全文获取类型
收费全文 | 57198篇 |
免费 | 9460篇 |
国内免费 | 13333篇 |
专业分类
测绘学 | 4801篇 |
大气科学 | 7049篇 |
地球物理 | 11745篇 |
地质学 | 32802篇 |
海洋学 | 8025篇 |
天文学 | 2294篇 |
综合类 | 3945篇 |
自然地理 | 9330篇 |
出版年
2024年 | 328篇 |
2023年 | 907篇 |
2022年 | 1735篇 |
2021年 | 1985篇 |
2020年 | 2083篇 |
2019年 | 2384篇 |
2018年 | 1910篇 |
2017年 | 2217篇 |
2016年 | 2407篇 |
2015年 | 2588篇 |
2014年 | 3090篇 |
2013年 | 3193篇 |
2012年 | 3394篇 |
2011年 | 3545篇 |
2010年 | 3076篇 |
2009年 | 3626篇 |
2008年 | 3575篇 |
2007年 | 3991篇 |
2006年 | 3781篇 |
2005年 | 3299篇 |
2004年 | 3103篇 |
2003年 | 2932篇 |
2002年 | 2623篇 |
2001年 | 2309篇 |
2000年 | 2179篇 |
1999年 | 1962篇 |
1998年 | 1698篇 |
1997年 | 1615篇 |
1996年 | 1438篇 |
1995年 | 1205篇 |
1994年 | 1221篇 |
1993年 | 1039篇 |
1992年 | 860篇 |
1991年 | 618篇 |
1990年 | 520篇 |
1989年 | 420篇 |
1988年 | 326篇 |
1987年 | 204篇 |
1986年 | 143篇 |
1985年 | 114篇 |
1984年 | 52篇 |
1983年 | 51篇 |
1982年 | 46篇 |
1981年 | 35篇 |
1980年 | 28篇 |
1979年 | 30篇 |
1978年 | 43篇 |
1977年 | 25篇 |
1976年 | 6篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Distributions of physical, chemical and biological characteristics were recorded for coastal waters off south-west Ireland during the summers of 1985–1987. A number of thermal fronts were identified from both shipboard measurements and satellite imagery. Upwelling was shown to be an important process in the area and enhanced phytoplankton biomass and productivity were associated with areas of upwelling and the fronts. Phytoplankton species composition, although varying between cruises, was associated with differences in hydrographic features. 相似文献
162.
-Based on the feasibility study of developing the navigation resources of the Guanhe River and the model test results of the mouth bar regulation, this paper presents some basic principles for the regulation of the channel on the mouth bar, for instance, the direction of navigation channel should be identical with that of the ebb tide current and the main waves, and perpendicular to the bathymetric contours. The principles for regulating mouth bars are also discussed in this paper. 相似文献
163.
164.
王树林 《中国海洋大学学报(自然科学版)》1995,(Z1)
以现代高速摄影技术和图像分析以及数据处理方法,针对高效振动磨机中弹性散体工质(如钢棒、球体等)的振动力学进行了深入的探讨和分析,为研究散体动力学和振动超细粉碎过程中的能量分布和传递规律以及能量与物质的相互转换机理奠定了基础,也为相关学科的发展提供了一种可以借鉴的方法。 相似文献
165.
166.
Current trends of space occupation by encrusting excavating sponges on Colombian coral reefs 总被引:1,自引:0,他引:1
Some sponges of the genus Cliona (Porifera, Hadromerida, Clionidae) simultaneously excavate and encrust calcareous substratum, competing aggressively for illuminated space with corals and other organisms. To interpret current trends of reef space occupation, the patterns of distribution and size of three Caribbean species were examined at San Andrés Island and Islas del Rosario in Colombia. While Cliona aprica was ubiquitous, C. caribbaea (= C. langae) preferred deep and protected reef zones, and C. tenuis shallow and wave‐exposed settings. In contrast to the effect on other excavating sponges, chronic exposure to raw sewage did not significantly increase the abundance of the studied sponges. Substratum occupation/availability ratios showed a positive tendency of the sponges toward certain coral skeletons, and a negative or neutral tendency toward calcareous rock, indicating that establishment may be easier on clean, recently dead coral than on older, heavily incrusted substratum. High relief generally limits sponge size to that of the illuminated portions of the substratum. A generally lower proportion of small individuals than of larger ones indicates currently low recruitment rates and low subsequent mortality. Successful events of higher recruitment seem to have occurred for C. tenuis. These are related to the massive acroporid coral die‐off in the early 1980s and to asexual dispersion during storms, resulting in a current 10% substratum cover. Reefs with high coral mortality were and/or are thus more susceptible to colonization and subsequent space occupation by these sponges, although relief may prevent space monopolization. 相似文献
167.
热带气旋活动对中国夏季雨带类型与ENSO的响应关系 总被引:2,自引:0,他引:2
本文分析研究了热带气旋1)活动与中国夏季2)3组(包括8种)主要多雨带类型的响应关系。同时对热带气旋活动与夏季大陆气温和ENSO事件的始终时间的响应关系,也进行了探讨。分析表明,夏季中国的雨带分布特征对热带气旋活动有着十分重要的指示意义。热带气旋活动与中国大陆气温有着正相关关系,与ENSO事件的发生有着反相关关系 相似文献
168.
169.
辽河盆地大民屯凹陷流体压力特征 总被引:1,自引:0,他引:1
大民屯凹陷是辽河断陷内4个下第三系凹陷之一。在综合利用钻井、试井及地震等资料的基础上,系统研究并论述了大民屯凹陷流体压力特征。基于57口井的声波测井资料,凹陷内泥岩压力特征可区分为正常压力、异常压力或强超压等类型;根据152口井391个点的压力测试数据,凹陷内产油层段的压力梯度多接近于1;利用公式法模拟计算了47条地震剖面的流体压力、剩余压力及压力系数的分布特征,凹陷内剖面压力系统自上而下一般由正常压力、弱超压和强超压3部分组成。此外,还根据流体压力演化的基本原理及钻井、岩性与试井等实际资料,模拟恢复了大民屯凹陷的压力演化史,其可划分为超压原始积累、超压部分释放及超压再积聚3个阶段。总体上,大民屯凹陷的超压强度低于渤海湾盆地其他地区的超压强度。 相似文献
170.
Following Bagnold's approach, a relationship between sediment transport and energy dissipation is developed. The major assumption made in the study is that the near bed velocity plays a dominant role in the process of sediment transport. A general relationship between energy dissipation and sediment transport is first proposed. Then the equations for total sediment transport are derived by introducing the appropriate expression of energy dissipation rate under different conditions, such as open channel flows, combination of wave and current, as well as longshore sediment transport. Within the flows investigated, the derived relationships are fairly consistent with the available data over a wide range of conditions. 相似文献