全文获取类型
收费全文 | 3363篇 |
免费 | 657篇 |
国内免费 | 1044篇 |
专业分类
测绘学 | 209篇 |
大气科学 | 884篇 |
地球物理 | 764篇 |
地质学 | 1971篇 |
海洋学 | 341篇 |
天文学 | 157篇 |
综合类 | 323篇 |
自然地理 | 415篇 |
出版年
2024年 | 15篇 |
2023年 | 92篇 |
2022年 | 188篇 |
2021年 | 160篇 |
2020年 | 136篇 |
2019年 | 167篇 |
2018年 | 166篇 |
2017年 | 159篇 |
2016年 | 195篇 |
2015年 | 180篇 |
2014年 | 221篇 |
2013年 | 226篇 |
2012年 | 205篇 |
2011年 | 202篇 |
2010年 | 221篇 |
2009年 | 178篇 |
2008年 | 177篇 |
2007年 | 167篇 |
2006年 | 146篇 |
2005年 | 117篇 |
2004年 | 87篇 |
2003年 | 66篇 |
2002年 | 98篇 |
2001年 | 111篇 |
2000年 | 114篇 |
1999年 | 164篇 |
1998年 | 138篇 |
1997年 | 151篇 |
1996年 | 137篇 |
1995年 | 143篇 |
1994年 | 110篇 |
1993年 | 79篇 |
1992年 | 67篇 |
1991年 | 60篇 |
1990年 | 46篇 |
1989年 | 41篇 |
1988年 | 37篇 |
1987年 | 20篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1962年 | 2篇 |
1957年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有5064条查询结果,搜索用时 15 毫秒
871.
安徽的地壳演化:Sr,Nd同位素证据 总被引:13,自引:0,他引:13
在地壳(幔)演化和板块构遣的框架内,评述了有关安徽南部(扬子地块东部,包括大别遣山带和江南遣山带)的同位素地质年代学和Nd,Sr同位素地球化学示踪研究的成果。该地区出露地表的中元古界溪口群浅变质岩代表皖南的基底,沿江地区和大别山区的基底包舍太古宇或/和古元古界古老岩石。此格局还影响到从震旦纪到古生代沉积岩的物源区,江南深断裂以北的沉积岩中有古老岩石的贡献,而以南的物源主要来自出露的中元古界岩石。扬子陆块南北缘(大别和江南遣山带)的晋宁期演化可能与罗迪尼亚超大陆演化有密切关系,但有关研究开展很少。三叠纪大陆深俯冲和超高压变质作用研究已成为国际地球科学的热点。晚中生代(120-140Ma)本区发生强烈的岩浆活动,并伴有重要矿床的形成。中酸性岩的形成是一种壳幔物质混合的过程。沿江地区陆下地幔具有富集特征,为扬子型岩石圈地幔与软流圈地幔混合的产物。从晚中生代到第四纪,基性岩指示其源区的地球化学性质有随时间变得越来越亏损的趋势。 相似文献
872.
Xin-Fa Deng Cheng-Hong Luo Peng Jiang Ying-Ping Ding 《Astrophysics and Space Science》2013,347(1):183-191
Using two volume-limited samples above and below the value of $M_{r}^{ *}$ constructed from the Main galaxy sample of the Sloan Digital Sky Survey Data Release 8 (SDSS DR8), we investigate correlations between galaxy morphology and star formation rate (SFR), specific star formation rate (SSFR) and stellar mass at different environmental density levels. For each sample, three subsamples at both density extremes and at the median density are selected. We found that examining either of our two volume-limited Main samples leads to the same conclusion: at different environmental density levels, SFR, SSFR and stellar mass are strongly correlated with galaxy morphology, which shows that SFR, SSFR and stellar mass of a galaxy depend on its environment as well as its morphology. 相似文献
873.
HE Tianrong LI Ting Yang Ruidong LUO Guangjun LANG Xiaofang An Yanling YAN Haiyu 《中国地球化学学报》2013,32(1):104-109
In this paper, the relationship between sulfate reduction potential and mercury methylation potential was studied in the Aha, Baihua and Hongfeng reservoirs from Guiyang City. The methylmercury (MeHg) concentrations of lake water in the Aha Reservoir were greatly elevated as compared to those of the Hongfeng and Baihua reservoirs, which was correlated with its distinctly high SRB abundance, SO42-, and S2- concentrations. Among the three reservoirs, however, the highest MeHg was observed in in the top several centimenters of pore water profile in the Hongfeng Reservoir where the lowest S2- in pore water occurred. The distributions of MeHg in lake water and pore water showed the highest methylation potential occurred at water-sediment surface for the Aha Reservoir and the in the top several centimenters of sediments for the Hongfeng Reservoir. It is guessed that the highest mercury methylation only occurs at the sites with certain sulfide concentrations. 相似文献
874.
875.
876.
877.
878.
879.
Techniques have been developed for the vegetative propagation of Tetraena mongolica,a rare and endangered species endemic to the western Ordos Plateau in the northcentral portion of China.The purpose of the study was to investigate the rooting characteris-tics of the plant species from the aspects of length and ages of cuttings,external hormone concentration,leaf retention,cutting orientations,and cutting positions.The results obtained from the experiments indicated that the rooting ratio of 2-year or 3-year old cuttings was larger than more than of 4-year old cuttings.The influence of external hormone concentration on rooting was ob-vious;the rooting ratio of cuttings was increased by external hormone treatment,especially when treated by ABT1(ABT No.1 Rooting Powder) 50 mg/L for 3 hours,in which case,the rooting ratio reached 91 percent.Leaf retention influenced rooting sig-nificantly;the rooting rate of cuttings became greater as the leaf retention increased.There was no significant difference in rooting capability between south and north orientations of the ortets.The rooting ratio of the cuttings obtained from the distal portions of shoots was significantly larger than those obtained from the middle and the basal portions of the shoots.On day three after treat-ment,calluses started appearing at the incisions of some cuttings dipped in 500 mg/L IAA(indole acetic acid).Most cuttings were healed or swelled,and 6 percent of cuttings rooted on day 6 after treatment.Higher rooting period occurred 7-10 days after the experiment was set up. 相似文献
880.
汶川大地震震害特点与成因分析 总被引:3,自引:0,他引:3
郭迅 《地震工程与工程振动》2009,29(6)
2008年5月12日汶川地震造成巨大人员伤亡和财产损失.本文从工程抗震角度分析了震区房屋倒塌的原因,指出地震时房屋倒塌与否与诸多因素有关.在此基础上,分析了汶川地震震害严重的四个主要因素:震级大,烈度高,断层破裂长;震区人口稠密,房屋、路桥等人工工程多;抗震设防水平低;地震诱发地质灾害严重.最后,将汶川地震震害与1976年唐山地震震害作了对比.所得结论可供理解汶川地震震害、改进结构抗震设计参考. 相似文献