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   48972篇
  免费   2688篇
  国内免费   33篇
林业   1701篇
农学   1661篇
基础科学   251篇
  5835篇
综合类   8196篇
农作物   1545篇
水产渔业   2717篇
畜牧兽医   26328篇
园艺   574篇
植物保护   2885篇
  2019年   416篇
  2018年   777篇
  2017年   823篇
  2016年   743篇
  2015年   607篇
  2014年   750篇
  2013年   1736篇
  2012年   1347篇
  2011年   1690篇
  2010年   1154篇
  2009年   1096篇
  2008年   1682篇
  2007年   1593篇
  2006年   1497篇
  2005年   1380篇
  2004年   1394篇
  2003年   1371篇
  2002年   1184篇
  2001年   1913篇
  2000年   1984篇
  1999年   1498篇
  1998年   569篇
  1997年   499篇
  1996年   449篇
  1995年   612篇
  1994年   524篇
  1993年   459篇
  1992年   1151篇
  1991年   1211篇
  1990年   1178篇
  1989年   1097篇
  1988年   1056篇
  1987年   1081篇
  1986年   1034篇
  1985年   966篇
  1984年   803篇
  1983年   683篇
  1982年   421篇
  1981年   382篇
  1979年   635篇
  1978年   500篇
  1977年   441篇
  1976年   408篇
  1975年   451篇
  1974年   523篇
  1973年   507篇
  1972年   531篇
  1971年   449篇
  1970年   424篇
  1969年   464篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Effects of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on the number and blastogenesis of lymphocytes were evaluated in clinically healthy dogs treated subcutaneously with rhG-CSF at a dose of 2.5 microg/kg for 3 days. Significant increases in the number of leukocytes and segmented neutrophils were observed after the administration of rhG-CSF. The number of lymphocytes also increased on days 1 and 2 after the treatment. Activities of phytohemagglutinin, concanavalin A, and pokeweed mitogen-induced lymphocyte blastogenesis (LB) were augmented to twice the pretreatment levels by the administration of rhG-CSF. These results suggested that administration of rhG-CSF activated lymphocyte functions such as LB in healthy dogs.  相似文献   
972.
973.
Development of antibiotic resistance in bacteria is a problem of great concern. It is important to establish the convenience of antimicrobial susceptibility tests in animal infections. The aim of this study was to test the susceptibility to antibiotics of Pseudomonas strains isolated from chronic canine otitis externa. We tested 23 strains of Pseudomonas: 19 Ps. aeruginosa, three Ps. fluorescens and one Pseudomonas spp. The most effective antibiotics were tobramycin (100% susceptible), marbofloxacin (91.3%) and ceftazidime (91.3%). Ticarcillin and gentamicin, commonly used for the treatment of otitis externa also showed good results (susceptibility of strains was 86 and 65.2% respectively). Lower susceptibility was found using enrofloxacin (52.1%) probably due to its indiscriminate use. We emphasize the need for a rational policy of antibiotic prescribing in order to prevent the selection of resistant strains.  相似文献   
974.
A 4-year-old Holstein cow from a farm where 2 cows had recently died suddenly was referred for evaluation of acute severe colic. Right flank laparotomy revealed a large mesenteric hematoma. Within 14 layer chromatographic analyses of the moldy hay and blood from the necropsied cow and the hospitalized cow were positive for dicumarol. A diagnosis of sweet vernal poisoning was confirmed on the basis of clinical and toxicologic findings. The cow was treated with supportive therapy, blood transfusions, and vitamin K1 and recovered without complications. Because sweet vernal grass is becoming common in certain areas and the use of round bales is commonplace, practitioners should be aware of the potential for this toxicosis.  相似文献   
975.
A 20-month-old 1.44-kg (3.2-lb) castrated male ferret was examined because of vomiting, defecating in an abnormal location, dyspnea, and signs of depression. Within 5 minutes of initial evaluation, the ferret became nonresponsive to all stimuli except deep pain. Despite intensive supportive treatment, the ferret died. Toxicologic analyses for ibuprofen were performed on serum, urine, and liver, using gas chromatography and mass spectrophotometry. Serum ibuprofen concentrations were 245 micrograms/g before and 269 micrograms/g after death. Acute ibuprofen toxicosis may cause severe lethargy progressing to coma, apnea, and death in ferrets. Ibuprofen toxicosis should be considered in differential diagnoses for ferrets with signs of depression, with or without clinical signs of gastrointestinal tract dysfunction.  相似文献   
976.
This data set consisted of over 29 245 field records from 24 herds of registered Nelore cattle born between 1980 and 1993, with calves sires by 657 sires and 12 151 dams. The records were collected in south‐eastern and midwestern Brazil and animals were raised on pasture in a tropical climate. Three growth traits were included in these analyses: 205‐ (W205), 365‐ (W365) and 550‐day (W550) weight. The linear model included fixed effects for contemporary groups (herd‐year‐season‐sex) and age of dam at calving. The model also included random effects for direct genetic, maternal genetic and maternal permanent environmental (MPE) contributions to observations. The analyses were conducted using single‐trait and multiple‐trait animal models. Variance and covariance components were estimated by restricted maximum likelihood (REML) using a derivative‐free algorithm (DFREML) for multiple traits (MTDFREML). Bayesian inference was obtained by a multiple trait Gibbs sampling algorithm (GS) for (co)variance component inference in animal models (MTGSAM). Three different sets of prior distributions for the (co)variance components were used: flat, symmetric, and sharp. The shape parameters (ν) were 0, 5 and 9, respectively. The results suggested that the shape of the prior distributions did not affect the estimates of (co)variance components. From the REML analyses, for all traits, direct heritabilities obtained from single trait analyses were smaller than those obtained from bivariate analyses and by the GS method. Estimates of genetic correlations between direct and maternal effects obtained using REML were positive but very low, indicating that genetic selection programs should consider both components jointly. GS produced similar but slightly higher estimates of genetic parameters than REML, however, the greater robustness of GS makes it the method of choice for many applications.  相似文献   
977.
An isolate Enterococcus hirae was used to determine its pathogenicity for chicken embryos and for chicks treated with betamethasone. E hirae was inoculated intravenously into four-day-old chicks which had been treated for three consecutive days with betamethasone, and chick embryos were inoculated into the allantoic cavity with 102 and 103 bacteria. E hirae was not pathogenic for the chicks or for the embryos.  相似文献   
978.
1. The effects of dietary penicillin on the urease activities of small intestine, large intestine, caecum and their contents, liver and kidney in chickens fed a diet containing 5 g/kg protein plus urea were examined.

