全文获取类型
收费全文 | 21676篇 |
免费 | 3714篇 |
国内免费 | 4453篇 |
专业分类
测绘学 | 1708篇 |
大气科学 | 2832篇 |
地球物理 | 3841篇 |
地质学 | 10975篇 |
海洋学 | 3292篇 |
天文学 | 332篇 |
综合类 | 1599篇 |
自然地理 | 5264篇 |
出版年
2024年 | 111篇 |
2023年 | 348篇 |
2022年 | 731篇 |
2021年 | 902篇 |
2020年 | 812篇 |
2019年 | 945篇 |
2018年 | 813篇 |
2017年 | 943篇 |
2016年 | 935篇 |
2015年 | 1021篇 |
2014年 | 1228篇 |
2013年 | 1134篇 |
2012年 | 1387篇 |
2011年 | 1321篇 |
2010年 | 1179篇 |
2009年 | 1388篇 |
2008年 | 1257篇 |
2007年 | 1506篇 |
2006年 | 1503篇 |
2005年 | 1343篇 |
2004年 | 1247篇 |
2003年 | 1156篇 |
2002年 | 1020篇 |
2001年 | 813篇 |
2000年 | 684篇 |
1999年 | 612篇 |
1998年 | 534篇 |
1997年 | 475篇 |
1996年 | 448篇 |
1995年 | 377篇 |
1994年 | 364篇 |
1993年 | 290篇 |
1992年 | 262篇 |
1991年 | 196篇 |
1990年 | 119篇 |
1989年 | 190篇 |
1988年 | 82篇 |
1987年 | 61篇 |
1986年 | 27篇 |
1985年 | 17篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1954年 | 5篇 |
1877年 | 2篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
C. Debi Prasad Ashok Ambastha Nandita Srivastava Sushanta C. Tripathy Mona J. Hagyard 《Journal of Astrophysics and Astronomy》1997,18(1):39-55
Super-active region NOAA 6555 was highly flare productive during the period March 21st–27th, 1991 of its disk passage. We
have st udied its chromospheric activity using high spatial resolution Hα filtergrams taken at Udaipur along with MSFC vector
magnetograms. A possible relationship of flare productivity and the variation in shear has been explored. Flares were generally
seen in those subareas of the active region which possessed closed magnetic field configuration, whereas only minor flares
and/or surges occurred in subareas showing open magnetic field configuration. Physical mechanisms responsible for the observed
surges are also discussed. 相似文献
2.
(姚建衢)(杨焕宗)COORDINATINGDEVELOPMENTOFAGRICULTURALRESOURCESANDENVIRONMENTOFTHETROPICREGIONINYUNNANPROVINCE¥YaoJianqu(Instituteof... 相似文献
3.
Afforestation has been suggested as a means of improving soil and water conservation in north‐western China, especially on the Loess Plateau. Understanding of the hydrological responses to afforestation will help us develop sustainable watershed management strategies. A study was conducted during the period of 1956 to 1980 to evaluate runoff responses to afforestation in a watershed on the Loess Plateau with an area of 1·15 km2, using a paired watershed approach. Deciduous trees, including locust (locusta L.), apricot (praecox L.) and elm (ulmus L.), were planted on about 80% of a treated watershed, while a natural grassland watershed remained unchanged. It was estimated that cumulative runoff yield in the treated watershed was reduced by 32% as a result of afforestation. A significant trend was also observed that shows annual runoff reduction increases with the age of the trees planted. Reduction in monthly runoff occurred mainly from June to September, which was ascribed to greater rainfall and utilization by trees during this period. Afforestation also resulted in reduction in the volume and peak flow of storm runoff events in the treated watershed with greater reduction in peak flow. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
4.
