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   960篇
  免费   77篇
  国内免费   80篇
林业   104篇
农学   145篇
基础科学   120篇
  80篇
综合类   301篇
农作物   42篇
水产渔业   118篇
畜牧兽医   145篇
园艺   37篇
植物保护   25篇
  2024年   5篇
  2023年   19篇
  2022年   36篇
  2021年   35篇
  2020年   38篇
  2019年   50篇
  2018年   33篇
  2017年   53篇
  2016年   57篇
  2015年   39篇
  2014年   68篇
  2013年   68篇
  2012年   69篇
  2011年   77篇
  2010年   55篇
  2009年   55篇
  2008年   38篇
  2007年   38篇
  2006年   40篇
  2005年   48篇
  2004年   25篇
  2003年   32篇
  2002年   28篇
  2001年   17篇
  2000年   20篇
  1999年   12篇
  1998年   6篇
  1997年   8篇
  1996年   4篇
  1995年   10篇
  1994年   4篇
  1993年   6篇
  1992年   8篇
  1991年   3篇
  1990年   2篇
  1989年   4篇
  1988年   2篇
  1987年   2篇
  1982年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有1117条查询结果,搜索用时 15 毫秒
101.
Oral malignant melanoma (OMM) in the dog is often locally aggressive with a high metastatic potential and there are few treatment options that have been demonstrated to improve outcome of this disease. The purpose of this study was to determine whether adjunctive treatment with the Oncept melanoma vaccine affected the outcome of dogs with OMM that had achieved loco‐regional cancer control. Medical records from 45 dogs that presented to the Animal Cancer and Imaging Center were reviewed, including 30 dogs with stage II and III disease. Dogs that received the vaccine did not achieve a greater progression‐free survival, disease‐free interval or median survival time than dogs that did not receive the vaccine.  相似文献   
102.
The attachment of the piscine gill parasite, Ergasilus mirabilis Oldewage & van As, 1987 is described by means of scanning electron microscopy and light microscopy. A variety of sensory structures occur on and around the host contact surface of the parasite and proliferation of gill tissue occurs at the site of attachment. It would appear that this proliferation of host tissue results from the feeding behaviour of the parasite rather than the actual attachment thereof.  相似文献   
103.
Ten Nubian goats were given oral doses of the fresh fruits and leaves of Cassia senna at 1, 5, and 10 g / kg /day. Eight goats died within 30 days and two others were slaughtered in a moribund condition on days 18 and 29. The clinical signs of diarrhoea, inappetence, loss of condition, and dyspnoea were well correlated with the pathological findings. There was an increase in G.O.T., ammonia, urea, and total cholesterol and a decrease in total protein in the serum of Cassia‐poisoned goats. Blood sugar level was reduced and the increase in the values of Hb, PCV, and RBC was due to haemoconcentration.  相似文献   
104.
大扁杏是半干旱地区,特别是浅山丘陵区及科尔沁沙地具有发展前途的生态经济树种,在一些地区已取得显著的效益。文章在充分调查研究的基础上,结合生态建设和产业需求,对大扁杏栽植的立地选择、品种配置及丰产栽培配套技术进行总结分析,目的是为通辽市浅山丘陵区和沙地生态治理及精准扶贫产业开发提供技术支撑。  相似文献   
105.
文章根据2012年真菌科学考察采集到的标本,根据传统分类学方法,对内蒙古贺兰山真菌资源状况进行了鉴定.研究结果显示:研究区共有真菌262种,隶属于7目27科79属,真菌多样性丰富;其中食用菌占全部真菌种类的一半以上,药用菌和毒菌资源分别占24.81%和15.27%.最后对开发真菌资源给出了建议.  相似文献   
106.
