全文获取类型
收费全文 | 842篇 |
免费 | 13篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 53篇 |
大气科学 | 29篇 |
地球物理 | 215篇 |
地质学 | 295篇 |
海洋学 | 36篇 |
天文学 | 201篇 |
综合类 | 3篇 |
自然地理 | 31篇 |
出版年
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 32篇 |
2017年 | 32篇 |
2016年 | 40篇 |
2015年 | 21篇 |
2014年 | 32篇 |
2013年 | 35篇 |
2012年 | 22篇 |
2011年 | 33篇 |
2010年 | 28篇 |
2009年 | 32篇 |
2008年 | 38篇 |
2007年 | 32篇 |
2006年 | 25篇 |
2005年 | 20篇 |
2004年 | 12篇 |
2003年 | 14篇 |
2002年 | 14篇 |
2001年 | 17篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 14篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 19篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 20篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1972年 | 12篇 |
1971年 | 10篇 |
排序方式: 共有863条查询结果,搜索用时 31 毫秒
81.
82.
Total mercury was estimated in liver, gonads and muscle of some of the marine fishes from the Indian Ocean. The highest mercury concentration was observed in the muscle of sharks while the total mercury concentration was practically non-detectable in the liver and gonads. The range of all the values was 0.09–0.21 ppm (wet weight basis) and is quite low to reflect any possible mercury contamination. 相似文献
83.
Dr. Ashok Sahni Mr. Harish Chandra Mitra 《International Journal of Earth Sciences》1980,69(3):824-848
The paper analytically discusses certain palaeoecological criteria in the reconstruction of Lower Miocene (Aquitanian-Burdigalian) palaeobiogeography of the Indian subcontinent. The period is characterised by major marine transgressions and a prolific marine invertebrate and terrestrial vertebrate faunas. Faunal affinities of molluscs from western (Sind-Baluchistan) and eastern (Garo Hills) sectors are distinct and different. Molluscs of Garo Hills show affinity to Burmese species, whereas Sind-Baluchistan species shows similarity to that of the Mediterranean region. Marine molluscs resemble with the present-day taxa of the Arabian Sea and Bay of Bengal, where more than 35% species are common. This similarity is also evidenced by marine elasmobranchs, where approximately 33% species and 86% genera are similar to that of the Recent taxa. Terrestrial mammals show an intermingling of southern U.S.S.R. and African forms along with the presence of probably some groups belonging to the Indian subcontinent.Angiosperms are the dominant group. The Lower Miocene floras of the eastern and the western sectors are entirely different. The palm,Sabal major andPinus are reported from various localities. The climate in the western sector and South India was tropical, whereas in the eastern sector, it was variable.The Lower Miocene period is also marked by the contraction of Sindhu Sea, Bangla Sea and the Burmese Gulf southwards resulting in the final disappearance of the sea by the Pliocene.
Zusammenfassung Die Paläobiogeographie des unteren Miocän (Aquitan-Burdigal) läßt sich auf dem indischen Subkontinent aus den palökologischen Daten rekonstruieren. Zu dieser Zeit gab es viele marine Invertebraten und terrestrische Vertebraten-Faunen, die große marine Transgression anzeigen. Die Mollusken des Westens (Find-Baluchistan) und Ostens (Garo-Gebirge) sind unterschiedlich. Die Mollusken des Garo-Gebirges sind mit den Spezies von Burma verwandt. Dagegen sind die Faunen von Sind-Baluchistan für die mediterrane Faunenprovinz typisch. Die marinen Mollusken sind verwandt mit den Faunen des Arabischen Meeres und der Bucht von Bengalen; etwa 35% der Spezies sind gleich. Von den marinen Elasmobranchien sind ungefähr 33 % Spezies und 86% Genera gleich wie man sie in den rezenten Faunen findet. Terrestrische Sänger zeigen eine Mischung von südlicher U.S.S.R. und Afrika mit einigen Teilen des Indischen Subkontinentes.In den Pflanzen-Gruppen herrschen die Angiospermen vor. Die Untermiocän-Flora der östlichen und westlichen Gebiete ist ganz unterschiedlich. Der Palme, dieSabal Major undPinus sind aus verschiedenen Lokalitäten bekannt. Das Klima im Westen und im Süden Indiens war tropisch, im Osten dagegen war es wechselfeucht.Das Untermiocän-Meer im Gebiet Sind, Bangladesh und Burma verschwindet vor dem Pliozän.
Résumé Cet article analyse certains critères paléoécologiques dans la reconstitution de la paléogéographie du Miocène inférieur (Aquitanien-Burdigalien) de l'Inde subcontinentale. La période est caractérisée par de grandes transgressions marines et par des faunes abondantes d'invertébrés marins et de vertébrés terrestres. Les affinités fauniques des mollusques sont différentes dans les secteurs occidentaux (Sind-Baluchistan) et orientaux (Garo Hills). Les mollusques des Garo Hills montrent des affinités avec les espèces de Burma, tandis que les espèces de Sind-Béloutchistan montrent des similitudes avec celles de la région méditerranéenne. Les mollusques marins ont des ressemblances avec les taxons actuels de la Mer d'Arabie et du Golfe du Bengal, où plus de 35% des espèces sont les mÊmes. Cette similarité vaut aussi pour les élasmobranches marin, dont 33% des espèces et 86% des genres ressemblent aux taxons récents. Les mammifères terrestres montrent un mélange de formes du sud de l'U.S.S.R. et de formes africaines, allant de pair avec la présence de certains groupes probables appartenant au sous-continent indien.Les angiospermes forment le groupe dominant. Les formes du Miocène inférieur des secteurs orientaux et occidentaux sont entièrement différentes. Le palmier, le grand Sabal et le pin, sont connus dans différentes localités. Le climat dans le secteur occidental et dans l'Inde méridionale était tropical, tandis que dans le secteur oriental, il était variable.La période du Miocène inférieur est également marquée par le rétrécissement de la Mer de Sindhu, de la Mer de Bangla et du Golfe de Burma vers le sud, avec comme résultat la disparition finale de la mer au Pliocène.
