全文获取类型
收费全文 | 200篇 |
免费 | 17篇 |
国内免费 | 92篇 |
专业分类
测绘学 | 7篇 |
地球物理 | 18篇 |
地质学 | 90篇 |
海洋学 | 141篇 |
综合类 | 27篇 |
自然地理 | 26篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 16篇 |
2019年 | 10篇 |
2018年 | 21篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 8篇 |
2014年 | 13篇 |
2013年 | 30篇 |
2012年 | 8篇 |
2011年 | 14篇 |
2010年 | 15篇 |
2009年 | 15篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 3篇 |
2005年 | 10篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1973年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有309条查询结果,搜索用时 15 毫秒
131.
中国近海裸甲藻类分类研究 总被引:1,自引:0,他引:1
裸甲藻的分类鉴定工作是其生理生态学研究和赤潮研究的基础,为进一步完善我国裸甲藻分类体系,并为裸甲藻鉴定提供参考依据,收集了国家海洋局第一海洋研究所近年来在中国近海海域进行浮游植物调查所采集的水样与网样标本,针对裸甲藻目进行鉴定,初步鉴定出裸甲藻25种,其中在我国海域首次记录的有6种。以《中国海洋生物名录》收录的分类体系为基础,参照World Register of Marine Species的最新分类系统,将鉴定的25种裸甲藻分为5个科15个属。 相似文献
132.
综合现有资料编制了我国海域常见的19种有毒水母种类的分类检索表.我国常见有毒水母分属于3纲8目14科17属,包括水螅水母类3种、管水母类2种、立方水母类2种、钵水母类12种,其中钵水母纲旗口水母目和根口水母目种类较多(各5种),其它目每目含1~2科且每科仅1属1种.对我国现有的水母分类体系中部分与国际通用体系不统一之处进行了厘正,如:火水母拉丁文种名应由Tamoya alata Uchida,1929厘正为Tamoya gargantua Haeckel,1880,建议将灯罩水母[Linuche draco (Haeckel,1880)]命名厘正为爪罩水母[Linuche unguiculata (Schwartz,1788)]等. 相似文献
133.
134.
The species-rich genus Mustelus (smoothhounds) of the shark family Triakidae is one of the most bio-economically important groups of elasmobranchs in the world’s oceans. Despite the commercial value of Mustelus, the systematics of the group remains largely unresolved and there is no global review or synthesis of knowledge about the conservation status and conservation genetics of smoothhounds across all oceanic regions. Here, we analysed published studies as well as grey literature to gain insight into the biogeographic, ecological and behavioural factors that shape genetic diversity in smoothhounds, and we identify critical knowledge gaps. From a series of molecular phylogenetic studies it can be inferred that the genus Mustelus is paraphyletic and that the aplacental species evolved secondarily from the placental species of the genus. The increasing availability of genetic data aids in disentangling systematic issues, such that more meaningful morphological characters can be chosen for use in practical field-identification keys for co-occurring smoothhounds. An integrative taxonomic approach to the genus Mustelus may offer the best chance of recording and protecting the biodiversity of these sharks. Furthermore, it is evident that different smoothhound species exhibit unique gene-flow patterns, suggesting varying rates within species and hence that species-level conservation approaches would be most appropriate. Molecular studies have advanced our understanding of smoothhound biology (including reproductive traits), ecology and evolution. While many knowledge gaps remain, a crucial lesson from this review is that, when doing assessments on a molecular level, it is important to place genetic results in a broader context, by assimilating biological and ecological data, if definitive conclusions are to be drawn. 相似文献
135.
Philip J. Gersmehl 《The Professional geographer》1985,37(3):329-334
In 1977, I published a set of coarse-resolution dot maps that showed the general distributions of soil orders in the 48 states. Through a sequence of copies made by various people, one of those maps eventually appeared in a planning document as a shaded-area map with the title “Principal Peatlands of the United States.” Along the way a saline desert muck of conjectural extent and location was “transformed” into a documented energy resource for the nation. The history of this map offers a clear lesson for mapmakers: we have a three-fold duty, to the data, to the map reader, and to any third party who might be affected by a foreseeable misinterpretation of our maps. 相似文献
136.
Eugene F. Stoermer 《Journal of Paleolimnology》2001,25(3):393-398
The present chaotic state of diatom taxonomy presents both significant difficulties and large opportunities for paleolimnologists. Lack of complete and generally available taxonomic treatises and rapid and substantial changes in nomenclature make it necessary for persons using diatom populations to infer environmental conditions to become more deeply and directly involved in diatom systematics, in the broad sense, than is generally realized. Paleolimnologists develop collections that are extremely valuable in addressing classic questions in evolution and biogeography, and should be encouraged to use these resources to advance diatom systematics, either themselves or in collaboration. 相似文献
137.
