全文获取类型
收费全文 | 179篇 |
免费 | 28篇 |
国内免费 | 47篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 20篇 |
地球物理 | 23篇 |
地质学 | 89篇 |
海洋学 | 56篇 |
天文学 | 12篇 |
综合类 | 9篇 |
自然地理 | 25篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 13篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 10篇 |
2014年 | 14篇 |
2013年 | 14篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 21篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有254条查询结果,搜索用时 15 毫秒
161.
162.
Abstract— Until recently, the SNC meteorites represented the only source of information about the chemistry and petrology of the Martian surface and mantle. The Mars Exploration Rovers have now analyzed rocks on the Martian surface, giving additional insight into the petrology and geochemistry of the planet. The Adirondack basalts, analyzed by the MER Spirit in Gusev crater, are olivine‐phyric basaltic rocks which have been suggested to represent liquids, and might therefore provide new insights into the chemistry of the Martian mantle. Experiments have been conducted on a synthetic Humphrey composition at upper mantle and crustal conditions to investigate whether this composition might represent a primary mantle‐derived melt. The Humphrey composition is multiply saturated at 12.5 kbar and 1375 °C with olivine and pigeonite; a primary anhydrous melt derived from a “chondritic” mantle would be expected to be saturated in orthopyroxene, not pigeonite. In addition, the olivine and pigeonite present at the multiple saturation are too ferroan to have been from a Martian mantle as is understood now. Therefore, it seems likely that the Humphrey composition does not represent a primary anhydrous melt from the Martian mantle, but was affected by mineral/melt fractionations at lower (crustal) pressures. 相似文献
163.
164.
福建漳江口湿地人类活动状况调查 总被引:2,自引:1,他引:2
福建漳江口红树林国家级自然保护区湿地是周边居民进行生产活动的重要场所,为当地居民提供了丰富的海产品资源。同时,当地居民在湿地上从事的各种生产活动对湿地的理化性质及生物多样性产生了重要的影响。为了了解保护区湿地上人类活动规律,运用走访调查和定时、定点调查的方法,对湿地上人类活动规律进行了调查。结果显示:保护区内湿地上的人类活动可以划分为红树林下捡拾海产品活动类型、夫妻船讨小海活动类型、公有河道捡拾海产品活动类型和滩涂养殖活动类型4种。其中第4种类型在1 a周期中又可以划分为除草、整地、施药消毒、再整地和养殖收获5个阶段。夫妻船讨小海人类活动的人数最多时为80人/d,最少时为16人/d,平均为50.4人/d;密度最大为7.5人/km2,最小为1.5人/km2,平均为4.8人/km2。公有河道捡拾海产品活动的人数最多时为62人/d,一般情况下较少,从几人到几十人不等,2005年12月中旬至2006年的4月初,该类活动基本停止,之后呈逐渐增加趋势。滩涂养殖的再整地阶段,人类活动的人数约为70人/d,密度为10人/km2;2005年10月下旬以后的蛏(Sinonovacula constricta)苗养殖阶段,人类活动的人数约为60人/d,平均密度约为10人/km2;整个11月份期间,与养殖有关的人类活动基本停止,养殖户在自家承包的滩涂上进行一些捡拾海产品的活动,但人数较少,最多时为55人/d,一般为10多人/d,密度为10~20人/km2;进入12月份后的收获季节,人类在滩涂上活动的人数及其密度急剧增加,为100多人/d到500多人/d不等,平均密度为44人/km2。在收获季节,人类活动的人数及其密度与有无商人收购蛏产品以及蛏的生长情况有关。总的来看,保护区湿地上人类活动可划分为3个阶段:第1阶段从2005年10月中旬至11月底;第2阶段始于12月初,止于2006年1月底;第3阶段为2006年2月初至4月底。第1阶段人类活动的人数平均为128人/d,平均密度为7.4人/km2;第2阶段分别为208人/d和12.0人/km2;第3阶段分别为358人/d和20.7人/km2。依据本次调查结果,建议采取如下对策:第一,适当限制夫妻船讨小海及公有河道捡拾海产品的船只数量,使其尽量保持在现有水平;第二,研究和探讨滩涂养殖过程中农药消毒的替代方法,尽量不用或少用农药;第三,保护区应特别加强滩涂养殖及收获阶段人类活动的管理,建议保护区尽可能地引导养殖户采取分片收获的方式来减少同一时段内滩涂上人类活动的人数及其密度。 相似文献
165.
