全文获取类型
收费全文 | 7324篇 |
免费 | 677篇 |
国内免费 | 674篇 |
专业分类
测绘学 | 2088篇 |
大气科学 | 578篇 |
地球物理 | 1635篇 |
地质学 | 1596篇 |
海洋学 | 587篇 |
天文学 | 70篇 |
综合类 | 805篇 |
自然地理 | 1316篇 |
出版年
2024年 | 23篇 |
2023年 | 94篇 |
2022年 | 316篇 |
2021年 | 368篇 |
2020年 | 336篇 |
2019年 | 369篇 |
2018年 | 195篇 |
2017年 | 270篇 |
2016年 | 266篇 |
2015年 | 279篇 |
2014年 | 335篇 |
2013年 | 421篇 |
2012年 | 420篇 |
2011年 | 409篇 |
2010年 | 327篇 |
2009年 | 340篇 |
2008年 | 386篇 |
2007年 | 465篇 |
2006年 | 407篇 |
2005年 | 329篇 |
2004年 | 320篇 |
2003年 | 302篇 |
2002年 | 248篇 |
2001年 | 259篇 |
2000年 | 180篇 |
1999年 | 160篇 |
1998年 | 178篇 |
1997年 | 137篇 |
1996年 | 91篇 |
1995年 | 93篇 |
1994年 | 93篇 |
1993年 | 62篇 |
1992年 | 41篇 |
1991年 | 31篇 |
1990年 | 27篇 |
1989年 | 22篇 |
1988年 | 27篇 |
1987年 | 18篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有8675条查询结果,搜索用时 15 毫秒
1.
平衡剖面的制作流程及其地质意义 总被引:9,自引:0,他引:9
平衡剖面技术是地质思维和计算机技术的结晶,使对断层构造的研究提高到定量阶段,其依据是在垂直构造走向的剖面上,地层长度和面积(2D)或体积(3D)是均衡的。在此原理基础上利用数学手段对盆地的构造发育史进行正演和反演模拟,直观地再现地下构造的原始几何形态,迅速提供地震剖面的构造解释方案,并对解释结果进行检验(不平衡的剖面其解释一般有问题),为深刻认识构造发育史、分析油气运移及聚集规律提供依据,提高了工作效率。其结果也为盆地模拟、油藏模拟、定量计算构造伸缩量等地质研究打下了坚实的基础[1]。 相似文献
2.
The SAS® computer software system, widely used and respected for its capabilities in statistical analysis and data base management, now includes a new set of graphic and cartographic procedures called SAS GRAPH?. We have used these cartographic procedures in research on mapping ethno-cultural census data from metropolitan areas in Ontario and in undergraduate and graduate courses in computer cartography. On the basis of that experience, we describe and evaluate SAS/GRAPH'S cartographic capabilities and illustrate with maps drawn by various devices. 相似文献
3.
Ning Gaidi 《地球科学与环境学报》1997,(2)
本文介绍了由8031单片机控制的LED发光二极管阵列构成的电子显示屏显示原理、显示屏数据锁存、驱动接口电路、键盘接口电路、字模存放电路及软件框图。 相似文献
4.
We have developed a method for analytically solving the porous medium flow equation in many different geometries for horizontal (two‐dimensional), homogeneous and isotropic aquifers containing impermeable boundaries and any number of pumping or injection wells located at arbitrary positions within the system. Solutions and results are presented for rectangular and circular aquifers but the method presented here is easily extendible to many geometries. Results are also presented for systems where constant head boundary conditions can be emulated internal to the aquifer boundary. Recommendations for extensions of the present work are briefly discussed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
5.
JINFeng-jun 《中国地理科学(英文版)》2003,13(2):97-103
It is very important to establish cooperative mechanism to guarantee all members to develop their e-conomies in the Yellow Sea Rim. In this paper, the development strategies ofshipplng centers and transportation networkare discussed based on economic giobalization tendency. The results argue that a united transportation network should bebuilt in order to promote the economic competition of Northeast Asia in the world. As a key component of the economiccooperation, a hierarchical shipping centers network should be established with Hong Kong, Shanghai, Pusan, Koho,and Tokyo as cores. The authorities of China, Japan, R. O. Korea and D. P. B. Korea should make more efforts tobuild a set of cooperation institutions based on raising the transportation efficiency. 相似文献
6.
WANGXie-kang HUANGEr CUIPeng 《中国地理科学(英文版)》2003,13(3):262-266
Debris flow is one of the most destructive phenomena of natural hazards. Recently, major natural haz-ard, claiming human lives and assets, is due to debris flow in the world. Several practical methods for forecasting de-bris flow have been proposed, however, the accuracy of these methods is not high enough for practical use because of the stochastic and non-linear characteristics of debris flow. Artificial neural network has proven to be feasible and use-fill in developing models for nonlinear systems. On the other hand, predicting the future behavior based on a time se-ries of collected historical data is also an important tool in many scientific applications. In this study we present a three-layer feed-forward neural network model to forecast surge of debris flow according to the time series data collect-ed in the Jiangjia Ravine, situated in north part of Yunnan Province of China. The simulation and prediction of debris flow using the proposed approach shows this model is feasible, however, further studies are needed. 相似文献
7.
李毅心 《成都信息工程学院学报》2006,21(2):206-209
积件技术是教学软件发展的方向,探讨了用Power Builder前台结合SQL Server关系数据库后台进行多媒体教学积件管理的应用模式,并结合具体教学示例,进行了分析说明。 相似文献
8.
9.
Advanced material constitutive models are used to describe complex soil behaviour. These models are often used in the solution of boundary value problems under general loading conditions. Users and developers of constitutive models need to methodically investigate the represented soil response under a wide range of loading conditions. This paper presents a systematic procedure for probing constitutive models. A general incremental strain probe, 6D hyperspherical strain probe (HSP), is introduced to examine rate‐independent model response under all possible strain loading conditions. Two special cases of HSP, the true triaxial strain probe (TTSP) and the plane‐strain strain probe (PSSP), are used to generate 3‐D objects that represent model stress response to probing. The TTSP, PSSP and general HSP procedures are demonstrated using elasto‐plastic models. The objects resulting from the probing procedure readily highlight important model characteristics including anisotropy, yielding, hardening, softening and failure. The PSSP procedure is applied to a Neural Network (NN) based constitutive model. It shows that this probing is especially useful in understanding NN constitutive models, which do not contain explicit functions for yield surface, hardening, or anisotropy. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
10.
着重讨论了网络用户经济效益的内涵以及用户的投入量和产出量,并提出了评价网络用户经济效益的指标体系,包括成本降低率,成本利润增长率、产品开发时间约率、市场占有增长率等系列指标。 相似文献