全文获取类型
收费全文 | 29644篇 |
免费 | 5345篇 |
国内免费 | 7080篇 |
专业分类
测绘学 | 1295篇 |
大气科学 | 6679篇 |
地球物理 | 7626篇 |
地质学 | 14941篇 |
海洋学 | 3458篇 |
天文学 | 1456篇 |
综合类 | 3289篇 |
自然地理 | 3325篇 |
出版年
2024年 | 120篇 |
2023年 | 538篇 |
2022年 | 1224篇 |
2021年 | 1477篇 |
2020年 | 1265篇 |
2019年 | 1308篇 |
2018年 | 1605篇 |
2017年 | 1473篇 |
2016年 | 1709篇 |
2015年 | 1306篇 |
2014年 | 1806篇 |
2013年 | 1562篇 |
2012年 | 1496篇 |
2011年 | 1552篇 |
2010年 | 1692篇 |
2009年 | 1691篇 |
2008年 | 1441篇 |
2007年 | 1399篇 |
2006年 | 1175篇 |
2005年 | 1067篇 |
2004年 | 861篇 |
2003年 | 860篇 |
2002年 | 859篇 |
2001年 | 810篇 |
2000年 | 1014篇 |
1999年 | 1455篇 |
1998年 | 1226篇 |
1997年 | 1305篇 |
1996年 | 1085篇 |
1995年 | 1000篇 |
1994年 | 897篇 |
1993年 | 784篇 |
1992年 | 638篇 |
1991年 | 464篇 |
1990年 | 317篇 |
1989年 | 348篇 |
1988年 | 291篇 |
1987年 | 199篇 |
1986年 | 165篇 |
1985年 | 121篇 |
1984年 | 100篇 |
1983年 | 78篇 |
1982年 | 76篇 |
1981年 | 54篇 |
1980年 | 50篇 |
1979年 | 31篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1958年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Zhao Kang Zhou Yun Yu Xiang Yan Yajing Song Yufeng Wang Junqiang Suo Tianyuan Guo Xiao 《Natural Resources Research》2021,30(5):3839-3852
Natural Resources Research - Depletion of shallow mineral resources caused by deep mining has become an inevitable trend, and deep mining can increase safety accidents and geological hazards.... 相似文献
182.
研究了麻城地区重、磁异常场特征,经反演计算获得了深部结构特征。对重力布格异常利用Parker-Oldenburg快速位场反演方法计算出莫霍面的展布,对航磁异常利用对数功率谱法和矩谱法计算出居里面深度。在此基础上,探讨该震区深部蕴震条件。主要结论是:①麻城-团凤断裂带为该区切割较深的主要控震构造;②1932年麻城6.0级地震发生在区域重力异常等值线梯度最大处,磁力异常区两局部正异常间的低值带,莫霍面及居里面隆起区边缘;③发震部位有其特定的深部蕴震构造及应力蕴震条件。 相似文献
183.
Rapid urbanization results in the conversion of natural soil to urban soil,and consequently,the storage and density of the soil carbon pools change.Taking Chongqing Municipality of China as a study case,this investigation attempts to better understand soil carbon pools in hilly cities.First,the vegetated areas in the study area were derived from QuickBird images.Then,topsoil data from 220 soil samples(0-20 cm) in the vegetated areas were collected and their soil organic carbon(SOC) densities were analyzed.Using the Kriging interpolation method,the spatial pattern of SOC was estimated.The results show that the SOC density exhibited high spatial variability in the urban topsoil of Chongqing.First,the SOC density in topsoil decreased according to slope in the order 2°-6° < 25°-90° < 0°-2° < 6°-15° < 15°-25°.Second,the newly developed areas during 2001-2010 had a lower SOC density than the areas built before 1988.Third,urban parks and gardens had a higher SOC density in topsoil,residential green land followed,and scattered street green land ranked last.For hilly cities,the variability of terrain affects the distribution of SOC.The Kriging results indicate that Kriging method combining slope with SOC density produced a high level of accuracy.The Kriging results show that the SOC density to the north of the Jialing River was higher than the south.The vegetated areas were estimated to amount to 73.5 km2 across the study area with an SOC storage of 0.192 Tg and an average density of 2.61 kg/m2. 相似文献
184.
INTRODUCTIONAntarctickrill(EuphausiasuperbaDana)isakeyorganismoftheAntarcticmarineecosystemandapotentialfisheryresource.Ithasbeenthesubjectofmuchresearch.Despitethelonghistoryofresearchdatingbacktothe1930’s,therearestillquestionsaboutitspopulationstructu… 相似文献
185.
