全文获取类型
收费全文 | 5787篇 |
免费 | 220篇 |
国内免费 | 48篇 |
专业分类
测绘学 | 112篇 |
大气科学 | 477篇 |
地球物理 | 1473篇 |
地质学 | 1920篇 |
海洋学 | 547篇 |
天文学 | 875篇 |
综合类 | 21篇 |
自然地理 | 630篇 |
出版年
2022年 | 28篇 |
2021年 | 66篇 |
2020年 | 68篇 |
2019年 | 79篇 |
2018年 | 119篇 |
2017年 | 94篇 |
2016年 | 148篇 |
2015年 | 147篇 |
2014年 | 152篇 |
2013年 | 272篇 |
2012年 | 190篇 |
2011年 | 279篇 |
2010年 | 205篇 |
2009年 | 281篇 |
2008年 | 245篇 |
2007年 | 229篇 |
2006年 | 239篇 |
2005年 | 206篇 |
2004年 | 186篇 |
2003年 | 169篇 |
2002年 | 184篇 |
2001年 | 95篇 |
2000年 | 116篇 |
1999年 | 96篇 |
1998年 | 103篇 |
1997年 | 78篇 |
1996年 | 72篇 |
1995年 | 101篇 |
1994年 | 92篇 |
1993年 | 79篇 |
1992年 | 75篇 |
1991年 | 55篇 |
1990年 | 83篇 |
1989年 | 70篇 |
1988年 | 70篇 |
1987年 | 74篇 |
1986年 | 77篇 |
1985年 | 88篇 |
1984年 | 108篇 |
1983年 | 92篇 |
1982年 | 88篇 |
1981年 | 65篇 |
1980年 | 85篇 |
1979年 | 69篇 |
1978年 | 76篇 |
1977年 | 52篇 |
1976年 | 66篇 |
1975年 | 57篇 |
1974年 | 49篇 |
1973年 | 63篇 |
排序方式: 共有6055条查询结果,搜索用时 31 毫秒
801.
802.
Stephen Serjeant Duncan Farrah James Geach Toshinobu Takagi Aprajita Verma Ali Kaviani Matt Fox 《Monthly notices of the Royal Astronomical Society》2003,346(4):L51-L56
We present the K -band Hubble diagrams ( K – z relations) of submillimetre-selected galaxies and hyperluminous galaxies (HLIRGs). We report the discovery of a remarkably tight K – z relation of HLIRGs, indistinguishable from that of the most luminous radio galaxies. Like radio galaxies, the HLIRG K – z relation at z ≲ 3 is consistent with a passively evolving ∼3 L * instantaneous starburst starting from a redshift of z ∼ 10 . In contrast, many submillimetre-selected galaxies are ≳2 mag fainter, and the population has a much larger dispersion. We argue that dust obscuration and/or a larger mass range may be responsible for this scatter. The galaxies so far proved to be hyperluminous may have been biased towards higher AGN bolometric contributions than submillimetre-selected galaxies due to the 60-μm selection of some, so the location on the K – z relation may be related to the presence of the most massive active galactic nucleus. Alternatively, a particular host galaxy mass range may be responsible for both extreme star formation and the most massive active nuclei. 相似文献
803.
Solar UV is the principal energy source impinging the atmosphere of Titan while the energy from the electrons in Saturn's magnetosphere is less than 0.5% of the UV light. Titan haze analogs were prepared by the photolysis of a mixture of gases that simulate the composition of its atmosphere (nitrogen, methane, hydrogen, acetylene, ethylene, and cyanoacetylene). The real (n) and imaginary (k) parts of the complex refractive index of haze analogs formed from four different gas mixtures were calculated from the spectral properties of the solid polymer in UV-visible, near infrared and infrared wavelength spectral regions. The value of n was constant at 1.6±0.1 throughout the 0.2-2.5 μm region. The variation of k with wavelength for the values derived for Titan has a lower error than the absolute values of k so the more significant comparisons are with the slopes of the k(λ) plots in the UV-VIS region. Three of the photochemical Titan haze analogs had slopes comparable to those derived for Titan from the Voyager data (Rages and Pollack, 1980, Icarus 41, 119-130; McKay and Toon, 1992, in: Proceedings of the Symposium on Titan, in: ESA SP, Vol. 338, pp. 185-190). The slopes of the k(λ) plots for haze analogs prepared by spark discharge (Khare et al., 1984, Icarus 60, 127-137) and plasma discharge (Ramirez et al., 2002, Icarus 156, 515-529) were also comparable to Titan's. These finding show that the k(λ) plots do not differentiate between different laboratory simulations of atmospheric chemistry on Titan in the UV-VIS near IR region (0.2-2.5 microns). There is a large difference between the k(λ) in the infrared between the haze analogs prepared photochemically and analogs prepared using a plasma discharges (Khare et al., 1984, Icarus 60, 127-137; Coll et al., 1999, Planet. Space Sci. 47, 1331-1340; Khare et al., 2002, Icarus 160, 172-182). The C/N ratio in the haze analog prepared by discharges is in the 2-11 range while that of the photochemical analogs is in the 18-24 range. The use of discharges and UV light for initiating the chemistry in Titan's atmosphere is discussed. 相似文献
804.
