全文获取类型
| 收费全文 | 5602篇 |
| 免费 | 1093篇 |
| 国内免费 | 1237篇 |
专业分类
| 测绘学 | 234篇 |
| 大气科学 | 233篇 |
| 地球物理 | 614篇 |
| 地质学 | 1927篇 |
| 海洋学 | 3461篇 |
| 天文学 | 14篇 |
| 综合类 | 385篇 |
| 自然地理 | 1064篇 |
出版年
| 2024年 | 63篇 |
| 2023年 | 145篇 |
| 2022年 | 270篇 |
| 2021年 | 304篇 |
| 2020年 | 326篇 |
| 2019年 | 339篇 |
| 2018年 | 263篇 |
| 2017年 | 258篇 |
| 2016年 | 301篇 |
| 2015年 | 294篇 |
| 2014年 | 383篇 |
| 2013年 | 380篇 |
| 2012年 | 350篇 |
| 2011年 | 398篇 |
| 2010年 | 333篇 |
| 2009年 | 399篇 |
| 2008年 | 311篇 |
| 2007年 | 347篇 |
| 2006年 | 389篇 |
| 2005年 | 356篇 |
| 2004年 | 275篇 |
| 2003年 | 277篇 |
| 2002年 | 200篇 |
| 2001年 | 163篇 |
| 2000年 | 171篇 |
| 1999年 | 136篇 |
| 1998年 | 76篇 |
| 1997年 | 78篇 |
| 1996年 | 65篇 |
| 1995年 | 50篇 |
| 1994年 | 46篇 |
| 1993年 | 41篇 |
| 1992年 | 38篇 |
| 1991年 | 27篇 |
| 1990年 | 20篇 |
| 1989年 | 12篇 |
| 1988年 | 10篇 |
| 1987年 | 8篇 |
| 1986年 | 9篇 |
| 1985年 | 5篇 |
| 1984年 | 7篇 |
| 1983年 | 2篇 |
| 1982年 | 5篇 |
| 1981年 | 1篇 |
| 1954年 | 1篇 |
排序方式： 共有7932条查询结果，搜索用时 15 毫秒
101.
Abstract. The marine plant communities of the littoral zone in different biotopes of the Greek coasts were investigated in 1980-81. Seasonal distribution and variation of marine plant biomass were assessed. The communities of Cystoseira crinita and C. compressa were outstanding with maximum biomass during the summer months. Corallina officinalis and Pterocladia capillacea + Viva rigida communities predominated with maximum biomass in autumn and exhibited a decrease in winter, except in stressed biotopes. The species diversity and productivity of seaweeds along the Greek coasts are interpreted in relation to a number of environmental parameters. 相似文献
102.
Fisheries in boreal ecosystems 总被引：2，自引：1，他引：2
103.
This study takes cognizance of the fact that the TIOMIN (TIOMIN Resources Inc. of Canada) project has resulted in controversy over its handling of environmental issues and especially the Environmental Impact Assessment (EIA). The authors address many of the protracted issues that have slowed the development of the mining project in Kwale. The main emphasis is on the impacts of the mining and mineral separation processes on the environment, including the governing legislation, the role of consultation and public participation, and socioeconomic issues. In their public documents TIOMIN has specified neither the type of minerals it wants to extract from the area nor their chemical composition. It is well known, however that the titanium minerals and zircon targeted have impurities of iron, thorium and uranium. In the absence of an Environmental Management Plan, the effects of stockpiling radioactive wastes and other impurities that could possibly lead to environmental degradation in both the terrestrial and marine environments have not been publically addressed. The measures proposed to mitigate ecological damage as a result of the establishment of a minerals processing plant in the area seem inadequate. Pollution resulting from accidental spillage or breakage could have significant impact on marine life and residents living near the mining site. Other issues that have not been addressed satisfactorily pertain to the use of surface and underground water. The area already faces a huge water deficit and the calculations presented on aquifer recharge and stream flow rates do not indicate the large quantities of water that would be required in the mineral processing plant. The project, if approved in its present state, risks violation of international conventions. Furthermore, it could cause a conflict between Kenya and Tanzania in the event of an oil spill at the proposed ship loading facility at Shimoni. The proposed mining area includes the district's most fertile land, is home to many fisherfolk and is a major tourist destination. An analysis of the effects of this project on other available opportunities must be thoroughly understood to ascertain the economic and environmental benefits and costs of the mining venture. The proposed compensation rate of $1,000 per acre, for resettlement for example, appears to be grossly inadequate. Compensation should take into account family size and structure family assets and the cost of relocation. 相似文献
104.
105.
106.
107.
Combining indicator trends to assess ongoing changes in exploited fish communities: diagnostic of communities off the coasts of France 总被引：1，自引：1，他引：1
108.
The Effect of Internal Fluid on the Response of Vortex-Induced Vibration of Marine Risers 总被引：5，自引：1，他引：5
Based on Iwan‘s wake oseillator model developed with the classical van der Pol equalion, the differential equation for the response of the vortex-induced vihration (VIV) of the riser considering the effect of the internal flowing fluid and the external marine environmental condition is derived. The effect of the intermal flowing fluid on the response of VIV of the riser is studied by means of the Finite Element Method. The results show that the effect of the internal fluid velocity on the VIV of the riser is strong when the natural frequency of the riser is close to the vortex shedding frequency. In addition, the increase of the top tension can decrease the sensitivity of the riser to the internal fluid velocity. 相似文献
109.
The atomic force microscopy (AFM) is a recently developed, bench-top instrument that can image the surface structures of biological
specimens at high resolution with simultaneous measurement of their size. This paper describes the application of AFM to marine
bacteria. Both natural and cultured bacteria were retained on a filter or placed on glass, washed, air-dried and observed
by AFM. The instrumental condition, the choice of suitable filter, effect of fixation and filtration, comparison with epifluorescent
microscopic (EFM) count, and the size and shape of bacterial cells were investigated. An Isopore filter was best for concentration
and subsequent observation because of its surface flatness. Cross section images showed that both rod and coccoid cells were
flattened, the former usually having a two-humped shape. Bacterial cells were differentiated from non-living particles based
on their cross section shape and size. Bacterial counts by AFM and EFM showed good agreement. Although size measurement is
easily done by the instrument, AFM tends to overestimate the size of microspheres. More work is thus needed on the size measurement
of living organisms. Because AFM easily provides images of natural bacterial cells at high magnification, it can be used as
a new tool to study the fine structures of marine bacteria.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
110.