全文获取类型
收费全文 | 10112篇 |
免费 | 1636篇 |
国内免费 | 2343篇 |
专业分类
测绘学 | 629篇 |
大气科学 | 1812篇 |
地球物理 | 2366篇 |
地质学 | 4282篇 |
海洋学 | 2317篇 |
天文学 | 136篇 |
综合类 | 658篇 |
自然地理 | 1891篇 |
出版年
2024年 | 77篇 |
2023年 | 224篇 |
2022年 | 366篇 |
2021年 | 474篇 |
2020年 | 476篇 |
2019年 | 535篇 |
2018年 | 416篇 |
2017年 | 471篇 |
2016年 | 482篇 |
2015年 | 521篇 |
2014年 | 634篇 |
2013年 | 716篇 |
2012年 | 675篇 |
2011年 | 663篇 |
2010年 | 568篇 |
2009年 | 617篇 |
2008年 | 575篇 |
2007年 | 650篇 |
2006年 | 580篇 |
2005年 | 489篇 |
2004年 | 453篇 |
2003年 | 429篇 |
2002年 | 348篇 |
2001年 | 319篇 |
2000年 | 320篇 |
1999年 | 278篇 |
1998年 | 250篇 |
1997年 | 252篇 |
1996年 | 208篇 |
1995年 | 179篇 |
1994年 | 154篇 |
1993年 | 138篇 |
1992年 | 136篇 |
1991年 | 83篇 |
1990年 | 76篇 |
1989年 | 55篇 |
1988年 | 40篇 |
1987年 | 21篇 |
1986年 | 27篇 |
1985年 | 22篇 |
1984年 | 19篇 |
1983年 | 20篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 2篇 |
1972年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
镇泾地区延长组河流相砂体分布与圈闭形成的关系研究 总被引:3,自引:1,他引:2
鄂尔多斯盆地镇泾地区侏罗系地层以三角洲-湖泊沉积体系为主,研究区范围内主要发育主河道和部分分流河道砂体。研究区构造平缓,主要为单斜地层、在东南部存在大型鼻状构造。通过对主要储层段(长6、8油层组)砂体分布及与构造之间关系进行研究,分析砂体走向与构造线方向的关系认为在构造单斜地区,当两者相交时(交角β≠0)是形成圈闭的关键因素之一,在大型鼻状构造地区因构造线的弯曲与河道砂体组合可以形成圈闭。根据研究区砂体分布和构造线组合出4种地层-岩性及岩性圈闭。利用构造图与砂体分布图对主要储层段存在的圈闭确定出长6、8油层组10个层圈闭。 相似文献
82.
To promote the rational development and use of clean coal resources in China, data on the regional and age distribution of sulfur, arsenic and other harmful elements in Chinese coal was broadly collected, tested for content, and analyzed. Coal in northwestern China is characterized by low to extremely low levels of sulfur; the coal of the Taiyuan Formation in northern China mainly has high-sulfur content; that of the Shanxi Formation is mainly characterized by low sulfur coal; and the Late Permian coal in southern China has overall higher sulfur content; other regions have low sulfur coal. The average content of harmful trace elements in the bulk of China's coal is similar to the corresponding content in the coal of the North America and the rest of the world, whereas the content of various elements (Hg, Sb and Se) is different in magnitude to the corresponding percentage in the crust. The average content of the elements Cr, Se, Co, Be, U, Br in Late Permian coal in S China ranks first in the country whereas the average content of Hg and CI in the coals of Late Carboniferous to Early Permian age in N China are the highest. The average content of Mn in Early and Middle Jurassic coal is higher in NW China. The high content of harmful elements in some coal should cause particular concern both in the development and utilization of coal. 相似文献
83.
84.
An important task in modern geostatistics is the assessment and quantification of resource and reserve uncertainty. This uncertainty
is valuable support information for many management decisions. Uncertainty at specific locations and uncertainty in the global
resource is of interest. There are many different methods to build models of uncertainty, including Kriging, Cokriging, and
Inverse Distance. Each method leads to different results. A method is proposed to combine local uncertainties predicted by
different models to obtain a combined measure of uncertainty that combines good features of each alternative. The new estimator
is the overlap of alternate conditional distributions. 相似文献
85.
