全文获取类型
收费全文 | 2044篇 |
免费 | 92篇 |
国内免费 | 129篇 |
专业分类
林业 | 161篇 |
农学 | 129篇 |
基础科学 | 97篇 |
153篇 | |
综合类 | 975篇 |
农作物 | 101篇 |
水产渔业 | 137篇 |
畜牧兽医 | 325篇 |
园艺 | 109篇 |
植物保护 | 78篇 |
出版年
2024年 | 11篇 |
2023年 | 25篇 |
2022年 | 52篇 |
2021年 | 50篇 |
2020年 | 52篇 |
2019年 | 77篇 |
2018年 | 44篇 |
2017年 | 48篇 |
2016年 | 78篇 |
2015年 | 88篇 |
2014年 | 91篇 |
2013年 | 97篇 |
2012年 | 144篇 |
2011年 | 147篇 |
2010年 | 97篇 |
2009年 | 145篇 |
2008年 | 121篇 |
2007年 | 163篇 |
2006年 | 148篇 |
2005年 | 93篇 |
2004年 | 65篇 |
2003年 | 64篇 |
2002年 | 49篇 |
2001年 | 48篇 |
2000年 | 52篇 |
1999年 | 22篇 |
1998年 | 25篇 |
1997年 | 25篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有2265条查询结果,搜索用时 15 毫秒
81.
82.
83.
Lynn H. Booth Vanessa J. Heppelthwaite Kathryn O’Halloran 《Journal of Soils and Sediments》2002,2(3):148-154
Objectives and Methods. The sensitivity of two biomarkers, the neutral red retention assay (NRRA) and cytochrome P450 were evaluated in the earthwormAporrectodea caliginosa for their potential to detect exposure to benzo[a]pyrene (BaP). Cytochrome P450 was also evaluated in the earthwormLumbricus rubellus, and measured using the substrate ethoxycoumarin. Optimal assay conditions (pH, and temperature) were determined, followed
by exposure of earthworms to 20 mg/kg BaP (a typical concentration at contaminated sites in New Zealand). Ethoxycoumarin-O-dealkylase
(ECOD) activity was measured after 7, 14, and 21 days exposure. The NRRA was evaluated in earthworms exposed to 0.2, 20, and
100 mg BaP/kg, and biomarker responses were compared with effects on body weight.
Results and Discussion Benzo[a]pyrene failed to induce ECOD activity in either earthworm species, and therefore it is not useful as a biomarker
of BaP exposure and was not evaluated further. In all cases, the NRRA was significantly affected in the absence of any effects
on earthworm body weight, indicating that this assay can detect exposure to BaP at a range of concentrations comparable to
those found at contaminated sites. The NRRA should be linked to reproductive endpoints, then it can be used as an early warning
indicator of adverse effects. Establishing biomarker stability under environmental conditions is an important step in biomarker
development. Therefore, the effects of soil type (sandy soil, silt loam, and a clay soil), moisture content (15–30%), and
temperature (5–20°) on the NRRA were determined. In all cases, there was no effect on the NRRA, indicating that this assay
is very stable under varying environmental conditions.
Conclusion and Outlook In conclusion, cytochrome P450 activity does not appear to be a useful indicator of PAH exposure in eitherA. caliginosa or L.rubellus, and due to the inherently low activity, it is not suitable as a routine biomarker for detecting environmental contamination
by these compounds. In contrast, the NRRA in the earthworm A.caliginosa is a promising indicator of PAH exposure at the concentrations likely to be found in contaminated sites in New Zealand, and
therefore has potential for evaluating these contaminated sites. If the NRRA can be linked to ecologically important life-cycle
endpoints, such as reproduction, then it could be used as an early warning indicator of adverse effects at contaminated sites,
i.e., by measuring biomarker responses in earthworms from a ‘contaminated area’ and comparing these with earthworms from a
matched control area. 相似文献
84.
85.
86.
87.
模拟酸雨对杨梅生理生化特征的影响 总被引:2,自引:0,他引:2
研究了不同强度模拟酸雨对6年生东魁杨梅生理生化特征的影响。结果表明:随着模拟酸雨胁迫加剧,叶片可见伤害症状严重,叶绿素a、叶绿素b、总叶绿素、类胡萝卜素含量以及叶绿素a/b比值显著降低,光系统I(IPSII)的潜在化学活性(Fv/Fo)和最大光化学效率(Fv/Fm)显著降低,水分利用效率和光合能力显著下降,细胞质膜透性增加,MDA含量增加,SOD、POD和CAT活性受到明显抑制,从而抑制杨梅的生长发育。 相似文献
88.
89.
法律素质作为农村领导干部政治素质的一个重要组成部分,对农村领导干部自身整体素质的提高有着重要的影响,同时也影响着我国法治建设的进程。提高农村领导干部法律素质已成为我们面临的一项重要课题和紧迫任务。本文拟从如何提高农村领导干部自身法律素质的角度进行阐述。 相似文献
90.
石河子及周围垦区的土壤粘重且呈盐碱性,由于犁底层的存在,土质很难得到改善。而深松作业则是打破犁底层的主要农业技术措施之一。为此,论述了IZSS-600-3型振动深松鼠道犁的构造和工作原理,分析了试验因素对试验指标的影响,为机具今后在农业生产中的应用和推广提供了依据和参考。 相似文献