全文获取类型
收费全文 | 12880篇 |
免费 | 2106篇 |
国内免费 | 2840篇 |
专业分类
测绘学 | 2120篇 |
大气科学 | 4771篇 |
地球物理 | 1323篇 |
地质学 | 2888篇 |
海洋学 | 535篇 |
天文学 | 71篇 |
综合类 | 1212篇 |
自然地理 | 4906篇 |
出版年
2024年 | 88篇 |
2023年 | 208篇 |
2022年 | 515篇 |
2021年 | 644篇 |
2020年 | 640篇 |
2019年 | 763篇 |
2018年 | 547篇 |
2017年 | 716篇 |
2016年 | 677篇 |
2015年 | 706篇 |
2014年 | 891篇 |
2013年 | 1115篇 |
2012年 | 995篇 |
2011年 | 977篇 |
2010年 | 769篇 |
2009年 | 745篇 |
2008年 | 763篇 |
2007年 | 879篇 |
2006年 | 819篇 |
2005年 | 684篇 |
2004年 | 598篇 |
2003年 | 529篇 |
2002年 | 451篇 |
2001年 | 402篇 |
2000年 | 344篇 |
1999年 | 249篇 |
1998年 | 222篇 |
1997年 | 208篇 |
1996年 | 138篇 |
1995年 | 142篇 |
1994年 | 102篇 |
1993年 | 71篇 |
1992年 | 55篇 |
1991年 | 37篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 24篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
201.
从土地荒漠化的概念出发,对山西省土地荒漠化的现状及特征进行了分析,指出土地荒漠化是目前困扰山西社会经济可持续发展的一个重要的生态环境问题,并提出了土地荒漠化的防治举措。 相似文献
202.
203.
204.
205.
吉林省西部沙化土地持续农业体系建立的实践 总被引:2,自引:1,他引:2
吉林省沙化土地的87.9%分布在吉林省西部白城、松原半干旱地区,统属科尔沁和松嫩沙地,面积9216.5km2,占吉林省西部总面积的19.6%。8年(1986年~1993年)实践证明:针对沙地环境特点建立的“乔、灌、草”、“果、药、杂”、“田、林、草”为主体的三种持续农业体系效果明显。 相似文献
206.
Nuclear power plant siting provided the first significant public opportunity to examine nuclear safety and to affect nuclear policy. These discussions were prompted and fueled by perceptions of nuclear risk. Now, as we begin the process of nuclear decommissioning, we are finding that power plant removal—unsiting–is also likely to attract public interest. This paper presents a preliminary survey of how we are likely to react to this emerging theme, applying these findings within a land use context to see if it is likely to produce issues salient to the public. In so doing it also examines how these issues could affect decommissioning timing and type. It suggests that the most likely prospect is that power plants will remain on the landscape long after they are closed. 相似文献
207.
浅层地下水氟的溶解/沉淀作用的定量研究 总被引:12,自引:0,他引:12
以河北邢台山前平原浅层高氟地下水为例,根据氟的化学热力学分析,确定了控制浅层地下水中氟迁移和富集的固相沉淀物,以及不同化学类型的浅层地下水中含氟固相沉淀物的溶解/沉淀条件;利用浅层地下水化学平衡反应模型和PHREEQE软件,确定了氟化的稳定区域,计算了氟化钙的饱和指数.研究结果表明,在浅层高氟地下水的整个形成过程中,都表现为氟由固相转入水相的趋势,有利于氟的迁移和富集 相似文献
208.
We present some preliminary results from a multi-layer soil temperature finite-difference model using the data set obtained
during the pilot experiment on land surface processes at Anand. We hope that the present results will prove useful during
the final field experiments scheduled for the coming monsoon season. 相似文献
209.
The occurrence of land subsidence in the Kingdom Saudi Arabia is either natural or man-made. Natural land subsidence occurs due to the development of subterranean voids by a solution of host rocks in carbonate and evaporite terrains, over many areas of Saudi Arabia. Man-induced land subsidence is either due to the removal of groundwater in the agricultural areas or to wetting of unstable soils. Therefore, earth fissures and a lowering of the ground surface in unconsolidated sediments took place in alluvial plains and volcanic vent terrains. Unstable soils include Sabkha soils and loess sediments. These types of soils occur in coastal plains, desert areas and volcanic terrains. When this soil is wetted either during agricultural activities, waste disposal or even during a rain storm, subsidence takes place due to either the removal of salts from the Sabkha soil or the rearrangement of soil particles in loess sediments. 相似文献
210.
B. Rajagopalan U. Lall D. G. Tarboton D. S. Bowles 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(1):65-93
A nonparametric resampling technique for generating daily weather variables at a site is presented. The method samples the
original data with replacement while smoothing the empirical conditional distribution function. The technique can be thought
of as a smoothed conditional Bootstrap and is equivalent to simulation from a kernel density estimate of the multivariate
conditional probability density function. This improves on the classical Bootstrap technique by generating values that have
not occurred exactly in the original sample and by alleviating the reproduction of fine spurious details in the data. Precipitation
is generated from the nonparametric wet/dry spell model as described in Lall et al. [1995]. A vector of other variables (solar
radiation, maximum temperature, minimum temperature, average dew point temperature, and average wind speed) is then simulated
by conditioning on the vector of these variables on the preceding day and the precipitation amount on the day of interest.
An application of the resampling scheme with 30 years of daily weather data at Salt Lake City, Utah, USA, is provided. 相似文献