全文获取类型
收费全文 | 231631篇 |
免费 | 12752篇 |
国内免费 | 173篇 |
专业分类
林业 | 9327篇 |
农学 | 7292篇 |
基础科学 | 1544篇 |
28672篇 | |
综合类 | 40755篇 |
农作物 | 8999篇 |
水产渔业 | 11581篇 |
畜牧兽医 | 117104篇 |
园艺 | 3089篇 |
植物保护 | 16193篇 |
出版年
2018年 | 3136篇 |
2017年 | 3547篇 |
2016年 | 3249篇 |
2015年 | 2751篇 |
2014年 | 3484篇 |
2013年 | 8915篇 |
2012年 | 6432篇 |
2011年 | 8001篇 |
2010年 | 5139篇 |
2009年 | 5257篇 |
2008年 | 7831篇 |
2007年 | 7467篇 |
2006年 | 7059篇 |
2005年 | 6546篇 |
2004年 | 6325篇 |
2003年 | 6440篇 |
2002年 | 6040篇 |
2001年 | 7118篇 |
2000年 | 6962篇 |
1999年 | 5594篇 |
1998年 | 2402篇 |
1997年 | 2377篇 |
1996年 | 2219篇 |
1995年 | 2703篇 |
1994年 | 2418篇 |
1993年 | 2306篇 |
1992年 | 4667篇 |
1991年 | 4882篇 |
1990年 | 4835篇 |
1989年 | 4838篇 |
1988年 | 4443篇 |
1987年 | 4526篇 |
1986年 | 4665篇 |
1985年 | 4510篇 |
1984年 | 3725篇 |
1983年 | 3364篇 |
1982年 | 2334篇 |
1981年 | 2155篇 |
1979年 | 3458篇 |
1978年 | 2875篇 |
1977年 | 2422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 500 毫秒
51.
D A Higgins 《Veterinary immunology and immunopathology》1992,34(3-4):367-377
Preparations of duck (Anas platyrhynchos) spleen and blood lymphocytes depleted of cells capable of phagocytosing carbonyl iron gave lower transformation responses to the mitogens phytohaemagglutinin (PHA), concanavalin A (Con A), Bandeiraea simplicifolia seed lectin (BSS), wheat germ agglutinin (WGA), lentil lectin (LL) and phorbol ester (PMA) than intact cell preparations. When cell populations were fractionated on the basis of their adherence to plastic, it was found that the adherent cells were responsive to PHA, Con A, BSS, WGA and PMA, while the non-adherent cells responded to LL. These observations confirm the expected requirement for phagocytic accessory cells in the induction of in vitro mitogen-driven duck lymphocyte responses. The responses of plastic-adherent populations of cells to most mitogens are believed to reflect the generally close physical relationship between the adherent accessory cells and the lymphocytes, although it remains possible that duck monocytes respond to some of the mitogens employed. The data also suggest that LL stimulates a population of cells different to those responding to other mitogens. 相似文献
52.
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
53.
54.
55.
The oscillatory potentials (OP) on the b-wave of the canine ERG are characterized. Normal values for an OP-index, implicit times and periodicity are given. The OP-index increases during dark adaptation as well as with increasing stimulus intensities for white light flashes. Scotopic blue and red stimuli, although balanced for the maximum b-wave amplitude, surprisingly result in higher OP-indices for red flashes. Implicit times decrease for all OP with increasing stimulus intensities. Scotopic balanced red light results in OP with markedly reduced implicit times compared to blue light stimulation. The intervals between two OPs remain constant during dark adaptation, however, intervals between OPs with longer implicit times tend to be shorter. In contrast, the b-waves for scotopic balanced stimuli show rhythmic oscillations with constant intervals between them, the intervals being shorter for blue light than for red light. The intervals between OPs tend to become shorter with increasing stimulus intensities. This investigation indicates that OPs are influenced but not generated by photoreceptors. The examination of a dog with optic nerve hypoplasia indicates that the ganglion cells do not contribute to the biogenesis of OPs. The prognostic value of OPs in the early diagnosis for hereditary retinal degenerations in the dog is discussed. 相似文献
56.
S A Dee 《Veterinary Clinics of North America: Food Animal Practice》1992,8(3):641-660
Porcine urogenital disease is the result of an imbalance of the normal microflora of the urinary and reproductive tracts brought about by hormonal, environmental, and management-related stress factors. Production and economic losses can be substantial, and diagnosing and treating the problem can be frustrating. Through proper hygiene, facility design, and culling procedures, the severity of the problem can be minimized. 相似文献
57.
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
58.
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
59.
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
60.
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