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   10103篇
  免费   608篇
  国内免费   50篇
林业   646篇
农学   481篇
基础科学   91篇
  1790篇
综合类   857篇
农作物   497篇
水产渔业   827篇
畜牧兽医   4556篇
园艺   154篇
植物保护   862篇
  2023年   90篇
  2022年   150篇
  2021年   287篇
  2020年   292篇
  2019年   343篇
  2018年   309篇
  2017年   341篇
  2016年   360篇
  2015年   239篇
  2014年   347篇
  2013年   531篇
  2012年   567篇
  2011年   622篇
  2010年   318篇
  2009年   352篇
  2008年   515篇
  2007年   531篇
  2006年   475篇
  2005年   447篇
  2004年   399篇
  2003年   368篇
  2002年   422篇
  2001年   261篇
  2000年   266篇
  1999年   231篇
  1998年   74篇
  1997年   68篇
  1996年   66篇
  1995年   66篇
  1994年   57篇
  1993年   51篇
  1992年   89篇
  1991年   62篇
  1990年   78篇
  1989年   89篇
  1988年   75篇
  1987年   61篇
  1986年   59篇
  1985年   65篇
  1984年   51篇
  1983年   47篇
  1982年   40篇
  1980年   29篇
  1979年   42篇
  1978年   25篇
  1977年   24篇
  1974年   28篇
  1973年   33篇
  1972年   32篇
  1970年   35篇
排序方式: 共有10000条查询结果,搜索用时 663 毫秒
451.
452.
453.
454.
Veterinary Research Communications - Propofol is a widely used drug in veterinary medicine to induce anesthesia; as well as the chosen compound for protocols of intravenous anesthesia. The present...  相似文献   
455.
A 2-month-old Warmblood colt presented with recurrent colic and regurgitation. Gastroscopy, performed on several occasions, and barium-contrast radiography revealed severe squamous gastric ulceration and stenosis at the level of the margo plicatus. Treatment with omeprazole reduced the extent and severity of the gastric ulcers but did not affect the stenosis. The foal was euthanised because of a poor prognosis, and post-mortem examination confirmed the clinical diagnosis. Severe squamous gastric ulceration, granulation tissue formation and cicatrisation of deep gastric lesions were considered to have caused the stenosis. Gastroduodenal outflow obstruction is a recognised disorder in foals, but stenosis at the level of the margo plicatus has not been reported in foals or adult horses. To the authors' knowledge, this is the first case of severe squamous gastric ulceration, complicated by stenosis at the level of the margo plicatus, in a foal. Although rare, gastric stenosis should be considered in foals suffering recurrent colic and regurgitation.  相似文献   
456.
蜻蜓目的3种食用种类与营养价值   总被引:7,自引:0,他引:7       下载免费PDF全文
蜻蜓是分布广泛的昆虫 ,部分种类的稚虫可以食用。调查和研究成果表明 :在云南省的许多地方都有食用蜻蜓稚虫的习俗 ,常见的食用种类有红蜻、角突箭蜓、舟尾丝等 3种 ,其中含有蛋白质、脂肪、氨基酸、矿质元素等营养成分。它们的蛋白含量平均为 58.92 % ,脂肪含量平均为2 5.3 7% ,氨基酸含量平均为 4 6.0 3 % ,人体必需氨基酸含量平均为 16.4 1% ,占氨基酸总量的3 5.69% ,3种蜻蜓稚虫 K、Zn、Ca、Fe的平均含量分别为 2 960、12 5.4、2 616.6、796.2 mg· kg-1。由此可见 ,蜻蜓稚虫是营养丰富的食用昆虫资源  相似文献   
457.
To determine if flower nutrient composition can be used to predict fruit quality, a field experiment was conducted over three seasons (1996-1999) in a commercial orange orchard (Citrus sinensis (L.) Osbeck cv. 'Valencia Late', budded on Troyer citrange rootstock) established on a calcareous soil in southern Portugal. Flowers were collected from 20 trees during full bloom in April and their nutrient composition determined, and fruits were harvested the following March and their quality evaluated. Patterns of covariation in flower nutrient concentrations and in fruit quality variables were evaluated by principal component analysis. Regression models relating fruit quality variables to flower nutrient composition were developed by stepwise selection procedures. The predictive power of the regression models was evaluated with an independent data set. Nutrient composition of flowers at full bloom could be used to predict the fruit quality variables fresh fruit mass and maturation index in the following year. Magnesium, Ca and Zn concentrations measured in flowers were related to fruit fresh mass estimations and N, P, Mg and Fe concentrations were related to fruit maturation index. We also established reference values for the nutrient composition of flowers based on measurements made in trees that produced large (> 76 mm in diameter) fruit.  相似文献   
458.
天宝国有林场属生态公益型林场。与传统的经营方式相比,分类经营后应采用全新的、既要适应市场要求、也要符合国家产业政策的经营方式。文章提出林场内部造林、营林、护林等建设项目的整套适应方法;并按目前林场经济发展水平,提出事业性支出财政补偿的水平及近期林场需确定的职工经济发展方向。  相似文献   
459.
The empirical calibration of Granier-type heat dissipation sap flow probes that relate temperature difference (DeltaT) to sap velocity (v) was reevaluated in stems of three tropical tree species. The original calibration was confirmed when the entire heated probe was in contact with conducting xylem, but mean v was underestimated when part of the probe was in contact with nonconducting xylem or bark. Analysis of the effects of nonuniform sap velocity profiles on heat dissipation estimates showed that errors increased as v and the proportion of the probe in nonconducting wood increased. If half of a 20-mm probe is in sapwood with a v of 0.15 mm s(-1) and the other half is in nonconducting wood, then mean v for the whole probe can be underestimated by as much as 50%. A correction was developed that can be used if the proportion of the probe in nonconducting wood is known. Even with the entire heated probe in contact with conducting xylem, v would be underestimated when radial velocity gradients are present. In this case, the error would be smaller except when velocity gradients are very steep, as can occur in species with ring-porous wood anatomy. Errors occur because the relationship between DeltaT and v is nonlinear. Mean DeltaT along the probe is therefore not a measure of mean v, and users of heat dissipation probes should not assume that v is integrated along the length of the probe. The same type of error can occur when DeltaT is averaged through time while v is changing, but the error is small unless there are sudden, step changes between zero and high sap velocity. It is recommended that relatively short probes (20 mm or less) be used and that probes longer than the depth of conducting sapwood be avoided. Multiple probes inserted to a range of depths should be used in situations where steep gradients in v are expected. If these conditions are met, heat dissipation probes remain useful and widely applicable for measuring sap flow in woody stems.  相似文献   
460.
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