全文获取类型
收费全文 | 1507篇 |
免费 | 103篇 |
国内免费 | 2篇 |
专业分类
林业 | 68篇 |
农学 | 27篇 |
基础科学 | 17篇 |
252篇 | |
综合类 | 264篇 |
农作物 | 48篇 |
水产渔业 | 84篇 |
畜牧兽医 | 670篇 |
园艺 | 43篇 |
植物保护 | 139篇 |
出版年
2023年 | 8篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 32篇 |
2019年 | 25篇 |
2018年 | 23篇 |
2017年 | 26篇 |
2016年 | 27篇 |
2015年 | 29篇 |
2014年 | 28篇 |
2013年 | 72篇 |
2012年 | 82篇 |
2011年 | 109篇 |
2010年 | 69篇 |
2009年 | 42篇 |
2008年 | 110篇 |
2007年 | 110篇 |
2006年 | 101篇 |
2005年 | 94篇 |
2004年 | 86篇 |
2003年 | 82篇 |
2002年 | 106篇 |
2001年 | 20篇 |
2000年 | 21篇 |
1999年 | 19篇 |
1998年 | 21篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 12篇 |
1989年 | 18篇 |
1988年 | 5篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1974年 | 5篇 |
1971年 | 3篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1962年 | 3篇 |
排序方式: 共有1612条查询结果,搜索用时 406 毫秒
71.
Dana M. Calhoun Paula A. Schaffer Jacklyn R. Gregory Katherine M. Hardy Pieter T. J. Johnson 《Journal of aquatic animal health》2015,27(4):185-191
Infections by the digenetic trematode, Ribeiroia ondatrae, cause severe limb malformations in many North American amphibians. Ribeiroia ondatrae also infects fishes as second intermediate hosts, but less is known about the pathology and immune responses initiated in infected fish, even though reports of infected fish date back to early 1900s. To this end, we experimentally exposed juvenile Bluegills Lepomis macrochirus to three doses of R. ondatrae cercariae and monitored the pathology, parasite infection success, and humoral responses over 648 h. All exposed fish became infected with metacercariae, and the average infection load increased with exposure dose. Histologically, infection was associated with acute hemorrhages in the lateral line and local dermis at 36 h, followed by progressive granulomatous inflammation that led to the destruction of encysted metacercariae. Correspondingly, over the course of 648 h we observed an 85% decline in average infection load among hosts, reflecting the host's clearance of the parasite. Infection was not associated with changes in fish growth or survival, but did correlate with leukocytosis and neutrophilia in circulating host blood. Understanding the physiological responses of R. ondatrae in Bluegill will help to clarify the ecological effects of this parasite and provide a foundation for subsequent comparisons into its effects on behavior, individual health, and population dynamics of Bluegill.
Received March 4, 2015; accepted August 9, 2015 相似文献
72.
73.
LoCascio RG Ninonuevo MR Freeman SL Sela DA Grimm R Lebrilla CB Mills DA German JB 《Journal of agricultural and food chemistry》2007,55(22):8914-8919
The molecular basis by which human breast milk supports the development of a protective intestinal microbiome in infants is unknown. After lactose and lipids, human milk oligosaccharides (HMOs) are quantitatively the third largest and most diverse component of breast milk. In this work, glycomic profiling of HMO consumption by bifidobacteria using Fourier transform ion cyclotron resonance mass spectrometry reveals that one species, Bifidobacterium longum biovar infantis ATCC 15697, an isolate from the infant gut, preferentially consumes small mass oligosaccharides, representing 63.9% of the total HMOs available. These HMOs were detected in human breast milk at the onset and constantly through the first month of lactation by use of high performance liquid chromatography-chip time-of-flight mass spectrometry. Further characterization revealed that strain ATCC 15697 possesses both fucosidase and sialidase activities not present in the other tested strains. This work provides evidence that these small mass HMOs are selectively metabolized by select bifidobacterial strains and represent a potential new class of bioactive molecules functioning as prebiotics to facilitate a protective gut colonization in breast-fed newborns. 相似文献
74.
