全文获取类型
收费全文 | 72384篇 |
免费 | 1451篇 |
国内免费 | 1350篇 |
专业分类
测绘学 | 2082篇 |
大气科学 | 5479篇 |
地球物理 | 14906篇 |
地质学 | 25316篇 |
海洋学 | 6382篇 |
天文学 | 16448篇 |
综合类 | 341篇 |
自然地理 | 4231篇 |
出版年
2022年 | 454篇 |
2021年 | 737篇 |
2020年 | 766篇 |
2019年 | 857篇 |
2018年 | 1718篇 |
2017年 | 1636篇 |
2016年 | 2038篇 |
2015年 | 1268篇 |
2014年 | 1971篇 |
2013年 | 3582篇 |
2012年 | 2319篇 |
2011年 | 3107篇 |
2010年 | 2765篇 |
2009年 | 3654篇 |
2008年 | 3150篇 |
2007年 | 3211篇 |
2006年 | 3052篇 |
2005年 | 2239篇 |
2004年 | 2207篇 |
2003年 | 2023篇 |
2002年 | 2007篇 |
2001年 | 1740篇 |
2000年 | 1655篇 |
1999年 | 1421篇 |
1998年 | 1446篇 |
1997年 | 1441篇 |
1996年 | 1172篇 |
1995年 | 1125篇 |
1994年 | 1026篇 |
1993年 | 904篇 |
1992年 | 835篇 |
1991年 | 818篇 |
1990年 | 846篇 |
1989年 | 797篇 |
1988年 | 723篇 |
1987年 | 878篇 |
1986年 | 745篇 |
1985年 | 892篇 |
1984年 | 1099篇 |
1983年 | 950篇 |
1982年 | 929篇 |
1981年 | 834篇 |
1980年 | 799篇 |
1979年 | 738篇 |
1978年 | 749篇 |
1977年 | 676篇 |
1976年 | 618篇 |
1975年 | 617篇 |
1974年 | 592篇 |
1973年 | 645篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
The authors describe the effect of copper pollution on the mitochondria from various areas of the Torpedo marmorata central nervous system. A high percentage of swollen mitochondria has been observed in neurons from animals experimentally exposed to high level of copper (4 ppm). The correlation with age pigment granules is discussed. 相似文献
143.
The impact of wave loads and pore-water pressure generation on initiation of sediment transport 总被引:3,自引:0,他引:3
Edward C. Clukey Fred H. Kulhawy Philip L. -F. Liu George B. Tate 《Geo-Marine Letters》1985,5(3):177-183
The build-up of pore-water pressure by waves can lead to sediment liquefaction and subsequent transport by traction currents. This process was investigated by measuring pore-water pressures both in a field experiment and laboratory wave tank tests. Liquefaction was observed in the wave tank tests. The results suggest that sand is less susceptible than silts to wave-induced liquefaction because of the tendency to partially dissipate pore-water pressures. However, previous studies have determined that pore-water pressures must approach liquefaction before current velocities necessary to initiate transport are reduced. Once liquefaction has occurred more sediment can be transported. 相似文献
144.
145.
In this paper the peculiarities of compiled oceanographic data sets, which consist primarily in the presence of some characteristic information as well as in the planned incomplete filling of the files with observations, are discussed. A number of special ways are suggested which essentially improve the packing density of computerized data without applying special archiving algorithms. The effectiveness of these methods has been tested by treating thein situ hydrological/chemical data file compiled in the Black Sea in 1988.Translated by Vladimir A. Puchkin. 相似文献
146.
147.
A special fine structure (slowly drifting chains of narrowband fiber bursts), firstly observed during the solar type-IV radio burst on April 24, 1985, is interpreted as the radio signature of whistler waves periodically excited by a switch-on/switch-off process of a loss-cone instability in a localized wave packet of the fast magnetoacoustic mode. 相似文献
148.
Photometry of more than 1000 bright stars of 20 associations and some fields in its vicinity is made, usingUBV plates taken with a 2-m Ritchey-Chrétien telescope of the National Observatory at the Bulgarian Academy of Sciences with limited magnitudes of about 20.6 inU andV, 21.6 inB. The colour-magnitudes of about 20.6 inU andV, 21.6 inB. The colour-magnitude and colour-colour diagrams of 12 associations and 8 fields are constructed and the brightest blue and red stars colour excesses, ages, and integrated luminosities of the associations are determined. The composite diagrams for all association and nonassociation measured stars are constructed too. Inside associations bright stars as well as non-stellar objects occur more often than outside. The brightest stars in S5 are withM
v7 and do not differ considerably from the brightest ones in the spiral arm S4 of M31. Approximately the same are the absolute magnitudes of the brightest stars in our Galaxy and M33. A small difference between the brightest stars of the latter galaxy with those of M31 is possible because the stars in M33 are younger. This is in agreement with the concept that Sc galaxies (for example M33) are younger than Sb ones (for example M31). The same could be the reason for the smaller ratio of blue to red supergiants in M33 than in M31. The age estimations of the associations in S5 together with those in S4 in M31 show that they are older than the associations in M33 which is in agreement with the above mentioned concept. 相似文献
149.
By use of the H observations of the Astrophysical Observatory in Catania, Italy and the Purple Mountain Observatory in Nanking, China as well as hard X-ray and gamma-ray burst data from the Solar Maximum Mission (SMM) Gamma-Ray Spectrometer (GRS), a major eruptive loop prominence was studied during the limb solar flare event of 1981 April 27.Our preliminary analysis shows that there seems to exist a second abrupt energy release for this event, almost 20 min after the end of the impulsive phase of the flare. This energy release is probably associated with the rapidity in upward motion or activation of the loop prominence.A possible candidate for such a process could be the reconnection of the old magnetic field with a newly emerging magnetic field.A theoretical gross estimate for the energy release and particle acceleration has also been made in this work. It appears that the proposed model for charged particle acceleration is very efficient. 相似文献
150.
L. D. Barr 《Astrophysics and Space Science》1989,160(1-2):71-85
The National Optical Astronomy Observatories (NOAO) are planning to buld two 8 m telescopes, one for Mauna Kea, Hawaii, the other for a site in Chile. Optical configurations, primary mirror systems, and the telescope mounting are discussed. A new optical testing method is outlined. The system imaging goal is 0.25 FWHM. Construction could begin in the early 1990's.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.Operated by the Association of Universities for Research in Astronomy Inc., under contract with the National Science Foundation. 相似文献