全文获取类型
收费全文 | 796篇 |
免费 | 21篇 |
国内免费 | 2篇 |
专业分类
林业 | 91篇 |
农学 | 14篇 |
基础科学 | 1篇 |
210篇 | |
综合类 | 53篇 |
农作物 | 138篇 |
水产渔业 | 34篇 |
畜牧兽医 | 213篇 |
园艺 | 33篇 |
植物保护 | 32篇 |
出版年
2021年 | 10篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 17篇 |
2015年 | 8篇 |
2014年 | 19篇 |
2013年 | 56篇 |
2012年 | 27篇 |
2011年 | 29篇 |
2010年 | 14篇 |
2009年 | 22篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 35篇 |
2005年 | 28篇 |
2004年 | 29篇 |
2003年 | 28篇 |
2002年 | 24篇 |
2001年 | 20篇 |
2000年 | 11篇 |
1999年 | 25篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1983年 | 11篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1972年 | 6篇 |
1970年 | 8篇 |
1969年 | 7篇 |
1965年 | 5篇 |
1959年 | 5篇 |
1941年 | 5篇 |
1940年 | 5篇 |
1936年 | 7篇 |
1935年 | 8篇 |
1934年 | 5篇 |
1928年 | 6篇 |
1926年 | 9篇 |
1924年 | 6篇 |
排序方式: 共有819条查询结果,搜索用时 15 毫秒
81.
82.
Jürgen Weber Jupp Kreutzmann Anita Plantikow Evelyn Claus Werner Manz Peter Heininger 《Journal of Soils and Sediments》2006,6(2):84-91
Goal, Scope and Background Numerous xenobiotics released into surface waters are transferred to suspended particulate matter and finally attached to
sediments. Aquatic organisms may be exposed to them by direct particle feeding, by physical contact with contaminated surfaces
as an exposure route, and by the uptake of dissolved contaminants after equilibration via the free water phase. In order to
assess potential sediment toxicity, each of these exposure routes has to be addressed. This paper presents a newly developed
particle contact assay that uses the fermentation performance of a specific Saccharomyces cerevisiae strain for the assessment
of toxic effects in sediments. The test procedure is based on the characteristic feature of growing yeast cells to attach
to sediment particles, which are also relevant for the accumulation of contaminants. The physical contact with lipophilic
contaminants mirrors an exposition pathway for the direct uptake into the cells. In order to quantitatively characterize the
toxic effects of particle attached pollutants on the fermentation performance, unpolluted native reference sediment was spiked
with representatives for widely distributed anthropogenic contaminants.
Methods Saccharomyces cerevisiae was established as sensitive eukaryotic microorganism for the ecotoxicological assessment of particle
attached anthropogenic contaminants in freshwater sediments. For this purpose, yeast cells were cultivated in sediment samples
and the resulting fermentation performance was continuously measured. Sediments artifically spiked with HCB, PCB, g-HCH, DDT,
and benzo(a)pyrene and solutions of each contaminant were comparatively investigated by means of their adverse effects on
yeast fermentation performance. Additionally, four native river sediments characterized by increasing levels of pollution
were assessed by the yeast particle contact assay, and simultaneously by standard aquatic tests with algae, daphniae, and
luminescent bacteria using pore water and elutriates. Results of the bioassays were related to specific sediment contamination
with respect to metals and organic priority pollutants.
Results and Discussion In sediments spiked with PCB and benzo(a)pyrene fermentation, performance was affected extensively below concentrations inhibiting
fermentation in contaminant solutions. This suggests a high efficiency of the exposure route by physical contact. The fermentation
performance was only slightly affected by single lipophilic pollutants, whereas mixtures of individually spiked sediments
caused critically reduced fermentation performance suggesting additive synergistic effects. Native river sediments modestly
to critically polluted by hazardous organic compounds lead to a slightly to dangerously reduced fermentation performance in
the yeast contact assay. These inhibitory effects were much less pronounced in the standard bioassays conducted with algae,
daphniae and luminescent bacteria, applying pore waters and elutriates as sample matrices. Using pore water, inhibition was
measured only in the most polluted sediment, elutriates lead to a slight inhibition of the algal growth in the undiluted sample
only. These results indicate an improved sensitivity of the yeast particle contact assay compared to the standard assays,
due to uptake and physical cell contact as additional routes of exposure.
Conclusion The yeast particle contact assay is a valuable tool for the assessment of ecotoxicological potential in freshwater sediments.
Since the assay addresses physical contact as an exposure route, it indicates bioavailability of lipophilic compounds in sediments.
Outlook The sensitive indication of bioavailable contaminants associated to sediment particles by the newly developed yeast particle
contact assay recommends it as a complementary microbial bioassay in a test battery for assessing major pathways of contaminants
in whole sediments. 相似文献
83.
Distributions of the vector Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae) (determined from light trap data) and 2 arboviruses (determined from seroconversions in sentinel cattle) were studied in eastern New South Wales in 1993–94. C brevitarsis was recorded progressively from endemic areas on the north coast, to Nowra on the south coast, and westward to Scone, in the Hunter Valley. C brevitarsis also survived through winter at Paterson, in the Hunter Valley. Its apparently focal reappearance in this marginal area had no obvious effect on the broad pattern of its progression or the dispersal of Akabane and bluetongue viruses. These viruses were first recorded from foci near Coffs Harbour, on the mid-north coast. Their first occurrences at different locations were associated with those of C brevitarsis, but not with each other. The viruses were found only within the recorded limits of the vector's distribution. Delays between the initial occurrence of C brevitarsis and first evidence of virus transmissions at locations ranged from 2 to 7 months. The delays decreased away from the points of focus and were negatively associated with the time of initial occurrence of the vector. Seroconversions to the viruses were related to the presence of C brevitarsis. However, the densities of C brevitarsis had no apparent effect on the initial numbers of cattle seroconverting to either virus. The results support the conclusion that the progressions of C brevitarsis and Akabane and bluetongue viruses were the result of gradual movements by the vector. 相似文献
84.
85.
86.
Werner Schuphan 《Plant foods for human nutrition (Dordrecht, Netherlands)》1977,27(3-4):359-373
Ohne Zusammenfassung 相似文献
87.
88.
Numbers of gastrointestinal helminth eggs of Wyoming cattle in two surveys: 1957 to 1961 and 1973 to 1977 总被引:1,自引:0,他引:1
From 1973 to 1977, a survey of internal parasites in Wyoming cattle was conducted via fecal analyses of 1,490 beef cattle. Sugar flotation techniques were used, with a factor of 2 times the actual egg counts. The prevalence of internal parasites of beef cattle in this survey was compared with that in a previous survey conducted on Wyoming beef cattle from 1957 to 1961. Results of analyses indicated no true change in mean eggs per gram of feces (epg) as follows: calves, 14 epg in 1961 and 20 epg in 1977; yearlings, 29 epg in 1961 and 19 epg in 1977; and adults, 22 epg in 1961 and 21 epg in 1977. 相似文献
89.
90.