全文获取类型
收费全文 | 11813篇 |
免费 | 1433篇 |
国内免费 | 1459篇 |
专业分类
测绘学 | 571篇 |
大气科学 | 1771篇 |
地球物理 | 3586篇 |
地质学 | 4868篇 |
海洋学 | 1112篇 |
天文学 | 1049篇 |
综合类 | 693篇 |
自然地理 | 1055篇 |
出版年
2024年 | 30篇 |
2023年 | 128篇 |
2022年 | 327篇 |
2021年 | 428篇 |
2020年 | 364篇 |
2019年 | 352篇 |
2018年 | 771篇 |
2017年 | 604篇 |
2016年 | 701篇 |
2015年 | 544篇 |
2014年 | 657篇 |
2013年 | 716篇 |
2012年 | 604篇 |
2011年 | 643篇 |
2010年 | 617篇 |
2009年 | 618篇 |
2008年 | 559篇 |
2007年 | 489篇 |
2006年 | 412篇 |
2005年 | 318篇 |
2004年 | 318篇 |
2003年 | 270篇 |
2002年 | 267篇 |
2001年 | 259篇 |
2000年 | 224篇 |
1999年 | 333篇 |
1998年 | 375篇 |
1997年 | 319篇 |
1996年 | 311篇 |
1995年 | 237篇 |
1994年 | 226篇 |
1993年 | 174篇 |
1992年 | 162篇 |
1991年 | 128篇 |
1990年 | 153篇 |
1989年 | 112篇 |
1988年 | 89篇 |
1987年 | 87篇 |
1986年 | 78篇 |
1985年 | 54篇 |
1984年 | 52篇 |
1983年 | 37篇 |
1982年 | 43篇 |
1981年 | 43篇 |
1980年 | 38篇 |
1979年 | 33篇 |
1977年 | 28篇 |
1976年 | 30篇 |
1973年 | 29篇 |
1971年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
皖南低丘茶园土壤动物群落结构研究 总被引:13,自引:0,他引:13
本文是1986年10月—1988年10月对皖南低丘茶园土壤动物群落结构调查和研究的结果。调查期间共获大、中、小型土壤动物9468个,分别隶属于6门13纲37类。其中线虫类、螨类和蚁类为优势类群;线蚓类、弹尾类、鞘翅类幼虫、双翅类幼虫、蜘蛛类为常见类群,两者共占全捕量的94.03%。中小型土壤动物平均密度为1—2万个/m~2,大型土壤动物密度为200—500个/m~2。30年树龄茶园土壤动物群落的组成和数量最丰富,多样性、均匀性和密度-类群指数最高,其变化规律一般是30年茶园>20年茶园>15年茶园;7年树龄茶园群落土壤动物个体数虽少,但组成并不贫乏,且分布均匀,故多样性与密度-类群指数较高。土壤结构较好的黄红壤茶园各项指数大于土层薄、排水不良的黄棕壤茶园。群落各项指数秋季均大于春季。 相似文献
972.
Wolf Tietze Gerhard Kortum W. R. Mead T. K. Poiker C. Paddick George Kish A. Njøs H. Mensching V. Haarmann Uzo M. Igbozurike M. M. Yoshino Mushtaqur Rahman Lage Wahlström J. Connell Kazimierz Dziewonski Wayland R. Swain J. Humlum G. W. Lüttig Haruko Kishimoto Mai Britt E. Mørk 《GeoJournal》1982,6(3):270-280
973.
Approximate spectral analysis by least-squares fit 总被引:4,自引:0,他引:4
Petr Vaníček 《Astrophysics and Space Science》1969,4(4):387-391
An approximate method of spectral analysis called successive spectral analysis based upon the mean-quadratic approximation of an empirical function by generalised trigonometric polynomial with both unknown frequencies and coefficients is developed. A few quotations describing some properties of the method as well as one of the possible methods for numerical solution are given. 相似文献
974.
