全文获取类型
收费全文 | 289540篇 |
免费 | 16517篇 |
国内免费 | 674篇 |
专业分类
林业 | 23977篇 |
农学 | 14085篇 |
基础科学 | 2980篇 |
44820篇 | |
综合类 | 34358篇 |
农作物 | 17270篇 |
水产渔业 | 17394篇 |
畜牧兽医 | 120394篇 |
园艺 | 6427篇 |
植物保护 | 25026篇 |
出版年
2020年 | 2903篇 |
2019年 | 3686篇 |
2018年 | 4094篇 |
2017年 | 4490篇 |
2016年 | 4887篇 |
2015年 | 4390篇 |
2014年 | 5754篇 |
2013年 | 16422篇 |
2012年 | 7168篇 |
2011年 | 9303篇 |
2010年 | 7600篇 |
2009年 | 8098篇 |
2008年 | 8638篇 |
2007年 | 7739篇 |
2006年 | 8400篇 |
2005年 | 7607篇 |
2004年 | 7431篇 |
2003年 | 7160篇 |
2002年 | 6629篇 |
2001年 | 7495篇 |
2000年 | 7120篇 |
1999年 | 6430篇 |
1998年 | 4283篇 |
1997年 | 4333篇 |
1996年 | 4062篇 |
1995年 | 4696篇 |
1994年 | 4143篇 |
1993年 | 3820篇 |
1992年 | 5281篇 |
1991年 | 5511篇 |
1990年 | 5302篇 |
1989年 | 5263篇 |
1988年 | 4769篇 |
1987年 | 4836篇 |
1986年 | 4859篇 |
1985年 | 4991篇 |
1984年 | 4523篇 |
1983年 | 4169篇 |
1982年 | 3309篇 |
1981年 | 3161篇 |
1980年 | 3120篇 |
1979年 | 3961篇 |
1978年 | 3480篇 |
1977年 | 3156篇 |
1976年 | 2856篇 |
1975年 | 2781篇 |
1974年 | 3309篇 |
1973年 | 3302篇 |
1972年 | 3045篇 |
1971年 | 2860篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
P. Buracco R. Guglielmino O. Abate V. Bocchini E. Cornaglia D. B. DeNicola† M. Cilli P. Ponzio 《The Journal of small animal practice》1992,33(6):279-284
The clinical course of a feline leukaemia virus (FeLV)-negative and feline immunodeficiency virus (FIV)-positive cat affected with a large granular lymphocyte lymphoma is presented. Cyto-logical examination showed neoplastic cells in the pleural effusion and in two abdominal masses. Bone marrow and peripheral blood were moderately involved and chemotherapy was used to control the tumour. Cytochemistry, immunohis-tochemistry and ultrastructural studies were applied to define the cellular lineage; cytochemistry suggested a T-cell lineage. 相似文献
62.
E. Conde A. M. Moreno I. Martin-Lacave A. Fernandez y H. Galera 《Anatomia, histologia, embryologia》1992,21(1):94-100
A systematic immunohistochemical study of the ultimobranchial tubule (UBT) has been carried out in 45 Wistar rats of different ages (0, 5, 10, 15, 20, 25, 30, 60 and 120 days). The existence of calcitonin immunoreactive cells in the UBT wall has been demonstrated in a 5-days old rat. In addition, immunohistochemical studies for thyroglobulin revealed positive staining in follicular cells connected to the UBT and, occasionally, in isolated cells lying within solid clusters from the UBT. These last results together with the continued and repeated existence of numerous mitosis and PAS (+) microfollicles, apparently rising from the UBT, support the hypothesis that the ultimobranchial body (UBB) may contribute partially to the formation of a part of the follicular component. 相似文献
63.
64.
65.
Abstract. The use of an indirect enzyme-linked immunosorbent assay ( elisa ) for the detection of channel catfish antibody to Edwardsiella ictaluri is described. Changes in agglutination titre in fish immunized with Edwardsiella ictaluri heat killed whole bacterins or lipopolysaccharides were reflected by corresponding changes in elisa readings. Relatively high correlations were observed among elisa OD readings, computed elisa titres and corresponding agglutination titres. 相似文献
66.
