全文获取类型
收费全文 | 7147篇 |
免费 | 680篇 |
国内免费 | 274篇 |
专业分类
测绘学 | 438篇 |
大气科学 | 788篇 |
地球物理 | 2280篇 |
地质学 | 2966篇 |
海洋学 | 456篇 |
天文学 | 555篇 |
综合类 | 259篇 |
自然地理 | 359篇 |
出版年
2022年 | 37篇 |
2021年 | 62篇 |
2020年 | 44篇 |
2019年 | 55篇 |
2018年 | 485篇 |
2017年 | 443篇 |
2016年 | 337篇 |
2015年 | 204篇 |
2014年 | 192篇 |
2013年 | 255篇 |
2012年 | 727篇 |
2011年 | 504篇 |
2010年 | 178篇 |
2009年 | 212篇 |
2008年 | 184篇 |
2007年 | 179篇 |
2006年 | 194篇 |
2005年 | 881篇 |
2004年 | 922篇 |
2003年 | 690篇 |
2002年 | 219篇 |
2001年 | 119篇 |
2000年 | 90篇 |
1999年 | 68篇 |
1998年 | 48篇 |
1997年 | 63篇 |
1996年 | 48篇 |
1995年 | 25篇 |
1994年 | 28篇 |
1993年 | 24篇 |
1992年 | 25篇 |
1991年 | 31篇 |
1990年 | 38篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 33篇 |
1986年 | 24篇 |
1985年 | 28篇 |
1984年 | 29篇 |
1983年 | 27篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 22篇 |
1978年 | 17篇 |
1976年 | 16篇 |
1975年 | 20篇 |
1973年 | 25篇 |
1972年 | 16篇 |
1971年 | 22篇 |
排序方式: 共有8101条查询结果,搜索用时 93 毫秒
71.
72.
韧性剪切变形对岩石地球化学行为的制约——以北阿尔金巴什考供韧性剪切带为例 总被引:6,自引:0,他引:6
韧性剪切变形对岩石地球化学行为的制约一直是地质学家们探讨的课题。本文以构成北阿尔金红柳沟——拉配泉俯冲碰撞杂岩带与北阿尔金地块边界的巴什考供斜向逆冲型韧性剪切带为例,通过对韧性剪切带内花岗岩变形前后不同变形强度构造岩的地球化学组成进行对比,确定等比线斜率,探讨韧性变形对岩石体积和成分变异的影响。计算结果表明,在糜棱岩化过程中,糜棱岩化花岗岩体积亏损21%,花岗质糜棱岩体积亏损31%。质量平衡计算结果和等比线图表明,韧;陛剪切作用导致SiO2,流失量最大,A12O3、K2O及Ba、Rb、Sr等都有不同程度的丢失,显示出较强的活动性,MnO、P2O5、Sc位于等比线上或附近,表现出相对的稳定性。岩石中活动组分的变异是流体渗滤作用引起的,不活动组分的变异是体.积亏损造成的。 相似文献
73.
Rao N.S. Ali M.M. Rao M.V. Ramana I.V. 《Geoscience and Remote Sensing Letters, IEEE》2005,2(4):437-439
Detection of ships and their tracks in the atmosphere from satellites was earlier demonstrated by Porch, Noone, and Kaufman, among others. In this letter, we have gone one step further to estimate the ship speed and direction by locating them and their tracks from multisatellite imagery. Exhausts from the ships create streaks of clouds in the atmosphere that help identify the same ship from two satellites. Ship velocities are estimated from displacements of ships. We have used optical sensors data from Moderate Resolution Imaging Spectroradiometer (MODIS) and Ocean Color Monitor (OCM) to demonstrate this technique. Estimated velocities of ships are within the expected range. Application of this approach has general interest to the navy, coast guards, shipping corporations, commercial ship owners, and fishermen. More satellite observations can be used to continuously monitor the ship velocities. 相似文献
74.
Check dam positioning by prioritization of micro-watersheds using SYI model and morphometric analysis — Remote sensing and GIS perspective 总被引:5,自引:0,他引:5
K. Nooka Ratnam Y. K. Srivastava V. Venkateswara Rao E. Amminedu K. S. R. Murthy 《Journal of the Indian Society of Remote Sensing》2005,33(1):25-38
Sediment Yield Index (SYI) model and results of morphometric analysis have been used to prioritize watersheds and to locate
sites for checkdam positioning in Tarafeni watershed in Midnapur district. West Bengal. Various thematic maps such as land
use/land cover, slope, drainage, soil etc. were prepared from 1RS ID LISS III digital data, SOI toposheets of 1:50,000 scale
and other reference maps. Morphometric parameters such as bifurcation ratio (Rb). drainage density (Dd), texture ratio (T), length of overland flow (Lo), stream frequency (Fu), compactness coefficient (Cc), circularity ratio (Rc), elongation ratio (Er), shape factor (Bs) and form factor (Rf) were computed. Automated demarcation of prioritization of micro-watersheds was done by using GIS overlaying technique by
assigning weight factors to all the identified features in each thematic map and ranks were assigned to the morphometric parameters.
Five categories of priority viz., very high, high, medium, low and very low, were given to all the watersheds in both the
methods. Sixty-two micro-watersheds using SYI method and twenty-three micro-watersheds using morphometric have been prioritized
as very high priority. Final priority map was prepared by considering the commonly occurred very high-prioritized micro-watersheds
in both SYI model and morphometric analysis. Twenty-four suitable sites were identified for check dam construction in 21 highly
prioritized watersheds. It is proved that integrated study of SYI model and morphometric analysis yield good result in prioritization
of watersheds. 相似文献
75.
