全文获取类型
收费全文 | 243247篇 |
免费 | 6524篇 |
国内免费 | 5096篇 |
专业分类
化学 | 115481篇 |
晶体学 | 3188篇 |
力学 | 15126篇 |
综合类 | 323篇 |
数学 | 50604篇 |
物理学 | 70145篇 |
出版年
2022年 | 2239篇 |
2021年 | 2807篇 |
2020年 | 3123篇 |
2019年 | 3401篇 |
2018年 | 14262篇 |
2017年 | 14038篇 |
2016年 | 11115篇 |
2015年 | 4089篇 |
2014年 | 5214篇 |
2013年 | 8130篇 |
2012年 | 11273篇 |
2011年 | 18394篇 |
2010年 | 11987篇 |
2009年 | 12375篇 |
2008年 | 13494篇 |
2007年 | 15221篇 |
2006年 | 6483篇 |
2005年 | 6752篇 |
2004年 | 6507篇 |
2003年 | 6478篇 |
2002年 | 5667篇 |
2001年 | 4793篇 |
2000年 | 3732篇 |
1999年 | 2876篇 |
1998年 | 2742篇 |
1997年 | 2398篇 |
1996年 | 2294篇 |
1995年 | 1927篇 |
1994年 | 1950篇 |
1993年 | 1915篇 |
1992年 | 1897篇 |
1991年 | 2012篇 |
1990年 | 1938篇 |
1989年 | 1888篇 |
1988年 | 1712篇 |
1987年 | 1658篇 |
1986年 | 1620篇 |
1985年 | 1746篇 |
1984年 | 1843篇 |
1983年 | 1603篇 |
1982年 | 1631篇 |
1981年 | 1431篇 |
1980年 | 1354篇 |
1979年 | 1544篇 |
1978年 | 1672篇 |
1977年 | 1665篇 |
1976年 | 1686篇 |
1975年 | 1543篇 |
1974年 | 1582篇 |
1973年 | 1569篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The economic valuation of works of art is a decisive subject in the general field of valuation. Unlike in other areas of valuation, the explanatory power of the directly observable and quantifiable variables is very low, therefore, aesthetic criteria must be used to obtain valuation models with a greater explanatory power. Frequently, these aesthetic criteria are not always precise, and experts usually express them as an interval of values. This paper describes different valuation models that use the goal programming optimisation method to include explanatory variables of the closing price in the form of intervals of values. We have also modelled the possibility that an expert can determine the relevance of each observation in the formation of the valuation function depending on the degree of precision with which the variables have been defined. 相似文献
992.
The stress-strain state of multilayered plates on an undeformable foundation is investigated. The design diagram of a transversely
loaded plate is formed by supplementing it with a symmetric one about the contact surface of the foundation. The double-thickness
plate obtained becomes loaded bilaterally and symmetrically about its midsurface. In such a way, only unflexural deformations
can be modeled, which reduces the number of unknowns and the general order of differentiation of the resolving system of equations.
The refined continual model developed takes into account the deformations of transverse shear and transverse compression in
high iterative approximations. The cases of a rigid contact between the foundation and the plate and frictionless slip of
the plate over the foundation are considered. Calculations confirm the efficiency of such an approach, which allows one to
obtain solutions qualitatively and quantitatively close to three-dimensional ones.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 643–654, September–October, 2006. 相似文献
993.
O. Životský K. Postava L. Kraus M. Foldyna J. Pištora 《Journal of magnetism and magnetic materials》2006
In this paper we investigate the surface magnetic properties of as-quenched (AQ) CoFeCrBSi ribbons prepared by planar flow casting method with using magneto-optic Kerr effect (MOKE). Measured hysteresis loops in longitudinal and transversal configurations enable us to obtain the information of ribbons surface magnetic properties. Moreover, we suggest new magneto-optic method, which is based on measurements of magneto-optical effects depending on DC current flowing through the ribbon. Experimental data of AQ ribbons are then compared with the model, which describes the influence of incidence angle on magneto-optical angles. 相似文献
994.
The use of phase-Doppler anemometry (PDA) to characterize the detail in-flight plasma sprayed particle behavior has been demonstrated
previously [Ma et al. Plasma Chem Plasma Process 24(1):85; 25(1):56] The present articles shows further that a direct relationship
may exist between the PDA measured particle volume flux and the coating microstructure and deposition efficiency (DE). In
the situation when the precise particle temperature information is not available, the PDA measured particle volume flux may
provide an alternative to predict quantitatively the variation of the coating microstructure and the DE. By monitoring the
in-flight particle volume flux variations, instead of the particle velocity, size and temperature individually and simultaneously,
the optimal settings of the plasma spraying parameters may also be determined conveniently. However, it is noted that the
effective applications of such approach depend largely on the particle surface morphology and the pre-determination of the
particle size range. 相似文献
995.
S. A. Logvinenko I. N. Timoshina Yu. V. Moseev 《Journal of Mathematical Sciences》1991,57(5):3361-3366
Modifications are introduced into the large-particle method to make it possible to use the method in arbitrary nonrectangular computing nets in the study of the flow of an ideal compressible gas over mobile thin permeable membranes. A problem in the aeroelasticity of a parachute is stated. An example is given of the solution of a problem in the stationary formulation for an axially symmetric parachute in the wake of a cylindrical leading body for supersonic flow.Translated fromDinamicheskie Sistemy, No. 6, 1987, pp. 16–22 相似文献
996.
997.
998.
O. P. Galkin V. S. Gostev O. E. Popov L. V. Shvachko R. F. Shvachko 《Acoustical Physics》2006,52(3):252-258
The experimental data on the sound field structure, which were obtained by emitting a continuous pseudonoise signal (a midfrequency of 3.2 kHz) in a two-channel oceanic waveguide, are compared with the calculations performed by the wave program with allowance for the fine structure of the sound speed inhomogeneities. A considerable increase in the intensity of the sound field with a definite angular spectrum is observed in the upper channel in the first shadow zone, and, in the experiment, the increase begins nearer to the sound source than predicted by the wave and ray calculations for a smooth sound speed profile. These features of the field structure are explained by the illumination of the shadow zone by the regular scattering of signals from highly anisotropic fine-structure inhomogeneities of the sound speed profile, which are clearly pronounced in the region of the given oceanic experiment. 相似文献
999.
1000.
Detection of hepatocarcinoma in rats by integration of the fluorescence spectrum: Experimental model
J. C. Marcassa J. Ferreira S. Zucoloto O. de Castro e Silva Jr. L. G. Marcassa V. S. Bagnato 《Laser Physics》2006,16(5):827-832
The incorporation of spectroscopic techniques into diagnostic procedures may greatly improve the chances for precise diagnostics. One promising technique is fluorescence spectroscopy, which has recently been used to detect many different types of diseases. In this work, we use laser-induced tissue fluorescence to detect hepatocarcinoma in rats using excitation light at wavelengths of 443 and 532 nm. Hepatocarcinoma was induced chemically in Wistar rats. The collected fluorescence spectrum ranges from the excitation wavelength up to 850 nm. A mathematical procedure carried out on the spectrum determines a figure of merit value, which allows the detection of hepatocarcinoma. The figure of merit involves a procedure which evaluates the ratio between the backscattered excitation wavelength and the broad emission fluorescence band. We demonstrate that a normalization allowed by integration of the fluorescence spectra is a simple operation that may allow the detection of hepatocarcinoma. 相似文献