全文获取类型
收费全文 | 245824篇 |
免费 | 12515篇 |
国内免费 | 174篇 |
专业分类
林业 | 12535篇 |
农学 | 8388篇 |
基础科学 | 1639篇 |
30950篇 | |
综合类 | 41356篇 |
农作物 | 10864篇 |
水产渔业 | 13240篇 |
畜牧兽医 | 117937篇 |
园艺 | 3854篇 |
植物保护 | 17750篇 |
出版年
2018年 | 5479篇 |
2017年 | 5841篇 |
2016年 | 4281篇 |
2015年 | 2804篇 |
2014年 | 3498篇 |
2013年 | 8920篇 |
2012年 | 7100篇 |
2011年 | 9826篇 |
2010年 | 6933篇 |
2009年 | 6290篇 |
2008年 | 8961篇 |
2007年 | 8805篇 |
2006年 | 7085篇 |
2005年 | 6621篇 |
2004年 | 6409篇 |
2003年 | 6574篇 |
2002年 | 6093篇 |
2001年 | 7121篇 |
2000年 | 7002篇 |
1999年 | 5594篇 |
1998年 | 2402篇 |
1997年 | 2377篇 |
1996年 | 2219篇 |
1995年 | 2704篇 |
1994年 | 2418篇 |
1993年 | 2310篇 |
1992年 | 4669篇 |
1991年 | 4882篇 |
1990年 | 4836篇 |
1989年 | 4839篇 |
1988年 | 4446篇 |
1987年 | 4527篇 |
1986年 | 4665篇 |
1985年 | 4510篇 |
1984年 | 3725篇 |
1983年 | 3364篇 |
1982年 | 2334篇 |
1981年 | 2154篇 |
1979年 | 3458篇 |
1978年 | 2875篇 |
1977年 | 2421篇 |
1976年 | 2327篇 |
1975年 | 2471篇 |
1974年 | 3057篇 |
1973年 | 3107篇 |
1972年 | 2975篇 |
1971年 | 2695篇 |
1970年 | 2546篇 |
1969年 | 2508篇 |
1967年 | 2159篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Carrillo JM Sopena JJ Rubio M Redondo JI Serra I Soler C 《Veterinary surgery : VS》2005,34(4):387-392
OBJECTIVE: To evaluate the use of polyamide bands, manufactured for securing electrical cables, for repair of oblique femoral fractures in rabbits. STUDY DESIGN: Experimental study. ANIMALS: Twelve nulliparous, 21-25-week-old, California female rabbits. METHODS: Rabbits were divided into 3 groups (n=4) and studied for 14, 28, or 56 days. A Z-shaped mid-diaphyseal femoral osteotomy was repaired with a 2.5 mm intramedullary pin and a polyamide 6.6 cerclage band. Healing was evaluated at intervals by physical examination, limb use, femoral radiographs, and callus histology. RESULTS: Rabbits had early limb use with good wound healing. From the 1st day, movement of the hip and stifle joints was satisfactory. Radiographically, fractures were healed at 28 days. Histologically, there was no foreign body reaction and bone healing was normal. CONCLUSION: Nylon cerclage band application was accomplished easily, maintained reduction, and resulted in good healing and limb use. CLINICAL RELEVANCE: Sterilized nylon bands, manufactured for electrical use, can be used for cerclage in rabbits. 相似文献
994.
Gunn GJ Saatkamp HW Humphry RW Stott AW 《Preventive veterinary medicine》2005,72(1-2):149-62; discussion 215-9
The objective of this paper is to present a preliminary assessment of variation in the economic impact of bovine viral diarrhoea virus (BVDV) at dairy farm level between a sample of nations within the EU and hence assess differences in pressure to respond to this disease that may be impeding progress in control and hence restricting collective benefits from healthier livestock. We used a questionnaire to obtain national average values of key epidemiological and economic parameters for a typical dairy farm from BVDV experts in the countries concerned. These parameters were converted into assessments of economic impact using a computer simulation model. Uncontrolled output losses for a BVDV-na?ve herd with virus introduced in year 1 of a 10-year epidemic represented 22, 7, 8, 5, 8 and 20% of the BVDV-free annuity for the UK, Northern Portugal, Holland, Norway, Italy and Germany, respectively. Differences between countries will be widened by differences in the risk of acquiring BVDV. These will be much reduced in countries, such as Norway that have a national BVDV eradication programme. Farmers in such countries can therefore justify spending much less on maintaining BVDV-free status than BVDV-free farms in other countries. This result illustrates the paradox that in countries where BVDV prevalence is high, farmers have least to gain from unilateral BVDV eradication because of the high cost of maintaining freedom from the disease. We discuss this issue in the light of increasing recognition at international level of the importance of BVDV control. 相似文献
995.
