全文获取类型
收费全文 | 10132篇 |
免费 | 1657篇 |
国内免费 | 2273篇 |
专业分类
测绘学 | 1155篇 |
大气科学 | 1287篇 |
地球物理 | 2399篇 |
地质学 | 5591篇 |
海洋学 | 1415篇 |
天文学 | 642篇 |
综合类 | 498篇 |
自然地理 | 1075篇 |
出版年
2024年 | 53篇 |
2023年 | 161篇 |
2022年 | 424篇 |
2021年 | 514篇 |
2020年 | 404篇 |
2019年 | 436篇 |
2018年 | 496篇 |
2017年 | 452篇 |
2016年 | 506篇 |
2015年 | 520篇 |
2014年 | 603篇 |
2013年 | 785篇 |
2012年 | 771篇 |
2011年 | 718篇 |
2010年 | 734篇 |
2009年 | 724篇 |
2008年 | 649篇 |
2007年 | 625篇 |
2006年 | 583篇 |
2005年 | 539篇 |
2004年 | 397篇 |
2003年 | 304篇 |
2002年 | 305篇 |
2001年 | 293篇 |
2000年 | 207篇 |
1999年 | 128篇 |
1998年 | 118篇 |
1997年 | 77篇 |
1996年 | 89篇 |
1995年 | 64篇 |
1994年 | 69篇 |
1993年 | 49篇 |
1992年 | 39篇 |
1991年 | 36篇 |
1990年 | 45篇 |
1989年 | 44篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 40篇 |
1984年 | 47篇 |
1983年 | 57篇 |
1982年 | 43篇 |
1981年 | 36篇 |
1980年 | 39篇 |
1979年 | 44篇 |
1978年 | 43篇 |
1977年 | 40篇 |
1975年 | 45篇 |
1974年 | 39篇 |
1973年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
172.
173.
174.
Two cases of on-ice and off-ice air flow characterizing the opposite weather situations over the ice-edge zone in the northern Baltic Sea are analysed on the basis of aircraft observations, and modelled using atwo-dimensional mesoscale model. The stable boundary layer (SBL) during theon-ice flow exhibited little thermal modification, but a low-level jet (LLJ) was generated at the 250-m high top of the SBL. In the model, the LLJ was associated with inertial oscillations in space, while the baroclinicity explained the shape of the wind profile well above the SBL. Although the observed LLJ was most pronounced over the ice, the modelling suggests that it was not generated by the ice edge but by the coastline some 400 km upwind of the ice edge, where a much more drastic change in the thermal stratification and surface roughness took place. The generation, maintenance, and strength of the LLJ were very sensitive to the parameterization of turbulent mixing in the SBL. In the case of the off-ice flow, the modification of the air mass and the development of a convective boundary layer (CBL) both over the ice and open sea were reasonably well modelled. Sensitivity runs suggested that it was essential to take into account the effects of subgrid-scale leads, a forest in the archipelago (which was crossed by the air flow), and water vapour condensationinto ice crystals. The heat flux from leads was particularly important for the heatbudget of the CBL, and the observed growth of the CBL was partly due to theeffective mixing over the rough and relatively warm forest. 相似文献
175.
As shown in comparison and study of the HIRS-Tb12 data and conventional data, temperature,
humidity and vertical motion are structured differently in the Southern and Northern Hemispheres, which are well
depicted with the HIRS-Tb12 data. When high pressures rapidly decrease over the regions of South China Sea
and Arabian Sea with the HIRS-Tb12 less than 200 W/m2, monsoons will set off in the South China Sea, Arabian
Sea and Bay of Bengal, respectively. From a year of significant drought to one of significant floods, the trend of
evolution is significantly different in the downdraft areas of the subtropical highs between the two hemispheres. 相似文献
176.
In the context of tower measured radiation datasets.following the correction principle meetinga diagnostic equation in data quality control and in terms of a technique for model construction ondata and ANN(artificial neural network)retrieval for BP correction of radiation measurementswith rough errors available,a BP model is presented.Evidence suggests that the developed modelworks well and is superior to a convenient multivariate linear regression model,indicating its wideapplications. 相似文献
177.
178.
泌阳凹陷湖相碳酸盐岩未成熟石油的形成条件 总被引:8,自引:0,他引:8
泌阳凹陷下第三系核桃园组H3^1-H2^3段湖相白云岩,分布有未熟油的工业性油流,原油来自同层段的湖相泥质白云岩,属自生自储式原油,通过凹陷中心云2井和云1井岩芯的有机地球化学研究,论述了白云岩系未熟油形成的内因和外因,有机质丰度高和优良的成油母质类型(包括被细菌改造“腐泥化”的母质)和良好的岩性组合是早期成油的物质基础;双层水体的咸水碱性环境是早期成油的外界条件。其成烃模式表明,泌阳凹陷湖相碳酸盐岩存在早期和晚期两个成烃高峰期。 相似文献
179.
Laurent Desmurs Othmar Müntener Gianreto Manatschal 《Contributions to Mineralogy and Petrology》2002,144(3):365-382
Exhumation of subcontinental mantle rocks and its exposure at the seafloor is known from different magma-poor passive continental margins. However, the transition from largely amagmatic passive rifting to seafloor spreading is still poorly documented. In this contribution we use MOR-type gabbroic and basaltic rocks to characterize the magmatism associated with the formation of an ancient ocean-continent transition preserved in the Platta nappe, eastern Switzerland. Gabbros form individual small intrusions into exhumed serpentinized subcontinental mantle rocks. Mineral and bulk-rock chemistry and simple modeling indicate that each gabbro body records different magmatic processes ranging from predominantly fractional crystallization to solidification without fractionation. Mg numbers and Ni contents of equilibrium olivine calculated from basalts and gabbros indicate that few mafic rocks are primary melts but most represent fractionated compositions ranging from T- to N-MORB. Whereas most mafic rocks may be explained by low to moderate degrees of melting of an N-MORB-type mantle, the source of some basalt is enriched in incompatible elements. This compositional variation seems to correlate with the spatial distribution of the mafic rocks within the ocean-continent transition whereby mafic rocks with T-MORB signatures occur close to the continental margin whereas N-MORB signatures are predominantly found oceanwards. As in an opening system time and space are closely linked, the chemical evolution of the mafic rocks along the ocean-continent transitions suggests continuous thinning of the subcontinental mantle and associated uplift of the underlying asthenosphere during the time between the crustal and the lithospheric breakup. 相似文献
180.