全文获取类型
收费全文 | 9367篇 |
免费 | 1095篇 |
国内免费 | 3524篇 |
专业分类
测绘学 | 476篇 |
大气科学 | 1672篇 |
地球物理 | 3145篇 |
地质学 | 5497篇 |
海洋学 | 976篇 |
天文学 | 404篇 |
综合类 | 694篇 |
自然地理 | 1122篇 |
出版年
2024年 | 65篇 |
2023年 | 178篇 |
2022年 | 119篇 |
2021年 | 197篇 |
2020年 | 80篇 |
2019年 | 132篇 |
2018年 | 183篇 |
2017年 | 63篇 |
2016年 | 151篇 |
2015年 | 148篇 |
2014年 | 257篇 |
2013年 | 247篇 |
2012年 | 301篇 |
2011年 | 375篇 |
2010年 | 211篇 |
2009年 | 289篇 |
2008年 | 311篇 |
2007年 | 429篇 |
2006年 | 486篇 |
2005年 | 554篇 |
2004年 | 538篇 |
2003年 | 379篇 |
2002年 | 442篇 |
2001年 | 482篇 |
2000年 | 512篇 |
1999年 | 232篇 |
1998年 | 175篇 |
1997年 | 192篇 |
1996年 | 164篇 |
1995年 | 211篇 |
1994年 | 184篇 |
1993年 | 382篇 |
1992年 | 341篇 |
1991年 | 432篇 |
1990年 | 380篇 |
1989年 | 422篇 |
1988年 | 444篇 |
1987年 | 372篇 |
1986年 | 261篇 |
1985年 | 357篇 |
1984年 | 294篇 |
1983年 | 218篇 |
1982年 | 170篇 |
1981年 | 121篇 |
1980年 | 173篇 |
1964年 | 89篇 |
1960年 | 52篇 |
1959年 | 108篇 |
1958年 | 120篇 |
1957年 | 127篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
Ruiz F 《Marine pollution bulletin》2001,42(6):482-490
The impact of river-transported metal pollution and industrial wastes on the metal distribution (Cr, Cu, Zn, Pb) in estuarine sediments was studied in the southwestern Spanish estuaries. Intertidal and subtidal surface sediments of the Tinto-Odiel Estuary are very highly polluted by heavy metals, with geoaccumulation indices up to 4 in the three sedimentary environments studied (channel, channel border and salt marsh). The single exception is the Punta Umbria channel, very protected from the point sources by salt marsh deposits and hydraulic processes. In the remaining two estuaries, pollution (Pb, Cu) was only significant near the harbour situated in the Piedras river mouth, whereas very low values were found in the Guadiana Estuary. In these last rivers, the enrichment factor increases from the channel to the salt marsh sediments. 相似文献
992.
Hydrocarbons in surface sediments from the Changjiang (Yangtze River) Estuary, East China Sea 总被引:9,自引:0,他引:9
Sedimentary aliphatic (AH) and polycyclic aromatic hydrocarbons (PAHs) were studied in the Changjiang Estuary and the adjacent East China Sea. Total AH ranged from 2.20 to 11.82 μg g−1 and consisted of n-alkanes and a dominant petroleum-related unresolved complex mixture (UCM). Within the n-alkanes, terrestrial plant wax compounds prevailed at nearly all stations. Of the PAHs, biogenic perylene dominated at stations receiving riverine inputs. Anthropogenic PAHs originating from combustion/pyrolysis processes varied from 17 to 157 ng g−1, while fossil PAH concentrations ranged from 42 to 187 ng g−1. Both biogenic and anthropogenic hydrocarbons are primarily derived from riverine discharges and accumulate at shallow-water stations. Distinct phase associations lead, nevertheless, to different sedimentation patterns. Fossil PAHs are enhanced at offshore stations where they are introduced directly by shipping activities. Biomarker fingerprints ascribe their source to Chinese crude oils. The overall levels of anthropogenic hydrocarbons are low compared to relevant areas worldwide and reveal a low/moderate level of hydrocarbon pollution. 相似文献
993.
JIANG Yao-hui YANG Wanzhi State Key Laboratory for Mineral Deposits Research Department of Earth Sciences Nanjing University Nanjing Nanjing Institute of Geology Mineral Resources Ministry of Land Resource. Nanjing Xinjian 《Continental Dynamics》2001,(2)
l. IntroductionGranite distributes widely in western KunlunMts. Many researches have been conducted byscientists (Wang Yuzhen et.al., l987; Zhang Yuquanet.al., l989, Fang Xilian et.al., I990, Jiang Chunfaet.al., 1992; Pan Yusheng, l992, Xu Ronghua et.al.,l 994; Jing Daogui et.al., l996, Zhang Yuquan et.al.,l998). But all of the researches have been donealong Sino-Pakistan road and Xinjiang-Tibet roadt"ith fOcus on isotopic dating of the intrusion andconducted a few on origin and tect… 相似文献
994.
