全文获取类型
收费全文 | 183785篇 |
免费 | 2405篇 |
国内免费 | 541篇 |
专业分类
化学 | 97251篇 |
晶体学 | 2544篇 |
力学 | 7608篇 |
综合类 | 4篇 |
数学 | 20630篇 |
物理学 | 58694篇 |
出版年
2021年 | 1613篇 |
2020年 | 1874篇 |
2019年 | 2077篇 |
2018年 | 2457篇 |
2017年 | 2520篇 |
2016年 | 3837篇 |
2015年 | 2351篇 |
2014年 | 3852篇 |
2013年 | 8888篇 |
2012年 | 6850篇 |
2011年 | 8015篇 |
2010年 | 5768篇 |
2009年 | 5580篇 |
2008年 | 7271篇 |
2007年 | 7134篇 |
2006年 | 6646篇 |
2005年 | 5999篇 |
2004年 | 5460篇 |
2003年 | 4903篇 |
2002年 | 4703篇 |
2001年 | 5368篇 |
2000年 | 3992篇 |
1999年 | 3073篇 |
1998年 | 2553篇 |
1997年 | 2479篇 |
1996年 | 2132篇 |
1995年 | 2122篇 |
1994年 | 2121篇 |
1993年 | 2026篇 |
1992年 | 2318篇 |
1991年 | 2245篇 |
1990年 | 2180篇 |
1989年 | 2122篇 |
1988年 | 2111篇 |
1987年 | 2106篇 |
1986年 | 2006篇 |
1985年 | 2643篇 |
1984年 | 2693篇 |
1983年 | 2368篇 |
1982年 | 2491篇 |
1981年 | 2293篇 |
1980年 | 2280篇 |
1979年 | 2462篇 |
1978年 | 2480篇 |
1977年 | 2434篇 |
1976年 | 2463篇 |
1975年 | 2378篇 |
1974年 | 2330篇 |
1973年 | 2505篇 |
1972年 | 1611篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
991.
Studies of breakdown threshold intensity for air at various pressures in the range of 24–760 torr using 0.355, 0.532 and 1.06
μm radiation are reported. We observep
−0.8 scaling ofI
th at 1.06 μm and a weak scaling ofp
−0.4 at 0.532 and 0.355 μm radiation. Strong dependence of breakdown spot size on laser power but weak dependence on air pressure
is observed. 相似文献
992.
I. G. Yudelevich B. I. Zaksas Ye. A. Petrova A. S. Cherevko 《Fresenius' Journal of Analytical Chemistry》1991,340(9):560-563
Summary A method for the atomic emission spectrometric analysis of air and water with inductively coupled and two-jet direct current plasmas has been developed. The method has been applied to the determination of impurity contents with good accuracy and sensitivity. 相似文献
993.
M A Alliegro K D Dyer E J Cragoe B M Glaser M C Alliegro 《Journal of chromatography. A》1992,582(1-2):217-223
An assay for amiloride was devised for efficient use with the wide variety of analogues available. Amiloride was extracted from 1-ml plasma samples by elution from a C8 preparative column with 6% acetonitrile-45% methanol-5.4% acetic acid, adjusted to pH 4.0 with trimethylamine. Samples were lyophilized, resuspended in 50% methanol, filtered through 0.22-microns Spin-X cartridges, applied to a reversed-phase C18 column, and eluted in a 0-50% acetonitrile gradient in 0.4% acetic acid, pH 4.5 (1.2 ml/min). Detection by ultraviolet absorbance at 360 nm was linear from 1 to 1000 ng. Versatility of the method was demonstrated with the analogues benzamil, 6-hydro-, 6-iodo-, 5-hexamethylene-, and 5-chlorobenzyl-2',4'-dimethylbenzyl-amiloride. 相似文献
994.
Unsteady flow dynamics in doubly constricted 3D vessels have been investigated under pulsatile flow conditions for a full cycle of period T. The coupled non‐linear partial differential equations governing the mass and momentum of a viscous incompressible fluid has been numerically analyzed by a time accurate Finite Volume Scheme in an implicit Euler time marching setting. Roe's flux difference splitting of non‐linear terms and the pseudo‐compressibility technique employed in the current numerical scheme makes it robust both in space and time. Computational experiments are carried out to assess the influence of Reynolds' number and the spacing between two mild constrictions on the pressure drop across the constrictions. The study reveals that the pressure drop across a series of mild constrictions can get physiologically critical and is also found to be sensitive both to the spacing between the constrictions and the oscillatory nature of the inflow profile. The flow separation zone on the downstream constriction is seen to detach from the diverging wall of the constriction leading to vortex shedding with 3D features earlier than that on the wall in the spacing between the two constrictions. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
995.
A formalism for the simulation by parallel processing of the propagation of ultrasonic pulses of arbitrary shape (i.e. not restricted to continuous waves) in complex media is presented. Recursive relationships yielding the time evolution of the displacement field are derived for both homogeneous and heterogeneous materials. In the latter case, formulas for cross-points at the intersection of up to eight different materials are obtained. A few examples of numerical results obtained with the proposed method are shown to demonstrate its applicability and efficiency. The problem of visualization of the results is also briefly discussed. 相似文献
996.
V. A. Donchenko M. V. Kabanov V. T. Kalaida B. I. Kulakov E. V. Ovcharenko I. G. Sokovets 《Russian Physics Journal》1998,41(5):476-484
The problems of determining and investigating the informative parameters of atmospheric electricity are discussed. It is shown
that short-period variations in atmospheric electricity are ecologically significant. An automated system for monitoring atmospheric
electricity and a method of processing the results of measurements are described.
V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh
Zavedenii, Fizika, No. 5, pp. 88–98, May, 1998. 相似文献
997.
998.
L. A. Chetkina V. E. Zavodnik A. N. Sobolev V. K. Bel'skii B. P. Bespalov A. G. Abolin 《Journal of Structural Chemistry》1991,32(3):442-445
L. Ya. Karpov Physical Chemical Research Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 3, pp. 141–144, May–June, 1991. 相似文献
999.
A refined technique is presented to project rotational bands observed in the well studiedZ≧60 rare-earth region into the region of stable ground-state deformation atA ~-100 with corresponding neutron numbers ofN ≧60. With this procedure, estimates of properties of so far unknown nuclei in the A~-100 region can be obtained. As an illustration, isotopes aroundN=64 are discussed within this projection method and within the frame-work of the recent quartet model. 相似文献
1000.
B. Tatischeff M. P. Comets Y. Le Bornec N. Willis B. Bonin J. C. Lugol B. Mayer Y. Terrien R. Beurtey A. Boudard J. M. Durand P. Fassnacht F. Hibou 《Zeitschrift für Physik A Hadrons and Nuclei》1987,328(2):147-149
Some evidence is presented for a narrow peak at 1969±2 MeV (FWHM=9±2 MeV) in the missing mass spectrum of the3He(p, d) reaction, with 3 standard deviations. The nature of this state, the mass of which is below the NN threshold, is discussed in connection with structures found in other experiments. 相似文献