全文获取类型
收费全文 | 8974篇 |
免费 | 1924篇 |
国内免费 | 2652篇 |
专业分类
测绘学 | 895篇 |
大气科学 | 1796篇 |
地球物理 | 2250篇 |
地质学 | 4933篇 |
海洋学 | 1460篇 |
天文学 | 404篇 |
综合类 | 937篇 |
自然地理 | 875篇 |
出版年
2024年 | 85篇 |
2023年 | 231篇 |
2022年 | 508篇 |
2021年 | 582篇 |
2020年 | 455篇 |
2019年 | 516篇 |
2018年 | 511篇 |
2017年 | 477篇 |
2016年 | 553篇 |
2015年 | 520篇 |
2014年 | 572篇 |
2013年 | 576篇 |
2012年 | 574篇 |
2011年 | 604篇 |
2010年 | 545篇 |
2009年 | 613篇 |
2008年 | 607篇 |
2007年 | 579篇 |
2006年 | 469篇 |
2005年 | 455篇 |
2004年 | 320篇 |
2003年 | 257篇 |
2002年 | 311篇 |
2001年 | 301篇 |
2000年 | 260篇 |
1999年 | 317篇 |
1998年 | 254篇 |
1997年 | 215篇 |
1996年 | 218篇 |
1995年 | 161篇 |
1994年 | 159篇 |
1993年 | 167篇 |
1992年 | 132篇 |
1991年 | 76篇 |
1990年 | 67篇 |
1989年 | 50篇 |
1988年 | 46篇 |
1987年 | 25篇 |
1986年 | 37篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 20篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 5篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1962年 | 9篇 |
1958年 | 4篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
羊栖菜茎部愈伤组织再生苗的解剖学研究 总被引:1,自引:0,他引:1
利用石蜡切片法对羊栖菜纵裂主枝上愈伤组织再生苗的发生过程进行了形态解剖学观察。发现此种成苗方式是在主枝 (茎 )或假根处由外皮层分裂形成愈伤组织 ,再由愈伤组织分化成苗的一种无性繁殖方式。愈伤组织形成再生苗有望成为羊栖菜人工养殖种苗的来源之一。 相似文献
102.
AstudyonbenthiccommunitystructureinwestoftheTaiwanStraitandneartheTaiwanShoals¥WuQiquan;JiangJinxiang;XuHuizhou;CaiErxiandLin... 相似文献
103.
本文根据滇西地区18个大地电磁测深点资料的数据处理和分析结果,对测区深部导电率在纵、横向上的变化特征进行了研究。结果表明:滇西地区深部电性为多层结构,大致可分四至五个电性结构层;深部电性结构横向变化大,明显受区域构造控制;该区上部地壳内普遍存在低阻层;上地幔高导层明显存在两个隆起区,一个以剑川—鹤庆为中心呈北北西向展布的隆起区,另一个以腾冲—潞西为轴呈南北向展布的隆起区。 本文还讨论了地壳上地幔电性结构与大地构造的关系,滇西北裂陷区盆地的形成,以及该区地震活动与深部构造的关系 相似文献
104.
105.
Guadalupian (Middle Permian) Conodont Faunas at Shangsi Section, Northeast Sichuan Province 总被引:1,自引:0,他引:1
This study recovered the Guadalupian conodont faunas from Shangsi (上寺) Section in Northeast Sichuan (四川). Four genera and nine species were identified, and three conodont zones were recognized and established; they include Jinogondolella nankingensis Zone, J. aserrata Zone, and J. postserrata Zone. The Roadian and Wordian boundary is set in the interval 5 m from the top of Bed 86 by the first appearance of the conodont J. aserrata. The Wordian and Capitanian boundary is set in the interval 2.3 m from the top of the Bed 95 by the first appearance of J. postserrata. Most of the specimens demonstrated low color alteration index (CAI) as 1.5-3, indicating that most part of the Maokou (茅口) Formation may have the suitable thermal conditions for the formation of oil source rocks. 相似文献
106.
107.
Two elongatoolithid dinosaur eggs from the Upper Cretaceous of Ganzhou, Jiangxi Province and the embryonic skeletons they bear are described. They represent the first oviraptorosaurian eggs with embryonic skeletons in China and provide the first example that an oospecies can be correlated to certain dinosaur taxon/taxa. The two eggs are the same as the pair of the eggs inside a female oviraptorosaurian pelvis from the same horizon of the same area in both macro- and micro-structures of the egg shells, and can he referred to the oospecies, Macroolithus yaotunensis Zhao, 1975. The morphology of the preserved part of the embryonic skeletons indicates that they may have been laid by an oviraptorid, Heyuannia huangi from Guangdong Province or a closely related oviraptorosaurian, which may have been lived in the Ganzhou area too in the Late Cretaceous. The embryonic skeletons of the two eggs are not in the same developing stage. In one of the eggs, the postzygapophysis of the preserved vertebrae are well ossified, indicating that it was just hatched. 相似文献
108.
Palygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess-red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate. In this paper, field emission scanning electron microscope and high-resolution transmission electron microscope observations on the red clay-loess-paleosol of the Renjiapo profile at Lingtai, Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma, but no occurrence has been found in eolian sediments since 3.2 Ma. Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis, and transformed from iilite-montmorilionite under the pore water action. In the Lingtai profile, the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility, dust flux and depositional rate. The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon, when changes took place in the East Asia paleoclimate pattern, i.e. a high-frequency strong fluctuation alternative evolution of the environment. Therefore, palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time. 相似文献
109.
110.
抗战时期,中央地质调查所内迁重庆北碚,中国西部科学院帮助其在纷乱的战时安定下来,开始相对稳定的科研工作,主要在西部地区开展调查、从事科研。地调所的科研血脉得以传承,成为战时国内矿产资源调查研究中心。 相似文献