全文获取类型
收费全文 | 10956篇 |
免费 | 1887篇 |
国内免费 | 2442篇 |
专业分类
测绘学 | 665篇 |
大气科学 | 2381篇 |
地球物理 | 2808篇 |
地质学 | 5153篇 |
海洋学 | 1322篇 |
天文学 | 688篇 |
综合类 | 1085篇 |
自然地理 | 1183篇 |
出版年
2024年 | 45篇 |
2023年 | 181篇 |
2022年 | 418篇 |
2021年 | 487篇 |
2020年 | 406篇 |
2019年 | 481篇 |
2018年 | 494篇 |
2017年 | 486篇 |
2016年 | 607篇 |
2015年 | 479篇 |
2014年 | 617篇 |
2013年 | 575篇 |
2012年 | 548篇 |
2011年 | 556篇 |
2010年 | 657篇 |
2009年 | 568篇 |
2008年 | 543篇 |
2007年 | 512篇 |
2006年 | 400篇 |
2005年 | 395篇 |
2004年 | 304篇 |
2003年 | 307篇 |
2002年 | 290篇 |
2001年 | 340篇 |
2000年 | 348篇 |
1999年 | 551篇 |
1998年 | 491篇 |
1997年 | 439篇 |
1996年 | 452篇 |
1995年 | 382篇 |
1994年 | 323篇 |
1993年 | 317篇 |
1992年 | 255篇 |
1991年 | 201篇 |
1990年 | 161篇 |
1989年 | 130篇 |
1988年 | 131篇 |
1987年 | 67篇 |
1986年 | 63篇 |
1985年 | 46篇 |
1984年 | 34篇 |
1983年 | 25篇 |
1982年 | 37篇 |
1981年 | 32篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 7篇 |
1976年 | 9篇 |
1973年 | 5篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
954.
Wenjiao Shi Yunfeng Hu Xiaoli Shi Zong Wang Huimin Yan Ziwei Xu Bo Ren Wenhui Kuang Xinliang Xu Weiming Cheng Yan Chen Dongbo Wu 《地理学报(英文版)》2016,26(12):1675-1688
Strategic transformation of regionalization for agricultural comprehensive development (ACD) was presented by the Ministry of Finance of the People’s Republic of China (MOF) in 2014. The regionalization is the premise and basis of the sustainable development and improved competitiveness for agriculture. Based on the environmental resources related to agriculture, such as cropland, climate, water resources, terrain, geomorphology, patterns of the ACD projects, distribution of ecological planning, etc., we devised 13 indices using the geographic comprehensive regionalization method. The indices took into account a combination of dynamic and static, qualitative and quantitative, as well as agricultural and ecological factors. The strategic transformation of regionalization for the ACD in Ningxia Hui Autonomous Region of China was performed; seven types were included: prioritized regions, prioritized and restricted regions, protected regions, protected and restricted regions, restricted and prioritized regions, restricted and protected regions, and restricted regions. A further 24 subtypes were used based on locations and ecological zones. The regionalization results showed that prioritized regions were mainly in northern Ningxia, the most suitable area for agriculture. The protected and restricted regions were in central and southern Ningxia. In the central part, drought was the limiting factor for agriculture, and water conservation projects there should be supported. The ecological environment is fragile in southern Ningxia, so there is a need for ecologically sound agriculture to be developed in this region. Such regionalization could achieve two goals, namely agricultural conservation and eco-environmental protection. It was performed following the requirement for scientific regionalization to include three types of regions (prioritized regions, protected regions, and restricted regions), and was applied at the township scale in a provincial or autonomous region for the first time. The results provide both guidance for the strategic transformation of the ACD in Ningxia, and a reference for similar work in other provinces. 相似文献
955.
