全文获取类型
收费全文 | 52657篇 |
免费 | 9254篇 |
国内免费 | 10764篇 |
专业分类
测绘学 | 4074篇 |
大气科学 | 5896篇 |
地球物理 | 11591篇 |
地质学 | 27670篇 |
海洋学 | 8236篇 |
天文学 | 3461篇 |
综合类 | 3433篇 |
自然地理 | 8314篇 |
出版年
2024年 | 236篇 |
2023年 | 656篇 |
2022年 | 1633篇 |
2021年 | 2070篇 |
2020年 | 1976篇 |
2019年 | 2513篇 |
2018年 | 1868篇 |
2017年 | 2105篇 |
2016年 | 2081篇 |
2015年 | 2357篇 |
2014年 | 2982篇 |
2013年 | 3426篇 |
2012年 | 3072篇 |
2011年 | 3321篇 |
2010年 | 2919篇 |
2009年 | 3461篇 |
2008年 | 3514篇 |
2007年 | 3652篇 |
2006年 | 3608篇 |
2005年 | 3248篇 |
2004年 | 2920篇 |
2003年 | 2717篇 |
2002年 | 2349篇 |
2001年 | 2102篇 |
2000年 | 2038篇 |
1999年 | 1816篇 |
1998年 | 1545篇 |
1997年 | 1190篇 |
1996年 | 973篇 |
1995年 | 832篇 |
1994年 | 791篇 |
1993年 | 659篇 |
1992年 | 485篇 |
1991年 | 403篇 |
1990年 | 283篇 |
1989年 | 248篇 |
1988年 | 177篇 |
1987年 | 108篇 |
1986年 | 67篇 |
1985年 | 70篇 |
1984年 | 36篇 |
1983年 | 36篇 |
1982年 | 19篇 |
1981年 | 20篇 |
1980年 | 14篇 |
1979年 | 6篇 |
1978年 | 24篇 |
1977年 | 6篇 |
1971年 | 5篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
E.A. Evstigneeva R.R. de Carvalho A.L. Ribeiro H.V. Capelato 《Astrophysics and Space Science》2003,284(2):487-490
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families
of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different
loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this
diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we
can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
32.
33.
34.
本文以丰富的实际资料,论证了地下水的卤素元素(F、Cl、Br、I)的形成、含量及其分布规律与含水介质成分、上覆岩土性质、地下水退流条件、氧化还原环境、地下水矿化度之间的关系。根据江汉平原东部区和鄱阳湖区地下水中Br、I元素的调查研究结果及它们形成的控制因素与分布规律,结合长江三角洲南部区水文地球化学环境条件分析对比,指出该区是一个形成Br、I矿泉水的有利地区。 相似文献
35.
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
36.
Zhang Chuanling 《地球科学与环境学报》1997,(1)
文中详细地论述了新疆阿尔泰哈巴河一带古生代火山岩的地质、岩石化学、稀土元素地球化学特征。将其分为三个类型,认为火山岩是在陆缘裂陷槽的区域构造背景下发生和演化的。对各类型火山岩岩浆来源,上升模式也做了初步讨论。 相似文献
37.
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
38.
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
39.
40.
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