全文获取类型
收费全文 | 7468篇 |
免费 | 1762篇 |
国内免费 | 2836篇 |
专业分类
测绘学 | 368篇 |
大气科学 | 3993篇 |
地球物理 | 1579篇 |
地质学 | 3001篇 |
海洋学 | 1417篇 |
天文学 | 76篇 |
综合类 | 544篇 |
自然地理 | 1088篇 |
出版年
2024年 | 54篇 |
2023年 | 134篇 |
2022年 | 306篇 |
2021年 | 377篇 |
2020年 | 388篇 |
2019年 | 470篇 |
2018年 | 396篇 |
2017年 | 402篇 |
2016年 | 410篇 |
2015年 | 470篇 |
2014年 | 593篇 |
2013年 | 693篇 |
2012年 | 638篇 |
2011年 | 608篇 |
2010年 | 472篇 |
2009年 | 591篇 |
2008年 | 535篇 |
2007年 | 648篇 |
2006年 | 499篇 |
2005年 | 493篇 |
2004年 | 389篇 |
2003年 | 334篇 |
2002年 | 258篇 |
2001年 | 259篇 |
2000年 | 245篇 |
1999年 | 224篇 |
1998年 | 216篇 |
1997年 | 165篇 |
1996年 | 123篇 |
1995年 | 136篇 |
1994年 | 121篇 |
1993年 | 111篇 |
1992年 | 74篇 |
1991年 | 52篇 |
1990年 | 37篇 |
1989年 | 35篇 |
1988年 | 31篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
21.
Unconsolidated sand, gravel and clay deposits near Beihai and in the Leizhou Peninsula in southern China form an unconfined
aquifer, aquitard and a confined aquifer. Water and soil samples were collected from the two aquifers in the coastal Beihai
area for the determination of chemical compositions, minerals and soluble ions. Hydrogeochemical modeling of three flow paths
through the aquitard are carried out using PHREEQC to determine water–rock interactions along the flow paths. The results
indicate that the dissolution of anorthite, fluorite, halite, rhodochrosite and CO2, and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the
unconfined aquifer to the confined aquifer. Cation exchanges between Na and Ca can also happen along the flow paths. 相似文献
22.
A Triassic carbonate unit has been intensively drained by zinc and lead ore mines and numerous borehole fields since the nineteenth
century. Its groundwater recharge has increased due to: pumping of water from boreholes, mining activity, and urbanization.
An approach to determine the amounts of the recharge at a variety of spatial scales is presented in the paper. Different methods
were used to identify and quantify recharge components on a regional and local scale: mathematical modelling was performed
for four aquifers included in an aquifer system, an analytical estimation based on the assumption that an average recharge
is equal to the average discharge of the hydrogeological system—for six man-made drainage centres, and the method of water
level fluctuation (WLF) was applied in one observation borehole. Results of modelling have been supplemented by observation
of environmental tracers (δ18O, δ2H, 3H), noble gases temperatures, and 4Heexc in groundwater. The regional aquifer’s current recharge according to estimations performed by means of modelling varies from
39 to 101 mm/year on average. Depending on the aquifer site the average precipitation ranges from 779 to 864 mm/year. In the
confined part of the aquifer average recharge ranges from 26 to 61 mm/year. Within outcrops average recharge varies from 96
to 370 mm/year. Current recharge estimated by the analytical method for man-made drainage centres varies from 158 up to 440 mm/year.
High values are caused by different recharge sources like precipitation, induced leakage from shallow aquifers, and water
losses from streams, water mains and sewer systems. Pumping of water, mining and municipal activities constitute additional
factors accounting for the intensified recharge. 相似文献
23.
利用高精度多梯度热培养系统,对英国威尔士地区两类典型的北方泥炭沼泽中酚类物质和溶解有机碳释放的热敏感性进行了为期1年的调查研究.研究结果表明,雨养泥炭沼泽(Bog)酚类物质释放的热敏感性Q10(总酚)月变化为0.92~1.57,而矿养泥炭沼泽(Fen)的月变化范围为0.93~1.30.酚类释放的热敏感性与土壤温度大致呈正相关关系.此外,土壤温度与溶解有机碳释放的热敏感性Q10(DOC)也呈正相关关系.总体上,雨养泥炭沼泽的热敏感性比矿养泥炭沼泽略高.除温度外,水文条件和植被等多种环境因子对酚类物质和溶解有机碳释放的热敏感性也有较大影响.研究结果还表明酚碳热敏感性比值Q10o(总酚)/Q10(DOC)相对稳定,土壤温度的变化对其影响有限. 相似文献
24.
