全文获取类型
收费全文 | 55572篇 |
免费 | 731篇 |
国内免费 | 575篇 |
专业分类
测绘学 | 1615篇 |
大气科学 | 3893篇 |
地球物理 | 10335篇 |
地质学 | 19890篇 |
海洋学 | 4944篇 |
天文学 | 13387篇 |
综合类 | 207篇 |
自然地理 | 2607篇 |
出版年
2022年 | 382篇 |
2021年 | 654篇 |
2020年 | 689篇 |
2019年 | 732篇 |
2018年 | 1695篇 |
2017年 | 1585篇 |
2016年 | 1987篇 |
2015年 | 1054篇 |
2014年 | 1856篇 |
2013年 | 2986篇 |
2012年 | 1937篇 |
2011年 | 2460篇 |
2010年 | 2143篇 |
2009年 | 2759篇 |
2008年 | 2357篇 |
2007年 | 2392篇 |
2006年 | 2240篇 |
2005年 | 1660篇 |
2004年 | 1662篇 |
2003年 | 1574篇 |
2002年 | 1509篇 |
2001年 | 1323篇 |
2000年 | 1245篇 |
1999年 | 1023篇 |
1998年 | 1069篇 |
1997年 | 978篇 |
1996年 | 838篇 |
1995年 | 800篇 |
1994年 | 705篇 |
1993年 | 622篇 |
1992年 | 611篇 |
1991年 | 625篇 |
1990年 | 642篇 |
1989年 | 521篇 |
1988年 | 537篇 |
1987年 | 566篇 |
1986年 | 509篇 |
1985年 | 633篇 |
1984年 | 719篇 |
1983年 | 637篇 |
1982年 | 586篇 |
1981年 | 511篇 |
1980年 | 488篇 |
1979年 | 488篇 |
1978年 | 471篇 |
1977年 | 374篇 |
1976年 | 351篇 |
1975年 | 358篇 |
1974年 | 316篇 |
1973年 | 352篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
341.
S. K. Goyal B. S. Chaudhary O. Singh G. K. Sethi P. K. Thakur 《Journal of the Indian Society of Remote Sensing》2010,38(2):355-364
The present study has analyzed the variability in depth to water level below ground level (bgl) vis-à-vis groundwater development
and rainfall from 1987 to 2007 in agriculture dominated Kaithal district of Haryana state in India. Spatial distribution of
groundwater depth was mapped and classified into different zones using ILWIS 3.6 GIS tools. Change detection maps were prepared
for 1987–1997 and 1997–2007. Groundwater depletion rates during successive decades were compared and critical areas with substantial
fall in groundwater levels were identified. Further, block wise trends of change in groundwater levels were also analyzed.
The water table in fresh belt areas of the district (Gulha, Pundri and Kaithal blocks) was observed to decline by a magnitude
ranging from 10 m to 23 m. In Kalayat and Rajaund blocks, the levels were found fluctuating in a relatively narrow range of
4–9 m. During 1997–2007, the depletion has been faster compared to the preceding decade. Excessive groundwater depletion in
major part of the district may be attributed to indiscriminate abstraction for irrigation and decrease in rainfall experienced
since 1998. Changes in cropping pattern and irrigation methods are needed in the study area for sustainable management of
the resource. 相似文献
342.
The grid DEM(digital elevation model) generation can be from any of a number of sources:for instance,analogue to digital conversion of contour maps followed by application of the TIN model,or direct elevation point modelling via digital photogrammetry applied to airborne images or satellite images.Currently,apart from the deployment of point-clouds from LiDAR data acquisition,the generally favoured approach refers to applications of digital photogrammetry.One of the most important steps in such deployment i... 相似文献
343.
R. Sridhar T. Thangaradjou L. Kannan S. Astalakshmi 《Journal of the Indian Society of Remote Sensing》2010,38(3):565-575
Coastal resources viz., coral reefs, seagrasses, mangroves, and coastal land features viz., sandy beach, mudflats and salt
pan/aquaculture ponds were classified and assessed in the Palk Bay region of the south-east coast of India using IRS LISS
III satellite image (1996, 2000, 2002 and 2004). The study recorded an areal coverage of 286.95 ha of reef area during 2004,
which is 177.54 ha lesser than that of the reef area of 1996. The reef vegetation composed mainly of seaweeds has gained over
29.44 ha during the same period. Likewise, sand over reef area has also increased alarmingly i.e. 120.34 ha between 1996 and
2004. The seagrass beds of Munaikkadu region of the Palk Bay are comparatively protected and have gained over 7.5 ha between
1996 and 2004. It has been found that both the dense (2.99 ha) and sparse (36.45 ha) mangroves have gained their areal coverage
considerably between 1996 and 2004. Whereas in Devipattinam region, many anthropogenic pressures are exerted only on the seagrass
resources which has led to the reduction of over 785.5 ha of dense seagrass beds between 1996 and 2004. The study clearly
indicated that the resources are under the pressures of low to high threats, especially the coral reefs and seagrasses, if
the pressures continue, coastal resources of the Palk Bay may face serious threats of destruction in this part of the Bay
in the years to come. 相似文献
344.
