全文获取类型
收费全文 | 101862篇 |
免费 | 30688篇 |
国内免费 | 58383篇 |
专业分类
测绘学 | 15991篇 |
大气科学 | 27571篇 |
地球物理 | 24121篇 |
地质学 | 73253篇 |
海洋学 | 26074篇 |
天文学 | 1647篇 |
综合类 | 9373篇 |
自然地理 | 12903篇 |
出版年
2024年 | 1064篇 |
2023年 | 2659篇 |
2022年 | 5135篇 |
2021年 | 6373篇 |
2020年 | 5919篇 |
2019年 | 8880篇 |
2018年 | 8254篇 |
2017年 | 7847篇 |
2016年 | 8099篇 |
2015年 | 8516篇 |
2014年 | 7983篇 |
2013年 | 9340篇 |
2012年 | 10122篇 |
2011年 | 10045篇 |
2010年 | 10137篇 |
2009年 | 9138篇 |
2008年 | 8614篇 |
2007年 | 8251篇 |
2006年 | 7779篇 |
2005年 | 6531篇 |
2004年 | 5655篇 |
2003年 | 4527篇 |
2002年 | 4393篇 |
2001年 | 4009篇 |
2000年 | 3320篇 |
1999年 | 2335篇 |
1998年 | 1883篇 |
1997年 | 1918篇 |
1996年 | 1498篇 |
1995年 | 1383篇 |
1994年 | 1253篇 |
1993年 | 1235篇 |
1992年 | 1088篇 |
1991年 | 777篇 |
1990年 | 770篇 |
1989年 | 619篇 |
1988年 | 534篇 |
1987年 | 427篇 |
1986年 | 373篇 |
1985年 | 285篇 |
1984年 | 318篇 |
1983年 | 202篇 |
1982年 | 239篇 |
1981年 | 164篇 |
1980年 | 119篇 |
1979年 | 161篇 |
1978年 | 62篇 |
1977年 | 54篇 |
1976年 | 53篇 |
1971年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
31.
重庆地面最高气温与最大风速年极值的渐近分布 总被引:3,自引:0,他引:3
利用重庆1951-1990年间地面最高气温和1956-1990年间地面最大风速年极值的记录,采用韦伯分布和耿贝尔分布分别对其渐近分布进行拟合.通过统计推断,找出重庆地面最高气温和地面最大风速年极值遵循的最佳渐近分布--韦伯分布. 相似文献
32.
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
33.
阿吾拉勒山体西段发育了厚度巨大的下二叠统火山岩,这些火山岩均属碱性玄武岩系列,以钾质类型为主,钠质类型次之,岩浆演化呈现出跨越B型趋势。这种火山活动是在大陆地壳内部产生的,代表了陆内裂谷演化的早期阶段。在早二叠世末期,由于受到新源运动的影响,这种火山活动被终止了。 相似文献
34.
35.
36.
After the survey of pollution sources, a study on surface water quality assessment and forecast is given by means of grey
system method, fuzzy mathematical method and multiple-index method. Based on it, aquatic environment quality features, treatment
measures and environmental strategies of the area are proposed. The quality of aquatic environment of 5 rivers in the Tumen
River area is studied. The results show that the pollution of surface water is serious; water quality of most rivers is between
grade IV and V except the Hunchun River, being higher than grade IV standard; pollution levels of most rivers have been basically
controlled except the of Burhatong River, which is deteriorating gradually. Pollutants of the rivers are comparatively regular,
mainly are SS, COD, BOD, AR-OH, NH3-N. The main pollution trades are chemical fibre industry, pulp and paper making industry and mining industry. If the growth
rate of gross industrial product is higher than 25 percent under the encouraging-model of regional exploitation, the pollutants’
load will overtake the bearing capacity of aquatic environment. Thus some protection program against pollution must be worked
out in order to achieve the harmonious development of economy society and environment.
A project from “Studies on Earlier Stage of Regional Development” of the Chinese Academy of Sciences 相似文献
37.
本文用简单的宇宙学模型 ,在标准烛光和均匀分布的假设下计算了γ射线暴的logN(>P)~logP分布 (大小谱 ) .在考虑了探测效率修正和死时间修正后 ,由宇宙学模型计算的理论结果和BATSE实测的大小谱没有显著的偏离 相似文献
38.
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
39.
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
40.
Yu Xin 《Astrophysics and Space Science》1992,194(1):159-163
A critical re-examination of the self-consistency of Einstein's gravitational radiation theory is given in the present paper with special reference to its claimed prediction of the observed data on PSR 1913+16.The author is Alfred Yu 相似文献