全文获取类型
收费全文 | 1338080篇 |
免费 | 29692篇 |
国内免费 | 7683篇 |
专业分类
化学 | 667940篇 |
晶体学 | 20375篇 |
力学 | 74726篇 |
综合类 | 103篇 |
数学 | 241464篇 |
物理学 | 370847篇 |
出版年
2021年 | 13485篇 |
2020年 | 15943篇 |
2019年 | 16065篇 |
2018年 | 12505篇 |
2016年 | 27909篇 |
2015年 | 20757篇 |
2014年 | 30425篇 |
2013年 | 74389篇 |
2012年 | 37973篇 |
2011年 | 34917篇 |
2010年 | 37063篇 |
2009年 | 39428篇 |
2008年 | 34363篇 |
2007年 | 29881篇 |
2006年 | 36090篇 |
2005年 | 28543篇 |
2004年 | 29880篇 |
2003年 | 28177篇 |
2002年 | 29200篇 |
2001年 | 28341篇 |
2000年 | 24711篇 |
1999年 | 22428篇 |
1998年 | 21029篇 |
1997年 | 20984篇 |
1996年 | 21125篇 |
1995年 | 19159篇 |
1994年 | 18618篇 |
1993年 | 18163篇 |
1992年 | 18057篇 |
1991年 | 18387篇 |
1990年 | 17614篇 |
1989年 | 17603篇 |
1988年 | 17192篇 |
1987年 | 17174篇 |
1986年 | 16071篇 |
1985年 | 22497篇 |
1984年 | 23760篇 |
1983年 | 20005篇 |
1982年 | 21647篇 |
1981年 | 20876篇 |
1980年 | 20218篇 |
1979年 | 20400篇 |
1978年 | 21731篇 |
1977年 | 21297篇 |
1976年 | 21008篇 |
1975年 | 19720篇 |
1974年 | 19389篇 |
1973年 | 19852篇 |
1972年 | 14353篇 |
1967年 | 12551篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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
992.
We consider the radiation from nonoscillating dipoles traveling with constant velocity directed parallel or antiparallel to
the velocity of a homogeneous transparent moving medium. It is assumed that the medium in its rest frame is isotropic and
has no spatial dispersion. We obtain expressions for the radiative energy losses and estimate the polarization energy losses
of electric and magnetic dipoles of different orientations. In particular, it is shown that the energy loss of a source is
negative if it moves in the direction of the medium motion and the source velocity is less than the medium velocity. Estimates
for the energy losses of dipoles in the cases of an electron beam and a flow of a weakly dispersive medium are given.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 6, pp. 502–512, June 2006. 相似文献
993.
We consider normal ≡ Gaussian seemingly unrelated regressions (SUR) with incomplete data (ID). Imposing a natural minimal set of conditional independence constraints, we find a restricted SUR/ID model whose likelihood function and parameter space factor into the product of the likelihood functions and the parameter spaces of standard complete data multivariate analysis of variance models. Hence, the restricted model has a unimodal likelihood and permits explicit likelihood inference. In the development of our methodology, we review and extend existing results for complete data SUR models and the multivariate ID problem. 相似文献
994.
R. J. Hinde 《Few-Body Systems》2006,38(2-4):187-191
We compute the vibrational coupling between two H2 molecules from ab initio quantum chemical calculations of the H2-H2 potential carried out at the full configuration interaction level of theory using the atom-centered aug-cc-pVTZ basis set
for hydrogen. We compare the full configuration interaction results with those obtained using two variants of coupled cluster
theory and find that a fully iterative treatment of connected triples may be required to estimate the H2-H2 vibrational coupling accurately using coupled cluster theory. 相似文献
995.
The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
996.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献
997.
998.
J. M. Rubi 《Journal of statistical physics》2006,123(2):497-498
999.
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
1000.
M. A. H. Dempster 《Journal of Mathematical Sciences》2006,133(4):1422-1444
This paper gives a comprehensive treatment of EVPI-based sequential importance sampling algorithms for dynamic (multistage)
stochastic programming problems. Both theory and computational algorithms are discussed. Under general assumptions it is shown
that both an expected value of perfect information (EVPI) process and the corresponding marginal EVPI process (the supremum
norm of the conditional expectation of its generalized derivative) are nonanticipative nonnegative supermartingales. These
processes are used as importance criteria in the class of sampling algorithms treated in the paper. When their values are
negligible at a node of the current sample problem scenario tree, scenarios descending from the node are replaced by a single
scenario at the next iteration. On the other hand, high values lead to increasing the number of scenarios descending from
the node. Both the small sample and asymptotic properties of the sample problem estimates arising from the algorithms are
established, and the former are evaluated numerically in the context of a financial planning problem. Finally, current and
future research is described. Bibliography: 49 titles.
__________
Published in Zapiski Nauchnykh Seminarov POMI, Vol. 312, 2004, pp. 94–129. 相似文献