全文获取类型
收费全文 | 493篇 |
免费 | 31篇 |
专业分类
林业 | 35篇 |
农学 | 28篇 |
85篇 | |
综合类 | 42篇 |
农作物 | 25篇 |
水产渔业 | 77篇 |
畜牧兽医 | 206篇 |
园艺 | 11篇 |
植物保护 | 15篇 |
出版年
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 5篇 |
2018年 | 19篇 |
2017年 | 13篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 36篇 |
2012年 | 40篇 |
2011年 | 29篇 |
2010年 | 28篇 |
2009年 | 11篇 |
2008年 | 21篇 |
2007年 | 20篇 |
2006年 | 26篇 |
2005年 | 19篇 |
2004年 | 14篇 |
2003年 | 18篇 |
2002年 | 24篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 12篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 12篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1969年 | 1篇 |
1966年 | 3篇 |
1958年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有524条查询结果,搜索用时 0 毫秒
81.
Grete Hansen Aas Olaug Taran Skjerdal Iren Stoknes Ingebrigt Bjørkevoll 《Journal Of Aquatic Food Product Technology》2013,22(3-4):149-161
Different packaging conditions of salt-cured cod fillets were studied during 2-years chilled storage. Yield and quality of salt-cured Atlantic cod fillets packed in sealed polystyrene boxes or in traditional cardboard boxes were compared. After 4 months, yield decreased by approximately 10% and decreased further when packed in cardboard boxes. Lipid oxidation was low after 12 months, and no microbiological spoilage was registered. The total amount of bacteria in the fish reduced with storage time, independent of packaging. The reddish color of halophilic bacteria was detected after 7–8 weeks at 18°C, but not if packed with MAP. 相似文献
82.
Birthe Pedersen Dr. Bjørn O. Eggum 《Plant foods for human nutrition (Dordrecht, Netherlands)》1983,32(2):185-196
Rye was milled into flours having extraction rates between 100 and 65%. The nutritive value of the various fractions was studied by chemical analyses and in balance trials with rats. The concentration of essential nutrients decreased when the extraction rate was lowered. The lysine content (g/16 g N) was 4.23 in whole rye, but only 3.76 in the 65% extraction flour, and a corresponding reduction in biological value was found. A reduction of 50% or more was observed for several minerals with zinc and phosphorus being most affected. The apparent zinc absorption and retention expressed in absolute values, were significantly higher from the flours of high extraction than from the more refined flours, in spite of a much higher phytate content in whole rye and lightly milled flours. It could be concluded that milling of rye into highly refined flours not only preclude considerable amounts of nutrients from human consumption, but the remaining flours have a much poorer nutritive value than flour made from whole rye. 相似文献
83.
Background
The gypsovag shrub Cistus clusii is locally dominant in semi-arid gypsum plant communities of North-Eastern Spain. This species commonly grows in species-poor patches even though it has nurse potential, suggesting interference on neighbouring species. Other Cistus species exert a chemically mediated interference on plant communities, suggesting that it might be a common phenomenon in this genus. This study aimed investigating whether C. clusii exerts chemically mediated interference on neighbouring species in gypsum plant communities. We tested in a greenhouse whether aqueous extracts from C. clusii leaves (L), roots (R) and a mixture of both (RL) affected germination, seedling survival, and growth of nine native species of gypsum communities, including C. clusii itself. We further assessed in the field richness and abundance of plants under the canopy of C. clusii compared to Gypsophila struthium (shrub with a similar architecture having a nurse role) and in open patches. Finally, we specifically assessed in the field the influence of C. clusii on the presence of the species tested in the greenhouse experiment.Results
Aqueous extracts from C. clusii (R and RL) negatively affected either germination or survival in four of nine species. In the field, richness and abundance of plants were lower under the canopy of C. clusii than under G. struthium, but higher than in open patches. Specifically, five of nine species were less frequent than expected under the canopy of C. clusii.Conclusions
Cistus clusii shows species-specific interference with neighbouring species in the community, which may be at least partially attributable to its phytotoxic activity. To our knowledge, this is the first report of species-specific interference by C. clusii.84.
Nilsson Anna L. K. Skaugen Thomas Reitan Trond L’Abée-Lund Jan Henning Gamelon Marlène Jerstad Kurt Røstad Ole Wiggo Slagsvold Tore Stenseth Nils C. Vøllestad L. Asbjørn Walseng Bjørn 《BMC ecology》2020,20(1):1-12
While nitrogen and carbon stable isotope values can reflect ecological segregation, prey choice and spatial distribution in seabirds, the interpretation of bulk stable isotope values is frequently hampered by a lack of isotopic baseline data. In this study, we used compound-specific isotope analyses of amino acids (CSIA-AA) to overcome this constraint and to study interspecific differences, seasonal and historical changes in trophic positions of five seabird species, three penguins and two petrels, from a sub-Antarctic seabird community. CSIA-AA allowed comparing trophic positions of seabirds with temperate and polar distributions. Gentoo and Magellanic penguins had the highest trophic positions during the breeding season (3.7 and 3.9), but decreased these (2.9 and 3.3) during the feed-up for moult. Intra-specific differences were also detected in Thin-billed prions, where carbon isotope values clearly separated individuals with polar and temperate distributions, both in the breeding and interbreeding periods. Thin-billed prions that foraged in polar waters had lower trophic positions (3.2) than conspecifics foraging in temperate waters (3.8). We further investigated historical changes by comparing museum samples with samples collected recently. Our pilot study suggests that Rockhopper penguins, Magellanic penguins and Thin-billed prions with temperate non-breeding distributions had retained their trophic levels over a 90–100 year period, while Gentoo penguins and Thin-billed prions with polar non-breeding distributions had decreased trophic levels compared to historical samples. In contrast, Wilson’s storm-petrels had slightly increased trophic levels compared to samples taken in 1924–1930. We applied compound-specific stable isotope analyses across a range of contexts, from intra-specific comparisons between stages of the breeding cycle to inter-specific seabird community analysis that would not have been possible using bulk stable isotope analyses alone due to differences in isotopic baselines. 相似文献
85.
