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   2150篇
  免费   237篇
  国内免费   106篇
林业   70篇
农学   90篇
基础科学   5篇
  39篇
综合类   516篇
农作物   89篇
水产渔业   228篇
畜牧兽医   1079篇
园艺   29篇
植物保护   348篇
  2024年   3篇
  2023年   32篇
  2022年   69篇
  2021年   87篇
  2020年   114篇
  2019年   88篇
  2018年   69篇
  2017年   87篇
  2016年   96篇
  2015年   87篇
  2014年   104篇
  2013年   124篇
  2012年   134篇
  2011年   152篇
  2010年   116篇
  2009年   112篇
  2008年   94篇
  2007年   111篇
  2006年   98篇
  2005年   75篇
  2004年   67篇
  2003年   49篇
  2002年   63篇
  2001年   63篇
  2000年   44篇
  1999年   29篇
  1998年   37篇
  1997年   38篇
  1996年   24篇
  1995年   25篇
  1994年   26篇
  1993年   18篇
  1992年   19篇
  1991年   28篇
  1990年   19篇
  1989年   17篇
  1988年   16篇
  1987年   9篇
  1986年   7篇
  1985年   8篇
  1984年   4篇
  1983年   5篇
  1981年   3篇
  1980年   5篇
  1979年   2篇
  1978年   5篇
  1976年   2篇
  1974年   1篇
  1956年   4篇
  1955年   1篇
排序方式: 共有2493条查询结果,搜索用时 31 毫秒
1.
鸡球虫病、坏死性肠炎等肠道感染可能对消化道内源性氨基酸损失产生较大影响。虽然对这一课题的了解不多,但相关文献报道了这些疾病对氨基酸表观回肠消化率的影响。在确定肠内氨基酸流动时必须考虑多种因素,包括肉鸡的年龄、是否有病原体、肠内氨基酸代谢等。胃肠道和肝脏共同承担向外周血释放氨基酸的任务,这些氨基酸是支持蛋白质合成所必需的。一般来说,肠道是氨基酸代谢反应的一个非常活跃的器官系统,它首先会满足自身对氨基酸的需求,然后才会将氨基酸输送到机体其他部分。因此,本综述旨在讨论影响肠内氨基酸流动的因素及日粮氨基酸和肠道感染对氨基酸利用和代谢的影响。  相似文献   
2.
Data on endoparasitic infections in dogs from dog shelters in Southeastern Europe are limited; thus, this study aimed to add to the existing knowledge on this topic by reporting on the prevalence of intestinal parasites in dogs from public dog shelters in the Republic of Serbia. In 2017 and 2018, individual and pooled fecal samples, were collected from 1267 dogs from six shelters. All samples were qualitatively examined for parasites using flotation tests. Seven taxa of intestinal parasites were identified: Cystoisospora spp., ascarids: Toxocara canis and Toxascaris leonina, hookworms, Trichuris vulpis, taeniids and Dipylidium caninum. The overall prevalence of intestinal parasites was 58. 3 % (78. 1 % in young dogs and 53.1 % in adult dogs). The parasites detected in both young (<1 year old) and adult dogs (>1 year old) were Cystoisospora spp. (20 % and 4.9 %), T. canis (33.5 % and 14.7 %), T. leonina (7.7 % and 2.3 %), and hookworms (16.9 % and 15 %), respectively. However, T. vulpis (9.6 %), taeniids (1.3 %), and D. caninum (5.4 %) were detected only in adult dogs. In the Belgrade shelter, young dogs had a higher prevalence of endoparasitic infections (18.9 %, 49/260) than adult dogs (14.8 %, 149/1007). In the Subotica, Jagodina and Niš shelters, young dogs had significantly higher (p < 0.001 and p < 0.05, respectively) prevalence of endoparasitic infections (10 %, 12.3 % and 14.6 %) than adult dogs (5.3 %, 8 % and 7.2 %). These results will be useful for establishing health care programs in dog shelters and implementing effective strategies for the control of intestinal parasites.  相似文献   
3.
