全文获取类型
收费全文 | 1792篇 |
免费 | 90篇 |
国内免费 | 111篇 |
专业分类
林业 | 328篇 |
农学 | 84篇 |
基础科学 | 53篇 |
547篇 | |
综合类 | 499篇 |
农作物 | 38篇 |
水产渔业 | 133篇 |
畜牧兽医 | 192篇 |
园艺 | 88篇 |
植物保护 | 31篇 |
出版年
2024年 | 19篇 |
2023年 | 32篇 |
2022年 | 53篇 |
2021年 | 51篇 |
2020年 | 48篇 |
2019年 | 76篇 |
2018年 | 42篇 |
2017年 | 73篇 |
2016年 | 69篇 |
2015年 | 67篇 |
2014年 | 88篇 |
2013年 | 102篇 |
2012年 | 122篇 |
2011年 | 162篇 |
2010年 | 164篇 |
2009年 | 170篇 |
2008年 | 111篇 |
2007年 | 113篇 |
2006年 | 90篇 |
2005年 | 82篇 |
2004年 | 77篇 |
2003年 | 52篇 |
2002年 | 42篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
排序方式: 共有1993条查询结果,搜索用时 328 毫秒
81.
《Journal Of Aquatic Food Product Technology》2013,22(4):23-34
Abstract Lightly salted lumpfish roe (3.5–4.8% fw/w] salt in the water-phase, pH 5.4, vacuum-packed) was stored at 5°C. After 2 1/2 or 3 months of storage, different degrees of spoilage, caused by bacterial activity, occurred in eleven roe batches. Off-odors ranged from no or very weak odors to strong sulphury, sour odors. The microflora consisted of lactic acid bacteria, Enterobacteriaceae and Vibrio spp. Concentration of lactic acid, acetic acid, trimethylamine and total volatile bases were unrelated to spoilage odors. Volatile sulfur compounds (H2S, probably CS2, CH3SH and CH3CH2SH or CH3SCH3), produced during storage, appeared to be contributors to spoilage odors. 相似文献
82.
83.
新世纪保护区面临的挑战及其有效对策 总被引:1,自引:0,他引:1
道路、水库、建筑物、不断扩大的农田和土地退化正在使自然景观的完整性受到严重破坏。所保存的未经干扰或少受干扰的天然生态系统的面积日益缩小,犹如海洋中的孤岛。生物多样性受到严重的威胁。在自然保护区中,物种迁移和基因流动的可能性也在不断地降低。生物区域规划被认为是一种较好的选择,它力求把保护区和栽培地区视为一个有机整体,遵循保护和发展密切结合的方针,制定行动计划并予以实施。本文根据保护区的管理情况、工作条件和科研状况等,对保护区或区域的类型进行了划分,针对现实,提出了如何实施生物区域规划。 相似文献
84.
Simulating the cumulative effects of multiple forest management strategies on landscape measures of forest sustainability 总被引:1,自引:2,他引:1
While the cumulative effects of the actions of multiple owners have long been recognized as critically relevant to efforts
to maintain sustainable forests at the landscape scale, few studies have addressed these effects. We used the HARVEST timber
harvest simulator to predict the cumulative effects of four owner groups (two paper companies, a state forest and non-industrial
private owners) with different management objectives on landscape pattern in an upper Michigan landscape managed primarily
for timber production. We quantified trends in landscape pattern metrics that were linked to Montreal Process indicators of
forest sustainability, and used a simple wildlife habitat model to project habitat trends. Our results showed that most trends
were considered favorable for forest sustainability, but that some were not. The proportion of all age classes and some forest
types moved closer to presettlement conditions. The trend for the size of uneven-aged patches was essentially flat while the
average size of patches of the oldest and youngest age classes increased and the size of patches of the remaining age classes
decreased. Forest fragmentation generally declined, but edge density of age classes increased. Late seral forest habitat increased
while early successional habitat declined. The owners use different management systems that cumulatively produce a diversity
of habitats. Our approach provides a tool to evaluate such cumulative effects on other landscapes owned by multiple owners.