Serum amyloid A protein (SAA) in horses: objective measurement of the acute phase response 总被引:1,自引:0,他引:1
M B Pepys M L Baltz G A Tennent J Kent J Ousey P D Rossdale 《Equine veterinary journal》1989,21(2):106-109
A sensitive and precise immunoassay for equine serum amyloid A protein (SAA) was established and used to determine, for the first time, the circulating concentration of this protein in health and disease. As in other species, equine SAA was present only at trace levels in healthy animals but behaved as an extremely sensitive and rapidly responding acute phase reactant following most forms of tissue injury, infection and inflammation, objectively reflecting the extent and activity of disease. Measurements of SAA should make a significant contribution to diagnosis and management of viral and bacterial infection in horses, and routine serial assays could provide an objective criterion for monitoring prospectively the general health of horses in training and racing. 相似文献
67.
A Sosnicki R G Cassens D R McIntyre R J Vimini M L Greaser 《British poultry science》1989,30(1):69-80
1. The incidence of microscopically detectable degenerative characteristics in 5 skeletal muscles (m. pectoralis thoracicus, m. supracoracoideus, m. biceps femoris, m. semitendinosus, m. femorotibialis medius) of turkeys was investigated. 2. Samples were obtained from 30 Large White turkey males 14, 16 and 18 weeks old. Hyaline degeneration, infiltration of mononuclear cells and necrotic fibres were observed. 3. Individual fibres varied greatly in size and muscle fibre nuclei were often shrunken and pyknotic. 4. Weak and/or uniform reaction for Ca++-ATPase and SDH in all types of muscle fibres and loss of alkaline phosphatase activity in cell membranes were noted. A positive reaction for acid phosphatase occurred in regions of perivascular infiltration and in necrotic muscle fibres. The majority of muscle fibres possessed high activity for phosphorylase a and b. 5. Based on the use of fluorescein alpha-bungarotoxin conjugate, motor end-plates appeared to be morphologically intact. Direct immunofluorescence with anti-chicken IgG showed positive reaction in muscle fibres undergoing necrosis and in the involved connective tissue. 6. Degenerative changes varied with age and were most marked in the oldest birds. 7. Because gross degenerative symptoms were absent from both the birds and the meat from them, the condition appears to be either different from or a precursor to the degenerative myopathy characterised by other authors. 相似文献
68.
Requirement for MHC class II positive accessory cells in an antigen specific bovine T cell response 总被引:1,自引:0,他引:1
Purified populations of bovine antigen presenting cells (APCs) and T cells have been isolated from peripheral blood and characterised using various monoclonal antibodies (mAbs) for cell surface markers. Bovine APCs were found in an adherent cell fraction and were non-specific esterase positive, phagocytic and expressed bovine major histocompatibility complex (MHC) class II determinants, all of which are typical macrophage characteristics. T cells were rigorously depleted of accessory cell function before being used in an antigen presenting cell assay. The generation of T helper cells in response to the soluble antigen, ovalbumin, was entirely dependent upon a critical number of APCs. Further the proliferative response was inhibited by several mAbs to bovine MHC class II molecules. Thus the interaction between bovine APCs and helper/inducer T lymphocytes (TH/I) appears to be similar to that in other species. 相似文献
69.
70.
M Steinhardt S Reimer U Bünger J Kutschke 《Archiv fuer experimentelle veterinaermedizin》1989,43(2):309-314
Comprehensive studies into domestic pigs and wild boars together with literature data provided a basis for an assessment of aerobic metabolic capacity (VO2max) of swine. The values quoted, from 20 to 94 ml/min-1/kg, had been due to several factors of methodological approach, growth, training, and nutrition as well as to pathophysiological aspects. For full capacity utilisation of VO2max, untrained pigs can be challenged at belt velocities between 0.8 and 1.8 m/s-1 and trained animals at 5 m/s-1. 相似文献