全文获取类型
收费全文 | 5560篇 |
免费 | 940篇 |
国内免费 | 635篇 |
专业分类
测绘学 | 1004篇 |
大气科学 | 480篇 |
地球物理 | 1460篇 |
地质学 | 2290篇 |
海洋学 | 716篇 |
天文学 | 42篇 |
综合类 | 448篇 |
自然地理 | 695篇 |
出版年
2024年 | 22篇 |
2023年 | 60篇 |
2022年 | 145篇 |
2021年 | 177篇 |
2020年 | 195篇 |
2019年 | 232篇 |
2018年 | 177篇 |
2017年 | 241篇 |
2016年 | 208篇 |
2015年 | 230篇 |
2014年 | 301篇 |
2013年 | 363篇 |
2012年 | 381篇 |
2011年 | 417篇 |
2010年 | 325篇 |
2009年 | 362篇 |
2008年 | 366篇 |
2007年 | 409篇 |
2006年 | 358篇 |
2005年 | 309篇 |
2004年 | 274篇 |
2003年 | 243篇 |
2002年 | 186篇 |
2001年 | 192篇 |
2000年 | 164篇 |
1999年 | 150篇 |
1998年 | 118篇 |
1997年 | 99篇 |
1996年 | 89篇 |
1995年 | 77篇 |
1994年 | 66篇 |
1993年 | 50篇 |
1992年 | 38篇 |
1991年 | 17篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有7135条查询结果,搜索用时 15 毫秒
161.
162.
三氮对人体的危害已引起人们的关注,NO3^--N是三氮的主体。本文分析了武川一四子王旗地区NO3^-的污染现状及其在水平和垂向上的分布特征和规律,研究了污染原因和过程,提出了相应的防治对策。 相似文献
163.
Several theoretical, empirical and semi-empirical methods are available in the literature to predict settlement of drilled
shafts in sandy soils. In the Arabian Gulf countries, specifically in the United Arab Emirates, equations and procedure from
the rest of the world are being used in analysis and design of drilled shafts without proper validation. It is the aim of
this study to assess the applicability and evaluate the accuracy of two well known, and commonly used methods for pile prediction
in the United Arab Emirates (UAE), namely Vesic (1977) and Poulos (1979), via comparison with data from field pile load tests
conducted on shafts drilled in the region. Some of these tests were conducted for the purpose of this study, while others
were made available through the courtesy of International Piling Contractors who are active in the region (e.g. Bauer International
and Swiss Borings). Pile load test data were analyzed to back-calculate the model parameters related to settlement under different
loading stages. Geological data and soil properties were obtained from studies conducted at the relevant sites. An effort
is made to correlate soil properties with the prediction models. Statistical analysis is conducted to assess the accuracy
of the results obtained from the two methods at different stages of loading via those obtained from pile load tests. Moreover,
a detailed parametric study is conducted to assess the effect of the related parameters on the predicted pile settlement and
the estimated settlement at different stages of loading. The study concluded with a recommendation of the most appropriate
models and procedures to be followed for predicting the settlement of drilled shafts in the UAE, together with useful charts
and correlation relations. Results showed that settlement values predicted by Vesic (1977) and Poulos (1979) overestimates
the true values.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
164.
In underground coal mining any increase in coal recovery rate is dependent on a decrease in pillar size. Backfilling is one way of reducing the required size of pillars and hence the volume of coal left underground. Therefore any comparisons made between a self-supported mine layout and backfill supported mine layout are based directly on pillar design. The most effective way to examine the effect of backfill on pillar support, and subsequently the rate of recovery, would be to incorporate the mechanisms of backfill support directly into the current design procedure for coal pillars. This paper presents a review of the mechanics of backfill support, a method of estimating the magnitude of that support based on earth pressure theory, and an example that incorporates backfill support into current coal pillar design. 相似文献
165.
Mountain Protection Forests against Natural Hazards and Risks: New French Developments by Integrating Forests in Risk Zoning 总被引:4,自引:0,他引:4
Forests can play a very significant role in protection against natural hazards and risks in mountain lands, especially against erosion and rockfalls. This paper first assesses knowledge concerning the capacity of forests to control natural hazards, with emphasis placed on forest location in catchments or slopes. Zoning aspects are then presented; based on the use of GIS, they allow determining priorities for forestry operations (cuts and biological engineering), in view to setting up an 'optimal management' of mountain forest ecosystems. Finally, an explanation is given of how the results of research are used for the management and planning of mountain ecosystems, illustrated by an example of researcher-practitioner transfer in France. Zoning, prevention, display and regular aspects are developed. On the basis of the experience and knowledge presented here, recommendations are proposed to better take into account the role of mountain forests in the control of natural hazards and risks. It is necessary to have an adapted legislative and economic framework, define priority forest intervention zones and determine an adapted sylviculture. 相似文献
166.
可持续发展是我们时代的主题,已被世界各国人民作为发展本国经济所追求的理想方式。作为国民经济建设先行官的地质工作组成部分的探矿工程(岩土钻掘工程)技术与可持续发展有密不可分的关系。针对我们所处的时代特征及人类生存发展的时代主题,面对国民经济建设新形势,简要阐述了探矿工程(岩土钻掘工程)技术与可持续发展的关系以及技术本身发展的有关问题。 相似文献
167.
168.
169.
以山西省祁县依法管理工程抗震设防要求为例,论述了强制性审核、确定一般工业、民用建设工程抗震设防要求的重要性及其深远意义。结合工作实际.总结了部分依法行政、规范管理和落实抗震设防要求的经验。 相似文献
170.