全文获取类型
收费全文 | 52709篇 |
免费 | 766篇 |
国内免费 | 628篇 |
专业分类
测绘学 | 1421篇 |
大气科学 | 4307篇 |
地球物理 | 10557篇 |
地质学 | 18423篇 |
海洋学 | 4375篇 |
天文学 | 11939篇 |
综合类 | 114篇 |
自然地理 | 2967篇 |
出版年
2021年 | 321篇 |
2020年 | 398篇 |
2019年 | 474篇 |
2018年 | 1040篇 |
2017年 | 1004篇 |
2016年 | 1329篇 |
2015年 | 807篇 |
2014年 | 1298篇 |
2013年 | 2536篇 |
2012年 | 1423篇 |
2011年 | 1909篇 |
2010年 | 1691篇 |
2009年 | 2302篇 |
2008年 | 2031篇 |
2007年 | 1936篇 |
2006年 | 1994篇 |
2005年 | 1566篇 |
2004年 | 1557篇 |
2003年 | 1510篇 |
2002年 | 1462篇 |
2001年 | 1233篇 |
2000年 | 1309篇 |
1999年 | 1131篇 |
1998年 | 1082篇 |
1997年 | 1096篇 |
1996年 | 901篇 |
1995年 | 881篇 |
1994年 | 831篇 |
1993年 | 688篇 |
1992年 | 677篇 |
1991年 | 631篇 |
1990年 | 697篇 |
1989年 | 627篇 |
1988年 | 604篇 |
1987年 | 716篇 |
1986年 | 640篇 |
1985年 | 742篇 |
1984年 | 844篇 |
1983年 | 840篇 |
1982年 | 766篇 |
1981年 | 698篇 |
1980年 | 674篇 |
1979年 | 626篇 |
1978年 | 626篇 |
1977年 | 589篇 |
1976年 | 519篇 |
1975年 | 529篇 |
1974年 | 546篇 |
1973年 | 535篇 |
1972年 | 341篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Potential changes in summertime hydroclimatology over the northeastern (NE) region of the USA induced by increases in greenhouse gas (GHG) concentrations are investigated using a state-of-the-art regional climate modeling system. Results for a higher emissions scenario illustrate changes that may occur if dependence on fossil fuels continues over the coming century. Summertime precipitation is projected to decrease across much of the central NE, but increase over the southernmost and northernmost portions of the domain. Evaporation is expected to increase across the entire domain. The balance between these two results in a decrease in soil moisture content across most of the domain (by approximately 10 mm) and an increase in the summertime soil-moisture depletion rate (by approximately 10 mm/month). At the same time, an increase in both atmospheric near-surface specific and saturation specific humidity is projected, resulting in an increase in relative humidity across the southern portion of the domain, with slight decreases over the northern portion. Combined with an average increase in summer temperatures of 3.5°C, the projected increase in relative humidity results in a marked increase in the average daily maximum heat index for the region on the order of 3.9°C, as well as a 350–400% increase in the number of days with heat index values exceeding 32.2°C (90°F)—the level of “extreme caution”. Taken together, these high-resolution, dynamically-generated projections confirm the potential for significant summertime climate change impacts on the NE over the coming century as suggested by previous studies. 相似文献
102.
T.H. Torsvik 《Physics of the Earth and Planetary Interiors》1985,39(3):194-207
Thermal demagnetization studies of lavas in the Strathmore area of the Midland Valley, Scotland, support overall palaeomagnetic data found in previous studies of these rocks. Reduced directional scatter as compared to some earlier studies, is attributed to more effective demagnetization, resolving some of the directional complexity of previous studies. Combined magnetic fabric and directional analysis suggest that at least some deviating directions may be explained by local tectonism. The existence of almost antiparallel directional groups and field tests give supporting evidence for a “primary” (deuteric) origin of the main magnetization of these rocks. Additionally, a second remanence component having shallow reverse directions of magnetization, is attributed to later remagnetization in Old Red Sandstone time. The Midland Valley results are seen in conjunction with other Palaeozoic palaeomagnetic results and possible geodynamic implications are discussed. 相似文献
103.
104.
The population and distribution of carbon-oxidizing and sulfate-reducing bacteria in the soils of the Mozhaisk Reservoir are studied. 相似文献
105.
The eleventh list of faint late M and carbon type stars detected on the plates of the First Byurakan Spectral Survey in zone -7° -3° and covering about 1000 square degrees is presented. From 126 detected stars, 88 are newly discovered objects: they are 6 carbon stars, 8 carbon star candidates, and 74 M-type stars; among the latter 38 (26 PSC + 12 FSC) are unclassified IRAS sources, and one object is an unclassified ROSAT source. Distances to the 6 newly discovered early-type carbon stars are estimated. Equatorial coordinates, red magnitudes, and spectral classes determined from the Palomar E-charts are provided. The lack of optical counterparts on Palomar O and E maps for two detected late M-type stars indicates a large variability in brightnesses of these objects (amplitude not smaller than 7.0 magnitude). 相似文献
106.
107.
N. V. Makarova V. M. Makeev T. V. Sukhanova P. S. Miklyaev A. L. Dorozhko I. V. Korobova 《Moscow University Geology Bulletin》2012,67(4):209-217
The neotectonic structures of the Lower Oka (Nizhneokskii) Region formed under different geodynamic conditions. This is attested by the morphology, orientation, internal structure, and jointing of the structures. The Oka-Tsna arc formed under the effect of tension from an inner source on the one hand and stress from the Alpian belt on the other hand. The latitudinally-oriented structures of the northwestern slope of the Tokmovo arc emerged as a result of uplift and widening. Both types of structure are combined within the limits of the Oka-Murom trough, which is a geodynamically active zone. 相似文献
108.
L. De Marchi J. Orm D. T. King D. R. Adrian J. J. Hagerty T. A. Gaither 《Meteoritics & planetary science》2019,54(11):2864-2878
Sedimentological (line‐logging) analysis of two drill cores, FC77‐3 and FC67‐3, situated, respectively, in the northwestern and southeastern quadrants of the Flynn Creek impact structure's crater‐moat area reveals that the ~27 m thick crater moat‐filling breccia consists of three subequal parts. These parts, which were deposited during early modification stage of this marine‐target impact structure, are distinguished on the basis of vertical trends in sorting, grain size, and counts of clasts per meter in comparison with other well‐known marine‐target impact structures, namely Lockne, Tvären, and Chesapeake Bay. The lower part is interpreted to represent mainly slump deposits, and the middle part is interpreted to represent a stage intermediate between slump and marine resurge, that is, a traction flow driven by overriding suspension flow. The upper part (size graded, and relatively well sorted and fine grained) is interpreted to represent marine resurge flow only. The upper part is capped by a relatively thin and relatively fine‐grained calcarenite to calcisiltite deposit. 相似文献
109.
James Glimm Shuling Hou Hongjoong Kim Yoon-ha Lee David H. Sharp Kenny Ye Qisu Zou 《Computational Geosciences》2001,5(3):173-197
We consider numerical solutions of the Darcy and Buckley–Leverett equations for flow in porous media. These solutions depend on a realization of a random field that describes the reservoir permeability. The main content of this paper is to formulate and analyze a probability model for the numerical coarse grid solution error. We explore the extent to which the coarse grid oil production rate is sufficient to predict future oil production rates. We find that very early oil production data is sufficient to reduce the prediction error in oil production by about 30%, relative to the prior probability prediction. 相似文献
110.