DNA barcode assessment of Ceramiales (Rhodophyta) in the intertidal zone of the northwestern Yellow Sea 总被引:1,自引:0,他引:1
A total of 142 specimens of Ceramiales(Rhodophyta) were collected each month from October 2011 to November 2012 in the intertidal zone of the northwestern Yellow Sea. These specimens covered 21 species,14 genera,and four families. Cluster analyses show that the specimens had a high diversity for the three DNA markers,namely,partial large subunit r RNA gene(LSU),universal plastid amplicon(UPA),and partial mitochondrial cytochrome c oxidase subunit I gene(COI). No intraspecific divergence was found in our collection for these markers,except for a 1–3 bp divergence in the COI of Ceramium kondoi,Symphyocladia latiuscula,and Neosiphonia japonica. Because short DNA markers were used,the phylogenetic relationships of higher taxonomic levels were hard to evaluate with poor branch support. More than half species of our collection failed to find their matched sequences owing to shortage information of DNA barcodes for macroalgae in Gen Bank or BOLD(Barcode of Life Data) Systems. Three specimens were presumed as H eterosiphonia crispella by cluster analyses on DNA barcodes assisted by morphological identification,which was the first record in the investigated area,implying that it might be a cryptic or invasive species in the coastal area of northwestern Yellow Sea. In the neighbor-joining trees of all three DNA markers,H eterosiphonia japonica converged with D asya spp. and was distant from the other Heterosiphonia spp.,implying that H. japonica had affinities to the genus Dasya. The LSU and UPA markers amplified and sequenced easier than the COI marker across the Ceramiales species,but the COI had a higher ability to discriminate between species. 相似文献
956.
贡湖水质富营养化综合评价及初步预测 总被引:13,自引:0,他引:13
对1996年7月贡湖三次调查资料进行的水质和富营养化现状综合评价显示:贡湖水质以Ⅲ-Ⅳ类为主,局部已出发V类,凯氏氮,非离子氨和总磷为主要污染物;营养型以中营养和中富营养类型分布面积较广。 相似文献
957.
吴盛殷 《中国天文和天体物理学报》1988,(3)
本文从简要总结迄今所发现的视超光速源开始。介绍近年来探测到的视超光速源之一——类星体3C 454.3的VLBI多频段,多历元观测及其主要结果。采用列表对比方式表明此源相对其他视超光速源的一般特征呈现的特殊性。最后对此特殊的视超光速源的可能解释作初步讨论。 本文可以看作是对3C453.3观测已有报导[12]和[13]的进一步补充。 相似文献
958.
本文致力研究创意产业集群与城市政策和效益之间的互动。研究的创意产业行业包括软件、多媒体、电子游戏、时装设计、出版、研究与开发。经验调查研究以多个城市的情况作为基础,这些城市包括美国的波士顿、旧金山、圣迭亚戈、西雅图、奥斯丁、华盛顿特区、爱尔兰的都柏林、东京和印度的班加罗尔。本文关键的研究问题是:什么类型的城市是富有创意的?什么区位因素是必不可少的?创意城市共同采取的政策措施有哪些?文章首先总结了影响地方特定创意产业集群的因素和政策措施;接着深入剖析两个成功的创意城市——波士顿和圣迭亚戈的案例,随后讨论城市各自的某些特征是否使得它们更适合发展某一特定的创意产业。 相似文献
959.
An application of a new method in permafrost environment assessment of Muli mining area in Qinghai-Tibet Plateau,China 总被引:1,自引:2,他引:1
The permafrost environment in the Muli mining area, an opencast mining site in the Qinghai-Tibet Plateau, China, is now undergoing
significant degradation because of the ongoing mining activities. The permafrost environment in this mining site had already
been evaluated by previous study, in which analytic hierarchy process was applied. Although this method can roughly characterize
the permafrost environment of this mining site, it has limitations by being easily affected by man-made factors. In view of
this limitation, this study attempts to employ a new method, the catastrophe progression method, to estimate the current stage
of the permafrost environment in this mining area. The results show that, by catastrophe progression method, currently the
calculated indexes of the permafrost freezing–thawing disintegration, permafrost thermal stability, permafrost ecological
fragility, and the permafrost environment are 0.43 (general situation), 0.77 (general situation), 0.71 (bad situation) and
0.83 (general situation), respectively. These values imply that the permafrost environment has been damaged by anthropologic
activities to a certain degree and potentially may be further degenerated. However, at this degree, a new equilibrium stage
of permafrost environment could be achieved if the current state of environmental degradation is stabilized and treatments
are constructed against further damages. 相似文献
960.