为明确黑胫病菌(Leptosphaeria biglobosa)在甘蓝型油菜叶片和茎中的侵染及扩展过程,利用绿色荧光蛋 白(GFP)标记的黑胫病菌株接菌油菜叶片,利用激光共聚焦显微镜观察菌株在油菜叶片和茎中的侵染过程。结果 表明,接种油菜叶片7 h后,分生孢子萌发并长出芽管;17 h后,芽管侵入气孔;24 h后,分生孢子全部萌发;36 h后萌 发的芽管形成菌丝;120 h后,菌丝在叶片表皮细胞间隙蔓延,并侵入叶肉细胞。13 d后,菌丝侵入茎部皮层组织; 15 d后,菌丝在皮层细胞间隙蔓延,并侵染至茎表皮;21 d后,菌丝侵染至维管组织;23 d后,菌丝侵染至茎韧皮部; 25 d后,茎导管被侵染,并向木质部扩展。本研究发现的L. biglobosa 在油菜叶片和茎中的侵染过程,可为油菜与黑 胫病菌互作的研究、黑胫病致病机理及防治提供参考。  相似文献   
4.
利用标记基因追踪病原菌在植物体内的入侵和定殖,是研究病原菌-寄主互作的重要手段。本研究利用电转化法将广宿主载体pBBR1MCS2-Tac-EGFP导入青枯雷尔氏菌(Ralstonia solanacearum)GMI1000菌株中,获得了青枯雷尔氏菌带绿色荧光标记的转化子。转接试验结果表明,转化子的抗生素抗性和绿色荧光强度有良好的遗传稳定性。pBBR1MCS2-Tac-EGFP不影响GMI1000菌株的致病力,且EGFP蛋白能够在植物中稳定表达。灌根法接种试验结果表明,病原菌在第1天即完成对根系的侵染,并在第6天扩散至其他组织,随后造成植株萎蔫。研究结果表明所获转化子可用于后续的病原菌侵染机理等方面的研究。  相似文献   
5.
Soybean rust, caused by the biotrophic fungus Phakopsora pachyrhizi, is the most important foliar disease of soybean (Glycine max) worldwide. Deployment of resistant soybean cultivars is the best option for managing this disease. Genes conferring resistance to P. pachyrhizi have been identified, but pathotypes of the rust fungus overcoming these resistance genes have also been found. To identify novel resistance genes, soybean genotypes from both local and international sources were screened at multiple locations in Tanzania and Uganda in 2016 and 2017. The results from this screening revealed that infection types, disease severities, and sporulation levels varied among the genotypes and locations. The majority of the genotypes had tan-coloured (TAN) lesions and developed moderate sporulation, implying susceptibility, while only seven of the 71 lines had reddish-brown (RB) lesions and showed low disease severities in all of the screening environments. We identified seven genotypes that were the most resistant to rust in the most locations over the two years. These genotypes will be useful for further studies and, ultimately, for rust management, as they show broad resistance to various pathotypes of the rust fungus.  相似文献   
6.
What occurs when virus infection is spreading within a mixed plant species population? This question is important not only for economically significant, mixed species managed systems but also for environmentally significant mixed wild species populations. It received attention in recently published ecological studies on wild plant species, but these, and recent general pasture research publications, rarely mention earlier virus studies involving mixed species managed pasture. This review seeks to rectify that situation. It describes 10 diverse examples of past research on mixed species managed pasture done over two decades on three continents that demonstrated plant species balance changes arising from virus infection. These examples showed that plants belonging to susceptible pasture cultivars sensitive to systemic virus infection are sufficiently weakened that their ability to withstand competition from nonhost plants of other pasture species, or weed species, was diminished sufficiently to alter the plant species balance. Also, a similar alteration occurred when they were competing with virus-resistant or virus-tolerant host plants of the same or other pasture species, or a virus-resistant weed species. Such competition also diminished seed production, which decreased their ability to regenerate. Notably, as reported subsequently with wild plant species populations, when two different pasture species infected by the same virus compete with each other, growth of the more sensitive species is suppressed. Because managed mixed species pastures constitute an important component of regenerative agriculture, retaining an optimal balance of pasture species and delaying pasture decline from weed invasion both require effective management of virus diseases.  相似文献   
7.
Aged plants are more difficult to infect than young plantlets. This modification of susceptibility is described as mature plant resistance (MPR). For potato virus Y (PVY), MPR is known to lead to low infection rates of plants inoculated at the postflowering stage and a decrease in the number of infected daughter tubers. However, the impact of inoculation date on the capacity of PVY to accumulate in daughter tubers has not been studied so far. Field and greenhouse experiments were carried out to better understand PVY epidemiology and to help potato growers to evaluate consequences of early/late infections on the quality of their crops. In field trials, potato plants (cv. Bintje) were covered by insectproof nets from planting to harvest except for a 14-day period to expose plants to natural PVY infections. Under controlled conditions, potato plants were mechanically inoculated with PVY at different dates from preflowering stages (early inoculations) to postflowering stage (late inoculations). At harvest, daughter tubers were individually collected and analysed to define proportions and viral load of infected tubers according to the time between virus inoculation and harvest. Our results showed that although the age of plants at the time of inoculation can modify their susceptibility to PVY infection, in return, early and late PVY inoculations lead to similar rates of infected tubers at the plant scale and equivalent viral accumulation in infected tubers. All together, these data revealed that both early/late infections are high risks for the sanitary quality of potato tubers.  相似文献   
8.
