全文获取类型
收费全文 | 1043篇 |
免费 | 52篇 |
专业分类
林业 | 36篇 |
农学 | 35篇 |
基础科学 | 21篇 |
148篇 | |
综合类 | 87篇 |
农作物 | 37篇 |
水产渔业 | 72篇 |
畜牧兽医 | 587篇 |
园艺 | 11篇 |
植物保护 | 61篇 |
出版年
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 25篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 19篇 |
2015年 | 18篇 |
2014年 | 19篇 |
2013年 | 54篇 |
2012年 | 27篇 |
2011年 | 47篇 |
2010年 | 25篇 |
2009年 | 32篇 |
2008年 | 55篇 |
2007年 | 58篇 |
2006年 | 38篇 |
2005年 | 44篇 |
2004年 | 38篇 |
2003年 | 31篇 |
2002年 | 39篇 |
2001年 | 30篇 |
2000年 | 30篇 |
1999年 | 33篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 8篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 19篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1975年 | 14篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1971年 | 11篇 |
1969年 | 11篇 |
1967年 | 8篇 |
排序方式: 共有1095条查询结果,搜索用时 31 毫秒
11.
Effect of K-diformate in starter diets on acidity, microbiota, and the amount of organic acids in the digestive tract of piglets, and on gastric alterations 总被引:17,自引:0,他引:17
The aim of this investigation was to study the effect of K-diformate on the intraluminal pH, microbial composition in digesta and feces, organic acids along the digestive tract, and alterations of the gastric epithelium of pigs. Pigs (n = 36) weaned at 28 d of age were allotted to two groups and fed without (control diet) or with 1.8% supplemental K-diformate. Fecal samples were taken from the rectum on d 0, 1, 3, 5, 7, 14, 21, and 28 postweaning. Half of the animals from each group were killed on d 7 and the other half on d 29 postweaning. Growth performance was not different for both groups (P > or = 0.73). The gastric epithelium was not negatively affected by K-diformate (P = 0.25). Potassium-diformate decreased (P < or = 0.04) or tended to decrease (P < or = 0.10) the counts of total anaerobic bacteria, lactic acid bacteria, and yeasts in feces and digesta samples from the stomach, distal small intestine, cecum, and middle segment of the colon. The pH along the gastrointestinal tract of piglets was not affected by K-diformate (P > or = 0.30). On d 7, the concentration of lactic acid along the gastrointestinal tract was similar with both diets (P = 0.15). On d 29, the concentrations of lactic acid tended to be lower along the small intestine (P < or = 0.08) and the stomach (P = 0.11) of the pigs fed K-diformate. Formic acid in digesta was detected at significant levels only in the distal segment of the small intestine of the control pigs (from 4 to 11 mmol/kg of wet digesta), whereas considerable amounts were measured in the stomach (from 23 to 40 mmol/kg of wet digesta) and all segments of the small intestine (from 7 to 25 mmol/kg of wet digesta) in the K-diformate-fed pigs on both days. On d 7, pigs fed the K-diformate diet had a tendency (P < or = 0.08) to have higher concentrations of organic acids (acetic + propionic + butyric) in the digesta of the distal small intestine, cecum, and proximal colon. On d 29, both groups had similar concentrations of these acids, irrespective of the segment of the gastrointestinal tract (P = 0.95). Our study showed that the addition of K-diformate to a starter diet for piglets decreased total anaerobic bacteria, lactic acid bacteria, coliforms, and yeasts in feces and in digesta from various segments of the gastrointestinal tract, without affecting the gastric or intestinal pH. 相似文献
12.
Plain spinal radiography was performed in 40 dachshunds at regular intervals from 6 or 12 months of age to 2 years of age. A follow-up study at 3 to 4 years of age included 12 dogs. High incidence rates of intervertebral disk calcification were seen at 6 to 18 months of age. The number of dogs affected and number of calcified disks seemed to reach a steady level or a maximum at about 24 to 27 months of age. Dissolution of previously calcified disks without clinical signs was demonstrated, causing decreasing numbers of visibly calcified disks after 2 years of age. Radiographic examination for calcified intervertebral disks in the dachshund is recommended at 24 to 30 months of age for heritability studies and selective breeding. 相似文献
13.
Helge Green Nina Heiberg Kirsten Lejbølle Dan Funck Jensen 《European journal of plant pathology / European Foundation for Plant Pathology》2001,107(3):349-359
The activity of Trichoderma harzianum in the spermosphere and rhizosphere of different plant species was studied by use of a beta-glucuronidase (GUS) transformant (strain T3a). Hereby, direct observation of micro-habitats supporting metabolic activity of T. harzianum is reported. Germination of conidia and mycelial growth were not supported by exudates from healthy roots of various ages. Instead, growth and activity of T. harzianum depended on access to dead organic substrates such as seed coats, decaying roots, and wounds, including those caused by infecting pathogens. A correlation between the GUS activity of T. harzianum and the biomass of Pythium ultimum in infected roots was established. On the basis of our observations, we suggest that the biocontrol ability of T. harzianum involves competition with the pathogen for substrates including the seed coat, and wounded or infected root tissue. 相似文献
14.