Verhoeckx KC Doornbos RP van der Greef J Witkamp RF Rodenburg RJ 《Journal of veterinary pharmacology and therapeutics》2005,28(6):531-537
In this study the anti-inflammatory properties of zilpaterol, a beta2-adrenergic receptor (AR) agonist specifically developed as a growth promoter in cattle were investigated. Although zilpaterol has a different structure compared with the beta2-AR agonists known to date, it was noted that it was able to bind to both the beta2-AR (Ki = 1.1 x 10(-6)) and the beta1-AR (Ki = 1.0 x 10(-5)). Using lipopolysaccharide (LPS)-exposed U937 macrophages, the production of cyclic adenosine-3',5'-cyclic monophosphate (cAMP) and tumor necrosis factor alpha (TNF-alpha) were investigated. Zilpaterol inhibited TNF-alpha release and induced intracellular cAMP levels in a dose-dependent manner. The inhibition of TNF-alpha release and induction of cAMP production was mainly mediated via the beta2-AR, as indicated by addition of beta1- and beta2-specific antagonists. The effects of zilpaterol were investigated in LPS-treated male Wistar rats after pretreatment with zilpaterol. Zilpaterol dosed at 500 microg/kg body weight reduced the TNF-alpha plasma levels. In conclusion, zilpaterol is a beta2-adrenergic agonist and an inhibitor of TNF-alpha production induced by LPS both in vivo and in vitro. 相似文献
996.
Approximately 88% of Norwegian dairy cattle are housed in tie stalls. Free stall housing for all dairy cattle will be implemented within 20 years. This means that the majority of existing stalls will be rebuilt in the near future. Fifty-seven free stall herds of the Norwegian Red breed were randomly selected and 1547 cows and 403 heifers were trimmed by 13 claw trimmers during the late winter and spring of 2002. The claw trimmers had been taught diagnosing and recording of claw lesions. Environment, management- and feeding routines were also recorded. Fifty-three herds had concrete slatted alleys while 4 had solid concrete. Thirty-five herds had concrete as a stall base, while 17 had rubber mats, 2 had wood and 3 had deep litter straw beds. The prevalence of lameness was 1.6% in hind claws. Models for lameness and claw lesions were designed to estimate the influence of different risk factors and to account for the cluster effects within herd and claw trimmer. Detected risk factors for lameness were: parity three and above and narrow cubicles; for heel horn erosions: lactation stage around 5-7 months after calving and solid concrete alleys; for haemorrhages of the white line: lactation stage around 3-5 months after calving and solid concrete alleys; for haemorrhages of the sole: parity one, lactation stage around 5-7 months after calving and short cubicles, for white line fissures: slatted concrete alleys; for asymmetrical claws: parities two and above and for corkscrewed claws: solid concrete alleys. The prevalence of lameness in heifers was low, however 29% had one or more claw lesions. Heifers that were housed in pens or free stalls had more heel-horn erosions, haemorrhages of the sole and white-line fissures than heifers in tie stalls. As new free stalls are being built, it is important to optimise the conditions for claw health. 相似文献
997.
