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   1825篇
  免费   136篇
  国内免费   2篇
林业   180篇
农学   68篇
基础科学   20篇
  376篇
综合类   76篇
农作物   138篇
水产渔业   299篇
畜牧兽医   608篇
园艺   48篇
植物保护   150篇
  2024年   3篇
  2023年   17篇
  2022年   40篇
  2021年   71篇
  2020年   77篇
  2019年   107篇
  2018年   86篇
  2017年   93篇
  2016年   89篇
  2015年   52篇
  2014年   85篇
  2013年   112篇
  2012年   128篇
  2011年   150篇
  2010年   82篇
  2009年   85篇
  2008年   130篇
  2007年   97篇
  2006年   71篇
  2005年   84篇
  2004年   80篇
  2003年   66篇
  2002年   45篇
  2001年   18篇
  2000年   7篇
  1999年   10篇
  1998年   8篇
  1997年   9篇
  1996年   5篇
  1995年   3篇
  1994年   7篇
  1993年   5篇
  1992年   5篇
  1991年   2篇
  1990年   3篇
  1989年   2篇
  1988年   3篇
  1987年   4篇
  1986年   5篇
  1984年   3篇
  1983年   2篇
  1981年   3篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
  1970年   2篇
  1963年   1篇
  1962年   1篇
  1954年   1篇
  1942年   1篇
排序方式: 共有1963条查询结果,搜索用时 812 毫秒
961.
Tropical Animal Health and Production - The objective of this study was to evaluate the effects of rumen-protected oil (soybean and palm oil) in supplements for beef cattle during the fattening...  相似文献   
962.
Tropical Animal Health and Production - The study aimed to evaluate heat-treated bean residue meal (Phaseolus vulgaris)—BRM—as an alternative protein source in diets for Nile tilapia...  相似文献   
963.

Carcass characteristic and meat quality from bulls and Nellore steers (n?=?64 total) subjected to different grazing heights (15, 25, 35, and 45 cm) were evaluated isolatedly, under continuous grazing and variable load, in pastures of Convert grass. The experimental period was from May 2015 to June 2017, in an area of 16 ha, divided into 16 paddocks of 1 ha. The experimental design was randomized blocks with four replications. Each paddock was grazed by three animals and regulators, used to adjust grazing heights. The final slaughter weight, hot carcass, and crude protein in the meat of steers were higher when the pastures were managed at 42 cm. When the pasture was managed between 25 and 35 cm in height, greater fat thickness, marbling, muscle:bone and muscle+fat:bone ratio and lower color* of the meat and percentage of bone were found. For the steers, the height of 40 cm provided higher fat thickness and marbling in the meat. The loss during thawing in meat was greater at 28 cm in height. The heights of grazing alter the carcass characteristics and meat of bulls and steers.

  相似文献   
964.
965.
We estimated the oceanic inventory of anthropogenic carbon dioxide (CO2) from 1980 to 1999 using a technique based on the global chlorofluorocarbon data set. Our analysis suggests that the ocean stored 14.8 petagrams of anthropogenic carbon from mid-1980 to mid-1989 and 17.9 petagrams of carbon from mid-1990 to mid-1999, indicating an oceanwide net uptake of 1.6 and 2.0 +/- 0.4 petagrams of carbon per year, respectively. Our results provide an upper limit on the solubility-driven anthropogenic CO2 flux into the ocean, and they suggest that most ocean general circulation models are overestimating oceanic anthropogenic CO2 uptake over the past two decades.  相似文献   
966.
967.
Carlaviruses are plant-infecting viruses with flexuous filamentous particles of approximately 650 nm in length and a positive single-stranded hexacistronic RNA molecule as the genome. In this study, we analysed 14 samples of brassicas plants, reportedly affected by carlaviruses, that were collected in distant and edaphoclimatic distinct regions in Brazil. The genomes of four viral isolates detected in leaf kale (Brassica oleracea var. acephala) plants displayed the typical genomic organization of carlaviruses, subdivided into two contrasting identity profiles. Isolates T25, T107, and T110 showed a higher sequence identity among them (c.93%) than with T90 (c.67%), which had the highest nucleotide sequence identity (85.2%) with the only documented genomic fragment, approximately 1 kb of the RNA 3′-end, of cole latent virus (CoLV). Identity values among the other three isolates and CoLV were consistently lower than 78.6%. Nucleotide and amino acid sequence identity values of the replicase cistron of the isolates T25 and T90 are below the threshold for species demarcation in the genus Carlavirus. Upon mechanical transmission, these two isolates induced different symptoms in brassicas and solanaceous plants. Overall, data indicated that these viruses belong to two related but distinct species of carlaviruses. While T90 was recognized as an isolate of CoLV, the remaining isolates were considered members of a new tentative carlavirus named Cole mild mosaic virus (CoMMV). Current work provides convincing support for the taxonomic status of the species Cole latent virus, enlarges the known diversity of carlaviruses, and makes available new molecular tools to improve surveys of brassica-infecting viruses.  相似文献   
968.
European Journal of Plant Pathology - Pine needle diseases, such as red band and brown spot needle blight, are serious pine diseases that threatens forests in many countries. Several outbreaks have...  相似文献   
969.
970.
Marginal land use changes can abruptly result in non-marginal and irreversible changes in ecosystem functioning and the economic values that the ecosystem generates. This challenges the traditional ecosystem services (ESS) mapping approach, which has often made the assumption that ESS can be mapped uniquely to land use and land cover data. Using a functional fragmentation measure, we show how landscape pattern changes might lead to changes in the delivery of ESS. We map changes in ESS of dry calcareous grasslands under different land use change scenarios in a case study region in Switzerland. We selected three ESS known to be related to species diversity including carbon sequestration and pollination as regulating values and recreational experience as cultural value, and compared them to the value of two production services including food and timber production. Results show that the current unceasing fragmentation is particularly critical for the value of ESS provided by species-rich habitats. The article concludes that assessing landscape patterns is key for maintaining valuable ESS in the face of human use and fluctuating environment.  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