James A. Van Allen 《Solar physics》1987,112(1):165-179
A survey of interplanetary proton (0.61 < E
p
< 3.41 MeV) events is summarized in graphical and tabular form for the period April 1973–December 1986. The observations were obtained by an effectively continuous data stream from the University of Iowa instrument on the Ames Research Center/NASA spacecraft Pioneer 11 as it moved outward in the solar system from 1.0 to 22.4 AU. Two hundred and sixty-five distinct events are identified. The spectra and intensities of the protons, presumed to be originally of solar origin, are influenced dramatically by propagative and accelerative processes in the interplanetary medium. 相似文献
805.
Knudsen cell-quadrupole mass spectrometry has been used to quantitatively determine the composition of the vapor phase produced by heating samples of the Holbrook chondrite to 1300 °C. Maximum observed vapor pressures (atm) of metals are 10?5.3 ± 0.3 Na, 10?5.8 ± 0.3 K, 10?5.3 ± 0.3 Fe, and 10?6.6 ± 0.3 Ni at 1200 °C. S2 (with minor SO2), H2O, and CO2 were also observed in the high-temperature gas phase. Release of intrinsically derived volatiles produced abundant vesicles in the heated sample residues. Some possible implications for chondrite evolution are briefly discussed 相似文献
806.
Anton M. Dainty M. Nafi Toksöz Kenneth R. Anderson P. Jacques Pines Y. Nakamura G. Latham 《Earth, Moon, and Planets》1974,9(1-2):11-29
Long, reverberating trains of seismic waves produced by impacts and moonquakes may be interpreted in terms of scattering in a surface layer overlying a non-scattering elastic medium. Model seismic experiments are used to qualitatively demonstrate the correctness of the interpretation. Three types of seismograms are found, near impact, far impact and moonquake. Only near impact and moonquake seismograms contain independent information. Details are given in the paper of the modelling of the scattering processes by the theory of diffusion.Interpretation of moonquake and artificial impact seismograms in two frequency bands from the Apollo 12 site indicates that the scattering layer is 25 km thick, with a Q of 5000. The mean distance between scatterers is approximately 5 km at 25 km depth and approximately 2 km at 14 km depth; the density of scatterers appears to be high near the surface, decreasing with depth. This may indicate that the scatterers are associated with cratering, or are cracks that anneal with depth. Most of the scattered energy is in the form of scattered surface waves.Communication presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973. 相似文献
807.
808.
Seismic data from the Apollo Passive Seismic Network stations are analyzed to determine the velocity structure and to infer the composition and physical properties of the lunar interior. Data from artificial impacts (S-IVB booster and LM ascent stage) cover a distance range of 70–1100 km. Travel times and amplitudes, as well as theoretical seismograms, are used to derive a velocity model for the outer 150 km of the Moon. TheP wave velocity model confirms our earlier report of a lunar crust in the eastern part of Oceanus Procellarum.The crust is about 60 km thick and may consist of two layers in the mare regions. Possible values for theP-wave velocity in the uppermost mantle are between 7.7 km s–1 and 9.0 km s–1. The 9 km s–1 velocity cannot extend below a depth of about 100 km and must decrease below this depth. The elastic properties of the deep interior as inferred from the seismograms of natural events (meteoroid impacts and moonquakes) occurring at great distance indicate that there is an increase in attenuation and a possible decrease of velocity at depths below about 1000 km. This verifies the high temperatures calculated for the deep lunar interior by thermal history models.Paper presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973. 相似文献
809.
James S. Fisher 《The Professional geographer》1981,33(4):466-474
The diversity of manufacturing in the United States South has shown a substantial increase during the post-World War II period. The basis for this changing industrial structure is found in the expansion of food processing and apparel industries but particularly since 1967 in a variety of higher-pay and higher-technology industries. The traditional textile states remain the least diversified and the slowest to change. 相似文献
810.
Paul S. Schopf David L.T. Anderson Ronald Smith 《Dynamics of Atmospheres and Oceans》1981,5(3):187-214
An investigation is made into the dispersion of oceanic internal Rossby waves at annual and semi-annual frequencies. Turning of the group velocity vector due to latitudinal variations in the radius of deformation cannot be neglected, particularly in basins as large as the Pacific. This turning allows disturbances to propagate from high lattitudes into the equatorial zone and distorts the solutions in the western part of the basin. For no mean flow, and a coastline aligned north-south, an almost exact focus of wave energy is found very close to the equator at a distance of just under from the eastern boundary, where is the eigenspeed of a high-frequency internal wave mode, and ω is the angular frequency of the low-frequency wave being studied. The focus depends on a long meridional wavelength excited at the coast, and a frequency small compared with , where is the radius of the Earth. For the lowest baroclinic mode and waves of annual period, this distance is about 12 000 km. Equivalence of the ray theory and the theory of equatorial meridional modes is demonstrated for the simple cases where the latter applies.The effects of mean currents and irregular coastlines are examined. Barotropic mean currents may change the turning latitude and ray shapes, inducing critical layers and enhancing reflection. Baroclinic mean currents are seen to affect the rays by simply changing the speed in proportion to the depth of the thermocline. As long as the mean currents are geostrophically balanced, no “effective beta” term from variations in the thermocline depth appears, in contrast to the topographic Rossby wave problem. 相似文献