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   1495篇
  免费   66篇
林业   77篇
农学   51篇
基础科学   18篇
  298篇
综合类   59篇
农作物   148篇
水产渔业   159篇
畜牧兽医   507篇
园艺   50篇
植物保护   194篇
  2023年   19篇
  2022年   53篇
  2021年   72篇
  2020年   65篇
  2019年   93篇
  2018年   66篇
  2017年   88篇
  2016年   70篇
  2015年   52篇
  2014年   52篇
  2013年   112篇
  2012年   96篇
  2011年   87篇
  2010年   62篇
  2009年   46篇
  2008年   69篇
  2007年   43篇
  2006年   52篇
  2005年   59篇
  2004年   39篇
  2003年   25篇
  2002年   39篇
  2001年   15篇
  2000年   14篇
  1999年   19篇
  1998年   7篇
  1997年   11篇
  1996年   5篇
  1995年   6篇
  1994年   5篇
  1993年   8篇
  1992年   6篇
  1991年   9篇
  1990年   9篇
  1989年   8篇
  1988年   4篇
  1987年   10篇
  1986年   4篇
  1985年   6篇
  1984年   7篇
  1983年   5篇
  1982年   5篇
  1977年   3篇
  1976年   3篇
  1975年   4篇
  1974年   3篇
  1970年   3篇
  1969年   3篇
  1967年   3篇
  1966年   3篇
排序方式: 共有1561条查询结果,搜索用时 546 毫秒
991.
992.
Calving ease (CE) is a trait of economic importance that affects animal welfare and farm profitability. The objective of present study was to investigate genetic and environmental factors affecting CE among Primiparous (PP) and multiparous (MP) buffaloes. A total of 9,627 records from 1999 MP and 2,110 PP recorded during the period from 1988 to 2018 were considered. Herd, season of calving, year of calving, birth weight, parity order and gestation length significantly affected CE rate, while age at first calving and sex of calf had no significant effects. Direct and maternal heritabilities of CE in PP and MP were 0.06 and 0.01, respectively. The low heritability of CE indicated that direct selection may not be an effective method to improve CE trait in Egyptian buffalo.  相似文献   
993.
Summary The temperature dependence of the NO production rate and the NO consumption rate constant was measured in an Egyptian soil, a soil from the Bavarian Forest, and a soil from the Donau valley, together with the temperature dependence of the potential rates of ammonium oxidation, nitrite oxidation, and denitrification, and the temperature dependence of the growth of NH inf4 sup+ -oxidizing, NO inf2 sup- -oxidizing, and NO inf3 sup- -reducing bacteria in most probable number assays. In the acidic Bavarian Forest soil, NO production was only stimulated by the addition of NO inf3 sup- but not NH inf4 sup+ . However, NO production showed no temperature optimum, indicating that it was due to chemical processes. Most probable numbers and potential activities of nitrifiers were very low. NO consumption, in contrast, showed a temperature optimum at 25°C, demonstrating that consumption and production of NO were regulated individually by the soil temperature. In the neutral, subtropical Egyptian soil, NO production was stimulated only by the addition of NH inf4 sup+ but not NO inf3 sup- . All activities and most probable numbers showed a temperature optimum at 25° or 30°C and exhibited apparent activation energies between 61 and 202 kJ mol-1. However, a few nitrifiers and denitrifiers were also able to grow at 8° or 50°C. Similar temperature characteristics were observed in the Donau valley soil, although it originated from a temperate region. In this soil NO production was stimulated by the addition of NH inf4 sup+ or of NO inf3 sup- . Both NO production and consumption were stimulated by drying and rewetting.  相似文献   
994.
Vitamin E was determined by the high-performance liquid chromatography (HPLC) method. All the plants tested showed differences in their alpha-tocopherol content and the differences were significant (p < 0.05). The highest alpha-tocopherol content was in Sauropus androgynus leaves (426.8 mg/kg edible portion), followed by Citrus hystrix leaves (398.3 mg/kg), Calamus scipronum (193.8 mg/kg), starfruit leaves Averrhoa belimbi (168.3 mg/kg), red pepper Capsicum annum (155.4 mg/kg), local celery Apium graveolens (136.4 mg/kg), sweet potato shoots Ipomoea batatas (130.1 mg/kg), Pandanus odorus (131.5 mg/kg), Oenanthe javanica (146.8 mg/kg), black tea Camelia chinensis (183.3 mg/kg),papaya Carica papaya shoots (111.3 mg/kg), wolfberry leaves Lycium chinense (94.4 mg/kg), bird chili Capsicum frutescens leaves (95.4 mg/kg), drumstick Moringa oleifera leaves (90.0 mg/kg), green chili Capsicum annum (87 mg/kg), Allium fistulosum leaves (74.6 mg/kg), and bell pepper Capsicum annum (71.0 mg/kg). alpha-Tocopherol was not detected in Brassica oleracea, Phaeomeria speciosa, Pachyrrhizus speciosa, Pleurotus sajor-caju, and Solanum melongena.  相似文献   
995.
996.
The mosquito Anopheles balabacensis balabacensis has been identified as a natural vector of at least two species of simian malaria in the monsoon forests of the northern Malay States. This mosquito is also a serious vector of human malaria from Viet Nam to northern Malaya. This is the first report of a mosquito which transmits both human and simian malaria in nature.  相似文献   
997.
Journal of Soils and Sediments - Deforestation is one of the ecosystem disservices associated with accelerated loss of soil organic carbon (SOC) and nitrogen (TN). The objective of our study was to...  相似文献   
998.
999.
1000.
Hegazy ME  Su JH  Sung PJ  Sheu JH 《Marine drugs》2011,9(7):1243-1253
Four new cembranoids, lobophylins A-D (1-4), and one novel secocembrane, lobophylin E (5) were isolated from a soft coral Lobophytum sp. The structures of new metabolites were elucidated on the basis of extensive spectroscopic methods. Among these metabolites, 1-4 are rarely found cembranoids possessing a tetrahydrofuran moiety with a 3,14-ether linkage. In addition, 5 is the first secocembrane possessing two tetrahydrofuran moieties with 3,14- and 4,7-ether linkages.  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