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   445篇
  免费   46篇
  国内免费   35篇
林业   35篇
农学   8篇
基础科学   21篇
  18篇
综合类   207篇
农作物   8篇
水产渔业   18篇
畜牧兽医   177篇
园艺   24篇
植物保护   10篇
  2024年   1篇
  2023年   6篇
  2022年   15篇
  2021年   14篇
  2020年   11篇
  2019年   16篇
  2018年   18篇
  2017年   30篇
  2016年   14篇
  2015年   21篇
  2014年   20篇
  2013年   34篇
  2012年   36篇
  2011年   25篇
  2010年   30篇
  2009年   38篇
  2008年   21篇
  2007年   53篇
  2006年   21篇
  2005年   29篇
  2004年   12篇
  2003年   12篇
  2002年   9篇
  2001年   6篇
  2000年   3篇
  1999年   2篇
  1998年   7篇
  1997年   3篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   4篇
  1992年   3篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1986年   1篇
  1956年   1篇
排序方式: 共有526条查询结果,搜索用时 15 毫秒
81.
捻转血矛线虫是牛羊等反刍动物常见的寄生蠕虫,该虫寄生在牛羊等宿主体内,可导致宿主贫血,给畜牧业生产带来巨大的损失。近年来,随着国内对动物福利理念的普及,基于动物福利的疫病防控技术受到越来越多的重视,然而却未见基于此的相关论述。论文就现有羊捻转血矛线虫病防控技术,包括药物防控、生物防控、疫苗预防等进行综述,为今后研发基于动物福利的羊捻转血矛线虫病防控技术提供参考。  相似文献   
82.
Intestinal wounds require precise closure after intestinal biopsy, enterotomy, or enterectomy in small animals. Preexisting factors such as intra‐abdominal sepsis and hypoalbuminemia as well as poor surgical technique increase the risk of intestinal dehiscence, with considerable negative impact on patient morbidity and mortality. Live dog studies have demonstrated the dangers of mucosal eversion especially in the septic abdomen. Approximating patterns preserve luminal diameter, heal optimally, and have equal bursting strength compared with inverting patterns after 24 hours. Simple interrupted and simple continuous suture patterns and disposable skin staples are established alternatives for manual wound closure. Knotless quilled suture currently used in laparoscopic gastropexy techniques shows bursting strength equal to monofilament sutures in dog cadaveric intestine. Dehiscence rates with hand sewn vs titanium automated stapling anastomosis are similar in uncomplicated cases; however, auto stapling devices may be the preferred method of anastomosis when preexisting abdominal sepsis is present and when patient size allows it. Regardless of the technique, current standard of care involves leak testing and omental wrapping, followed by early postoperative feeding. The past decade has ushered in an exciting new era of laparoscopic assisted techniques that have the potential to reduce postoperative pain and patient morbidity. An understanding of these applications will establish the future of minimally invasive small animal intestinal surgery for veterinary specialists. In summary, surgeons have a variety of methods at their disposal for optimal clinical outcome in small animal intestinal surgery.  相似文献   
83.
Amphiphilic poly(phenylquinoline)-block-polystyrene rod-coil diblock copolymers were observed to self-organize into robust, micrometer-scale, spherical, vesicular, cylindrical, and lamellar aggregates from solution. These diverse aggregate morphologies were seen at each composition, but their size scale decreased with a decreasing fraction of the rigid-rod block. Compared to coil-coil block copolymer micelles, the present aggregates are larger by about two orders of magnitude and have aggregation numbers of over 10(8). The spherical and cylindrical aggregates have large hollow cavities. Only spherical aggregates with aggregation numbers in excess of 10(9) were formed in the presence of fullerenes (C60, C70) in solution, resulting in the solubilization and encapsulation of over 10(10) fullerene molecules per aggregate.  相似文献   
84.
Rutgers桃(红叶)与白芒蟠桃(绿叶)光合生理特性的比较   总被引:21,自引:1,他引:20  
在田间条件下对Rutgers桃(红叶)和白芒蟠桃(绿叶)的光合生理特性进行了比较研究。结果表明:Rutgers桃的光合能力显著低于白芒蟠桃,净光合速率日积分值仅为白芒蟠桃的65%,表观量子效率、羧化效率分别较白芒蟠桃降低30%和66%。Rutgers桃的花色素苷含量是白芒蟠桃的760倍,而单位叶面积的叶绿素含量二者没有显著差异。因此,Rutgers桃与白芒蟠桃光合能力的差异并不是叶绿素含量差异造成的。  相似文献   
85.
