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   1852篇
  免费   110篇
  国内免费   122篇
林业   173篇
农学   176篇
基础科学   101篇
  266篇
综合类   610篇
农作物   112篇
水产渔业   155篇
畜牧兽医   338篇
园艺   120篇
植物保护   33篇
  2024年   22篇
  2023年   30篇
  2022年   57篇
  2021年   65篇
  2020年   67篇
  2019年   90篇
  2018年   48篇
  2017年   79篇
  2016年   89篇
  2015年   81篇
  2014年   109篇
  2013年   136篇
  2012年   138篇
  2011年   127篇
  2010年   124篇
  2009年   151篇
  2008年   108篇
  2007年   110篇
  2006年   79篇
  2005年   67篇
  2004年   67篇
  2003年   44篇
  2002年   36篇
  2001年   21篇
  2000年   25篇
  1999年   15篇
  1998年   14篇
  1997年   20篇
  1996年   16篇
  1995年   17篇
  1994年   6篇
  1993年   10篇
  1992年   7篇
  1991年   3篇
  1990年   4篇
  1988年   2篇
排序方式: 共有2084条查询结果,搜索用时 15 毫秒
901.
选取体重(24.71 kg±2.07 kg)相近的4月龄哈萨克土种公羔羊20只,在伊犁昭苏马场特克斯河北岸天然草场进行了放牧,研究暖季放牧条件下羔羊血清生化指标与体重变化的关系。结果表明,4~8月龄羔羊月平均日增重依次为(175±34) g、(92±36) g、(158±46) g、(81±36) g,4~5月龄和6~7月龄平均日增重显著高于5~6月龄和7~8月龄(P<0.05)。血清生化指标中碱性磷酸酶(ALP)、乳酸脱氢酶(LDH)、谷草转氨酶(GOT)各月龄含量差异不显著(P>0.05);5、7月龄总蛋白(TP)含量高于4、8月龄,并显著高于6月龄(P<0.05);4、5月龄白蛋白(ALB)含量显著高于6、7、8月龄(P<0.05);5、7月龄球蛋白(GLB)含量分别高于4、6、8月龄,7月龄显著高于6月龄(P<0.05);4、6月龄白/球(A/G)高于5、8月龄,显著高于7月龄(P<0.05);尿素氮(BUN)含量4、5、7、8月龄间差异不显著(P>0.05),但显著高于6月龄(P<0.05);5、7月龄GLU含量显著高于6、8月龄(P<0.05);总胆固醇(TC)、谷丙转氨酶(GPT)、低密度脂蛋白胆固醇(LDL- C)、高密度脂蛋白胆固醇(HDL-C)含量在4~8月龄逐渐升高(HDL-C5月龄略有下降),TC、GPT含量相邻月龄间差异不显著(P>0.05),LDL-C、HDL- C含量7、8月龄显著高于4、5、6月龄(P<0.05);甘油三酯(TG)含量在整个试验期总体呈下降趋势,相邻月龄间仅7月龄含量显著高于8月龄(P<0.05);游离脂肪酸(FFA)含量8月龄显著高于其余各月龄(P<0.05),6月龄高于4月龄,并显著高于5、7月龄(P<0.01)。  相似文献   
902.
To find the effect of journey duration on the stress levels of weaned piglets a combination of physiological welfare indicators was used. One hundred and thirty-six piglets were monitored in two replicates of a short (0.6 h) and a long (8.3 h) commercial transport from a rearing to a growing–finishing farm. Variables studied were haematocrit, red blood cell count (RBC), total white blood cell count (WBC), differential WBC counts, serum pig's major acute phase protein (Pig-MAP), haptoglobin (Hp), cortisol, glucose, creatine phosphokinase (CPK), lactate dehydrogenase (LDH), total protein, and albumin before loading and immediately after unloading. A marked increase in leucocytes (< 0.01) and a tendency to lower eosinophil concentrations (= 0.086) were observed in those piglets transported during the short journeys. On the other hand, the decrease in lymphocytes was particularly remarkable in the long journeys (< 0.01). No increase in Hp concentrations after the transports was found, but an increase in Pig-MAP concentrations was observed at the end of the long journeys (< 0.001). Cortisol concentrations did not show significant changes in either short or long journeys. According to CPK (< 0.05) and LDH activities, some physical fatigue was detected at the end of transports, particularly in the short journeys. The decrease in haematocrit values in the short journeys (< 0.05), and the absence of variations in RBC, albumin, and total protein concentrations would indicate that the loss of body water during both transport durations was reduced. Sex did not affect the response of piglets to transport, which could be attributable to the young age of the animals. Changes in albumin concentrations (< 0.05), together with the tendencies to higher WBC (= 0.092) and neutrophil counts (= 0.076), suggest a more marked response to the stress of transport in heterozygous for the halothane gene (Nn) piglets than in homozygous negative (NN) piglets. Overall results indicate that, although transports were generally stressful, it is unclear which of the two durations was more detrimental for piglet welfare, and suggest a different stress response to transport with respect to that of older pigs.  相似文献   
903.
Indicators of piglet survival in an outdoor farrowing system   总被引:1,自引:0,他引:1  
Pre-weaning piglet mortality continues to be a major welfare and economic concern. In outdoor farrowing systems, there is a particular need to broaden breeding goals by incorporating selection for piglet survival to improve both productivity and welfare. This study aimed to identify behavioural and physiological survival indicators that are influential in outdoor systems and that could provide additional information for use when selecting for piglet survival. Data were collected from 511 piglets from Large White × Landrace × Duroc sows and Generalised Linear Mixed Models determined which indicators were most important for piglet survival in an outdoor system. With respect to prenatal mortality (surviving vs. stillborn piglets) high ponderal index (< 0.001) or body mass index (P < 0.001) in conjunction with being born earlier in the farrowing birth order (< 0.001) were the most important survival indicators. Birth weight (< 0.001) and rectal temperature 1 h after birth (= 0.032) were the most significant postnatal survival indicators. However survival indicators identified as important in indoor, conventional farrowing crates, such as landmark behaviours (latency to reach the udder, a teat and to suckle colostrum), were not influential in this system. These results highlight the importance of studying potential indicators of survival in alternative farrowing systems to the farrowing crate.  相似文献   
904.
