全文获取类型
收费全文 | 3779篇 |
免费 | 684篇 |
国内免费 | 213篇 |
专业分类
4676篇 |
出版年
2024年 | 26篇 |
2023年 | 126篇 |
2022年 | 123篇 |
2021年 | 142篇 |
2020年 | 231篇 |
2019年 | 238篇 |
2018年 | 224篇 |
2017年 | 245篇 |
2016年 | 264篇 |
2015年 | 234篇 |
2014年 | 242篇 |
2013年 | 335篇 |
2012年 | 194篇 |
2011年 | 210篇 |
2010年 | 172篇 |
2009年 | 174篇 |
2008年 | 197篇 |
2007年 | 193篇 |
2006年 | 130篇 |
2005年 | 151篇 |
2004年 | 119篇 |
2003年 | 102篇 |
2002年 | 70篇 |
2001年 | 82篇 |
2000年 | 72篇 |
1999年 | 52篇 |
1998年 | 48篇 |
1997年 | 28篇 |
1996年 | 33篇 |
1995年 | 35篇 |
1994年 | 27篇 |
1993年 | 27篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 2篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有4676条查询结果,搜索用时 15 毫秒
991.
Linking ecosystem characteristics to final ecosystem services for public policy 总被引:5,自引:0,他引:5
下载免费PDF全文
![点击此处可从《Ecology letters》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Christina P. Wong Bo Jiang Ann P. Kinzig Kai N. Lee Zhiyun Ouyang 《Ecology letters》2015,18(1):108-118
Governments worldwide are recognising ecosystem services as an approach to address sustainability challenges. Decision‐makers need credible and legitimate measurements of ecosystem services to evaluate decisions for trade‐offs to make wise choices. Managers lack these measurements because of a data gap linking ecosystem characteristics to final ecosystem services. The dominant method to address the data gap is benefit transfer using ecological data from one location to estimate ecosystem services at other locations with similar land cover. However, benefit transfer is only valid once the data gap is adequately resolved. Disciplinary frames separating ecology from economics and policy have resulted in confusion on concepts and methods preventing progress on the data gap. In this study, we present a 10‐step approach to unify concepts, methods and data from the disparate disciplines to offer guidance on overcoming the data gap. We suggest: (1) estimate ecosystem characteristics using biophysical models, (2) identify final ecosystem services using endpoints and (3) connect them using ecological production functions to quantify biophysical trade‐offs. The guidance is strategic for public policy because analysts need to be: (1) realistic when setting priorities, (2) attentive to timelines to acquire relevant data, given resources and (3) responsive to the needs of decision‐makers. 相似文献
992.
李文志 《现代生物医学进展》2007,7(11):1701-1703
目的:调查我院常用抗G~ 致病菌的抗生素的种类效价情况,为抗G~ 致病菌的合理用药提供依据。方法:从2978个样本中分离到953株G~ 致病菌,用全自动微生物分析仪-VITEK32进行菌种鉴定及16种抗生素的药敏实验。结果:953株G~ 致病菌经鉴定属于11大类,其中金黄色葡萄球菌、表皮葡萄球菌、溶血葡萄球菌、草绿色链球菌和肠球菌属是五类主要的G~ 致病菌,依次分别占总分离量的30.3%、17.3%、15.1%、9.8%和6.8%;在检测的16种抗生素对排在前五位的G~ 致病菌的平均效价最低的五类抗生素是:青霉素(24.22%)、红霉素(26.22%)、头孢唑林(28.06%)、与链霉素(30.52%)和庆大霉素(31.06%)。而抗G~ 致病菌整体效果最好的是:螯合新泰林(93.72%)、万古霉素(82.62%)和四环素(78.68%)。结论:研究结果表明越来越多抗生素抗临床常见G~ 致病菌的效价呈现逐年递减的趋势。 相似文献
993.
