全文获取类型
收费全文 | 202874篇 |
免费 | 1383篇 |
国内免费 | 360篇 |
专业分类
化学 | 102654篇 |
晶体学 | 2781篇 |
力学 | 10115篇 |
综合类 | 16篇 |
数学 | 24281篇 |
物理学 | 64770篇 |
出版年
2021年 | 2085篇 |
2020年 | 2189篇 |
2019年 | 2593篇 |
2018年 | 3778篇 |
2017年 | 3873篇 |
2016年 | 4763篇 |
2015年 | 2354篇 |
2014年 | 4162篇 |
2013年 | 7984篇 |
2012年 | 6726篇 |
2011年 | 7923篇 |
2010年 | 6254篇 |
2009年 | 6347篇 |
2008年 | 7478篇 |
2007年 | 7410篇 |
2006年 | 6600篇 |
2005年 | 6393篇 |
2004年 | 6262篇 |
2003年 | 5368篇 |
2002年 | 5187篇 |
2001年 | 5543篇 |
2000年 | 4207篇 |
1999年 | 3155篇 |
1998年 | 2872篇 |
1997年 | 2721篇 |
1996年 | 2590篇 |
1995年 | 2342篇 |
1994年 | 2298篇 |
1993年 | 2356篇 |
1992年 | 2384篇 |
1991年 | 2635篇 |
1990年 | 2519篇 |
1989年 | 2575篇 |
1988年 | 2438篇 |
1987年 | 2462篇 |
1986年 | 2293篇 |
1985年 | 2868篇 |
1984年 | 2872篇 |
1983年 | 2492篇 |
1982年 | 2551篇 |
1981年 | 2450篇 |
1980年 | 2235篇 |
1979年 | 2537篇 |
1978年 | 2715篇 |
1977年 | 2775篇 |
1976年 | 2858篇 |
1975年 | 2642篇 |
1974年 | 2594篇 |
1973年 | 2755篇 |
1972年 | 2200篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
961.
962.
963.
M. V. Patrakeev A. A. Lakhtin I. A. Leonidov A. V. Nikolaev V. L. Kozhevnikov 《Ionics》1997,3(1-2):89-95
A heat machine is studied of regenerative type, based on solid electrolytes with unipolar oxygen conductivity. The achieved
specific power is about 0.2 mW/cm2. Electrical characteristics are derived as a function of temperature, pressure and gas composition in the working chamber
of the converter. Factors which influence the specific power as well as optimal regimes for the functioning of the device
are determined. 相似文献
964.
D. I. Moldavanskii 《Ukrainian Mathematical Journal》1991,43(12):1569-1571
Necessary and sufficient conditions for the isomorphism of two groups, each defined by a single relation of the type a–1bma=bn, are obtained.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 12, pp. 1684–1686, December, 1991. 相似文献
965.
Summary The results of local meteorology, solar radiation and ground-level ozone measurements taken in Antarctica during the second
Italian expedition (December 86–February 87) at Terra Nova Bay are presented. During the summer months the site of the Italian
base camp is characterized by a thin strip of deglaciated ground, along which the temperature measurements close to the ground
and up to 6 m high show a strongly superdiabatic profile. This irregular trend of the temperature in the surface layer is
mainly due to the notable incoming amounts of radiation and to the extreme transparency of the atmosphere. This is also shown
by the low values of the ratio between total radiation and diffuse radiation. The ground is thus subjected to intense heating,
especially in the warmer hours of the day, while the surface layer of the atmosphere will be characterized by strong upward
heat fluxes and by turbulent convective movements. Vertical-temperature-profile measurements show an almost forced persistence
in the superdiabatic trend, which tends towards isothermic values only as a resultof rapid variations in the direction and
intensity of the wind, connected to the downward flux of cold air masses, shown also by the simultaneous increases in ground-level
ozone concentrations which would support the presence of dry-deposition processes in the lower layer. However, the complex
local orography and the horizontal discontinuity (sea, deglaciated coast, snow-covered surfaces) do not permit a correct application
of profile flux relations, normally used in studies on groundlevel dry-deposition.
Paper presented at the IV Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 22–24, 1987, Rome. 相似文献
966.
P. I. H. Bastiaens S. G. Mayhew E. M. O'Naulláin A. van Hoek A. J. W. G. Visser 《Journal of fluorescence》1991,1(2):95-103
Both a mode-locked argon-ion laser and synchrotron radiation were used as excitation sources to obtain time-resolved polarized fluorescence of the two FAD cofactors in electron transferring flavoprotein fromMegasphaera elsdenii. Red-edge excited and blue-edge detected fluorescence anisotropy decay curves did not contain a fast relaxation process which was observed upon mainband excitation and detection. This relaxation was assigned to homo-energy transfer between the two FAD cofactors. Failure of energy transfer as observed with edge spectroscopy on this protein excludes restricted reorientational motion of the flavins as a possible mechanism of depolarization. From the global analysis of the fluorescence anisotropy decay surface obtained at multiple excitation and detection wavelengths, the distance between and the relative orientation of the flavins could be estimated. The methodology described has general applicability in other multichromophoric biopolymers and has the potential to acquire accurate geometrical parameters in these systems. 相似文献
967.
The Q-band electron spin echo (ESE) spectrometer which was created using modern microwave components is described. This simple incoherent apparatus was used with the X-band one for the study of phosphate and silicate glasses doped with non-Kramers rare earth Tb3+ ions. the EPR spectra measured by the ESE method have frequency independent peaks. The experimental results presumably show the existence of several types of paramagnetic centers in studied systems. 相似文献
968.
A. A. Novakova G. A. Sirotynina V. I. Kyrko G. V. Sidorova 《Hyperfine Interactions》1992,69(1-4):663-666
Transmission- and depth-selective-conversion-electron Mössbauer spectroscopy (DCEMS) were applied to study variation of structural state in the bulk and in the surface layer (500, 1000, 1500 Å thick) of amorphous alloy under certain optimum conditions of the dynamic loading. The alloy structure remains amorphous. However, a certain variation of the short range order. An amorphous oxide Fe2O3 is formed on the amorphous alloy surface. 相似文献
969.
By applying stepwise phase modulation of recoilless gamma radiation in a coincidence experiment, constructive interference
is produced in transmission geometry between the source and the absorber fields. The resulting regenerated decay signal is
called a gamma echo. Here it is demonstrated that during the decay of the 14.4 keV state of57Fe multiple echo signals can be generated. 相似文献
970.
A. I. Vanin 《Journal of Applied Spectroscopy》1997,64(2):242-245
Light scattering by groups of spherical particles is considered. It is shown that the structure of the groups and their orientational
distribution can be judged from the spectrum and polarization of the scattered light.
Syktyvkar State University, 55, Oktyabr'skii Ave., Syktyvkar, 167001, Russia. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 64, No. 2, pp. 228–231, March–April, 1997. 相似文献