The gravity inversion is to restore genetic density distribution of the underground target to be explored for explaining the internal structure and distribution... 相似文献
186.
187.
A type IV radio burst accompanied by several normal- and reverse-drifting type III bursts, multiple long-term quasi-periodic pulsations and spikes was observed with the radio spectrometers (1.0–2.0 and 2.6–3.8 GHz) at National Astronomical Observatories of China (NAOC) on 23 September 1998. In combination with the images of Siberian Solar Radio Telescope (SSRT) of Russia, the complex and multiple magnetic structures inferred from the radio bursts reveal the existence of both large-scale and small-scale magnetic structures. This event suggests that the geometries of coronal magnetic fields contain multiple discrete electron acceleration/injection sites at different heights, and extended open and closed magnetic field lines. It can be shown that the energetic electrons gain access to open, diverging and closed field lines thus producing different types of radio bursts. From the characteristics of position, polarization, dispersion and displacement of the sources, the model of the type IV event is supported, which involves synchrotron emission from the electrons confined by the rapid scattering through the interaction of hydromagnetic wave with particles. 相似文献
188.
Identification of the “source” and “sink” patterns influencing non-point source pollution in the Three Gorges Reservoir Area 总被引:6,自引:0,他引:6
Non-point source pollution is one of the primarily ecological issues affecting the Three Gorges Reservoir Area. In this paper, landscape resistance and motivation coefficient, which integrated various landscape elements, such as land use, soil, hydrology, topography, and vegetation, was established based on the effects of large-scale resistance and motivation on the formation of non-point source pollution. In addition, cost models of the landscape resistance and motivation coefficients were constructed based on the distances from the landscape units to the sub-basin outlets in order to identify the “source” and “sink” patterns affecting the formation of non-point source pollution. The results indicated that the changes in the landscape resistance and motivation coefficients of the 16 sub-basins exhibited inverse relationships to their spatial distributions. The landscape resistance and motivation cost curves were more volatile than the landscape resistance and motivation coefficient curves. The landscape resistance and motivation cost trends of the 16 sub-basins became increasingly apparent along the flow of the Yangtze River. The landscape resistance and motivation cost models proposed in this paper could be used to identify large-scale non-point source pollution “source” and “sink” patterns. Moreover, the proposed model could be used to describe the large-scale spatial characteristics of non-point source pollution formation based on “source” and “sink” landscape pattern indices, spatial localization, and landscape resistance and motivation coefficients. 相似文献
189.
基于2005~2015年全国统计年鉴数据,采用统计地图法和空间自相关分析,分析中国高校科研人才的时空分布特征(不包括港澳台数据),并采用面板负二项回归模型,识别高校科研人才空间分布的决定因素。研究结果表明:①中国的高校科研人才分布表现出较强的空间不均衡性,总体趋势为东南密集,西北稀疏,科研人才高度集中在北京、天津、上海;②高校科研人才分布具有一定的空间集聚特征,其热点地区为北京、天津、上海和江苏等沿海省市,冷点地区集中分布在广大的西部地区和黑龙江省。2005~2015年,高级职称人才的空间集聚程度有所减弱,而中初级职称科研人才的空间集聚程度有所加强;③人才政策、高等教育规模和层次、公共服务水平和信息化水平是所有高校科研人才空间分布的主要影响因素。从职称差异的角度来看,薪酬和失业率等经济因素仅对初级职称科研人才的分布有影响,医疗、文化公共服务水平和人才政策仅对中高级职称科研人才的分布有影响,高等教育的规模与层次对各种职称人才的分布均有影响;从地区差异的角度来看,西部地区高校科研人才受到经济因素影响更为明显,而中东部高校科研人才受到公共服务水平影响的更为明显。 相似文献
190.
Based on the NCEP (National Centers for Environmental Prediction) data, the relationship between the Sea Surface Temperature
Anomalies (SSTAs) in the North Pacific and the atmospheric circulation anomalies in January 2008 is analyzed in this study.
The SSTA mode most correlated with the Geopotential Height anomalies (GHAs) in January 2008 in the North Pacific exhibited
a basin-wide horseshoe pattern with a warm center in November 2007. This persistent SSTA pattern would induce positive GHAs
in the Aleutian Low area and East Asia and the northward extension of the West Pacific Subtropical High in January 2008 by
maximum diabatic heating in the atmosphere over the Kuroshio Oyashio Extension (KOE) area, leading to the occurence of the
circumpolar trough-ridge wave train anomaly in January 2008. 相似文献