Bruce TJ Hooper AM Ireland L Jones OT Martin JL Smart LE Oakley J Wadhams LJ 《Pest management science》2007,63(1):49-56
Field-trapping experiments with synthetic 2,7-nonadiyl dibutyrate, the female-produced sex pheromone of the orange wheat blossom midge, Sitodiplosis mosellana (Géhin), demonstrated that pheromone traps were highly attractive to males and caught very few non-target organisms. Different formulations of pheromone were tested to identify the optimum release rate and dispenser type for use in pheromone traps in the UK. Key findings were that racemic pheromone was as effective as enantiomerically pure (2S,7R)-2,7-nonadiyl dibutyrate, that release rates higher than 0.5 microg day(-1) were not necessary and that the optimal formulation was a 1 mg pheromone loading in a rubber septum. Pheromone traps gave a reliable indication of peak midge emergence, onset of flight and abundance of midges throughout the season. A strong correlation between maximum trap catch and crop infestation levels was obtained. 相似文献
75.
76.
Weiwei Yan Kang-Soon Shin Shih-Jon Wang Hua Xiang Thomas Divers Sean McDonough James Bowman Anne Rowlands Bruce Akey Hussni Mohamed Yung-Fu Chang 《Journal of veterinary science (Suw?n-si, Korea)》2014,15(2):249-258
Clostridium (C.) difficile is a common cause of nosocomial diarrhea in horses. Vancomycin and metronidazole have been used as standard treatments but are only moderately effective, which highlights the need for a novel alternative therapy. In the current study, we prepared antiserum of equine origin against both C. difficile toxins A and B as well as whole-cell bacteria. The toxin-neutralizing activities of the antibodies were evaluated in vitro and the prophylactic effects of in vivo passive immunotherapy were demonstrated using a conventional mouse model. The data demonstrated that immunized horses generated antibodies against both toxins A and B that possessed toxin-neutralizing activity. Additionally, mice treated with the antiserum lost less weight without any sign of illness and regained weight back to a normal range more rapidly compared to the control group when challenged orally with 107
C. difficile spores 1 day after serum injection. These results indicate that intravenous delivery of hyperimmune serum can protect animals from C. difficile challenge in a dose-dependent manner. Hence, immunotherapy may be a promising prophylactic strategy for preventing C. difficile infection in horses. 相似文献
77.
Reducing rice field algae and cyanobacteria abundance by altering phosphorus fertilizer applications
In California’s water-seeded rice systems, algal/cyanobacterial biomass can be a problem during rice establishment and can lead to yield reductions. Laboratory, enclosure, and field-scale experiments were established to evaluate the effects of fertilizer P management on algal/cyanobacterial growth. Two field-scale experiments evaluated the response of algal/cyanobacterial growth to three P management strategies: conventional surface applied, incorporated into the soil, and delaying P applications by 30 days. Results from these experiments indicated rice fields that received conventional surface-applied P fertilizer had 4–8 times more algal/cyanobacterial biomass and 3–11 times higher concentrations of soluble reactive phosphate (SRP) than those in which P fertilizer was incorporated or delayed. Laboratory experiments evaluated the ability of field water to support growth of Nostoc spongiaeforme. Results indicate that water from the incorporated or delayed P application fields was P limited for N. spongiaeforme growth. Water from the surface-applied fields was not P limited. Enclosure experiments evaluated the effects of delayed P applications on algal/cyanobacterial biomass and rice yields. Algal/cyanobacterial cover and biomass increased in enclosures which received added P. Soluble reactive phosphate concentrations were also significantly greater in these enclosures. Delaying the application by up to 28 days did not reduce rice yields in the enclosures. One management implication is that reducing SRP concentrations early in the season in rice field water will result in reduced algal/cyanobacterial biomass. Strategies to reduce water SRP include incorporating fertilizer P or delaying the P application by up to 30 days. 相似文献
78.
