全文获取类型
收费全文 | 1878篇 |
免费 | 272篇 |
国内免费 | 273篇 |
专业分类
测绘学 | 101篇 |
大气科学 | 134篇 |
地球物理 | 328篇 |
地质学 | 954篇 |
海洋学 | 49篇 |
天文学 | 4篇 |
综合类 | 122篇 |
自然地理 | 731篇 |
出版年
2024年 | 2篇 |
2023年 | 18篇 |
2022年 | 49篇 |
2021年 | 65篇 |
2020年 | 74篇 |
2019年 | 75篇 |
2018年 | 76篇 |
2017年 | 78篇 |
2016年 | 88篇 |
2015年 | 89篇 |
2014年 | 109篇 |
2013年 | 150篇 |
2012年 | 118篇 |
2011年 | 120篇 |
2010年 | 105篇 |
2009年 | 91篇 |
2008年 | 129篇 |
2007年 | 113篇 |
2006年 | 129篇 |
2005年 | 106篇 |
2004年 | 83篇 |
2003年 | 75篇 |
2002年 | 83篇 |
2001年 | 65篇 |
2000年 | 67篇 |
1999年 | 49篇 |
1998年 | 42篇 |
1997年 | 44篇 |
1996年 | 29篇 |
1995年 | 17篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有2423条查询结果,搜索用时 203 毫秒
931.
IINTRODUCTION climate chang巳 divided d叮/wet penodS and discussed itsrelationships with cold/warm vanatlon and solar activityRecords ofellmate dlsasterhave been abundantly(CHEN198飞 1989).IOund In Chinese historical literature.Previous works The present study tends to establish the dry/wethave collected such records to study the historical elf-series since 960 A.D.ofTal… 相似文献
932.
一个流域内既有地表水资源,又有地下水资源,如何根据本流域的自然地质条件更合理地开发利用这些水资源,是个战略决策问题。本文以典型流域为实例,对适宜地表及地下调蓄水资源的条件进行了分析,对中小流域水资源合理调蓄问题提出了笔者的看法。 相似文献
933.
934.
Nigel J. H. Smith 《The Professional geographer》1987,39(1):1-8
The number of crop genebanks, designed to conserve crop genetic resources and make them available to breeders, has risen dramatically in recent years. While few dispute the need to conserve crop germplasm to help boost and sustain agricultural productivity, the role of genebanks and their global distribution has become embroiled in controversy. Some suggest that genebanks are servicing mainly multinational seed companies and that industrial countries harbor the lion's share of crop germplasm collections. This article describes the importance of genebanks, analyzes their distribution and beneficiaries, and outlines how geographers can become more involved in the conservation and use of crop genetic resources. 相似文献
935.
常州市农业产业对生态环境的影响及治理对策 总被引:8,自引:1,他引:8
作为长江流域传统农业生产大市的常州,随着农业产业结构调整的不断推进,其生态环境的可持续发展正面临着严峻挑战。通过对常州市水质、土壤、空气、声等农业生态环境质量现状的实地调查分析,结合该地各农业产业对生态环境造成污染的不同特点,提出如要从根本上治理农业生态环境污染,农业产业布局的调整是非常重要的一个方面,并对此作了新的布局规划;此外,还指出完善环境管理和改善生产技术也是治理生态环境污染的两个重要对策。 相似文献
936.
Control of gas emissions in underground coal mines 总被引:4,自引:0,他引:4
Klaus Noack 《International Journal of Coal Geology》1998,35(1-4)
A high level of knowledge is now available in the extremely relevant field of underground gas emissions from coal mines. However, there are still tasks seeking improved solutions, such as prediction of gas emissions, choice of the most suitable panel design, extension of predrainage systems, further optimization of postdrainage systems, options for the control of gas emissions during retreat mining operations, and prevention of gas outbursts. Research results on these most important topics are presented and critically evaluated. Methods to predict gas emissions for disturbed and undisturbed longwall faces are presented. Prediction of the worked seam gas emission and the gas emission from headings are also mentioned but not examined in detail. The ventilation requirements are derived from the prediction results and in combination with gas drainage the best distribution of available air currents is planned. The drainage of the gas from the worked coal seam, also referred to as predrainage, can be performed without application of suction only by over or underworking the seam. But in cases where this simple method is not applicable or not effective enough, inseam-boreholes are needed to which suction is applied for a relatively long time. The reason for this is the low permeability of deep coal seams in Europe. The main influences on the efficiency of the different degasing methods are explained. Conventional gas drainage employing cross measure boreholes is still capable of improvement, in terms of drilling and equipment as well as the geometrical borehole parameters and the operation of the overall system. Improved control of gas emissions at the return end of retreating faces can be achieved by installation of gas drainage systems based on drainage roadways or with long and large diameter boreholes. The back-return method can be operated safely only with great difficulty, if at all. Another method is lean-gas drainage from the goaf. The gas outburst situation in Germany is characterized by events predominantly in the form of ‘nonclassical' outbursts categorized as ‘sudden liberation of significant quantities of gas'. Recent research results in this field led to a classification of these phenomena into five categories, for which suitable early detection and prevention measures are mentioned. 相似文献
937.
