全文获取类型
收费全文 | 5026篇 |
免费 | 164篇 |
国内免费 | 54篇 |
专业分类
测绘学 | 171篇 |
大气科学 | 433篇 |
地球物理 | 1145篇 |
地质学 | 1835篇 |
海洋学 | 486篇 |
天文学 | 831篇 |
综合类 | 19篇 |
自然地理 | 324篇 |
出版年
2023年 | 13篇 |
2022年 | 43篇 |
2021年 | 69篇 |
2020年 | 77篇 |
2019年 | 71篇 |
2018年 | 162篇 |
2017年 | 153篇 |
2016年 | 217篇 |
2015年 | 140篇 |
2014年 | 171篇 |
2013年 | 250篇 |
2012年 | 207篇 |
2011年 | 307篇 |
2010年 | 230篇 |
2009年 | 315篇 |
2008年 | 261篇 |
2007年 | 212篇 |
2006年 | 241篇 |
2005年 | 220篇 |
2004年 | 308篇 |
2003年 | 231篇 |
2002年 | 163篇 |
2001年 | 112篇 |
2000年 | 111篇 |
1999年 | 95篇 |
1998年 | 103篇 |
1997年 | 69篇 |
1996年 | 39篇 |
1995年 | 43篇 |
1994年 | 47篇 |
1993年 | 35篇 |
1992年 | 42篇 |
1991年 | 23篇 |
1990年 | 38篇 |
1989年 | 16篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1986年 | 22篇 |
1985年 | 15篇 |
1984年 | 21篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 22篇 |
1978年 | 22篇 |
1977年 | 22篇 |
1976年 | 15篇 |
1975年 | 18篇 |
1974年 | 17篇 |
1973年 | 17篇 |
1971年 | 12篇 |
排序方式: 共有5244条查询结果,搜索用时 15 毫秒
101.
102.
103.
Spatial assessment and redesign of a groundwater quality monitoring network using entropy theory, Gaza Strip, Palestine 总被引:3,自引:0,他引:3
Using entropy theory, a methodology was developed for the evaluation and redesign of groundwater quality monitoring wells in the Gaza Strip in Palestine. Essential to the methodology is the development of a Transinformation Model (TM) which yields the amount of information transfer and the dependency between the wells as a function of distance. The TM parameters, such as the minimum transinformation and the range, were employed for evaluating the network which revealed that most of the distances between wells were less than the range. It also indicated that a high percentage of redundant information existed in the network. Therefore, the network was reduced by superimposing a square pattern over the monitored area and selecting one well per square block in a stratified pattern. The methodology was tested using the chloride data collected from 1972–2000 from 417 groundwater quality monitoring wells in the Gaza Strip. The number of the groundwater quality monitoring wells in the Gaza Strip was reduced by 53%, while there was 26% redundant information based on the minimum existing distance between wells. This methodology is meant to help monitor the groundwater quality (salinity) in the Gaza Strip. 相似文献
104.
Warren J. de Bruyn Mike Harvey Jill M. Cainey Eric S. Saltzman 《Journal of Atmospheric Chemistry》2002,41(2):189-209
Atmospheric dimethyl sulfide (DMS) and sulfur dioxide (SO2) concentrations were measured at Baring Head, New Zealandduring February and March 2000. Anti-correlated DMS and SO2 diurnalcycles, consistent with the photochemical production of SO2 from DMS, were observed in clean southerly air off the ocean. The data is used to infer a yield of SO2 from DMS oxidation. The estimated yields are highly dependent on assumptions about the DMS oxidation rate. Fitting the measured data in a photochemical box model using model-generated OH levels and the Hynes et al. (1986) DMS + OH rate constant suggests that theSO2 yield is 50–100%, similar to current estimates for the tropical Pacific.However, the observed amplitude of the DMS diurnal cycle suggests that the oxidation rate is higher than that used by the model, and therefore, that theSO2 yield is lower in the range of 20–40%. 相似文献
105.
