全文获取类型
收费全文 | 9219篇 |
免费 | 1397篇 |
国内免费 | 1228篇 |
专业分类
测绘学 | 1177篇 |
大气科学 | 1254篇 |
地球物理 | 2244篇 |
地质学 | 3702篇 |
海洋学 | 1370篇 |
天文学 | 56篇 |
综合类 | 731篇 |
自然地理 | 1310篇 |
出版年
2024年 | 40篇 |
2023年 | 107篇 |
2022年 | 232篇 |
2021年 | 338篇 |
2020年 | 338篇 |
2019年 | 394篇 |
2018年 | 265篇 |
2017年 | 383篇 |
2016年 | 407篇 |
2015年 | 418篇 |
2014年 | 602篇 |
2013年 | 563篇 |
2012年 | 536篇 |
2011年 | 666篇 |
2010年 | 497篇 |
2009年 | 591篇 |
2008年 | 680篇 |
2007年 | 685篇 |
2006年 | 575篇 |
2005年 | 477篇 |
2004年 | 404篇 |
2003年 | 353篇 |
2002年 | 333篇 |
2001年 | 308篇 |
2000年 | 274篇 |
1999年 | 233篇 |
1998年 | 225篇 |
1997年 | 161篇 |
1996年 | 149篇 |
1995年 | 126篇 |
1994年 | 110篇 |
1993年 | 95篇 |
1992年 | 75篇 |
1991年 | 42篇 |
1990年 | 34篇 |
1989年 | 37篇 |
1988年 | 24篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
依据多目标区域生态地球化学调查已经取得的部分成果(如:国土环境质量状况、农田区土壤肥力和营养状况、规划特色优势农作物产地、部分地方病分布区和影响因素等),从发展循环经济、提高土地管理水平和发展现代化农业等方面提出了深化调查成果的意见和方向。 相似文献
912.
腾冲来凤山北麓前缘,潜伏一段阻水构造——地下水位坡降带。从研究13个水文钻井、119口民间井、2个泉水露头地下水位特征入手,采用古水文和现代水文地质研究方法,论证此段阻水构造的存在。 相似文献
913.
玉溪市萝卜子地水源地地下水允许开采量评价 总被引:1,自引:0,他引:1
萝卜子地供水水源地,水文地质条件较复杂。利用多年地下水动态及抽水试验资料上,进行基岩富水地段地下水的补给量计算,以补给量作为该水源地的允许开采量合理。 相似文献
914.
Jean S. Kane Philip J. Potts Thomas Meisel Michael Wiedenbeck 《Geostandards and Geoanalytical Research》2007,31(3):285-288
The International Association of Geoanalysts (IAG) published a protocol for the certification of reference materials in close accord with the International Organisation for Standardisation (ISO) guidelines (Kane et al. 2003). This article supplements that protocol, providing additional discussion of best approaches for pre-selecting laboratories for participation in certification projects. This discussion also makes a distinction between inter-laboratory certifications, where n = 15 is the general standard, and expert laboratory certifications, where a much smaller number of laboratories will be deemed qualified to provide data of the quality needed for certification. 相似文献
915.
The eastern Ethiopian highland is endowed with large potential of water resources in terms of rainfall, groundwater and surface
water. Yet, due to overpumping of lake water and groundwater and environmental degradation, Lakes Haromaya and Adele have
completely dried up. The environmental degradation, due to deforestation and clearing of land for farming, has increased the
rate of siltation in the lakes that dramatically decreases the lakes’ volume and surface albedo, which increased the rate
of evaporation. The impact of these factors is aggravated due to decreasing net recharge to the lake and the alluvial aquifer.
Over the last 35 years, pumping of lake water for irrigation, mainly for subsistence farming, domestic and industrial use
shows an increasing trend. Hence, the available water for drinking and industrial purposes decreased drastically. In this
research, classical Penman aerodynamic combined energy budget, Penman nomogram methods, conventional soil moisture water balance
method and Penman–Monteith model were adopted to estimate free evaporation, actual and potential evapotranspirations. The
results indicate that evaporation is the dominant factor for the loss of water and water abstraction is 316% higher than the
effective precipitation, which is 110 mm/year. Therefore, overexploitation of the available resources has played an aggravating
role for the loss of the lakes in the area. The main cause for such resource depletion is the lack of integrated water resources
management strategies. The current water shortage in the area has mainly affected urban residents of Harar, Awoday and Alemaya
towns and the surrounding villages, which depend heavily on the two lakes. To alleviate the current crises interbasin water
transfer and rainwater harvesting would be possible alternatives besides ameliorating environmental situation of the basin. 相似文献
916.