针对四轴卧式镗床旋转轴需测几何误差的数目不统一与完备性缺失的问题,提出了基于形状创成函数的四轴卧式镗床旋转轴PIGEs形成机理分析方法与旋转轴完备几何误差测量辨识方法。基于形状创成机理构建了卧式镗床几何误差创成函数,确定了旋转轴可通过误差补偿进行调整的最少与位置无关的几何误差(Position-independent geometric error, PIGEs)数目。建立了卧式镗床旋转轴4项PIGEs、6项与位置有关的几何误差(Position-dependent geometric error, PDGEs)、6项安装误差(Setup error, SEs)与球杆仪(Double ball bar, DBB)测量轨迹半径之间的完备性函数模型,设计了基于DBB的四轴联动Viviani曲线测量轨迹,构建了旋转轴6项PDGEs的NURBS表征与PIGEs、SEs辨识方法。开展了误差补偿对比实验验证,结果表明,利用几何误差完备性测量与辨识结果进行误差补偿,较仅单一补偿6项PDGEs可提升圆轨迹测量精度40.69%。  相似文献   
86.
研究了沙质草地与高平原草地六种牧草的总糖含量与还原糖含量变化情况.结果表明:沙质草地与高平原草地供试牧草的总糖含量变化(除糙隐子草外)和还原糖含量变化不同;除羊草和寸草苔外,其余几种牧草的还原糖含量都是高平原草地高于沙质草地.  相似文献   
87.
紫薇的园林特性及开发应用   总被引:4,自引:0,他引:4  
该文对紫薇的生物学特性、生态适应性及观赏特性进行了归纳和评价,并系统总结了紫薇的历史文化内涵,阐述了其在园林绿地中的应用途径,指出紫薇资源在园林应用开发方面存在的问题与进一步发展的对策。  相似文献   
88.
金卫斌  熊勤学  薛莲 《湖北农业科学》2011,50(11):2220-2224
根据2001~2007年江汉平原四湖地区增强型植被指数(EVI)的时序数据,运用时间序列谐波分析法(HANTS)进行去云处理,计算各个像元EVI时序值的平方和N,将N>0.25的像元划为植被覆盖区,N<0.25的像元划为非植被覆盖区.对植被覆盖区采用二次差分法判断EVI时序数据的峰值出现次数,年内峰值出现1次的为林地和...  相似文献   
89.
Research carried out to assess the impact of open-pollinated Tomato leaf curl virus (ToLCV)-resistant tomatoes and hybrids on the livelihoods of resource-poor farmers in Southern India is described and discussed. Three high-yielding ToLCV-resistant tomato varieties were developed initially using conventional breeding and screening techniques involving inoculation by ToLCV-viruliferous whitefly, Bemisia tabaci. In 2003 and 2004, respectively, these varieties were released officially by the Karnataka State Seed Committee and the Indian Ministry of Agriculture through notification in the Gazette of India. From 2003 to 2005, eleven seed companies bought breeder seed of the ToLCV-resistant varieties and used them to begin breeding F1 hybrids from them. Socio-economic studies carried out to assess the benefits obtained from growing the ToLCV-resistant varieties found that farmers could gain up to 10 times the profit by growing the ToLCV-resistant varieties compared to the pre-existing ToLCV-susceptible varieties. Adoption of ToLCV-resistant tomatoes was also associated with reduced pesticide use. Extra income from tomato sales was prioritised by farmers to pay for children's education, better nutrition and medicines. In a joint effort with the commercial seed sector in India, a promotional field day was organised in 2007. As well as the three ToLCV-resistant varieties, 62 ToLCV-resistant hybrid tomatoes were exhibited during a farmer-field day by 17 commercial seed companies and several public institutes. Tomatoes with ToLCV-resistance are now grown widely in South India and seeds of the three open-pollinated varieties have been distributed to more than 12 countries. In 2007, a conservative estimate of the financial-benefit to cost of the research ratio was already more than 837:1.  相似文献   
90.
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