全文获取类型
收费全文 | 232篇 |
免费 | 14篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 24篇 |
地球物理 | 77篇 |
地质学 | 54篇 |
海洋学 | 14篇 |
天文学 | 39篇 |
综合类 | 1篇 |
自然地理 | 35篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 1篇 |
2018年 | 9篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 17篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 10篇 |
2009年 | 16篇 |
2008年 | 18篇 |
2007年 | 15篇 |
2006年 | 16篇 |
2005年 | 4篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有249条查询结果,搜索用时 15 毫秒
91.
92.
U. Hwang R. Petre A. E. Szymkowiak S. S. Holt 《Journal of Astrophysics and Astronomy》2002,23(1-2):81-87
We present a newChandra observation of Tycho’s supernova remnant with the Advanced CCD Imaging Spectrometer. Multicolor Xray imaging reveals new
details of the outer shock and ejecta. At energies between 4 and 6 keV, the outline of the outer shock is clearly revealed
in X-rays for the first time. The distribution of the emission from lines of Si and Fe are confirmed to have a different morphology
from each other, and the Si ejecta are shown to extend to the blast shock at several locations. Characteristic spectra of
the outer shock and ejecta are also presented. 相似文献
93.
We have reanalyzed the Voyager 1 UVS solar occultations by Titan to expand upon previous analyses and to resolve inconsistencies that have been noted in the scientific literature. To do so, we have developed a detailed model of the UVS detector and improved both the data reduction methods and retrieval techniques. In comparison to the values previously determined by Smith et al. (1982, J. Geophys. Res. 87, 1351-1359) we find N2 densities that are 25-60% higher, CH4 densities that are smaller by a factor of 3-7, and C2H2 densities that are roughly two orders of magnitude smaller. Our values for the thermospheric temperature are 153-158 K, which are approximately 20-40 K colder than previous estimates. We also report the first-ever determination from Voyager UVS data of density profile information for C2H4, HCN, and HC3N. Finally, we present a simple engineering model that is consistent with our new results in the upper atmosphere and merges smoothly with the model of Yelle et al. (1997, in: HUYGENS Science, Payload and Mission, in: ESA SP, vol. 1177, pp. 243-256) in the lower atmosphere. Our results provide improved constraints for photochemical models and offer scientists a better understanding of Titan's upper atmosphere as we head into the Cassini era in the exploration of the saturnian system. 相似文献
94.
C.R. Benn M. Vigotti M. Pedani J. Holt K.-H. Mack R. Curran S.F. Sánchez 《Monthly notices of the Royal Astronomical Society》2002,329(1):221-226
In a pilot search for high-redshift radio quasi-stellar objects (QSOs), we have obtained spectra of 55 FIRST sources with very red starlike optical identifications. 10 of the candidates are QSOs with redshifts (four were previously known), six with . The remaining 45 candidates comprise: one broad-absorption-line (BAL) QSO; three low-redshift galaxies with narrow emission lines; 18 probable radio galaxies; and 23 M stars (mainly misidentifications). The success rate (high-redshift QSOs / spectroscopically-observed candidates) for this search is 1/2 for , and 1/9 for . With an effective search area of 4030 deg2 , the surface density of high-redshift QSOs discovered with this technique is 0.0015 deg−2 . 相似文献
95.
Laurel Saito Bill Christian Jennifer Diffley Holly Richter Melissa M. Rohde Scott A. Morrison 《Ground water》2021,59(3):322-333
Groundwater is a critical resource not only for human communities but also for many terrestrial, riparian, and aquatic ecosystems and species. Yet groundwater planning and management decisions frequently ignore or inadequately address the needs of these natural systems. As a consequence, ecosystems dependent on groundwater have been threatened, degraded, or eliminated, especially in arid regions. There is growing acknowledgment that governmental protections for these ecological resources are necessary, but current legal, regulatory and voluntary provisions are often inadequate. Groundwater management premised on “safe yield,” which aims to balance human withdrawals with natural recharge rates, typically provides little to no consideration for water needed by ecosystems. Alternatively, the “sustainable yield” concept aims to integrate social, economic and environmental needs for groundwater, but the complexity of groundwater systems creates substantial uncertainty about the impact that current or future groundwater withdrawals will have on ecosystems. Regardless of the legal or regulatory framework, guidance is needed to help ensure environmental water needs will be met, especially in the face of pressure to increase human uses of groundwater resources. In this paper, we describe minimum provisions for planning, managing, and monitoring groundwater that collectively can lower the risk of harm to groundwater-dependent ecosystems and species, with a special emphasis on arid systems, where ecosystems and species may be especially reliant upon and sensitive to groundwater dynamics. 相似文献
96.
Abstract This paper considers the complexity in resolving the conflicts between mine drainage, water supply, and environmental protection for the coal basin of North China, and presents a management optimization framework that addresses these multiple conflicting issues simultaneously in the most cost effective manner. Due to the various unpredictable accidents which may occur in the coal mining process, such as water bursts, gas leaks, fire and collapse of coal beds, the beneficial use of drainage water from the coal mines is generally low. This case study attempts to address the problem of low beneficial usage for drainage water using the Jiaozuo coal mining district in Henan Province, China. By combining a finite-element groundwater simulation model with an optimization code, the economic benefits of using the drainage water as a stable water supply is maximized, while the adverse impact of mine drainage on the environment is controlled. The results indicate that the management model developed in this study achieves an excellent economic outcome and can serve as a potentially powerful tool for solving mining-related water management problems in the coal basin of North China. Citation Wu, Q., Hu, B. X., Wan, L. & Zheng, C. (2010) Coal mine water management: optimization models and field application in North China. Hydrol. Sci. J. 55(4), 609–623. 相似文献
97.
98.
99.
Can saltwater toxicity be predicted from freshwater data? 总被引:3,自引:0,他引:3
K M Leung D Morritt J R Wheeler P Whitehouse N Sorokin R Toy M Holt M Crane 《Marine pollution bulletin》2001,42(11):1007-1013
The regulation of substances discharged to estuarine and coastal environments relies upon data derived from ecotoxicity tests. Most such data are generated for freshwater rather than saltwater species. If freshwater toxicity data are related to saltwater toxic effects in a systematic and predictable way, the former can be used to predict the latter. This would have economic advantages due to a reduction in toxicity testing of saltwater species. If toxicity data are plotted as species sensitivity distributions, four theoretical relationships between freshwater and saltwater can be envisaged. Examples show that each one of these relationships is supported by empirical data. These examples show that although there is considerable potential for freshwater to saltwater prediction, species parity and representativeness need to be examined for each chemical substance to avoid bias. 相似文献
100.
Australian farmers navigate their contemporary circumstances through the use of different business and legal arrangements that are shaped by the commercial realities of farming and the aspirations of farm-owning households. In posing the question ‘Family or Enterprise?’, this paper examines the extent to which various household and farm business indicators are associated with different forms of farm ownership, namely sole proprietorships, partnerships, trusts and companies. Results from a postal survey of farm enterprises in Victoria, Australia suggest that both household and enterprise factors contribute to the business structure used, although the strongest determinants appear to be those factors that are less well understood in the rural geographical and sociological literature: household composition, farmer age and farm size. Greater scrutiny of the business instruments deployed by farmers to manage family and enterprise pressures should inform expectations of the fate of family farming in advanced financialised economies. 相似文献