全文获取类型
收费全文 | 1152篇 |
免费 | 72篇 |
国内免费 | 3篇 |
专业分类
林业 | 56篇 |
农学 | 24篇 |
基础科学 | 5篇 |
130篇 | |
综合类 | 191篇 |
农作物 | 39篇 |
水产渔业 | 157篇 |
畜牧兽医 | 573篇 |
园艺 | 26篇 |
植物保护 | 26篇 |
出版年
2023年 | 6篇 |
2022年 | 3篇 |
2021年 | 27篇 |
2020年 | 23篇 |
2019年 | 32篇 |
2018年 | 27篇 |
2017年 | 33篇 |
2016年 | 31篇 |
2015年 | 22篇 |
2014年 | 25篇 |
2013年 | 51篇 |
2012年 | 67篇 |
2011年 | 73篇 |
2010年 | 46篇 |
2009年 | 38篇 |
2008年 | 59篇 |
2007年 | 65篇 |
2006年 | 81篇 |
2005年 | 59篇 |
2004年 | 59篇 |
2003年 | 55篇 |
2002年 | 63篇 |
2001年 | 26篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1976年 | 3篇 |
1972年 | 6篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1936年 | 3篇 |
1902年 | 2篇 |
排序方式: 共有1227条查询结果,搜索用时 15 毫秒
51.
Suraj Gunawardana Dulari Thilakarathne Indra S. Abegunawardana Preeni Abeynayake Colin Robertson Craig Stephen 《Tropical animal health and production》2014,46(7):1105-1112
A study of the risk factors associated with mastitis in Sri Lankan dairy cattle was conducted to inform risk reduction activities to improve the quality and quantity of milk production and dairy farmer income. A cross-sectional survey of randomly selected dairy farms was undertaken to investigate 12 cow and 39 herd level and management risk factors in the Central Province. The farm level prevalence of mastitis (clinical and subclinical) was 48 %, similar to what has been found elsewhere in South and Southeast Asia. Five cow level variables, three herd level variables, and eight management variables remained significant (p?0.05) in the final logistic regression analysis. Expected risk factors relating to unhygienic environments and inadequate knowledge or practice of mastitis control were found. Other factors included parity, milk yield, milking practices, access to veterinary services, use of veterinary products, stall structure, and stall hygiene. Many of the risk factors could be addressed by standard dairy cattle management techniques, but implementation of mastitis control programs as a technical approach is likely to be insufficient to achieve sustainable disease control without consideration of the social and political realities of smallholder farmers, who are often impoverished. 相似文献
52.
Emily C. Glunk Craig C. Sheaffer Marcia R. Hathaway Krishona L. Martinson 《Journal of Equine Veterinary Science》2014
The impact of horse preference and grass morphology on grazing muzzle effectiveness has not been investigated. The objective of this study was to determine the effectiveness of grazing muzzle use at reducing forage intake when horses grazed grasses with different morphology and preferences. The study was conducted in 2012 and 2013. Four horses were grazed in 2012, and three horses were grazed in 2013. Four species of perennial cool-season grasses were grazed in 2012 including Kentucky bluegrass (Poa pratensis L.), meadow fescue (Schedonorus pratensis Huds.), perennial ryegrass (Lolium perenne L.), and reed canarygrass (Phalaris arundinacea L.). In 2013, only Kentucky bluegrass and reed canarygrass were grazed because of winter kill of other species. Horses were allowed to graze a small pasture seeded with an individual species for 4 hours each day in June and August of 2012 and August and September of 2013. Horses grazed the same grass species for two consecutive days, one day with a muzzle and one day without. Before and after each grazing, a strip was mechanically harvested to determine initial and residual herbage mass. The difference was used to estimate forage intake. The effectiveness of a grazing muzzle was not affected by forage species (P ≥ .05). Use of a grazing muzzle decreased the amount of forage consumed by an average of 30% compared with not using a grazing muzzle (P < .0001). Results will aid horse owners and professionals in estimating forage intake of muzzled horses on pasture. 相似文献
53.
A novel, proprietary, oral suspension of trimethoprim plus sulfadiazine (TMP/SDZ) had no serious adverse effects on clinical, laboratory, or pathologic parameters of mature horses when administered at up to five times the intended combined dosage of 24 mg/kg twice daily for 30 consecutive days. Loose feces was the most common observation that was likely related to TMP/SDZ treatment, and the incidence of loose feces was greater in groups treated with higher dosages of TMP/SDZ. However, all episodes were self-limiting, and no horses were treated for loose feces. 相似文献
54.
Jacqueline Wilson Craig W. Osenberg Colette M. St. Mary Craig A. Watson William J. Lindberg 《Aquarium Sciences and Conservation》2001,3(1-3):95-105
Artificial reefs may provide a useful tool to enhance production of marine ornamentals and to divert detrimental harvesting activities from sensitive natural habitat. The efficacy of this strategy depends, in part, on the extent to which artificial reefs contribute to new production (vs. attract fishes from natural habitat) and therefore benefit harvested populations on a local and regional basis. Here the attraction and production hypotheses and their application to marine ornamentals are presented. Specifically, it is discussed how the strength and timing of density dependence can affect the response of fish population dynamics to artificial reefs. In addition to this discussion, examples of density dependence in marine ornamentals and related reef fishes are provided. Based on this information, a simple conceptual model is presented to clarify the role of density dependence, and this is followed by a discussion on the use of artificial reefs in the management and production of marine ornamentals. Finally, unresolved scientific issues that remain to be addressed are provided. 相似文献
55.
56.
