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   2125篇
  免费   159篇
林业   54篇
农学   43篇
基础科学   7篇
  235篇
综合类   398篇
农作物   62篇
水产渔业   104篇
畜牧兽医   1210篇
园艺   37篇
植物保护   134篇
  2023年   15篇
  2021年   26篇
  2020年   32篇
  2019年   38篇
  2018年   37篇
  2017年   48篇
  2016年   44篇
  2015年   35篇
  2014年   48篇
  2013年   89篇
  2012年   71篇
  2011年   97篇
  2010年   52篇
  2009年   44篇
  2008年   76篇
  2007年   86篇
  2006年   70篇
  2005年   70篇
  2004年   76篇
  2003年   79篇
  2002年   87篇
  2001年   59篇
  2000年   77篇
  1999年   52篇
  1998年   17篇
  1997年   13篇
  1996年   17篇
  1995年   22篇
  1992年   40篇
  1991年   48篇
  1990年   41篇
  1989年   27篇
  1988年   26篇
  1987年   33篇
  1986年   34篇
  1985年   34篇
  1984年   20篇
  1983年   29篇
  1982年   12篇
  1979年   32篇
  1978年   16篇
  1977年   15篇
  1976年   13篇
  1973年   17篇
  1972年   20篇
  1971年   24篇
  1970年   29篇
  1969年   12篇
  1967年   17篇
  1966年   18篇
排序方式: 共有2284条查询结果,搜索用时 8 毫秒
71.
extract

Spergula arvensis (Spurrey, known locally as Yarr) is a fine- stemmed, viscid, erect or sprawling annual up to 30cm tall, with small white flowers and narrow, needle-shaped leaves in whorls at each stem node. It is a common weed of recently cultivated pastures. We have found no record of toxicity associated with ingestion of this plant, apart from a suggestion of illness when fed to caged birds (Roy et al., 1998). One of the authors (JDH) can recall a calcium-responsive recumbency in a small number of ewes grazing a poorly established swede crop in summer in which Yarr was the predominant green feed available.  相似文献   
72.
73.
The effects of acetoacetic acid, acetone, bilirubin, beta-carotene, three cephalospoprin antibiotics, glucose, hemoglobin and lipid on the kinetic Jaffé reaction and an enzymatic reaction for the determination of creatinine concentration were studied in bovine, canine, feline and equine serum. There were no obvious species' differences. The kinetic Jaffé reaction was unaffected by the addition of beta-carotene and hemoglobin. Acetone, cefazolin, cefoxitin, ceftiofur and glucose caused a positive bias while acetoacetic acid, bilirubin, and lipid caused a negative bias when added to the kinetic Jaffé reaction. The enzymatic reaction was unaffected by the addition of acetoacetic acid, acetone, beta-carotene, cefazolin, cefoxitin, glucose and hemoglobin while added lipid, bilirubin and ceftiofur caused a negative bias in the test results. Over all species and interferents, there was no difference in the precision of the two assay methods. In a series of sera from hospitalized patients, the two methods were highly correlated in a linear fashion. The enzymatic creatinine assay deals effectively with most interferents but has a greater cost and shorter shelf-life compared with the kinetic Jaffé reaction.  相似文献   
74.
The rate of fatty acid synthesis of perirenal adipose tissue of fetal lambs decreased by 90% during the last month of gestation. There was also a 90% decrease in the activity of fatty acid synthetase during this period, but the activity of this enzyme exceeded lipogenic flux by a factor of 10. The activity of acetyl CoA carboxylase in the active state (initial activity) was very similar to the lipogenic flux in adipose tissue from lambs at 120 d of gestation; although activity decreased towards term, the decline was insufficient to account for the fall in rate of fatty acid synthesis. The study also shows that assay of acetyl CoA carboxylase in the active state of ovine adipose tissue and of caprine mammary gland requires the presence of citrate, thus differing from that for rat adipose tissue. Evidence that pyruvate carboxylase can interfere in the assay of acetyl CoA carboxylase also is presented.  相似文献   
75.
