |
2003年 | 6085篇 |
2002年 | 5851篇 |
2001年 | 7797篇 |
2000年 | 5769篇 |
1999年 | 4352篇 |
1998年 | 3445篇 |
1997年 | 3305篇 |
1996年 | 3020篇 |
1995年 | 2818篇 |
1994年 | 2722篇 |
1993年 | 2564篇 |
1992年 | 3164篇 |
1991年 | 3102篇 |
1990年 | 2966篇 |
1989年 | 2811篇 |
1988年 | 2791篇 |
1987年 | 2854篇 |
1986年 | 2634篇 |
1985年 | 3445篇 |
1984年 | 3450篇 |
1983年 | 2908篇 |
1982年 | 2976篇 |
1981年 | 2785篇 |
1980年 | 2742篇 |
1979年 | 3001篇 |
1978年 | 3058篇 |
1977年 | 3008篇 |
1976年 | 2961篇 |
1975年 | 2801篇 |
1974年 | 2814篇 |
1973年 | 2925篇 |
1972年 | 1848篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
B. P. Harlamov 《Journal of Mathematical Sciences》2006,133(3):1371-1377
An inverse process with independent positive increments is considered. For such a process, the first hitting time τx of level x as a function of x ≥ 0 is a proper process with independent positive increments. In terms of first hitting times
and their Levy measures, multidemensional distribution densities and Laplace transformations are derived. Stationary distributions
of increments of the process are investigated. Bibliography: 8 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 311, 2004, pp. 286–297. 相似文献
92.
The consequences of Ge deposition on Br-terminated Si(1 0 0) were studied with scanning tunneling microscopy at ambient temperature after annealing at 650 K. One monolayer of Br was sufficient to prevent the formation of Ge huts beyond the critical thickness of 3 ML. This is possible because Br acts as a surfactant whose presence lowered the diffusivity of Ge adatoms. Hindered mobility was manifest at low coverage through the formation of short Ge chains. Further deposition resulted in the extension and connection of the Ge chains and gave rise to the buildup of incomplete layers. The deposition of 7 ML of Ge resulted in a rough surface characterized by irregularly shaped clusters. A short 800 K anneal desorbed the Br and allowed Ge atoms to reorganize into the more energetically favorable “hut” structures produced by conventional Ge overlayer growth on Si(1 0 0). 相似文献
93.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献
94.
95.
Three new cytotoxic polyacetylenes, PQ-1 (1), PQ-2 (2) and PQ-3 (3), have been isolated from Panax quinquefolium. The structures of these acetylenes were determined by analyses of their 1H-1H and 1H-13C COSY spectra. All these compounds exhibited strong cytotoxic activities against leukemia cells (L 1210) in tissue culture. 相似文献
96.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
97.
98.
99.
Y. Wardi 《Journal of Optimization Theory and Applications》1989,61(3):473-485
A stochastic algorithm for finding stationary points of real-valued functions defined on a Euclidean space is analyzed. It is based on the Robbins-Monro stochastic approximation procedure. Gradient evaluations are done by means of Monte Carlo simulations. At each iteratex
i
, one sample point is drawn from an underlying probability space, based on which the gradient is approximated. The descent direction is against the approximation of the gradient, and the stepsize is 1/i. It is shown that, under broad conditions, w.p.1 if the sequence of iteratesx
1,x
2,...generated by the algorithm is bounded, then all of its accumulation points are stationary. 相似文献
100.
P. David J. Hartfiel H. Janszen R. von Mutius J. Arvieux L. Farvacque B. Berthier B. Bonin J. C. Lugol 《Zeitschrift für Physik A Hadrons and Nuclei》1987,326(4):367-372
The excitation function of the fission probability P E E x) for238U has been measured in the reaction238U(α, α′ f) at 480 MeV bombarding energy. The reaction mechanism of this reaction is discussed for excitation energies belowB nf , the threshold for second chance fission, and aboveB nf up toE x =37 MeV. In comparing with results from fission induced by photons and by particle transfer reactions the (α, α′f) reaction gives too low values for the fission probabilityP f at excitation energies well aboveB nE . The role of the quasi-elastic knock-out process in this reaction is discussed. 相似文献