全文获取类型
收费全文 | 12310篇 |
免费 | 1155篇 |
国内免费 | 996篇 |
专业分类
测绘学 | 2918篇 |
大气科学 | 1023篇 |
地球物理 | 1415篇 |
地质学 | 1839篇 |
海洋学 | 954篇 |
天文学 | 37篇 |
综合类 | 1065篇 |
自然地理 | 5210篇 |
出版年
2024年 | 40篇 |
2023年 | 107篇 |
2022年 | 553篇 |
2021年 | 635篇 |
2020年 | 594篇 |
2019年 | 702篇 |
2018年 | 535篇 |
2017年 | 680篇 |
2016年 | 651篇 |
2015年 | 674篇 |
2014年 | 687篇 |
2013年 | 972篇 |
2012年 | 801篇 |
2011年 | 770篇 |
2010年 | 570篇 |
2009年 | 600篇 |
2008年 | 572篇 |
2007年 | 689篇 |
2006年 | 642篇 |
2005年 | 494篇 |
2004年 | 517篇 |
2003年 | 364篇 |
2002年 | 338篇 |
2001年 | 239篇 |
2000年 | 198篇 |
1999年 | 150篇 |
1998年 | 125篇 |
1997年 | 102篇 |
1996年 | 74篇 |
1995年 | 53篇 |
1994年 | 66篇 |
1993年 | 50篇 |
1992年 | 59篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
21.
Abstract. Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populations. 相似文献
22.
23.
24.
Seasonal and Spatial Variations of Iceberg Drift off Dronning Maud Land, Antarctica, Detected by Satellite Scatterometers 总被引:1,自引:0,他引:1
Shigeru Aoki 《Journal of Oceanography》2003,59(5):629-635
Seasonal and spatial variations of iceberg drift were studied using continuous satellite scatterometer images off Dronning
Maud Land, East Antarctica. Generally, iceberg drift speed showed a westward increase to the Greenwich Meridian. Seasonal
variations of the drift speed were high in autumn—early winter and low in spring, and their magnitudes also increased westward.
Seasonal variations of the drift speed were significantly correlated with variations of sea levels at Syowa and Mawson Stations,
and hence qualitatively consistent with geostrophic current variations. Thus, the scatterometer data are demonstrated to be
useful in monitoring iceberg trajectory and oceanic current variations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
引入差比关系法分析西北太平洋TOPEX/POSEIDON卫星高度计测高数据 总被引:7,自引:0,他引:7
TOPEX/POSEIDON(T/P)卫星高度计数据信息中存在周期成分混淆问题.对其中的一类混淆引入差比关系方法对混淆的分潮进行分离.卫星轨道交叉点资料包括升轨和降轨资料,资料量比沿轨点资料多1倍,经分析发现:在已有为期6a多的观测资料时间序列中,在沿轨处混淆的分潮如K1和SSA在交叉点处不再混淆,可以直接分离.因此首先对交叉点资料进行调和分析.然后由交叉点的分析结果得到分潮间的差比关系,处理到相近的沿轨点处,从而得到沿轨点的调和常数.用引入差比关系方法,对西北太平洋海区6a多的T/P卫星高度计资料进行了潮汐分析,并与沿岸及岛屿验潮站资料进行了比较,所得结果较满意. 相似文献
26.
27.
28.
29.
High-resolution underway temperature and conductivity measurements collected by R/V Knorr during winter and spring 2003 are used to characterize errors associated with spatial aliasing in the northern and central Adriatic Sea. During winter, 99th percentile temperature, salinity and density errors were 0.62 °C, 0.25 and 0.12 kg/m3 (0.25 °C, 0.10 and 0.05 kg/m3) for sampling at 10 km (5 km) horizontal resolution, respectively. The corresponding values in spring were 1.31 °C, 0.50 and 0.40 kg/m3 (0.93 °C, 0.25 and 0.22 kg/m3) for the 10 km (5 km) sample spacing, respectively. The largest errors were associated with energetic regions over the shallow, western Adriatic, in front of the Po River mouth and off the tip of the Istrian peninsula. The deeper eastern basin exhibited smaller errors. The variability of errors in time and space reflected the variability of small-scale density features, characterized by wavelengths as small as 2 km in winter and 1 km in spring and being more pronounced in the western and northern parts of the Adriatic. As these results indicate that errors associated with undersampling can be considerable, they should be taken into account while planning future CTD measurements in the region. 相似文献
30.