全文获取类型
收费全文 | 1885篇 |
免费 | 466篇 |
国内免费 | 590篇 |
专业分类
测绘学 | 60篇 |
大气科学 | 11篇 |
地球物理 | 1149篇 |
地质学 | 1272篇 |
海洋学 | 199篇 |
天文学 | 10篇 |
综合类 | 74篇 |
自然地理 | 166篇 |
出版年
2024年 | 10篇 |
2023年 | 21篇 |
2022年 | 57篇 |
2021年 | 72篇 |
2020年 | 105篇 |
2019年 | 91篇 |
2018年 | 102篇 |
2017年 | 85篇 |
2016年 | 99篇 |
2015年 | 120篇 |
2014年 | 142篇 |
2013年 | 137篇 |
2012年 | 144篇 |
2011年 | 170篇 |
2010年 | 140篇 |
2009年 | 144篇 |
2008年 | 128篇 |
2007年 | 154篇 |
2006年 | 145篇 |
2005年 | 121篇 |
2004年 | 109篇 |
2003年 | 90篇 |
2002年 | 87篇 |
2001年 | 53篇 |
2000年 | 71篇 |
1999年 | 44篇 |
1998年 | 46篇 |
1997年 | 46篇 |
1996年 | 34篇 |
1995年 | 26篇 |
1994年 | 39篇 |
1993年 | 22篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 18篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 1篇 |
排序方式: 共有2941条查询结果,搜索用时 31 毫秒
41.
T-matrix approach to shale acoustics 总被引:2,自引:0,他引:2
Morten Jakobsen John A. Hudson Tor Arne Johansen 《Geophysical Journal International》2003,154(2):533-558
42.
43.
论上海软土地基⑦⑧⑨层压缩模量Es的定值问题 总被引:2,自引:0,他引:2
上海地区深部土层⑦⑧⑨层埋深在30~70m。对其压缩模量Es的定值问题,现行《上海市地基基础设计规范》(DGJ08 11 1999)(后文中简称《规范》)长期以来确定室内试验E0 1~0 2值为沉降计算值,导致沉降计算值与建(构)筑物实际沉降量之间相差2~8倍。为符合规范的变形要求,设计人员不得不采取桩加粗、加长、加密的办法,从而造成桩基投资的极大浪费。为了正确认识深部土层的Es值,上海岩土工程界进行了多种形式的试验研究。近年来,笔者结合上海高、大、深、重建(构)筑物的工程实践,深入进行上海深部⑦⑧⑨层压缩模量Es的试验研究,获得许多新的认识,对其定值问题作了研究,提出⑦⑧⑨层的建议值,供同行参考研讨。 相似文献
44.
45.
Introduction The rock medium shows mainly elastic character under low-temperature, low-pressure and external force for short duration, yet it shows rheologic property under high-temperature, high-pressure and long-time external force. It is reasonable that the rapid earthquake generating process lasted for tens seconds is analyzed by the elastic theory. As for the earthquake generating process for hundreds or thousand years, nevertheless, the rheologic property of rock must be taken into accou… 相似文献
46.
A new earthquake resistant structural system for multi‐storey frame structures, based on a dual function of its bracing components, is developed. This consists of a hysteretic damper device and a cross‐bracing mechanism with a kinetic closed circuit, working only in tension, so that cable members can be used for this purpose. Solutions are presented regarding the connections' design of three types of structural frame system, that are concerned throughout the study: braced moment free frame, braced moment resisting frame with moment free supports, and with moment resisting supports. The dynamic behaviour of the system is investigated on the basis of an SDOF model, and based on the response spectra method an approximate design approach of the controlled structures is shown. From the time history analysis of the structural systems for the El Centro earthquake the areas of appropriate stiffness relations of the frames to the hysteretic dampers and the cable braces are deduced, so that the energy dissipation of the system may be controlled by the damper‐cable bracing mechanism. Based on the results of these studies, a predesign approach is developed for the implementation of the control system in frame structures. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
47.
In the new trend of seismic design methodology, the static pushover analysis is recommended for simple or regular structures whilst the time‐history analysis is recommended for complex structures. To this end, the applicable range of the pushover analysis has to be clarified. This study aims at investigating the applicability of pushover analysis to multi‐span continuous bridge systems with thin‐walled steel piers. The focus is concentrated on the response demand predictions in longitudinal or transverse directions. The pushover analysis procedure for such structures is firstly summarized and then parametric studies are carried out on bridges with different types of superstructure‐pier bearing connections. The considered parameters, such as piers' stiffness distribution and pier–0.5ptdeck stiffness ratio, are varied to cover both regular and irregular structures. Finally, the relation of the applicability of pushover analysis to different structural formats is demonstrated and a criterion based on the higher modal contribution is proposed to quantitatively specify the applicable range. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
48.
Nicolas Luco Yasuhiro Mori Yosuke Funahashi C. Allin Cornell Masayoshi Nakashima 《地震工程与结构动力学》2003,32(14):2267-2288
Predictors (or estimates) of seismic structural demands that are less computationally time‐consuming than non‐linear dynamic analysis can be useful for structural performance assessment and for design. In this paper, we evaluate the bias and precision of predictors that make use of, at most, (i) elastic modal vibration properties of the given structure, (ii) the results of a non‐linear static pushover analysis of the structure, and (iii) elastic and inelastic single‐degree‐of‐freedom time‐history analyses for the specified ground motion record. The main predictor of interest is an extension of first‐mode elastic spectral acceleration that additionally takes into account both the second‐mode contribution to (elastic) structural response and the effects of inelasticity. This predictor is evaluated with respect to non‐linear dynamic analysis results for ‘fishbone’ models of steel moment‐resisting frame (SMRF) buildings. The relatively small number of degrees of freedom for each fishbone model allows us to consider several short‐to‐long period buildings and numerous near‐ and far‐field earthquake ground motions of interest in both Japan and the U.S. Before doing so, though, we verify that estimates of the bias and precision of the predictor obtained using fishbone models are effectively equivalent to those based on typical ‘full‐frame’ models of the same buildings. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
49.
GPS测量控制网为了与地面国家控制网进行联合的平差,必须与国家坐标系进行联测,GPS接收机有时也必须安置在有三角钢标的旧有控制点上。通过对此分析研究了三角钢标对GPS测量的影响,对设计和实施GPS测量的用户具有一定的参考价值。 相似文献
50.
RMR法与Q法是国内外八、九十年代岩体质量和参数估算的常用方法,然而RMR法和Q法对质量较差的岩体不太实用,而RMi法是一种既适用于软岩又适用于硬岩的岩体质量评价和参数估算方法。本文在介绍RMi法基本原理的基础上,对贵州省鱼简河水库坝基岩体变形模量进行确定。 相似文献