首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   24773篇
  免费   1301篇
  国内免费   10篇
林业   876篇
农学   752篇
基础科学   154篇
  3593篇
综合类   3509篇
农作物   891篇
水产渔业   1336篇
畜牧兽医   13155篇
园艺   266篇
植物保护   1552篇
  2019年   248篇
  2018年   415篇
  2017年   507篇
  2016年   470篇
  2015年   337篇
  2014年   457篇
  2013年   959篇
  2012年   795篇
  2011年   949篇
  2010年   686篇
  2009年   669篇
  2008年   966篇
  2007年   916篇
  2006年   808篇
  2005年   735篇
  2004年   643篇
  2003年   705篇
  2002年   605篇
  2001年   803篇
  2000年   799篇
  1999年   633篇
  1998年   274篇
  1997年   277篇
  1995年   256篇
  1993年   227篇
  1992年   422篇
  1991年   516篇
  1990年   433篇
  1989年   411篇
  1988年   400篇
  1987年   409篇
  1986年   363篇
  1985年   388篇
  1984年   339篇
  1983年   287篇
  1982年   243篇
  1979年   383篇
  1978年   289篇
  1977年   290篇
  1976年   299篇
  1975年   317篇
  1974年   332篇
  1973年   302篇
  1972年   290篇
  1971年   245篇
  1970年   224篇
  1969年   289篇
  1968年   269篇
  1967年   326篇
  1966年   304篇
排序方式: 共有10000条查询结果,搜索用时 351 毫秒
991.
992.
Isolates of Actinobacillus (Haemophilus) pleuropheumoniae were studied by restriction endonuclease fingerprinting (REF) analysis using the enzymes BamHI and HindIII. Restriction fragments were resolved by polyacrylamide gel electrophoresis and visualized by silver staining. Except for serotypes 1 and 9, reference strains of A. pleuropneumoniae serotypes 1 to 10 had clearly distinguishable REF profiles. Analysis of REF profiles of southern Ontario field isolates revealed limited heterogeneity amongst isolates of serotype 1 or serotype 5. The REF profiles of the serotype 7 isolates studied showed greater variation. Heterogeneity could not be correlated with the presence of plasmids nor with antibiotic resistance. Limited heterogeneity could also be detected amongst REF profiles of A. pleuropneumoniae isolates recovered from a closed herd suggesting that there is a small amount of genetic variation within clonal populations.  相似文献   
993.
Extra iron (5 ppm) in a normal commercial milk replacer given from the end of the sixth week until the end of the sixteenth week of the fattening period influenced food conversion positively without a loss in meat quality. Even when the extra iron was given to the end of the fattening period there was no perceptible improvement of the haematological status of the calf, though liver iron concentration was increased. During all the experiments no stainable iron could be found in bone marrow smears. Iron and copper concentration measured in liver biopsies appeared to give reliable information about, respectively, iron and copper status of the veal calf. In relation to the colour of the meat at slaughter the blood haemoglobin concentration during the fattening period was found to be the most reliable parameter.  相似文献   
994.
Relative gene expression pattern of fatty acid transport proteins (FATP and cd36), intracellular fatty acid-binding proteins (FABP3, FABP10 and FABP11), β-oxidation-related genes [carnitine palmitoyl transferase II (CPTII), peroxisome proliferator-activated receptor β (PPARβ), acyl-CoA oxidase (AOX), long-chain fatty acyl-CoA synthetase (FACS), acyl-CoA dehydrogenase (dehydrogenase)] and uncoupling protein 2 (UCP2) was assessed by RT-qPCR in Atlantic salmon muscle (red and white), liver, heart, myosepta and visceral fat. FABP11, a FABP isoform not previously described in Atlantic salmon, was highly expressed in visceral fat and myosepta and at the lower level in red muscle, white muscle, myosepta and heart. Furthermore, Atlantic salmon were fed either a diet containing fish oil (FO) or a complete replacement of FO with a vegetable oil blend (55% rapeseed oil, 30% palm oil and 15% linseed oil; VO) for the production cycle (27 months from start of feeding and until ∼4.5 kg mean weight). The expression of genes related to β-oxidation, fatty acid uptake and transport in the white muscle indicate ( n  = 3) significant down-regulation in VO fed Atlantic salmon and correlated with previously reported white muscle triacylglycerol stores and β-oxidation. FABP11 in visceral fat and myosepta was also down-regulated in VO fed fish.  相似文献   
995.
