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   188546篇
  免费   10073篇
  国内免费   119篇
林业   8453篇
农学   6191篇
基础科学   1131篇
  22880篇
综合类   31088篇
农作物   7227篇
水产渔业   9356篇
畜牧兽医   97854篇
园艺   2458篇
植物保护   12100篇
  2019年   1689篇
  2018年   2706篇
  2017年   2960篇
  2016年   2776篇
  2015年   2422篇
  2014年   2993篇
  2013年   7426篇
  2012年   5284篇
  2011年   6363篇
  2010年   4313篇
  2009年   4288篇
  2008年   6314篇
  2007年   6210篇
  2006年   5782篇
  2005年   5341篇
  2004年   5183篇
  2003年   5249篇
  2002年   4851篇
  2001年   6023篇
  2000年   5936篇
  1999年   4846篇
  1998年   1910篇
  1997年   1906篇
  1996年   1749篇
  1995年   2148篇
  1994年   1765篇
  1993年   1821篇
  1992年   3734篇
  1991年   3909篇
  1990年   3981篇
  1989年   3953篇
  1988年   3662篇
  1987年   3613篇
  1986年   3592篇
  1985年   3479篇
  1984年   2844篇
  1983年   2546篇
  1982年   1741篇
  1979年   2592篇
  1978年   2055篇
  1977年   1789篇
  1976年   1737篇
  1975年   1897篇
  1974年   2296篇
  1973年   2404篇
  1972年   2365篇
  1971年   2148篇
  1970年   2136篇
  1969年   1947篇
  1967年   1740篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The veterinary school admission interview is a widely used selection tool, yet concerns persist about its reliability, validity, and cost. Relative to medicine, optometry, and dentistry schools, veterinary schools have been more likely to conduct panel interviews and to fix the interview's weight in selection decisions, strategies that increase interview validity. This article provides strategies for further increasing the veterinary school interview's validity. Interview reliability and validity studies point to key strategies the veterinary school admissions committee can implement before the interview: (1) establishing the interview's purpose(s); (2) conducting a "job" analysis to identify desirable candidate skills, knowledge, and attributes; (3) developing a structured and panel interview where interviewers, if possible, are blind to other admission data; (4) training interviewers; (5) setting a reasonable interview schedule; and (6) determining methods for analyzing applicant data. During the interview, interviewers should proceed through a structured series of steps: (1) open the interview with a specified agenda; (2) probe for information using structured questions and anchored rating scales; (3) close the interview to allow for candidate questions; and (4) evaluate the interview data. After the interview, the admissions committee should (1) analyze the interview data within and across interviewers and (2) analyze the data across all selection tools in order to assign relative weights to the selection tools.  相似文献   
993.
994.
1.?Severe foot and hock dermatitis in broiler chickens can reduce growth rate and increase susceptibility to bacterial infection, affecting both profitability and welfare. However, little is known about the underlying physiological changes associated with foot and hock lesions.

2.?This study compared global hepatic gene expression in control birds and those with ammonia-induced foot and hock lesions using Agilent 44?K chicken oligonucleotide microarrays (8 birds per group).

3.?In total, 417 genes were differentially expressed of which 174 could be mapped onto the genome. Genes associated with energy metabolism, thyroid hormone activity and cellular control were affected, while there was also evidence of an up-regulation of genes linked to a pro-inflammatory response.

4.?It is conceivable that pain is the underlying cause for the observed changes in energy metabolism genes.

