全文获取类型
收费全文 | 2385篇 |
免费 | 79篇 |
国内免费 | 34篇 |
专业分类
测绘学 | 49篇 |
大气科学 | 164篇 |
地球物理 | 629篇 |
地质学 | 815篇 |
海洋学 | 216篇 |
天文学 | 419篇 |
综合类 | 6篇 |
自然地理 | 200篇 |
出版年
2021年 | 22篇 |
2020年 | 29篇 |
2019年 | 28篇 |
2018年 | 55篇 |
2017年 | 44篇 |
2016年 | 79篇 |
2015年 | 53篇 |
2014年 | 54篇 |
2013年 | 109篇 |
2012年 | 63篇 |
2011年 | 91篇 |
2010年 | 97篇 |
2009年 | 110篇 |
2008年 | 91篇 |
2007年 | 115篇 |
2006年 | 91篇 |
2005年 | 76篇 |
2004年 | 88篇 |
2003年 | 76篇 |
2002年 | 69篇 |
2001年 | 47篇 |
2000年 | 51篇 |
1999年 | 43篇 |
1998年 | 44篇 |
1997年 | 44篇 |
1996年 | 37篇 |
1995年 | 39篇 |
1994年 | 35篇 |
1993年 | 19篇 |
1992年 | 45篇 |
1991年 | 40篇 |
1990年 | 44篇 |
1989年 | 29篇 |
1988年 | 25篇 |
1987年 | 25篇 |
1986年 | 19篇 |
1985年 | 36篇 |
1984年 | 48篇 |
1983年 | 38篇 |
1982年 | 27篇 |
1981年 | 38篇 |
1980年 | 34篇 |
1979年 | 26篇 |
1978年 | 27篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1974年 | 21篇 |
1973年 | 17篇 |
1972年 | 14篇 |
排序方式: 共有2498条查询结果,搜索用时 10 毫秒
31.
32.
A simple shaker table for seismometer calibration 总被引:1,自引:0,他引:1
Frederick K. Duennebier George H. Sutton David Harris David A. Byrne 《Marine Geophysical Researches》1984,6(3):311-328
A unique and simple shaker table (shake table or shaking table), designed, constructed, and installed at the Hawaii Institute of Geophysics, has proven to be a valuable aid in testing and calibrating short period seismometers, as well as ocean bottom and ocean sub-bottom seismometer/tilt meter packages. It consists of a platform suspended in a stairwell by a single elastic cord (10 m extended length) driven by GeoSpace HS-10 geophones. Platform motion is monitored by orthogonal reference geophones and tilt meters. The relatively low natural periods of the platform, about 1.9 sec vertical and 6.5 sec horizontal, provide sufficient isolation from local vibrations that calibration can be made near operational amplitudes. Vertical or horizontal driver geophones can be driven by a commercial signal generator or white noise generator, or from magnetic tape output. The table can also be tilted with respect to the drivers to determine tilt tolerances and to calibrate tilt meters. A Hewlett-Packard 3582-A spectrum analyzer, used to analyze both reference and output signals, provides near real-time system cabibration and is an efficient means for investigating parasitic system resonances. The analyzer can also provide a white noise signal source to the driver geophones.Hawaii Institute of Geophysics Contribution 1443. 相似文献
33.
34.
Lysosomal destabilization assays have been used as valuable biomarkers of pollutant exposures in a variety of bivalve and fish species. The responses of oysters, Crassostrea virginica, deployed at and native to various reference and degraded sites were evaluated for lysosomal destabilization during both summer and winter seasons. In both native and deployed oysters, lysosomal destabilization rates tended to be higher during the winter at both reference and polluted sites. There are at least two hypothetical explanations. Greater lysosomal destabilization rates may be related to physiological changes associated with mobilization of nutrient reserves during the winter and gametogenesis. However, lysosomal destabilization in deployed oysters was correlated with tissue metal concentrations. These data also support a second hypothesis that seasonal differences in physico-chemical factors (such as reduced levels of acid volatile sulfides) may increase the bioavailability of metals during the winter so that adverse effects are more pronounced. 相似文献
35.
36.
This paper brings together unpublished historical data sets and published literature to review the role of climatic, oceanographic and ecological processes in the marine ecosystem of the eastern Canadian Archipelago. Physical data include characteristics of the water masses, circulation patterns, sea ice conditions, and climatic records from 1950s onward. Biological data include unpublished data sets on nutrients, primary and secondary production, and sedimentation, which were collected during the 1980–1990s in the eastern Canadian Archipelago. These results show high year-to-year variability in nutrient inventories and ratios, the magnitude of the ice algae and phytoplankton bloom, the timing of ice algae sedimentation in the spring, and the composition of the zooplankton community. The significance of this high interannual variability and its effect on pelagic–benthic coupling processes is discussed in the context of climatic and oceanographic forcing, with emphasis on recent (past decade) Arctic changes. An estimate of total primary production in the Archipelago is also presented, along with published production estimates for other Arctic shelves, showing that the Archipelago may support up to 32% of the total primary production of Arctic shelves. The high year-to-year variability in production and carbon transfer pathways (e.g. pelagic versus benthic) in the Archipelago suggest that the system might be resilient to the increased variability in climatic conditions occurring in the past decade. However, this increased variability combined with directional change in climatic and oceanographic conditions might also modify the existing balance of ecological processes. For example, shifts in the timing of events appear to have already occurred in the past decade, with potential cascading effects throughout the ecosystem. 相似文献
37.
本文报导了应用纤维素乙酸平板电泳方法,测定采于中国山东省东方红盐场卤虫(Artemia)的同功酶。经测定,8种同功酶其中有6种是多态的,即:苹果酸脱氢酶(MDH)、异柠檬酸酶(IDH)、谷氨酸草醋酸转移酶(GOT)、葡糖-6-磷酸盐脱氢酶(D6PHD)、6-磷酸萄糖脱氢酶(6PGDH)和磷酸葡糖异构酶(PGI)。本文所提供的研究方法,不仅适用于基础研究,而且在水产养殖业上有助于对卤虫的筛选和确证。 相似文献
38.
A code of practice for ocean mining has been developed by the International Marine Minerals Society. The code provides general guiding Principles for development of marine mineral resources and delineates Operating Guidelines for application, as appropriate, at specific mining sites. In total 11 operating guidelines are provided to serve as benchmarks for industry and targets for regulatory agencies and other stakeholders. They include the following commitments: •To sustainable development, •To environmentally responsible corporate ethics, •To the development of effective community partnership, •To implementation of environmental risk management, •To the integration of environmental management into all phases of development, •To the establishment of corporate environmental performance targets, •To timely environmental improvements and upgrading, •To responsible rehabilitation of operations sites and decommissioning of facilities, and •To accurate and timely, reporting and documentation, archiving, and performance review. 相似文献
39.
During the Quaternary, the Mac. Robertson shelf of East Antarctica was deeply eroded by glaciers and currents exposing the underlying basement, resulting in a scalped shelf. Major geomorphic zones are: (1) high-relief, ridge and valley topography (200–1400 m); (2) smooth sea floors associated with low-energy, depositional shelf valleys and basins (400–800 m); (3) low-relief, planated banktops (100–200 m); and (4) iceberg gouged and current reworked seaward-bank margins and upper slope (200 to < 630 m). About 90% of the shelf's surface has net erosional conditions and about 10% is net depositional. The sedimentary processes and deposits may be common to large areas of the East Antarctic margin. 相似文献
40.