Mineralogical study of base metal tailings with various sulfide contents, oxidized in laboratory columns and field lysimeters 总被引:7,自引:0,他引:7
S. C. Shaw L. A. Groat J. L. Jambor D. W. Blowes C. J. Hanton-Fong R. A. Stuparyk 《Environmental Geology》1998,33(2-3):209-217
Oxidation of a flotation-derived, low-sulfide tailings containing approximately 0.4 wt.% S was compared with simultaneously
oxidized tailings containing 1.0 wt.% S and 2.5 wt.% S to assess their acid generating characteristics. Each tailings type
was exposed to oxidation for three years in laboratory columns and in lysimeter pits in the field. In these tailings the sulfide
mineral of principal concern with respect to acid generation is pyrrhotite (Fe
1-x
S). In past studies the alteration of pyrrhotite has been characterized by initial replacement with marcasite (FeS2) and ferric iron sulfates, which are followed by development of ferric oxyhydroxides such as goethite and lepidocrocite.
Macroscopic characterization of the tailings shows varying and progressive degrees of oxidation correlative with the three
different sulfur contents. As expected, the tailings with the lowest sulfur content are the least oxidized, and those with
the highest sulfur content have reacted the most. The column tests, which represent accelerated reaction conditions relative
to those for the lysimeter pits, show much higher degrees of oxidation, and a markedly more distinct boundary between the
oxidized and unoxidized zones; as well, differences among the three tailings types are more pronounced.
Received: 31 October 1997 · Accepted: 27 May 1997 相似文献
938.
Iron oxyhydroxide precipitates associated with acid mine drainage (AMD) from the Stearns Coal Zone in southeastern Kentucky
were analyzed for their metal (Al, Cu, Pb, Mn, Ni, and Zn) content. The most concentrated metals within these sediments are
nickel (27–32×103μmol/kg), manganese (16–29×103μmol/kg), and aluminum (13–22×103μmol/kg) as determined by HCl-HNO3 digestion. Metal concentrations associated with the organic fraction as determined by H2O2 digestion were generally far lower, with the exception of aluminum. "Batch" experiments (at initial pH=2.0) were used to
analyze the stability of these metals associated with a contaminated soil. Aluminum was the most mobile of the metals, presumably
the result of the formation of aluminum-sulfate aqueous complexes. The solubilization rates for nickel and iron were very
similar, suggesting that nickel, unlike the other metals, coprecipitated with iron in these sulfatic oxyhydroxides.
Received: 9 October 1997 · Accepted: 15 December 1997 相似文献
939.
西藏羊八井现代地下热水系统硫矿的成矿作用 总被引:15,自引:3,他引:12
通过对羊八井盆地地热流体的地球化学、气体成分、同位素特征以及泉华、岩矿等资料的研究 ,确认该地下热水溶液中的水主要来自大气降水 ,部分来自深部 ;矿质大部分源自对围岩的淋滤和溶解 ,少部分物质 ,如易挥发成分则与岩浆体有关 ;热源则由地壳浅部岩浆体供给。根据羊八井地热水成矿作用特点和矿化分布规律 ,提出成矿区主要位于地热流体卸压排泄系统成矿的论点 ,并建立了羊八井盆地地热水系统成矿概念模型。地热田内自然硫及其它硫化矿物的形成过程中微生物起着重要的作用 相似文献
940.
Soilisanepigeneticspherehavingthedensestbiologicalmasandthehighestbiologicalenergy,whichisabasementprovidingtheplantwithwate... 相似文献