全文获取类型
收费全文 | 1715篇 |
免费 | 260篇 |
国内免费 | 182篇 |
专业分类
测绘学 | 252篇 |
大气科学 | 148篇 |
地球物理 | 93篇 |
地质学 | 504篇 |
海洋学 | 277篇 |
天文学 | 25篇 |
综合类 | 286篇 |
自然地理 | 572篇 |
出版年
2024年 | 17篇 |
2023年 | 69篇 |
2022年 | 74篇 |
2021年 | 83篇 |
2020年 | 76篇 |
2019年 | 101篇 |
2018年 | 70篇 |
2017年 | 79篇 |
2016年 | 56篇 |
2015年 | 80篇 |
2014年 | 180篇 |
2013年 | 89篇 |
2012年 | 126篇 |
2011年 | 111篇 |
2010年 | 107篇 |
2009年 | 89篇 |
2008年 | 127篇 |
2007年 | 57篇 |
2006年 | 56篇 |
2005年 | 47篇 |
2004年 | 34篇 |
2003年 | 50篇 |
2002年 | 43篇 |
2001年 | 36篇 |
2000年 | 28篇 |
1999年 | 32篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 28篇 |
1995年 | 28篇 |
1994年 | 32篇 |
1993年 | 16篇 |
1992年 | 31篇 |
1991年 | 23篇 |
1990年 | 13篇 |
1989年 | 15篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1960年 | 3篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2157条查询结果,搜索用时 15 毫秒
111.
东海捕虾桁拖网选择性能不佳,对渔业资源的保护和渔业的合理管理带来了负面的影响.刚性栅栏是实现拖网渔具种类选择性捕捞的主要装置,本文根据在吕四渔场开展刚性栅栏海上生产试验,结合SELECT模型分析不同栅条间距(15、20和25mm)的刚性栅栏对短吻舌鳎、小黄鱼和棘头梅童鱼的分隔效率.结果表明,随着栅条间距的增大,栅栏对鱼类的重量分隔率逐渐减小,分隔栅栏对鱼类的50%选择体长(L50S))逐渐增大;对于短吻舌鳎,个体接触分隔栅栏的概率可使用常数来表示,即接触概率与个体尺寸无关,接触概率在0.2-0.4之间,并随着栅条间距的增大而增大(不显著,P>0.05):对于小黄鱼和棘头梅童鱼,所有进入网囊的个体都将接触刚性栅栏;不同鱼类接触栅栏概率的显著差异说明不同鱼类在网囊中的不同行为习性. 相似文献
112.
There exists a tongueshaped swelldominance pool known as Swell Pool (SP) in the Eastern Pacific region. The monthlymean wave transports (WT) for each month of 2000 is computed using the wave products of ECMWF reanalysis data. By comparing the 2000 monthlymean WT and monthlymean wind field from QUICKSCAT, large differences are found between the wave transport direction and the wind direction over the Eastern Pacific. This may serve as an evidence for the existence of the SP in this region. The work done in this study indicates that the sources of swell in the Tropical Eastern Pacific (TEP) are in the westerly regions of the Southern and Northern Pacific. 相似文献
113.
Natural assemblages of marine bacteria were chosen in a batch culture experiments. The impact of varying nitrogen substrate concentrations and the substrate C:N ratios (C:NS) on the bacterial C:N ratio (C:NB), the bacterial growth efficiency (BGE) and ammonium regeneration was mainly examined. The C:NS ratios varied from 5:1 (carbon limitation) to 40:1 (nitrogen limitation) with varying combinations of glucose and NO3-. The C:NB ratio had positive relationship with the C:NS ratio (r=0.93, n=8), whose value was 3.77 when the C:NS ratio was 5:1 but increased to 6.47 when the C:NS ratio was 40:1. These results indicate that the C:NB ratio is a potential diagnostic tool for determining the bacterial growth in natural waters controlled by either, carbon or nitrogen. BGE decreased with the declining nitrate concentration and negatively related to C:Ns (r=-0.51, n=8). The average value of BGE was 0.20. This value was a little lower than other reports, which could be induced by the nitrogen source used in our experiments. Finally, regeneration time of ammonium delayed with the increasing C:NS ratio, which indicates that there were different metabolism mechanisms when bacterial growth was limited by carbon source and nitrogen source. 相似文献
114.
A dual channel difference (DCD) method is applied to detect nighttime sea fog/stratus over the Huanghai Sea using the infrared (IR) data of shortwave (3.5–4.0 μm) and longwave (10.3–11.3 μm) channels from the Multi-functional Transport Satellite (MTSAT)-1R, i.e., shortwave minus longwave brightness temperature difference (SLTD). Twenty-four sea fog events over the Huanghai Sea during March to July of 2006 and 2007 are chosen to determine a suitable value of SLTD for nighttime sea fog/stratus detection, and ... 相似文献
115.
The results of the new concept of coastal sea circulation are demonstrated by numerical simulations for the first time. The numerical experiments in three types of rectangular model seas illustrate the dependence of circulation on tidal phases due to the convectively nonlinear effect which is estimated by a newly defined drift dispersion in-dex. Then, the present theory is applied in the Bohai Sea of China. At the Bohai Straits and the Huanghe River mouth area the circulation direction even reverses owing to different initial tidal phases which shows that the the-ory copes with nonlinearity well. The calculated M2 tide-induced residual circulation shows that a clockwise gyre exists in the center of an anticlockwise gyre in the central Bohai Sea due to the topographic features. In the Bo-hai Gulf the tide induced circulation shows a 3D structure with outflow at the surface and the inflow at the bottom which can partly explains the spread of the Huanghe River fresh water out of the Bohai Gulf and the inflow of the sediment from the Huanghe River. 相似文献
116.
深海经济问题国际研究动态及启示 总被引:1,自引:0,他引:1
深海经济问题已经成为国际学术界关于海洋经济问题研究的新领域.文章从深海资源与环境、深海渔业、深海工业和深海运输等方面对深海经济国际文献进行了初步梳理,以期为我国深海经济问题的深入研究提供借鉴. 相似文献
117.
A Lagrangian tracer model is set up for Hangzhou Bay based on Coupled Hydrodynamical Ecological model for Regional Shelf Sea
(COHERENS). The study area is divided into eight subdomains to identify the dominant physical processes, and the studied periods
are March (the dry season) and July (the wet season). The model performance has been first verified by sea-surface elevation
and tidal current observations at several stations. Eight tracer experiments are designed and Lagrangian particle tracking
is simulated to examine the impact of physical processes (tide, wind and river runoff) on the transport of passive tracer
released within the surface layer. Numerical simulations and analysis indicate that: (1) wind does not change the tracer distribution
after 30 days except for those released from the south area of the bay during the wet season; (2) the tide and the Qiantang
River runoff are important for particle transport in the head area of the bay; (3) the Changjiang River runoff affects the
tracer transport at the mouth of the bay, and its impact is smaller in the dry season than in the wet season.
Supported by the Natural Science Foundation of China (No.40576080); National High Technology Research and Development Program
of China (863 Program, No. 2007AA12Z182) 相似文献
118.
针对传统淤泥渣土运输管理的特点,阐述淤泥渣土运输管理系统的设计思想和关键技术,将G IS技术、视频监控技术、网络技术有机融合,实现淤泥渣土运输管理的自动化和动态化的目标。 相似文献
119.
毋庸置疑,对煤进行洁净处理和脱硫或者采用碳捕获与储存技术,可以最大限度地减轻燃煤发电对环境的影响,但还有一种选择,就是减少煤的用量。 相似文献