全文获取类型
收费全文 | 39264篇 |
免费 | 6173篇 |
国内免费 | 8433篇 |
专业分类
测绘学 | 5062篇 |
大气科学 | 5181篇 |
地球物理 | 6499篇 |
地质学 | 20681篇 |
海洋学 | 4397篇 |
天文学 | 3826篇 |
综合类 | 2600篇 |
自然地理 | 5624篇 |
出版年
2024年 | 261篇 |
2023年 | 682篇 |
2022年 | 1403篇 |
2021年 | 1683篇 |
2020年 | 1519篇 |
2019年 | 1879篇 |
2018年 | 1305篇 |
2017年 | 1636篇 |
2016年 | 1676篇 |
2015年 | 1818篇 |
2014年 | 2226篇 |
2013年 | 2167篇 |
2012年 | 2336篇 |
2011年 | 2460篇 |
2010年 | 2150篇 |
2009年 | 2632篇 |
2008年 | 2520篇 |
2007年 | 2657篇 |
2006年 | 2568篇 |
2005年 | 2406篇 |
2004年 | 2074篇 |
2003年 | 2005篇 |
2002年 | 1723篇 |
2001年 | 1532篇 |
2000年 | 1536篇 |
1999年 | 1321篇 |
1998年 | 1177篇 |
1997年 | 818篇 |
1996年 | 684篇 |
1995年 | 587篇 |
1994年 | 555篇 |
1993年 | 464篇 |
1992年 | 325篇 |
1991年 | 304篇 |
1990年 | 204篇 |
1989年 | 156篇 |
1988年 | 133篇 |
1987年 | 76篇 |
1986年 | 39篇 |
1985年 | 34篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 15篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
北部湾北部海上油田的开发工作始于50年代,60~70年代作了大量地质工作。改革开放后,油气勘查取得突破性进展。累计发现油气构造6个,含油面积超过40km2,石油地质储量约4亿t,已开发油田2个,揭开我国南方油气资源开发序幕 相似文献
23.
概略地叙述了西宁地区的泥石流形成条件和形成机理,并将西宁地区泥石流划分为稀性泥石流类及泥石质泥石流种类。在此基础上提出防治泥石流灾害的意见。 相似文献
24.
J. M. De Buizer 《Monthly notices of the Royal Astronomical Society》2003,341(1):277-298
The results of a survey searching for outflows using near-infrared imaging are presented. Targets were chosen from a compiled list of massive young stellar objects associated with methanol masers in linear distributions. Presently, it is a widely held belief that these methanol masers are found in (and delineate) circumstellar accretion discs around massive stars. If this scenario is correct, one way to test the disc hypothesis is to search for outflows perpendicular to the methanol maser distributions. The main objective of the survey was to obtain wide-field near-infrared images of the sites of linearly distributed methanol masers using a narrow-band 2.12-μm filter. This filter is centred on the H2 v = 1–0 S(1) line; a shock diagnostic that has been shown to successfully trace CO outflows from young stellar objects. 28 sources in total were imaged of which 18 sources display H2 emission. Of these, only two sources showed emission found to be dominantly perpendicular to the methanol maser distribution. Surprisingly, the H2 emission in these fields is not distributed randomly, but instead the majority of sources are found to have H2 emission dominantly parallel to their distribution of methanol masers. These results seriously question the hypothesis that methanol masers exist in circumstellar discs. The possibility that linearly distributed methanol masers are instead directly associated with outflows is discussed. 相似文献
25.
26.
Flavio Scappini Cesare Cecchi-Pestellini Harvey Smith William Klemperer Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2003,341(2):657-661
We consider sulphur depletion in dense molecular clouds, and suggest hydrated sulphuric acid, H2 SO4 · n H2 O, as a component of interstellar dust in icy mantles. We discuss the formation of hydrated sulphuric acid in collapsing clouds and its instability in heated regions in terms of the existing hot core models and observations. We also show that some features of the infrared spectrum of hydrated sulphuric acid have correspondence in the observed spectra of young stellar objects. 相似文献
27.
28.
We present a new general scheme for calculating the structure and dynamics of radiation-pressure-driven photoionized flows. The new method goes one step beyond the Sobolev approximation. It involves a numerical solution of the radiative transfer in absorption lines, including the effects of differential expansion and line interactions such as line locking and blanketing. We also present a new scheme for calculating the radiation pressure due to trapped line photons in finite, differentially expanding flows. We compare our results for the radiation pressure force with those obtained using the Sobolev approximation and show the limitations of the latter. In particular, we demonstrate that the Sobolev method gives a poor approximation near discontinuity surfaces and its neglect of line blanketing can lead to erroneous results in high-velocity flows. We combine the newly calculated radiation pressure force with self-consistent photoionization and thermal calculations to study the dynamics and spectral features of broad absorption-line flows and highly ionized gas flows in active galactic nuclei (AGN). A comparison with Sobolev-type calculations shows that the latter overestimates the terminal velocity of the flow and, conversely, underestimates its opacity. We also show that line locking on broad emission lines can have a significant effect on the dynamics and spectral features of AGN flows. 相似文献
29.
30.
Virtual Huanghe River System: Framework and Technology 总被引:2,自引:0,他引:2
LU Heli LIU Guifang SUN Jiulin 《中国地理科学(英文版)》2006,16(3):255-259
1 Introduction Huanghe (Yellow) River basin is located in 32°–42°N, 96°–119°E. The area of the catchment is more than 752,000km2. The river is 5464km long with a drop in elevation of 4830m. Among the whole area, the moun- tainous and stone area accounts for 29%, loess and hills area 46%, sandy area 11% and plain area 14%, respec- tively. Different natural landscapes exist in this area. The Huanghe River flows through the Loess Plateau, where the soil is eroded seriously (Wang, 2002;… 相似文献