全文获取类型
收费全文 | 177812篇 |
免费 | 9670篇 |
国内免费 | 116篇 |
专业分类
林业 | 7476篇 |
农学 | 5343篇 |
基础科学 | 1150篇 |
20588篇 | |
综合类 | 32683篇 |
农作物 | 6640篇 |
水产渔业 | 8695篇 |
畜牧兽医 | 90646篇 |
园艺 | 2152篇 |
植物保护 | 12225篇 |
出版年
2018年 | 2217篇 |
2017年 | 2458篇 |
2016年 | 2296篇 |
2015年 | 2030篇 |
2014年 | 2453篇 |
2013年 | 6489篇 |
2012年 | 4703篇 |
2011年 | 5748篇 |
2010年 | 3634篇 |
2009年 | 3726篇 |
2008年 | 5654篇 |
2007年 | 5444篇 |
2006年 | 5231篇 |
2005年 | 4894篇 |
2004年 | 4760篇 |
2003年 | 4765篇 |
2002年 | 4598篇 |
2001年 | 5509篇 |
2000年 | 5341篇 |
1999年 | 4333篇 |
1998年 | 1735篇 |
1997年 | 1757篇 |
1996年 | 1675篇 |
1995年 | 2037篇 |
1994年 | 1846篇 |
1993年 | 1789篇 |
1992年 | 3673篇 |
1991年 | 3789篇 |
1990年 | 3827篇 |
1989年 | 3810篇 |
1988年 | 3518篇 |
1987年 | 3612篇 |
1986年 | 3705篇 |
1985年 | 3577篇 |
1984年 | 3029篇 |
1983年 | 2714篇 |
1982年 | 1842篇 |
1981年 | 1727篇 |
1979年 | 2736篇 |
1978年 | 2254篇 |
1977年 | 1928篇 |
1976年 | 1785篇 |
1975年 | 1884篇 |
1974年 | 2573篇 |
1973年 | 2482篇 |
1972年 | 2487篇 |
1971年 | 2262篇 |
1970年 | 2096篇 |
1969年 | 1998篇 |
1967年 | 1672篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
N. J. Olby K. K. Chan M. P. Targett J. E. F. Houlton 《The Journal of small animal practice》1997,38(5):213-216
A Jack Russell terrier with a history of progressive exercise intolerance was examined at the age of four months and again 10 months later. Clinical examination revealed a stunted, thin dog with a stilted gait. The dog had raised lactate levels before and after feeding and a raised lactate/pyruvate ratio after feeding, indicating a metabolic abnormality. Histochemical evaluation of muscle biopsies revealed subsarcolemmal accumulation of oxidative activity when stained with nicotinamide adenine dinucleotide tetrazolium reductase and ragged red fibres when stained with modified Gomori trichrome; all fibre types were involved. Ultrastructural examination of the muscle confirmed the presence of subsarcolemmal accumulations of mitochondria. Histochemical staining for the activity of enzymes of the Krebs cycle, oxidative phosphorylation and other metabolic cytosolic enzymes failed to demonstrate an abnormality. In view of the clinical picture and the biochemical and histological findings, a tentative diagnosis of mitochondrial myopathy was made. The difficulties associated with diagnosing mitochondrial disorders are discussed. 相似文献
912.
Diagnosis of pulmonary thromboembolism in a cat using echocardiography and pulmonary scintigraphy 总被引:1,自引:0,他引:1
J-L. POUCHELON V. CHETBOUL P. DEVAUCHELLE F. DELISLE W. MAI V. VIAL 《The Journal of small animal practice》1997,38(7):306-310
A 10-year-old male cat was presented with sudden onset of respiratory difficulties. Clinical examinatlon revealed an acute dyspnoea with cyanosis associated with a left systolic heart murmur. Standard thoracic radiographs excluded pulmonary oedema and showed very few pulmonary changes given the intensity of the respiratory compromlse. Echocardiographic examination revealed hypertrophic cardiomyopathy and a thrombus In the right pulmonary artery. Pulmonary sclntlgraphy confirmed a pulmonary thromboembolism with hypovascularisatlon of the left cranial lobe and of the ventral segment of the right lobe. Conservative treatment was instituted using an antibiotic (doxycycllne), anticoagulants (heparin, coumadine) and a calcium lnhlbitor (diltiazem). The cat was given absolute rest. The general condition of the animal improved. 相似文献
913.
