全文获取类型
收费全文 | 35789篇 |
免费 | 7235篇 |
国内免费 | 12618篇 |
专业分类
测绘学 | 4358篇 |
大气科学 | 4538篇 |
地球物理 | 5989篇 |
地质学 | 30418篇 |
海洋学 | 3470篇 |
天文学 | 231篇 |
综合类 | 3034篇 |
自然地理 | 3604篇 |
出版年
2024年 | 183篇 |
2023年 | 563篇 |
2022年 | 1264篇 |
2021年 | 1521篇 |
2020年 | 1594篇 |
2019年 | 2005篇 |
2018年 | 1629篇 |
2017年 | 1957篇 |
2016年 | 2155篇 |
2015年 | 2225篇 |
2014年 | 2722篇 |
2013年 | 2658篇 |
2012年 | 2800篇 |
2011年 | 2779篇 |
2010年 | 2339篇 |
2009年 | 2334篇 |
2008年 | 2288篇 |
2007年 | 2487篇 |
2006年 | 2306篇 |
2005年 | 2056篇 |
2004年 | 1907篇 |
2003年 | 1652篇 |
2002年 | 1534篇 |
2001年 | 1464篇 |
2000年 | 1335篇 |
1999年 | 1236篇 |
1998年 | 1152篇 |
1997年 | 1041篇 |
1996年 | 931篇 |
1995年 | 772篇 |
1994年 | 672篇 |
1993年 | 529篇 |
1992年 | 400篇 |
1991年 | 327篇 |
1990年 | 202篇 |
1989年 | 176篇 |
1988年 | 149篇 |
1987年 | 102篇 |
1986年 | 65篇 |
1985年 | 42篇 |
1984年 | 18篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1972年 | 2篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
论述了在县域内实行矿产资源的统一规划、统一勘探、统一开发的重要性;实现公益性地质矿产调查与商业性地质勘查工作分制运行,以加强矿产资源调查评价与勘查,进而为县域经济可持续发展提供矿产资源保障。 相似文献
993.
994.
Aldar P. Gorbunov 《冰川冻土》2004,26(Z1):197-200
The coarse-detrital deposits have the properties of cold accumulation and maintenance of cold for a long time. Now, at some place where the mean annual temperature of air is positive, one even can get the permafrost by artificial formation of the burial mound. According to these properties, some lowenergy storehouses are built for various purposes. 相似文献
995.
本文在青藏铁路区域水文地质调查工作的基础上,以系统理论的基本原理为出发点,利用地下水系统数值模型的运行,来对拉萨城市地下水系统可开采资源进行评价,取得了比较理想的结果. 相似文献
996.
Beamer Rock, a 50-m-wide island in the Firth of Forth, produces a distinctive von Kármán vortex street wake, the characteristics of which depend on the speed and direction of the tidal flow. ADCP (acoustic Doppler current profiler), CTD (conductivity–temperature–depth) and aerial photograph data were collected from the region during flood and ebb tidal flow under neap and spring conditions. Good agreement was found between the observations and the results from a fixed-grid depth-averaged numerical tidal model. The island wake parameter correctly predicted the unsteady nature of the wake, and the Strouhal number (defined in terms of flow past a circular cylinder) was found to give excellent predictions of the wake wavelength when scaled on the island width. Contrary to published results, the study shows that it is possible to accurately simulate an unsteady island wake using a relatively coarse fixed-grid numerical model.Responsible Editor: Jens Kappenberg 相似文献
997.
Water-level fluctuations may be used to promote the expansion of emergent vegetation along lakeshores. We present the case of the lake Volkerak-Zoommeer in the Netherlands, a fresh-water lake created in 1987 after the enclosure of an estuary. Using an experimental area in which the water level could be manipulated, it was shown that partial summer drawdown of the shoreline created suitable conditions for germination and growth of tall emergent species (in particular Phragmites australis). Plant survival and growth depended on subsequent water-level fluctuations and grazing by waterbirds. Based on the experiment and empirical data, a model was developed to predict the effects of the water-level regime on potential reed bed development. The model was applied for four hydrological scenarios that have been considered for the water-level management of the lake. 相似文献
998.
IntroductionItisdefinitelystipulatedintheLawofthePeople'sRepublicofChinaonProtectingagainstandMitigatingEarthquakeDisastersthattheseismicsafetyevaluationmustbemadeformajorprojects(includinglifelineprojects)and,accordingtotheresultsobtained,theseismicresistancerequirementsshouldbedetermined.Thenecessityofseismicsafetyevaluationhasbeenrecog-nizedgradually,butthetopicontheeffectofsafetyevaluationhasnotbeenreferredmuch.Gener-allyspeaking,althoughmostpeopleapprovethesocialeffectofsafetyevaluatio… 相似文献
999.
IntroductionWhenpropagatingthroughananisotropicmedium,ashearwavesplitsintotwo(quasi)shearwaveswithdifferentpropagationspeedsandpolarizedorthogonally.Owingtotherecentdevel-opmentofseismicobservationsystem,detectionofshearwavessplittingwithverysmalldelaytimesbetweenfasterandslowershearwavesbecameavailableandprovidedpowerfulapproachfordetectionofcrustalanisotropy.Crampin(1978)emphasizedtheroleofalignedmicrocracksasacauseofcrustalanisotropyandpointedoutthatforverticallyalignedmicrocracksthedirecti… 相似文献
1000.
Introduction Sichuan-Yunnan region is a major area with frequent strong earthquakes in Chinese mainland, especially the middle-southern segment of South-North Seismic Zone, where many strong earth-quakes occurred in history. In the past 30 years, Sichuan-Yunnan region has two seismically active periods: one is from Tonghai earthquake in 1970 to Longling-Songpan earthquake in 1976, the other is from Lancang earthquake in 1988 to now. During this two periods, the M=7.7 Tonghai, M=7.1 Dagua… 相似文献