全文获取类型
收费全文 | 4331篇 |
免费 | 147篇 |
国内免费 | 93篇 |
专业分类
测绘学 | 157篇 |
大气科学 | 295篇 |
地球物理 | 1118篇 |
地质学 | 1527篇 |
海洋学 | 378篇 |
天文学 | 701篇 |
综合类 | 22篇 |
自然地理 | 373篇 |
出版年
2022年 | 30篇 |
2021年 | 48篇 |
2020年 | 47篇 |
2019年 | 63篇 |
2018年 | 87篇 |
2017年 | 105篇 |
2016年 | 119篇 |
2015年 | 113篇 |
2014年 | 139篇 |
2013年 | 259篇 |
2012年 | 131篇 |
2011年 | 231篇 |
2010年 | 166篇 |
2009年 | 228篇 |
2008年 | 237篇 |
2007年 | 209篇 |
2006年 | 191篇 |
2005年 | 174篇 |
2004年 | 136篇 |
2003年 | 162篇 |
2002年 | 138篇 |
2001年 | 84篇 |
2000年 | 87篇 |
1999年 | 61篇 |
1998年 | 69篇 |
1997年 | 58篇 |
1996年 | 65篇 |
1995年 | 54篇 |
1994年 | 55篇 |
1993年 | 43篇 |
1992年 | 48篇 |
1991年 | 43篇 |
1990年 | 35篇 |
1989年 | 38篇 |
1988年 | 37篇 |
1987年 | 42篇 |
1986年 | 44篇 |
1985年 | 58篇 |
1984年 | 47篇 |
1983年 | 50篇 |
1982年 | 53篇 |
1981年 | 57篇 |
1980年 | 48篇 |
1979年 | 39篇 |
1978年 | 48篇 |
1977年 | 28篇 |
1976年 | 30篇 |
1975年 | 24篇 |
1974年 | 31篇 |
1973年 | 31篇 |
排序方式: 共有4571条查询结果,搜索用时 15 毫秒
201.
202.
Since 1984, roughly 100 main sequence stars within 50 parsecs of the Sun have been identified as possibly possessing replenished, circumstellar dust disks. Optical to submillimeter imaging has resolved disk-like structure around 7 main sequence stars. We review these results, and discuss how they elucidate the existence and properties of exoplanetary systems. 相似文献
203.
We refer to two papers by Goodman (1995, 1996) on the heating of the chromosphere by large-scale electric currents, and to our paper (Lorrain and Koutchmy, 1993) on magnetic elements. Goodman assumes that the dynamo that runs a magnetic element stops operating at t = 0. From then on, the magnetic field decays exponentially, and the induced currents heat the chromosphere. The time constants calculated by Goodman disagree with the observed values, possibly because he disregards the driving dynamo. Also, he assumes static conditions, but his magnetic force density appears suddenly when the dynamo stops, and it is about equal to the gravitational force density. The magnetic force acts downward and fluctuations in the current flowing through the magnetic element should induce vertical oscillations at the photosphere. This point should be investigated further. 相似文献
204.
Paul F. Hudak 《Ground Water Monitoring & Remediation》1998,18(2):93-96
A graphical method was devised for designing contaminant detection monitoring networks in aquifers. The approach eliminates bias in detection efficiency among well pairs, thereby improving the overall efficiency of a ground water monitoring network. In the equidistant configurations derived by the graphical approach, all wells are located the same distance from a landfill, but the distance is measured parallel to ground water flow, Measured perpendicular to ground water flow, there is also an equal spacing between wells in an equidistant network. A simulation model was used to compare an equidistant network to a peripheral monitoring configuration, in which wells were spaced evenly along the downgradient boundaries of a landfill. The equidistant network yielded a 12.4% higher detection efficiency and also facilitated earlier release detection. In practice, the graphical approach that yields equidistant configurations can be used to identify candidate monitoring networks to detect potential releases from landfills. 相似文献
205.
Mrinal K. Paul 《Pure and Applied Geophysics》1964,59(1):33-37
Summary The propagation of Love type waves on a spherical model' in the mantle of which the rigidity and density vary exponentially with the radial distance while in the core they remain constant — has been investigated. The frequency equation that has been worked out has been examined in detail for the existence of root in the particular cases when they involve Bessel Functions of smallest and largest orders. 相似文献
206.
Accelerometer measurements made by Spirit and Opportunity during their entries through the martian atmosphere are reported. Vertical profiles of atmospheric density, pressure, and temperature with sub-km vertical resolution were obtained using these data between 10 and 100 km. Spirit's temperature profile is ∼10 K warmer than Opportunity's between 20 and 80 km. Unlike all other martian entry profiles, Spirit's temperature profile does not contain any large amplitude, long wavelength oscillations and is nearly isothermal below 30 km. Opportunity's temperature profile contains a strong inversion between 8 and 12 km. A moderate dust storm, which occurred on Mars shortly before these two atmospheric entries, may account for some of the differences between the two profiles. The poorly known angle of attack and unknown wind velocity may cause the temperature profiles to contain errors of tens of Kelvin at 10 km, but these errors would be an order of magnitude smaller above 30 km. On broad scales, the two profiles are consistent with Mars Global Surveyor Thermal Emission Spectrometer (TES) pressure/temperature profiles. Differences exist on smaller scales, particularly associated with the near-isothermal portion of Spirit's profile and the temperature inversion in Opportunity's profile. 相似文献
207.
Pascale Jablonka Javier Gorgas Paul Goudfrooij 《Astrophysics and Space Science》2002,281(1-2):367-370
We present a few results of a work in progress tackling the radial spectroscopic properties of bulges of spiral galaxies.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
208.
209.
The effect of pyrolysis at increasing temperature on sporopollenin, lignite and sporopollenin oxidized at 200°C has been investigated using measured infrared band absorption coefficients.Oxidation of sporopollenin in air at 200°C is marked by a decrease in the content of saturated hydrocarbon chains and a strong increase in the concentration of carboxylic acid groups.Pyrolysis of a thick bed of sporopollenin at increasing temperatures leads to the removal of a large proportion of oxygenated functions, before the removal of hydrocarbons. For lignite and oxidized sporopollenin, the loss of both types of functional groups extends over a broader temperature range. Reorganization of the carbonaceous residue at high temperature is hindered if a sufficiently low content of oxygenated functions, carbonyl and carboxyl as well as hydroxyl and ether groups, is not reached before the elimination of hydrocarbons. 相似文献
210.
Solar irradiation fluxes are determined between 150 and 210 nm from stigmatic spectra of the Sun obtained by means of a rocket-borne spectrograph. Absolute intensities at the disk center with a spectral resolution of 0.04 nm and a spatial resolution of 7 arc sec are presented. From center-to-limb intensity variations determined from the same spectra, mean full disk intensities of the quiet Sun can be deduced. In order to compare them with other measurements, the new solar fluxes have been averaged over a bandpass of 1 nm. 相似文献