全文获取类型
收费全文 | 58320篇 |
免费 | 9822篇 |
国内免费 | 13300篇 |
专业分类
测绘学 | 8560篇 |
大气科学 | 8799篇 |
地球物理 | 11277篇 |
地质学 | 28595篇 |
海洋学 | 7136篇 |
天文学 | 3638篇 |
综合类 | 4342篇 |
自然地理 | 9095篇 |
出版年
2024年 | 274篇 |
2023年 | 697篇 |
2022年 | 1977篇 |
2021年 | 2289篇 |
2020年 | 2383篇 |
2019年 | 2926篇 |
2018年 | 2198篇 |
2017年 | 2609篇 |
2016年 | 2657篇 |
2015年 | 2969篇 |
2014年 | 3447篇 |
2013年 | 3704篇 |
2012年 | 3673篇 |
2011年 | 3852篇 |
2010年 | 3165篇 |
2009年 | 3869篇 |
2008年 | 3846篇 |
2007年 | 4011篇 |
2006年 | 3876篇 |
2005年 | 3542篇 |
2004年 | 3119篇 |
2003年 | 2855篇 |
2002年 | 2504篇 |
2001年 | 2179篇 |
2000年 | 2141篇 |
1999年 | 1901篇 |
1998年 | 1681篇 |
1997年 | 1267篇 |
1996年 | 1095篇 |
1995年 | 957篇 |
1994年 | 883篇 |
1993年 | 745篇 |
1992年 | 503篇 |
1991年 | 431篇 |
1990年 | 302篇 |
1989年 | 234篇 |
1988年 | 205篇 |
1987年 | 121篇 |
1986年 | 71篇 |
1985年 | 60篇 |
1984年 | 38篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1978年 | 25篇 |
1977年 | 10篇 |
1973年 | 9篇 |
1954年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
41.
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
42.
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
43.
本文在已有数据处理方法的基础上,利用近代数值逼近理论,给出了从时空域角度描述地壳垂直运动过程的一种具体的函数解析形式。最后给出了一个实际算例。 相似文献
44.
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
45.
The finite‐element formulation and integration algorithms developed in Part I are used to analyse a number of practical problems involving unsaturated and saturated soils. The formulation and algorithms perform well for all the cases analysed, with the robustness of the latter being largely insensitive to user‐defined parameters such as the number of coarse time steps and error control tolerances. The efficiency of the algorithms, as measured by the CPU time consumed, does not depend on the number of coarse time steps, but may be influenced by the error control tolerances. Based on the analyses presented here, typical values for the error control tolerances are suggested. It is also shown that the constitutive modelling framework presented in Part I can, by adjusting one constitutive equation and one or two material parameters, be used to simulate soils that expand or collapse upon wetting. Treating the suction as a strain variable instead of a stress variable proves to be an efficient and robust way of solving suction‐dependent plastic yielding. Moreover, the concept of the constitutive stress is a particularly convenient way of handling the transition between saturation and unsaturation. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
46.
47.
利用Logisitic曲线模型和扩展支撑模型对居民可支配收入预测和单项消费预测,以河北省居民的收入及其消费支出为实例,研究了城镇居民和农民的可支配收入分配和单项边际消费倾向,合理建立了预测模型,并理论计算了1999~2003年的通信消费方面的边际消费倾向、预测了2004~2008年通信消费情况。最后,根据预测结果对通信网络建设提出了一些有价值的建议。 相似文献
48.
Yunfei Bao Shengbo Chen 《东北亚地学研究》2006,9(1):100-108
IntroductionThe radiance leaving the earth-atmosphere sys-tem which can be sensed by a satellite borne ra-diometer is the sum of radiation emission fromtheearth surface and each atmospheric level that aretransmittedtothe top of the atmosphere.The radia-tion emissionfromthe earthsurface andthe radianceof each atmospheric level can be separated fromtheradiance at the top the atmospheric level a satellitemeasured.Thus,the earth surface parameters willbe retrieved from the surface radiance after a… 相似文献
49.
Flavio Scappini Cesare Cecchi-Pestellini Harvey Smith William Klemperer Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2003,341(2):657-661
We consider sulphur depletion in dense molecular clouds, and suggest hydrated sulphuric acid, H2 SO4 · n H2 O, as a component of interstellar dust in icy mantles. We discuss the formation of hydrated sulphuric acid in collapsing clouds and its instability in heated regions in terms of the existing hot core models and observations. We also show that some features of the infrared spectrum of hydrated sulphuric acid have correspondence in the observed spectra of young stellar objects. 相似文献
50.