全文获取类型
收费全文 | 454篇 |
免费 | 31篇 |
专业分类
林业 | 10篇 |
农学 | 13篇 |
49篇 | |
综合类 | 91篇 |
农作物 | 26篇 |
水产渔业 | 58篇 |
畜牧兽医 | 194篇 |
园艺 | 12篇 |
植物保护 | 32篇 |
出版年
2023年 | 4篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 5篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 5篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 22篇 |
2012年 | 19篇 |
2011年 | 15篇 |
2010年 | 9篇 |
2009年 | 12篇 |
2008年 | 14篇 |
2007年 | 21篇 |
2006年 | 15篇 |
2005年 | 14篇 |
2004年 | 14篇 |
2003年 | 20篇 |
2002年 | 23篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1983年 | 4篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1974年 | 6篇 |
1972年 | 3篇 |
1971年 | 7篇 |
1970年 | 8篇 |
1969年 | 3篇 |
1896年 | 5篇 |
1888年 | 3篇 |
1884年 | 4篇 |
排序方式: 共有485条查询结果,搜索用时 734 毫秒
81.
Amara H. Estrada Herbert W. Maisenbacher III VMD Robert Prošek DVM MS Jesse Schold PhD Melanie Powell BS James M. VanGilder BS 《Journal of Veterinary Cardiology》2009,11(2):79-88
Objective
To compare left ventricular synchronization and systolic performance with transvenous pacing of the right ventricular apex (RVA), left ventricular free wall (LVF) or simultaneous pacing of the RVA and LVF (BiV).Animals, materials and methods
Seven canine patients with complete heart block. Prospective study evaluating effect of pacing site. Twenty four hours following implantation of transvenous BiV pacing systems, electrocardiograms and echocardiograms were assessed during pacing from the: (1) Right Atrial Appendage/RVA (RAA/RVA), (2) RAA/LVF, and (3) RAA/BiV.Results
QRS duration was significantly shorter with BiV pacing versus LVF pacing (p < 0.001), or RVA pacing (p < 0.001). Echocardiographic indices of systolic performance fractional shortening (FS), ejection fraction (EF), cardiac output (CO) were significantly higher with BiV pacing than with pacing from the RVA (P = 0.023, 0.006, and 0.002 respectively). Cardiac output, measured by the biplane Simpson's method, was higher with LVF versus RVA pacing (P = 0.036). There was no difference in FS or EF when comparing LVF to RVA pacing. Tissue Doppler measurements of synchronization and systolic performance did not show any difference between pacing mode, but a significantly increased number of segments were seen to contract following aortic valve closure during LVF pacing (P = 0.0268) and RVA pacing (P = 0.0197) as compared to BiV pacing.Conclusions
Findings suggest that BiV pacing improves cardiac output and systolic performance versus RVA pacing. This improvement however, is not reflected in tissue Doppler indices of synchronization and systolic performance. 相似文献82.
Fontenelle JP Powell CC Hill AE Radecki SV Lappin MR 《Journal of Feline Medicine and Surgery》2008,10(1):41-46
Bartonella henselae has been implicated as a causative agent of chronic uveitis in people and in some cats. The objective of this study was to determine whether Bartonella species seroprevalence or titer magnitude varies among cats with uveitis, cats without ocular diseases recorded and healthy cats, while controlling for age and risk of flea exposure based on state of residence. There was no difference in seroprevalence rates or titer magnitude between cats with uveitis and cats with non-ocular diseases. Healthy cats were more likely to be seropositive for Bartonella species than cats with uveitis. The median Bartonella species titer was 1:64 for all groups, although healthy cats were more likely to have higher titers than cats with uveitis and cats with non-ocular disease. The results suggest that serum antibody tests alone cannot be used to document clinical uveitis associated with Bartonella species infection. 相似文献
83.
Salmon testes meal as a functional feed additive in fish meal and plant protein‐based diets for rainbow trout (Oncorhynchus mykiss Walbaum) and Nile tilapia (Oreochromis niloticus L.) fry 下载免费PDF全文
Kyeong‐Jun Lee Samad Rahimnejad Madison S Powell Frederick T Barrows Scott Smiley Peter J Bechtel Ronald W Hardy 《Aquaculture Research》2015,46(7):1590-1596
Fishery processing by‐products are a large resource from which to produce fishmeal and other products for a variety of uses. In this study, testes meal (TM) produced from pink salmon processing by‐product was evaluated as a functional ingredient in aquafeeds. Nile tilapia and rainbow trout fry were fed five isonitrogenous and isoenergetic experimental diets for 4 and 9 weeks respectively. Two diets were fishmeal‐based (FM) and three were plant protein‐based (PP). Salmon TM was added to the FM and PP diets at 7% to replace 20% of fishmeal protein (FMTM and PPTM respectively). An additional control diet was prepared in which fishmeal was added to the PP diet to supply an equivalent amount of protein as supplied by TM (PPFM). Inclusion of TM in both the FM‐ and PP‐based diets resulted in higher final body weights, although differences were only significant between rainbow trout fed FM or FMTM diets. Similar differences were calculated for other indices of fish performance, e.g. specific growth rate, feed conversion ratio, protein efficiency ratio and protein retention efficiency. Feed intake was significantly higher for fish fed FMTM compared with FM in rainbow trout. For tilapia, final weights were numerically higher, but not significantly different for fish fed diets containing TM compared with non‐TM diets (FM vs. FMTM; PP vs. PPTM). Performance of trout or tilapia fed the PPFM diet did not increase compared with the PP diet. The results indicate that TM addition to both FM and PP diets increased feed intake and also increased metabolic efficiency, demonstrating that TM can be a functional ingredient in aquafeeds. 相似文献
84.
