全文获取类型
收费全文 | 8071篇 |
免费 | 1282篇 |
国内免费 | 1305篇 |
专业分类
测绘学 | 550篇 |
大气科学 | 1435篇 |
地球物理 | 2558篇 |
地质学 | 3774篇 |
海洋学 | 751篇 |
天文学 | 514篇 |
综合类 | 460篇 |
自然地理 | 616篇 |
出版年
2024年 | 23篇 |
2023年 | 89篇 |
2022年 | 204篇 |
2021年 | 266篇 |
2020年 | 206篇 |
2019年 | 239篇 |
2018年 | 671篇 |
2017年 | 554篇 |
2016年 | 451篇 |
2015年 | 325篇 |
2014年 | 291篇 |
2013年 | 308篇 |
2012年 | 861篇 |
2011年 | 624篇 |
2010年 | 324篇 |
2009年 | 298篇 |
2008年 | 286篇 |
2007年 | 240篇 |
2006年 | 283篇 |
2005年 | 942篇 |
2004年 | 962篇 |
2003年 | 718篇 |
2002年 | 263篇 |
2001年 | 169篇 |
2000年 | 136篇 |
1999年 | 128篇 |
1998年 | 86篇 |
1997年 | 107篇 |
1996年 | 118篇 |
1995年 | 81篇 |
1994年 | 72篇 |
1993年 | 52篇 |
1992年 | 43篇 |
1991年 | 42篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 23篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1965年 | 3篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
不同季节底梄生物数量的动态由其组成种的种群特点所决定。在一些生命周期短(一年左右)、生长速度快(新生个体当年可以长成)的种处于优势的情况下,生物数量的季节变化就比较显著;而生命周期长、其种群由多个年龄组的个体构成的种占优势的情况下,一年之中种群数量就相对稳定。另一方面,底栖生物数量的急剧改变又决定于经济种的捕食活动和优势种的生物学过程。台湾海峡系经济鱼、虾类的集中分布区,尤以上升流区范围内的集群最密集。为了便于深入研究上升流与经济鱼、虾类资源的关系,本文着重探讨上升流范围内底栖生物数量的动态特点。 相似文献
32.
Erkan G?ka?an Cem Gazio?lu Bedri Alpar Zeki Yücel ?ükrü Ersoy O?uz Gündo?du Cenk Yalt?rak Buser Tok 《Geo-Marine Letters》2002,21(4):183-199
Active faults aligning in NW–SE direction and forming flower structures of strike-slip faults were observed in shallow seismic data from the shelf offshore of Avcılar in the northern Marmara Sea. By following the parallel drainage pattern and scarps, these faults were traced as NW–SE-directed lineaments in the morphology of the northern onshore sector of the Marmara Sea (eastern Thrace Peninsula). Right-lateral displacements in two watersheds of drainage and on the coast of the Marmara Sea and Black Sea are associated with these lineaments. This right-lateral displacement along the course of these faults suggests a new, active strike-slip fault zone located at the NW extension of the northern boundary fault of the ?ınarcık Basin in the Marmara Sea. This new fault zone is interpreted as the NW extension of the northern branch of the North Anatolian Fault Zone (NAFZ), extending from the ?ınarcık Basin of the Marmara Sea to the Black Sea coast of the Thrace Peninsula, and passing through B üy ük ?ekmece and K ü ? ük ?ekmece lagoons. These data suggest that the rupture of the 17 August 1999 earthquake in the NAFZ may have extended through Avcılar. Indeed, Avcılar and İzmit, both located on the Marmara Sea coast along the rupture route, were strongly struck by the earthquake whereas the settlements between Avcılar and İzmit were much less affected. Therefore, this interpretation can explain the extraordinary damage in Avcılar, based on the newly discovered rupture of the NAFZ in the Marmara Sea. However, this suggestion needs to be confirmed by further seismological studies. 相似文献
33.
