全文获取类型
收费全文 | 19852篇 |
免费 | 2178篇 |
国内免费 | 2884篇 |
专业分类
测绘学 | 2443篇 |
大气科学 | 2094篇 |
地球物理 | 2857篇 |
地质学 | 6593篇 |
海洋学 | 2269篇 |
天文学 | 229篇 |
综合类 | 2706篇 |
自然地理 | 5723篇 |
出版年
2024年 | 78篇 |
2023年 | 283篇 |
2022年 | 395篇 |
2021年 | 445篇 |
2020年 | 340篇 |
2019年 | 533篇 |
2018年 | 295篇 |
2017年 | 250篇 |
2016年 | 327篇 |
2015年 | 442篇 |
2014年 | 1844篇 |
2013年 | 1113篇 |
2012年 | 1453篇 |
2011年 | 1474篇 |
2010年 | 1313篇 |
2009年 | 1511篇 |
2008年 | 1256篇 |
2007年 | 1091篇 |
2006年 | 990篇 |
2005年 | 1284篇 |
2004年 | 1028篇 |
2003年 | 1147篇 |
2002年 | 929篇 |
2001年 | 783篇 |
2000年 | 599篇 |
1999年 | 588篇 |
1998年 | 464篇 |
1997年 | 424篇 |
1996年 | 387篇 |
1995年 | 319篇 |
1994年 | 304篇 |
1993年 | 211篇 |
1992年 | 229篇 |
1991年 | 215篇 |
1990年 | 179篇 |
1989年 | 170篇 |
1988年 | 36篇 |
1987年 | 27篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 5篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1965年 | 5篇 |
1943年 | 5篇 |
1941年 | 5篇 |
1930年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
81.
82.
83.
HUANGGuoqiang DONGShuanglin WANGFang 《中国海洋大学学报(英文版)》2005,4(1):56-60
Attractabilities of different diets and dietary selectivity of Chinese shrimp, Fenneropenaeus chinensis were studied through behavior observation and feeding experiment, respectively. The five diets used in the experiment are: Fish Flesh (FF), Shrimp Flesh (SF), Clam Foot (CF), Polychaete Worm (PW), and Formulated Diet (FD). No significant differences of attractability exist between any two different diets when every two natural diets or all five diets are provided simultaneously. On the other hand, significant differences of attractability exist between FD and every single natural diet when they are provided simultaneously. Results of behavioral observation indicate that natural diets are more attractive than FD. In feeding experiment, Chinese shrimp has distinct selectivity on different diets. It positively selects CF and PW, negatively selects FF and SF, and excludes FD absolutely. The results of the present studies indicate that the dietary selectivity of shrimp was based not only on the attractabilities of the diets, but also on the responses such as growth and food conversion. 相似文献
84.
85.
“要全面提升国土资源宣传工作水平!”这既是国土资源部党组发出的号召,同时也是广大国土资源干部职工和社会各界的强烈呼声.我们应积极响应,迅速行动,全面落实. 相似文献
86.
TL ages of 56 loess samples collected from Xinjiang and the middle reaches of the Yellow River were determined by using fine-grained quartz and man-made light source bleaching techniques.The results indicate that :1.The well-preserved loess sections in Xinjiang began depositing 400000 a ago.The loess/paleosol series may be comparable with that observed in the middle reaches of the Yellow River but the depositing time was probably delayed by 30000-50000a.2.The bottom boundary age of the Malan loess varies from one place to another.The TL dates can be divided into two group:70000-130000 a and 30000-50000 a.The TL data are con-sistent with the appearance of two warmer climate periods since the Pleistocene,indicating obvious regional differences in stratigraphic development of loess,i.e.,paleosol occurred in the warm climate period in the same location,but loess was deposited in other locations.The initial age of loess deposition tends to become older from west to east and from south to north .In contrast ,the cold cli-matic belt showed an opposite trend.The TL ages of loess provide strong evidence for the Quaternary stratigraphy throughout geological times and the shift tendency of climatic belt.3.The depositing rate of the Malan loess along the middle reaches of the Yellow River varies from place to place but the TL age shows a linear relationship with the depositing thickness.The de-positing rate of loess in the north is higher than that in the south,suggesting that loess materials are derived from desert areas of northern China. 相似文献
87.
本文系统描述了中国南部二叠、三叠纪“混生生物群”。根据笔者的统计,目前巳经发现有“二叠纪型”分子36属53种与三叠纪菊石、双壳类、牙形剌共生。 笔者认为中国南部可以以牙形剌Anchignathodus parvus 的出现作为三叠系的底界,双壳类Pteria ussurica variabilis,菊石 Hypophiceras的出现可以作为三叠系开始的辅助标志。文中还将这一界线与世界上其它地区的二叠、三叠系界线进行了对比。 相似文献
88.
89.
90.
2007年10月24日18时5分,我国在西昌卫星发射中心用长征三号甲运载火箭将嫦娥一号卫星成功送入太空。卫星经过4次加速、1次中途轨道修正、3次近月制动、两次轨道维持,准确地进入近月点193km、远月点194km的绕月科学探测工作轨道。 相似文献