86.
Patterns of crystallographic preferred orientation are referred to as texture. The specific subject of texture analysis is
the experimental determination and interpretation of the statistical distribution of orientations of crystals within a specimen
of polycrystalline material, which could be metals or rocks. The objective is to relate an observed pattern of preferred orientation
to its generating processes and vice versa. In geosciences, texture of minerals in rocks is used to infer constraints on their
tectono-metamorphic history. Since most physical properties of crystals, such as elastic moduli, the coefficients of thermal
expansion, or chemical resistance to etching depends on crystal symmetry and orientation, the presence of texture imparts
directional properties to the polycrystalline material.
A major issue of mathematical texture analysis is the resolution of the inverse problem to determine a reasonable orientation
density function on SO(3) from measured pole intensities on
, which relates to the inverse of the totally geodesic Radon transform. This communication introduces a wavelet approach into
mathematical texture analysis. Wavelets on the two-dimensional sphere
and on the rotational group SO(3) are discussed, and an algorithms for a wavelet decomposition on both domains following the
ideas of Ta-Hsin Li is given. The relationship of these wavelets on both domains with respect to the totally geodesic Radon
transform is investigated. In particular, it is shown that the Radon transform of these wavelets on SO(3) are again wavelets
on
. A novel algorithm for the inversion of experimental pole intensities to an orientation density function based on this relationship
is developed. 相似文献
87.
We used transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to study magmatic crystals in the Ben
Lomond rhyolite lava dome, Taupo Volcanic Center, New Zealand. Using TEM and SEM to investigate the size distributions of
these crystals, we identified three size populations: microphenocrysts (>1.2 μm wide), microlites (>0.6 μm wide), and smaller
crystals (<0.6 μm wide) which we term "nanolites". The predominant mineral phases of the microlites and nanolites are augites,
pigeonites, and hypersthenes. The compositions and microstructures within these pyroxenes indicate disequilibrium crystallization
at approximately 850–900 °C and undercoolings as high as 300 °C from equilibrium crystallization temperatures. Complex microstructures
resulting from subsolidus reactions in augite and pigeonite are consistent with moderate cooling rates within the upper obsidian
layer of the Ben Lomond rhyolite dome. This study demonstrates the existence of sub-micron magmatic crystals in a rhyolite
and illustrates the potential of TEM to provide unique information about the crystallization and cooling histories of glassy
volcanic rocks.
Received: May 8, 1995 / Accepted: November 27, 1995 相似文献
88.
Erik Rüttener Juan José Egozcue Dieter Mayer-Rosa Stephan Mueller 《Natural Hazards》1996,14(2-3):165-178
Seismic hazard analysis is based on data and models, which both are imprecise and uncertain. Especially the interpretation of historical information into earthquake parameters, e.g. earthquake size and location, yields ambiguous and imprecise data. Models based on probability distributions have been developed in order to quantify and represent these uncertainties. Nevertheless, the majority of the procedures applied in seismic hazard assessment do not take into account these uncertainties, nor do they show the variance of the results. Therefore, a procedure based on Bayesian statistics was developed to estimate return periods for different ground motion intensities (MSK scale).Bayesian techniques provide a mathematical model to estimate the distribution of random variables in presence of uncertainties. The developed method estimates the probability distribution of the number of occurrences in a Poisson process described by the parameter . The input data are the historical occurrences of intensities for a particular site, represented by a discrete probability distribution for each earthquake. The calculation of these historical occurrences requires a careful preparation of all input parameters, i.e. a modelling of their uncertainties. The obtained results show that the variance of the recurrence rate is smaller in regions with higher seismic activity than in less active regions. It can also be demonstrated that long return periods cannot be estimated with confidence, because the time period of observation is too short. This indicates that the long return periods obtained by seismic source methods only reflects the delineated seismic sources and the chosen earthquake size distribution law. 相似文献
89.
90.
Grain size and grain shape analysis of fault rocks 总被引:4,自引:0,他引:4