全文获取类型
收费全文 | 4655篇 |
免费 | 1172篇 |
国内免费 | 768篇 |
专业分类
测绘学 | 917篇 |
大气科学 | 320篇 |
地球物理 | 879篇 |
地质学 | 2760篇 |
海洋学 | 723篇 |
天文学 | 21篇 |
综合类 | 446篇 |
自然地理 | 529篇 |
出版年
2024年 | 16篇 |
2023年 | 65篇 |
2022年 | 161篇 |
2021年 | 213篇 |
2020年 | 214篇 |
2019年 | 228篇 |
2018年 | 154篇 |
2017年 | 254篇 |
2016年 | 238篇 |
2015年 | 260篇 |
2014年 | 310篇 |
2013年 | 373篇 |
2012年 | 374篇 |
2011年 | 371篇 |
2010年 | 326篇 |
2009年 | 322篇 |
2008年 | 298篇 |
2007年 | 290篇 |
2006年 | 307篇 |
2005年 | 272篇 |
2004年 | 254篇 |
2003年 | 244篇 |
2002年 | 161篇 |
2001年 | 138篇 |
2000年 | 138篇 |
1999年 | 104篇 |
1998年 | 99篇 |
1997年 | 70篇 |
1996年 | 57篇 |
1995年 | 39篇 |
1994年 | 41篇 |
1993年 | 33篇 |
1992年 | 28篇 |
1991年 | 28篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1972年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有6595条查询结果,搜索用时 15 毫秒
101.
Katy A. Boon Peter Rostron Michael H. Ramsey 《Geostandards and Geoanalytical Research》2011,35(3):353-367
In the assessment of potentially contaminated land, the number of samples and the uncertainty of the measurements (including that from sampling) are both important factors in the planning and implementation of an investigation. Both parameters also effect the interpretation of the measurements produced, and the process of making decisions based upon those measurements. However, despite their importance, previously there has been no method for assessing if an investigation is fit‐for‐purpose with respect to both of these parameters. The Whole Site Optimised Contaminated Land Investigation (WSOCLI) method has been developed to address this issue, and to allow the optimisation of an investigation with respect to both the number of samples and the measurement uncertainty, using an economic loss function. This function was developed to calculate an ‘expectation of (financial) loss’, incorporating costs of the investigation itself, subsequent land remediation, and potential consequential costs. To allow the evaluation of the WSOCLI method a computer program ‘OCLISIM’ has been developed to produce sample data from simulated contaminated land investigations. One advantage of such an approach is that as the ‘true’ contaminant concentrations are created by the program, these values are known, which is not the case in a real contaminated land investigation. This enables direct comparisons between functions of the ‘true’ concentrations and functions of the simulated measurements. A second advantage of simulation for this purpose is that the WSOCLI method can be tested on many different patterns and intensities of contamination. The WSOCLI method performed particularly well at high sampling densities producing expectations of financial loss that approximated to the true costs, which were also calculated by the program. WSOCLI was shown to produce notable trends in the relationship between the overall cost (i.e., expectation of loss) and both the number of samples and the measurement uncertainty, which are: (a) low measurement uncertainty was optimal when the decision threshold was between the mean background and the mean hot spot concentrations. (b) When the hot spot mean concentration is equal to or near the decision threshold, then mid‐range measurement uncertainties were optimal. (c) When the decision threshold exceeds the mean of the hot spot, mid‐range measurement uncertainties were optimal. The trends indicate that the uncertainty may continue to rise if the difference between hot spot mean and the decision threshold increases further. (d) In any of the above scenarios, the optimal measurement uncertainty was lower if there is a large geochemical variance (i.e., heterogeneity) within the hot spot. (e) The optimal number of samples for each scenario was indicated by the WSOCLI method, and was between 50 and 100 for the scenarios considered generally; although there was significant noise in the predictions, which needs to be addressed in future work to allow such conclusions to be clearer. 相似文献
102.