Pheromone trapping was used to monitor populations of the moth Helicoverpa armigera at five cotton‐based agro‐ecological sites – river, vegetable, orchard, forest and clean cultivation (areas under only cotton cultivation) – in the Bahawalpur district, Pakistan. Three locations at each site were chosen and three pheromone traps at each location were installed in cotton fields. Moth catches were recorded at 15–20 day intervals from 24 October 2004 to 19 December 2006. In 2004, the river sites showed the maximum trapped population of H. armigera (0.22/trap) followed by 0.165 per trap at the vegetable sites. Orchard, clean cultivation and forest sites had zero moth catches. In 2005, the river sites again showed the highest trapped population (0.57/trap), followed by clean cultivation (0.45/trap), vegetable (0.44/trap), orchard (0.40/trap) and forest (0.29/trap). The moths appeared during July to December and March to May. In 2006, sites showed non‐significant difference, with a population range of 0.47 to 0.97 moths per trap. On average, river sites peaked at 0.49 per trap, followed by vegetable (0.38), clean cultivation (0.47), orchard (0.35) and forest (0.25) sites. The peak was observed on 3 April 2006, and moths appeared during February to July and October to December. The minimum temperature in river, forest and clean cultivation sites; the maximum temperature in orchard sites; and the average temperature in river, orchard, forest and clean cultivation sites showed significant positive correlations with trapped moth populations. Relative humidity showed significant negative correlation with population at the orchard sites in 2005. All weather factors during 2004 and 2006 showed non‐significant correlations with the moth populations. No model was found to be best fit by multiple linear regression analysis; however, relative humidity, minimum temperature, maximum temperature, minimum temperature and maximum temperature contributed 8.40, 10.23, 2.43, 4.53 and 2.53% to the population fluctuation of the moth at river, vegetable, orchard, forest and clean cultivation sites, respectively. 相似文献
994.
【目的】为了明确绿盲蝽Apolygus lucorum不同地理种群对化学杀虫剂的抗性现状及发展趋势,并为制定有效的化学防治措施及抗性治理策略提供参考,【方法】本文采用玻璃瓶药膜法,连续4年监测了采自黄河流域、长江流域棉区绿盲蝽田间种群对高效氯氰菊酯和毒死蜱的抗性水平及变化动态。【结果】(1)与室内饲养的廊坊敏感品系(Susceptible strain from Langfang,SLF)相比,长江流域棉区江苏南京及安徽滁州种群对2种药剂均未产生明显抗性(<5倍),江苏盐城种群对高效氯氰菊酯(3.4~8.5倍)和毒死蜱(3.3~5.8倍)仅有低水平抗性;(2)黄河流域棉区河南安阳、山东滨州及河北沧州种群对高效氯氰菊酯(7.1~22倍)、毒死蜱(5.2~20倍)均产生了中低水平抗性。【结论】2011至2014年间,各地理种群对两种药剂的敏感性在不同年度之间变异幅度小于3倍,抗性发展比较缓慢。黄河流域、长江流域棉区绿盲蝽田间种群对上述2种药剂敏感性的差异可能与当地用药历史和用药量有关。 相似文献
995.
红外相机技术在我国野生动物监测中的应用: 问题与限制 总被引:2,自引:0,他引:2
红外相机(camera traps)作为对野生动物进行“非损伤”性采样的技术, 已成为研究动物多样性、种群生态学及行为学的常用手段之一。其发展和普及为中国野生动物多样性和物种保育研究带来了诸多机会。如今, 国内大多数自然保护区都在运用红外相机技术开展物种监测工作。本文结合20年来已发表的相关研究, 从内容、实验设计以及发展趋势方面, 总结了目前红外相机技术在应用过程中出现的共性问题; 并就相机对动物的干扰性、影像识别、研究的适用范围及安全保障四个方面, 对该项技术在实践中存在的限制进行了探讨。最后结合红外相机技术未来的发展方向, 提出了建立技术规范、数据集成和共享、影像数据版权维护、提高监测效率等问题。 相似文献
996.
