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   310篇
  免费   15篇
  国内免费   2篇
林业   16篇
农学   6篇
基础科学   7篇
  55篇
综合类   72篇
农作物   16篇
水产渔业   17篇
畜牧兽医   114篇
园艺   9篇
植物保护   15篇
  2023年   2篇
  2022年   6篇
  2021年   10篇
  2020年   10篇
  2019年   7篇
  2018年   8篇
  2017年   6篇
  2016年   8篇
  2015年   11篇
  2014年   3篇
  2013年   8篇
  2012年   16篇
  2011年   28篇
  2010年   10篇
  2009年   13篇
  2008年   21篇
  2007年   14篇
  2006年   19篇
  2005年   16篇
  2004年   12篇
  2003年   5篇
  2002年   4篇
  2001年   2篇
  2000年   5篇
  1999年   4篇
  1998年   4篇
  1997年   2篇
  1996年   3篇
  1995年   3篇
  1991年   3篇
  1990年   2篇
  1989年   2篇
  1985年   3篇
  1983年   3篇
  1982年   2篇
  1980年   3篇
  1979年   3篇
  1978年   6篇
  1977年   4篇
  1974年   3篇
  1971年   2篇
  1970年   2篇
  1967年   4篇
  1949年   2篇
  1944年   2篇
  1942年   2篇
  1932年   1篇
  1930年   1篇
  1920年   1篇
  1918年   1篇
排序方式: 共有327条查询结果,搜索用时 27 毫秒
51.
Enhanced expression of cyclooxygenase-2 in glaucomatous dog eyes   总被引:3,自引:1,他引:3  
Objective Cyclooxygenase‐2 (COX‐2)‐derived prostaglandins (PGs) are shown to play important pathophysiologic roles in various disease states. Recently, the effectiveness of topical PGs in reducing intraocular pressure (IOP) has stimulated further interest in the physiologic function of COX‐2 and PGs in normal and glaucomatous eyes. Therefore, we investigated the cell‐type distribution and expression of COX‐2 in normal and glaucomatous dog eyes. Procedures Using isoform‐specific antibodies, we immunohistochemically evaluated COX‐2 expression in formalin‐fixed and paraffin‐embedded normal (n = 5) and glaucomatous (n = 17) dog eyes. Results In the normal eyes, only minimal COX‐2 immunoreactivity was observed in the ciliary epithelium. In the glaucomatous eyes, COX‐2 expression was further observed in the cornea and corneoscleral limbus. In the cornea, moderate to strong COX‐2 expression was observed in all corneal layers (epithelium, stromal cells and endothelium), with the greatest expression present in the epithelial layer. In the corneoscleral limbus area, COX‐2 immunoreactivity was noted in the stromal cells of sclera, trabecular meshwork and endothelial cells of the angular aqueous plexus. Conclusions Increased expression of COX‐2 in dog glaucomatous eyes suggests that COX‐2‐derived PGs may have a potential role in the pathogenesis of canine glaucoma.  相似文献   
52.
对墨西哥大刍草、玉草3号和玉草6号3种不同类型饲草玉米在孕穗期、抽雄期和吐丝期的产量、青贮品质及其营养价值进行了分析。结果表明:品种和生育期对鲜、干草产量有显著影响,而二者之间的交互作用对鲜、干草产量影响不显著;3个品种鲜、干草产量均在吐丝期最高,其中,玉草6号鲜、干草产量极显著高于玉草3号和墨西哥大刍草。从抽雄期及以后,所有饲草玉米干物质(DM)含量均达20%以上,符合青贮对水分的要求。粗蛋白(CP)含量从孕穗期到吐丝期逐渐降低,变幅为8.19%DM~12.80%DM;各时期CP含量均以玉草6号最高,玉草3号和墨西哥大刍草CP含量差异较小。可溶性糖(WSC)含量在孕穗期最高,纤维含量随生育期延长均呈上升趋势。青贮发酵品质在不同生育期差异显著,孕穗期pH值为3.69,乳酸(LA)含量为7.00%DM,发酵品质最优。品种主效应分析表明,玉草6号发酵品质最好,玉草3号和墨西哥大刍草差异不显著。综合分析品种和生育期对青贮发酵品质和营养成分的影响,玉草6号在孕穗期青贮,相对饲用价值达103.28,发酵品质和营养价值最好;玉草3号和墨西哥大刍草在抽雄期青贮发酵品质和营养价值最佳。  相似文献   
53.
