全文获取类型
收费全文 | 47587篇 |
免费 | 5284篇 |
国内免费 | 7597篇 |
专业分类
测绘学 | 3919篇 |
大气科学 | 6416篇 |
地球物理 | 10066篇 |
地质学 | 24783篇 |
海洋学 | 4288篇 |
天文学 | 2434篇 |
综合类 | 4455篇 |
自然地理 | 4107篇 |
出版年
2024年 | 123篇 |
2023年 | 478篇 |
2022年 | 1270篇 |
2021年 | 1475篇 |
2020年 | 1219篇 |
2019年 | 1385篇 |
2018年 | 6020篇 |
2017年 | 5111篇 |
2016年 | 3921篇 |
2015年 | 1693篇 |
2014年 | 1754篇 |
2013年 | 1759篇 |
2012年 | 2706篇 |
2011年 | 4455篇 |
2010年 | 3711篇 |
2009年 | 3879篇 |
2008年 | 3255篇 |
2007年 | 3587篇 |
2006年 | 1196篇 |
2005年 | 1197篇 |
2004年 | 1104篇 |
2003年 | 1056篇 |
2002年 | 940篇 |
2001年 | 749篇 |
2000年 | 722篇 |
1999年 | 829篇 |
1998年 | 671篇 |
1997年 | 629篇 |
1996年 | 591篇 |
1995年 | 454篇 |
1994年 | 475篇 |
1993年 | 389篇 |
1992年 | 338篇 |
1991年 | 262篇 |
1990年 | 205篇 |
1989年 | 173篇 |
1988年 | 161篇 |
1987年 | 87篇 |
1986年 | 82篇 |
1985年 | 63篇 |
1984年 | 40篇 |
1983年 | 27篇 |
1982年 | 46篇 |
1981年 | 41篇 |
1980年 | 44篇 |
1979年 | 25篇 |
1978年 | 8篇 |
1976年 | 13篇 |
1958年 | 21篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
对1995年至2001年《Natue》和《Science》上发表的天文学论文的统计表明,行星天文学领域的论文数量明显超过天文学的其它分支学科,占天文学总论文数的1/3左右。从这个角度来看,行星天文学是天文学最活跃和重要的分支学科之一。对这些论文具体内容的分析可以给出当前行星天文学领域的若干热点问题。相比之下,我国对这一重要领域的关注和投入还远远不够。 相似文献
22.
An empirical kinematic method developed by Hakamada and Akasofu (1982) is calibrated on the basis of a one-dimensional MHD solution. The calibrated results are used to simulate the stream-stream interaction and the background corotating structure in a simple situation and also during 22 November–6 December 1977. The solar wind disturbances caused by solar activities during this period are then introduced into the above background stream in simulating the heliospheric disturbance event which was observed by an aligned set of spacecraft at distances between 0.6 and 1.6 a.u. The observations and the simulated results are satisfactory, and a little more refinement in the simulation could reconstruct reasonably well the data by filling the data gaps in the solar wind speed, the density and the IMF magnitude. 相似文献
23.
罗卫敏 《成都信息工程学院学报》2004,19(2):209-213
针对信息系统安全的考虑,介绍在PowerBuilder环境中对用户权限的具体控制. 相似文献
24.
CHUDongsheng LIANGMeng SHIXin ZHANGLing 《中国海洋大学学报(英文版)》2004,3(1):106-110
1 Introduction Inrecentyearstherehasbeengrowingresearchin terestinthetwo dimensional (2 D )systemtheory .The 2 Dsystemsmayfindapplicationsinareassuchasmarineseismicdataprocessingandimageprocessing .Althoughmoreandmorevaluableresultshavebeengained ,mos… 相似文献
25.
介绍了云南天文台天体测量工作的发展过程,论述了在空间时代地面光学基本天体测量的必要性和应具备的条件,并且叙述了在新的要求和条件下,地面光学基本天体测量工作应该发挥的作用和广阔的发展前景。 相似文献
26.
Based on the δ13C and δ18O fluctuation of lacustrine carbonate, CaCO3 content and sporo-pollen data, a palaeoclimatic history of Bosten Lake during the Holocene has been outlined, several stages
of climatic changes are divided, and the following result es are obtained: (1) Palaeoclimatic changes revealed by carbonate
isotope around Bosten Lake are basically identical with that revealed by other geological records in Xinjiang. Environmental
changes presented apparent Westlies Style model: during cold period, relative humidity increased, δ18O, δ13C and CaCO3 appeared low; but in warm periods, the dry regime aggravated. (2) The temperature reflected by δ18O exist evident features being increase in the late period during the Holocene. Together with the δ13C, pollen and CaCO3 analyses, several cold and warm phases which are of broad regional significance can be identified. The warm peaks occurred
at about 11.0 ka B.P., 9.4 ka B.P., 7.5 ka B.P., 5.0 ka B.P., 3.0 ka B.P. and 2.0 ka B.P.; the cold peaks at 11.5 ka B.P.,
10.5 ka B.P., 8.8 ka B.P., 5.5 ka B.P., 3.3 ka B.P., 2.2 ka B.P. and 1.5 ka B.P.. (3) Several climatic events with the nature
of “abrupt climatic changes” are revealed in the periods of 11.0 ka B.P. −10.5 ka B.P., 9.4 ka B.P. −8.8 ka B.P., 5.5 ka B.P.
−5.0 ka B.P. and 2.0 ka B.P. −1.5 ka B.P.. (4) The results show that carbonate isotopic record of lacustrine sediment in arid
area is very sensitive to climatic changes, and may be play a very important role in understanding the features and mechanism
of palaeoclimatic changes. 相似文献
27.
28.
概略地叙述了西宁地区的泥石流形成条件和形成机理,并将西宁地区泥石流划分为稀性泥石流类及泥石质泥石流种类。在此基础上提出防治泥石流灾害的意见。 相似文献
29.
30.
APPLICATION OF ANALYTIC HIERARCHY PROCESS TO ASSESSING THE ECOLOGICAL VULNERABILITY OF WETLANDS IN THE JIANGHAN PLAIN 总被引:5,自引:1,他引:4
WANGXue-lei NINGLong-mei HUWang-bin 《中国地理科学(英文版)》2003,13(3):272-276
Wetlands in the Jianghan Plain are important components of wetland types in lake area in the middle and lower reaches the Changjiang (Yangtze) River and they fulfill many uses and functions related to hydrology,waste assimilation, ecosystem productivity and biodiversity. Owing to natural factors and human activities, especially excessive reclamation from lakes, the shrinking process of the lakes has been accelerated. Wetland ecosystem has shown the characteristics of vulnerability. According to the analysis of wetland ecological function in the Jianghan Plain, this paper presented an index system related to productivity, stability and environmental capacity. By using the method of Analytic Hierarchy Process, we computed the values of the relative weights of the indexes, and evaluated the vulnerability level of the wetland ecosystem by the method of multi-indexes. The case study showed that the fragile extent of wetland ecosystem in the Jianghan Plain is 5.6. This means that the wetland ecosystem in the Jiang-han Plain is laid to the state of middle vulnerability. Therefore, the wetland conservation and eco-rehabilitation in the JiangJaan Plain should be paid attention to. 相似文献