OBJECTIVE: To evaluate biochemical analytes in vitreous humor collected after death in West Indian manatees (Trichechus manatus latirostris). DESIGN: Prospective study. ANIMALS: 73 West Indian manatees of various ages and both sexes. PROCEDURE: The condition of manatee carcasses submitted for routine postmortem examination was categorized as fresh, moderately autolyzed, or severely autolyzed. The eyes were removed, frozen for shipping, and thawed on arrival at the laboratory. Vitreous humor was extracted, and various biochemical analytes were measured. Values for each analyte were compared with published reference ranges for corresponding biochemical analytes in serum. Values were also compared among the carcass condition groups. RESULTS: Creatinine and urea nitrogen concentrations in vitreous humor were significantly higher in severely autolyzed carcasses than in fresh carcasses. Potassium concentrations in vitreous humor were significantly higher in moderately autolyzed carcasses than in fresh carcasses but were highly variable in severely autolyzed carcasses. These data were consistent with those reported in other species. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that measurement of biochemical analytes in vitreous humor of manatees is feasible and has potential for assisting in the postmortem diagnosis of certain metabolic, renal, and nutritional diseases; determining severity of autolysis at time of necropsy; and determining the time of occurrence of human-induced trauma. 相似文献
998.
Canine eosinophilic granuloma (CEG) is a rare skin disease of unknown origin. It has been reported in Siberian huskies, Cavalier King Charles spaniels and occasionally in other breeds. The lesions comprise nodules or plaques, mostly localised in the oral cavity. A case of a single cutaneous nodular lesion of CEG on the eyelid of a Siberian husky is described. Complete remission was achieved with oral glucocorticoid treatment. 相似文献
999.
REASONS FOR PERFORMING STUDY: Previous studies have implicated tension in the deep digital flexor tendon (DDFT) in the rotation of the distal phalanx (DP) after the breakdown of the dorsal laminae caused by laminitis. Howeveer, once the DP has rotated, the DDFT should become shorter, reducing the force it exerts on the DP. OBJECTIVE: To compare DDFT force and ground reaction forces (GRFs) in normal ponies and ponies with rotation of the DP as a sequel to laminitis. METHODS: Six normal ponies (Group 1) and 6 sound ponies with 6-13 degrees of rotation of the DP in relation to the dorsal hoof wall (Group 2) were assessed at trot using forceplate and motion analysis. The force in the DDFT was calculated by assuming that the extending moment at the distal interphalangeal (DIP) joint resulting from the GRF was equal to the flexing moment created by the force in the DDFT during the stance phase (inverse dynamics). RESULTS: In early stance, the peak DDFT force (mean+/-s.d.) in the normal ponies was 1.92+/-1.63 N/kg. However, in Group 2, the point of zero moment was palmar to the centre of rotation of the DIP joint for the first 40% of stance and hence DDFT force was zero. Force in the DDFT reached a peak of 10.00+/-3.56 N/kg at 60.7+/-5.6% of stance in Group 1 and 6.41+/-1.37 N/kg at 79.2+/-9.6% of stance in Group 2. CONCLUSIONS: DDFT force in Group 2 laminitic ponies was much reduced until late stance, when it neared normal values. POTENTIAL RELEVANCE: Further studies of ponies with rotation of the DP as a sequel to laminitis should assist farriery aimed at reducing the force in the DDFT through the breakover phase of stance to protect damaged dorsal laminae. 相似文献
1000.
The glycosoaminoglycans in the digestive apparatus of immature fish have important biological functions and are involved in morphofunctional differentiation. The aim of this study was to investigate the glycoconjugate histochemistry in the different parts of the digestive apparatus (oesophagus, stomach, intestine) of Umbrina cirrosa (L.) fry using classical histochemical reactions (periodic acid-Schiff, Alcian blue pH 2.5, Alcian blue/periodic acid-Schiff, high iron diamine, low iron diamine) in conjunction with glycolytic digestions that degrade different classes of glycosoaminoglycans. No differences were observed in the reactivity to conventional histochemical staining of the oesophagus, stomach or intestine among 27-, 34- or 44-day-old fry. In the oesophagus, the mucopolysaccharides contained chondroitin sulphates B and A and/or C, heparan sulphate and chondroitin. In the stomach, only neutral glycoconjugates were revealed, whereas in the intestine there were only chondroitin sulphates. Some differences in the type and content of glycoconjugates were found in Umbrina cirrosa (L.) fry compared to those of adult subjects, probably related to different dietary habits and to changes in the environmental conditions. 相似文献