M.L. BASTOS F. CARVALHO F. REMIÃO M.E. MENDES M.A. FERREIRA M.E. SOARES & J.A. TIMBRELL 《Journal of veterinary pharmacology and therapeutics》1997,20(1):33-37
Repeated oral administration of salbutamol to lambs for 28 days was found to decrease levels of taurine significantly in the serum and heart, and the mean excretion of taurine into urine was significantly less than in controls. Serum urea, low density lipoprotein and high density lipoprotein were also significantly reduced. Consistent with these changes, fat content in muscle was reduced, whereas protein content was not significantly changed. Body weight was not significantly changed by salbutamol treatment but heart and kidney weights (relative to body weight) were significantly increased. Salbutamol excretion in urine was relatively constant and residues were detected in certain organs and tissues, notably liver, bile and kidney. Changes in urinary and serum taurine level may reflect subtle changes in protein metabolism not detectable as changes in body weight or gross protein content. 相似文献
914.
Peter D. Constable BSc Phd Robert N. Streeter Gerard J. Koenig Nigel R. Perkins Hani M. Gohar Dawn E. Morin 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1997,11(2):71-79
The objectives of this study were to investigate the determinants of the anion gap (AG) in cattle and to evaluate the utility of AG in detecting hyperlactatemia in sick neonatal calves and adult cattle. The AG was calculated as AG = ([Na+] + [K+]) - ([Cl-] + [HCO3]), with all values in mEq/L. The AG of healthy neonatal calves (n = 16) was 29.6 ± 6.2 mEq/L (mean ± SD), and the blood L-lactate concentration ranged from 0.5 to 1.2 mM/L. The AG was significantly (P > .05) correlated with serum phosphate (r = .66) and creatinine (r = .51) concentrations. The AG of neonatal calves with experimentally induced diarrhea (n = 16) was 28.6 ± 5.6 mEq/L, and the blood L-lactate concentration ranged from 1.1 to 2.9 mM/L. The AG was significantly correlated with blood L-lactate concentration (r = .67), serum phosphate concentration (r = .63), creatinine concentration (r = .76), and blood pH (r = -.61). The AG of adult cattle with abomasal volvulus (n = 41) was 20.5 ± 7.8 mEq/L, and the blood L-lactate concentration ranged from 0.6 to 15.6 mM/L. The AG was significantly correlated with blood L-lactate concentration (r = .60), serum phosphate concentration (r = .71), creatinine concentration (r = .65), albumin concentration (r = .47), total protein concentration (r = .54), blood pyruvate concentration (r = .67), and blood pH (r = -.41) but not plasma β-OH butyrate concentration. The results indicate that the AG in cattle is only moderately correlated with blood L-lactate concentration and is similarly correlated with serum phosphate and creatinine concentrations in neonatal calves and adult cattle, as well as with serum albumin and total protein concentrations in adult cattle. Anion gap determination is of limited usefulness in predicting blood L-lactate concentration in sick cattle, whereas the correlation between AG and serum creatinine concentration in sick cattle suggests that an increased AG should alert the clinician to the potential presence of uremic anions. 相似文献
915.
916.
1. The purpose of this study was to examine the relationship between stockperson attitude and behaviour; bird behaviour and productivity in the chicken meat industry. 2. No relationship between stockperson attitude and behaviour was observed, which is in contrast to studies in the pig and dairy industries. 3. Evidence is provided for the existence of sequential relationships between stockperson behaviour, bird fear levels and productivity in the broiler farms examined. 4. The mechanism(s) responsible for the negative relationships between fear levels and production is unclear. It is hypothesised that chronic stress or a series of acute stress responses may be the mechanism through which fear affects productivity. 5. The relationship between human behaviour, bird fear levels and productivity indicates the potential that exists to improve productivity and perhaps welfare of commercial broilers by reducing fear levels in broiler chickens. 相似文献
917.
