全文获取类型
收费全文 | 4982篇 |
免费 | 784篇 |
国内免费 | 675篇 |
专业分类
测绘学 | 1314篇 |
大气科学 | 479篇 |
地球物理 | 993篇 |
地质学 | 2236篇 |
海洋学 | 645篇 |
天文学 | 71篇 |
综合类 | 284篇 |
自然地理 | 419篇 |
出版年
2024年 | 7篇 |
2023年 | 48篇 |
2022年 | 128篇 |
2021年 | 171篇 |
2020年 | 160篇 |
2019年 | 216篇 |
2018年 | 141篇 |
2017年 | 199篇 |
2016年 | 184篇 |
2015年 | 186篇 |
2014年 | 323篇 |
2013年 | 292篇 |
2012年 | 374篇 |
2011年 | 346篇 |
2010年 | 322篇 |
2009年 | 291篇 |
2008年 | 284篇 |
2007年 | 397篇 |
2006年 | 337篇 |
2005年 | 283篇 |
2004年 | 260篇 |
2003年 | 263篇 |
2002年 | 182篇 |
2001年 | 178篇 |
2000年 | 171篇 |
1999年 | 144篇 |
1998年 | 130篇 |
1997年 | 79篇 |
1996年 | 84篇 |
1995年 | 52篇 |
1994年 | 52篇 |
1993年 | 31篇 |
1992年 | 35篇 |
1991年 | 14篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有6441条查询结果,搜索用时 218 毫秒
181.
通过分析地图扫描数字化的误差因素.运用质量控制图评价学生实验数据质量,能够直观地对学生实验数据做出判断,同时也能比较各个实验小组及班级之间总体实验水平,及时发现实验准备工作中及实验方法本身的有关问题。 相似文献
182.
183.
184.
In our previous study (Earthquake Engineering and Structural Dynamics 2003; 32 :2301), we have developed a probabilistic algorithm for active control of structures. In the probabilistic control algorithm, the control force is determined by the probability that the structural energy exceeds a specified target critical energy, and the direction of a control force is determined by the Lyapunov controller design method. In this paper, an experimental verification of the proposed probabilistic control algorithm is presented. A three‐story test structure equipped with an active mass driver (AMD) has been used. The effectiveness of the control algorithm has been examined by exciting the test structure using a sinusoidal signal, a scaled El Centro earthquake and a broadband Gaussian white noise; and, especially, experiments on control have been performed under different conditions to that of system identification in order to prove the stability and robustness of the proposed control algorithm. The experimental results indicate that the probabilistic control algorithm can achieve a significant response reduction under various types of ground excitations even when the modeling error exists. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
185.
A new computational framework is developed for the design and retrofit of building structures by considering aseismic design as a complex adaptive process. For the initial phase of the development within this framework, genetic algorithms are employed for the discrete optimization of passively damped structural systems. The passive elements may include metallic plate dampers, viscous fluid dampers and viscoelastic solid dampers. The primary objective is to determine robust designs, including both the non‐linearity of the structural system and the uncertainty of the seismic environment. Within the present paper, this computational design approach is applied to a series of model problems, involving sizing and placement of passive dampers for energy dissipation. In order to facilitate our investigations and provide a baseline for further study, we introduce several simplifications for these initial examples. In particular, we employ deterministic lumped parameter structural models, memoryless fitness function definitions and hypothetical seismic environments. Despite these restrictions, some interesting results are obtained from the simulations and we are able to gain an understanding of the potential for the proposed evolutionary aseismic design methodology. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
186.
187.
188.
The Wilhelmine Alpe section near Immenstadt (Allgäu, south Germany), which represents one of the best continuously exposed outcrops within the northern Alpine foreland basin, has been analyzed for magnetostratigraphic and palynostratigraphic signals. The section comprises the marine-to-terrestrial transition from Lower Marine (UMM) to Lower Freshwater Molasse (USM) sediments. Based on the correlation of the local magnetic pattern with the geomagnetic polarity timescale (GPTS) and palynostratigraphic data, an age of about 31 Ma is suggested for the UMM–USM transition in the Wilhelmine Alpe section. A comparison with coeval magnetostratigraphic sections from central and eastern Switzerland indicates that the regression of the UMM sea along the southern margin of the Molasse basin occurred strongly heterochronously between 31.5 and 30 Ma. The heterochroneity is attributed to the deposition of fan-delta and alluvial fan sediments which document that the overall marine conditions during the UMM were accompanied by strong clastic input derived from the rising Alps. This clastic contribution had a much stronger influence on the depositional pattern than previously thought. 相似文献
189.
190.
厦门市海沧区北市花岗岩矿滑坡发生于2004年10月30日14时。滑坡位于呆场的西端帮顶部的第四系填土和淤泥质土层中,滑体将该区域原设的抗滑桩剪断、拔出、推移,土石迅速越过矿区运输公路,塌落到采场工作面,将正在作业的2名工人和生产设备掩埋。滑坡宽度约60m,最大垂直厚度约14m,总体积约13000m^3。由于滑坡对原有防护体系的破坏,根据滑体调查和极限平衡计算结果,滑坡处于不稳定状态,直接威胁着整个采场设备和未来生产的安全。必须对北市花岗岩矿滑坡进行专项治理。滑坡宜采用治水、削坡减载和支挡相结合的综合治理措施。 相似文献