全文获取类型
收费全文 | 6421篇 |
免费 | 1314篇 |
国内免费 | 1660篇 |
专业分类
测绘学 | 674篇 |
大气科学 | 1114篇 |
地球物理 | 1295篇 |
地质学 | 3413篇 |
海洋学 | 995篇 |
天文学 | 300篇 |
综合类 | 685篇 |
自然地理 | 919篇 |
出版年
2024年 | 25篇 |
2023年 | 94篇 |
2022年 | 240篇 |
2021年 | 304篇 |
2020年 | 262篇 |
2019年 | 291篇 |
2018年 | 362篇 |
2017年 | 319篇 |
2016年 | 333篇 |
2015年 | 293篇 |
2014年 | 404篇 |
2013年 | 433篇 |
2012年 | 385篇 |
2011年 | 414篇 |
2010年 | 461篇 |
2009年 | 447篇 |
2008年 | 375篇 |
2007年 | 381篇 |
2006年 | 350篇 |
2005年 | 281篇 |
2004年 | 236篇 |
2003年 | 220篇 |
2002年 | 242篇 |
2001年 | 256篇 |
2000年 | 253篇 |
1999年 | 282篇 |
1998年 | 207篇 |
1997年 | 183篇 |
1996年 | 184篇 |
1995年 | 162篇 |
1994年 | 157篇 |
1993年 | 120篇 |
1992年 | 94篇 |
1991年 | 71篇 |
1990年 | 57篇 |
1989年 | 33篇 |
1988年 | 36篇 |
1987年 | 24篇 |
1986年 | 28篇 |
1985年 | 21篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1958年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有9395条查询结果,搜索用时 15 毫秒
11.
在文献」1「4 基础上,根据近年文选址实践中提出的问题,先进一步讨论了大气相干直径和时间的的物理和意义,然后强调了自由大气湍流的天文成像效应及选址中进行研究和测量的重要性。最后对差分像运动方法测量视宁度的定标和系统误差等问题作了分析。 相似文献
12.
13.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
14.
15.
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
16.
本文根据石油地质勘探的最新资料和元-济人工地震地壳测深剖面相应地段重新解释的结果,分析了邢台7.2级地震的构造背景和发震断裂。研究结果表明,7.2级地震震中位于束鹿断陷盆地南部次凹的东缘,该次凹发育在由新河断裂等4条缓倾铲形正断裂分制围限地台盖层而成的“斛”状构造块体上,块体之下的地壳中存在两条倾向相反的高角度断裂;地震与断陷主断裂及其控制的断陷盆地并非是简单的对应关系,7.2级地震的发震断裂不是单一的缓倾铲形新河断裂或其下方的高角度的F_3断裂和深部的东断裂,而是它们的组合,且高角度断裂是发震断裂的主要部分 相似文献
17.
The distribution of L absorption lines has been investigated in the fractal scheme. It is found that (1) the L absorption clouds distribute completely different from that of galaxies; (2) the L absorption clouds are anti-associated with galaxies and quasars. These results may imply that there are two kinds of objects formed by different processes of clustering. This is favourable for the cosmic-string theory on the formation of large-scale structure of the Universe. In the string model, the objects can be divided into two kinds according to their clustering with or without string loops as their initial density perturbation.On leave from the Center of Astrophysics, University of Science and Technology of China, Hefei, P.R. China. Y. Chu is a research fellow of Alexander von Humboldt-Foundation. 相似文献
18.
Ni Xiang-bin Jiang Yao-tiao Chen Zai-zhang Fang Cheng 《Chinese Astronomy and Astrophysics》1985,9(4):273-277
We propose a new heating mechanism of faculae. We think that the formation of faculae is a result of the Joule dissipation of the Hall current generated by the interaction of the convection field of granules in an active region and the inter-granular magnetic field. For a region to generate effectively Hall current, its characteristic length must be such that the magnetic Reynolds number is less than 1. The equation of energy balance in the facula region is .For five observational models of faculae, we calculated the corresponding velocity fields, and the results are in basic agreement with the observed fields. The present mechanism explains the dependence of the facula brightness on the magnetic and velocity fields, the apparent distribution of the faculae on the solar disk and suggest a possible interpretation of the five structures of faculae. 相似文献
19.
Unconsolidated sand, gravel and clay deposits near Beihai and in the Leizhou Peninsula in southern China form an unconfined
aquifer, aquitard and a confined aquifer. Water and soil samples were collected from the two aquifers in the coastal Beihai
area for the determination of chemical compositions, minerals and soluble ions. Hydrogeochemical modeling of three flow paths
through the aquitard are carried out using PHREEQC to determine water–rock interactions along the flow paths. The results
indicate that the dissolution of anorthite, fluorite, halite, rhodochrosite and CO2, and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the
unconfined aquifer to the confined aquifer. Cation exchanges between Na and Ca can also happen along the flow paths. 相似文献
20.
新疆北部基性岩脉40Ar/39Ar年代学研究 总被引:8,自引:4,他引:4
晚古生代以来,新疆北部地区侵入了一系列的基性岩脉,成为了解该地区地壳生长过程的重要窗口.本文采用激光40Ar/39Ar年代学方法,对整个北疆地区出露的基性岩脉进行了精细年代学研究.从数据特征上分析.低本底激光加40Ar/39Ar方法能对低钾含量、极少量样品(0.1mg~5mg)进行精细定年,所以非常适合进行基性岩脉的精细定年.本文展示的基性岩脉激光40Ar/39Ar方法的高质量数据显示新疆北部基性岩脉群的活动时限跨越332~174Ma,为石炭纪-侏罗纪.由数据分析可以看出,新疆北部基性岩脉群在时间上,呈现脉动式侵位特征,在332~174Ma之间,有多达6~7次脉动式活动,时间间隔大致为20~30Ma.从基性岩脉所揭示的大地构造含义来分析,新疆北部地区从石炭纪到侏罗纪处在一个相似的地壳演化阶段.为一个陆壳垂向生长、区域构造应力场显示拉张的构造环境,并在时间、空间上具有相对统一的特征. 相似文献