全文获取类型
收费全文 | 31829篇 |
免费 | 17620篇 |
国内免费 | 42168篇 |
专业分类
测绘学 | 2675篇 |
大气科学 | 20969篇 |
地球物理 | 11957篇 |
地质学 | 33512篇 |
海洋学 | 15663篇 |
天文学 | 1044篇 |
综合类 | 3990篇 |
自然地理 | 1807篇 |
出版年
2024年 | 121篇 |
2023年 | 219篇 |
2022年 | 329篇 |
2021年 | 583篇 |
2020年 | 1827篇 |
2019年 | 5275篇 |
2018年 | 5669篇 |
2017年 | 5382篇 |
2016年 | 5394篇 |
2015年 | 4695篇 |
2014年 | 4187篇 |
2013年 | 4799篇 |
2012年 | 4443篇 |
2011年 | 4204篇 |
2010年 | 4152篇 |
2009年 | 3489篇 |
2008年 | 2774篇 |
2007年 | 2759篇 |
2006年 | 2400篇 |
2005年 | 2304篇 |
2004年 | 2667篇 |
2003年 | 2411篇 |
2002年 | 2123篇 |
2001年 | 1899篇 |
2000年 | 1544篇 |
1999年 | 1551篇 |
1998年 | 1660篇 |
1997年 | 1728篇 |
1996年 | 1333篇 |
1995年 | 1295篇 |
1994年 | 1169篇 |
1993年 | 1141篇 |
1992年 | 959篇 |
1991年 | 740篇 |
1990年 | 705篇 |
1989年 | 585篇 |
1988年 | 495篇 |
1987年 | 400篇 |
1986年 | 319篇 |
1985年 | 261篇 |
1984年 | 288篇 |
1983年 | 170篇 |
1982年 | 208篇 |
1981年 | 147篇 |
1980年 | 115篇 |
1979年 | 116篇 |
1978年 | 51篇 |
1977年 | 45篇 |
1972年 | 51篇 |
1971年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
101.
On the practice of estimating fractal dimension 总被引:11,自引:0,他引:11
Coastlines epitomize deterministic fractals and fractal (Hausdorff-Besicovitch) dimensions; a divider [compass] method can be used to calculate fractal dimensions for these features. Noise models are used to develop another notion of fractals, a stochastic one. Spectral and variogram methods are used to estimate fractal dimensions for stochastic fractals. When estimating fractal dimension, the objective of the analysis must be consistent with the method chosen for fractal dimension calculation. Spectal and variogram methods yield fractal dimensions which indicate the similarity of the feature under study to noise (e.g., Brownian noise). A divider measurement method yields a fractal dimension which is a measure of complexity of shape. 相似文献
102.
A new multidimensional scaling (MS) technique, referred to as the Pijk model, is formulated on the basis of associations among triple objects (samples or variables), instead of pairs of objects as used in the usual MS methods, such as factor analysis. The computational scheme provided for this method is the reduction of an original problem to a standard eigenvalue-eigenvector problem. The major goal of the technique is simplification and reduction of data structures and the rescaling of original objects into a new and reduced space, so that patterns and relations of the original objects can be conventiently examined in two-dimensional factor plots. The Pïjk method is illustrated and tested by using a set of geochemical data related to the epithermal gold and silver vein deposits in the Walker Lake quadrangle of Nevada and California. The characteristics of element associations suggested in the Pijk analysis are consistent with field observations. A preliminary comparison between the new method and the ordinary factor analysis also is made on the basis of the same data set. Results are encouraging in that analysis by the Pijk model captures triple-object associations that might be missed by the ordinary factor analysis which considers only pair-variable correlations 相似文献
103.
IGU-Reports
Commission health and development 相似文献104.
H. Flanquart C. Meur-Férec Ph. Deboudt V. Morel A.-P. Hellequin et al. 《GeoJournal》1991,24(2):223-223
Reports
Littoral '92 相似文献105.
造山带中富集型上地幔的成因——以萨尔托海蛇绿岩块为例 总被引:1,自引:0,他引:1
发育于造山带中的蛇绿岩,其剖面下部的地幔橄榄岩部分是造山带地区富集型上地幔的直接标本。其地球化学特点是:主要元素Al_2O_3、TiO_2、CaO、Na_2O、K_2O强烈亏损,而REE,痕量元素和87Sr/86Sr则强烈富集;同时,143Nd/144Nd<0.511836,亦表明它们属于一个富集型的源区。 形成富集型上地幔的主要机制是地幔交代作用,富含不相容元素的低熔岩浆和富Ca-LREE流体与已亏损的地幔橄榄岩发生脉状交代和渗透交代反应,从而造成上地幔中不相容元素的富集。造山带富集型上地幔形成的构造环境是:洋壳从扩张脊向两侧运移并最终拼入造山带这段时间内。富集型上地幔不但存在于大陆区,而且亦存在于造山带地区,它可能是一种全球性的地球内部的化学作用。 相似文献
106.
Basant Kumar Jha 《Astrophysics and Space Science》1991,175(2):225-228
An analytical study is performed to examine the effects of temperature-dependent heat source on free-convective flow of non-Newtonian fluid (Walters's liquidB). The expression for the velocity field has been obtained by the Laplace transform technique. The influence of the various parameter entering into the problem is extensively discussed. 相似文献
107.
108.
109.
110.
Kumar K Taragi RC 《Population geography : a journal of the Association of Population Geographers of India》1986,8(1-2):58-63
There are great spatial variations in the distribution of the fast growing populations of India. About 70% of the 1981 population is concentrated in only 40% of the geographical area. Such a pattern of population concentration, with its spatio-temporal dimension, can be understood better if examined at the macro-regional level considering the physico-climatic and socio-economic diversity of the country. This is done by way of analyzing district level data for India as a whole and also for its various macro-regions. The study reveals that the Great Plains and Coastal Plains and Islands have a homogenous distribution and a higher population increase. The Deccan Plateau shows the most homogenous dispersion of population. The population is declining in the Northern Mountains and the Great Plains but accentuating in the Coastal Plains and Islands and the Deccan Plateau. The north and south of India are showing opposite trends in population concentration. 相似文献