全文获取类型
收费全文 | 214篇 |
免费 | 5篇 |
国内免费 | 14篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 3篇 |
地球物理 | 14篇 |
地质学 | 4篇 |
海洋学 | 201篇 |
综合类 | 3篇 |
自然地理 | 7篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 7篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 2篇 |
2015年 | 8篇 |
2014年 | 4篇 |
2013年 | 25篇 |
2011年 | 4篇 |
2010年 | 2篇 |
2009年 | 21篇 |
2008年 | 11篇 |
2007年 | 18篇 |
2006年 | 5篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 16篇 |
2000年 | 20篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
排序方式: 共有233条查询结果,搜索用时 15 毫秒
211.
Larval fishes were sampled in the Kwaaihoek surf zone on the south east coast of South Africa. On six occasions between February and May 2002, larval fishes were collected in two habitat types identified in the inner surf zone using a modified beach-seine net. The surf zone habitats were classified as either sheltered trough areas or adjacent exposed surf areas. Temperature, depth and current measurements were taken at all sites. Trough habitats consisted of a depression in surf topography characterised by reduced current velocities and greater average depth than adjacent surf areas. In total, 325 larval fishes were collected. Of these, 229 were collected in trough and 96 in surf habitats. At least 22 families and 37 species were represented in the catch. Dominant families were the Mugilidae, Sparidae, Atherinidae, and Engraulidae. Dominant species included Liza tricuspidens and Liza richardsonii (Mugilidae), Rhabdosargus holubi and Sarpa salpa (Sparidae), Atherina breviceps (Atherinidae) and Engraulis japonicus (Engraulide). Mean CPUE of postflexion larvae of estuary-dependent species was significantly greater in trough areas. The proportion of postflexion larval fishes in trough habitat was significantly greater than that of preflexion stages, a result that was not apparent in surf habitat sampled. CPUE of postflexion larvae of estuary-dependent fishes was negatively correlated with current magnitude and positively correlated with habitat depth. Mean body length of larval fishes was significantly greater in trough than in surf habitats. These results provide evidence that the CPUE of postflexion larvae of estuary-dependent fishes is higher in trough habitat in the surf zone and this may be indicative of active habitat selection for areas of reduced current velocity/wave action. The implications of this behaviour for estuarine recruitment processes are discussed. 相似文献
212.
213.
Karen D. JohnsonWebb 《The Professional geographer》2002,54(3):406-421
The North Carolina Hispanic population has grown at a rapid pace in recent years. Before 1980, the majority of Hispanics in North Carolina were engaged primarily in migrant agricultural work. Hispanics who are part of the new influx are arriving in urban areas and are working at nonagricultural pursuits. Previous research and anecdotal evidence suggest that Hispanic newcomers come from other U.S. jurisdictions and from abroad. Labor migration occurs in response to demand for labor, and labor demand is meditated by employers’ preferences and hiring practices. However, focusing solely on employer demand for labor ignores the role of past U.S. immigration policy and the large growth in services employment in the Sunbelt that have fueled the Hispanic in–migration. This research project explored the attitudes and recruiting behavior of employers in the Triangle region of North Carolina. A newspaper content analysis was undertaken, and interviews were conducted with selected intermediaries and a group of employers. Qualitative analysis of the data collected revealed that these employers utilize the social networks of their immigrant Hispanic employees to recruit new workers. They also use a variety of other recruiting methods to recruit Hispanics both locally and from abroad. If this practice is widespread, it may be fueling the influx of Hispanic immigrants to North Carolina. Employers interviewed extolled the work ethic of Hispanic workers and often bypassed native–born workers, whom they felt were inferior employees. These findings have ramifications for future immigration policy and for the success of welfare–to–work programs. Employer demand for labor is one factor that must be considered when formulating new immigration policy. 相似文献
214.
215.
216.
217.
218.
219.
220.
To assess the potential contribution of soil seed banks to seedling recruitment, and to the vegetative processes of dune systems
in semi-arid areas, a comparison of temporal variation in soil seed bank was made between active and stabilized dune systems
in northeastern Inner Mongolia, China. The results showed that between-year difference in seed density for the stabilized
system was smaller than that for the active one, but there were similar variations with season in seed bank for both dune
systems. Furthermore, seed densities of the dominant species on the respective dune type (i.e., annuals on the stabilized
dune and psammophytes on the active dune) varied more sharply with season, but more gently in annual variation than those
of other phytogroups. These findings suggest that (1) seeds of annuals in the soil of the stabilized dune, or seeds of psammophytes
in the soil of the active dune contributed much to seedling recruitment or plant species colonization, (2) the relationship
between soil seed bank and seedling recruitment was complex in both dune systems. 相似文献