全文获取类型
收费全文 | 1669篇 |
免费 | 48篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 48篇 |
大气科学 | 153篇 |
地球物理 | 308篇 |
地质学 | 563篇 |
海洋学 | 154篇 |
天文学 | 343篇 |
综合类 | 2篇 |
自然地理 | 153篇 |
出版年
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 31篇 |
2018年 | 45篇 |
2017年 | 35篇 |
2016年 | 39篇 |
2015年 | 32篇 |
2014年 | 56篇 |
2013年 | 105篇 |
2012年 | 66篇 |
2011年 | 81篇 |
2010年 | 60篇 |
2009年 | 68篇 |
2008年 | 70篇 |
2007年 | 54篇 |
2006年 | 57篇 |
2005年 | 56篇 |
2004年 | 72篇 |
2003年 | 45篇 |
2002年 | 51篇 |
2001年 | 33篇 |
2000年 | 29篇 |
1999年 | 24篇 |
1998年 | 21篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 12篇 |
1988年 | 22篇 |
1987年 | 19篇 |
1986年 | 21篇 |
1985年 | 32篇 |
1984年 | 26篇 |
1983年 | 28篇 |
1982年 | 19篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1979年 | 26篇 |
1978年 | 28篇 |
1977年 | 24篇 |
1976年 | 15篇 |
1975年 | 9篇 |
1973年 | 17篇 |
1972年 | 18篇 |
1971年 | 18篇 |
排序方式: 共有1724条查询结果,搜索用时 15 毫秒
91.
92.
Following the spill of fuel oils from the New Carissa in February 1999, approximately 300 km of beaches on the Pacific coast of North America were surveyed. A long-term observation program focused on the documentation of stranded tar balls in the vicinity of the spill site. Systematic beach surveys which were conducted over the period March 1999 to April 2001 and semi-logarithmic scale, time-series plots proved the most useful format for identifying trends. Beach monitoring continued through to August 2001. by which time 212 tar balls had been analyzed by GC/MS for their chemical characteristics. The samples of tar balls collected between February 1999 and August 2001 were qualitatively compared with New Carissa source oils (NCSO) and 101 (48%) were not consistent with NSCO. The presence of tar balls that are not related to an incident can confound attempts to define cleanup or endpoint criteria and to assess possible injury to natural resources. 相似文献
93.
Korzennik SG Brown TM Fischer DA Nisenson P Noyes RW 《The Astrophysical journal》2000,534(2):L147-L150
We present deep Hubble Space Telescope (HST) imaging, as well as ground-based imaging and spectroscopy, of the optical afterglow associated with the long-duration gamma-ray burst GRB 990712 and its host galaxy. The data were obtained 48-123 days after the burst occurred. The magnitudes of the host (R=21.9, V=22.5) and optical afterglow (R=25.4, V=25.8, 47.7 days after the burst) favor a scenario in which the optical light follows a pure power-law decay with an index of alpha approximately -1.0. We find no evidence for a contribution from a supernova like SN 1998bw. This suggests that either there are multiple classes of long-duration gamma-ray bursts or that the peak luminosity of the supernova was more than 1.5 mag fainter than SN 1998bw. The HST images and EFOSC2 spectra indicate that the gamma-ray burst was located in a bright, extended feature (possibly a star-forming region) 1.4 kpc from the nucleus of a 0.2L*B galaxy at z=0.434, possibly a Seyfert 2 galaxy. The late-time afterglow and host galaxy of GRB 990712 bear some resemblance to those of GRB 970508. 相似文献
94.
The ambient pressure elastic properties of a natural clinopyroxene (C2/c symmetry) from Kilbourne Hole, NM have been determined.
In terms of end-members, diopside (CaMgSi2O6), hedenbergite (CaFeSi2O6), jadeite (NaAlSi2O6), cosmochlor (NaCrSi2O6), and Mg-Tschermak (MgAl(AlSi)O6), its composition is Di72He9Jd3Cr3Ts12. The analytic density, based on chemistry and cell parameters is 3.327 (0.003) g/cm3. The elastic constants [c11, c12, c13, c15, c22, c23, c25, c33, c35, c44, c46, c55, c66] are [273.8 (0.9), 83.5 (1.3), 80.0 (1.1), 9.0 (0.6), 183.6 (0.9), 59.9 (1.6), 9.5 (1.0), 229.5 (0.9), 48.1 (0.6), 76.5 (0.9),
8.4 (0.8), 73.0 (0.4), 81.6 (1.0)] GPa where uncertainties are reported at the 95% confidence level. The aggregate (mean of
Hashin-Strikman bounds) adiabatic bulk modulus is 117.2 (0.7) GPa, and the shear modulus is 72.2 (0.2) GPa. Although measured
moduli are broadly consistent with trends in elasticity versus atomic volume, deviations from the systematics would produce
significant (percent level) changes in calculated velocities for candidate mantle mineral assemblages. The compositional dependence
of elasticity for several clinopyroxenes is explored on the basis of just the Di+He and Jd+Ts mole fractions. The bulk modulus
lies within experimental uncertainties of the linear mixture of end-member properties while the shear modulus deviates by
3%.
Received: 29 September 1997 / Revised, accepted: 4 March 1998 相似文献
95.
96.
Hydrocarbons are reported for another wilderness lake including polynuclear aromatics. All hydrocarbons appear to be of natural origin. 相似文献
97.
98.
For many years, high-grade metamorphism and multiphase deformation have discouraged mineral exploration in the Grenville terrain of the Canadian Shield. However, detailed studies of known zinc occurrences in the Grenville Supergroup metasediments of Quebec now reveal that mineralization is stratigraphically controlled and consistently limited to mapable lithologic units. Within the vast regions composed predominantly of calcitic marbles, zinc mineralization is found to be confined to the much more limited areas of dolomitic marble, and more precisely, to the lithologic transition from metaclastic beds to meta-dolomites. Massive sphalerite mineralization of the Balmat-type is very closely restricted to this contact zone, while disseminated sphalerite with sparse amounts of galena are commonly observed in the adjacent dolomite. With these guidelines, and with evidence that mineralization is fundamentally stratiform in nature, it has now been demonstrated that mineralized stratigraphic horizons can be located beyond the areas of previously known sphalerite showings, and consequently the potential for important discoveries of zinc mineralization in the Grenville Supergroup has become very attractive to the present-day mining industry. 相似文献
99.
100.