全文获取类型
收费全文 | 44146篇 |
免费 | 4193篇 |
国内免费 | 6191篇 |
专业分类
测绘学 | 2985篇 |
大气科学 | 5989篇 |
地球物理 | 9844篇 |
地质学 | 21774篇 |
海洋学 | 3960篇 |
天文学 | 2419篇 |
综合类 | 3958篇 |
自然地理 | 3601篇 |
出版年
2024年 | 90篇 |
2023年 | 378篇 |
2022年 | 1028篇 |
2021年 | 1186篇 |
2020年 | 967篇 |
2019年 | 1126篇 |
2018年 | 5649篇 |
2017年 | 4911篇 |
2016年 | 3670篇 |
2015年 | 1318篇 |
2014年 | 1334篇 |
2013年 | 1415篇 |
2012年 | 2221篇 |
2011年 | 3866篇 |
2010年 | 3190篇 |
2009年 | 3400篇 |
2008年 | 2783篇 |
2007年 | 3248篇 |
2006年 | 813篇 |
2005年 | 886篇 |
2004年 | 883篇 |
2003年 | 946篇 |
2002年 | 780篇 |
2001年 | 604篇 |
2000年 | 698篇 |
1999年 | 950篇 |
1998年 | 803篇 |
1997年 | 786篇 |
1996年 | 760篇 |
1995年 | 670篇 |
1994年 | 594篇 |
1993年 | 503篇 |
1992年 | 419篇 |
1991年 | 296篇 |
1990年 | 232篇 |
1989年 | 192篇 |
1988年 | 188篇 |
1987年 | 111篇 |
1986年 | 114篇 |
1985年 | 72篇 |
1984年 | 64篇 |
1983年 | 56篇 |
1982年 | 62篇 |
1981年 | 66篇 |
1980年 | 69篇 |
1979年 | 32篇 |
1978年 | 16篇 |
1976年 | 16篇 |
1974年 | 12篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
我们于1989年11月30日晚对PG0027+260进行了时间分辨率为108秒的高速CCD测光,得到了一条完整的光变曲线,从而确认其为激变食变星系统,轨道周期0.146~d 相似文献
62.
Simulation of double cold cores of the 35°N section in the Yellow Sea with a wave-tide-circulation coupled model 总被引:1,自引:0,他引:1
Based on the MASNUM wave-tide-circulation coupled numerical model, the temperature structure along 35°N in the Yellow Sea
was simulated and compared with the observations. One of the notable features of the temperature structure along 35°N section
is the double cold cores phenomena during spring and summer. The double cold cores refer to the two cold water centers located
near 122°E and 125°E from the depth of 30m to bottom. The formation, maintenance and disappearance of the double cold cores
are discussed. At least two reasons make the temperature in the center (near 123°E) of the section higher than that near the
west and east shores in winter. One reason is that the water there is deeper than the west and east sides so its heat content
is higher. The other is invasion of the warm water brought by the Yellow Sea Warm Current (YSWC) during winter. This temperature
pattern of the lower layer (from 30m to bottom) is maintained through spring and summer when the upper layer (0 to 30m) is
heated and strong thermocline is formed. Large zonal span of the 35°N section (about 600 km) makes the cold cores have more
opportunity to survive. The double cold cores phenomena disappears in early autumn when the west cold core vanishes first
with the dropping of the thermocline position.
Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No.
49736190). 相似文献
63.
Da-Ming Chen 《中国天文和天体物理学报》2001,1(4):287-290
1 INTRODUCTIONObservations of the most famous starburst galaxy M82 with the High-Resolution Cameraon board the Chandra X-Ray Observatory, showed that there are nine sources in the celltral11 x 11 region, but no son-roe was detected at the galactic center (Matsumoto et al. 2001).Comparing the observations on 1999 October 28 and those on 2000 January 20, the authorsfound an extremely large time variability of the source CXO M82 J095550.2 694047, which islocated gll away from the galact… 相似文献
64.
低频扩频中伪随机序列产生方法的研究 总被引:2,自引:0,他引:2
伪随机序列的产生是实现BPC低频时码发播台扩展频谱技术升级的一个重要环节。针对BPC低频时码发播台的现有系统,提出了伪随机序列的产生方案,并对其性能作了分析。 相似文献
65.
66.
Technique for Controlling Spread of Limnotic Oncomelania 总被引:1,自引:0,他引:1
Schistosomiasis is a parasitic disease mostly found in areas along the Changjiang River of China. The disease is spread solely through an intermediary named oncomelania, so its spread of schistosomiasis can be controlled by properly designing water intakes which prevent oncomelania from entering farming land or residential areas. This paper reports a successful design process and a new oncomelania-free intake device. The design of the new intake is based on a sound research program in which extensive experimental studies were carried out to gain knowledge of oncomelania eco-hydraulic behavior and detailed flow field information through CFD simulation. 相似文献
67.
The present paper reports 9 species of pontoniine shrimps collected from Hainan IS-land ,South China Sea ,by the Joint Chinese-German Marine Biology Expeditions,in which Peri-climenaeus arabicus (Calman,1939) and Periclimenaeus hecate (Nobili,1904) are recorded for the first time from Hainan Island. 相似文献
68.
地倾斜台站数字化、模拟观测数据频率特性研究 总被引:2,自引:2,他引:0
分析了四川、云南的部分地倾斜数字化观测与模拟观测资料的特性,从频率范围,周期10天以上的FFT谱特性,固体潮波振幅,相位特征值等方面,论述了地倾斜数字化资料较模拟记录资料的信息组成变化,并对资料的分析与应用进行了初步探讨。 相似文献
69.
APPLICATION OF GEOGRAPHICAL PARAMETER DATABASE TO ESTABLISHMENT OF UNIT POPULATION DATABASE 总被引:1,自引:1,他引:0
Now GIS is turning into a good tool in handling geographical, economical, and population data, so we can obtain more and more information from these data. On the other hand, in some cases, for a calamity, such as hurricane, earthquake, flood, drought etc., or a decision-making, such as setting up a broadcasting transmitter, building a chemical plant etc., we have to evaluate the total population in the region influenced by a calamity or a project. In this paper, a method is put forward to evaluate the population in such special region. Through exploring the correlation of geographical parameters and the distribution of people in the same region by means of quantitative analysis and qualitative analysis, unit population database (1km× 1km) is established. In this way, estimating the number of people in a special region is capable by adding up the population in every grid involved in this region boundary. The geographical parameters are obtained from topographic database and DEM database on the scale of 相似文献
70.
1StrongtideandastronomicalconditionsPartial solar eclipse occurred 4 times in 1964, 1982 and 2000 respectively. Time interval is about 3 Saros periods (one Saros period is 18 years and 10.33~11.33 days). Total lunar eclipse occurred 2 times in 1964 and 2000 respectively and 3 times in 1982. However, there was no lunar eclipse in 1966, 1984 and 2002. It seems that they had similar astro-nomical conditions and the best was in 1982. The studies about the effect of tide on the global climate… 相似文献