全文获取类型
收费全文 | 91315篇 |
免费 | 28612篇 |
国内免费 | 56139篇 |
专业分类
测绘学 | 14109篇 |
大气科学 | 26633篇 |
地球物理 | 21971篇 |
地质学 | 67818篇 |
海洋学 | 24225篇 |
天文学 | 1497篇 |
综合类 | 8569篇 |
自然地理 | 11244篇 |
出版年
2024年 | 937篇 |
2023年 | 2317篇 |
2022年 | 4570篇 |
2021年 | 5610篇 |
2020年 | 5481篇 |
2019年 | 8483篇 |
2018年 | 7958篇 |
2017年 | 7500篇 |
2016年 | 7731篇 |
2015年 | 8040篇 |
2014年 | 7486篇 |
2013年 | 8660篇 |
2012年 | 9332篇 |
2011年 | 9133篇 |
2010年 | 9163篇 |
2009年 | 8232篇 |
2008年 | 7573篇 |
2007年 | 7384篇 |
2006年 | 6905篇 |
2005年 | 5763篇 |
2004年 | 5136篇 |
2003年 | 4120篇 |
2002年 | 4072篇 |
2001年 | 3698篇 |
2000年 | 3031篇 |
1999年 | 2189篇 |
1998年 | 1826篇 |
1997年 | 1856篇 |
1996年 | 1446篇 |
1995年 | 1368篇 |
1994年 | 1244篇 |
1993年 | 1217篇 |
1992年 | 1060篇 |
1991年 | 763篇 |
1990年 | 757篇 |
1989年 | 612篇 |
1988年 | 533篇 |
1987年 | 421篇 |
1986年 | 357篇 |
1985年 | 276篇 |
1984年 | 312篇 |
1983年 | 190篇 |
1982年 | 235篇 |
1981年 | 154篇 |
1980年 | 113篇 |
1979年 | 148篇 |
1978年 | 64篇 |
1977年 | 50篇 |
1976年 | 49篇 |
1971年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
991.
为研究钢筋砼摩擦耗能支撑框架结构的动力反应性能 ,对其中的摩擦耗能器单元和框架杆单元的单元刚度和力学模型做了分析。钢筋砼摩擦耗能支撑单元由支撑杆单元和钢板—橡胶摩擦耗能器单元组成 ,支撑单元可取空间杆单元 ,摩擦耗能器单元为平面应力矩形单元。摩擦耗能器单元的剪切恢复力曲线为理想的弹塑性曲线 ,根据耗能器单元的力学模型 ,可确定其在每一时刻的刚度 ;框架结构空间杆单元的恢复力模型采用双线型模型 ,根据杆单元的力学模型 ,可确定其在每一时刻的刚度。并利用所编制的程序对十层单榀两跨空间普通框架和摩擦耗能支撑框架在地震作用下进行了弹塑性反应时程分析 ,结果表明耗能支撑框架的顶层最大位移明显小于普通框架 相似文献
992.
Early Yanshanian post-orogenic granitoids in the Nanling region
Petrological constraints and geodynamic settings 总被引:1,自引:0,他引:1
Petrological constraints and geodynamic settings 总被引:1,自引:0,他引:1
Early Yanshanian magmatic suites predominate absolutely in the Nanling granite belt. They consist mainly of monzogranite and K-feldspar granite. There occur associations of early Yanshanian A-type granitoids (176 Ma-178 Ma) and bimodal volcanic rocks (158 Ma-179 Ma) in southern Jiangxi and southwestern Fujian in the eastern sector of the granite belt and early Yanshanian basalts (177 Ma-178 Ma) in southern Hunan in the central sector of the belt. Both the acid end-member rhyolite in the bimodal volcanic rock association and A-type granitoids in southern Jiangxi have the geochemical characteristics of intraplate granitic rocks and the basic end-member basalt of the association is intraplate tholeiite, while the basaltic rocks in southern Hunan include not only intraplate tholeiite but also intraplate alkali basalt. Therefore the early Yanshanian magmatic suites in the Nanling region are undoubtedly typical post-orogenic rock associations. Post-orogenic suites mark the end of a post-collision or late orogenic event and the initiation of Pangaea break-up, indicating that a new orogenic Wilson cycle is about to start. Therefore it may be considered that the early Yanshanian geodynamic settings in the Nanling region should be related to post-orogenic continental break-up after the Indosinian orogeny and the break-up did not begin in the Cretaceous. 相似文献
993.