浅谈微生物在海洋环境保护中的应用 总被引:2,自引:0,他引:2
在污水和废水处理等坏境净化领域采用生物技术已久,基因工程在此领域的应用正朝着构建能降解特殊化合物的微生物方向迈进;基因操作技术被用来提高某些微生物体内特异性酶类水平,而这些酶具有特异性生物降解转化作用。微生物已在海洋环境保护中被制作生物传感器等用来进行坏境检测;利用微生物的氨化、硫化、硝化等生化特性进行水质净化;利用某些微生物合成特殊物质来代替塑料等难降解物质并在这些领域中获得显著成效。 相似文献
997.
Sources of (co)variation in alternative siring routes available to male great tits (Parus major)
下载免费PDF全文
![点击此处可从《Evolution; international journal of organic evolution》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yimen G. Araya‐Ajoy Sylvia Kuhn Kimberley J. Mathot Alexia Mouchet Ariane Mutzel Marion Nicolaus Jan J. Wijmenga Bart Kempenaers Niels J. Dingemanse 《Evolution; international journal of organic evolution》2016,70(10):2308-2321
Males of socially monogamous species can increase their siring success via within‐pair and extra‐pair fertilizations. In this study, we focused on the different sources of (co)variation between these siring routes, and asked how each contributes to total siring success. We quantified the fertilization routes to siring success, as well as behaviors that have been hypothesized to affect siring success, over a five‐year period for a wild population of great tits Parus major. We considered siring success and its fertilization routes as “interactive phenotypes” arising from phenotypic contributions of both members of the social pair. We show that siring success is strongly affected by the fecundity of the social (female) partner. We also demonstrate that a strong positive correlation between extra‐pair fertilization success and paternity loss likely constrains the evolution of these two routes. Moreover, we show that more explorative and aggressive males had less extra‐pair fertilizations, whereas more explorative females laid larger clutches. This study thus demonstrates that (co)variation in siring routes is caused by multiple factors not necessarily related to characteristics of males. We thereby highlight the importance of acknowledging the multilevel structure of male fertilization routes when studying the evolution of male mating strategies. 相似文献
998.
目的:探讨和总结老年人24小时食管pH监测的有效的护理方法。方法:我病区自2010年6月到2010年12月接受24小时食管pH监测的患者共50例,分为老年组(≥60岁)和非老年组,采用使用电池的动态pH监测仪进行监测。结果:本研究的50例老年患者中,46例置管一次成功,4例因咽部敏感给予2%的利多卡因10ml咽下后第二次均置管成功。本组检查后无一例造成咽部及胃部的损伤,无误吸等并发症发生。结论:24小时食管pH监测是一种安全、简便、无创伤、客观的检查技术,通过动态pH监测,可检测有无胃食管反流,并算出食管真正接触到反流胃酸的时间。正确的操作方法及细致到位的护理可减少老年患者检查时的痛苦,并有效预防并发症的发生。 相似文献
999.
碳贸易的核心问题是要有足够的碳封存量在抵消CO2的排放之后还能有碳额度进入市场买卖。该文结合固碳概念,从固碳技术、减量成本、对生态系统碳汇功能的影响等多方面对目前存在的和有潜力的各种减排与固碳途径进行了比较分析,认为陆地植被对CO2的吸收是最安全有效的固碳过程,它们能够在一定的浓度范围内吸收CO2,从而节省分离、提纯等技术的费用。进而该文分别对森林、草地、农田等3种陆地植被的固碳功能与不同固碳策略对固碳效果的影响两个方面进行详细具体的比较分析,得出森林生态系统具有强大的碳吸收能力,草地与农田土壤有机碳库在固碳方面的作用也十分显著。最后结合我国实际,提出4项适用于碳贸易的生物固碳方式,即保护天然林,推广种植速生丰产人工林;保育天然草地、建设人工草地;建立规模化沼气产业链;注重利用边际土地种植生物质能源,促进生物质能源的开发。 相似文献
1000.