57.
Andrea D Stapp Craig A Gifford Dennis M Hallford Jennifer A Hernandez Gifford 《畜牧与生物技术杂志(英文版)》2014,5(1):2
Background
Heifers not used as breeding stock are often implanted with steroids to increase growth efficiency thereby altering hormone profiles and potentially changing the environment in which ovarian follicles develop. Because bovine granulosa cell culture is a commonly used technique and often bovine ovaries are collected from abattoirs with no record of implant status, the objective of this study was to determine if the presence of an implant during bovine granulosa cell development impacts follicle stimulating hormone-regulated steroidogenic enzyme expression. Paired ovaries were collected from 16 feedlot heifers subjected to 1 of 3 treatments: non-implanted (n = 5), Revalor 200 for 28 d (n = 5), or Revalor 200 for 84 d (n = 6). Small follicle (1 to 5 mm) granulosa cells were isolated from each pair and incubated with phosphate buffered saline (n = 16) or 100 ng/mL follicle stimulating hormone (n = 16) for 24 h.Results
Granulosa cells of implanted heifers treated with follicle stimulating hormone produced medium concentrations of progesterone similar (P = 0.22) to non-implanted heifers, while medium estradiol concentrations were increased (P < 0.10) at 28 and 84 d compared to non-implanted heifers indicating efficacy of treatment. Additionally, real-time PCR analysis in response to follicle stimulating hormone treatment demonstrated a decrease in steroidogenic acute regulatory protein (P = 0.05) mRNA expression in heifers implanted for 84 d and an increase in P450 side chain cleavage mRNA in granulosa cells of heifers implanted for 28 (P < 0.10) or 84 d (P < 0.05) compared to non-implanted females. However, no difference in expression of 3-beta-hydroxysteroid dehydrogenase (P = 0.57) and aromatase (P = 0.23) were demonstrated in implanted or non-implanted heifers.Conclusions
These results indicate follicles which develop in the presence of high concentrations of androgenic and estrogenic steroids via an implant tend to demonstrate an altered capacity to respond to follicle stimulating hormone stimulation. Thus, efforts should be made to avoid the use of implanted heifers to study steroidogenesis in small follicle granulosa cell culture systems. 相似文献58.
Hung-Yueh Yeh Craig A. Shoemaker Phillip H. Klesius 《Fish physiology and biochemistry》2006,32(1):83-92
The hemoglobin-β gene of channel catfish, Ictalurus punctatus, was cloned and sequenced. Total RNA from head kidneys was isolated, reverse transcribed and amplified. The sequence of the
channel catfish hemoglobin-β gene consists of 600 nucleotides. Analysis of the nucleotide sequence reveals one open reading frame and 5′- as well as 3′-untranslated
regions. The open reading frame of the sequence potentially encodes 148 amino acids with a calculated molecular mass of 16.3 kDa.
The pI and charge at pH 7.0 of the deduced hemoglobin-β protein were 7.28 and 0.47, respectively. Overall, 22 amino acid residues were conserved throughout the sequences, including
His64 and His93, the sites for heme-binding. Unlike the counterpart of other common cultured fish such as Salmo salar, Oncorhynchus nerka, Oncorhynchus mykiss, Cyprinus carpio and Ctenopharyngodon idella, the hemoglobin-β of channel catfish did not have cysteine. The amino acid sequence of channel catfish hemoglobin-β shows 84% homology with that of Silurus asotus (both are in the order Siluriformes). However, comparison with those of other fish species shows homology ranging from 53 to 68%. Structural analysis by the
3D-PSSM program displays that channel catfish hemoglobin-β has eight α-helices, A–H. 相似文献
59.
Excavating sponges that are destructive to farmed pearl oysters in Western and Northern Australia 总被引:1,自引:0,他引:1
Species of the family Clionaidae (Porifera: Demospongiae) that excavate shell of the silver‐lip pearl oyster, Pinctada maxima, in north Western and Northern Australia are described. Two species belong to the genus Cliona and one species to the closely related genus Pione. Cliona orientalis has only recently been reported from Australia in living and dead coral on the Great Barrier Reef, and this is the first report of this species from north Western and Northern Australia. Cliona dissimilis is reported from Australia for the first time. Pione velans was first described from Shark Bay, Western Australia and this study extends its distribution from Albany, south Western Australia to Port Bremer in the Northern Territory. The most common species found was C. dissimilis. Pione velans and C. orientalis were also present, although the latter species was rare. Cliona dissimilis and P. velans were found to be sexually reproductive in some shells with specimens of C. dissimilis with oocytes in May and P. velans in September 1999. Egg development was synchronous, indicating that the sponges were oviparous and would broadcast gametes in a spawning event. 相似文献
60.
Oxygen uptake in the Antarctic teleost Pagothenia borchgrevinki. Limitations imposed by X-cell gill disease 总被引:1,自引:0,他引:1
Fish in a population of Pagothenia borchgrevinki in McMurdo Sound, Antarctica, are affected by a gill disease (X-cell disease) which causes tissue hyperplasia that results
in a decreased gill surface area and an increased water/blood diffusion distance. P. borchgrevinki acquires 95% of its oxygen via the gills, but damage to the gills by X-cell disease did not affect this function. There was
no compensatory shift to cutaneous respiration. X-cell disease reduced the ability for oxygen uptake at low ambient PO
2 and the decreased uptake was related to the extent of the disease. O
2 max was greatly reduced in X-cell affected fish and substantially reduced their aerobic potential. This effect may impair
the ability of diseased fish to catch prey and avoid predators. 相似文献