5.?Changes in hepatic gene expression provide new information on how a chicken's physiological mechanisms alter to cope with foot and hock lesions. The findings support other data indicating that birds with increased severity of lesions are likely to be in pain and that growth will be compromised. Reduction of the incidence of dermatitis by improved husbandry should therefore benefit both welfare and commercial performance.  相似文献   
995.
An increase in the rate of human infections with Salmonella enteritidis (SE) occurred between 2007 and 2010 in British Columbia (BC). During the same time period, an increase in SE from poultry‐sourced isolates and increased clinical severity in poultry were also observed in BC. This article describes a multi‐sectoral collaboration during a 3‐year investigation, and the actions taken by public health and animal health professionals. Human cases were interviewed, clusters were investigated, and a case–control study was conducted. Environmental investigations were conducted in food service establishments (FSE). Suspect foods were tested. Laboratory data from poultry‐sourced isolates were analysed. Five hundred and eighty‐four human cases of SE with the same pulsed‐field gel electrophoresis pattern were identified between May 2008 and August 2010. Seventy‐three percentage of cases reported consumption of eggs. The odds of egg consumption were 2.4 times higher for cases than controls. Implicated FSE were found to use ungraded eggs, which had been distributed illegally. Investigation suggested that there were multiple suppliers of these eggs. Collaboration between public health and animal health professionals led to data sharing, improved understanding of SE, engagement with the poultry industry and public communication. Multi‐disciplinary, multi‐sectoral and multi‐pronged investigations are recommended to identify the likely source of illness in large, protracted foodborne outbreaks caused by commonly consumed foods.  相似文献   
996.
Reasons for performing the study: Flexion tests are a common tool during the prepurchase and clinical lameness examination, yet studies quantifying the effect of flexion, apart from distal forelimb flexion in sound horses, are sparse. Objectives: To investigate the effect of proximal hindlimb flexion on perceivable and measurable changes in movement symmetry in horses with objective movement symmetry falling within the margins of ‘sound’. Methods: Thirteen horses, selected based on objective movement symmetry, were instrumented with inertial sensors on left and right tuber coxae and over the os sacrum. Vertical movement symmetry was quantified at trot before and after proximal hindlimb flexion, with a repeat of flexion after 5 min. Video recordings of the horses were assessed visually. Results: Proximal hindlimb flexion introduced additive changes in movement symmetry to the individual baseline movement, with a tendency towards smaller effects with increasing stride number. The main systematic effect was a decrease in upward movement of the os sacrum following mid‐stance of the flexed limb and an increase in upward movement following mid‐stance of the nonflexed limb, also manifesting in a ‘hip hike’ of the flexed limb; these findings reflected increased movement asymmetry following flexion. Depending on individual baseline asymmetry, flexion can also increase movement symmetry. Conclusions: Proximal hindlimb flexion can exacerbate subtle asymmetry when performed carefully. Variation in measured symmetry following flexion within and between horses showed that the individual response to flexion is highly variable. Potential relevance: Proximal hindlimb flexion may elevate the asymmetry of a slightly lame limb above the threshold for visibility, thus assisting in the clinical gait examination. Further work is needed to examine the causes for a positive response to flexion and possible differences between sound and lame horses as well as horses of different athletic disciplines.  相似文献   
997.
998.
999.
The protective effect of Enterococcus faecium EF55 in chickens challenged with Salmonella enterica serovar Enteritidis phage type 4 (SE PT4) was assessed. The antibacterial effect on the bacterial microflora in the small intestine in relation to white blood cell count, phenotyping of peripheral blood and intestinal lymphocytes, functional activity of lymphocytes and phagocytes and mucin quantitation were investigated. Day-old chicks (85) were randomly divided into four groups. The probiotic group (EF) and Salmonella + probiotic group (EFSE) received E. faecium EF55 (109 CFU – 3 g/group/day) for 21 days. The Salmonella group (SE) and EFSE group were infected with Salmonella Enteritidis (108 CFU in 0.2 ml PBS) in a single dose per os on day four of the experiment. The control group chicks (C) were fed a commercial diet without added bacteria. Supplementation of EF55 in the diet of the chickens in the EFSE group, challenged with S. Enteritidis, caused the density of the intestinal mucin layer to increase significantly in non-specific regions (duodenum and jejunum), but decrease significantly in target regions (caeca) for S. Enteritidis. Probiotic treatment also appeared to result in a significantly higher number of lymphocytes in peripheral blood and a tendency to increase CD3, CD4, CD8, and IgM positive cells 3 days post-infection with S. Enteritidis. The results demonstrated an antibacterial effect and suggested that EF55 had a moderating effect on intestinal mucin production and leukocytic response in the early phase of S. Enteritidis infection.  相似文献   
1000.
A group of 160 Flemish pig farmers (n=160) were surveyed about their attitude towards surgical castration with anaesthesia (SCA) and without (SCN), immunocastration (IC), sperm sexing (SS) and the production of entire males (EM). The farmers' general preference was recorded as SCN>SS>SCA=IC>EM. The farmers' self-reported knowledge of the strategies was associated with their preference for SCA (negatively) and SS (positively). Herd size was correlated with farmers' preference for SCA (negatively) and SS (positively). Farmers perceived surgical castration without anaesthesia as the most favourable strategy in terms of farm profitability, animal performance and effectiveness against boar taint, but they expected the lowest consumer acceptance for this strategy. Surgical castration with anaesthesia was ranked the least favourable in terms of labour conditions. Production of entire males was viewed as the least profitable and the least effective strategy. Sperm sexing was positively perceived, particularly in terms of labour conditions, animal welfare, effectiveness and expected consumer acceptance. The farmers' opinion was quite homogeneous, especially regarding surgical castration without anaesthesia and production of entire males. Increasing our understanding of the farmers' perceptions will hopefully facilitate communication about this intricate issue.  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