Qin Chengzhi 《中国地震研究》2004,18(2):178-187
The migration of strong earthquakes is an important research topic because the migration phenomena reflect partly the seismic mechanism and involve the prediction of tendency of seismic activity. Research on migration of strong earthquakes has mostly focused on finding the phenomena. Some attempts on getting regularity were comparatively subjective. This paper suggests that there should be indices of migration in earthquake dataset and the indexes should have statistical meaning if there is regularity in the migration of strong earthquakes. In this study, three derivative attributes of migration, i.e., migration orientation, migration distance and migration time interval, were statistically analyzed. Results in the North China region show that the migration of strong earthquakes has statistical meaning. There is a dominant migration orientation (W by S to E by N), a dominant distance (≤100km and on the confines of 300~700km), and a dominant time interval (≤1a and on the confines of 3~4a). The results also show that the migration will differ slightly with different magnitude range or earthquake activity phase. 相似文献
5.
Nikolay Sidorenkov 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):27-38
Spectral analysis of the components of the relative atmospheric angular momentum vector is performed based on the series of these components for the 6 h intervals within the period of 1958–2000. These series have been computed in the Subbureau of the Atmospheric Angular Momentum of the International Earth Rotation Service using the NCEP/NCAR reanalysis of atmospheric observations. The basic harmonics of diurnal tides are determined. New results on the fortnight's and week's duration oscillations of the equatorial components of the atmospheric angular momentum are obtained. The zonal tides transformation mechanisms in the atmosphere are discussed. It is shown that the main mechanism of the zonal tides effect on the atmospheric variability is the amplitude modulation of daily oscillations of the relative atmospheric angular momentum. The effects of the atmospheric tides on the Earth rotation are discussed. 相似文献
6.
本文论述了保安地区火山岩的地质、岩石、副矿物、岩石化学、微量元素、稀土元素、稳定同位素、火山岩相及火山机构等特征。并对其演化规律、形成机制与成矿作用的关系,作了初步探讨。 相似文献
7.
N. K. Lebedeva 《Stratigraphy and Geological Correlation》2008,16(2):182-197
The results of palynomorph biofacies analysis in the Upper Cretaceous deposits of the Ust-Yenisei region are presented. The established facies confinement and indicative features of separate palynomorph groups are used, along with identified dinocyst morphotypes and taxa, in paleogeographic reconstructions. Seven palynomorph associations characterizing continental, coastal-marine, shallow-and deep-water facies are distinguished based on quantitative proportions between morphological groupings and individual taxa. As boundaries between distinguishable biostratigraphic and facies subdivisions do not coincide, dinocysts were likely insignificantly dependent in distribution on facies in the West Siberian epicontinental basin at least. On the other hand, distribution trends of particular dinocyst morphotypes and other microphytofossils are correlative with transgressive-regressive cycles and can be used for reconstruction of paleoenvironments. 相似文献
8.
本文对南海中部陆坡区和海盆区的5个岩芯中的 Si,Al,Fe,Mn,Ca,Mg 和 CaCO_3成分做了分析,并对其分布特征与有关影响因素进行了讨论。受沉积区环境差异的影响,元素的分布具有区域性特征;受海区特定地理位置的影响,元素的分布呈现出过渡性特征(浅海到大洋的过渡);受沉积过程中环境变化的影响,元素的分布展示了周期性变化或旋回性。根据岩芯中元素的分布特征,并参考有关古地磁,氧碳同位素和钙质超微化石的测试分析结果,将本区岩芯划分为14层地球化学层,并将本区划分为两个沉积地球化学区,揭示了早更新世以来本区沉积环境的变化和存在的两种沉积模式。 相似文献
9.
Species composition and distribution of marine nematode community in the North Taiwan Strait 总被引:9,自引:4,他引:9
Cai Lizhe Hong Huasheng Zou Chaozhong Fang Shaohu L Xiaomei Zhang Yueping 《海洋学报(英文版)》2001,20(2):221-229
I~IOW~ne nelnatode is a ban gIOup of benthic OrgAnsrns. Abbot 5 000 spotes Of free-livingnelnatedes have ben dedbo so far, and it has ho estimated that abbot 20 (XX) are as yetunknoWn. Chinese bothologist has Paid attention to marine nelnatodes in China seas in yare. The spatial distribution and shoes commotion of marine nelnatedes in the HUanghe EstUary, Qinhuangdao waters, QingdaO Bay and Xiamen ~ have ho reported (Zhang etal., 1990, 1991, 1993; ac and Li, 1998). ~ new shoes in the… 相似文献