全文获取类型
收费全文 | 99154篇 |
免费 | 5325篇 |
国内免费 | 4384篇 |
专业分类
林业 | 8087篇 |
农学 | 8419篇 |
基础科学 | 3612篇 |
14185篇 | |
综合类 | 18611篇 |
农作物 | 4671篇 |
水产渔业 | 4831篇 |
畜牧兽医 | 38080篇 |
园艺 | 2162篇 |
植物保护 | 6205篇 |
出版年
2022年 | 1352篇 |
2021年 | 1991篇 |
2020年 | 1862篇 |
2019年 | 1960篇 |
2018年 | 1945篇 |
2017年 | 2342篇 |
2016年 | 2265篇 |
2015年 | 2589篇 |
2014年 | 2586篇 |
2013年 | 4391篇 |
2012年 | 4116篇 |
2011年 | 4723篇 |
2010年 | 3808篇 |
2009年 | 3736篇 |
2008年 | 4233篇 |
2007年 | 4326篇 |
2006年 | 3994篇 |
2005年 | 3899篇 |
2004年 | 2653篇 |
2003年 | 2504篇 |
2002年 | 2249篇 |
2001年 | 3104篇 |
2000年 | 3089篇 |
1999年 | 3003篇 |
1998年 | 1767篇 |
1997年 | 1547篇 |
1996年 | 1494篇 |
1995年 | 1461篇 |
1994年 | 1311篇 |
1993年 | 1282篇 |
1992年 | 1841篇 |
1991年 | 1921篇 |
1990年 | 1873篇 |
1989年 | 1684篇 |
1988年 | 1511篇 |
1987年 | 1398篇 |
1986年 | 1296篇 |
1985年 | 1180篇 |
1984年 | 962篇 |
1983年 | 764篇 |
1982年 | 565篇 |
1979年 | 812篇 |
1978年 | 627篇 |
1976年 | 528篇 |
1974年 | 627篇 |
1973年 | 609篇 |
1972年 | 641篇 |
1971年 | 604篇 |
1970年 | 593篇 |
1969年 | 540篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
29 samples of commonly used surfaces were tested for their water characteristics (litre weight, water capacity, water binding, water evaporation) and their contribution to airborne fungal spores (dust formation, dust setting). The results are discussed in comparison to the literature with regard to the environment. The results are: 1. Any surface--no matter of what material--eventually causes air pollution with fungal spores and dust. 2. Correct watering prevents air pollution by any surface. 3. Artificial products have no advantage over natural materials in the parameters tested. 4. The question of proper disposal of old surface material has to be clarified before purchase. The results show that a mixture of sand and wood shavings should be recommended as a surface for indoor arenas, especially in regard to environmental protection and proper disposal. 相似文献
72.
J W Tyler J S Cullor M C Thurmond D W Hird K M Parker 《American journal of veterinary research》1989,50(1):126-130
Serologic recognition of common lipopolysaccharide core antigens has been related to enhanced resistance to gram-negative bacterial disease in several species. Class-specific titers (IgG, IgM) were determined by direct ELISA, using intact Escherichia coli (J5) as a plate antigen. Serum samples were obtained from 224 neonatal swine between the ages of 36 and 60 hours. The mean (+/- SEM) log10 IgG titer against gram-negative core antigens was 1:1,713 +/- 0.4718 and the mean log10 IgM titer was 1:202 +/- 0.5644. The IgG titer was directly related with litter size, birth weight, and serum total IgG concentration; IgM titer was directly related with dam parity and serum total IgG concentration. 相似文献
73.
The feasibility of producing salmonella-free turkeys was investigated over a 5-year period. In Phase 1, a hatchery-breeder flock operation was monitored extensively for 4 years. Hatching eggs from a primary breeder over this period (1978-81) resulted in salmonella-free day-old poults from which 7500 hens and 600 tons were selected for breeders each of the 4 years. Approximately 2.5 million poults were produced over the 4 years. Salmonella arizonae was isolated from the hatchery debris over a 2-week period in 1980. The pelleted feed contained no animal protein products except fish solubles. A sample of feed from each delivery was cultured with no salmonella isolations. Environmental samples of dust and litter remained negative for salmonella. Phase 2 involved monitoring seven grow-out flocks initiated with salmonella-free poults with extra precautions directed at the feed and environment. The intestinal tracts of five of seven flocks at the time of marketing were negative for salmonella. Phase 3 involved a primary breeder-hatchery that had a 10-year history of S. sandiego infection in its breeder flocks and poults. A vaccination program using an autogenous oil-adjuvant bacterin supplementing other sanitation and management efforts resulted in elimination of S. sandiego. Because the breeder went out of business, it was not possible to determine if the freedom from salmonella could be sustained over a period of years. 相似文献
74.
75.
双孢蘑菇覆土层有益微生物消长规律 总被引:1,自引:0,他引:1
将土样制备成稀释液,采用平板涂布培养法,分析双孢蘑菇覆土期、充分发菌期,原基形成期、采收前和采收后2d5个时期土样中几种有益微生物和消长规律。结果表明,原基表成前和采收后,采白色和采收后2d5下时期土样中几种有益微生物的消化规律。结果表明,原其开前和采收后,采白色孢杆菌(Bacillus)、固氮苗(Azotobacter)和假单胞杆菌(Pseudomonas)数量增加;链霉菌(Streptomyces)数量增减比较平缓,而土灰色芽孢杆菌的数量一直呈下降趋势。 相似文献
76.
77.
78.
钾肥施用量对脐橙产量和品质的影响 总被引:30,自引:0,他引:30
1996~1999年连续4年在湖北省秭归县进行了脐橙钾肥施用量田间试验。结果表明,尽管各处理脐橙产量年度变化很大,但施钾显著提高产量和经济效益,1997~1999年施钾平均增产26.3%~41.8%,施钾(K2O)125、250、375kg/hm2年均增加纯利 10110、15840、9970元/hm2,产投比分别为 19.38、15.40和7.04;在试验条件下施钾(K2O)250kg/hm2增产效果最好;施钾有提高脐橙外观品质和内在品质的趋势,例如施钾提高或保持单果重、增加果皮厚度、提高维生素C含量等;但施钾对品质的影响年度间差异较大,尚需进一步研究。 相似文献
79.
80.
Lactate Kinetics in veterinary Critical Care: A Review 总被引:3,自引:0,他引:3
Michael S. Lagutchik DVM Gregory K. Ogilvie DVM Wayne E. Wingfield MS DVM Timothy B. Hackett DVM MS 《Journal of Veterinary Emergency and Critical Care》1996,6(2):81-95.
Elevation in blood lactate concentration, with or without accompanying metabolic acidosis, is a hallmark finding in patients with circulatory compromise, and is also consistently noted in other conditions affecting critically ill or injured individuals. Little is reported in a veterinary literature regarding lactate measurement in the emergency and critical care setting, despite impressive reports of the clinical usefulness of lactate measurement in people. The purpose of this article is to review lactate kinetics and the clinical utility of lactate measurement. Limitations to lactate evaluation will also be discussed. 相似文献