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   38747篇
  免费   2267篇
  国内免费   285篇
林业   1599篇
农学   1429篇
基础科学   325篇
  5589篇
综合类   5701篇
农作物   1514篇
水产渔业   1826篇
畜牧兽医   20078篇
园艺   466篇
植物保护   2772篇
  2021年   380篇
  2020年   443篇
  2019年   488篇
  2018年   796篇
  2017年   840篇
  2016年   760篇
  2015年   637篇
  2014年   795篇
  2013年   1858篇
  2012年   1348篇
  2011年   1567篇
  2010年   1071篇
  2009年   1109篇
  2008年   1519篇
  2007年   1352篇
  2006年   1278篇
  2005年   1109篇
  2004年   1060篇
  2003年   1053篇
  2002年   939篇
  2001年   1258篇
  2000年   1238篇
  1999年   936篇
  1998年   395篇
  1997年   420篇
  1996年   343篇
  1995年   393篇
  1994年   345篇
  1992年   660篇
  1991年   784篇
  1990年   690篇
  1989年   727篇
  1988年   668篇
  1987年   625篇
  1986年   669篇
  1985年   592篇
  1984年   466篇
  1983年   416篇
  1979年   554篇
  1978年   431篇
  1977年   358篇
  1976年   365篇
  1975年   397篇
  1974年   460篇
  1973年   475篇
  1972年   447篇
  1970年   367篇
  1969年   400篇
  1968年   359篇
  1967年   360篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
61.
62.
The objective of this study was to investigate epidemiological risk factors for porcine non-specific colitis (NSC). Forty-seven Scottish pig farms, with and without a clinical history of diarrhoea during the growing period (15-40 kg), were selected. The study included farm visits, clinical inspection of pigs, completion of farm management questionnaires, pathological tests into the cause of the diarrhoea and analysis of the non-starch polysaccharide (NSP) content of feeds. The results from 17 farms designated as NSC and 10 control farms suggest dietary associations with NSC. Farms with NSC fed diets with significantly higher levels of NSPs, especially containing the sugars glucose, arabinose and xylose. Few management factors were identified, although the high prevalence of infectious colitis reduced the power of the study.  相似文献   
63.
Equine proliferative enteropathy (EPE) is a disease of foals caused by the obligate intracellular organism Lawsonia intracellularis. This emerging disease affects mainly weanling foals and causes fever, lethargy, peripheral oedema, diarrhoea, colic and weight loss. The diagnosis of EPE may be challenging and relies on the presence of hypoproteinaemia, thickening of segments of the small intestinal wall observed upon abdominal ultrasonography, positive serology and molecular detection of L. intracellularis in faeces. Although the clinical entity, diagnostic approach and treatment of EPE are well established and described, the epidemiology for this disease has remained largely unaddressed. This article focuses on new developments in the field of EPE, including epidemiology, pathophysiology, clinical signs, diagnosis, treatment and prevention. The Summary is available in Chinese – see Supporting information.  相似文献   
64.
Veterinary pharmacovigilance, as it operates in the European Union (EU), covers a very broad remit, including adverse effects in treated animals, exposed humans and the environment, and in addition, it extends to cover the violation of maximum residue limits. The mainstay of veterinary pharmacovigilance is the spontaneous reporting scheme working along side other systems such as those reporting on residues surveillance. One of the most well established schemes in the EU is that operating in the UK and this paper examines the evolution of that scheme and some of its findings, data from other countries, and information available from the literature. It also tentatively examines the ways that pharmacovigilance can be used for regulatory purposes, and the contribution from pharmacoepidemiology.  相似文献   
65.
Bread-making quality indices (dough strength and dough mixing stability) in relation to flour protein content, glutenin/gliadin ratio, and high-molecular-weight (HMW) subunits of glutenin have been investigated in Triticum aestivum progenies during a three year agronomic trial. Dough strength (W) proved to be a fairly stable characteristic, slightly but positively correlated with flour protein content. High could be associated with a high glutenin/gliadin ratio as well as with the presence of specific HMW. subunits of glutenin, while high protein content tended to favour a balanced dough tenacity-extensibility ratio (P/L = 0.4—0.6). Satisfactory values of dough-mixing stability were frequently observed in association with good expression of W showing that the two quality traits may coexist without much difficulty in the same genotype. From the plant breeding standpoint the data suggest feasible to obtain high dough strength by concentrating in a genotype the HMW subunits of glutenin known to have a beneficial effect on W. However, very high W may present unfavourable P/L ratios. This possibility is enhanced when the flour has a low protein content which often occurs in high yielding genotypes.  相似文献   
66.
The performance of a Didcot-type thermometer screen on an Automatic Weather Station and a conventional Stevenson screen were compared, both with each other and against an aspirated Assmann psychrometer. Maximum temperature in the Didcot screen exceeded the conventional screen maximum by up to 1 K on calm, sunny days, and Didcot minimum temperatures were as much as 1.5 K less than the screen minima on still, clear nights; mean temperature discrepancies between screens were + 0.3 and − 0.4 K for maxima and minima, respectively. The apparent psychrometric constant for the Didcot screen was 1.0 mbar K−1 which increased to 1.2 mbar K−1 when u < 2 m s−1 in contrast to the value of 0.799 mbar K−1 frequently used for the Stevenson screen.  相似文献   
67.
Ultrastructural features of Mycoplasma gallisepticum in tracheal explants were examined using the transmission and stereoscan electron microscope. The organisms were characteristically cocco-bacilliform except when in close contact with the host cells when they assumed an elongated and irregular form characteristically terminating in a bleb which was often embedded in the cell surface. In such organisms there were peripherally aligned fibrillar structures oriented towards the bleb which may have a functional relationship with a probing or moving habit of the mycoplasma.  相似文献   
68.
69.
70.
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