There is a lack of quantitative assessments available on the effect of agricultural intensification on soil aggregate distribution and microbial properties. Here, we investigated how short-term nitrogen(N) intensification induced changes in aggregate size distribution and microbial properties in a soil of a hot moist semi-arid region(Bangalore, India). We hypothesised that N intensification would increase the accumulation of macroaggregates 2 mm and soil microbial biomass and activity, and that the specific crop plant sowed would influence the level of this increase. In November 2016, surface(0–10 cm) and subsurface(10–20 cm) soil samples were taken from three N fertilisation treatments, low N(50 kg N ha~(-1)), medium N(75 and 100 kg N ha~(-1) for finger millet and maize, respectively),and high N(100 and 150 kg N ha~(-1) for finger millet and maize, respectively). Distribution of water-stable aggregate concentrations,carbon(C) and N dynamics within aggregate size class, and soil microbial biomass and activity were evaluated. The high-N treatment significantly increased the concentration of large macroaggregates in the subsurface soil of the maize crop treatment, presumably due to an increased C input from root growth. Different N fertilisation levels did not significantly affect C and N concentrations in different aggregate size classes or the bulk soil. High-N applications significantly increased dehydrogenase activity in both the surface soil and the subsurface soil and urease activity in the surface soil, likely because of increased accumulation of enzymes stabilised by soil colloids in dry soils. Dehydrogenase activity was significantly affected by the type of crop, but urease activity not. Overall, our results showed that high N application rates alter large macroaggregates and enzyme activities in surface and subsurface soils through an increased aboveground and corresponding belowground biomass input in the maize crop.  相似文献   
107.
Elbow-inlet passage is widely used in large drainage pumping stations.Flow uniformity at the exit section directly determines its hydraulic performance.Flow uniformity must be optimized to improve the operational efficiency of the large axial-flow pumping station.Modeling and numerical simulation methods were used to investigate the elbow-inlet passage,and the accuracy of the calculation results was verified.The key geometric parameters affecting the uniformity of the flow were optimized by the orthogonal experiment design.The optimal schemes were obtained and compared with the original scheme.The results show that flow uniformity V u after optimization is 95.41%,which is increased by 1.04%.The pumping station efficiency is increased by 1.89%,thereby confirming the applicability and accuracy of the proposed scheme,especially for the optimization of flow uniformity of the exit section of the elbow-inlet passage.  相似文献   
108.
针对灌区水资源优化配置模型存在等式约束的特点,在分析粒子群算法寻优策略的基础上,建立了基于粒子群的大系统优化模型.同时.提出有效的控制粒子速度大小的方法, 克服了粒子因速度过大易逃出约束空间而造成程序中断的不足,成功地将粒子群优化算法应用于作物灌溉制度的寻优中.利用此模型将有限的水资源分配到灌区中的不同子区、子区中的不同作物以及作物的各生育阶段,取得了较好的效果.  相似文献   
109.
覆膜槽沼气规模化干法发酵技术与装备研究   总被引:5,自引:2,他引:3  
韩捷  向欣  李想 《农业工程学报》2008,24(10):100-104
研制了以覆膜槽生物反应器(MCT)为核心的沼气规模化干法发酵系统。该系统采用"软管充气膨胀压力密封联接装置",实现了反应器厌氧―好氧状态的快捷转换,解决了大规模快速进出料的问题,并可直观判断反应器中沼气的存留量,操作简便、安全;利用固态有机物料好氧发酵产生的生物能获得中温厌氧发酵所需温度,并辅以高效的保温措施,无需外加热源,即可维持厌氧发酵的中温(35~42℃)运行;采用单元化设计,通过增减启动厌氧反应器的数量,可满足不同用气量的要求。建设了生物反应器容积为180 m3的沼气干法发酵中试工程。该中试工程容积产气率为0.598 m3/(m3.d),沼气甲烷含量55%~60%。  相似文献   
110.
The polymerase chain reaction–denaturing gradient gel electrophoresis (PCR‐DGGE) of 16S ribosomal RNA gene was used to investigate bacterial communities in the intestines of large yellow croaker at six different ages (12 d, 18 d, 26 d, 40 d, 3 mo, and 1 yr old) as well as within the corresponding feed and culture water. In addition, Illumina Miseq sequencing was utilized to compare intestinal microbiota between 12‐d‐old and 1‐yr‐old individuals. PCR‐DGGE results revealed that the culture water had the highest bacterial diversity, followed by the feed, while the intestines had the lowest diversity. The intestinal microbiota at six ages changed severely; however, the change did not follow any trend. The large yellow croaker intestines harbored specific bacterial communities that differed from those in both feed and water. Illumina Miseq sequencing results revealed that the diversity of intestinal bacteria in 12‐d‐old fish was higher than that in 1‐yr‐old fish, and the bacterial composition differed significantly between them. γ‐Proteobacteria and Pseudoalteromonas supplied the most abundant phylum and genus in the 12‐d‐old fish intestine. However, in the 1‐yr‐old fish intestine, Firmicutes and Clostridium were the most dominant, respectively. The study may contribute to a better understanding of gut microbiota and dynamics of the large yellow croaker and the relationship with their surrounding 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