全文获取类型
收费全文 | 18109篇 |
免费 | 880篇 |
国内免费 | 948篇 |
专业分类
林业 | 2677篇 |
农学 | 1607篇 |
基础科学 | 531篇 |
2386篇 | |
综合类 | 7623篇 |
农作物 | 1222篇 |
水产渔业 | 238篇 |
畜牧兽医 | 1151篇 |
园艺 | 720篇 |
植物保护 | 1782篇 |
出版年
2024年 | 90篇 |
2023年 | 299篇 |
2022年 | 496篇 |
2021年 | 566篇 |
2020年 | 607篇 |
2019年 | 678篇 |
2018年 | 484篇 |
2017年 | 684篇 |
2016年 | 839篇 |
2015年 | 615篇 |
2014年 | 841篇 |
2013年 | 1198篇 |
2012年 | 1495篇 |
2011年 | 1218篇 |
2010年 | 1010篇 |
2009年 | 1096篇 |
2008年 | 993篇 |
2007年 | 1080篇 |
2006年 | 906篇 |
2005年 | 730篇 |
2004年 | 628篇 |
2003年 | 488篇 |
2002年 | 385篇 |
2001年 | 348篇 |
2000年 | 299篇 |
1999年 | 264篇 |
1998年 | 217篇 |
1997年 | 171篇 |
1996年 | 148篇 |
1995年 | 177篇 |
1994年 | 131篇 |
1993年 | 133篇 |
1992年 | 122篇 |
1991年 | 121篇 |
1990年 | 107篇 |
1989年 | 81篇 |
1988年 | 58篇 |
1987年 | 55篇 |
1986年 | 25篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
以檀香种子为材料,研究了不同浓度赤霉素、播种基质以及伴生树种对幼苗生长的影响,结果表明:采用1 000 mg/L赤霉素处理种子24h可促进种子发芽,发芽率达85%以上;以砂壤土+竹炭粉为播种基质出苗率最高;利用抛荒龙眼地并以龙眼树作为檀香成林期伴生植物对檀香生长具有促进作用,栽培12个月时测定,檀香树高、地径分别达172.3cm和2.48cm,为抛荒龙眼地重新利用提供新的思路。 相似文献
132.
土壤中的有机污染物可从根系进入植物体内,并可进一步通过食物链富集,从而威胁人群健康。植物根际微生物种类繁多、数量巨大,其中很多根际细菌可通过成膜作用在植物根表形成细菌生物膜,协助植物抵抗外界的不良环境或促进植物生长。有机污染物在被植物根系吸收的过程中,多需经过根表细菌生物膜这一特殊界面。综述了根际细菌在植物根表的成膜作用,以及根表功能细菌生物膜对污染物根际环境过程的影响及作用机理,分析了利用根表功能细菌生物膜调控植物吸收有机污染物的可行性,试图为防治土壤有机污染、降低作物污染风险、保障农产品安全等提供理论依据。 相似文献
133.
Background, Aim and Scope
Part 1: Behaviour of Polycyclic Musks in Sewage Sludge of Different Treatment Plants in Summer and Winter
Part 2: Investigation of Polycyclic Musks in Soils and Plants
- Preamble. In Part 1 of the study, screening tests were performed to investigate the occurrence of PCMs in sewage sludges.
For a preliminary risk assessment, further information is needed about their behaviour in the terrestrial environment. Hence,
Part 2 examined the adsorption of PCMs to soil, their dissipation and leaching in soil and their uptake by plants.
Background, Aim and Scope Polycyclic Musks (PCMs) enter the environment via the waste water system. Because of their persistence, they can accumulate
in different matrices like sewage sludge or biota. By the use of sewage sludge as a fertilizer, PCMs are transferred to agricultural
soils. Therefore, in Part 1 of the study, screening tests were performed to investigate the occurrence of PCMs in sewage sludge.
For a preliminary risk assessment, further information is needed about their behaviour in the terrestrial environment. Hence,
Part 2 of the study examined the adsorption of PCMs to soil, their dissipation and leaching in soil, and their uptake by plants.
Materials and Methods:
In the screening study, samples of activated sewage sludge were taken both in summer and in winter at 21 treatment plants.
