全文获取类型
收费全文 | 5320篇 |
免费 | 575篇 |
国内免费 | 1039篇 |
专业分类
测绘学 | 48篇 |
大气科学 | 183篇 |
地球物理 | 711篇 |
地质学 | 2781篇 |
海洋学 | 1114篇 |
天文学 | 1431篇 |
综合类 | 197篇 |
自然地理 | 469篇 |
出版年
2024年 | 34篇 |
2023年 | 95篇 |
2022年 | 128篇 |
2021年 | 169篇 |
2020年 | 168篇 |
2019年 | 166篇 |
2018年 | 134篇 |
2017年 | 167篇 |
2016年 | 171篇 |
2015年 | 181篇 |
2014年 | 265篇 |
2013年 | 215篇 |
2012年 | 221篇 |
2011年 | 320篇 |
2010年 | 225篇 |
2009年 | 419篇 |
2008年 | 368篇 |
2007年 | 368篇 |
2006年 | 382篇 |
2005年 | 316篇 |
2004年 | 315篇 |
2003年 | 270篇 |
2002年 | 258篇 |
2001年 | 229篇 |
2000年 | 236篇 |
1999年 | 191篇 |
1998年 | 205篇 |
1997年 | 109篇 |
1996年 | 109篇 |
1995年 | 88篇 |
1994年 | 65篇 |
1993年 | 54篇 |
1992年 | 41篇 |
1991年 | 37篇 |
1990年 | 39篇 |
1989年 | 40篇 |
1988年 | 20篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 31篇 |
1984年 | 22篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有6934条查询结果,搜索用时 31 毫秒
1.
2.
红阳煤田含煤地层太原组与山西组,是一套典型的“海陆交互相”沉积。依据剖面上沉积相序列变化特点,可划分为14个沉积旋回,每个沉积旋回均含有一层煤。有二种聚煤环境:一是海水退出潮坪后形成的泥炭沼泽聚积的煤层;二是扇三角洲平原形成的泥炭沼泽聚积的煤层。 相似文献
3.
4.
5.
6.
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
7.
Lawrence M. Mayer Peter T. Rahaim William Guerin Stephen A. Macko Les Watling Franz E. Anderson 《Estuarine, Coastal and Shelf Science》1985,20(4):491-503
A variety of measures of organic matter concentration and quality were made on samples collected from the top few mm of intertidal mudflat sediment over the course of a year, in order to assess the relative importance of biological and sedimentological influences on sedimentary organic matter. Winter and summer were times of relatively fine-grained sediment accumulation, caused by biological deposition or stabilization processes and resulting in higher organic matter concentrations. Stable carbon isotope and Br:C ratios indicated a planktonic source of bulk organic matter. Ratios of organic carbon to specific surface area of the sediments were consistent with an organic monolayer coverage of sediment grains. Correction for changing grain size during the year showed no change in the organic concentration per unit surface area, in spite of organic matter inputs by in situ primary production, buildup of heterotroph biomass and mucus coatings, and biodeposition of organic-rich seston. There were also no indications of changes in bulk organic quality, measured as hydrolyzable carbohydrates and amino acids, in response to these biological processes. It is concluded that biological processes on a seasonal time scale affect the bulk organic matter of these sediments via a modulation of grain size rather than creation or decay of organic matter. 相似文献
8.
9.
B. Ahmed G. J. Alner H. Araujo J. C. Barton A. Bewick M. J. Carson D. Davidge J. V. Dawson T. Gamble S. P. Hart R. Hollingworth A. S. Howard W. G. Jones M. K. Joshi V. A. Kudryavtsev T. B. Lawson V. Lebedenko M. J. Lehner J. D. Lewin P. K. Lightfoot I. Liubarsky R. Lüscher J. E. McMillan B. Morgan G. Nicklin S. M. Paling R. M. Preece J. J. Quenby J. W. Roberts M. Robinson N. J. T. Smith P. F. Smith N. J. C. Spooner T. J. Sumner D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702
The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented. 相似文献
10.
We present warm dark matter (WDM) as a possible solution to the missing satellites and angular momentum problem in galaxy
formation and introduce improved initial conditions for numerical simulations of WDM models, which avoid the formation of
unphysical haloes found in earlier simulations. There is a hint, that because of that the mass function of satellite haloes
has been overestimated so far, pointing to higher values for the WDM particle mass.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献