Zdislav Šíma 《Astrophysics and Space Science》1973,24(2):421-448
In this paper, the model of the ring envelope round the primary component and the stream of the gaseous mass flowing from
the secondary component to the primary is constructed on the basis of theoretical computations concerning the exchange of
the mass between the components of the binary. The paper studies the influence of the gaseous mass on the profiles of spectral
lines before and after occultation; the influence of the stream on the profile in case the secondary is near elongation, is
also investigated. The line profiles obtained by numerical computations show that their changes caused by outflowing mass
should be well detectable from spectrograms taken at particular phase of the binary. Changes in the lines may influence the
measurement of radial velocities. The method for distinguishing the influence of the stream from the influence of the ring
is described. 相似文献
975.
976.
Rigorous equations in compact symbolic matrix notation are introduced to transform coordinates and velocities between ITRF
frames and modern GPS-based geocentric geodetic datums. The theory is general but, after neglecting higher than second-order
terms, it is shown that the equations revert to the formulation currently applied in most major continental datums. We discuss
several examples: the North American Datum of 1983 (NAD83), the European Terrestrial Reference System of 1989 (ETRS89), the Geodetic Datum of Australia of 1994 (GDA94), and the South American Geocentric Reference System (SIRGAS).
Electronic Publication 相似文献
977.
The solar eclipse on August 11, 1999, observed in the region covered by many geomagnetic observatories, has offered a unique opportunity to look for an effect of the eclipse on geomagnetic pulsations. The pulsation activity digital data have been taken from Budkov Observatory in the Czech Republic (in the X component only), from observatories in Germany (Niemegk, Fürstenfeldbruck, Bad Bergzabern), in Hungary (Nagycenk), and for comparison in South Africa (Hermanus, conjugate-point station), and in Finland (Sodankylä, far from the eclipse zone). At all these stations the field in all three component has been recorded. The pulsation amplitudes in the X component exhibit a long-term minimum near the time of the eclipse. Spectral analysis of selected short intervals confirmed this decrease and also revealed a decrease of the average pulsation period during the eclipse. Such a change in the amplitude or in the period was not observed outside of the eclipse interval or in other days. Investigation in some narrower frequency bands showed that the maximal decrease occurred in the 15–20 s band. All these changes can be found in records from all the stations near the eclipse totality belt, also in records at the conjugate-point station, where no eclipse occurred. No signature has been found in records at the station situated far from the eclipse zone. 相似文献
978.
Studia Geophysica et Geodaetica - 相似文献
979.
In order to establish the magnetic carriers and assess the reliability of previous paleomagnetic results obtained for Eocene marine marls from the south Pyrenean basin, we carried out a combined paleo- and rock-magnetic study of the Pamplona-Arguis Formation, which crops out in the western sector of the southern Pyrenees (N Spain). The unblocking temperatures suggest that the characteristic remanent magnetization (ChRM) is carried by magnetite and iron sulphides. The ChRM has both normal and reversed polarities regardless of whether it resides in magnetite or iron sulphides, and represents a primary Eocene magnetization acquired before folding. Rock magnetic results confirm the presence of magnetite and smaller amounts of magnetic iron sulphides, most likely pyrrhotite, in all the studied samples. Framboidal pyrite is ubiquitous in the marls and suggests that iron sulphides formed during early diagenesis under sulphate-reducing conditions. ChRM directions carried by magnetic iron sulphides are consistent with those recorded by magnetite. These observations suggest that magnetic iron sulphides carry a chemical remanent magnetization that coexists with a remanence residing in detrital magnetite. We suggest that the south Pyrenean Eocene marls are suitable for magnetostratigraphic and tectonic purposes but not for studies of polarity transitions, secular variations and geomagnetic excursions, because it is difficult to test for short time differences in remanence lock-in time for the two minerals. The presence of iron sulphide minerals contributing to the primary magnetization in Eocene marine marls reinforces the idea that these minerals can persist over long periods of time in the geological record. 相似文献
980.
Observational estimation of heat budgets on drifting ice and open water over the Arctic Ocean 总被引:9,自引:0,他引:9
It is of major scientific interests to determine the parameters of momentum, heat and vapor exchange in the planetary boundary layer in order to study the effects of ocean-ice-atmosphere interactions and their feedback mechanisms on global climate[1]. Lin… 相似文献