The Relative Impact of Regional Scale Land Cover Change and Increasing CO2 over China 总被引:2,自引:0,他引:2
A series of 17-yr equilibrium simulations using the NCAR CCM3 (T42 resolution) were performed to investigate the regional scale impacts of land cover change and increasing CO2 over China. Simulations with natural and current land cover at CO2 levels of 280,355, 430, and 505 ppmv were conducted. Results show statistically significant changes in major climate fields (e.g. temperature and surface wind speed) on a 15-yr average following land cover change. We also found increases in the maximum temperature and in the diurnal temperature range due to land cover change. Increases in CO2 affect both the maximum and minimum temperature so that changes in the diurnal range are small. Both land cover change and CO2 change also impact the frequency distribution of precipitation with increasing CO2 tending to lead to more intense precipitation and land cover change leading to less intense precipitation-indeed, the impact of land cover change typically had the opposite effect versus the impacts of CO2. Our results provide support for the inclusion of future land cover change scenarios in long-term transitory climate inodelling experiments of the 21st Century. Our results also support the inclusion of land surface models that can represent future land cover changes resulting from an ecological response to natural climate variability or increasing CO2. Overall, we show that land cover change can have a significant impact on the regional scale climate of China, and that regionally, this impact is of a similar magnitude to increases in CO2 of up to about 430 ppmv. This means that that the impact of land cover change must be accounted for in detection and attribution studies over China. 相似文献
995.
94;1;F;H;H124_1;F094_1;苑杰;53-60清代东北马政探析王颖超;北京师范大学文学院 北京100875清代;;东北;;马政;;大凌河马场;;驿站清政府在东北实施的一系列与马有关的制度主要包括大凌河马场的设立和驿站、驿马的设置。顺治五年,清政府为了征战之需,在东北辽西设立大凌河马场,马场对维护和巩固清统治者的地位起到了重要的军事作用。清代末期,由于清政 相似文献
996.
Boubacar KANE Pierre Y. JULIEN 《国际泥沙研究》2007,22(2):114-119
An extensive database of reservoir sedimentation surveys throughout continental United States is compiled and analyzed to determine specific degradation SD relationships as function of mean annual rainfall R, drainage area A, and watershed slope S. The database contains 1463 field measurements and specific degradation relationships are defined as function of A, R and S. Weak trends and significant variability in the data are noticeable. Specific degradation measurements are log normally distributed with respect to R, A, and S and 95% confidence intervals are determined accordingly. The accuracy of the predictions does not significantly increase as more independent variables are added to the regression analyses. 相似文献
997.
W. R. OSTERKAMP J. R. GRAY J. B. LARONNE J. R. MARTIN 《国际泥沙研究》2007,22(3):238-246
A "Watershed-Scale Sediment Information Network" (WaSSIN), designed to complement UNESCO’s International Sedimentation Initiative, was endorsed as an initial project by the World Association for Sedimentation and Erosion Research. WaSSIN is to address global fluvial-sediment information needs through a network approach based on consistent protocols for the collection, analysis, and storage of fluvial-sediment and ancillary information at smaller spatial scales than those of the International Sedimentation Initiative. As a second step of implementation, it is proposed herein that the WaSSIN have a general structure of two components, (1) monitoring and data acquisition and (2) research. Monitoring is to be conducted in small watersheds, each of which has an established database for discharge of water and suspended sediment and possibly for bed load, bed material, and bed topography. Ideally, documented protocols have been used for collecting, analyzing, storing, and sharing the derivative data. The research component is to continue the collection and interpretation of data, to compare those data among candidate watersheds, and to determine gradients of fluxes and processes among the selected watersheds. To define gradients and evaluate processes, the initial watersheds will have several common attributes. Watersheds of the first group will be: (1) six to ten in number, (2) less than 1000 km2 in area, (3) generally in mid-latitudes of continents, and (4) of semiarid climate. Potential candidate watersheds presently include the Weany Creek Basin, northeastern Australia, the Zhi Fanggou catchment, northern China, the Eshtemoa Watershed, southern Israel, the Metsemotlhaba River Basin, Botswana, the Aiuaba Experimental Basin, Brazil, and the Walnut Gulch Experimental Watershed, southwestern United States. 相似文献
998.
The mean value concept in mono-linear regression of multi-variables and its application to trace studies in geosciences 总被引:1,自引:1,他引:1
A J T JULL 《中国科学D辑(英文版)》2007,50(12):1828-1834
The "mean value concept" in a mono-linear regression of multi-variables is clarified.Its applications to reconstruction of the past 90-year salinity of the sea surface water in Xisha Islands and to tracing the past 80 ka paleo-geomagnetic events from the Luochuan loess 10Be record are introduced in detail,which show the significance and the potential of the "mean value concept" in geoscience research. 相似文献
999.
1000.