全文获取类型
收费全文 | 109917篇 |
免费 | 1608篇 |
国内免费 | 722篇 |
专业分类
测绘学 | 2378篇 |
大气科学 | 7336篇 |
地球物理 | 21366篇 |
地质学 | 39442篇 |
海洋学 | 9916篇 |
天文学 | 25041篇 |
综合类 | 289篇 |
自然地理 | 6479篇 |
出版年
2022年 | 711篇 |
2021年 | 1219篇 |
2020年 | 1353篇 |
2019年 | 1494篇 |
2018年 | 2989篇 |
2017年 | 2807篇 |
2016年 | 3274篇 |
2015年 | 1735篇 |
2014年 | 3193篇 |
2013年 | 5626篇 |
2012年 | 3507篇 |
2011年 | 4619篇 |
2010年 | 4190篇 |
2009年 | 5298篇 |
2008年 | 4675篇 |
2007年 | 4794篇 |
2006年 | 4401篇 |
2005年 | 3202篇 |
2004年 | 3163篇 |
2003年 | 3015篇 |
2002年 | 2914篇 |
2001年 | 2512篇 |
2000年 | 2465篇 |
1999年 | 1983篇 |
1998年 | 2066篇 |
1997年 | 1938篇 |
1996年 | 1682篇 |
1995年 | 1633篇 |
1994年 | 1399篇 |
1993年 | 1347篇 |
1992年 | 1232篇 |
1991年 | 1278篇 |
1990年 | 1269篇 |
1989年 | 1102篇 |
1988年 | 1023篇 |
1987年 | 1173篇 |
1986年 | 1089篇 |
1985年 | 1330篇 |
1984年 | 1482篇 |
1983年 | 1441篇 |
1982年 | 1330篇 |
1981年 | 1247篇 |
1980年 | 1122篇 |
1979年 | 1065篇 |
1978年 | 1010篇 |
1977年 | 933篇 |
1976年 | 884篇 |
1975年 | 878篇 |
1974年 | 855篇 |
1973年 | 946篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
222.
Edward A. Boyle 《Geochimica et cosmochimica acta》2005,69(21):5165-5166
223.
R.E. Peterson 《Marine Geology》1976,21(1):59-62
A recent article by Beer et al. (1974) in Marine Geology describes an in-situ suspended sediment sampling system which utilizes a pump/motor unit, filter holders, and a lead-acid battery power source. Two aspects of their article may be misleading: the use of certain filter material as X-ray diffraction mounts, and the technique by which an oil-filled battery case may be operated. 相似文献
224.
Marine molluscan shells from para-type and other loclities of the Holsteinian interglaciation were dated by Th/U and the electron spin resonance (ESR) method to more than 350,000 and 370,000 yr B.P., beyond the limit of Th/U dating. The high age estimate is corroborated by a K/Ar age of 420,000 yr B.P. determined from volcanic ash near the base of the Ariendorf paleosol in the Middle Rhine valley believed to be a pedostratigraphic equivalent of the Holsteinian. Shells from the Herzeele marine unit III, an equivalent of the Wacken (Dömnitz) warm stage in northern France and subsequent to the Holsteinian, revealed ages between 300,000 and 350,000 yr B.P. A correlation of these two warm stages with marine oxygen-isotope stages 11 and 9 on the SPECMAP and CARTUNE time scales is suggested. From the benthic oxygen-isotope record one may infer that no exceptionally high global sea-level rise corresponds to the large transgressions of the Holstein Sea in northern Germany. Therefore, a significant proportion of the transgression was probably the result of an unusually large local glacial-isostatic depression caused by the extreme buildup of ice during the preceding Elster glaciation (stage 12). According to the deep-sea record, it lasted approximately 50% longer than the subsequent cold stage 10. The outstanding soil formation with Braunlehm and the well-developed thermal optimum of the Holsteinian are tentatively related to a phase of minimum sea-ice cover in the Norwegian-Greenland Sea, as deduced from long benthic carbon-isotope records from the central Atlantic. 相似文献
225.
In this 8th compilation, the following results of observations are given: 207 observed minima of 56 eclipsing binaries, 100 maxima of 21 RR Lyrae- and δ Cephei-stars, 82 results of 32 Mira stars and long period variables, and 47 results of 9 RV Tauri stars, semiregular, and irregular variables, from the years 1966 up to 1968. 相似文献
226.
The sodian stellerite (a zeolite) occurs as lustrous white or slightly pink, easily cleavable lamellae, filling cavities and fractures in an acid lava (andesite or rhyolite) in the cliff below S. Efisio Tower, near Capo Pula, Cagliari, Sardegna, Italy. The principal forms present are {010}, {011}, {111}. Single crystal photographs show an orthorhombic symmetry and Ammm (or Ammm) space group. An indexed X-ray diffraction powder pattern is provided. Unit cell dimensions, chemical formula, density, optical properties and thermal behaviour are given. 相似文献
227.
228.
Summary Snow has been studied widely in hydrology for many decades whereas recent meteorological interest in snow is caused by increased
emphasis on high latitudes and wintertime in climate-change research as well as by the need to improve weather-forecast models
during these conditions. Ground-based measurements of snow properties are needed both to improve understanding of surface-atmosphere
exchange processes and to provide ground truth to new remote-sensing algorithms. This justifies a review of techniques to
measure snow in combination with establishment of criteria for the suitability of the methods for process studies. This review
assesses the state-of-art in ground-based snow-measurement techniques in the end of the 1990s in view of their accuracy, time
resolution, possibility to automate, practicality and suitability in different terrain. Methods for snow-pack water equivalent,
depth, density, growth, quality, liquid-water content and water leaving the snow pack are reviewed. Synoptic snow measurements
in Fennoscandian countries are widely varying and there is no single standard on which process-related studies can build.
A long-term, continuous monitoring of mass and energy properties of a snow cover requires a combination of point-measurement
techniques. Areally representative values of snow properties can be achieved through a combination of automatically collected
point data with repeated manual, areally covering measurements, remote-sensing data and digital elevation models, preferably
in a GIS framework.
Received August 27, 1999 相似文献
229.
Investigations in a newly constructed subsea road tunnel in the Iddefjord granite at Hvaler and test-pumping of boreholes on land indicate that a topographic or geophysical anomaly is no guarantee of a substantially transmissive fracture zone. Many prominent fracture zones appear to have depressed transmissivity due to secondary swelling-clay mineral infillings. No current geophysical technique can adequately distinguish these zones from transmissive ones. Given that siting of boreholes on the basis of geology alone can be unreliable, hydrogeologists should concentrate on quantifying the chances of a successful boring, and optimizing those chances by sensible location, favourable borehole orientation and use of artificial enhancement techniques. 相似文献
230.
R. A. Treidl 《Boundary-Layer Meteorology》1970,1(2):155-168
When relatively warm, moist air moves over a snow surface, sensible heat and moisture are extracted from its lower layers and used to melt the snow. The depth of the cooled layer depends on horizontal wind speeds and the presence of high vertical wind shear. The mechanism for air mass modification appears to be turbulent mixing. 相似文献