Qian Fenlan Yu Hongjian Lan Youchang Chen Zhi Zhou Mingyu Farn Parungo Wu Peiming 《海洋学报(英文版)》1996,15(1):69-84
AtmosphericinputoftraceelementstothewesternPacificOceanandtheKuroshiooceanarea¥QianFenlan;YuHongjian;LanYouchang;ChenZhi;Zhou... 相似文献
34.
提出以2,6-二氯苯胺为原料,经重氮化、氟硼酸重氮盐热分解、硝化、氟化等步骤,制成2,3,4-三氟硝基苯。优点是工艺简单,收率较高. 相似文献
35.
36.
本文分析了济州岛南部区域温度双跃层现象的类型及其成因。特别阐明了双跃层的波状现象,指出:强流锋区的侧向效应,黑潮次—中层混合水的爬升,黄海冷水团边缘密度环流引起的侧向流动,以及上、下层流速、流向不一致引起的剪切作用,是导致双跃层波状现象的主要原因。发现上、下跃层之间存在着“跃层间环流”,这是一个有趣的海洋学现象,它将导致双扩散的发生和有利于双跃层的维持。 相似文献
37.
-Morphology, reproduction, ecology and isoenzyme electrophoresis of a Capitella complex in Qingdao were examined from 1983 to 1984. We determined that the Capitella complex in Qingdao was composed of at least three sibling species: Capitella cf capitata, Capitella sp. I and Capitella sp. IT. Although these three species are very similar in morphology, they differ in: three kinds of isoenzyme electrophoresis, staining reactions, developmental pattern, larval morphology and dispersal, reproductive strategies, breeding season and population ecology. In addition, they show a series of minor quantitative variations in adult morphology, especially in number and morphology of setae. Such differences can be detected only at the population level. Some ecological data such as density, growth rate, mortality and sex distribution are also provided in this paper. 相似文献
38.
Channels of cross - equatorial flow and their characteristics Winds at every 5 deg. grid point from 30°E to 180° over the equator at 850 hPa and 200hPa from December 1984 to February 1985 have been separated into U(zonal wind) andV(meridional wind).The V component has been used to represent cross- equatorial flow. FromFig. 1 we obtained that as during the Northern summer,there are also severa1 regions in which 相似文献
39.
Scaling analysis of deposition from turbidity currents 总被引:3,自引:0,他引:3
Many oil-bearing sedimentary deposits are formed by the settling of particles from turbidity currents. Modeling sedimentary processes that form these turbidites enables the calculation of properties such as extent, depth, porosity and permeability of hydrocarbon-bearing reservoirs. This paper estimates the extent and thickness of turbidites from the initial conditions of the turbidity flow. This is achieved by the application of scaling analysis of the partial differential equations that govern the dynamics of and deposition from turbidity currents. We apply the results of scaling analysis to five modern submarine fans. The predicted and actual values of the dimensions of the fan deposits match well. We then compare the derived results against tabulated sizes of ancient turbidites. The comparisons are good as long as we correctly identify the flow regimes in which the deposition took place. The good agreements observed in the two cases show that the estimates obtained using scaling analysis can provide useful first-guess values for the dimensions of the deposits. 相似文献
40.
Temperature data at different layers of the past 45 years were studied and we found adiploe mode in the thermocline layer (DMT): anomalously cold sea temperature off the coast of Sumatra and warm sea temperature in the western Indian Ocean. First, we analyzed the temperature and the temperature anomaly (TA) along the equatorial Indian Ocean in different layers. This shows that stronger cold and warm TA signals appeared at subsurface than at the surface in the tropical Indian O-cean. This result shows that there may be a strong dipole mode pattern in the subsurface tropical Indian Ocean. Secondly we used Empirical Orthogonal Functions (EOF) to analyze the TA at thermocline layer. The first EOF pattern was a dipole mode pattern. Finally we analyzed the correlations between DMT and surface tropical dipole mode (SDM), DMT and Nino 3 SSTA, etc. and these correlations are strong. 相似文献