86.
Vaaje-Kolstad G Westereng B Horn SJ Liu Z Zhai H Sørlie M Eijsink VG 《Science (New York, N.Y.)》2010,330(6001):219-222
Efficient enzymatic conversion of crystalline polysaccharides is crucial for an economically and environmentally sustainable bioeconomy but remains unfavorably inefficient. We describe an enzyme that acts on the surface of crystalline chitin, where it introduces chain breaks and generates oxidized chain ends, thus promoting further degradation by chitinases. This enzymatic activity was discovered and further characterized by using mass spectrometry and chromatographic separation methods to detect oxidized products generated in the absence or presence of H(2)(18)O or (18)O(2). There are strong indications that similar enzymes exist that work on cellulose. Our findings not only demonstrate the existence of a hitherto unknown enzyme activity but also provide new avenues toward more efficient enzymatic conversion of biomass. 相似文献
87.
Faecal samples were collected from 1,190 wild cervids in Norway and analyzed for cysts/oocysts of the protozoan parasites Giardia and Cryptosporidium. Samples were from calves, yearlings and adults of moose (Alces alces), red deer (Cervus elaphus), roe deer (Capreolus capreolus) and reindeer (Rangifer tarandus) shot during the hunting season. Cryptosporidium was found in 15 (3.3%) of 455 moose, 1 (0.3%) of 289 red deer, 18 (6.2%) of 291 roe deer, but was not found in any of 155 reindeer. Giardia was found in 56 (12.3%) moose, 5 (1.7%) red deer, 45 (15.5%) roe deer and 11 (7.1%) reindeer. The calves had the highest prevalence of infection, but this was only statistically significant for Giardia in moose and for Cryptosporidium and Giardia in roe deer. Calves generally had the highest intensity of infection, but this difference was only statistically significant for calves with Giarda and the highest intensity of infection. Both Giardia and Cryptosporidium were found in samples from several geographical areas, indicating that these parasites are distributed among the cervid population in all parts of Norway, especially in moose and roe deer. This is the first published report of Cryptosporidium in moose and of Giardia in reindeer. 相似文献
88.
Carlos Henry Loáisiga Agnese Kolodinska Brantestam Oscar Diaz Björn Salomon Arnulf Merker 《Genetic Resources and Crop Evolution》2011,58(7):1021-1028
Teosintes are the closest relatives to modern maize, Zea mays L. ssp. mays. They are wild grasses with a native distribution area from Mexico to Nicaragua and represent an important genetic resource.
However, the genetic diversity of Nicaraguan teosinte (Zea nicaraguensis Iltis et Benz) has not yet been determined. This teosinte species has decreased in the last 25 years and now must be regarded
as an endangered species. An analysis of the genetic diversity of Zea nicaraguensis was carried out in a total of 240 individuals from seven populations. Eleven Simple Sequences Repeat (SSR) primer pairs were
used. A total of 42 alleles were found, the range of alleles per locus was 2–5 (mean 3.8) and the numbers of genotypes varied
between primers. The primer Bnlg 1538 showed the highest value, with 45 genotypes through all populations. The genetic diversity observed (Ho) between all
populations varied from 0.51 to 0.63, with an average of 0.563. One of the populations had as many as 40 alleles. Analysis
of molecular variance (AMOVA) revealed that most of the variation was within population, at a significantly high level (P < 0.001). Rare alleles were detected in all populations, but unique alleles were only found in four populations. These results
are highly relevant when developing conservation strategies and show that preserving populations in their natural habits is
highly important. 相似文献
89.
90.
Bj?rn Berger Andreas Brühschwein Lina Eddicks Andrea Meyer-Lindenberg 《The Canadian veterinary journal. La revue veterinaire canadienne》2016,57(4):377-381
A unicameral bone cyst in the proximal humerus of a 3-year-old Norwegian forest cat was diagnosed by dynamic contrast-enhanced magnetic resonance imaging, surgical exploration, and histopathology. Surgical curettage and incorporation of bone cement led to full recovery. An osteosarcoma developed at the surgical site 17 months later. Thoracic radiographs showed pulmonary lesions consistent with metastasis. 相似文献