The approach holds promise for helping landowner groups develop and evaluate cooperative strategies to improve landscape patterns
for forest sustainability. 相似文献
85.
《Journal of Sustainable Forestry》2013,32(1-2):359-384
Summary This paper presents a new approach to the conceptualization and assessment of well-being in forest-dependent communities. Studies of well-being in agrarian communities, boomtowns (communities undergoing rapid growth), and forest-dependent communities are examined to highlight common themes in natural resource-dependent community studies. Social indicators are discussed and a summary of weaknesses presented. The county, a commonly used unit of analysis, is rejected in favor of a more socially relevant unit. This new approach to well-being in forest communities begins with definitions of the terms community and forest dependence. The work of Amartya Sen, whose conceptualization of well-being focuses on the real opportunities people have and their achievements in light of their opportunities, forms the foundation of the new approach proposed here. Sen's conceptualization is broadened by focusing on the community and acknowledging the importance of a sense of place. Methodologically, this new approach adds to the evaluation of social indicators an assessment of community capacity that consists of three components: physical, human, and social capital. It also involves evaluating how residents draw on and develop these aspects of their community to meet local needs and create opportunities. This results in a well-being assessment that includes static as well as dynamic measures of how communities respond to and create opportunities to improve local well-being. 相似文献
86.
李天星 《(《农业科学与技术》)编辑部》2009,(6)
在达尔文(1859)看来,新物种只有通过竞争或者自然选择的方式淘汰原有物种才能进入由其他物种占据的生境并成功定居下来。然而,新物种进入生境并成功定居还有另外一个途径,那就是由于超级居群能在全球尺度上改变整个地球环境,从而能在原有环境中创造出一些全新的微环境来,正是这些全新的微环境使新物种避开了和原有定居者的剧烈竞争,很容易地进入了一直由其他物种占据的生境中并成功地定居下来。换句话说,超级居群导致了全球环境的分化,导致了全球尺度上的生境多样性。同时,超级居群通过环境的异质化为新物种准备好了很多全新的微环境,新物种在全新的微环境中的成功定居实现了新物种和原有定居者的长期共存。而这种长期共存导致了整个生物圈的生物多样性的增加。超级居群是地球上很多新环境的创造者,是生境多样性和生物多样性之间的桥梁,据此就能很容易地解释新物种为什么不时能和原有定居者共存甚至依赖于原有定居者,从而导致二者间剧烈竞争缺失的现象。 相似文献
88.
为建立芝麻抗旱性快速鉴定体系及筛选芝麻抗旱品种,采用盆栽反复干旱法,设置正常水分(CK)和干旱胁迫(DS)两种处理,对31份芝麻材料进行生理生化指标测定和综合评价,同时利用qRT-PCR检测SOD合成相关基因的表达量。结果表明:芝麻苗期O2、可溶性糖(SS)、脯氨酸(Pro)含量和超氧化物歧化酶(SOD)、过氧化物酶(POD)活性与CK相比均显著上升,各指标综合抗旱系数和抗旱指数的变异系数最高的分别是SOD(98.64%)和O2(154.01%);抗旱指数与O2含量、SOD活性呈极显著正相关关系,这两个指标可作为芝麻苗期抗旱性鉴定的重要指标。聚类分析将31份芝麻材料划分为5类抗旱类型,分别为高抗型、中抗型、低抗型、低感型和高感型。利用综合评价方法,筛选出高抗材料2份(‘汾芝10号’和‘豫-11-1’),中抗旱材料4份,低抗旱材料9份,敏感材料10份,高感材料5份;筛选出O2含量和SOD活性可作为芝麻种质资源苗期抗旱特性快速鉴定的指标。 相似文献
89.
文章介绍了可持续发展评价指标体系的概念、功能,可持续发展评价指标体系构建常用的系统法、目标法、归类法,指标设置应遵循的原则,指标权重的确定方法以及指标的综合评价方法和发展展望。 相似文献