In order to get an overview of the contamination situation, sampling covered different types of treatment plants (in rural,
urban, industrial areas). Analytical methods for the determination of HHCB, AHTN, ADBI, ATTN, AHDI and ATII in the sludge
samples were developed and applied.
Results:
The analytical screening of PCMs showed their presence in activated and dried sewage sludge samples. HHCB and AHTN represented
about 95% of the PCMs investigated. Their concentrations in the activated sludge samples varied between 2.9 and 10.4 mg/kg
dry mass (dm) and 1.1 to 4.2 mg/kg dm, respectively. Although different types of sewage treatment plants were investigated,
similar PCM levels were found, showing the widespread input of these compounds into domestic waste water.
Discussion:
PCM concentrations in activated sludge varied widely. The variation drops substantially when concentrations are related to
the varying dry mass. In dehydrated sludge, PCM concentrations were up to 24 mg/kg dm for HHCB and up to 6.9 mg/kg dm for
AHTN. These high values are comparable to those obtained in other investigations analysing PCMs. If the degradation of organic
mass during anaerobic decomposition is included in the evaluation, the figures obtained are comparable to those for activated
sludge. Elimination in sewage sludge was higher in summer than in winter. Therefore, the contamination of the sludges in winter
reached higher levels compared to the summer.
Conclusions:
The results show that PCMs are widespread contaminants in sewage sludge.
Recommendations and Perspectives:
PCM should be considered in a risk assessment as potential contaminants of sewage sludge destined for agricultural use.
Due to the high PCM levels in sewage sludge, further investigations into the degradation and elimination behaviour in sewage
sludge have to be carried out, including that involving PCM metabolites such as lactone derivatives. 相似文献
134.
135.
Qi Haikun Wang Sai Xu Dongyong Lu Zhengying Zhao Wenchao Hao Yanjie Zhang Xiang Li Wei Han Huanyong Wang Jiangtao Wang Hongzhe Chen Hongzhang Wang Lin Du Mingwei Tian Xiaoli Li Zhaohu 《棉花学报》2013,32(5):425-437
[Objective] The objective of this study was to investigate the stability and universality of cotton chemical topping by applying mepiquat chloride (1,1-dimethyl-piperidinium chloride, DPC) in different cotton-growing regions. [Method] Field experiments were conducted in 2018 at 10 locations in the Yellow River basin (Hejian and Handan, Hebei province; Dezhou and Wudi, Shandong province), the Yangtze River basin (Dafeng, Jiangsu province; Huanggang, Hubei province), and Xinjiang area (Shihezi location I and loacation II, northern Xinjiang and Luntai and Shaya, southern Xinjiang). Local cultivars/lines were used, and the experiments were performed using a randomized complete block design with three or four replicates. Accompanied with typical DPC multi-application in each location, chemical topping was conducted at 10 days before manual topping (T1) or at the same time with manual topping (T2) by applying four dosages of DPC (0, 90, 180, 270 g·hm-2), manual topping was used as the first control and non-topping as the second control. [Result] The time of chemical topping significantly affected cotton plant height (except for the results in Handan, Dezhou and Wudi) and the number of fruit branches (except for the results in Dafeng and Huanggang). It was observed that earlier chemical topping would result in lower cotton plant height and a fewer fruit branches. In Hejian and Shihezi location I, the average plant height across DPC chemical topping at T1 stage was not only lower than that of T2 stage but also 3.3 cm and 4.6 cm lower than that of manual topping, respectively. In most locations, chemical topping at T1 stage increased around two fruit branches per plant compared with manual topping, while in T2 stage the increased fruit branches per plant ranged from 2.3 to 7.7. Also, we found that a higher dosage of DPC resulted in shorter plant height (except for that in Huanggang). In some locations, plant heights of chemical topping with 180 g·hm-2 or 270 g·hm-2 DPC were even shorter than that of manual topping. The number of fruit branches per plant of 0 g·hm-2 DPC increased by 2.4-8.3 compared with manual topping. However, chemical topping with 90-270 g·hm-2 DPC significantly reduced the number of fruit branches compared with 0 g·hm-2 DPC. There were no significant differences in the number of fruit branches among three DPC dosages (90, 180, and 270 g·hm-2). In Handan, seed cotton yield of chemical topping at T2 stage was significantly lower than that of manual topping due to the decreased boll number, which is possibly associated with the high temperature and drought weather after chemical topping. While at other locations, most treatments of chemical topping by using DPC did not produce significant effects on yield. In addition, chemical topping by using DPC did not delay cotton maturity, characterized by their similar boll-opening rate and the first harvest rate to those of manual topping before spraying harvest aids. [Conclusion] Cotton chemical topping with DPC is more stable and universal across different cotton-growing regions. We suggest that 90-180 g·hm-2 DPC could be used at the same time with manual topping for cotton chemical topping. 相似文献
136.
