首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   760篇
  免费   14篇
  国内免费   11篇
测绘学   47篇
大气科学   26篇
地球物理   120篇
地质学   296篇
海洋学   25篇
天文学   238篇
综合类   13篇
自然地理   20篇
  2022年   15篇
  2021年   17篇
  2020年   13篇
  2019年   14篇
  2018年   47篇
  2017年   45篇
  2016年   38篇
  2015年   21篇
  2014年   43篇
  2013年   54篇
  2012年   33篇
  2011年   32篇
  2010年   34篇
  2009年   39篇
  2008年   27篇
  2007年   20篇
  2006年   28篇
  2005年   15篇
  2004年   9篇
  2003年   5篇
  2002年   5篇
  2001年   8篇
  2000年   13篇
  1999年   10篇
  1998年   6篇
  1997年   3篇
  1996年   8篇
  1994年   8篇
  1993年   6篇
  1992年   7篇
  1991年   7篇
  1989年   7篇
  1988年   16篇
  1987年   12篇
  1986年   14篇
  1985年   4篇
  1984年   11篇
  1983年   8篇
  1982年   7篇
  1981年   5篇
  1980年   11篇
  1979年   7篇
  1978年   9篇
  1976年   4篇
  1975年   4篇
  1974年   3篇
  1973年   5篇
  1972年   5篇
  1971年   6篇
  1970年   5篇
排序方式: 共有785条查询结果,搜索用时 750 毫秒
21.
22.
In this paper, the hypsometric curves and integrals of four neighboring micro-watersheds draining into Patiala-Ki-Rao stream which is situated in the Shivalik foothills of district SAS Nagar in the Punjab state (India) has been presented to access and compare the erosion regimes under different management practices. Area-elevation ratio method has been used to compute hypsometric curve and integral values for each micro-watershed through ArcGIS 10.3 and Microsoft Excel. The 9-year data of runoff and sediment yield for all these micro-watersheds under different management practices has been analyzed for their effect on land cover and soil quality. Thus, the results of present study are very useful for comparing, planning, implementing, and controlling soil erosion in similar watersheds.  相似文献   
23.
Characterization of the Panandhro lignite deposits from western Indian state of Gujarat, based on the geochemical and palynological evidences, has been performed to assess the floral composition, maturity and hydrocarbon potential of the sequence. Elementally, the lignites consist of moderate carbon, low hydrogen and moderate sulfur contents. The samples are characterized by high TOC contents (lignite: av. 46.43 wt.%, resin: 62.47 wt.%). The average HI values for the lignite is 136 mg HC/g TOC, and that of the associated resin is 671 mg HC/g TOC. The highest Tmax is recoded in lignite (422°C) and lowest in the resin (39°C) samples. The FTIR spectrum of lignite is characterized by highly intense OH stretching peak ~3350 cm-1, aliphatic CHx stretching peaks between 3000-2800 cm-1, aromatic C=O stretching and an aromatic C=C stretching. The spectrum of resin shows strongest absorption due to aliphatic CHx stretching between 2940-2915 cm-1 and 2870-2850 cm-1, and deformation by the medium peak between 1450 and 1650 cm-1. The recovered palynofloral assemblage indicates the dominance of angiosperm pollen grains with maximum abundance of Arecaceae family, and subdominant pteridophytic spores. Marine influence is indicated by the presence of abundant dinoflagellate cysts. The occurrence of flora from a variety of ecological niches suggests a luxuriant diverse vegetation pattern existed in the vicinity of depositional site under humid tropical conditions. The overall characteristics of the lignite deposits point towards their ability to generate (upon maturation) hydrocarbons as they have types III–II admixed kerogen (organic matters).  相似文献   
24.
In the present investigation, an attempt has been made to explore the possibility of hydrocarbon prospects in the carbonaceous shale deposits of Spiti and Chikkim formations exposed in the Spiti valley of the Tethys Himalaya. Twenty samples, collected from successive levels of these litho-units, have been subjected to maceral analysis, Rock-Eval Pyrolysis and six samples to Fourier Transform Infra-red Spectroscopy (FTIR) and nuclear magnetic resonance (NMR) analyses. The study reveals the presence of mainly kerogen-III type of organic matter but some of the shale samples have shown a good amount of total organic carbon (TOC) to the tune of 3.19% which is sufficient to produce hydrocarbon. The results indicate the presence of methane occurring as free and fixed hydrocarbon in the shale samples. Few levels are especially rich in hydrocarbon. They have shown encouraging results with potential for generating liquid as well as lighter hydrocarbon. The data is also supported by the FTIR and NMR studies.  相似文献   
25.
