全文获取类型
收费全文 | 22936篇 |
免费 | 4218篇 |
国内免费 | 7335篇 |
专业分类
测绘学 | 2682篇 |
大气科学 | 7047篇 |
地球物理 | 4908篇 |
地质学 | 8747篇 |
海洋学 | 4590篇 |
天文学 | 1477篇 |
综合类 | 1940篇 |
自然地理 | 3098篇 |
出版年
2024年 | 119篇 |
2023年 | 320篇 |
2022年 | 810篇 |
2021年 | 948篇 |
2020年 | 1156篇 |
2019年 | 1361篇 |
2018年 | 1053篇 |
2017年 | 1167篇 |
2016年 | 1195篇 |
2015年 | 1393篇 |
2014年 | 1479篇 |
2013年 | 1743篇 |
2012年 | 1659篇 |
2011年 | 1585篇 |
2010年 | 1271篇 |
2009年 | 1497篇 |
2008年 | 1511篇 |
2007年 | 1838篇 |
2006年 | 1682篇 |
2005年 | 1511篇 |
2004年 | 1265篇 |
2003年 | 1054篇 |
2002年 | 937篇 |
2001年 | 739篇 |
2000年 | 852篇 |
1999年 | 812篇 |
1998年 | 673篇 |
1997年 | 486篇 |
1996年 | 415篇 |
1995年 | 358篇 |
1994年 | 348篇 |
1993年 | 306篇 |
1992年 | 232篇 |
1991年 | 154篇 |
1990年 | 111篇 |
1989年 | 124篇 |
1988年 | 83篇 |
1987年 | 60篇 |
1986年 | 54篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1954年 | 5篇 |
1877年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
241.
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
242.
243.
2000年夏季莱州湾生态环境要素的分布特征 总被引:1,自引:0,他引:1
论文依据 2 0 0 0年夏季 8月 2 9日至 9月 2日莱州湾的 1次综合性生态环境调查资料 ,给出了表、中、底 3层的平均温度、盐度、主要营养盐浓度及其比例和叶绿素 a浓度 ,分析了莱州湾的温盐结构、主要营养盐和叶绿素 a的分布特征。由于莱州湾的水深较浅 ,各要素的垂直分布都比较均匀。生态环境要素的水平分布表现为小清河口为高温、低盐、高营养盐和高叶绿素 a浓度区 ,小清河口东测的湾顶区域为高温、高盐、相对低的营养盐和叶绿素 a浓度区。此次观测到的盐度较 1997年以前有明显升高。莱州湾各层平均的 N/ P和 Si/ N分别为 16.73和 1.67,都比 1998~ 1999年渤海中部的值大 ,但 N/ P比 1992 ,1995和 1996年莱州湾的 N/ P明显偏低。叶绿素 a浓度与硅酸盐浓度之间有较好的相关关系 (α=0 .0 1) ,表、中、底 3层叶绿素 a浓度同硅酸盐浓度的线性相关系数分别为 :0 .5 4 ,0 .68和 0 .67 相似文献
244.
245.
246.
247.
Are invasive species most successful in habitats of low native species richness across European brackish water seas? 总被引:5,自引:0,他引:5
Marjo Paavola Sergej Olenin Erkki Leppkoski 《Estuarine, Coastal and Shelf Science》2005,64(4):738-750
European brackish water seas (Baltic Sea, Black Sea and Sea of Azov, Caspian Sea) are subject to intense invasion of non-indigenous species (NIS). In these seas, salinity is the most important range limiting factor and native species seem to reach a minimum species richness at intermediate salinities. This trend, revealed by Remane in 1934 and later on confirmed by many other scientists, was compared to the salinity range of already established NIS in the European brackish water seas. It turned out that most NIS are well adapted to the salinities holding lowest native species richness, already in their native area, and that NIS richness maximum in brackish water seas occurs in the salinity intervals of native species richness minimum. A predictable pattern in the salinity range of NIS can be used as a tool in initial risk assessment of future invasions in brackish water seas, especially when mapping highly potential donor and recipient areas. A product of empty niches, suitable environmental conditions, and availability of proper vectors might be the most effective predictor for the invasibility of brackish water areas. 相似文献
248.
Jean-Benoît Charrassin Young-Hyang Park Yvon Le Maho Charles-Andr Bost 《Deep Sea Research Part I: Oceanographic Research Papers》2004,51(12):2091-2103
The use of diving animals as autonomous vectors of oceanographic instruments is rapidly increasing, because this approach yields cost-efficient new information and can be used in previously poorly sampled areas. However, methods for analyzing the collected data are still under development. In particular, difficulties may arise from the heterogeneous data distribution linked to animals’ behavior. Here we show how raw temperature data collected by penguin-borne loggers were transformed to a regular gridded dataset that provided new information on the local circulation off Kerguelen. A total of 16 king penguins (Aptenodytes patagonicus) were equipped with satellite-positioning transmitters and with temperature–time–depth recorders (TTDRs) to record dive depth and sea temperature. The penguins’ foraging trips recorded during five summers ranged from 140 to 600 km from the colony and 11,000 dives >100 m were recorded. Temperature measurements recorded during diving were used to produce detailed 3D temperature fields of the area (0–200 m). The data treatment included dive location, determination of the vertical profile for each dive, averaging and gridding of those profiles onto 0.1°×0.1° cells, and optimal interpolation in both the horizontal and vertical using an objective analysis. Horizontal fields of temperature at the surface and 100 m are presented, as well as a vertical section along the main foraging direction of the penguins. Compared to conventional temperature databases (Levitus World Ocean Atlas and historical stations available in the area), the 3D temperature fields collected from penguins are extremely finely resolved, by one order finer. Although TTDRs were less accurate than conventional instruments, such a high spatial resolution of penguin-derived data provided unprecedented detailed information on the upper level circulation pattern east of Kerguelen, as well as the iron-enrichment mechanism leading to a high primary production over the Kerguelen Plateau. 相似文献
249.
250.