Mohamed M. Hantush Rao. S. Govindaraju Miguel A. Marioand Zhonglong Zhang 《Journal of Hydrology》2002,260(1-4):58-74
This paper develops mass fraction models for transport and fate of agricultural pollutants in structured two-region soils. Mass fraction index models, based on a semi-infinite domain solution, are derived that describe leaching at depth, vapor losses through soil surface, absorption, and degradation in the dynamic- and stagnant-water soil regions. The models predict that leaching is the result of the combined effect of the upward vapor-phase transport relative to downward advection, residence time relative to half-life, dispersion, and lateral diffusive mass transfer. Simulations show that leached fraction of volatile compounds does not always decrease monotonically with increased residence time relative to the pollutant half-life, as a result of complex interactions among the different physical and biochemical processes. The results show that leaching, volatilization, and degradation losses can be affected significantly by lateral diffusive mass transfer into immobile-water regions and advection relative to dispersion (i.e. Peclet number) in the mobile-water regions. It is shown that solute diffusion into the immobile phase and subsequent biochemical decay reduces leaching and vapor losses through soil surface. Potential use of the modified leaching index for the screening of selected pesticides is illustrated for different soil textures and infiltration rates. The analysis may be useful to the management of pesticides and the design of landfills. 相似文献
76.
Gravity and magnetic signatures of volcanic plugs related to Deccan volcanism in Saurashtra, India and their physical and geochemical properties 总被引:1,自引:0,他引:1
D.V. ChandrasekharD.C. Mishra G.V.S. Poornachandra RaoJ. Mallikharjuna Rao 《Earth and Planetary Science Letters》2002,201(2):277-292
The Bouguer anomaly and the total intensity magnetic maps of Saurashtra have delineated six circular gravity highs and magnetic anomalies of 40-60 mGal (10−5m/s2) and 800-1000 nT, respectively. Three of them in western Saurashtra coincide with known volcanic plugs associated with Deccan Volcanic Province (DVP), while the other three in SE Saurashtra coincide with rather concealed plugs exposed partially. The DVP represents different phases of eruption during 65.5±2.5 Ma from the Reunion plume. The geochemical data of the exposed rock samples from these plugs exhibit a wide variation in source composition, which varies from ultramafic/mafic to felsic composition of volcanic plugs in western Saurashtra and an alkaline composition for those in SE Saurashtra. Detailed studies of granophyres and alkaline rocks from these volcanic plugs reveal a calc-alkaline differentiation trend and a continental tectonic setting of emplacement. The alkaline plugs of SE Saurashtra are associated with NE-SW oriented structural trends, related to the Gulf of Cambay and the Cambay rift basin along the track of the Reunion plume. This indicates a deeper source for these plugs compared to those in the western part and may represent the primary source magma. The Junagadh plug with well differentiated ring complexes in western Saurashtra shows well defined centers of magnetic anomaly while the magnetic anomalies due to other plugs are diffused though of the same amplitude. This implies that other plugs are also associated with mafic/ultramafic components, which may not be differentiated and may be present at subsurface levels. Paleomagnetic measurements on surface rock samples from DVP in Saurashtra suggest a susceptibility of 5.5×10−2 SI units with an average Koenigsberger ratio (Qn) of almost one and average direction of remanent magnetization of D=147.4° and I=+56.1°. The virtual geomagnetic pole (VGP) position computed from the mean direction of magnetization for the volcanic plugs and Deccan basalt of Saurashtra is 30°N and 74°W, which is close to the VGP position corresponding to the early phases of Deccan eruption. Modeling of gravity and magnetic anomalies along two representative profiles across Junagadh and Barda volcanic plugs suggest a bulk density of 2900 and 2880 kg/m3, respectively and susceptibility of 3.14×10−2 SI units with a Qn ratio of 0.56 which are within the range of their values obtained from laboratory measurements on exposed rock samples. The same order of gravity and magnetic anomalies observed over the volcanic plugs of Saurashtra indicates almost similar bulk physical properties for them. The inferred directions of magnetization from magnetic anomalies, however, are D=337° and 340° and I=−38° and −50° which represent the bulk direction of magnetization and also indicate a reversal of the magnetic field during the eruption of these plugs. Some of these plugs are associated with seismic activities of magnitude ≤4 at their contacts. Based on this analysis, other circular/semi-circular gravity highs of NW India can be qualitatively attributed to similar subsurface volcanic plugs. 相似文献
77.
新时期我国区域经济地理学发展问题初探 总被引:4,自引:0,他引:4
我国新时期的区域经济地理学在取得全面发展的同时,在理论体系,研究方法和实践领域等方面还需要进一步的发展,文章根据学习和实践区域经济地理学的体会,初步提出基础理论和应用理论,思维方法和技术方法等方面发展见解,并指出区域创新系统和国际经济技术合作等学科应注意拓展的重要实践领域,最后提出我国区域经济地理学科发展的建议。 相似文献
78.
79.
成都市民消费结构与休闲活动关系研究 总被引:6,自引:0,他引:6
城市居民消费水平,消费结构会影响其休闲消费能力,消费意愿,消费方式,消费态度和休闲时空结构,文章以成都市7个城区歌舞,茶棋牌,电影及城市公园休闲活动调查为基础,探讨了城市居民消费结构及其变化与休闲活动特征的关系。研究结果表明,城市居民消费结构的改变对歌舞,茶棋牌娱乐活动影响最大。 相似文献
80.