高等植物叶绿素的生物合成对其正常光合作用起关键作用。本文根据前期芯片杂交结果, 采用RT-PCR和RACE技术克隆了3个茶树叶绿素合成相关基因, 分别为谷氨酸-tRNA还原酶(CsGluTR)、叶绿素合酶(CsChlS)、叶绿素酸醋氧化酶(CsCAO), 对应的GenBank的登录号为HQ660371、HQ660370、HQ660369。序列分析表明, CsGluTR基因全长2165 bp, 开放阅读框长1665 bp, 编码554个氨基酸, 推测的蛋白分子量约为60.6 kD, 理论等电点为8.78;CsChlS基因全长1463 bp, 其中开放阅读框长1125 bp, 编码374个氨基酸, 推测的蛋白分子量约为40.5 kD, 理论等电点为8.58;CsCAO基因全长2146 bp, 其中开放阅读框长1611 bp, 编码536个氨基酸, 推测的蛋白分子量约为60.8 kD, 理论等电点为8.03。比对分析表明, 3个基因编码的氨基酸序列与其他植物中同源基因的相似性均在70%以上。利用荧光定量PCR技术检测3个基因在不同白化阶段的表达,表明, CsChlS和CsCAO基因具有明显的表达协同性, 它们在叶片中的表达量与叶片的颜色变化高度同步;而CsGluTR在白化叶片和正常叶片中的表达差异相对较小, 同时在新生芽叶转绿过程中最先恢复正常表达水平。说明在白化叶片中, 叶绿素的合成机制受到较大影响, 叶绿素合成受阻导致的叶片内色素类物质含量降低或消失是叶片白化的直接原因。 相似文献
137.
海南岛油脂植物种质资源 总被引:4,自引:0,他引:4
能源危机成为当今世界重大的热点问题,能源植物是缓解能源危机的重要突破口。通过查阅相关文献,概述了海南岛主要含油部位含油量≥30%的油脂植物50科116属163种,引种栽培74种,野生资源89种,油脂植物种质资源丰富,分布集中,热带特征明显,且多为木本。全国有53种木本油料的种子油可作为发展生物柴油最适合原料,其中31种海南有分布。列举了含油量高、适合在海南气候条件下生长、具有开发潜力的油脂植物18种并对海南岛油脂植物资源的开发利用提出建议。 相似文献
138.
大蕉未成熟雄花接种到胚性愈伤组织诱导培养基中,4~5个月后可诱导出胚性愈伤组织,并可在继代培养基上长期增殖。这些继代培养了6年多的松软易碎的胚性愈伤组织转移到含有0.2 mg/L 6-BA的分化培养基中,可诱导出芽,得到了53株再生植株,这些再生植株可进一步扩大繁殖。组织学切片证明长期继代培养的愈伤组织维持了胚性的状态。 相似文献
139.
140.
基于盆栽试验,研究了不同干旱胁迫(重度胁迫,中度胁迫和正常供水)与复水条件下植物生长营养液处理对马铃薯根系活力、叶片光合速率、气孔导度和蒸腾速率及产量的影响。结果表明,不同干旱胁迫与复水条件下,植物生长营养液均能有效改善马铃薯根系活力及光合特性。与CK相比,根系活力增加3.19%~20.23%,光合速率增加6.36%~32.70%,气孔导度降低5.49%~32.32%,蒸腾速率降低2.30%~28.10%。马铃薯产量增加3.19%~7.55%,增产幅度为:重度胁迫>中度胁迫>正常供水。3种干旱胁迫下,植物生长营养液对重度胁迫马铃薯产量的增幅最大。 相似文献