全文获取类型
收费全文 | 2933篇 |
免费 | 81篇 |
国内免费 | 20篇 |
专业分类
测绘学 | 72篇 |
大气科学 | 242篇 |
地球物理 | 567篇 |
地质学 | 879篇 |
海洋学 | 319篇 |
天文学 | 695篇 |
综合类 | 1篇 |
自然地理 | 259篇 |
出版年
2021年 | 18篇 |
2020年 | 24篇 |
2019年 | 36篇 |
2018年 | 44篇 |
2017年 | 28篇 |
2016年 | 56篇 |
2015年 | 44篇 |
2014年 | 58篇 |
2013年 | 156篇 |
2012年 | 65篇 |
2011年 | 114篇 |
2010年 | 74篇 |
2009年 | 147篇 |
2008年 | 106篇 |
2007年 | 112篇 |
2006年 | 106篇 |
2005年 | 82篇 |
2004年 | 82篇 |
2003年 | 83篇 |
2002年 | 82篇 |
2001年 | 68篇 |
2000年 | 82篇 |
1999年 | 66篇 |
1998年 | 79篇 |
1997年 | 47篇 |
1996年 | 52篇 |
1995年 | 42篇 |
1994年 | 51篇 |
1993年 | 40篇 |
1992年 | 38篇 |
1991年 | 39篇 |
1990年 | 45篇 |
1989年 | 39篇 |
1988年 | 28篇 |
1987年 | 49篇 |
1986年 | 33篇 |
1985年 | 57篇 |
1984年 | 60篇 |
1983年 | 61篇 |
1982年 | 60篇 |
1981年 | 62篇 |
1980年 | 52篇 |
1979年 | 39篇 |
1978年 | 38篇 |
1977年 | 50篇 |
1976年 | 32篇 |
1975年 | 38篇 |
1974年 | 21篇 |
1973年 | 27篇 |
1972年 | 18篇 |
排序方式: 共有3034条查询结果,搜索用时 31 毫秒
991.
The absolute electrical conductivity at15deg C of several lots of standard seawater has been measured with great precision as a function of chlorinity. Potassium chloride (KCI) solutions of known concentration and having almost the same conductivity were also measured and the concentration giving the same conductivity at15deg C as35.0000permil standard seawater (Chl =19.37394permil ) was found to be 32.4352 g/kg. 相似文献
992.
993.
McConnell Mark L. Ryan James M. Smith David M. Lin Robert P. Emslie A. Gordon 《Solar physics》2002,210(1-2):125-142
Although designed primarily as a hard X-ray imager and spectrometer, the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI)
is also capable of measuring the polarization of hard X-rays (20–100 keV) from solar flares. This capability arises from the
inclusion of a small unobstructed Be scattering element that is strategically located within the cryostat that houses the
array of nine germanium detectors. The Ge detectors are segmented, with both a front and rear active volume. Low-energy photons
(below about 100 keV) can reach a rear segment of a Ge detector only indirectly, by scattering. Low-energy photons from the
Sun have a direct path to the Be and have a high probability of Compton scattering into a rear segment of a Ge detector. The
azimuthal distribution of these scattered photons carries with it a signature of the linear polarization of the incident flux.
Sensitivity estimates, based on Monte Carlo simulations and in-flight background measurements, indicate that a 20–100 keV
polarization sensitivity of less than a few percent can be achieved for X-class flares. 相似文献
994.
P. A. Sturrock P. J. Baum J. M. Beckers C. E. Newman E. R. Priest H. Rosenberg D. F. Smith D. G. Wentzel 《Solar physics》1976,46(2):411-431
This report summarizes the proceedings of a meeting held on 17–20 September 1974, at Stanford University. The purpose was to explore plasma physics problems which arise in the study of solar physics. Sessions were concerned with specific questions including the following: Is the solar plasma thermal or non-thermal? What spectroscopic data are required? What types of magnetic field structures exist? Do MHD instabilities occur? Do resistive or non-MHD instabilities occur? What mechanisms of particle acceleration have been proposed? What information do we have concerning shock waves? Very few questions were answered categorically but, for each question, there was discussion concerning the observational evidence, theoretical analyses, and existing or potential laboratory and numerical experiments. 相似文献
995.
996.
An eclipse of Titan by Saturn was observed on December 20, 1979, to measure the aerosol content in the atmosphere of Saturn. The measurements were made with the 74-in. telescope of the Helwan Observatory, Egypt, in the bandpass 6300–7300 Å and extend to ~5 magnitudes of eclipse darkening. The faint portion of the lightcurve unambiguously requires the presence of aerosol in the lower stratosphere of Saturn. The aerosol extends to at least 20 km above the tropopause and has a one-way stratospheric vertical optical depth of 0.4?0.02+0.04 at 6700 Å. The results apply to the sunset terminator at a cronographic latitude of 23°S. 相似文献
997.
This study represents an attempt to quantitatively assess the capability of a spaceborne radar altimeter to infer ocean surface wind speeds from a measurement of the backscattered power at vertical incidence. The study uses data acquired during 184 near overflights of NOAA data buoys with the GEOS-3 satellite radar altimeter and encompasses a wind-speed range from less than 1 to 18 m/s. An algorithm is derived from the data comparison for converting measurements of the normalized scattering cross section of the ocean surface at 13.9 GHz into estimates of the surface wind speed at the standard anemometer height of 10 m. The algorithm is straightforward and potentially useful for on-board processing of raw altimeter data for the purpose of providing real-time estimates of surface wind speed. For winds in the range of 1 to 18 m/s, the mean difference between the altimeter-inferred winds and the buoy measurements is negligible while the standard deviation of the difference is 1.74 m/s. 相似文献
998.
The Timmersoi meteorite, a new type L5 hypersthene chondrite from the Niger Republic is described and microprobe analyses of its olivine, orthopyroxene, clinopyroxene, plagioclase, kamacite, taenite, troilite, chromite, whitlockite, chlorapatite and limonite presented. Veins and patches of black “glassy” material are regarded as products of shock melting. In places this material contains immiscible droplets of troilite each with one or more well-formed crystals of taenite. Calculations indicate equilibrium between olivine and orthopyroxene with a temperature of equilibration of about 850 °C. 相似文献
999.
Observations of the Sun were made at 3 mm wavelength during the total eclipse of 1976 October 23. Analysis of the record obtained near third contact indicates that the Sun at this wavelength is slightly limb-brightened, and that the solar radius is 1.007 times the photospheric radius. 相似文献
1000.
D. F. Smith 《Solar physics》1970,13(2):444-447
The purpose of this note is to examine the suggestion of Fokker (1970) to explain why the second branch of U-bursts is ill-developed and to present an alternate possible explanation which was suggested by an examination of the trajectories derived by him.Postdoctoral Fellow on the U.S.-U.S.S.R. Cultural Exchange 相似文献