76.
77.
A computer program was used to analyse data from a large commercial pig unit over two years to assess reproductive efficiency and the efficiency of weaner production. Monthly inspections of the farm and quarterly post mortem examinations of all dead pigs provided further information. The effects of controlled changes in management on production were assessed. Overall the number of piglets reared per sow per year was increased from 15-1 to 17-2 and the eight-week weights improved from a mean of 10-3 kg to 15-0 kg during the two year-study period.  相似文献   
78.
Summary Two experiments are described involving 33 crossbred (mainly Simmental and Jersey × Zebu) and 33 Zebu (Horro and Boran) bulls and steers. In experiment I, growth rates of crossbred and Zebu cattle rotationally grazed on either native pasture or Rhodes grass(Chloris gayana) were compared during a 140 day grazing period at a stocking rate of 2.4 animals/ha. In experiment II, growth rate of cattle rotationally grazed for 140 days on native pasture was compared with that of a similar group grazed on Rhodes grass either rotationally or continuously at a stocking rate of seven animals/ha.On native pasture the average daily gain by Zebu animals was similar to that of the crossbreds whilst on Rhodes grass liveweight gain of Zebu animals was lower than that of the crossbreds. Daily gains of cattle were significantly (P<0.01) greater on continuous compared with rotationally grazed Rhodes grass.
Rendimiento En Peso De Bovinos Cruzados Y Cebu En Pradera Nativa Y Pasto Rhodes
Resumen Se describen dos experimentos; el primero con 33 animales cruzados (Simmental y Jersey × Cebú) y el segundo con 33 Cebú (Horro y Boran) toros y novillos. En el experimento I, se compararon las ratas de crecimiento del ganado cruzado y del Cebú en pastoreo rotacional en pradera nativa o pasto Rhodes (Chloris gayana), durante 140 días, con una carga animal de 2.4 animales por hectárea. En el experimento II, se comparó la rata de crecimiento de un grupo de ganado en pastoreo rotacional en pradera nativa durante 140 días, con aquella de un grupo similar en pasto Rhodes con pastoreo rotacional o continuo, con una carga animal de siete por hectárea. En pradera nativa, el promedio de ganacia diaria de los animales Cebú fue similar a aquel del grupo de animales cruzados, mientras que en pasto Rhodes la ganancia de peso de los animales Cebú fue más baja que aquella de los animales cruzados. Las ganancias diarias de peso de los animales fueron significativamente (P<0.01) mayores en pastoreo contínuo, comparado con el pastoreo rotacional en pasto Rhodes.

Performances Ponderales De Zebus Et De Metis Zebus Entretenus Sur Des Paturages Naturels Et Das Paturages D'Herbe De Rhodes
Résumé Deux expériences utilisant 33 métis (principalement Simmental et Jersey x Zébu) et 33 zébus (Horro et Boran), taureaux et bouvillons sont décrites.Dans la première, les gains de poids des métis et des zébus entretenus à raison de 2,4 animal à l'hectate par rotation, soit sur des pâturages naturels ou sur de l'herbe de Rhodes ont été comparés durant 140 jours.Dans la seconde expérience, le taux d'accroissement pondéral du bétail entretenu, par rotations des pâturages, pendant 140 jours sur des pâturages naturels a été comparé avec celui d'un groupe identique d'animaux entretenus sur de l'herbe de Rhodes soit par rotation, soit de façon permanente à raison de 7 têtes à l'hectare sur les pâturages naturels; le gain journalier de poids par zébu a été semblable à celui des métis tandis que le gain de poids des zébus entretenus sur de l'herbe de Rhodes a été inférieur à celui des métis. Les gains journaliers de poids ont été significativement (P<0,01) plus élevés chez les animaux en pacage permanent comparés avec ceux obtenus par la rotation des pâturages d'herbe de Rhodes.
  相似文献   
79.
80.
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