全文获取类型
收费全文 | 8821篇 |
免费 | 2033篇 |
国内免费 | 3281篇 |
专业分类
测绘学 | 1518篇 |
大气科学 | 1361篇 |
地球物理 | 1732篇 |
地质学 | 5971篇 |
海洋学 | 1470篇 |
天文学 | 115篇 |
综合类 | 778篇 |
自然地理 | 1190篇 |
出版年
2024年 | 88篇 |
2023年 | 273篇 |
2022年 | 594篇 |
2021年 | 681篇 |
2020年 | 552篇 |
2019年 | 655篇 |
2018年 | 625篇 |
2017年 | 549篇 |
2016年 | 624篇 |
2015年 | 590篇 |
2014年 | 654篇 |
2013年 | 742篇 |
2012年 | 828篇 |
2011年 | 804篇 |
2010年 | 806篇 |
2009年 | 696篇 |
2008年 | 659篇 |
2007年 | 673篇 |
2006年 | 592篇 |
2005年 | 457篇 |
2004年 | 360篇 |
2003年 | 267篇 |
2002年 | 288篇 |
2001年 | 280篇 |
2000年 | 209篇 |
1999年 | 127篇 |
1998年 | 75篇 |
1997年 | 62篇 |
1996年 | 54篇 |
1995年 | 35篇 |
1994年 | 37篇 |
1993年 | 31篇 |
1992年 | 46篇 |
1991年 | 31篇 |
1990年 | 21篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1958年 | 1篇 |
1957年 | 4篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
151.
152.
153.
论城市应急避险场所建设 总被引:1,自引:0,他引:1
做好减灾工作,加强应急避险场所建设是一项重要的任务,是落实以人为本,构建和谐社会的具体体现之一。1城市应急避险场所的性质笔者认为,城市避险场所的定义为:城市应急避险场所是为城市或城镇受到各种灾害侵袭而暂时离开居所的人群临时提供的、利用各种空旷场地和大型馆所预先设立的躲避灾难、居留和生活的公共场所。各种灾害包括自然灾害、事故灾难、突发公共卫生灾害、突发社会安全事件等。受助人群包括当地居民以及受灾当地的外来人群。避险场所提供的是临时性的居留场所,其基本服务是政府免费提供的,一旦灾难结束或受灾家园得到重建,停… 相似文献
154.
Introduction The observation records of strong ground motion previously, on the one hand, supplied basicdata both to research on earthquake engineering and to constitute the criterion of aseismatic de-signing of all project structures; on the other hand, it provided important information for the re-search on the process of epicenter burst in seismology. With the development of research on strongground motion observation, especially the development of the new generation accelerograph,which… 相似文献
155.
Introduction The anisotropy of the Earth crust medium is a common phenomenon(Crampin,1984).More and more observation materials and study results have proved that on most of the Earth′s upper crust is spread fluid-filled cracks and microcracks,which are aligned according to the contempo-rary stress-field.Such distributions of aligned cracks show effectively anisotropy to seismic wave and the phenomenon is called extensive-dilatancy anisotropy(EDA)(Crampin et al,1984).At the same time,it is … 相似文献
156.
WU Yaping ZHU Yuanlin GUO Chunxiang SU Qiang & MA Wei . School of Civil Engineering Lanzhou Jiaotong University Lanzhou China . State Key Laboratory of Frozen Soil Engineering Cold Arid Regions Environmental Engineering Research Institute Chinese Academy of Sciences Lanzhou China 《中国科学D辑(英文版)》2005,48(7)
In the construction of Qinghai-Tibet railway,to avoid diseases caused by frost heave and thaw col-lapse of frozen ground,besides the normal bridges over the rivers,a lot of dry bridge structures have been built to replace subgrade in the regions of high tem-perature and high ice content frozen soil.So,the problems on forming mechanism of bearing capacity of pile foundation in cold regions already become one of hot spot problems in frozen soil engineering.Freezing force and frost heave force ar… 相似文献
157.
鲁东南岚山头含柯石英榴辉岩主要产于花岗质片麻岩内,是苏鲁超高压变质带主要榴辉岩体密集分布区之一。流体包裹体研究表明,榴辉岩矿物及细脉石英中捕获有四种类型包裹体:在超高压-高压榴辉岩相条件下捕获的 N_2±CO_2包裹体;在高压榴辉宕重结晶阶段被捕获的 CO_2-H_2O 包裹体和含子矿物高盐度 H_2O 溶液包裹体:在超高压岩石折返过程中的最晚(角闪岩相退变质甚至更晚)阶段捕获的低盐度 H_2O 溶液包裹体。利用榴辉岩矿物及脉体石英中捕获的流体包裹体相互期次关系,可以对本区超高压变质作用板片折返过程中的流体演化史进行重建。 相似文献
158.