 地被菊枯萎病由镰孢菌引起,是一种土传性病害,严重威胁地被菊生产。本试验用2个强致病力镰孢菌菌株,即尖孢镰孢菌(Fusarium oxysporum)、茄镰孢菌(F. solani)接种5个地被菊品种的幼苗,测定了病菌侵染下不同品种的形态、生理和生化响应的差异,以建立抗病品种筛选的生理和生化指标。地被菊品种间抗性水平可根据病情指数划分;受病菌侵染后,叶片叶绿素含量下降,抗病品种‘俏粉阁'叶绿素含量相对较高;丙二醛含量增加,抗病品种‘乳荷'和‘俏粉阁'的丙二醛含量显著低于感病品种‘玲珑';在病菌侵染早期,脯氨酸含量、超氧化物歧化酶和过氧化物酶活性在抗病品种受到迅速诱导增加,随后下降。运用隶属函数对其抗病能力进行综合评定,地被菊品种对尖孢镰孢菌(F. oxysporum)抗病性从强到弱依次为:‘俏粉阁'>‘乳荷'>‘火焰'>‘鲜红'>‘玲珑',地被菊品种对茄镰孢菌(F. solani)抗病性从强到弱依次为:‘俏粉阁'>‘乳荷'>‘鲜红'>‘火焰'>‘玲珑',为地被菊生产和开展菊花抗病机理研究提供了依据。  相似文献   
9.
为探讨C-Myc表达、谷氨酰胺代谢和神经坏死病毒复制三者之间的关系,本研究首先克隆了斜带石斑鱼鳍条细胞(GF-1)中的C-Myc基因(GF-1-C-Myc),结果显示GF-1-CMyc基因cDNA全长814 bp,开放阅读框(ORF)为285 bp,编码95个氨基酸(aa),有亮氨酸拉链结构域与螺旋-环-螺旋(HLH)结构域。实验表达和纯化了GF-1-C-Myc蛋白,并制备其多克隆抗体。采用实时定量PCR技术(qRT-PCR)与免疫印迹法(WB)检测了GF-1-C-Myc基因的表达和神经坏死病毒的复制。结果显示,缺乏谷氨酰胺会同时抑制GF-1-C-Myc基因的表达和神经坏死病毒(NNV)的复制,添加谷氨酰胺可同时促进GF-1-C-Myc的表达和NNV的复制;此外,NNV感染可上调GF-1-C-Myc基因的表达,并显著消耗GF-1细胞培养液中的谷氨酰胺。研究表明,GF-1-C-Myc基因可调控宿主谷氨酰胺代谢,从而有利于神经坏死病毒的复制。本结果为防控NNV的感染提供了参考。  相似文献   
10.
马铃薯晚疫病菌(Phytophthora infestans)能侵染多种茄科植物,它引起的马铃薯晚疫病,是马铃薯生产中的第一大病害。为了开发能在田间快速检测马铃薯晚疫病病原的方法,利用P. infestans T30-4基因组测序数据的contig 1.18131,设计qPCR和LAMP引物,优化扩增条件后得到引物的特异性和灵敏度,最后通过检测田间收获薯块,比较形态学传统方法、qPCR及LAMP的差异。特异性检测结果发现,qPCR和LAMP仅在含有P. infestans DNA模板的体系有阳性扩增,在寄主和其他微生物DNA中均无扩增;在优化的条件下,qPCR和LAMP的检测下限可达1×10 -6ng/μL,在有寄主和其他微生物DNA存在的条件下,引物的灵敏度没有显著差异。利用两种快速方法对在大理、丽江及昆明3个地区田间收获薯块上检测发现,qPCR和LAMP方法得到的检出率差异极为不显著(P=0.420),两种快速检测方法和形态学鉴定方法检出率差异极显著(P=0.009)。在大理、丽江及昆明3个地区的薯块中,两种分子检测方法检出率均比形态学方法高。其中,qPCR检测方法比形态学方法分别提高了12.00%、2.00%、8.70%;LAMP检测方法比形态学方法分别提高了11.30%、2.00%、8.70%。  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