全文获取类型
收费全文 | 750篇 |
免费 | 56篇 |
国内免费 | 1篇 |
专业分类
林业 | 35篇 |
农学 | 19篇 |
基础科学 | 5篇 |
82篇 | |
综合类 | 161篇 |
农作物 | 18篇 |
水产渔业 | 62篇 |
畜牧兽医 | 375篇 |
园艺 | 13篇 |
植物保护 | 37篇 |
出版年
2023年 | 10篇 |
2022年 | 13篇 |
2021年 | 17篇 |
2020年 | 14篇 |
2019年 | 20篇 |
2018年 | 25篇 |
2017年 | 31篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 19篇 |
2013年 | 29篇 |
2012年 | 51篇 |
2011年 | 54篇 |
2010年 | 14篇 |
2009年 | 17篇 |
2008年 | 59篇 |
2007年 | 35篇 |
2006年 | 45篇 |
2005年 | 28篇 |
2004年 | 36篇 |
2003年 | 29篇 |
2002年 | 28篇 |
2001年 | 9篇 |
2000年 | 17篇 |
1999年 | 15篇 |
1998年 | 3篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 11篇 |
1991年 | 19篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1967年 | 2篇 |
1931年 | 3篇 |
1930年 | 3篇 |
排序方式: 共有807条查询结果,搜索用时 15 毫秒
781.
Duplicate water samples from an unstocked tank and from each of four tanks stocked with starved “1-group” plaice were analysed both quantitatively and qualitatively. It was found that bacterial counts obtained from samples taken from stocked tanks were significantly higher than those taken from an unstocked tank. Allowing for limited sampling, the flora of the water circulating through an unstocked tank did not radically differ from the flora of the water following the addition of starved fish. The predominant group was the Pseudomonas Group IV/Achromobacter/Alcaligenes/Agrobacterium group. 相似文献
782.
Prairie voles (Microtus ochrogaster) are a socially monogamous rodent species and their cooperative behaviors require extensive communication between conspecifics. Rodents use ultrasonic vocalizations (USVs) to communicate and because a prairie vole breeder pair must engage in extensive cooperation for successful reproduction, auditory communication may be critical for this species. Therefore, we sought to characterize USVs in adult male and female prairie voles, and to determine how these calls are influenced by social context, salient social stimuli and the psychostimulant drug of abuse amphetamine (AMPH). Here, we characterize prairie vole USVs by showing the range of frequencies of prairie vole USVs, the proportion of various call types, how these call types compare between males and females, and how they are influenced by social stimulation and AMPH. AMPH caused a robust increase in the number of USVs in both males and females and there was a dramatic sex difference in the complexity of call structures of AMPH‐induced USVs, with males emitting more elaborate calls. Moreover, we show that novel (i.e. salient) social cues evoked differential increases in USVs across sex, with males showing a much more robust increase in USV production, both with respect to the frequency and complexity of USV production. Exposure to an estrous female in particular caused an extraordinary increase in USVs in male subjects. These data suggest that USVs may be a useful measure of social motivation in this species, including how social behaviors can be impacted by drugs of abuse. 相似文献
783.
784.
Shravani Basu Sean Mayes Michael Davey Jeremy A. Roberts Sayed N. Azam-Ali Richard Mithen Remy S. Pasquet 《Euphytica》2007,157(1-2):59-68
Controlled crosses in bambara groundnut were attempted between a range of thirty-six bambara groundnut landraces (thirty domesticated
(V. subterranea var. subterranea) and six wild (V. subterranea var. spontanea)). Ten F1 seed were produced. Of these, eight germinated producing F2 populations. On seed set, four populations could be unambiguously confirmed as true crosses by F3 seed coat colour. A single F2 population, derived from a domesticated landrace from Botswana (DipC; female parent) crossed with a wild accession collected
in Cameroon (VSSP11; male parent) was used to study a range of agronomic and domestication traits. These included; days to
emergence, days to flowering, internode (fourth) length at harvest, number of stems per plant, leaf area, Specific Leaf Area
(SLA), Carbon Isotope Discrimination (CID), 100 seed weight, testa colour and eye pattern around the hilum. On the basis of variation for internode length and stems
per plant, 14 small F3 families were selected and grown under field conditions to further investigate the genetic basis of the ‘spreading’ versus
‘bunched’ plant character, a major difference between wild and cultivated bambara groundnut. Results presented suggest that
traits including leaf area, SLA, CID and 100 seed weight are controlled by several genes. In contrast, the variation for traits
such as internode length, stems per plant, days to emergence and seed eye pattern around the hilum are likely to be under
largely monogenic control. The results of this work are discussed in relation to the domestication of bambara groundnut. 相似文献
785.