M. Mejías J. Garcia-Orellana J. L. Plata M. Marina E. Garcia-Solsona B. Ballesteros P. Masqué J. López C. Fernández-Arrojo 《Environmental Geology》2008,54(3):521-536
A methodology for the characterization of deep carbonate aquifers has been developed and applied to El Maestrazgo Jurassic
aquifer in Castellón, Spain. Characterization of these aquifer formations, located at more than 300 m deep, consisted of a
previous phase of compilation, analysis and synthesis of the existing information about the area, followed by a coordinated
combination of different speciality studies: geology, stratigraphy, structural analysis, hydrogeology, hydrochemistry, geophysics
and remote sensing. Geological studies included geological mapping, definition of stratigraphical units and facies and structural
analysis. The aim of the hydrogeology study was to define aquifer formations, recharge area, aquifer points inventory and
groundwater flow directions for the establishment of piezometric and water quality observation nets. Special techniques were
applied, like thermal infrared aerial images and the evaluation of submarine groundwater discharge by means of natural radium
isotopes. Hydrochemical techniques, including majority elements characterization and stable isotopes (18O, 2H and 3H) determination, allowed classifying hydrochemical facies and establishing a renewal pattern for water within the system.
Geophysics was useful in determining the aquifer geometry, the features of the basement and the petrophysical characteristics
of the geological formations. Preliminary results show an important tectonic complexity and the possibilities for groundwater
uses in the area of study. 相似文献
25.
气候变化对塔里木河来自天山的地表径流影响 总被引:21,自引:10,他引:11
塔里木河水资源主要来自天山南坡两条源流,选择西段阿克苏河和中段开都河-孔雀河作为研究区.1956-2003年研究河源山区气温呈持续升温且降水波动增加的趋势,其中1995-2003年升温强劲,升温速率高出48 a期间平均的3倍以上;降水自1986年后持续增加,20世纪90年代较80年代增幅达18%,并显示出河源山区湿岛向塔里木盆地扩展.因高山缺少气象观测,出山径流过程变化可以综合反映中高山带的气候变化.塔里木河来自天山的地表径流在1986-2003年间持续增长,以冰川融水补给为主的库玛拉克河,1994年以来年径流量增加已在前期平均值基础上提升了一个台阶;开都河以降水径流补给为主,1986-2002年出现了观测记录以来的丰水期,并使1986年后博斯腾湖水位快速上升,恢复到1958年记录的最高水位以上.两河年径流变化趋势基本相似,但也显示有西、中段的气候变化局部差异,出现丰枯水期的不一致;然而,在近16 a升温过程中,年径流增长幅度和快慢相近. 相似文献
26.
27.
本文以赤道东太平洋海温作为主导因子,分析其与东亚温带气旋的关系。得出:高海温多气旋,低海温少气旋的对应关系较为明显。并进一步对不符合这种主要关系的年份从环流型。下垫面海温等作了分类鉴别分析。 相似文献
28.
29.
本文提出一个以带有定时器的低功耗微处理机为主体的温度记录器。其定时器用于开动微处理机,可由一个开关定为0.5、1、3或30分钟。仪器通过处理一个电容器向热敏电阻放电的时间来测量温度。仪器在工作中能显示温度值,并把温度值保存在微处理机的RAM之中。总共资料容量为2816次测值,量程为0~35℃,精度±0.1℃,分辨±0.02℃。 温度记录器具有液晶显示器,可直接读出温度值,配有标准计算机接口RS-232,能把保存的资料方便地倒给个人计算机。 这项工作是伍兹霍尔海洋研究所A.Bradley博士指导的。他提出的原理对研制可靠而廉价的温度记录器是一条新的途径。 相似文献
30.
Abstract. The oxygen consumption of Eudendrium glomeratum was measured monthly, throughout the period of active presence of the species in the field, to obtain indications on its physiological condition in the different phases of the cycle. Sets of one hundred polyps were assayed in the laboratory under normothermic (according to field temperature: 14–19°C) and hyperthermic conditions (22–25°C). The different response to identical temperatures at the extremes of the cycle, together with a differential ability to face stressful conditions in the same periods, suggests that other factors, besides temperature, regulate the seasonal cycle of Eudendrium glomeratum. 相似文献