为解决确定性模型可能为地下水源地划分带来的保护不足或过保护问题,探索采用基于正交拉丁超立方抽样法的地下水模型研究,并结合粒子反向追踪技术,进行地下水流随机模拟和对应保护区的概率统计分析,最终得到具有分布概率的保护区范围。为验证该方法的实用性与可靠性,选取北京市平谷区王都庄应急水源地进行实例应用研究。在考虑渗透系数和降雨补给量随机抽样组合基础上进行地下水流动随机模拟,并完成对应保护区划分和加权统计。与确定性模拟划分结果相对比:一级保护区中,确定性模拟划分结果仅相当于随机模拟结果中统计概率70%以上的范围;对于二级保护区,确定法对应保护面积相当于随机模拟结果中50%概率以上的范围。实例研究表明,基于正交拉丁超立方抽样的随机模拟法可完成多个不确定性输入变量条件下的随机模拟,且在小样本数的基础上获得理想结果,适用于复杂水文地质条件下的地下水源地保护区划分研究。 相似文献
103.
南方(湖南、贵州、四川、云南、重庆等)煤田在绳索取心钻进时,遇到的问题及解决办法有一定的普遍性。针对该区的地层特点,提出了合理的钻进方法及钻具配套方案;根据施工区的条件及孔深要求,进行了设备配套的研究;从研究区内事故发生的普遍性入手,摸索出一套较为合理的事故处理方案和工艺配套措施。通过多方面的研究,形成了一套比较合理的配套方案,据此方案在云贵川湘等地施工,均取得了较好的经济效益与社会效益方面。 相似文献
104.
105.
六盘水市矿产资源丰富,尤以煤炭为主,但从目前煤炭资源开发利用现状来看,其结构布局尚欠合理,开发利用方式比较粗放,存在"采富弃贫、大矿小开、一矿多开、技术落后、安全条件差、资源回收率低"等现象,环境保护与恢复治理的难度也越来越大。为了提高煤炭资源开采利用效率,从规模结构、技术结构、产品结构三个方面提出了六盘水市煤炭资源开发利用结构调整与优化方法:要求新建矿山在30万t/a以上,最低服务年限不低于25年,将目前的小型煤矿山减少到125个;采用高新技术和先进技术,促进矿企产业升级;进行产品结构调整,改变采矿、选矿、冶炼方式,实现集约型经营。 相似文献
106.
科学合理、规范有序、持续发展——大力推进上海市浅层地热能开发利用 总被引:1,自引:0,他引:1
浅层地热能是绿色环保可再生清洁能源,其开发利用对建设资源节约型、环境友好型社会具有重要意义。介绍了上海开展浅层地热能的科研工作与开发应用成功实践,探讨了产业化发展中应重视和加强的技术和管理等方面的主要关键问题。 相似文献
107.
Researches on breaking-induced currents by waves are summarized firstly in this paper. Then, a combined numerical model in orthogonal curvilinear coordinates is presented to simulate wave-induced current in areas with curved boundary or irregular coastline. The proposed wave-induced current model includes a nearshore current module established through orthogonal curvilinear transformation form of shallow water equations and a wave module based on the curvilinear parabolic approximation wave equation. The wave module actually serves as the driving force to provide the current module with required radiation stresses. The Crank-Nicolson finite difference scheme and the alternating directions implicit method are used to solve the wave and current module, respectively. The established surf zone currents model is validated by two numerical experiments about longshore currents and rip currents in basins with rip channel and breakwater. The numerical results are compared with the measured data and published numerical results. 相似文献
108.
为有效整合和管理各类海岛规划信息资源,针对海岛数据的特点,结合海岛规划管理和业务功能的需求,提出基于B/S和C/S的混合结构来构建规划管理信息系统的思想,设计了系统的基本框架和主要功能,探讨了系统实现过程中的关键技术,为海岛规划管理信息系统研发、综合管理和信息共享提供一个有效的解决方案。 相似文献
109.
110.
介绍了三态内容寻址存储器的硬件组成,分析了三态内容寻址存储器的工作原理,结合March算法的理论设计了三态内容寻址存储器故障诊断的方法,并介绍了故障检测的流程,在VxWorks的操作系统下以Tornado为开发平台实现了三态内容寻址存储器的故障诊断功能,最后给出了实验结果。实际应用表明结果可靠性能高能满足用户的需求。 相似文献