全文获取类型
收费全文 | 12603篇 |
免费 | 1950篇 |
国内免费 | 3154篇 |
专业分类
测绘学 | 347篇 |
大气科学 | 1570篇 |
地球物理 | 2708篇 |
地质学 | 4229篇 |
海洋学 | 5805篇 |
天文学 | 127篇 |
综合类 | 862篇 |
自然地理 | 2059篇 |
出版年
2024年 | 40篇 |
2023年 | 112篇 |
2022年 | 398篇 |
2021年 | 444篇 |
2020年 | 423篇 |
2019年 | 536篇 |
2018年 | 451篇 |
2017年 | 520篇 |
2016年 | 460篇 |
2015年 | 534篇 |
2014年 | 753篇 |
2013年 | 806篇 |
2012年 | 687篇 |
2011年 | 791篇 |
2010年 | 670篇 |
2009年 | 938篇 |
2008年 | 854篇 |
2007年 | 927篇 |
2006年 | 853篇 |
2005年 | 804篇 |
2004年 | 740篇 |
2003年 | 632篇 |
2002年 | 605篇 |
2001年 | 491篇 |
2000年 | 459篇 |
1999年 | 430篇 |
1998年 | 365篇 |
1997年 | 325篇 |
1996年 | 296篇 |
1995年 | 249篇 |
1994年 | 266篇 |
1993年 | 200篇 |
1992年 | 164篇 |
1991年 | 104篇 |
1990年 | 74篇 |
1989年 | 106篇 |
1988年 | 42篇 |
1987年 | 30篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 18篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
ABSTRACTThe purpose of this study is to examine local level spatiotemporal rainfall and temperature variability in drought-prone districts of rural Sidama, Central Rift Valley region of Ethiopia. The study used 129 gridded monthly rainfall and temperature data of 32 years (1983–2014). The gridded rainfall and temperature records were encoded into GIS software and evaluated through different statistical and geospatial techniques. Mann-Kendal rank test and F distribution tests were used to test temporal and spatial statistical significance, respectively, of the data. The analysis revealed that Belg and Kiremt are the main rainfall seasons, constituting 81% of the annual rainfall. Although annual, Kiremt, and Belg rainfall amounts appear to have decreased over time, the decreasing trend is statistically significant only for Belg rainfall records. On the other hand, rainfall standard anomaly results indicated seven droughts of different magnitudes: one extreme, two severe, and four moderate. The study also revealed increasing temperature trends over the years under consideration that are statistically significant. The findings of this study on rainfall contradict other findings obtained around the study area. Thus, climate change adaptations need to focus on location-specific climate data analysis so that the intended adaptive interventions can be successful. 相似文献
2.
唐森铭 《中国海洋湖沼学报》2002,(1)
INTRODUCTIONThemainpurposeofthisstudywastodeterminethemagnitudeandfrequencyofharmfuldiatomanddinoflagellateoutbreaksinHongKong’swesternandeasternwaters (e .g.LammaStraitsandPortShelterrespectively)fortheperiodJanuary 1 997toDecember1 999.Thiswasdoneinordertod… 相似文献
3.
本文简要介绍了陆地系列地球资源卫星的轨道特征,并以陆地—5号资源卫星为例,根据南山站的座标计算出该站对陆地—5号资源卫星的可观测范围及以该站为中心的卫星的覆盖区域。 相似文献
4.
Himmerfjärd is a Swedish estuary bordering on the Baltic. The estuary lacks astronomical tides and its circulation is driven by winds and freshwater runoff. Because of a tertiary sewage treatment plant located at its inner end, the estuary is becoming increasingly eutrophic. A field study was carried out for a 78-day period in late summer and early fall of 1977 to determine rates of nutrient transport and to construct nutrient budgets. Since physical parameters (current velocity, temperature, salinity, winds and water level changes) were measured more frequently than nutrients (phosphate, nitrate, nitrite and ammonium) it was necessary to develop a suitable method to calculate nutrient flux time series and net nutrient fluxes. Over the study period, Himmerfjärd imported phosphorus and exported nitrogen. Direction of nutrient fluxes and changes in flux direction were consistent with the structure of the baroclinic currents. 相似文献
5.
JINFeng-jun 《中国地理科学(英文版)》2003,13(2):97-103
It is very important to establish cooperative mechanism to guarantee all members to develop their e-conomies in the Yellow Sea Rim. In this paper, the development strategies ofshipplng centers and transportation networkare discussed based on economic giobalization tendency. The results argue that a united transportation network should bebuilt in order to promote the economic competition of Northeast Asia in the world. As a key component of the economiccooperation, a hierarchical shipping centers network should be established with Hong Kong, Shanghai, Pusan, Koho,and Tokyo as cores. The authorities of China, Japan, R. O. Korea and D. P. B. Korea should make more efforts tobuild a set of cooperation institutions based on raising the transportation efficiency. 相似文献
6.
MEN Wu ) WEI Hao ) and LIU Guangshan ) * ) College of Oceanography Environmental Science Xiamen University State Key Laboratory of Marine Environmental Science 《中国海洋大学学报(英文版)》2006,5(3):228-234
1Introduction Therearefourradiumisotopesinnature,ofwhich224Ra,226Raand228Rahavebeenwidelyinvestigated inmarineresearch,butthespecificactivityof223Rais toolowtobemeasured,therefore,itsapplicationsarelimited(Moore,1969;Broeckeretal.,1976;KuandLin,1976;Nozak… 相似文献
7.
昆仑山口大地震与地形变异常的讨论 总被引:7,自引:5,他引:2
针对昆仑山口大地震,总结了多种地形变(大地测量)手段所显示的异常变化及其时空分布,结果显示:8.1级大震前存在空间尺度大,时间尺度的地形变前兆异常,简要介绍了相关的异常图像,给出了初步解释,并对未来震情的发展进行了探讨,认为近期内强震活动向华北迁移的可能性不大。 相似文献
8.
Pco2 of air and seawater samples from the East China Sea(ECS) were measured in situ in autumn, 1994,Ocean currents,terrestrial fluviation,biological activities,etc.,Pco2 char-acters in air and seawater were investigated,CO2 flux and its character in the East China Sea are discussed on the basis of the Pco2 profiles of air and seawater,It was clear that the nearshore was the source of CO2;and tht the oulter sea area was the sink of CO2; and that the shelf area of the EXS is a net sink for atmospheric CO2 in autumn. 相似文献
9.
从地形地貌特征、重磁地球物理场、深部构造与断裂构造以及地震活动、震源机制等多方面论述北东东向构造是南海北缘的主要活动构造。对于长期以来认为新华夏系北东向构造是该区主要活动构造的观点来说,这是一种新的学术思想。 相似文献
10.
本文使用红外天文卫星(IRAS)巡天数据的最新版本IRAS天空巡天图(ISSA),经过进一步处理,得到了S140S141和S142SharplessHII区-分子云复合体的红外发射强度、温度及其光深的分布.在此基础上对各HII区的一些物理参量进行了统计分析,得到了分子云复合体的红外发射总光度以及复合体中尘埃的分布情况,对小尺度尘埃(VSG)的丰度进行了分析.并对各恒星形成区中的致密团块进行了研究,揭示出其中一些可能的恒星形成区域.同时,对S140区中的有关红外点源作出了能谱分析,并对S141区的激发星进行了讨论. 相似文献