全文获取类型
收费全文 | 49880篇 |
免费 | 659篇 |
国内免费 | 326篇 |
专业分类
测绘学 | 1347篇 |
大气科学 | 3913篇 |
地球物理 | 9380篇 |
地质学 | 16444篇 |
海洋学 | 4197篇 |
天文学 | 12256篇 |
综合类 | 110篇 |
自然地理 | 3218篇 |
出版年
2020年 | 345篇 |
2019年 | 342篇 |
2018年 | 851篇 |
2017年 | 834篇 |
2016年 | 1100篇 |
2015年 | 720篇 |
2014年 | 1206篇 |
2013年 | 2470篇 |
2012年 | 1123篇 |
2011年 | 1564篇 |
2010年 | 1460篇 |
2009年 | 1955篇 |
2008年 | 1789篇 |
2007年 | 1793篇 |
2006年 | 1685篇 |
2005年 | 1550篇 |
2004年 | 1514篇 |
2003年 | 1421篇 |
2002年 | 1362篇 |
2001年 | 1235篇 |
2000年 | 1161篇 |
1999年 | 1123篇 |
1998年 | 1066篇 |
1997年 | 1068篇 |
1996年 | 856篇 |
1995年 | 841篇 |
1994年 | 797篇 |
1993年 | 751篇 |
1992年 | 716篇 |
1991年 | 686篇 |
1990年 | 785篇 |
1989年 | 681篇 |
1988年 | 651篇 |
1987年 | 742篇 |
1986年 | 626篇 |
1985年 | 828篇 |
1984年 | 953篇 |
1983年 | 915篇 |
1982年 | 861篇 |
1981年 | 822篇 |
1980年 | 723篇 |
1979年 | 699篇 |
1978年 | 695篇 |
1977年 | 631篇 |
1976年 | 598篇 |
1975年 | 518篇 |
1974年 | 599篇 |
1973年 | 589篇 |
1972年 | 365篇 |
1971年 | 339篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
In this paper we report on the MEM power spectrum analysis of brightness temperature fluctuations observed at 2.8 GHz during the total solar eclipse of 16 February 1980. The observed periodicities range from 3.5 min to 64 min. These periodicities may arise due to spatial and/or temporal variations in the solar radio emission. The observed periodicities imply presence of scale sizes ranging from 70,000 to 600,000 km assuming that the brightness fluctuations arise because of spatial variation only. On the other hand, if these fluctuations are due to temporal variation, the observed periodicities correspond well to predicted modes of solar global oscillations. 相似文献
112.
113.
114.
115.
116.
117.
R. Huth 《Theoretical and Applied Climatology》1999,64(3-4):151-162
Summary The question discussed in this study is how to calculate linear trends in data that are not distributed evenly in time. This
is examined with time series of ten climate elements at a single station, stratified according to a classification based on
daily circulation patterns. Trends are calculated in three different ways: (i) from seasonal means, which is a common approach,
(ii) from means of individual events, the event being defined as a sequence of days classified as one particular type, preceded
and succeeded by another type, and (iii) from individual daily values. The most common method of estimating trend significance,
i.e. the t-test of the Pearson correlation coefficient, has been shown to be applicable to seasonal and event-mean trends for all variables.
For daily trends, the Monte Carlo test should be used instead. The daily, event-mean and seasonal trends differ from each
other considerably for many combinations of climate variable and circulation type. The reason for this difference is identified.
Received December 3, 1998 Revised June 21, 1999 相似文献
118.
The area of sea subjected to heated effluent discharged from the power station at Piombino is very suitable for the study of problems connected with thermal pollution of the nearshore environment. Construction of the power station is planned to go ahead by successive operational stages, producing correspondingly increased amounts of heat discharged into the marine environment. At present it produces 640 MW and discharges 190 Mcal s?1 into the sea.This paper studies the benthic communities after the power station had been operating for about 1 yr. Comparison of these data with those about subsequent operational stages will presumably allow to establish to what extent the environment can receive, without damage, increasing amounts of heat. 相似文献
119.
A collection of brachiopods by the Institute of Oceanology, Academia Sinica (Qingdao), contains eight species from seven genera.
Six of the species have been recorded previously from China seas—Lingula adamsi, L. anatina, Discinisca stella, Pelagodiscus atlanticus, Campages mariae, Terebratalia coreanica. Two species (Terebratulina hataiana andFrenulina sanguinolenta) have been described from other parts of the Pacific area. The apparent absence of any endemic species is a noteworthy feature
of Chinese in comparison with Japanese faunas. 相似文献
120.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1982,3(4):383-392
Photoelectric radial-velocity measurements have confirmed O. C. Wilson’s finding that BD 33° 2206, the secondary star in the
wide visual binary ADS 8470, is a spectroscopic binary. It has an eccentric orbit with a period of 100 days. Its γ-velocity
is close to the constant radial velocity of the visual primary, confirming the physical association of the stars. 相似文献