166.
167.
M. J. LE BAS 《Meteoritics & planetary science》2001,36(9):1183-1188
Abstract— A report is presented for a possible revised classification of lunar igneous rocks that still uses the division of Moon rocks into mare and highland types. It subdivides the mare rocks into basalts depending on TiO2 content and glasses depending on colour, and subdivides the highland rocks principally into KREEP basalts and into coarse‐grained igneous rocks comparable to and using terrestrial igneous rock terminology. 相似文献
168.
MENGXianghua GEMing LIUYanxue KUANGHongwei LIUWeifu FrancoiseG.BOURROUILH-LEJAN RobertBOURROUILH 《《地质学报》英文版》2004,78(3):775-783
Based on a study of Neoproterozoic carbonates in the Jilin-Liaoning-Xuzhou-Huaiyang area, especially its cyclic sequence stratigraphy and Sr isotopes, two maximum sea flooding events (at 820 Ma and 835 Ma) have been identified. The resulting isochronous stratigraphic correlation proves that these Precambrian strata were connected between the Qingbaikou and the Nanhuan systems with a time range from 750 Ma to 850 Ma. The disappearance of microsparite carbonate and coming of a glacial stage offer important evidence for worldwide stratigraphic correlation and open a window for further correlation of the stratigraphic successions across the Sino-Korean and Yangtze Plates. A new correlation scheme is therefore provided based on our work. 相似文献
169.
170.
Tristan da Cunha, South Atlantic: Geochemistry and Petrogenesis of a Basanite-Phonolite Lava Series 总被引:1,自引:1,他引:1
The island of Tristan da Cunha, located at 37?S, 12?W in theSouth Atlantic, is the largest of a group of three islands,the others being Nightingale and Inaccessible. Tristan da Cunhacomprises a continuous series of alkaline lavas ranging in compositionfrom ankaramitic basanite through phonotephnte and tephnphonoliteto phonolite. Moderately porphyritic basanite is the dominantrock type ({small tilde}on the island. Major and trace element variations in the lavas describe well-definedtrends with increasing differentiation which are generally consistentwith control by fractional crystallization of phenocryst phases.None of the lavas can be considered to be primary in composition,mg-numbers range from 40 to 62, and covariation of certain minorand trace elements (e.g., Sr, Ba, P) suggests the presence ofat least two distinct fractionation trends. Sr, Nd, and Pb isotopicanalyses of a subset of the lavas confirm previously publisheddata for the island, but show a slightly greater range: 87Sr/86Sr= 0{dot}704950{dot}70517; 143Nd/144Nd = 0{dot}512590{dot}51247;206Pb/204Pb = 18{dot}4718-{dot}74. Quantitative modelling of the compositional variations suggeststhat the ankaramitic basanites are partial olivine + clinopyroxene+ titanomagnetite (?minor plagioclase) cumulates, with {smalltilde}40% crystal accumulation being required to account forthe most porphyritic varieties. The range in composition frombasanite to phonotephrite can be accounted for by up to 50%fractional crystallization of clinopyroxene, olivine, titanomagnetite,and plagioclase, with minor apatite and, in some models, amphibole.Average proportions of these phases in the fractionate are Cpx40, TiMgt 20, Plag 30, Oliv 10. As much as 20% amphibole fractionationis required in models involving the phonotephrites. The compositionsof the evolved tephriphonolites and phonolites are consistentwith extensive (up to 80%) fractional crystallization of aninitial basanitic magma with clinopyroxenc (14%), amphibole(1723%), plagioclase (620%) alkali feldspar (013%),and titanomagnetite (46%)?minor apatite and sphene beingthe dominant fractionating phases. Inferred trace element and isotopic characteristics of the sourceregions of the Tristan lavas are distinct from those givingrise to the Walvis Ridge, Gough Island, or Discovery Seamountbasalts. Normalized trace element abundances of the Tristanlavas are more similar to those of Marion Island, whereas Sr-,Nd-, dnd Pb-isotopic ratios are most similar to nearby InaccessibleIsland lavas. If Tristan da Cunha is the present-day surfaceexpression of the upwelling mantle plume that previously gaverise to the Walvis Ridge, then the source material tapped bythe lavas is distinctly heterogeneous (or has changed with time)within the limits imposed by maintaining the general characteristicsof DUPAL-type mantle. 相似文献