The concentrations of monoamines in the hypothalamus were determined in yellow perch Perca flavescens before and after injection with lipopolysaccharide (LPS; 3 mg kg−1 fish weight) or saline to test for the presence of neurochemical changes potentially associated with changes in plasma cortisol
characteristic of intraperitoneal (ip) challenge with LPS. In the first experiment, yellow perch were injected with saline
or LPS and the hypothalamus removed and plasma sampled before and at 0.5, 1.5, 3.0, and 6 h after injection. Plasma cortisol
was elevated in both saline- and LPS-injected fish through 1.5 h after injection and returned to levels resembling pre-injection
by 3 h after injection. Significantly higher amounts of cortisol in plasma from LPS-injected relative to saline-injected fish
were observed 6 h following injection. A significant decrease relative to levels observed 0.5–3 h after handling was observed
in serotonin concentrations at 6 h following LPS and saline injection with a concomitant increase in the ratio of 5-hydroxyindoleacetic
acid:serotonin. In the second experiment, hypothalamic monoamines were sampled before and at 3, 6, 9, 12, and 24 h after injection
with LPS or saline. Significant increases from pre-injection levels were observed in the ratio 5-hydroxyindoleacetic acid:serotonin
at 9, 12, and 24 h after injection, but no differences were detected between LPS- and saline-injected fish. These results
support a model linking serotonergic system activation following handling stress, but no correlations with the sustained elevations
of plasma cortisol associated with inflammatory challenge were observed. 相似文献
79.
Ryan Daly Denham Parker Geremy Cliff Gareth L. Jordaan Nkabi Nomfundo Rhett H. Bennett Bruce Q. Mann 《水产资源保护:海洋与淡水生态系统》2021,31(4):777-788
- The white-spotted wedgefish (Rhynchobatus djiddensis) is a Critically Endangered shark-like ray in the family Rhinidae. Throughout its Western Indian Ocean distribution, it is targeted for its valuable meat and fins and is reported to have undergone major population declines. However, there remains a need for species specific time-series data to accurately assess localized population declines.
- This study used two independent long-term (37 and 40 years) time-series catch data from competitive shore angling and shark nets to investigate the size composition and catch per unit effort (CPUE) and conduct a risk assessment for the population on the east coast of South Africa.
- From 1977 to 2017 the competitive shore fishery captured 7,703 individual R. djiddensis, whilst shark nets in the same region captured 2,856 individuals from 1981 to 2017. Individuals captured in the nets had a sex ratio of 1.8:1 females to males, and were larger than those caught by the anglers. Although the mean annual sizes of net-caught individuals were above the size of reported sexual maturity, there was little evidence to suggest that any individuals captured were reproductively active.
- Both the competitive shore fishery and shark net catches exhibited strong seasonal trends with the majority of R. djiddensis catches occurring from October to May peaking in austral summer. Standardized CPUE from the competitive shore fishery declined substantially between 1977 and 2017 and shark net catches exhibited a significant (p < 0.05) fourfold decline in annual nominal CPUE from 1981 to 2017.
- Ultimately, a risk assessment showed a 65.1% decline in abundance over a period of three generation lengths, which indicates that the sampled population of R. djiddensis in South Africa should be classified as Endangered according to the IUCN Red List using criterion A2b. The conservation implications of this are discussed.
80.
There is a wealth of evidence showing that a moderate level of non-stop exercise improves the growth and feed conversion of
many active fishes. A diverse number of active fish are currently being farmed, and an optimal level of exercise may feasibly
improve the production efficiency of these species in intensive culture systems. Our experiments have set out to resolve the
growth benefits of juvenile New Zealand yellowtail kingfish (Seriola lalandi) enforced to swim in currents at various speeds over two temperatures (14.9 and 21.1°C). We also probed potential sources
of physiological efficiency in an attempt to resolve how growth is enhanced at a time of high energetic expenditure. Results
show that long-term exercise yields a 10% increase in growth but this occurs in surprisingly low flows (0.75 BL s−1) and only under favourable environmental temperatures (21.1°C). Experiments using a swim flume respirometer indicate that
exercise training has no effect on metabolic scope or critical swimming speeds but it does improve swimming efficiency (lower
gross costs of transport, GCOT). Such efficiency may potentially help reconcile the costs of growth and exercise within the
range of available metabolic energy (scope). With growth boosted in surprisingly low flows and elevated water temperatures
only, further investigations are required to understand the bioenergetics and partitioning of costs in the New Zealand yellowtail
kingfish. 相似文献