Bovolo F. Bruzzone L. Capobianco L. Garzelli A. Marchesi S. Nencini S. 《Geoscience and Remote Sensing Letters, IEEE》2010,7(1):53-57
345.
346.
347.
Anjana Pant S. G. Chavan P. S. Roy K. K. Das 《Journal of the Indian Society of Remote Sensing》1999,27(3):133-139
Habitat analysis for sambar in terms of food, cover, water, space and extent of edge in Corbett National Park using remote sensing and GIS has been attempted. Other physical parameters include climate, topography, fire history, disturbance regimes, weeds etc. IRS-IB LISS II data (FCC, hardcopy) on 1:50.000 scale was interpreted to generate vegetation cover and density map. Other maps showing drainage, water bodies, roads, human habitations and contours were prepared using Survey of India topographical maps. During evaluation of sambar habitat information regarding habitat parameters and their tolerance was collected from existing literature as well as during field observations. Twenty-two transects of one km. length were laid down in all the strata randomly to collect information regarding the structure and composition of the forest and also habitat use (direct and indirect evidences) by sambar. This was then integrated using condition-based equations in the GIS domain to generate suitability maps. Actual sightings on the ground to a large extent supported the results. 相似文献
348.
G P Singh 《Journal of the Indian Society of Remote Sensing》1999,27(1):1-8
An attempt is made to mark regional geology of part of Lalitpur district. The area is characterized by flat topography gently sloping east ward with isolated hillocks. The well contrasted lithology has been marked on the basis of variation in tone, drainage pattern and texture. The main lithounits are foliated granites/gneiss, banded iron formation, granites, ultra basic, quartz reef and basic dykes. The structural elements of lineaments are visible on aerial photos and imagery which range in length from 1 to 10 km. The lineaments at places intersect with each other. The major trends are NNW- SSE. NE- SW. NNH- SSW. These NNW- SSE and NE-SW lineaments are retlected by well aligned body of quartz- sericite schist and quartz reef respectively. 相似文献
349.
M D Shamim Ansari R. K. Mahey S. S. Sidhu 《Journal of the Indian Society of Remote Sensing》1999,27(4):185-192
To predict the crop yield from spectral parameters, a field experiment was conducted on cotton crop during 1997-98 Kharif season on a sandy loam soil at the Punjab Agricultural Unjversity, Ludhiana. India. Spectral reflectance and agronomic measurements were made for cotton species (American and Desi cotton), sown on two dates (May 1 and May 29) under five nitrogen levels (0, 40, 80, 120 and 160 kg/ha). Regression analysis showed that growth variables had poor correlation with seed cotton yield for all three models, however, yield attributes were significantly and highly correlated for second degree model with seed cotton yield. The integrated Radiance Ratio (RR) and Normalized Difference Vegetation Index (NDVI) measured over time were significantly correlated quadratically with seed cotton yield on three time segment periods viz., 81–110, 111–140 and 141–200 DAS, but highest correlation values were obtained during 81–110 DAS, In American cotton, the highest correlation coefficient for RR and NDVI were 0.91 and 0.81, respectively; whereas for Desi cotton these values were 0.88 and 0.84, respectively. 相似文献
350.
S M Ramasamy S Balaji C J Kumanan 《Journal of the Indian Society of Remote Sensing》1999,27(2):91-104
The interpretation of satellite imagery of part of South India falling South of 15 degree North latitude shows that the regional anticlines, synclines, domes and basins of the Precambrian group of metamorphites are aligned in three major hill ranges/domains such as Chitra-durga domain in the north, the Mangalore-Ootacamund-Bangalore domain in the centre and the Cochin-Cape Comorin-Madurai-Chittoor domain in the south. These hills are crescent shaped with their axes of elongation oriented in NNW-SSE direction. The lineaments with ENE-WSW, NE-SW/WNW-ESE and NNW-SSE azimuthal frequencies respectively exhibit extensional, shear and release geometries. Such deformational fabric shows that the tectonic evolution of South India was controlled by two major compressive forces, the first one aligned in N-S direction and the second in ENE-WSW direction. 相似文献