全文获取类型
收费全文 | 80525篇 |
免费 | 4537篇 |
国内免费 | 82篇 |
专业分类
林业 | 3650篇 |
农学 | 2787篇 |
基础科学 | 531篇 |
9986篇 | |
综合类 | 12523篇 |
农作物 | 3197篇 |
水产渔业 | 4096篇 |
畜牧兽医 | 41773篇 |
园艺 | 953篇 |
植物保护 | 5648篇 |
出版年
2019年 | 840篇 |
2018年 | 1209篇 |
2017年 | 1322篇 |
2016年 | 1273篇 |
2015年 | 1038篇 |
2014年 | 1295篇 |
2013年 | 3154篇 |
2012年 | 2364篇 |
2011年 | 2721篇 |
2010年 | 1761篇 |
2009年 | 1799篇 |
2008年 | 2687篇 |
2007年 | 2578篇 |
2006年 | 2352篇 |
2005年 | 2263篇 |
2004年 | 2119篇 |
2003年 | 2234篇 |
2002年 | 2087篇 |
2001年 | 2438篇 |
2000年 | 2390篇 |
1999年 | 1904篇 |
1998年 | 763篇 |
1997年 | 826篇 |
1995年 | 907篇 |
1994年 | 762篇 |
1993年 | 767篇 |
1992年 | 1554篇 |
1991年 | 1677篇 |
1990年 | 1653篇 |
1989年 | 1657篇 |
1988年 | 1540篇 |
1987年 | 1495篇 |
1986年 | 1561篇 |
1985年 | 1487篇 |
1984年 | 1296篇 |
1983年 | 1093篇 |
1982年 | 773篇 |
1979年 | 1202篇 |
1978年 | 906篇 |
1977年 | 856篇 |
1976年 | 814篇 |
1975年 | 847篇 |
1974年 | 1052篇 |
1973年 | 1089篇 |
1972年 | 1036篇 |
1971年 | 969篇 |
1970年 | 949篇 |
1969年 | 909篇 |
1968年 | 763篇 |
1967年 | 855篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
FREDRIK E. HOPPE DVM PHD DAVE A. HAGER DVM PAUL W. POULOS JR. DVM PHD STINA EKMAN DVM P. G. LINDGREN MD PHD 《Veterinary radiology & ultrasound》1986,27(4):99-101
A manual, ultrasound-guided biopsy technique was compared to a new automatic method using a new biopsy device. The liver and the left kidney of 10 dogs were biopsied using the two methods. The specimens from the biopsies were compared for size and quality. Results demonstrate that larger and higher quality samples were obtained with the new automatic method. 相似文献
232.
Lymphocyte beta -adrenoceptor downregulation in great danes with occult dilated cardiomyopathy (DCM) and with DCM and heart failure. 总被引:2,自引:0,他引:2
M Borgarelli P Badino L Bergamasco C Bussadori R Odore G Re A Tarducci U Dotta 《Veterinary journal (London, England : 1997)》1999,158(2):128-134
The importance of the adrenergic nervous system in supporting the failing heart has long been known. The adrenergic drive on cardiac structure and function has however some adverse effects, which include myocardial beta-adrenoceptor (beta-AR) downregulation and decreased beta-adrenergic responsiveness to cathecolamines. In dog lymphocytes, beta(1)-AR and beta(2)-AR populations are almost equally represented (with a slight prevalence of beta(2)) and a significant correlation between cardiac and lymphocytic adrenoceptors has been found. The aim of the present study was to investigate possible differences between the concentration of lymphocytic beta-AR in healthy dogs, dogs with dilated cardiomyopathy (DCM) and dogs with occult DCM. Three groups of great danes were considered: a control group (n =10), dogs with DCM (n =9) and dogs with occult DCM (n =4). Lymphocytic beta-AR populations were determined in all dogs. A substantial and significant decrease (P<0.05) in total-AR, beta(1)-AR and beta(2)-AR concentrations in the lymphocytes of dogs with symptomatic DCM and occult DCM compared to the control group was found. Although the mean value of the lymphocyte beta(1)-AR number in the asymptomatic group was double compared to the DCM group, this difference was not statistically significant. We conclude that in dogs beta-AR downregulation occurs early in the course of dilated cardiomyopathy. This finding may suggest the value of early use of a beta-blocker in the therapeutic regimen. Moreover, the continuous monitoring of lymphocytic beta-AR may represent a useful tool for the development of a more effective individual therapy. 相似文献
233.
Pearson GR Bazeley KJ Jones JR Gunning RF Green MJ Cookson A Woodward MJ 《The Veterinary record》1999,145(13):370-373
Escherichia coli O26:K60, with genetic attributes consistent with a potentially human enterohaemorrhagic E. coli was isolated from the faeces of an eight-month-old heifer with dysentery. Attaching and effacing lesions were identified in the colon of a similarly affected heifer examined postmortem, and shown to be associated with E. coli O26 by specific immunolabelling. 相似文献
234.
235.