1. The normal range in colour of broiler breast muscle was assessed using an objective (instrumental) measure of colour in portioned breast fillets at a commercial processing plant. In addition, the relationship between colour and ultimate muscle pH (pH(ult)) was also examined. 2. Considerable variation in colour was evident although minimal inter-flock variation was found. The exceptions were 2 free range flocks which produced breast fillets significantly lighter and less red. 3. Extremes of colour are likely to be discriminated against at the point of purchase. 4. A clear relationship between pH(ult) and L* values was found which provides more evidence for the existence of a PSE like condition in broiler breast meat. 相似文献
918.
OBJECTIVE: To study the role of lectures from the perspective of staff and students involved in the veterinary course at The University of Queensland. METHODS: The Nominal Group Technique of Delbecq et al, which provides the maximum opportunity for group members to put forward points, was used to help develop a questionnaire which was completed by 351 students (a response rate of 84%) and 35 staff (76%) from the five years of the veterinary course, and was analysed using the SAS System for Windows. RESULTS: Almost all the staff and students agreed that lectures should fulfil many roles including stimulating and motivating students and encouraging them to think, as well as presenting ideas and concepts and an indication of the structure and relevance of the material. They should provide a guide for effective deep learning, but not encourage rote (or superficial) learning. A smaller percentage of staff and even fewer students agreed that lectures did fulfil these roles, especially those directed at encouraging students to look beyond simple memorisation of facts. The perceived disparity between reality and the ideal was greater amongst the older, clinical students than amongst their more junior colleagues. CONCLUSIONS: The focus of attention in lectures needs to change from the superficial, rote learning of information to deep, active learning directed at using information to solve problems that are perceived by the students to be relevant. If done in a stimulating and interesting way, this should develop skills in reasoning and critical analysis as well as providing a framework for storage and recall. It should also increase the motivation towards learning both during the veterinary course, and over the professional lifetime. Furthermore, the place of the lecture in veterinary education needs to be reassessed regularly in the face of newly-emerging educational technology. 相似文献
919.
Analysis of semen quality from each testis/duct system of a turkey with a duplicated cloaca and vent
A case is described wherein a turkey male (tom) possessed two vent areas with duplicated cloacae served by one large intestine. Both cloacae were functional in that feces were excreted and semen could be collected from each. The left vas deferens and ureter emptied into the left cloaca, and the right vas deferens and ureter emptied into the right cloaca. This allowed semen from each testis/duct to be collected separately from the corresponding cloaca. Thus, a unique opportunity was presented to collect semen separately from the left and right testis/duct system for semen analysis and fertility determination. Sperm concentration and percentage of dead sperm were not significantly different when semen from left vs. right reproductive tract were compared. The concentrations of spermiophages in semen from both reproductive tracts fell into the range reported for normal semen (0-8 x 10(5)/ml); however, semen from the right side had consistently higher spermiophage concentrations than that from the left side. On the basis of observations from one male made possible by an anatomic anomaly, it appears that the fecundities of the left and right testis/duct systems of the turkey male do not significantly differ and that recruitment of spermiophages into one tract (because of immunologic challenge, etc.) does not necessarily mean that the opposite testis/ducts will respond similarly. 相似文献
920.
The human and veterinary literature on the effect of antimicrobials on the clinical and bacteriological cure in uncomplicated Salmonella gastroenteritis is reviewed. Comparison of data on the efficacy of conventional antimicrobials (chloramphenicol, neomycin, ampicillin, amoxycillin, tetracycline, trimethoprim/sulfonamide combinations) and the newer fluoroquinolones indicate that quinolones may shorten the course of clinical disease in contrast to the conventional antimicrobials. Postconvalescent excretion of Salmonella was not affected by the conventional antimicrobials whereas the data on the fluoroquinolones in this respect are conflicting. The fluoroquinolones are the drugs of choice in human medicine for severe Salmonella infections and for the elimination of the carrier state. These drugs have not been evaluated in this respect in veterinary medicine. Well designed prospective placebo-controlled studies regarding the effect of antimicrobials, especially the fluoroquinolones, on the clinical cure and the postconvalescent shedding of Salmonella in animals are imperative to develop optimal therapeutic strategies. 相似文献