Erika Hussar Sean Richards Zhi-Qing Lin Robert P. Dixon Kevin A. Johnson 《Water, air, and soil pollution》2012,223(9):5535-5548
South Chattanooga has been home to foundries, coke furnaces, chemical, wood preserving, tanning, and textile plants for over 100?years. Most of the industries were in place before any significant development of residential property in the area. During the 1950s and 1960s, however, the government purchased inexpensive property and constructed public housing projects in South Chattanooga. Many neighborhoods that surround the Chattanooga Creek were previous dumping grounds for industry. Polycyclic aromatic hydrocarbons (PAHs) comprised the largest component of the dumping and airborne industrial emissions. To address human exposure to these PAHs, a broad study of South Chattanooga soil contaminant concentrations was conducted on 20 sites across the city. Sixteen priority pollutant PAHs were quantified at two depths (0?C10 and 10?C20?cm) and compared against reference site soils, as well as to soils from industrially impacted areas in Germany, China, and the USA. From these data, the probability that people would encounter levels exceeding the United States Environmental Protection Agency (USEPA) residential preliminary remediation goals (PRG) was calculated. Results indicate that South Chattanooga soils have relatively high concentrations of total PAHs, specifically benzo[a]pyrene (B[a]P). These high concentrations of B[a]P were somewhat ubiquitous in South Chattanooga. Indeed, there is a high probability (88?%) of encountering soil in South Chattanooga that exceeds the USEPA PRG for B[a]P. However, there is a low probability (15?%) of encountering a site with ??PAHs exceeding USEPA PRG guidelines. 相似文献
786.
787.
Zhou Y Su Y Li B Liu F Ryder JW Wu X Gonzalez-DeWhitt PA Gelfanova V Hale JE May PC Paul SM Ni B 《Science (New York, N.Y.)》2003,302(5648):1215-1217
A subset of nonsteroidal anti-inflammatory drugs (NSAIDs) has been shown to preferentially reduce the secretion of the highly amyloidogenic, 42-residue amyloid-beta peptide Abeta42. We found that Rho and its effector, Rho-associated kinase, preferentially regulated the amount of Abeta42 produced in vitro and that only those NSAIDs effective as Rho inhibitors lowered Abeta42. Administration of Y-27632, a selective Rock inhibitor, also preferentially lowered brain levels of Abeta42 in a transgenic mouse model of Alzheimer's disease. Thus, the Rho-Rock pathway may regulate amyloid precursor protein processing, and a subset of NSAIDs can reduce Abeta42 through inhibition of Rho activity. 相似文献
788.
May RM 《Science (New York, N.Y.)》2003,302(5645):565-6; author reply 565-6
789.
Abiogenic hydrocarbon production at lost city hydrothermal field 总被引:1,自引:0,他引:1
Proskurowski G Lilley MD Seewald JS Früh-Green GL Olson EJ Lupton JE Sylva SP Kelley DS 《Science (New York, N.Y.)》2008,319(5863):604-607
Low-molecular-weight hydrocarbons in natural hydrothermal fluids have been attributed to abiogenic production by Fischer-Tropsch type (FTT) reactions, although clear evidence for such a process has been elusive. Here, we present concentration, and stable and radiocarbon isotope, data from hydrocarbons dissolved in hydrogen-rich fluids venting at the ultramafic-hosted Lost City Hydrothermal Field. A distinct "inverse" trend in the stable carbon and hydrogen isotopic composition of C1 to C4 hydrocarbons is compatible with FTT genesis. Radiocarbon evidence rules out seawater bicarbonate as the carbon source for FTT reactions, suggesting that a mantle-derived inorganic carbon source is leached from the host rocks. Our findings illustrate that the abiotic synthesis of hydrocarbons in nature may occur in the presence of ultramafic rocks, water, and moderate amounts of heat. 相似文献
790.