全文获取类型
收费全文 | 981篇 |
免费 | 178篇 |
国内免费 | 196篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 7篇 |
地球物理 | 279篇 |
地质学 | 279篇 |
海洋学 | 588篇 |
综合类 | 90篇 |
自然地理 | 104篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 20篇 |
2021年 | 45篇 |
2020年 | 38篇 |
2019年 | 27篇 |
2018年 | 38篇 |
2017年 | 45篇 |
2016年 | 36篇 |
2015年 | 42篇 |
2014年 | 65篇 |
2013年 | 103篇 |
2012年 | 56篇 |
2011年 | 75篇 |
2010年 | 50篇 |
2009年 | 68篇 |
2008年 | 50篇 |
2007年 | 67篇 |
2006年 | 81篇 |
2005年 | 59篇 |
2004年 | 43篇 |
2003年 | 32篇 |
2002年 | 39篇 |
2001年 | 30篇 |
2000年 | 30篇 |
1999年 | 24篇 |
1998年 | 28篇 |
1997年 | 26篇 |
1996年 | 21篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 18篇 |
1992年 | 17篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1355条查询结果,搜索用时 0 毫秒
101.
为了解九孔鲍养殖环境中细菌生理菌群的生态作用,对分离自养殖水体的33株菌株的产酶能力和种类进行了研究。结果表明,具有分泌胞外蛋白酶、脂肪酶和纤维素酶能力的菌株分别为39.4%、57.6%和30.3%;在这33株菌中,产至少一种胞外酶的菌株比例高达63.6%。API鉴定结果表明,在有能力分泌胞外蛋白酶、脂肪酶和纤维素酶的菌株中,弧菌菌群所占的比例分别为46%、42%和40%,而其中河流弧菌又占各弧菌菌群比例的83.3%、62.5%和100%。充分阐明弧菌,尤其是河流弧菌为优势菌,在鲍鱼养殖微生物态中起的重要作用。 相似文献
102.
Laura M. Kracker 《The Professional geographer》1999,51(3):440-450
Rather than seeing the oceans as an expansive void, researchers using acoustic technologies can detect the heterogeneity of biological resources and view the marine environment as a three-dimensional landscape. Underwater remote sensing, using acoustics, provides high resolution maps of the spatial distribution of organisms in aquatic ecosystems. Analyzing the spatial pattern of species distribution within the water column and the impact of that organization on ecological processes bridges the fields of fisheries and spatial analysis. Tools and concepts familiar to geographers, such as remote sensing, GIS, and landscape ecology, contribute to the investigation of large lake and marine ecosystems. 相似文献
103.
《The Professional geographer》1999,51(3):469-479
Rosa Ainley (ed.) New Frontiers of Space, Bodies and Gender David Bell and Gill Valentine (eds.) Consuming Geographies: We Are What We Eat Ruth Fincher and Jane M. Jacobs (eds.) Cities of Difference Richard Grant and Jan Nihman (eds.) The Global Crisis in Foreign Aid Martin Kellman and Rosanne Tackaberry Tropical Environments: The Functioning and Management of Tropical Ecosystems Glenn R. McGregor and Simon Nieuwolt Tropical Climatology Martin Oppermann (ed.) Sex Tourism and Prostitution: Aspects of Leisure, Recreation, and Work Keith Smith and Roy Ward Floods: Physical Processes and Human Impacts 相似文献
104.
The specific methods used for recovery of the aquatic ecological system in the shallow lake are proposed. This research has been done from three aspects:1) the design of the species used for the ecological recovery; 2) the design of optimization and allocation of the aquatic communities; and 3) the design of regional arrangement of the aquatic communities. On the basis of research, the pioneer plant and the species used to establish the communities are proposed. The aquatic plant allocation focuses on the emergent aquatic plant and submergent aquatic plant. Meanwhile, the regional arrangement has been done in the aquatic plant recovery area in the Caohai Lake and the east west bank of the outer lake. 相似文献
105.
A survey was made of the number of the heterotrophic bacteria in surface seawater of Great Wall Bay and its adjacent waters, Antarctica during the period of austral summers from Dec.1993 to Feb. 1994. The result shows that the number of the heterotrophic bacteria in the surface waterof the surveyed area is about 798 CFU. cm-3, ranging from 53 to 4 250 CFU. cm-3. Comparison of thenumbers for three months shows a declining tendency month by month. Comparing with the previous results, this one shows that the heterotrophic bacteria number changes somewhat, but slightly. It is lower than that in nearshore waters but higher than that in the open area. This shows that there is a positive correlative relationship between CFU and NH4- N, which means that heterotrophic bacteria should be an important agent in NH4-N reproduction in the environment surveyed. There is an significant negative correlation both between CFU and NOZ-N, and between CFU and PO4-P. This means that the NOZ-N, PO.-P, which were decomposed and transformed by bacteria, were used rapidly by phytoplankton. 相似文献
106.
