全文获取类型
收费全文 | 279篇 |
免费 | 15篇 |
专业分类
林业 | 8篇 |
农学 | 1篇 |
28篇 | |
综合类 | 52篇 |
农作物 | 2篇 |
水产渔业 | 9篇 |
畜牧兽医 | 189篇 |
园艺 | 2篇 |
植物保护 | 3篇 |
出版年
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 21篇 |
2012年 | 9篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 14篇 |
2007年 | 7篇 |
2006年 | 10篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 17篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1990年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1969年 | 4篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1954年 | 1篇 |
1938年 | 1篇 |
1934年 | 1篇 |
1926年 | 1篇 |
1919年 | 1篇 |
1917年 | 3篇 |
1915年 | 1篇 |
1900年 | 1篇 |
1896年 | 1篇 |
1893年 | 1篇 |
1880年 | 1篇 |
排序方式: 共有294条查询结果,搜索用时 0 毫秒
31.
32.
33.
Youngman P Zuber P Perkins JB Sandman K Igo M Losick R 《Science (New York, N.Y.)》1985,228(4697):285-291
The regulated activation of numerous sets of genes in multiple chromosomal locations is a hallmark of cellular differentiation in both eukaryotes and prokaryotes. Certain species of bacteria that experience complex developmental cycles are especially attractive as systems in which to study the mechanisms of this kind of gene regulation because they are highly amenable to both biochemical and genetic approaches. Bacillus subtilis, which undergoes extensive cellular differentiation when it sporulates, is one such system. Many new methods are now available in this Gram-positive species for identifying, manipulating, and studying the regulation of genes involved in spore formation, including the use of transposable genetic elements that create gene fusions in vivo as an automatic consequence of insertions into genes. 相似文献
34.
A semi-portable flow-through cloud water monitoring system was developed for measurements of cloud water conductivity and pH in remote sites lacking AC line power. This system was tested from May to September on Camels Hump mountain, Vermont. High temporal resolution data from seven cloud events were collected during the 1991 growing season. Mean cloud water conductivity and pH for all events was 467 μmhos cm?1 and 3.2, respectively. The highest conductivity was 997 (μmhos cm?1 recorded on 19 September 1991 and the lowest pH of 2.9 was recorded during several events over the summer. Data from this system may be used to achieve a better understanding of the chemical environment in areas experiencing forest decline. 相似文献
35.
Neil R Smalheiser Vetle I Torvik Amanda Bischoff-Grethe Lauren B Burhans Michael Gabriel Ramin Homayouni Alireza Kashef Maryann E Martone Guy A Perkins Diana L Price Andrew C Talk Ruth West 《Journal of Biomedical Discovery and Collaboration》2006,1(1):8
Arrowsmith is a unique computer-assisted strategy designed to assist investigators in detecting biologically-relevant connections between two disparate sets of articles in Medline. This paper describes how an inter-institutional consortium of neuroscientists used the UIC Arrowsmith web interface http://arrowsmith.psych.uic.edu in their daily work and guided the development, refinement and expansion of the system into a suite of tools intended for use by the wider scientific community. 相似文献
36.
Coleman JN Lotya M O'Neill A Bergin SD King PJ Khan U Young K Gaucher A De S Smith RJ Shvets IV Arora SK Stanton G Kim HY Lee K Kim GT Duesberg GS Hallam T Boland JJ Wang JJ Donegan JF Grunlan JC Moriarty G Shmeliov A Nicholls RJ Perkins JM Grieveson EM Theuwissen K McComb DW Nellist PD Nicolosi V 《Science (New York, N.Y.)》2011,331(6017):568-571
If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS(2), WS(2), MoSe(2), MoTe(2), TaSe(2), NbSe(2), NiTe(2), BN, and Bi(2)Te(3) can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS(2) and MoS(2) effectively reinforce polymers, whereas WS(2)/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties. 相似文献
37.
Bennett RN Mellon FA Rosa EA Perkins L Kroon PA 《Journal of agricultural and food chemistry》2004,52(19):5856-5862
Azima tetracantha L. (needle bush; bee sting bush; Salvadoraceae) is used as a food and for various herbal medicines in Africa, India, and Madagascar, but there is very little information on the secondary metabolites in this species. High concentrations of N-methoxy-3-indolylmethyl-glucosinolate, a common glucosinolate of Brassica crops such as Brussels sprouts and broccoli, were found in the roots and seeds of A. tetracantha. Lower concentrations were detected in the stems and young leaves. The roots also contained another indole glucosinolate that was provisionally identified, from MS data and comparison with indole glucosinolate standards, as N-hydroxy-3-indolymethyl-glucosinolate. The roots, stems, and leaves contained neoascorbigen (the condensation product of N-methoxy-indole-3-carbinol and ascorbic acid). The seeds of A. tetracantha contained a complex mixture of 26 flavonoids predominantly as glycosides and acyl-glycosides, with traces of aglycones. The core aglycones of these flavonoids were identified as quercetin, isorhamnetin (3'-O-methylquercetin), rhamnetin (7-O-methylquercetin), and rhamnazin (7, 3'-di-O-methylquercetin). No flavonoids or anthocyanins were detected in other tissues, and procyanidins were undetectable. The dimeric piperidine alkaloids azimine, azcarpine, and carpaine were found in all tissues of A. tetracantha. 相似文献
38.
Gillian A. Perkins Laura B. Goodman Koji Tsujimura Gerlinde R. Van de Walle Sung G. Kim Edward J. Dubovi Nikolaus Osterrieder 《Veterinary microbiology》2009,139(3-4):375-378
A single nucleotide polymorphism in the equine herpesvirus 1 (EHV-1) DNA polymerase gene (ORF30 A2254 to G) has been associated with clinical signs of equine herpes myeloencephalopathy (EHM). The purpose of our study was to determine the odds ratio for this genetic marker and EHM using a panel of field isolates from North America collected over the past twenty-three years. EHV-1 isolates cultured at the Cornell University Animal Health Diagnostic Laboratory from 1984 to 2007 were retrieved along with their clinical histories. DNA was extracted from these EHV-1 cultures and allelic discrimination was performed using real-time PCR. The results were confirmed by sequencing of the target region in ORF30. PCR and sequencing were in 100% agreement and showed that 19 out of the 176 isolates had the ORF30 G2254 allele (11%), of which16 were EHM cases and 3 respiratory or abortion cases. The odds of having neurologic disease with the ORF30 G2254 genotype were computed as 162 times greater than those with the opposite allele ORF30 A2254 (95% confidence interval: 35–742). Despite this strong statistical significance, 24% (5/21) of horses with neurologic disease in our study population harbored the “non-neurologic” form of the allele (ORF30 A2254), suggesting that other factors may also contribute to the onset of EHM. 相似文献
39.
Breadfruit (Artocarpus altilis (Park) Fosberg) is a highly perishable tropical fruit which can be packed in sealed polyethylene bags and stored under refrigeration. The storage period between harvesting and softening was greater for fruit harvested partially mature than fully mature and for fruit which were harvested by picking or catching rather than traditional procedures. In 4 storage trials and a single shipping trial, the majority of partially mature fruits harvested by picking were still firm after 15 days although a significant proportion had commenced softening. 相似文献
40.