Visceral leishmaniasis was diagnosed in a 5-year-old English Foxhound born and housed in an Ohio research colony. Physical examination revealed pyrexia, hematochezia, panuveitis, splenomegaly, and lymphadenopathy. Hematologic and serum biochemical abnormalities consisted of anemia, thrombocytopenia, hypoalbuminemia, hyperglobulinemia, azotemia, and proteinuria. Postmortem examination revealed widely disseminated (spleen, bone marrow, lymph node, liver, kidney, lungs) Leishmania amastigotes within macrophages.  相似文献   
54.
This study was designed to compare morbidity and mortality due to bovine respiratory disease (BRD) in 1,400 ranch-fresh, northern US calves that received either no metaphylaxis (MTX) (Group 1), MTX prompted by pen morbidity (Group 2), MTX prompted by a decline in feed intake (Group 3), or on-arrival MTX (Group 4). Ceftiofur crystalline free acid (6.6 mg/kg) was the MTX antimicrobial used. Decreased feed intake did not meet the study threshold, so Groups 1 and 3 were combined into a single control group. The percentage of calves not treated for BRD was 14% to 15% higher in Groups 4 and 2 (72.7% and 73.4%, respectively) compared with the controls (58.2%; P less than or equal to .02). Mortality was numerically higher in Group 2 (3.4%) compared with Groups 4 and 1 (0.9% and 1.6%, respectively). There were no differences in average daily gain or feed consumption. In northern, ranch-fresh calves, MTX as a health management practice reduces the incidence of BRD and has better utility when performed on-arrival versus relying on morbidity as a signal for timing antimicrobial administration.  相似文献   
55.
Landscape Ecology - Increases in fire frequency, intensity and extent are occurring globally. Relative to historical, Indigenous managed conditions, contemporary landscapes are often characterised...  相似文献   
56.
Abstract

Granger causality tests revealed leading indicators of shrimp futures prices, implying that futures prices do not reflect all available market information and potentially fail to be an exemplary price discovery mechanism. Trading simulations confirmed that the use of some leading indicators allowed profitable arbitrage in shrimp futures trading. Shrimp futures were deficient as a hedging tool, as well. Correlations between futures and wholesale cash prices were often low, and basis risk rivaled price risk. Lack of liquidity is a likely explanation for shrimp futures’ shortcomings as a hedging tool and price discovery mechanism.  相似文献   
57.
Carnivore extinctions frequently have cascading impacts through an ecosystem, so effective management of ecological communities requires an understanding of carnivore vulnerability. This has been hindered by the elusive nature of many carnivores, as well as a disproportionate focus on large-bodied species and particular geographic regions. We use multiple survey methods and a hierarchical multi-species occupancy model accounting for imperfect detection to assess extinction risk across the entire carnivore community in Ghana’s Mole National Park, a poorly studied West African savanna ecosystem. Only 9 of 16 historically occurring carnivore species were detected in a camera-trap survey covering 253 stations deployed for 5469 trap days between October 2006 and January 2009, and our occupancy model indicated low overall likelihoods of false absence despite low per-survey probabilities of detection. Concurrent sign, call-in, and village surveys, as well as long-term law enforcement patrol records, provided more equivocal evidence of carnivore occurrence but supported the conclusion that many carnivores have declined and are likely functionally or fully extirpated from the park, including the top predator, lion (Panthera leo). Contrary to expectation, variation in carnivore persistence was not explained by ecological or life-history traits such as body size, home range size or fecundity, thus raising questions about the predictability of carnivore community disassembly. Our results imply an urgent need for new initiatives to better protect and restore West Africa’s embattled carnivore populations, and they highlight a broader need for more empirical study of the response of entire carnivore communities to anthropogenic impact.  相似文献   
58.
This article builds on the food sovereignty literature to ask pointed questions about the interplay of market forces and political liberalism. Specifically, we use cuisine as a lens to interrogate the assumption that multiculturalism is compatible with Indigenous food sovereignty. Because multicultural inclusion is the means by which Indigenous Peoples’ gastronomies are commodified and alienated, they experience not gastronomic multiculturalism but culinary colonialism. Accordingly, food sovereignty in colonial contexts must embrace both the active sharing and the mindful withholding of food as political acts, and acknowledge that culinary culture is not simply a market commodity but also a politically-embedded process. In drawing together the threads of this argument, we advocate for a broadening of the discussion on Indigenous food sovereignty to include the resistance and resurgence enacted through gastronomy.  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