全文获取类型
收费全文 | 10236篇 |
免费 | 3110篇 |
国内免费 | 1889篇 |
专业分类
测绘学 | 778篇 |
大气科学 | 1975篇 |
地球物理 | 2418篇 |
地质学 | 6031篇 |
海洋学 | 1230篇 |
天文学 | 517篇 |
综合类 | 912篇 |
自然地理 | 1374篇 |
出版年
2025年 | 9篇 |
2024年 | 237篇 |
2023年 | 304篇 |
2022年 | 549篇 |
2021年 | 643篇 |
2020年 | 542篇 |
2019年 | 608篇 |
2018年 | 650篇 |
2017年 | 625篇 |
2016年 | 607篇 |
2015年 | 538篇 |
2014年 | 598篇 |
2013年 | 578篇 |
2012年 | 564篇 |
2011年 | 648篇 |
2010年 | 622篇 |
2009年 | 562篇 |
2008年 | 527篇 |
2007年 | 535篇 |
2006年 | 411篇 |
2005年 | 399篇 |
2004年 | 318篇 |
2003年 | 290篇 |
2002年 | 341篇 |
2001年 | 345篇 |
2000年 | 327篇 |
1999年 | 414篇 |
1998年 | 295篇 |
1997年 | 336篇 |
1996年 | 274篇 |
1995年 | 263篇 |
1994年 | 206篇 |
1993年 | 230篇 |
1992年 | 180篇 |
1991年 | 118篇 |
1990年 | 100篇 |
1989年 | 88篇 |
1988年 | 83篇 |
1987年 | 50篇 |
1986年 | 42篇 |
1985年 | 34篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
11.
西藏聂拉木高喜马拉雅结晶岩系在区域上以单一的叶理和单一的拉伸线理占主要地位,其变形带的组构主要反映了透入性的伸展变形;根据显微构造分析表明早期由北往南推覆,晚期由南向北伸展,且晚期表现非常明显。 相似文献
12.
LBS定位技术研究与发展现状 总被引:9,自引:0,他引:9
90年代末,随着移动通信业的发展,诞生了"基于位置服务(Location Based Service,LBS)"的概念,并由此产生了一系列的产业链,创造了巨大的商业价值。近年来计算技术、无线网络通信技术以及电子技术的迅猛发展,导致了新一代技术革命的到来,极大地丰富原有的LBS定位模式,也对LBS提出了更新、更高的要求。本文描述了LBS的概念,及其兴起与发展的过程;从室外、室内两方面介绍了当前的LBS定位方法,并作了比较和分析;阐述了目前LBS定位中所存在的技术难点及研究重点;最后,对LBS的研究方向提出了看法,并对未来的LBS发展蓝图作出了展望。 相似文献
13.
Yanhu?He Jie?Yang Xiaohong?ChenEmail author 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(11):3083-3097
Water resources provide the foundation for human development and environmental sustainability. Water shortage occurs more or less in some regions, which usually causes sluggish economic activities, degraded ecology, and even conflicts and disputes over water use sectors. Game theory can better reflect the behaviors of involved stakeholders and has been increasingly employed in water resources management. This paper presents a framework for the allocation of river basin water in a cooperative way. The proposed framework applies the TOPSIS model combined with the entropy weight to determine stakeholders’ initial water share, reallocating water and net benefit by using four solution concepts for crisp and fuzzy games. Finally, the Fallback bargaining model was employed to achieve unanimous agreement over the four solution concepts. The framework was demonstrated with an application to the Dongjiang River Basin, South China. The results showed that, overall, the whole basin gained more total benefits when the players participated in fuzzy coalitions rather than in crisp coalitions, and \(\left\{ {NHS_{Fuzzy} \,and\, SV_{Crisp} } \right\}\) could better distribute the total benefit of the whole basin to each player. This study tested the effectiveness of this framework for the water allocation decision-making in the context of water management in river basins. The results provide technical support for water right trade among the stakeholders at basin scale and have the potential to relieve water use conflicts of the entire basin. 相似文献
14.
Food security has drawn great attention from both researchers and practitioners in recent years. Global warming and its resultant extreme drought events have become a great challenge to crop production and food price stability. This study aimed to establish a preliminary theoretical methodology and an operational approach for assessing the physical vulnerability of two wheat varieties (“Yongliang #4” and “Wenmai #6”) to agricultural drought using Environmental Policy Integrated Climate model (EPIC). Drought hazard index was set up based on output variables of the EPIC water stress (WS), including the magnitude and duration of WS during the crop-growing period. The physical vulnerability curves of two wheat varieties to drought were calculated by the simulated drought hazard indexes and loss ratios. And the curve’s effect on drought disaster risk was defined as A, B and C sections, respectively. Our analysis results showed that (a) physical vulnerability curves varied between two wheat varieties, which were determined by genetic parameters of crops; (b) compared with spring wheat “Yongliang 4#” winter wheat “Wenmai 6#” was less vulnerable to drought under the same drought hazard intensity scenario; (c) the wheat physical vulnerability curve to drought hazard displayed a S shape, suggesting a drought intensity–dependent magnifying or reducing effect of the physical vulnerability on drought disasters; (d) the reducing effect was mainly in the low-value area of vulnerability curve, whereas the magnifying effect was in the middle-value area, and the farming-pastoral zone and the Qinling Mountain–Huaihe River zone formed important spatial division belts. 相似文献
15.
16.
17.
18.
19.
高岭石—莫来石反应系列:^27Al和^29SiMAS NMR研究 总被引:21,自引:2,他引:21
根据艰我国八个不同成因和特征的高岭土样品在450-1450℃热处理产物的MAS NMR谱和XRD,IR,DTA等研究结果,结合有关资料讨论了高岭石-莫来石反应序列的几个重要问题:1.高岭石的结构,尤其是五配位铝;2.980℃放热峰后的高温相是γ-Al2O3而不是Al-Si尖晶石;3.对于莫来石化过程,认为初始莫来石850-950℃变高岭石形成,二次莫来石由分凝的SiO2和γ-Al2O3在1200- 相似文献
20.
It is necessary for China to establish a feasible method to verify whether an emergency evacuation plan (EEP) provides timely evacuation under the threat of flooding as a result of dam failure. Based on simulating the inundation area resulting from failure of the Huaxi Dam, this paper puts forward a quantitative approach to assess the effectiveness of an EEP by estimating the evacuation clearance times. Differences between urban and rural areas are considered, and two transportation modes are selected. Total evacuation clearance times in rural and urban areas are 135 and 80?min, respectively. Results show that total evacuation clearance times are longer than the time it takes for the flood wave to reach some communities in the area. The paper also makes some suggestions on how to decrease the total clearance time and thus enhance the effectiveness of the EEP for the Huaxi Dam. 相似文献