L. Shen A.H. Estrada E. Côté M.A. Powell B. Winter K. Lamb 《Journal of Veterinary Cardiology》2017,19(2):144-152
Introduction
To determine the relationship between aortoseptal angle (AoSA) and the short- and long-term systolic pressure gradient (PG) reduction following combined cutting and high-pressure balloon valvuloplasty (CB/HPBV) in dogs with severe subaortic stenosis.Animals
Retrospective study of 22 client-owned dogs of various breeds with severe subaortic stenosis (mean left ventricular to aortic PG = 143 mmHg; range = 80–322 mmHg) that underwent CB/HPBV.Materials and methods
Initial angiographic and left apical and right-sided parasternal long-axis view echocardiographic video loops were used for measuring the angle between the plane of the interventricular septum and the longitudinal axis of the ascending aorta. The PG reduction ratio immediately after CB/HPBV and 6 and 12 months later were compared with AoSA.Results
Weak correlations were observed for all instances of PG reduction ratio and AoSA type. Significantly greater mean differences of PG reduction ratio were observed for angles >160° than for angles <160° at 24 h (>160° mean: 54.45, standard error [SE]: ±3.8; <160° mean: 39.88, SE: ±2.09), 6 months (>160° mean: 57.73, SE: ±10.9; <160° mean: 28.22, SE: ±3.42), and 12 months (>160° mean: 76.11, SE: ±17.5; <160° mean: 27.61, SE: ±6.44; p=0.003).Conclusions
Dogs with AoSA >160° on right-sided parasternal long-axis view echocardiograms responded with a greater PG reduction following CB/HPBV than did dogs with AoSA <160°. This suggests that AoSA is associated with long-term outcomes of CB/HPBV, and measurement could help in the evaluation of dogs that are candidates for CB/HPBV. 相似文献85.
Elaine C Fitches Howard A Bell Michelle E Powell Emma Back Chiara Sargiotti Robert J Weaver John A Gatehouse 《Pest management science》2010,66(1):74-83
BACKGROUND: The toxicity of a fusion protein, ButalT/GNA, comprising a venom toxin (ButaIT) derived from the red scorpion, Mesobuthus tamulus (F.), and Galanthus nivalis agglutinin (GNA), was evaluated under laboratory conditions against several pest insects. Insecticidal activity was compared with SFI1/GNA, a fusion comprising a venom toxin (SFI1) derived from the European spider Segestria florentina (Rossi) and GNA, which has been previously demonstrated to be effective against lepidopteran and hemipteran pests, and to GNA itself. RESULTS: Injection assays demonstrated that both fusion proteins were toxic to lepidopteran larvae, dipteran adults, coleopteran adults and larvae and dictyopteran nymphs. ButalT/GNA was more toxic than SFI1/GNA in all cases. GNA itself made a minor contribution to toxicity. Oral toxicity of ButalT/GNA towards lepidopteran pests was confirmed against neonate Spodoptera littoralis (Boisd.), where incorporation at 2% dietary protein resulted in 50% mortality and > 85% reduction in growth compared with controls. ButaIT/GNA was orally toxic to Musca domestica L. adults, causing 75% mortality at 1 mg mL?1 in aqueous diets and, at 2 mg g?1 it was orally toxic to Tribolium castaneum (Herbst.), causing 60% mortality and a 90% reduction in growth. CONCLUSIONS: Toxicity of the ButaIT/GNA recombinant fusion protein towards a range of insect pests from different orders was demonstrated by injection bioassays. Feeding bioassays demonstrated the potential use of the ButaIT/GNA fusion protein as an orally active insecticide against lepidopteran, dipteran and coleopteran pests. These experiments provide further evidence that the development of fusion protein technology for the generation of new, biorational, anti‐insect molecules holds significant promise. © Crown Copyright 2009. Reproduced with permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd. 相似文献
86.
