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   28713篇
  免费   1518篇
  国内免费   12篇
林业   1208篇
农学   827篇
基础科学   173篇
  4277篇
综合类   4144篇
农作物   1076篇
水产渔业   1702篇
畜牧兽医   14642篇
园艺   386篇
植物保护   1808篇
  2021年   284篇
  2020年   304篇
  2019年   398篇
  2018年   561篇
  2017年   620篇
  2016年   602篇
  2015年   431篇
  2014年   598篇
  2013年   1159篇
  2012年   1050篇
  2011年   1266篇
  2010年   854篇
  2009年   821篇
  2008年   1221篇
  2007年   1166篇
  2006年   1026篇
  2005年   931篇
  2004年   818篇
  2003年   894篇
  2002年   745篇
  2001年   833篇
  2000年   818篇
  1999年   667篇
  1998年   300篇
  1997年   299篇
  1995年   273篇
  1992年   442篇
  1991年   535篇
  1990年   451篇
  1989年   423篇
  1988年   413篇
  1987年   414篇
  1986年   374篇
  1985年   396篇
  1984年   354篇
  1983年   293篇
  1982年   251篇
  1979年   387篇
  1978年   295篇
  1977年   293篇
  1976年   304篇
  1975年   319篇
  1974年   338篇
  1973年   302篇
  1972年   293篇
  1971年   251篇
  1969年   289篇
  1968年   272篇
  1967年   327篇
  1966年   308篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Three trials were carried out with broilers to compare the effect of different calorie to protein (C : P) ratios in practical‐type diets with the amount of carcass fat at 8 or 9 weeks of age. The latter was estimated on the basis of the concentration of fat or dry matter in a sample of back skin and by visually scoring the amount of abdominal fat.

Rearing broilers on diets containing protein levels slightly above or below the accepted optimum did not affect growth rate. However, in most comparisons the high‐protein diets brought about better food to gain ratios, and in all comparisons they produced relatively lean carcasses. Increasing or decreasing the protein level of finisher diets resulted in a decrease or increase, respectively, in the degree of fatness. A 2‐week period was sufficient to create or reverse these trends in a pronounced manner.

Dietary oil supplementation per se did not increase the amount of carcass fat as long as the C : P ratio was kept constant. If there existed any consistent trend at all, it appeared to act in the opposite direction, towards a decrease in carcass fat.  相似文献   

52.
53.
Ishaaya  I.  Ascher  K. R. S.  Yablonski  Sara 《Phytoparasitica》1981,9(3):207-209
Phytoparasitica - The effect of BAY SIR 8514, diflubenzuron and Hercules 24108 on larval growth, pupation and emergence ofTribolium confusum was determined. BAY SIR 8514 was about twice as active...  相似文献   
54.
In the last two to three decades a significant increase of viral zoonotic infections was observed. These zoonoses are not only newly (or previously unrecognized) emerging diseases, but also due to the reappearance of diseases thought to have been defeated (re-emerging diseases). "New" viral diseases can arise when viruses broaden their host-range (monkey poxvirus; equine morbillivirus), or can be a consequence of intrinsic properties of the virus itself, such as high mutation rates (influenza A virus). Most new or reemerging viral zoonoses are due to infections with hemorrhagic viruses. Many of them are transmitted by insects (arboviruses, e.g. yellow fever virus) or by rodents (e.g. Hanta viruses), others by contact with patients and nosocomial infections (e.g. Ebola virus). The emergence and increase of these diseases are a consequence of anthropogenic environmental changes, such as distortions of the ecological balance and changes in agriculture. In addition, the uncontrolled growth of the cities in tropical and subtropical regions without improvement of the public health measures and the increasing international animal trade and travel also favour the spread and recurrence of these diseases.  相似文献   
55.
Plant susceptibility to herbicides is related to several factors, including the environmental conditions under which the plants develop. Two experiments were carried out using Synedrellopsis grisebachii plants in two different developmental stages (vegetative and reproductive), with the goal of studying plant susceptibility to the herbicide, glyphosate, and the dependence of this susceptibility on light intensity (full sunlight and 70% shading), correlated with leaf anatomy. The experimental design for both experiments was completely randomized, with a 2 × 7 factorial scheme, with two light intensities and seven different doses of glyphosate (0D, 1/4D, 1/2D, D, 2D, 4D and 6D, where D is the recommended dose of 1800 g ae ha?1) as the factors and four replicates per treatment. The leaf anatomy was characterized with optical and scanning electron microscopy. The plants that were grown in full sunlight were more tolerant of glyphosate because of thickening of the adaxial epidermis, parenchyma and main vein structures, which required higher glyphosate doses for effective weed control. The plants that were in the reproductive stage were more tolerant of glyphosate, probably because of lower glyphosate absorption and translocation to the reproductive organs.  相似文献   
56.
An endoscopic survey was performed to assess arytenoid cartilage movement during quiet respiration in 48 Clydesdale horses. Physical characteristics which could influence the length of the recurrent laryngeal nerves were also recorded from these horses and the relationship of these characteristics to the presence of abnormal left arytenoid cartilage movements was assessed statistically. Some degree of abnormal arytenoid movement was observed in 50% of the animals over one year of age. No significant correlation between sex, age, estimated weight, height, or neck length could be found although affected animals were, on average, slightly taller, lighter and longer necked.  相似文献   
57.
A commercially available inactivated Mycoplasma gallisepticum (MG) bacterin was administered to chickens on a multiple-age farm endemically infected with MG. A total of 3400 MG-free pullets were vaccinated with the MG bacterin at 19 weeks of age, and 4300 unvaccinated pullets served as controls. The vaccinated group became serologically positive by the rapid plate agglutination (RPA) test within 3 weeks, and the unvaccinated group became positive in 7 weeks. The hemagglutination-inhibition test responses were observed at approximately the same time as the RPA in both of the groups. Egg production and mortality through 50 weeks of age did not differ significantly between the two groups. MG was isolated from birds of the vaccinated and control groups near the termination of the study.  相似文献   
58.
Despite its small area and intensively cropped landscape, East Java accounts for 30% of Indonesia's cattle population. About two million households draw on family labour to raise cattle in backyard sheds and small enclosures, largely for cash income. In this paper, we examine the opportunity for such small‐scale producers to benefit from Indonesia's economic transformation, given the rising urban demand for beef. The paper reports on a study in two contrasting sites in East Java – irrigated lowlands and rainfed uplands – to explore the constraints facing small‐scale cattle producers in these environments, the means by which they have adapted to these constraints (especially by going beyond the farm household to access feed supplies) and possible means to enhance their production systems and incomes. The findings suggest that such cattle production systems can provide a viable source of livelihood, even for resource‐poor households; hence, appropriately adapted cattle improvement programmes are a sensible component of a pro‐poor development strategy.  相似文献   
59.
60.
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