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   137759篇
  免费   7641篇
  国内免费   123篇
林业   5947篇
农学   4076篇
基础科学   859篇
  15792篇
综合类   25135篇
农作物   5357篇
水产渔业   6358篇
畜牧兽医   71861篇
园艺   1581篇
植物保护   8557篇
  2018年   1835篇
  2017年   2031篇
  2016年   1854篇
  2015年   1588篇
  2014年   2006篇
  2013年   4928篇
  2012年   3653篇
  2011年   4359篇
  2010年   2864篇
  2009年   2950篇
  2008年   4435篇
  2007年   4167篇
  2006年   3900篇
  2005年   3678篇
  2004年   3539篇
  2003年   3699篇
  2002年   3364篇
  2001年   4104篇
  2000年   4114篇
  1999年   3197篇
  1998年   1293篇
  1997年   1354篇
  1995年   1504篇
  1994年   1294篇
  1993年   1344篇
  1992年   2727篇
  1991年   3013篇
  1990年   2876篇
  1989年   2902篇
  1988年   2676篇
  1987年   2687篇
  1986年   2781篇
  1985年   2692篇
  1984年   2194篇
  1983年   1935篇
  1982年   1334篇
  1979年   2099篇
  1978年   1616篇
  1977年   1462篇
  1976年   1331篇
  1975年   1453篇
  1974年   1875篇
  1973年   1894篇
  1972年   1887篇
  1971年   1779篇
  1970年   1754篇
  1969年   1626篇
  1968年   1433篇
  1967年   1516篇
  1966年   1313篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
181.
182.
Twenty-one Bunaji (White Fulani, Zebu) and 21 Friesian X Bunaji cross-bred bull calves, approximately 6 months of age, were each divided after weaning into two groups and fed isocaloric rations containing 14.45% (high protein) and 8.51% (low protein) crude protein for 10 months. Serum samples were collected biweekly for 10 months and analysed for serum proteins. Age had no significant effect. The Bunaji had significantly (P less than 0.05) higher total protein, albumin, and alpha 1-globulin than Friesian X Bunaji. While there was no significant difference in body condition score between the two breeds, the Friesian X Bunaji had a significantly (P less than 0.05) higher growth rate. Animals on high protein diets had significantly (P less than 0.05) higher total protein, albumin, alpha 2-globulin, gamma-globulin and total globulin than those on low protein. However, alpha 1-globulin and beta-globulin were not significantly (P greater than 0.05) different for the two treatment groups.  相似文献   
183.
E. DUVEILLER 《EPPO Bulletin》1994,24(1):135-157
The literature related to bacterial leaf streak of cereals, due to various pathovars of Xanthomonas campestris , is confusing and dispersed. This review presents a synthesis of the knowledge that has been accumulated on the disease in cereals since the early reports on barley and wheat. The aim is to present the current status on geographical distribution of the disease, to explain possible confusions in symptoms, and to show the limited quantitative information available on losses and on host/pathogen interactions. Disease etiology and means of control are also reviewed. The objective is to define the present situation of black chaff in wheat, barley and triticale, and to delineate the major research needs in these crops. Difficulties in controlling bacterial leaf streak arise as a result of limited epidemiological knowledge and of the absence of satisfactory seed treatment permitting the eradication of the bacterium. There is an urgent need for a seed certification scheme and for more information on genetic resistance, with a view to limiting outbreaks of this sporadic but devastating disease.  相似文献   
184.
Muscle biopsies were taken from the middle gluteal muscle of 28 Standardbred trotters, 3-4 years of age. The 13 horses in Group T were trained consistently from 18 months of age, whereas the 15 horses in Group UT were not exposed to any systematic training before 3 years of age. Group T horses had a lower percentage of Type IIB fibres (31%) than did Group UT horses (39%). Citrate synthase (CS) activity, representing oxidative capacity, was higher in Group T (72 mmol kg-1 min-1) than in Group UT (47 mmol kg-1 min-1). Biopsies were taken from 4 horses in each group when they were foals and then annually until 3-4 years of age. Results from this study indicate that regular training of Standardbreds from 18 months of age resulted in increased CS activity and a decrease in the percentage of Type IIB fibres. This study shows that training, not growth, is the main factor that induces a high oxidative capacity and a high Type IIA/IIB fibre ratio in muscle of Standardbred trotters.  相似文献   
185.
Lyophilised serum offers significant advantages over frozen serum when it comes to shipping such material over long distances. Babesia bigemina and B bovis were cultured in medium supplemented by either frozen-thawed or lyophilised-rehydrated serum. There were no significant differences between the two types of medium in the growth of parasites and percentage of infected cells during subcultivation for 18 days.  相似文献   
186.
187.
This paper reviews the radiological features of 50 canine incisive or maxillary tumours and discusses the value of radiological assessment in the diagnosis and staging of these tumours. The 50 tumours examined included 21 sarcomas, 15 carcinomas, three melanomas and an assortment of benign tumours of the oral cavity. There was not any site specificity for the different histological tumour types within the upper dental arcade, although fibrosarcomas had a tendency to be maxillary whereas the squamous cell carcinomas were equally distributed between the incisive and maxillary regions. Seventy-eight per cent of fibrosarcomas, 82 per cent of squamous cell carcinoma and all three melanomas examined showed radiological evidence of bone involvement. Radiographic changes were also seen in the benign tumours. The pattern of growth of tumours correlated with the radiological changes observed. Malignant tumours showed a tendency to irregular or aggressive bone loss whereas bone production predominated in the benign tumours.  相似文献   
188.
189.
Antibody responses to a commercial avian encephalomyelitis virus (AEV) vaccine administered by different routes were measured by an enzyme-linked immunosorbent assay (ELISA). Responses to single doses of vaccine administered by the ocular route to 10% of a flock were comparable with those obtained when all birds received a single dose in the drinking water. However, ocular vaccination of 5% of the flock resulted in significantly lower responses than those obtained when 10% were vaccinated. Maternal antibody was shown by the ELISA to persist in chickens from vaccinated flocks for up to 21 days after hatching. Day-old chickens with serum absorbances of < 0.3 at 492 nm, as determined by the ELISA, were shown to be susceptible to intracerebral challenge with the neurotropic Van Roekel strain of AEV.  相似文献   
190.
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