LOYD E. Powell CHARLOTT Pratt 《The Journal of Horticultural Science and Biotechnology》2013,88(4):331-348
Growth substances extracted from the ovules of developing fruits of July Queen, Halehaven and Fall Late peaches–respectively early, midseason and late-maturing cultivars–were studied. Whole and fractionated extracts were bioassayed, and the growth of the fruit and the development of the seed were examined.Determination of “total” growth-promoting substances during the development of the fruits resulted in concentration curves that were generally similar from year to year. The seeds of each cultivar, regardless of its season of maturation, produced a first flush of growth substances that seemed to be correlated with either nucellus or endosperm development. The second and major growth substance peak came at the time of rapid embryo growth and maximum endosperm development. At this time fruits of July Queen ripened and abscissed. A third flush of growth substance was detected at the same time in Halehaven and Fall Late seeds, at which time the embryo was essentially complete. The mature fruits of Halehaven then abscissed, but Fall Late fruits remained on the tree for another three or four weeks before maturation and abscission. It was concluded that the concentration of seed growth substances as measured here was not related to the final-flush of growth of peach fruits, or to the abscission of mature fruits.In dissected ovules of Halehaven peaches the endosperm was the most concentrated source of total growth substances on a dry weight basis but, because of its small size, it contributed less of them on a per-seed basis than did the the integuments at first, and later the embryo. The nucellus was a minor source of growth substances, both on a concentration and on a per-ovule basis. Apparently, the total growth substances that constituted the second and major auxin peak in Halehaven peach ovules came mostly from the integuments, endosperm and embryo, whereas the third peak could be attributed almost entirely to substances from the embryo. These studies of individual ovule tissues were made after that period of development during which the first growth substance peak made its appearance.Studies of growth substances in the flesh of developing peach fruits revealed only trace amounts with no consistent pattern, although there is some evidence that a true picture may not have been obtained because of interference by inhibitors.Silica gel partition column chromatography showed the presence of several growth-promoting substances which changed qualitatively and quantitatively during the growing season. One of these was probably indole-3- acetic acid, its identification being based primarily on studies by gas chromatography and spectrophotofluorometry. 相似文献
87.
A. H. Marshall T. A. Williams M. T. Abberton T. P. T. Michaelson-Yeates P. Olyott H. G. Powell 《Grass and Forage Science》2004,59(1):91-99
Interspecific hybrids between white clover (Trifolium repens L.) and Caucasian clover (Trifolium ambiguum M. Bieb.) have been developed to introgress the rhizomatous growth habit into white clover, to increase persistence and drought tolerance. The forage quality of T. repens, T. ambiguum and the backcross 1 (BC1) and backcross 2 (BC2) hybrids and companion grass, when grown in mixtures with an intermediate perennial ryegrass (Lolium perenne L.) under a cutting‐only management, was measured. In vitro dry‐matter digestibility (DMD), water‐soluble carbohydrate (WSC) and crude protein (CP) concentrations of the legume and grass fractions were measured throughout the growing season over three harvest years. Trifolium repens had a lower WSC but a higher CP concentration than the perennial ryegrass companion in all harvest years and at all cuts. The legume fractions from the BC1 and BC2 hybrid plots had a higher WSC and a lower CP concentration but an in vitro DMD value comparable with white clover throughout the growing season and in each harvest year. The grass fractions from the mixtures with the backcross hybrids had a higher WSC and a lower CP concentration than the grass fraction from the T. repens plots, in all harvest years and throughout the growing season. No difference in in vitro DMD between parental species and backcross hybrids was observed. The implications of these results for the development of these hybrids and animal performance are discussed. 相似文献
88.
89.
Jessica K. Baron DVM DACVS-SA Sue A. Casale DVM DACVS Eric Monnet DVM PhD FAHA DACVS DECVS Philipp D. Mayhew BVM&S DACVS Jeffrey J. Runge DVM DACVS Christelle M. Follette DVM Kevin Phipps DVM Margaret E. Powell DVM Alicja I. Reczynska DVM Nathan T. Squire VMD Bruce A. Barton PhD John Berg DVM DACVS 《Veterinary surgery : VS》2020,49(Z1):O148-O155
90.
Catherine R. Back Henry L. Stennett Sam E. Williams Luoyi Wang Jorge Ojeda Gomez Omar M. Abdulle Thomas Duffy Christopher Neal Judith Mantell Mark A. Jepson Katharine R. Hendry David Powell James E. M. Stach Angela E. Essex-Lopresti Christine L. Willis Paul Curnow Paul R. Race 《Marine drugs》2021,19(2)
To tackle the growing problem of antibiotic resistance, it is essential to identify new bioactive compounds that are effective against resistant microbes and safe to use. Natural products and their derivatives are, and will continue to be, an important source of these molecules. Sea sponges harbour a diverse microbiome that co-exists with the sponge, and these bacterial communities produce a rich array of bioactive metabolites for protection and resource competition. For these reasons, the sponge microbiota constitutes a potential source of clinically relevant natural products. To date, efforts in bioprospecting for these compounds have focused predominantly on sponge specimens isolated from shallow water, with much still to be learned about samples from the deep sea. Here we report the isolation of a new Micromonospora strain, designated 28ISP2-46T, recovered from the microbiome of a mid-Atlantic deep-sea sponge. Whole-genome sequencing reveals the capacity of this bacterium to produce a diverse array of natural products, including kosinostatin and isoquinocycline B, which exhibit both antibiotic and antitumour properties. Both compounds were isolated from 28ISP2-46T fermentation broths and were found to be effective against a plethora of multidrug-resistant clinical isolates. This study suggests that the marine production of isoquinocyclines may be more widespread than previously supposed and demonstrates the value of targeting the deep-sea sponge microbiome as a source of novel microbial life with exploitable biosynthetic potential. 相似文献