全文获取类型
收费全文 | 1130篇 |
免费 | 93篇 |
国内免费 | 338篇 |
专业分类
1561篇 |
出版年
2023年 | 13篇 |
2022年 | 7篇 |
2021年 | 20篇 |
2020年 | 29篇 |
2019年 | 37篇 |
2018年 | 42篇 |
2017年 | 46篇 |
2016年 | 61篇 |
2015年 | 50篇 |
2014年 | 55篇 |
2013年 | 100篇 |
2012年 | 67篇 |
2011年 | 47篇 |
2010年 | 43篇 |
2009年 | 57篇 |
2008年 | 63篇 |
2007年 | 77篇 |
2006年 | 64篇 |
2005年 | 86篇 |
2004年 | 67篇 |
2003年 | 63篇 |
2002年 | 51篇 |
2001年 | 49篇 |
2000年 | 50篇 |
1999年 | 18篇 |
1998年 | 29篇 |
1997年 | 35篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 26篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有1561条查询结果,搜索用时 15 毫秒
141.
Yan Hu Wang-Zhen Guo Tian-Zhen Zhang 《Acta Botanica Sinica》2009,(1):107-112
A bacterial artificial chromosome (BAC) library was constructed for Gossypium hirsutum acc. TM-1, a genetic and genomic standard line for Upland cotton. The library consists of 147 456 clones with an average insert size of 122.8 kb ranging from 97 to 240 kb. About 96.0% of the clones have inserts over 100 kb. Therefore, this library represents theoretically 7.4 haploid genome equivalents based on an AD genome size of 2 425 Mb. Clones were stored in 384 384- well plates and arrayed into multiplex pools for rapid and reliable library screening. BAC screening was carried out by four-round poiymerase chain reactions using 23 simple sequence repeats (SSR) markers, three sequence-related amplified polymorphism markers and one pair of primers for a gene associated with fiber development to test the quality of the library. Correspondingly, in total 92 positive BAC clones were identified with an average four positive clones per SSR marker, ranging from one to eight hits. Additionally, since these SSR markers have been localized to chromosome 12 (A12) and 26 (D12) according to the genetic map, these BAC clones are expected to serve as seeds for the physical mapping of these two homologous chromosomes, sequentially map-based cloning of quantitative trait loci or genes associated with important agronomic traits. 相似文献
142.
Transcriptome analysis reveals a comprehensive insect resistance response mechanism in cotton to infestation by the phloem feeding insect Bemisia tabaci (whitefly) 总被引:1,自引:0,他引:1 下载免费PDF全文
Jianying Li Lizhen Zhu J. Joe Hull Sijia Liang Henry Daniell Shuangxia Jin Xianlong Zhang 《Plant biotechnology journal》2016,14(10):1956-1975
143.
新疆棉田土壤质量综合评价方法 总被引:3,自引:0,他引:3
以新疆主要棉区为研究对象,测定了哈密、博乐、昌吉、奎屯、石河子、阿克苏及喀什棉田土壤耕层的pH、盐分、有机质、全氮、速效磷、速效钾及Cr、Cu、Zn、As、Pb 共计11个指标,综合分析土壤理化性质和重金属含量,采用土壤质量综合指数(SQI)对新疆主要棉区棉田土壤质量进行综合评价.结果表明: 新疆棉区棉田土壤呈碱性,pH均值为7.87,盐分含量均值为3.44 g·kg-1,为轻度盐化土壤,有机质和全氮含量均偏低,速效磷、速效钾含量较为丰富,与第二次全国土壤普查数据相比,土壤pH、盐分含量、有机质和全氮均呈下降趋势,土壤速效磷明显增长,部分地区土壤速效钾呈现出不同程度的升高趋势;Cr、Cu、Zn、As、Pb 5种重金属含量分别为45.88、40.66、68.30、12.88、16.68 mg·kg-1,均未超过国家二级标准,但与新疆土壤元素背景值相比,Cu、Zn、As均有累积现象.当重金属内梅罗综合污染指数(PN)小于0.5时,土壤理化性质越好,土壤综合质量越好.土壤有机质、全氮、Cu、Zn和As是影响新疆棉区棉田土壤质量的重要因素.新疆棉区棉田土壤质量总体属于中等水平,昌吉、奎屯质量最高,SQI为0.52,阿克苏质量最低,SQI为0.31,不同棉区土壤质量呈现为:北疆>东疆>南疆. 相似文献
144.
145.