贵州关岭生物群中植物化石的发现及其意义 总被引:4,自引:1,他引:4
关岭生物群是近年来在我国贵州关岭地区瓦窑组中发现的一个十分重要的生物群 ,其中的植物化石经研究计有 Equisetites cf.arenaceus(Jaeger) Bronn.、Ctenozamitessarrani Zeiller。依据植物化石 C.sarrani常见于晚三叠世和 E.cf.arenaceus系似木贼属中较古老的类型 ,指出含植物化石的地层时代为晚三叠世卡尼期。瓦窑组系海相沉积 ,其中的植物化石无疑为异地埋藏 ,但从化石通常保存尚好来看 ,估计搬运的距离不会很远 ,它们可能是从距海岸不远的陆地被河流带到较平静的海湾或海槽而沉积下来的。此外 ,从该组植物茎干化石具清楚的年轮分析 ,推测卡尼期时 ,贵州关岭一带为非热带雨林地区 ,一年中气候不是四季如一 ,而是有明显的季节变化 相似文献
106.
107.
108.
成矿作用研究表明 ,在地球的演化历史中 ,成矿数量有从少到多 ,聚矿能力有由弱到强的演化趋势。中生代为全球规模的成矿大爆发阶段 ,究其原因可能与地球的发展演化密切相关。地球形成的早期 ,由于地球物质尚未充分分异 ,成矿强度不大。当然 ,有部分在地球演化早期形成的矿床 ,在后来的多次构造改造过程中被改造迁移 ,甚至消失。中生代地球进入了一个强烈的地幔热柱活动时期 ,聚集于D”层及外核的成矿物质可通过地幔热柱多级演化向上迁移 ,并在幔枝构造的有利构造扩容带中成矿 ,幔枝构造则成为中生代主要的成矿控矿构造类型 相似文献
109.
José F. Noguera Lluís Rivero Xavier Font Andrés Navarro Francisco Martínez 《Environmental Geology》2002,41(8):898-905
110.
Javier Fernández-Suárez Fernando Corfu Ricardo Arenas Alberto Marcos José R. Martínez Catalán Florentino García Jacobo Abati Francisco J. Fernández 《Contributions to Mineralogy and Petrology》2002,143(2):236-253
. A isotope dilution thermal ionisation mass spectrometry U-Pb geochronological study was carried out on the high-pressure and high-temperature units (HP-HT units) overlying the oceanic suture in the Allochthonous Complexes of the NW Iberian Variscan Belt. The rocks investigated are seven granulite- to eclogite-facies paragneisses and one leucosome within mafic high-pressure granulites in the Ordenes and Cabo Ortegal Complexes of NW Spain. U-Pb dating of zircon, monazite, titanite and rutile reveal the presence of a pervasive Early Ordovician metamorphic event at ca. 500-480 Ma and a later Early Devonian event at ca. 400-380 Ma. The U-Pb ages, in conjunction with petrological and structural data, indicate that the high-pressure event recorded by these rocks is Early Ordovician in age. Monazite ages in the paragneisses suggest that peak metamorphic conditions were reached at ca. 500-485 Ma. Subsequently, the rock ensemble underwent exhumation accompanied by partial melting and zircon growth at ca. 485-470 Ma. Melting of mafic granulites was coeval with this latter episode as indicated by zircon crystallisation age in the leucosomes dated at ca. 486 Ma. Based on these data and on the general features of magmatism and metamorphic evolution, it is proposed that this process took place at a convergent plate boundary within a peri-Gondwanan oceanic domain. Monazite, titanite and rutile data in some of the samples studied show evidence of a second metamorphic episode that took place between ca. 400 and 380 Ma (with a peak at ca. 390-385 Ma). This Early Devonian event, at variance with the previous one, was not pervasive, but, rather, was localised in areas of intense Variscan tectonothermal reworking. It is claimed that this later metamorphic event was recorded by the U-Pb system in areas where monazite and titanite growth was enhanced by fluid circulation in highly strained rocks (Variscan shear zones). According to previous structural studies and Ar-Ar dating of fabrics, this Early Devonian episode took place as the HP-HT units were deformed and thrusted upon the ophiolitic units in the early stages of the Variscan collision. 相似文献