全文获取类型
收费全文 | 84379篇 |
免费 | 1410篇 |
国内免费 | 1112篇 |
专业分类
测绘学 | 2252篇 |
大气科学 | 6237篇 |
地球物理 | 16280篇 |
地质学 | 30438篇 |
海洋学 | 7617篇 |
天文学 | 19014篇 |
综合类 | 435篇 |
自然地理 | 4628篇 |
出版年
2022年 | 631篇 |
2021年 | 1039篇 |
2020年 | 1108篇 |
2019年 | 1154篇 |
2018年 | 2252篇 |
2017年 | 2154篇 |
2016年 | 2655篇 |
2015年 | 1555篇 |
2014年 | 2568篇 |
2013年 | 4371篇 |
2012年 | 2886篇 |
2011年 | 3753篇 |
2010年 | 3295篇 |
2009年 | 4205篇 |
2008年 | 3600篇 |
2007年 | 3655篇 |
2006年 | 3504篇 |
2005年 | 2592篇 |
2004年 | 2514篇 |
2003年 | 2363篇 |
2002年 | 2270篇 |
2001年 | 1947篇 |
2000年 | 1863篇 |
1999年 | 1517篇 |
1998年 | 1600篇 |
1997年 | 1491篇 |
1996年 | 1291篇 |
1995年 | 1254篇 |
1994年 | 1073篇 |
1993年 | 960篇 |
1992年 | 946篇 |
1991年 | 921篇 |
1990年 | 1012篇 |
1989年 | 820篇 |
1988年 | 785篇 |
1987年 | 917篇 |
1986年 | 785篇 |
1985年 | 973篇 |
1984年 | 1135篇 |
1983年 | 976篇 |
1982年 | 955篇 |
1981年 | 855篇 |
1980年 | 821篇 |
1979年 | 790篇 |
1978年 | 767篇 |
1977年 | 672篇 |
1976年 | 621篇 |
1975年 | 617篇 |
1974年 | 594篇 |
1973年 | 645篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
We consider long barotropic waves in a system of two rectangular basins connected by a channel in the case where waves are
generated by the moving region of disturbances of atmospheric pressure passing above one of the basins. By using a numerical
model, we compute the characteristics of the wave process for various values of the parameters of this system. The results
of numerical calculations are compared with the corresponding characteristics obtained for the case of a closed basin. We
also analyze the distinctive features of long-wave processes induced in the presence of the channel.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
142.
We present Strömgrenuvby photometric observations and a series of radial velocities obtained with the Coravel scanner for the 11th magnitude star catalogued in the Guide Star Catalogue as GSC 0114401023. This star was serendipitously identified on UV frames taken with the Very-Wide-Field-Camera aboard Spacelab-1. Radial velocities show the star to be binary and we have determined accurate orbital elements. Photometric data and orbital elements are consistent with the system being a previously-unrecognized eclipsing binary, with period = 33.8766 days and eccentricity = 0.262.Based on observations collected at the Observatoire de Haute Provence (OHP), CNRS, Saint-Michel l'Observatoire, France, and at the European Southern Observatory (ESO), La Silla, Chile. 相似文献
143.
Natural disasters like floods, tornadoes, tropicalcyclones, heat and cold wavewreak havoc and cause tremendous loss ofproperty all over the world. Most ofthe natural disasters are either dueto weather or are triggered due toweather related processes.Extreme weather events claimed thousands oflives and caused damage on vastscale. Recent super cyclone which affectedOrissa in 1999, Bangladesh cyclone of1970 and Hurricane Andrew in 1992 areexamples of some of the more damagingtropical cyclones which affected developingas well as the developed world. Heatand cold waves are also extreme events,which cause enormous losses in terms oflives lost and human discomfort and ailmentsarising out of them. The heat waveof 1995 and 1998 are still fresh in the mindof the Indian public. The estimated lossof human lives due to heat wave in 1998 was morethan 15,000. Economic losses asa result of these disasters and in particular inassociation with tropical cyclones haveincreased enormously over the last three decades.During 1961–1991, total loss oflives from drought alone was 1,333,728 overthe whole world. In terms of economiclosses, there is 8–10 fold increase from thebase figure of 1960. The socio-economicimpact of natural disaster is complex dependingupon the vulnerability of the placeand mitigation strategies that are put in place.Meteorology plays a crucial role in forewarningpeople about the severe/extremeweather systems and a constant endeavour by themeteorological services worldover has gone a long way towards minimizing thelosses caused by natural disasters.The paper summarises the natural disasterstatistics over south Asia and the possibleprediction strategies for combating theirsocio-economic impacts. 相似文献
144.
145.
146.
In this paper, we derive the scaling laws for different radiating fluids. The studied regimes are relevant for both laboratory astrophysics and High Energy Density Physics. Using Lie groups theory, we obtain scaling laws, the similarity properties and the number of free parameters to rescale experiments. 相似文献
147.