Vegetative insecticidal protein (Vip) is a newly discovered family of toxin protein isolated from Bacillus thuringiensis (Bt). An 88.5-kDa Vip3Aa protein was secreted by a local strain of the bacterium during the vegetative growth phase. The full length of the coding region ‘2.3 kbp’ of the vip3Aa gene was isolated from plasmid DNA, cloned in pGEM-T vector and finally cloned in pQE-30 expression vector. Nucleotide sequence revealed 98% homology with that of the previously isolated genes. Expression of the vip3Aa in Escherichia coli was carried out and the expressed protein was detected in the concentrated supernatant, not in the pellet. This indicated that vip3Aa is secreted into the culture medium. Expressed protein was purified, blotted, and assayed against the cotton leaf worm Spodoptera littoralis. The LC50 was found to be 142.4 µ/mL while the LC50 was 90 ppm for the wild strain. These results suggest the use of either the isolated Bt strains or the expressed vip3Aa in an integrated pest management program against lepidopteran insect pests. 相似文献
146.
147.
How predation by Podisus nigrispinus is influenced by developmental stage and density of its prey Alabama argillacea 总被引:1,自引:0,他引:1 下载免费PDF全文
Bárbara Davis B. dos Santos Francisco S. Ramalho José B. Malaquias Aline C. S. Lira Jéssica K. S. Pachú Francisco S. Fernandes José C. Zanuncio 《Entomologia Experimentalis et Applicata》2016,158(2):142-151
The functional response of a predator to the density of its prey is affected by several factors, including the prey's developmental stage. This study evaluated the functional response of Podisus nigrispinus (Dallas) (Hemiptera: Heteroptera: Pentatomidae) females to fourth instars and pupae of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae), an important pest of cotton (Gossypium hirsutum L., Malvaceae) in Brazil. The prey were exposed to the predator for 12 and 24 h, and in densities of 1, 6, 12, 18, 24, and 30 items per predator female. The predation data were subjected to polynomial regression logistic analysis to determine the type of functional response. Holling and Rogers' equations were used to estimate parameters such as attack rate and handling time. Podisus nigrispinus females showed functional response types II and III by preying on larvae and pupae, respectively. The attack rate and handling time did not differ between the 12 and 24 h exposure times. Predation rate was higher at higher larval and pupal densities; predation was highest at a density of 30 prey items per female, and it was similar at 18 and 24 prey per predator. Understanding the interaction of predators and their food resources helps to optimize biological control strategies. It also helps the decision‐making and the improvement of release techniques of P. nigrispinus in the field. 相似文献
148.
通过生物测定和生物化学方法比较了棉铃虫玎Helicoverpa armigera敏感和抗性种群对溴氰菊酯毒力反应及其3种解毒酶的差异。结果表明,田间抗性种群和室内药剂汰选的抗性种群对溴氰菊酯均有较高的抗性,其抗性倍数分别达到195.8和37 375倍。水解酯酶和多功能氧化酶是导致棉铃虫对溴氰菊酯产生高抗性的重要酶系。特异性抑制剂活体内外抑制作用测试发现,敏感种群和抗性种群均含有较高量的乙酰胆碱酯酶,但两个种群对抑制剂的亲和力反应不同,表明乙酰胆碱酯酶在敏感种群和抗性种群中发生了不同的变化,这种变化可能与棉铃虫对溴氰菊酯的抗性有关。由此推断,棉铃虫对拟除虫菊酯这类中枢神经系统神经毒剂产生抗性,乙酰胆碱酯酶发生变化可能也是一个重要因子。 相似文献
149.
150.
<i>Aspergillus tubingensis</i> Causes Leaf Spot of Cotton (<i>Gossypium hirsutum</i> L.) in Pakistan
Maria Khizar Urooj Haroon Musrat Ali Samiah Arif Iftikhar Hussain Shah Hassan Javed Chaudhary Muhammad Farooq Hussain Munis 《Phyton》2020,89(1):103-109
Cotton (Gossypium hirsutum L.) is a key fiber crop of great commercial
importance. Numerous phytopathogens decimate crop production by causing
various diseases. During July-August 2018, leaf spot symptoms were recurrently
observed on cotton leaves in Rahim Yar Khan, Pakistan and adjacent areas. Infected
leaf samples were collected and plated on potato dextrose agar (PDA) media.
Causal agent of cotton leaf spot was isolated, characterized and identified as
Aspergillus tubingensis based on morphological and microscopic observations.
Conclusive identification of pathogen was done on the comparative molecular
analysis of CaM and β-tubulin gene sequences. BLAST analysis of both sequenced
genes showed 99% similarity with A. tubingensis. Koch’s postulates were followed
to confirm the pathogenicity of the isolated fungus. Healthy plants were inoculated
with fungus and similar disease symptoms were observed. Fungus was re-isolated
and identified to be identical to the inoculated fungus. To our knowledge, this is the
first report describing the involvement of A. tubingensis in causing leaf spot disease
of cotton in Pakistan and around the world. 相似文献