A polymelus monster was observed in a 7-week-old slaughterhouse chicken. The supernumerary limbs were smaller than the normal appendages but contained an equal number of digits.  相似文献   
996.
997.
Clinical, pathological and epidemiological details of scrapie-like encephalopathies are described in an arabian oryx and a greater kudu. Clinical signs included ataxia and loss of condition with a short, progressive clinical course (22 and three days, respectively). Histopathological examination of the brains revealed spongiform encephalopathy characteristic of that observed in scrapie and bovine spongiform encephalopathy (BSE). It seems probable that these cases have a common aetiology with BSE. Scrapie-like spongiform encephalopathies have now been described in five species of exotic artiodactyls in Britain indicating a, hitherto inapparent, wider range of ruminant species as natural hosts for these diseases.  相似文献   
998.
The pharmacokinetics of kitasamycin after intravenous and oral administration in a dose of 300 mg/kg b.wt. was studied in 18 healthy and 18 Salmonella gallinarum naturally infected chickens. The tissue residue of the studied antibiotic was estimated in 36 normal chickens when it was given orally for 7 successive days. Therapeutic level of kitasamycin was achieved after 15 minutes and persisted for 20-22 hours after its oral administration. Higher serum kitasamycin concentrations were recorded in Salmonella gallinarum infected chickens. The elimination half-life of kitasamycin calculated after single intravenous injection was 9.03 hours in diseased chickens corresponding to 3.74 hours in healthy birds. The body clearance was significantly reduced in diseased chickens (23.86 ml/kg/min) when compared to that in normal ones (62.03 ml/kg/min). Kitasamycin treated broilers should not be slaughtered before 3 days from the last dose as it was detected only in bile and caecum at that time but not in edible tissues.  相似文献   
999.
Excessive administration of phenylbutazone was associated with development of right dorsal ulcerative colitis. The clinical signs of right dorsal colitis include chronic colic and weight loss. The laboratory abnormalities include panhypoproteinemia and a high WBC count in the abdominal fluid. Medical management of the chronic colic and protein-losing enteropathy associated with the ulcerative lesions in the right dorsal colon and surgical bypass of the right dorsal colon did not result in long-term resolution of clinical signs. Resection of the ulcerated right dorsal colon through a right lateral approach at the 16th rib resulted in resolution of intestinal protein loss and colic. The results of this case suggest that surgical resection of the ulcerated right dorsal colon may be the recommended treatment for right dorsal ulcerative colitis.  相似文献   
1000.
Yersiniosis in Farmed Deer   总被引:1,自引:0,他引:1  
Samples from 77 chital (Axis axis), 42 fallow (Dama dama), 26 red (Cervus elaphus), 7 rusa (Cervus timorensis) and 1 sambar deer (Cervus unicolor) were examined. Yersinia pseudotuberculosis infection was diagnosed as the cause of death in 6 (23%) of the red and 23 (30%) of the chital deer. Yersiniosis was the most common infectious cause of death diagnosed. Affected deer were usually found moribund or dead, often with faecal staining of the perineum. Gross pathology in chital included a fibrinous enterocolitis, enlarged congested mesenteric lymph nodes and multiple pale foci through the liver. Gross changes in red deer were limited to intense congestion of the intestinal mucosa and enlargement and congestion of mesenteric lymph nodes. Microscopic intestinal changes in both species consisted of microabscessation or diffuse suppurative inflammation of the intestinal mucosa with numerous bacterial colonies in the lamina propria. Multifocal suppurative mesenteric lymphadenitis was a common finding. Multifocal suppurative or non-suppurative hepatitis was frequently present in the liver of chital but was uncommon in the red deer. Yersiniosis occurred during the cooler months from June to November, with younger age classes most commonly affected. Y. pseudotuberculosis serotypes I, II and III were isolated in the ratio 17:3:0 in the chital deer and 1:1:2 in red deer. The clinical, epidemiological and bacteriological features are similar to those documented previously by New Zealand workers. The increased susceptibility to disease of red deer and chital compared to fallow deer and perhaps other species has not previously been documented.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号