全文获取类型
收费全文 | 51297篇 |
免费 | 8845篇 |
国内免费 | 10794篇 |
专业分类
测绘学 | 4633篇 |
大气科学 | 5410篇 |
地球物理 | 11276篇 |
地质学 | 29031篇 |
海洋学 | 5343篇 |
天文学 | 3843篇 |
综合类 | 3666篇 |
自然地理 | 7734篇 |
出版年
2024年 | 114篇 |
2023年 | 448篇 |
2022年 | 1268篇 |
2021年 | 1537篇 |
2020年 | 1642篇 |
2019年 | 1785篇 |
2018年 | 1528篇 |
2017年 | 1804篇 |
2016年 | 1922篇 |
2015年 | 2103篇 |
2014年 | 2600篇 |
2013年 | 2661篇 |
2012年 | 2922篇 |
2011年 | 3156篇 |
2010年 | 2690篇 |
2009年 | 3301篇 |
2008年 | 3334篇 |
2007年 | 3714篇 |
2006年 | 3601篇 |
2005年 | 3188篇 |
2004年 | 2995篇 |
2003年 | 2897篇 |
2002年 | 2553篇 |
2001年 | 2238篇 |
2000年 | 2111篇 |
1999年 | 1981篇 |
1998年 | 1716篇 |
1997年 | 1488篇 |
1996年 | 1335篇 |
1995年 | 1122篇 |
1994年 | 1142篇 |
1993年 | 971篇 |
1992年 | 745篇 |
1991年 | 539篇 |
1990年 | 465篇 |
1989年 | 370篇 |
1988年 | 273篇 |
1987年 | 181篇 |
1986年 | 124篇 |
1985年 | 89篇 |
1984年 | 38篇 |
1983年 | 33篇 |
1982年 | 36篇 |
1981年 | 21篇 |
1980年 | 25篇 |
1979年 | 32篇 |
1978年 | 35篇 |
1977年 | 24篇 |
1976年 | 5篇 |
1954年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
从地形地貌特征、重磁地球物理场、深部构造与断裂构造以及地震活动、震源机制等多方面论述北东东向构造是南海北缘的主要活动构造。对于长期以来认为新华夏系北东向构造是该区主要活动构造的观点来说,这是一种新的学术思想。 相似文献
112.
DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHEHEXIREGION,CHINA肖洪浪,高前兆,李福兴DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHE... 相似文献
113.
114.
115.
甘新蒙北山地区成矿带划分和基本特征对比 总被引:3,自引:1,他引:2
在对甘新蒙北山地区成矿地质背景和成矿在时空上的联系性等综合研究分析基础上,运用新理论、新认识,以板块构造单元划分为基础,将本区划分为3个Ⅲ级成矿带、11个Ⅳ级成矿带,并对Ⅲ级成矿带特征进行了阐述,以期为矿产勘查和地质大调查工作部署提供新的思路和依据。进一步就主要矿床(点)、构造单元、矿种、赋矿建造、控矿因素、成矿类型、成矿时代等方面进行了对比,认为各Ⅳ级成矿带在区域上具有相对稳定的展布范围,具有相同的构造环境和成矿条件、类似的矿种和成矿时代,存在一定的相似性、可比性,并且各成矿带具有一定的潜在找矿价值。 相似文献
116.
Dipak Munshi Patrick Valageas 《Monthly notices of the Royal Astronomical Society》2005,356(2):439-455
The present generation of weak lensing surveys will be superseded by surveys run from space with much better sky coverage and high level of signal-to-noise ratio, such as the Supernova/Acceleration Probe ( SNAP ). However, removal of any systematics or noise will remain a major cause of concern for any weak lensing survey. One of the best ways of spotting any undetected source of systematic noise is to compare surveys that probe the same part of the sky. In this paper we study various measures that are useful in cross-correlating weak lensing surveys with diverse survey strategies. Using two different statistics – the shear components and the aperture mass – we construct a class of estimators which encode such cross-correlations. These techniques will also be useful in studies where the entire source population from a specific survey can be divided into various redshift bins to study cross-correlations among them. We perform a detailed study of the angular size dependence and redshift dependence of these observables and of their sensitivity to the background cosmology. We find that one-point and two-point statistics provide complementary tools which allow one to constrain cosmological parameters and to obtain a simple estimate of the noise of the survey. 相似文献
117.
山区公路软基病害研究 总被引:2,自引:0,他引:2
随着高等级公路建设规模的扩大,山区公路所面临的路基病害特别是软土路基病害问题也逐渐增多。结合对陕南勉(县)一宁(强)高速公路工程实例分析,对山区软土成因及其特性进行了初步分析,认为山区软土属以坡洪积、湖积和冲积为主的软土,也有少量是由坡残积物堆积而形成。山区软土的特殊性表现在成分的复杂性、分布的不均匀性、隐蔽性和物理力学性质的特殊性。根据其特性以及中国山区公路软基普遍存在的病害问题,总结了山区公路软基的主要病害类型为剪切拉裂破坏、浸水沉陷破坏、剥蚀坍塌破坏、推挤滑动破坏。还提出了相应的软基处理方法及建议。 相似文献
118.
It has been found that the near-infrared flux variations of Seyfert galaxies satisfy relations of the form Fi ≈α i j +β i j Fj , where Fi , Fj are the fluxes in filters i and j ; and α i , j , β i , j are constants. These relations have been used to estimate the constant contributions of the non-variable underlying galaxies. The paper attempts a formal treatment of the estimation procedure, allowing for the possible presence of a third component, namely non-variable hot dust. In an analysis of a sample of 38 Seyfert galaxies, inclusion of the hot dust component improves the model fit in approximately half the cases. All derived dust temperatures are below 300 K, in the range 540–860 K or above 1300 K. A noteworthy feature is the estimation of confidence intervals for the component contributions: this is achieved by bootstrapping. It is also pointed out that the model implies that such data could be fruitfully analysed in terms of principal components. 相似文献
119.
120.
We report the first detection, with Chandra , of X-ray emission from the jet of the powerful narrow-line radio galaxy 3C 346. X-rays are detected from the bright radio and optical knot at which the jet apparently bends by approximately 70°. The Chandra observation also reveals a bright galaxy-scale atmosphere within the previously known cluster and provides a good X-ray spectrum for the bright core of 3C 346. The X-ray emission from the knot is synchrotron radiation, as seen in lower-power sources. In common with these sources, there is evidence of morphological differences between the radio/optical and X-ray structures, and the spectrum is inconsistent with a one-component continuous-injection model. We suggest that the X-ray-bright knot is associated with a strong oblique shock in a moderately relativistic, light jet, at ∼ 20° to the line of sight, and that this shock is caused by the jet interacting with the wake in the cluster medium behind the companion galaxy of 3C 346. The general jet curvature can result from pressure gradients in the cluster atmosphere. 相似文献