Guan J.Wei F.Sun G.Huang J.Wang L. 《大地构造与成矿学》2015,(2):344-354
The Ningzhen metallogenic district is an important part of the Middle-Lower Yangtze River Valley metallogenic belt. LA-ICP-MS zircon U-Pb dating of the three intermediate-acid intrusions, i.e., Anjishan, Xinqiao, and Shima, in the central part of the Ningzhen district, indicates that those intrusions were emplaced in the Late Early Cretaceous, with ages of 107.0±1.1 Ma-108.0±1.6 Ma, 108.0±1.3 Ma, and 102.5±1.1 Ma, respectively. Combined with the molybdenite Re-Os isotope age (106-108 Ma) of porphyry copper deposit in this regions, the Ningzhen district exists an intensively magmatic-metallogenic-thermal event at 102.5-108.0 Ma. The age of this event is similar with the age of the third period of large scale mineralization in South China, however obviously later than the magmatic activity of other ore field (124-148 Ma) in the Middle-Lower Yangtze River Valley metallogenic belt. It is suggested that the tectonic-magmatic-thermal events in the Ningzhen area is formed under regional lithospheric extension environment, which is also consistent with the tectonic background of the third period of large scale mineralization in South China. The zircon U-Pb ages of the intrusions and the Re-Os ages of molybdenites from the porphyry deposits in the study area demonstrate that the Ningzhen district underwent intensive magmatism and hydrothermal mineralization during the period from 102.5 to 108.0 Ma, which is consistent with the third pulse of large scale mineralization in the South China. ©, 2015, Science Press. All right reserved. 相似文献
148.
Tertiary age and paleostructural inferences of the eclogitic imprint in the Austroalpine outliers and Zermatt–Saas ophiolite, western Alps 总被引:2,自引:0,他引:2
G. Dal Piaz G. Cortiana A. Del Moro S. Martin G. Pennacchioni P. Tartarotti 《International Journal of Earth Sciences》2001,90(3):668-684
The Austroalpine Sesia-Lanzo inlier and upper Austroalpine Dent Blanche, Mt. Mary and Pillonet outliers occur on top of the western-Alpine orogenic wedge and, as a whole, override the structurally composite ophiolitic Piemonte zone. Instead, the Mt. Emilius, Glacier-Rafray, Etirol-Levaz and other lower Austroalpine eclogitic outliers are inserted within the Piemonte zone, between its upper (Combin) and lower (Zermatt-Saas) tectonic elements, or within the latter. Rb-Sr dating on phengitic micas show that the eclogitic imprint in the lower Austroalpine outliers, conventionally regarded as Late Cretaceous by comparison with the Sesia-Lanzo inlier, is of Eocene age (49-40 Ma), like the underlying Zermatt-Saas ophiolite (45-42 Ma) between the Aosta valley and Gran Paradiso massif. 40Ar-39Ar plateau ages on the same mica concentrates of the ophiolitic Zermatt-Saas nappe (46-43 Ma) are consistent with Rb-Sr dating, whereas that on the Austroalpine Glacier-Rafray klippe (92 Ma) is influenced by argon excess. The lower Austroalpine outliers underwent the subduction metamorphism concurrently with the Zermatt-Saas nappe, 20-25 Ma later than the eclogitic Sesia-Lanzo inlier and blueschist Pillonet klippe. The temporal gap and present intra-ophiolitic position mean that the lower Austroalpine outliers were probably derived from an intraoceanic extensional allochthon (Mt. Emilius domain) stranded inside the Piemonte-Ligurian ocean far from the Dent Blanche-Sesia domain and Adriatic margin. 相似文献
149.
Evaluating the effect of the global ionospheric map on aiding retrieval of radio occultation electron density profiles 总被引:1,自引:0,他引:1
Radio occultation (RO) has been proven to be a powerful technique for ionospheric electron density profile (EDP) retrieval. The Abel inversion currently used in RO EDP retrieval has degraded performance in regions with large horizontal gradients because of an assumption of spherical symmetry as indicated by many studies. Some alternative methods have been proposed in the past; the global ionospheric map (GIM)-aided Abel inversion is most frequently studied. Since the number of RO observations will likely increase rapidly in the near future, it is worthwhile to continue to improve retrieval method. In this study, both the simulations and the real data test have been done to evaluate the GIM-aided Abel inversion method. It is found that the GIM-aided Abel inversion can significantly improve upon the standard Abel inversion in either the F or the E region if an accurate GIM is available. However, the current IGS GIM does not appear accurate enough to improve retrieval results significantly, because of the spherical symmetry assumption and sparse global navigation satellite system (GNSS) stations used in its creation. Generating accurate GIM based on dense GNSS network to aid the Abel inversion might be an alternative method. 相似文献
150.
V. A. Hagen-Thorn A. V. Hagen-Thorn S. G. Jorstad L. O. Takalo A. Sillanpää T. Pursimo P. Boltwood 《Astrophysics》2001,44(3):283-291
The results of multicolor observations of the blazar 3C 66A, obtained in the course of the project OJ-94, are analyzed. It is established that the energy distribution of the variable source in the optical and IR ranges can be represented, on the average, by a power law: F -0.92. Since the blazar's emission is strongly polarized, there is no doubt of the synchrotron nature of the variable source responsible for the blazar's activity. 相似文献