N. Janardhana Raju 《Environmental Geology》2007,52(6):1067-1074
In the management of water resources, quality of water is just as important as its quantity. In order to know the quality
and/or suitability of groundwater for domestic and irrigation in upper Gunjanaeru River basin, 51 water samples in post-monsoon
and 46 in pre-monsoon seasons were collected and analyzed for various parameters. Geological units are alluvium, shale and
quartzite. Based on the analytical results, chemical indices like percent sodium, sodium adsorption ratio, residual sodium
carbonate, permeability index (PI) and chloroalkaline indices were calculated. The pre-monsoon waters have low sodium hazard
as compared to post-monsoon season. Residual sodium carbonate values revealed that one sample is not suitable in both the
seasons for irrigation purposes due the occurrence of alkaline white patches and low permeability of the soil. PI values of
both seasons revealed that the ground waters are generally suitable for irrigation. The positive values of Chloroalkaline
indices in post-monsoon (80%) and in pre-monsoon (59%) water samples indicate absence of base-exchange reaction (chloroalkaline
disequilibrium), and remaining samples of negative values of the ratios indicate base-exchange reaction (chloroalkaline equilibrium).
Chadha rectangular diagram for geochemical classification and hydrochemical processes of groundwater for both seasons indicates
that most of waters are Ca–Mg–HCO3 type. Assessment of water samples from various methods indicated that majority of the water samples in both seasons are suitable
for different purposes except at Yanadipalle (sample no. 8) that requires precautionary measures. The overall quality of groundwater
in post-monsoon season in all chemical constituents is on the higher side due to dissolution of surface pollutants during
the infiltration and percolation of rainwater and at few places due to agricultural and domestic activities. 相似文献
917.
我国炼焦煤资源丰富,但优质炼焦煤一直处于短缺局面。根据全国已有煤质数据分析,从优质(主要考虑挥发分指标)、环保(主要考虑硫分和灰分指标)两个方面结合有害微量元素含量,将炼焦煤划分为四种类型,确定了优质环保型炼焦煤资源的评价步骤,对全国五个赋煤区优质环保型炼焦煤的资源量等级进行了统计分析。 相似文献
918.
随着国有企业现代企业制度的建立,我国各项法律法规也日益完善。企业如何实现依法经营、强化内部管理,运用法律手段化解经营风险,是当前国有企业亟待解决的问题。国务院国资委下发的《中央企业重大法律纠纷案件管理暂行办法》要求中央企业逐步建立法律风险防范机制,设立企业法律顾问,把依法经营纳入企业管理的各个环节。分析了同有企业面临的法律风险现状和重要性之后,提出了建立法律风险防范机制的几项措施手段,以便为国企的健康发展保驾护航。 相似文献
919.
磁铁矿采空区处理施工工艺与技术方法探讨 总被引:3,自引:0,他引:3
文章系统地介绍了采用地质钻机成孔,高压注浆机进行充填注浆的施工方法。为了将水泥砂浆及水泥粉煤灰浆填入采空区,采用能施加高压的输送泵及高压注浆设备、铸铁注浆管、水泥封孔的注浆工艺处理采空区铁路路基。在信息化施工过程中,通过试验不断地调整设计方法、改进施工工艺,在处理巨型磁铁矿采空区工程实践中达到了预期的目标。施工中,在控制充填边界、封孔方法及施工工艺等方面有一定的创新。提出的采空区施工技术控制、质量检测与评价方法,对同类工程勘察、设计及施工具有一定的参考价值。 相似文献
920.
The development and utilization of water and land resources in the Shiyang River basin are the highest among the inland rivers
in northwestern China. Using GIS and the landscape structure analysis program FRAGSTATS, landscape metrics of a study area
in the lake-district in Minqin Oasis in the lower reaches of Shiyang River basin were calculated and analyzed based on TM
images from 1987 to 2001 at class level and landscape level, respectively. Transformation matrix of the landscape mosaics
was also examined. The driving forces of landscape changes were analyzed, including the dynamics of runoff and groundwater
resources and their exploitation, and influences of policies and market economy. The results showed that: (1) Patch number
of farmland and desert decreased, but their mean patch area increased, indicating that reclamation and desertification was
very serious in the study area. Contagion index for oasis increased and edge density and landscape diversity were reduced.
(2) Farmland and desert areas have enlarged by 1,520.46 and 4,941.27 hm2, respectively. This increase was at the cost of woodland and grassland, which shrank by 1,520.46 and 4,941.27 hm2, respectively. (3) The net utilization of surface water decreased by 50% in the last 10 years, and dropped to 22.3 × 106 m3 in the later 1990s. Exploitation of groundwater increased remarkably, up to 80 × 106 m3 per year in the last 5 years. (4) The capability of the economic structure to withstand pressures of the market economy has
depressed distinctly because of the simplified planting pattern, which is dominated by salinity-enduring cash crops, such
as cotton. Based on the above analysis, strategies of ecological reconstruction in the lake-district were suggested. 相似文献