The age of the marine Nodular Limestone Formation of the Bagh Group is refined at Substage level through ammonoid and inoceramid index taxa. The study is based on the fresh collections from three well-defined successive intervals (Lower Karondia, Upper Karondia and Chirakhan members) of this formation having excellent exposures in different localities of the Narmada Basin, central India. The first record of the widely distributed Turonian ammonoid genera Spathites Kummel and Decker and Collignoniceras Breistroffer from the Nodular Limestone Formation constrained its age exclusively to Turonian. The Early Turonian species Spathites (Jeanrogericeras) aff. revelieranus (Courtiller) and Mytiloides labiatus (Sclotheim) occur in the lower part, while the Middle Turonian marker Collignoniceras cf. carolinum (d’Obrbigny) and Inoceramus hobetsensis (Nagao and Matsumoto) occurs in the upper part of the Karondia Member. The record of the index species Inoceramus teshioensis (Nagao and Matsumoto) in association with Placenticeras mintoi Vredenburg from Chirakhan Member allows a definite Late Turonian age. The present contribution is an attempt to resolve the controversies in the age of the Nodular Limestone Formation and also demarcation of the three divisions (Early, Middle and Late) of the Turonian Stage in the Narmada Basin, central India.  相似文献   
26.
Yadav  Ganesh  Singh  R. B.  Anand  Subhash  Pandey  B. W.  Mohanty  Ashutosh  Dash  Sushree Sangita 《GeoJournal》2021,87(4):469-483

Ambient air pollution, particularly in the urban environment of developing countries, has turned out to be a major health risk factor. We explore the compounded impact of age sensitivity, exposure, poverty, co-morbidity, etc., along with composite air pollution in determining morbidity and health burden of people in Lucknow, India. This cross-sectional study is confined to analyse respiratory health status across different socio-economic and geographic locations using n = 140 in-depth questionnaire method. We used mean daily ambient air pollution data of PM10, PM2.5, SO2, and NO2 for the 2008–2018 period. We used the ecological model framework to assess the risk at different hierarchical levels and compounded severity on a spatial scale. We also used Logistic regression model with log odds and odds ratio to analyze the association of risks outcomes with composite air pollution scores calculated using the principal component analysis method. There is a strong association of location-specific respiratory disease prevalence with an overall 32 percent prevalence. The prevalence of ecological model 1 (individual domain) is 4.3 percent, while ecological model 2 (community domain) has the highest prevalence at 32.4 percent. The logistic regression model shows that respiratory disease load is positively associated with age sensitivity (P < .001) and composite pollution level (P < .001). For another model with suffocation as the outcome variable, composite pollution level (P < .001) and exposure (P < .001) are positively associated. Optimum interventions are required at Ecological models 1, 2, and 3 levels for better respiratory health outcomes.

  相似文献   
27.
This paper analyses the significance, structure, and organisation of the manufacturing sector in Fiji, drawing on the author's earlier much larger study of industrialisation in Fiji. The latest Fijian census of industrial production (1984) and the author's 1983 survey of manufacturers in Fiji provide the main statistical basis of the study, which shows that the manufacturing sector is a moderately important component of the Fijian economy. It is dominated by resource industries, particularly food processing, but a wide range of manufacturing activities have, nonetheless, developed. There is a substantial number of small manufacturing establishments with a few large establishments, the latter, however, making an overwhelmingly important contribution to employment, gross output and value added. The market structure in the manufacturing sector is dominated by monopolies and oligopolies resulting from Fiji's small domestic market and its import substitution industrialisation strategy. There is an absence of informal sector activities in Fijian manufacturing, most firms being incorporated companies. The state has a major role as a direct producer in Fijian manufacturing. There are bound to be major changes in the manufacturing sector due to Fiji's current political crisis, but this paper does not address these because of the recency of the events and the consequent unavailability of relevant data.  相似文献   
28.
Monthly-mean winds and currents have been used to identify the driving mechanisms of seasonal coastal circulation in the North Indian Ocean. The main conclusions are: (i) the surface circulation off Arabia is typical of a wind-driven system with similar patterns of longshore current and wind stress; (ii) circulation off the west coast of India is consistent with the dynamics of a wind-driven eastern boundary current only during the southwest monsoon. During the northeast monsoon it is possible that the influence of the interior flow is important. (iii) There are at least three mechanisms that influence the surface circulation off the east coast of India: wind-stress, influence of fresh-water run off and contribution of the interior flow. It is difficult at present to assess the relative importance of these three processes.  相似文献   
29.
30.
The LC50 for exposure of 48 and 96 h is 34.64 and 18.5 mg/l Cd2+, respectively. During the exposure to 3.5 mg/l Cd2+ from the 13th day significant differences of length and mass occur with respect to the control. Over a total of 31 days of experiment the reduction of growth rates is 11% for the longitudinal growth and 16% for the increase in weight.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号