上海地震台阵的地震定位方法 总被引:5,自引:0,他引:5
详细介绍了上海地震台阵数据处理软件系统中的地震定位方法,用台阵的聚束方法得到地震的方位角和视慢度,根据统计得到的视慢度-震中距表推算震中距。并结合了地震台网的定位方法,由单台记录的各类主要震相从J-B走时表得到震中距,然后进行地震定位。该定位方法可对近震、远震进行定位处理,并由深震相得到震源深度。 相似文献
994.
995.
996.
997.
根据实际业务工作的需要,使用C++Builder可视化开发工具,开发了Windows环境下的河南省农业气象情报资料处理系统,该系统具有报码分析、文本生成和图形显示等功能。 相似文献
998.
According to statistic analysis on sea surface temperature(SST)anomaly features in theNorth Pacific in winters and springs prior to the summer flood/drought in the middle and lowerreaches of the Yangtze River(hereafter referred to as MLRY),a strong signal SST key area thataffects local flood/drought is put forward,that is the equatorial eastern Pacific.The response ofgeneral circulation in the Northern Hemisphere to SST anomaly in the key area is furtherinvestigated. The low frequency wave train structure of correlation between the eastern PacificSST and the height at 500 hPa in the Northern Hemisphere is also studied,which reflects thedynamic features of teleresponse of local flood/drought at extratropics to tropical SST anomaly.Through introducing SST anomaly in the strong signal area in numerical experiments,the flood inYangtze River Valley is successfully simulated and the similar wave train pattern in the flow field isobtained too.Altogether,the physical picture and dynamic mode of the flood in the Yangtze RiverValley are described in this work. 相似文献
999.
Lower Cretaceous red sedimentary rocks from the depositional basin of East Qilian fold belt have been collected for a paleomagnetic study. Stepwise thermal demagnetization reveals two or three components of magnetization from dark red sandstones. Low-temperature magnetic component is consistent with the present Earth Field direction in geographic coordinates. High-temperature magnetic components are mainly carried by hematite. The mean pole of 19 sites for high-temperature magnetic components after tilt-correction is λ=62.2°N, φ=193.4°E, A95=3.2°, and it passes fold tests at 99% confidence level and reversal tests at 95% confidence level. The paleopole is insignificantly different from that of Halim et al. (1998) from the same sampling area at the 95% confidence level. Compared with paleomagnetic results for North China, South China, and Eurasia, our results suggest that no significant relative latitudinal displacement has taken place between Lanzhou region and these blocks since Cretaceous time. Remarkably, the pole of Lanzhou shows a 20° clockwise rotation with respect to those of North China, South China, and Eurasia. Geological information indicates that the crustal shortening in the western part of Qilian is greater than that in eastern part. In this case, the clockwise rotation of sampling area was related to India/Eurasia collision, and this collision resulted in a left-lateral strike-slip motion of the Altun fault in north Tibetan Plateau after the Cretaceous. 相似文献
1000.
Mt. Qomolangma lies in the collision zone between the fringe of Eurasia plate and Indian plate. The crustal movement there
is still very active so far. In the past three decades China carried out five geodetic campaigns in Mt. Qomolangma and its
north vicinal area, independently or cooperatively with other countries, including triangulation, leveling, GPS positioning,
atmospheric, astronomical and gravity measurements. On the basis of the observation results achieved in the campaigns the
crustal movements in the area were studied and explored. A non-stationary phenomenon both in time and space of the crustal
vertical movement in the area is found. There seems to be some relevance between the phenomenon of non-stationary in time
and seismic episode in China. The phenomenon of non-stationary in space is possibly relevant to the no-homo- geneity of crustal
medium and non-uniform absorption of terrestrial stress. The horizontal crustal movement in the area is in the direction of
NEE at a speed of 6–7 cm per year, and the trend of strike slip movement is manifested evidently in the collision fringe of
Indian plate and Qinghai-Xizang block. 相似文献