P. H. A. Sneath 《Mathematical Geology》1977,9(2):123-143
A method is described for testing the distinctness of two clusters in Euclidean space. One first calculates the projections, q,of the N1
and N2
members of the clusters onto the line joining the cluster centroids. From the distributions of qan index of disjunction, W,is calculated, which corresponds to an index of overlap, VG.The quantity W√(N1+N2)is distributed as noncentral tsubject to assumptions on the multivariate normal distribution of the clusters. This allows a test of whether the observed
disjunction is significantly greater than a chosen figure, which is equivalent to testing whether the overlap of the clusters
is significantly less than a corresponding value of VG.Two clusters that appear distinct may be produced simply by the partitioning of a homogeneous swarm into two contiguous regions.
Provided that the clusters form a dichotomy in a dendrogram, and that the clustering method yields geometrically convex clusters,
a conservative test of this situation can be derived by determining the excess of Wover the value expected for a rectangular distribution. 相似文献
138.
Daniel J. Dzurek 《GeoJournal》2005,64(4):263-274
Conflicts over territory have resulted in innumerable wars and other violent incidents, but the reasons that some territory
is more highly valued or volatile than other areas may not be obvious. This paper demonstrates a taxonomy for analyzing international
territorial disputes that seeks to capture their tangible and symbolic dimensions and to weigh them as the international community
might. Twenty-six territorial disputes, including offshore areas and separatist issues, were examined and scored according
to 15 criteria for objective prominence and 7 criteria related to how a country might view the dispute in terms of its national
interest. The taxonomy used Saaty’s Analytic Hierarchy Process to identify tangible and intangible properties, measure their
interrelations, and produce intermediate and overall ranks. Each dispute was evaluated for prominence by examining intensifying
(symbolic) factors, measures of magnitude, and characteristics that retard resolution. The magnitude of a dispute was judged
to contribute the most to overall prominence, having twice the weight of the other two factors. The top five disputes in terms
of prominence were the Kurdish issue, Kashmir, Tibet, Nagorno-Karabakh, and Xinjiang. The second hierarchy evaluated the disputes
from the perspective of an international actor, in this case the United States. When judged by U.S. national interest, the
most important factors were the deployment of U.S. forces in the claimant countries and if one of the claimants were a U.S.
ally. Finally, the results from the two hierarchies were compared. 相似文献
139.
Two new species of Eretmophyllum Thomas are described from the lower (Toarcian) and upper (Aalenian) Prisayan Formation of the Irkutsk Basin, Eastern Siberia, Russia based on distinct morphological and cuticular features of the leaves that distinguish them from other species of the genus. Eretmophyllum polypapillosum sp. nov. is characterized by the presence of 2–3 papillae on the lower and upper epidermis of ordinary cells. Taphonomically, the leaf burials of E. polypapillosum sp. nov. indicate that it preferred mesophilic forests developed on river terraces and/or low watersheds. Eretmophyllum yershowskiensis sp. nov. is represented exclusively by leaf cuticles extracted by coal maceration, and it probably inhabited the low banks of peat bogs. The presence of the genus Eretmophyllum in the Early Jurassic of France and Eastern Siberia shows that it was already widespread in the territory of Eurasia, distributed from Western Europe to Eastern Siberia. This indicates the possible existence of Eretmophyllum species elsewhere in the Early Jurassic such as Central Asia and Northwest China. 相似文献
140.
Jumaat H Adam Nurulhuda Edy Muslim Abdul Halim Hashim Abd Rahim Othman Hafiza Abd Hamid Gire Kibe Gopir Lydia M Pilik Ramlan Omar Muhammad Barzani Qasim Jumat Salimon Sahibin Abd Rahim Marlia Mohd Hanafiah 《湿地科学》2005,3(3):183-189
1INTRODUCTION NepentheswhichareknownlocallyinPeninsular Malaysiaasperiukkerabelongtoamonogenericfami lyNepenthaceae.Atpresent,atotalofninespecies(excludingnaturalhybrids)arerecordedfromPenin sularMalaysia.Ofthese,fourspeciesareendemic,whilsttheotherfivespeciesarefoundoutsidethepen insula.Thespeciescanarbitrarilybeclassifiedinto thelowlandspeciesandthehighlandspecies(Clarke,2002;Shivas,1984;Kurata,1976).Threespeciesarefoundinthehighlandhabitatscom monlyatanelevationofabove1000mforaboves… 相似文献