喀斯特地区旅游开发的自然景观保护--以贵州省绥阳县为例 总被引:3,自引:0,他引:3
该文以贵州省绥阳县为例,针对我国西南喀斯特地区旅游开发中自然环境的特点,探讨溶洞景观的保护、喀斯特地表生态环境保护、水体的保护与综合治理等问题。 相似文献
159.
Distinguishing streamflow trends caused by changes in climate,forest cover,and permafrost in a large watershed in northeastern China 下载免费PDF全文
Understanding how rivers respond to changes in land cover, climate, and subsurface conditions is critical for sustainably managing water resources and ecosystems. In this study, long‐term hydrologic, climate, and satellite data (1973–2012) from the Upper Tahe River watershed (2359 km2) in the Da Hinggan Mountains of northeast China were analysed to quantify the relative hydrologic effects of climate variability (system input) and the combined influences of forest cover change and permafrost thaw (system characteristics) on average annual streamflow (system response) using 2 methods: the sensitivity‐based method and the Kendall–Theil robust line method. The study period was subdivided into a forest harvesting period (1973–1987), a forest stability period (1988–2001), and a forest recovery period (2002–2012). The results indicated that the combined effects of forest harvesting and permafrost thaw on streamflow (+ 47.0 mm) from the forest harvesting period to the forest stability period was approximately twice as large as the effect associated with climate variability (+20.2 mm). Similarly, from the forest stability period to the forest recovery period, the decrease in average annual streamflow attributed to the combined effects of forest recovery and permafrost thaw (?38.0 mm) was much greater than the decrease due to climate variability (?22.2 mm). A simple method was used to separate the distinct impacts of forest cover change and permafrost thaw, but distinguishing these influences is difficult due to changes in surface and subsurface hydrologic connectivity associated with permafrost thaw. The results highlight the need to consider multiple streamflow drivers in future watershed and aquatic ecosystem management. Due to the ecological and hydrological susceptibility to disturbances in the Da Hinggan Mountains, forest harvesting will likely negatively impact ecohydrological processes in this region, and the effects of forest species transition in the forest recovery process should be further investigated. 相似文献
160.
Piecewise prediction model for watershed‐scale erosion and sediment yield of individual rainfall events on the Loess Plateau,China 下载免费PDF全文
Yu Guo‐Qiang Zhang Mao‐Sheng Li Zhan‐Bin Li Peng Zhang Xia Cheng Sheng‐Dong 《水文研究》2014,28(21):5322-5336
Establishing a universal watershed‐scale erosion and sediment yield prediction model represents a frontier field in erosion and soil/water conservation. The research presented here was conducted on the Chabagou watershed, which is located in the first sub‐region of the hill‐gully area of the Loess Plateau, China. A back‐propagation artificial neural model for watershed‐scale erosion and sediment yield was established, with the accuracy of the model, then compared with that of multiple linear regression. The sensitivity degree of various factors to erosion and sediment yield was quantitatively analysed using the default factor test. On the basis of the sensitive factors and the fractal information dimension, the piecewise prediction model for erosion and sediment yield of individual rainfall events was established and further verified. The results revealed the back‐propagation artificial neural network model to perform better than the multiple linear regression model in terms of predicting the erosion modulus, with the former able to effectively characterize dynamic changes in sediment yield under comprehensive factor conditions. The sensitivity of runoff erosion power and runoff depth to the erosion and sediment yield associated with individual rainfall events was found to be related to the complexity of surface topography. The characteristics of such a hydrological response are thus closely related to topography. When the fractal information dimension is greater than the topographic threshold, the accuracy of prediction using runoff erosion power is higher than that of using runoff depth. In contrast, when the fractal information dimension is smaller than the topographic threshold, the accuracy of prediction using runoff depth is higher than that of using runoff erosion power. The developed piecewise prediction model for watershed‐scale erosion and sediment yield of individual rainfall events, which introduces runoff erosion power and runoff depth using the fractal information dimension as a boundary, can be considered feasible and reliable and has a high prediction accuracy. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献