2. About 0.88 of the total urease activity determined was observed in intestinal contents, of which 0.95 of the activity was accounted for by caecal contents, 0.05 by colo‐rectal contents and none by small intestinal contents. Intestinal tissues (caecum included), liver and kidney accounted for 0.03, 0.06 and 0.02, respectively, of the total urease activity.

3. Dietary penicillin decreased urease activity to 0.17 in caecal contents and to 0.05 in colo‐rectal contents of the corresponding control values (P< 0.01). The urease activity of caecal tissue was lowered by penicillin to half that of control activity (P < 0.05) but none of the activities of other tissues were affected.

4. It is concluded that, even when the urease activity is stimulated by dietary urea, 20 mg/kg dietary penicillin can strikingly lower it in the caecum, where most of the urease activity in the chicken body is to be found.  相似文献   

979.
Although primary malignant pulmonary neoplasia of horses is rarely encountered, this diagnosis was confirmed in 2 horses on the basis of necropsy and histopathologic findings. One horse, with cystic mucinous adenocarcinoma, had respiratory tract and neurologic signs directly attributable to the neoplasm, and a tentative antemortem diagnosis of pulmonary neoplasia was made. The other horse, with anaplastic bronchogenic carcinoma, did not have clinical signs of pulmonary neoplasia.  相似文献   
980.
The effect of the pH on the boiling test was studied in 68 beef and 108 pork muscles. The pH had a significant effect on the sensory scores obtained from the boiling test. The effect was particularly pronounced in the odour of meat. In beef the odour scores remain steady for samples with a pH value under about 6.2 and start to increase rapidly in higher pH values. In pork the increase in scores appears to be linear. The odour observed in high pH meat was described by the judges as abnormal and ammonialike. In the case of meat with a high pH, the results of the boiling test at meat inspection should be interpreted with extreme caution.  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