全文获取类型
收费全文 | 11899篇 |
免费 | 2205篇 |
国内免费 | 2892篇 |
专业分类
测绘学 | 680篇 |
大气科学 | 2748篇 |
地球物理 | 3142篇 |
地质学 | 6022篇 |
海洋学 | 1298篇 |
天文学 | 522篇 |
综合类 | 1205篇 |
自然地理 | 1379篇 |
出版年
2024年 | 34篇 |
2023年 | 178篇 |
2022年 | 519篇 |
2021年 | 589篇 |
2020年 | 441篇 |
2019年 | 507篇 |
2018年 | 611篇 |
2017年 | 600篇 |
2016年 | 672篇 |
2015年 | 546篇 |
2014年 | 672篇 |
2013年 | 682篇 |
2012年 | 575篇 |
2011年 | 595篇 |
2010年 | 611篇 |
2009年 | 647篇 |
2008年 | 632篇 |
2007年 | 566篇 |
2006年 | 475篇 |
2005年 | 419篇 |
2004年 | 351篇 |
2003年 | 440篇 |
2002年 | 451篇 |
2001年 | 395篇 |
2000年 | 470篇 |
1999年 | 616篇 |
1998年 | 496篇 |
1997年 | 533篇 |
1996年 | 490篇 |
1995年 | 401篇 |
1994年 | 350篇 |
1993年 | 277篇 |
1992年 | 233篇 |
1991年 | 177篇 |
1990年 | 141篇 |
1989年 | 133篇 |
1988年 | 117篇 |
1987年 | 78篇 |
1986年 | 58篇 |
1985年 | 46篇 |
1984年 | 32篇 |
1983年 | 32篇 |
1982年 | 19篇 |
1981年 | 21篇 |
1980年 | 22篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1962年 | 4篇 |
1958年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 833 毫秒
21.
形变大地测量学的进展、问题与地震预报 总被引:12,自引:7,他引:5
简要概括了形变大地测量学的革命性进展,研讨了它的科学特色、功能和定义以及对地球科学和防灾减灾的推动。形变大地测量学有助于从根本上击破多年来制约地震预报的“瓶颈”,但也存在不少急待解决的问题。着重研讨了在21世纪前10年,形变大地测量学如何依托多年的学科积累并充分受益于人造卫星和数字化等新技术,开展创新性研究和试验以推进地震预报。为此,对当前的研究工作提出了12条科学技术途径。最后对学科名称提出了建议。 相似文献
22.
Shi Zhi-dong Li Zhong-yuanUniversity of Science Technology of China Hefei PRC Advanced Centre for Earth Science Astronomy Third World Academy of Science 《紫金山天文台台刊》1996,(2)
Areview about K-H instability related to comet tail is presented.The effect of dust graing on KHI is theoretically analysed and relations of critical shear to excit KHI with the properties of dust grains both for sheared ion flow and for sheared dust flow re put out.Their possible application in comet tail is suggested. 相似文献
23.
PROPAGATION OF 30—60 DAY LOW FREQUENCY OSCILLATIONS AND THEIR INFLUENCE UPON THE SUBTROPICAL WESTERLIES JET STREAM DURING NORTHERN HEMISPHERE WINTER
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSOyear,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters andtheir influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta-tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that inthe winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone aremainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982—1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonalchanges of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinalprogression or regression of about 40 day period.There are marked differences between propagat-ing passages of low frequency modes responsible for changes of subtropical jet stream in the normalyear(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude showobvious phases.In general,the one in late winter is stronger than that in early winter,strongestone occurs in February. 相似文献
24.
25.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
26.
27.
28.
笔者曾对广西芒场锡多金属矿田的稳定同位素进行研究。本文根据硫、铅、氢、氧、碳等稳定同位素组成和锶的初始值提供的信息.探讨了矿床成因。并结合矿田矿床地质特征、控矿条件及有关统计参数,参考前人对矿床认识的基础上,修正提出了该矿田混合热液成矿模式,可供类似矿床研究和找矿的参考。 相似文献
29.
Vertical profiles of chl-a and primary productivity in the middle continental shelf area and eddy area of the East China Sea
were studied using data from a cruise in the East China Sea in February to March, 1997 and a cruise in July, 1998. The results
showed that chl-a vertical distribution closely related to in situ hydrological and nutrient conditions. Chla-a concentration
ranged from 0.22 to 0.35 mg/m3 and 0.93–1.09 mg/m3 in the eddy area and in the middle continental shelf area, respectively. In both areas, chl-a concentrations in deep layers
were slightly higher than those in shallow layers, but was of the same order of magnitude. In summer, when a thermocline existed
in the water column, highest chl-a concentrations appeared at the base of the thermocline layers in both areas. In the eddy
area, chl-a concentration maximized at 31.743 mg/m3, and averaged 1.143 mg/m3 below 30 m depth. In the middle continental shelf area, the highest chl-a concentration was 2.120 mg/m3, the average was 1.168 mg/m3. The primary productivity reached 1418.76 mgC/(m2·d) in summer and 1360.69 mgC/(m2·d) in winter. In the eddy area, the primary productivity was 787.50 mgC/(m2·d) in summer and 159.04 mgC/(m2·d) in winter. Vertical carbon sinking rate from the deep layer to the bottom in both areas is also discussed in this paper.
Contribution NO. 4183 from the Institute of Oceanology, Chinese Academy of Sciences.
Project No. 49636210 supported by NSFC. 相似文献
30.
The sand–loess transition zone in north China is sensitive to climate change, and is an ideal place to investigate past environmental changes. However, past climate change at millennial–centennial timescales in this region has not been well reconstructed because of limited numerical dating. Alternations of sandy loam soils with aeolian sand layers in the Mu Us and Otindag sand fields, which lie along the sand–loess transition zone, indicate multiple intervals of dune activity and stability. This change is probably a response to variations of the East Asian monsoon climate during the late Quaternary. The single aliquot regeneration (SAR) optically stimulated luminescence (OSL) dating protocol, which has been successfully applied to aeolian deposits worldwide, is applied to these two sand fields in this study. The OSL ages provide reliable constraints for reconstruction of past climate changes at suborbital timescale. Sections in both sand fields contain aeolian sand beds recording millennial‐scale episodes of dry climate and widespread dune activation, including episodes at about the same time as Heinrich Event 5 and the Younger Dryas in the North Atlantic region. These results demonstrate the potential of aeolian sediments in semi‐arid north China to record millennial‐scale climatic events, and also suggest that dry–wet climate variation at the desert margin in China may be linked to climatic change elsewhere in the Northern Hemisphere, through atmospheric circulation. This article was published online on 27 November 2008. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected (16 December 2008). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献