硅酸盐细菌GY92对伊利石的释钾作用 总被引:26,自引:2,他引:24
1992年在贵阳郊区玉米地中分离出一株硅酸盐细菌GY92,为探求GY92对伊利石的释钾作用,对采用的有关材料和方法、相关实验所获的GY92个体形态及培养特征、部分生理生化特征及其对伊利石的释钾作用等结果作了较详细的介绍,同时就GY92对伊利石的释钾机理等问题进行了简单讨论。 相似文献
107.
黔中地区是岩溶作用发育的喀斯特区域.1993年秋和1994年春末采自该地区不同类型水样的水化学分析表明:碳酸盐岩裂隙泉水呈中偏碱性,为[C]Ca-Ⅱ型;秋季离子总量、HCO3-及Ca2+浓度大于春季.裂隙泉水流经地表一定距离后,HCO3-降低,pH及SO42-、Cl-、K+、Na+明显增高.黄果树的天星桥、水帘洞及落水潭三个部位河水的SO42-、Na+以及Fe3+、NO3-等浓度的季节性变化也更加明显.春季因瀑布暴气,CO2的逸出,钙华生成更强烈一些.红枫湖作为喀斯特区域地表水的汇集地,HCO3-与SO42-的当量比值仅2.1~2.4;Ca2+与Mg2+比值上升为2.4~4.2,Cl-浓度较碳酸盐岩裂隙泉水增高1倍;Na+浓度增高一个数量级.说明流域内地表土层溶蚀及人为污染影响的增强.土层孔隙水属强矿化水,而湖水呈现过渡特征.碳酸盐沉淀作用、硫酸盐矿化作用及固氮氨化作用,导致水质组成的显着差异. 相似文献
108.
发光细菌在渔业水域污染物急性毒性快速检测中的应用 总被引:1,自引:0,他引:1
以明亮发光杆菌为指示生物,对渔业水域中污染物的急性毒性进行了检测,同时研究了PH值、温度对试验结果的影响。研究表明,发光细菌毒性试验是一种快速、简便的毒性测试方法,在温度20~30℃,pH6.0~9.0条件下所进行的测试,其结果与鱼类毒性试验可以互相替代。 相似文献
109.
WEI Peng AN Shazhou KE Mei LI Chao HOU Yurong LAN Jiyong KANG Shuai JIN Junpeng 《资源与生态学报(英文版)》2021,12(6):840-848
Enclosure is commonly used in the restoration of degraded grasslands. However, the effects of enclosure on grassland plant and soil restoration remain controversial, particularly in deserts. To assess the effects of enclosure on desert plants and soil properties, using high throughput sequencing, the differences between plants and soil were systematically analyzed before and after enclosure construction. The soil organic carbon, total nitrogen and total phosphorus contents of the three desert flora increased and decreased, but the difference was not significant; enclosure increased plant height, coverage, aboveground biomass, and species richness by 58.99%, 59.35%, 33.29%, and 51.21%, respectively, in a Seriphidium transiliense formation; by 15.49%, 33.52%, 20.85%, and 5.13%, respectively, in a Haloxylon persicum formation; and by 83.80%, 31.51%, 76.66% and 33.33%, respectively, in an Anabasis salsa formation. For soil bacteria, enclosure significantly increased the average number of operational taxonomic units and Shannon-Wiener index by 12.74% and 2.92%, respectively, under S. transiliense formation and by 17.08% and 3.17%, respectively, under H. persicum formation. However, enclosure had no significant effect on the average number of operational taxonomic units or Shannon-Wiener index under A. salsa formation. Enclosure significantly increased desert plants, soil bacterial diversity, and desert plant community productivity; however, the increase in soil nutrient content was not significant. These results demonstrate that enclosure is effective for restoring desert ecosystems but may have little effect on the soil nutrient content. 相似文献
110.
墨西哥湾GC238区冷泉碳酸盐岩的微结构与石化微生物特征 总被引:3,自引:0,他引:3
采于墨西哥湾GC238海底天然气渗漏区浅表层的冷泉碳酸盐岩呈结核状产出,由方解石微晶和胶结物及少量的黄铁矿构成。胶结物由直径为0.1~0.5m的方解石化的球体、卵形体、棒状体组成,充填于方解石晶体之间。冷泉碳酸盐岩结核下表面发育有由方解石化的球体、卵形体、棒状体组成的薄层,其中的一些球状集合体(约5m)断面显示发育有核和外壳的层圈结构。黄铁矿呈草莓状,也具有相似的层圈结构。这种层状结构与活体古细菌被硫酸盐还原细菌包裹的层圈结构相似。样品中所保存的球体、卵形体、棒状体及其所组成的层圈结构可能是石化的甲烷氧化古细菌和硫酸盐还原细菌。 相似文献