(Aquitanian Nurdigalian) . . (Sind- Beluchistan) (Garo Hills) . , . : 35% . Elasmobranchs 33 % 86 % . , . . , Sabal major . , , , , , — . Sindhu, .相似文献
84.
Single span highway bridges of composite construction are idealized as beams as well as orthotropic plates. A standard HS–20–44 highway vehicle is represented by a planar, two-axle, sprung mass system with frictional device. The response equations are derived in terms of the natural modal co-ordinates of the bridge and of displacement co-ordinates of the vehicle. The road surface irregularities, generally found at the junctions of the approach road and bridge ends, are idealized as a 45° ramp. The maximum impact factors for bending moment and deflection are obtained due to the ramp and in combination with the braking of vehicle for symmetric as well as essentric loading of the vehicle. 相似文献
85.
Mohan L. Gupta 《Journal of Volcanology and Geothermal Research》1981,10(4):279-292
Heat flow values from some additional locations in the Cenozoic Cambay Basin have been determined. Together with the previously published data, they show that the heat flow is moderate (55–67 mW/m′) in the southern part of the basin towards Broach and Ankleswar, and that there is a clear trend of high heat flow (75–93 mW/m2; range of average values for six different, widely separated, locations) in a part of the basin located north of the Mahisagan river between Cambay and Mehsana along a stretch of about 140 km. Conductive steady state geotherms, calculated using observed high surface heat flow values and appropriate models show, beneath the Cambay-Mehsana area, a large degree of melting in the lower crust and upper mantle, which is not suggested by the existing geodata. Considering this aspect and taking into account the existence of a normal crust about 37 km thick below the Cambay-Tarapur and Ahmedabad-Mehsana blocks (as obtained from deep seismic soundings), it has been inferred that the heat flow anomaly is due to transient thermal perturbations introduced from tectonic activity in the form of magmatic intrusions. A careful analysis of heat flow, gravity and other related geodata point out and support the possibility of a Miocene/Pliocene basic intrusive body at a depth of around 10 km under the Cambay-Mehsana area. Further, the consistent trend of the thermal and gravity fields indicates thinning of the postulated intrusive body from Cambay towards Mehsana. 相似文献
86.
G P Gupta 《Journal of Earth System Science》1978,87(11):231-234
The ionospheric absorption data measured by the sweep frequency method have been compared with the solar x-ray data in the band of 1–8 Å during quiet- and disturbed-sun conditions. The degree of solar x-ray control of the ionospheric absorption and the corresponding limit of solar x-ray flux have been discussed. 相似文献
87.
88.
V. S. Singh V. Krishnan M. R. K. Sarma C. P. Gupta R. L. Dhar 《Environmental Geology》1999,37(1-2):90-95
Detailed hydrogeological studies in a granitic micro-watershed have been carried out to determine the extent, behavior, and
characteristics of the aquifer. The study includes analysis of lithologs, drill time log, pumping tests, and slug tests. Realistic
field conditions have been taken into account for characterizing the aquifer system. Slug tests were carried out to estimate
aquifer parameters at the wells which could not sustain pumping.
Received: 20 November 1997 · Accepted: 23 February 1998 相似文献
89.
Satluj Valley is known to have a history of landslides and related mass movement activities since the geological times. Geological and geomorphological settings combined with anthropogenic activities constitute a propensity towards slope failure. During the last two decades,the area witnessed substantial increase in athropogenic pressure,mainly due to the exploitation of hydropower potential,changing landuse pattern and population growth. In addition,a shift of the climatic patterns in the form of larger area falling under the influence of rains was observed. These natural as well as anthropogenic changes in the area have resulted in increased spatial coverage of landslide in the area. This paper documents these changes during 1990~2006. 相似文献
90.
Reshu Agarwal Rakesh Gupta J. K. Garg 《Journal of the Indian Society of Remote Sensing》2009,37(3):473-481
A three-step hierarchical Semi Automated Empirical Methane Emission Model (SEMEM) has been used to estimate methane emission
from wetlands and waterlogged areas in India using Moderate Resolution Imagine Spectroradiometer (MODIS) sensor data onboard
Terra satellite. Wetland Surface Temperature (WST), methane emission fluxes and wetland extent have been incorporated as parameters
in order to model the methane emission. Analysis of monthly MODIS data covering the whole of India from November 2004 to April
2006 was carried out and monthly methane emissions have been estimated. Interpolation techniques were adopted to fill the
data gaps due to cloudy conditions during the monsoon period. AutoRegressive Integrated Moving Average (ARIMA) model has been
fitted to estimate the emitted methane for the months of May 2006 to August 2006 using SPSS software. 相似文献