In the 1980s ecosystem research projects were implemented world-wide since there was a pressing need to quantify the impacts of anthropogenic pollutants. Soil ecosystem analyses concentrated first on the quantification of the element and energy transfer between pools. Since mineralization of organic substrates and the release of nutrients and elements are due to the heterotrophic activity of the microbial decomposer compartment, this subsystem of terrestrial ecosystems gained importance. Direct microscopic observation methods were inadequate for the quantification of environmental impacts on the microflora. We adopted the maintenance requirement concept for the quantification of environmental impacts or stress effects on the soil microbial community. The paper gives a brief inside to the concept of maintenance from autecological studies and describes the underlying points which lead to our experimental approach of its application at the synecological level (i.e., microbial biomass as a single ecological entity) - a process which rested on long-term continuous research.  相似文献   
905.
本试验以荷斯坦奶牛为试验对象,研究不同环境温度、湿度下对奶牛血清生化指标的影响。结果表明:随着环境温度的逐渐下降和舍内湿度的升高,血清TP、Glu含量显著升高(P〈0.05),血清ALB含量明显下降,血清BUN含量呈波动性变化;血清Ca含量显著下降,血清P含量在舍外-2.5℃时最低,以后随着温度的进一步降低而显著升高。本试验说明奶牛血清中的某些生化指标可随环境温湿度的变化而变化。  相似文献   
906.
多效唑对盆栽蜡梅的矮化效应及抗性的影响   总被引:1,自引:0,他引:1  
用500、1000、2000 mg·L-13种不同浓度的多效唑(PP333)对盆栽蜡梅进行灌根处理,研究多效唑对盆栽蜡梅矮化处理效果及生物学效应的影响.结果表明:各处理均提高了蜡梅叶片叶绿素含量,并随浓度增加而增大,蜡梅植株抗性随着多效唑浓度增加出现先增后减的趋势,其中1000 mg·L-1多效唑处理抗性最强.多效唑施用浓度与盆栽蜡梅当年发枝数、技长、节间长及开花时间呈负相关,各处理对蜡梅枝条伸长生长均有抑制作用,对花朵直径影响较小,中、低浓度多效唑处理能显著增加花蕾数量,其中1000 mg·L-1多效唑处理花蕾数最多.本试验以1000 mg·L-1多效唑200 mL灌根处理盆栽蜡梅效果最佳.  相似文献   
907.
不同因子对切花月季卡罗拉扦插繁殖率的影响   总被引:1,自引:0,他引:1  
为提高月季扦插繁殖率,对切花月季卡罗拉进行了4因素(基质、激素种类、遮阴、扦插深度)3水平的正交扦插繁殖试验L9(34)。结果表明:各因子中基质对生根率、根长和根系数的影响大于激素种类、遮阴和扦插深度;扦插繁殖基质以土+蛭石+锯末(45∶35∶20),ABT 200mg/L,50%遮阴,扦插深度留3个芽眼为佳,此条件下卡罗拉月季扦插生根率为93.33%,且地下部分生长势较好,其根重、叶重、根长、根数和根系活力各项生根指标较高,该扦插繁殖基质可以在扦插切花月季卡罗拉生产中推广应用。  相似文献   
908.
王瑞苓  汪元超  刘建祥  汪梦婷 《安徽农业科学》2012,40(26):12957-12958,12960
[目的]以思茅松幼苗为研究对象,研究NaCl胁迫对其种子发芽和幼苗生长的影响。[方法]分别用25、50、100、200、300 mmol/L的NaCl处理种子,分析各处理下思茅松种子发芽情况,幼苗生长情况以及对4种生理生化指标的影响。[结果]在100 mmol/L盐分范围内,幼苗能正常生长,发芽率与发芽势与对照无显著差异。在100 mmol浓度下,幼苗的SOD酶含量最大。200 mmol/L浓度时,思茅松幼苗的发芽率、发芽势降低,植物的可溶性糖、叶绿素总量最大。300 mmol/L,幼苗不能正常生长,出苗死亡率高,畸形苗多。幼苗体内的MDA含量随着盐胁迫浓度的增加而增加。[结论]思茅松幼苗在100 mmol/L以内的盐分范围内能正常生长。  相似文献   
909.
陆伟  张晓明 《安徽农业科学》2012,40(24):12063-12064,12067
[目的]探讨不同浓度壳聚糖对毒死蜱胁迫下番茄植株生理生化指标的缓解作用。[方法]以番茄植株为材料,研究了不同浓度(0、50、100、200、400 mg/L)壳聚糖处理对毒死蜱胁迫下番茄植株的超氧化物歧化酶(SOD)、过氧化物酶(POD)、丙二醛(MDA)、可溶性蛋白积累、可溶性糖积累的缓解作用。[结果]壳聚糖对毒死蜱胁迫下番茄植株的部分生理指标起到了缓解作用,低浓度的壳聚糖(50、100 mg/L)效果明显。SOD活性得到了提高,MDA积累下降,对POD活性、可溶性蛋白和可溶性糖积累的缓解作用较小。[结论]该研究为缓解毒死蜱对植物的胁迫作用提供了依据。  相似文献   
910.
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