Pedersen HD Häggström J Falk T Mow T Olsen LH Iversen L Jensen AL 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1999,13(1):56-64
Observer variation in diagnosing mild mitral regurgitation in dogs by cardiac auscultation was assessed by having 6 veterinarians with different levels of experience examine 57 Cavalier King Charles Spaniels. Comparisons with color Doppler echocardiography and phonocardiography were made, and the effects of 2 physical maneuvers on the auscultatory findings were evaluated. Using mildly diseased dogs, interobserver agreement in diagnosing the presence or absence of left-sided murmurs ranged from 63% to 88%. The agreement with phonocardiography (range, 53-91%) increased with the amount of observer experience. The 2 most experienced observers could discern soft ejection murmurs from regurgitant murmurs and were able to diagnose 89% of the dogs with regurgitant jets larger than 30% of the left atrial area. In general, less experienced observers diagnosed most jets larger than 50%. In many dogs with small jets, no murmur was found by auscultation and phonocardiography. The audibility of mild regurgitation was significantly reduced in dogs that were difficult to auscultate. Early systolic murmurs were typical of mild regurgitation, whereas holosystolic murmurs typified severe regurgitation. In a few dogs, late systolic murmurs alternated with holosystolic murmurs. Systolic clicks were found phonocardiographically in 18 dogs with mild to moderate regurgitation, but the audibility apparently was low. In many mildly affected dogs, physical maneuvers increased murmur intensity. Thus, some form of dynamic auscultation might facilitate the diagnosis of mild regurgitation. Auscultatory findings in mild regurgitation appear to depend on observer experience, circulatory status, and how difficult the dog is to auscultate. 相似文献
15.
Tegtmeier C Bloch B Jensen NE Jensen HE 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1999,46(8):517-523
The initial lung lesions in two calves intrabronchially inoculated with Haemophilus somnus are described. The animals were euthanized within 7 h after challenge. The in situ location of H. somnus and accompanying lesions were examined by light microscopy, immunohistochemistry and transmission electron microscopy (TEM). Inoculation with H. somnus resulted in the development of acute pulmonary lesions within 3.5 h. H. somnus antigen was demonstrated only within the luminal spaces of the airways and in one area of bronchio-associated lymphoid tissue (BALT). As observed by TEM, the bacteria were phagocytized by both neutrophils and alveolar macrophages. Antigen was never demonstrated in the pulmonary intravascular macrophages. 相似文献
16.
Effect of infection by bovine viral diarrhea virus (BVDV) in vitro on interleukin-1 activity of bovine monocytes 总被引:2,自引:0,他引:2
The effect of bovine viral diarrhea virus (BVDV) infection in vitro on the interleukin-1 (IL-1) activity of bovine monocytes was studied. Supernatants from BVDV-infected monocytes suppressed IL-1-stimulated proliferation of mouse thymocytes and masked lipopolysaccharide-stimulated IL-1 activity of bovine monocytes in the mouse comitogen thymocyte assay. Suppression of mouse thymocyte proliferation was restored by the addition of IL-1. IL-1 inhibitory activity was induced both by the prototype variants BVDV/NADL cytopathic and BVDV/NY-1 noncytopathic and by BVDV variants isolated from persistently infected cattle. Suppressed IL-1 activity was also found in supernatants from monocytes from persistently infected cattle following infection with BVDV in vitro. No differences in levels of IL-1 mRNA synthesis were detected between BVDV-infected and uninfected monocytes by RNA-cDNA hybridization. These results suggest that infection of bovine monocytes with BVDV results in the production and/or activation of a soluble inhibitor of IL-1 activity. 相似文献
17.
18.
19.
20.
Tasker S Binns SH Day MJ Gruffydd-Jones TJ Harbour DA Helps CR Jensen WA Olver CS Lappin MR 《The Veterinary record》2003,152(7):193-198
Blood samples from 426 healthy and sick cats in the UK were tested in a PCR assay for 'Candidatus Mycoplasma haemominutum' and Mycoplasma haemofelis (basonym Haemobartonella felis). Seventy-two of the cats (16.9 per cent) were positive for 'Candidatus M. haemominutum' alone, six (1.4 per cent) were positive for M. haemofelis alone and one (0.2 per cent) was positive for both. Logistic regression analysis indicated that older male cats were significantly more likely to be infected with 'Candidatus M. haemominutum', but there was no significant association between it and any of the haematological variables measured. M. haemofelis infection was uncommon in the anaemic cats sampled, and there were too few positive cases for multivariable analysis to be performed for M. haemofelis-positive status. 相似文献