OBJECTIVE: To investigate the relationship between diet, growth rate and the presence of caudal cervical malformation in Doberman puppies. DESIGN: A prospective study of 15 Dobermann puppies from three unrelated litters, aged from 0 to 16 weeks. PROCEDURE: The growth rate in terms of body weight gain and increase in ulna length were measured weekly for all puppies. In addition the nutritional quality of the diets was assessed. Radiographs of the cervical spine were taken at 6 and between 12 and 16 weeks of age and examined for the presence of caudal cervical vertebral malformation. A mixed model for repeated measures data was used to investigate the relationship between the growth rate of the puppies and the fixed effects age, dam, diet, gender and presence of caudal cervical malformation. RESULTS: Five of the puppies had changes consistent with caudal cervical malformation. The diets fed were either balanced or transiently deficient in protein, calcium, phosphorus and/or magnesium. There was no significant association between growth rate and the variables dam, gender and the presence of caudal cervical vertebral malformation. There was no significant association between diet and increase in ulna length, but a trend existed between body weight gain and the feeding of a balanced diet (P = 0.0672). CONCLUSION: Caudal cervical vertebral changes can be detected radiographically as early as 6 weeks of age in some Dobermann puppies. A balanced diet and growth rate are not significant factors in its initial development. 相似文献
236.
By G. Mommens L. J. Peelman A. Van Zeveren G. D . 'Ieteren N. Wissocq 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》1999,116(5):325-330
Genetic variation is being used extensively for individual identification and linkage analysis, and may be useful for interpopulation studies. Previously, blood groups and biochemical variants in blood cell and serum proteins have been used to study (evolutionary) relationships in mammals. But genetic divergence and gene flow among closely related populations are difficult to measure with these classical markers because their mutation rate is so low that new mutations have not had sufficient time to appear and become fixed. So they have a small number of alleles and a relatively low level of heterozygosity. These markers are now replaced by DNA markers, mostly microsatellites. These microsatellite loci are useful genetic markers at which alleles differ in length due to differences in the number of short sequence motifs arranged adjacent to one another. They are abundantly distributed throughout the mammalian genome. They have a large number of alleles, a high level of heterozygosity and are inherited in true Mendelian fashion. These characteristics make them valuable for parentage control, linkage analysis, genome mapping and phylogenetic studies. In terrestrial vertebrates with limited mobility, genetic differentiation often increases with the distance between populations or corresponds to the extent of geographic and habitat barriers (R oy et al. 1994). Investigations of short tandem repeats yield a considerable volume of genetic data regarding the similarities and divergence times of different cattle populations. Microsatellite markers are suitable for the estimation of these parameters as they are not generally subject to direct selection and environmental influences. Computation of genetic distances based on data from several loci can be used to evaluate the taxonomic relationship between populations. The aim of this study was to estimate the relative genetic variability between Belgian cattle breeds and to reconstruct the evolutionary relationship among them, also using two small genetically isolated cattle-like populations. 相似文献
237.
Cerebral phaeohyphomycosis in a dog 总被引:2,自引:0,他引:2
G Migaki H W Casey W B Bayles 《Journal of the American Veterinary Medical Association》1987,191(8):997-998
Cerebral phaeohyphomycosis was diagnosed in a 9-year-old spayed dog that had a series of epileptic convulsions a day before death. About 6 weeks before her death, she had been treated for severe demodectic mange. During this period, persistent leukopenia, lymphocytopenia, and thrombocytopenia were found by blood analyses. At necropsy, multiple large pyogranulomatous lesions were found in the cerebrum and meninges. Dematiaceous fungi with brown, branching, septate hyphae and budding yeasts were found within tissue cells and in the necrotic areas. 相似文献
238.
Two caudolateral approaches to the canine scapulohumeral joint that do not require myotomy, tenotomy, or osteotomy were used to expose the humeral heads of both scapulohumeral joints in 10 clinically normal dogs. One approach (method 1) was used on the left shoulder of 5 dogs and on the right shoulder of the other 5 dogs. The other approach (method 2) was used on the opposite joints. The amount of humeral head articular cartilage that could be exposed with each approach was measured. The amount of articular cartilage exposed with method 1 was significantly greater than that exposed with method 2 (P less than 0.0001). Method 1 also provided for exposure of the caudomedial aspect of the scapulohumeral joint. Method 1 was used unilaterally in 20 dogs with osteochondritis dissecans. This approach provided excellent exposure of the humeral head and osteochondritis dissecans lesion. Of the 16 dogs that were available for follow-up evaluation, 1 developed a seroma after surgery. Other complications were not observed or reported. 相似文献
239.
240.
G V Alm 《Veterinary immunology and immunopathology》1987,17(1-4):173-182
Lymphokines are polypeptide factors produced by lymphocytes and other leukocytes, which modulate leukocyte activities in immune responses. Some of the more important lymphokines are reviewed in detail, with emphasis on those that have been cloned. These include interferon -alpha and -beta, interferon gamma, interleukin 2, interleukin 1, tumor necrosis factor and lymphotoxin, B lymphocyte growth factors, hemopoietic growth factors, and others. 相似文献