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   23561篇
  免费   1471篇
  国内免费   2328篇
林业   1748篇
农学   1343篇
基础科学   1081篇
  2274篇
综合类   11918篇
农作物   2072篇
水产渔业   1118篇
畜牧兽医   3254篇
园艺   1612篇
植物保护   940篇
  2024年   190篇
  2023年   463篇
  2022年   1008篇
  2021年   968篇
  2020年   911篇
  2019年   897篇
  2018年   599篇
  2017年   1017篇
  2016年   752篇
  2015年   1020篇
  2014年   1239篇
  2013年   1483篇
  2012年   1803篇
  2011年   1890篇
  2010年   1776篇
  2009年   1596篇
  2008年   1545篇
  2007年   1470篇
  2006年   1364篇
  2005年   1079篇
  2004年   740篇
  2003年   647篇
  2002年   934篇
  2001年   875篇
  2000年   624篇
  1999年   235篇
  1998年   41篇
  1997年   35篇
  1996年   24篇
  1995年   17篇
  1994年   19篇
  1993年   15篇
  1992年   19篇
  1991年   12篇
  1990年   10篇
  1989年   8篇
  1988年   11篇
  1987年   3篇
  1986年   2篇
  1984年   2篇
  1983年   1篇
  1981年   3篇
  1965年   1篇
  1962年   3篇
  1956年   5篇
  1955年   4篇
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
51.
许多固氮树种速生丰产,萌生能力强,叶片,木屑含氮率较高,可为食用菌栽培提供理想原料,而且固氮树种在绿花荒山,保持水土,提高地力方面作用显著,以固氮树种发展短轮伐期食用菌专用林,具有较高的经济效益和生态效益,本文介绍了银合欢,黑荆,大叶相思,银荆,桤木,南洋楹和马占相思等在食用菌栽培上的应用概况,各地可因地制宜栽培合适的固氮树种作为食用菌专用林。  相似文献   
52.
日光温室黄瓜栽培CO_2浓度的消长规律初探   总被引:7,自引:0,他引:7  
近 3a(年 )的研究结果表明 :日光温室内CO2 浓度有明显的季节变化和日变化。在整个生长期内因通风时间和通风量的不同 ,日光温室内的CO2 浓度 11月和 3月较高 ,5月较低。各时期日变化基本相同 ,但变化幅度因季节而异 ,上午随Pn的逐渐增大而下降 ,中午 12 :0 0~ 14 :0 0时降至最低 ,下午又随Pn的减小而缓慢回升。叶片的光合作用、呼吸作用和土壤呼吸是影响日光温室内CO2 浓度日变化的主要因素。有机肥施用量对室内土壤呼吸和日光温室CO2 浓度有较大影响 ,在有机肥充足的条件下 ,室内CO2 浓度基本满足黄瓜光合作用的需要 ,无须补施 ,如果在作物生长期间再定时随水向土壤中冲施有机肥 ,效果就更好  相似文献   
53.
在液体培养条件下测定了发酵液中5个灰树花菌株蛋白质含量的变化。结果表明,接种后第6天发酵液中蛋白质含量最高,Gf961菌株发酵液中的蛋白质含量为0.58%,Gf962菌株发酵液中的蛋白质含量最低,为0.30%,随着培养时间的延长,发酵液中蛋白质含量逐渐下降,接种后第9天最低,随后以呈上升趋势。但上升的幅度较小。试验为确定从发酵液中提取蛋白质的最佳时期提供了一定的理论依据。  相似文献   
54.
CPPU在柿试管繁殖中的应用   总被引:6,自引:0,他引:6  
艾鹏飞  罗正荣 《果树学报》2002,19(4):272-274
对CPPU和ZT在柿试管繁殖中的应用价值进行了比较研究,结果表明:CPPU是一种可代替ZT的特效细胞分裂素,添加有CPPU0.2mg/L的MS(1/2N)培养基能促进芽的增殖和生长,且用此培养基继代培养的试管苗生根能力也有所提高。  相似文献   
55.
AIM:To examine the effect of external counterpulsation(ECP) on renin-angiotensin system(RAS) and hemodynamics in dogs with myocardial ischemia and their relationship. METHODS:Acute myocardial ischemia was induced by occluding the left anterior descending of the dogs. The local renin activity, angiotensin Ⅱ(AngⅡ) level, angiotension-converting enzyme(ACE) activity were tested by biochemical methods and hemodynamics was recorded by a 8-channel physiological recorder.RESULTS:Ischemia could actiivate renin,ACE and AngⅡ in cardiovasculature and ECP reduced them except for renin in ischemic myocardium. Ischemia also could activate RAS in lung and kidney, which play an important role on circulating RAS, and ECP reduced them. Furthermore, ECP could improve hemodynamics and there existed a close relationship between local AngⅡlevel and hemodynamics. CONCLUSION:ECP can reduce local RAS and improve hemodynamics in dogs with myocardial ischemia, which might be one of mechanisms underlying the protective effect of ECP on ischemic myocardium.  相似文献   
56.
AIM:To investigate the effect of Se-containing spirulina phycocyanin (Se-SPC) on liver injury of mice induced by carbon tetrachloride (CCl4). METHODS:The mouse model was conducted by intragastric feeding with 2% CCl4 oil for three times, meanwhile Se-SPC, spirulina phycocyanin (SPC) and Na2SeO3 were injected (ip) to various groups for 7 days. Then selenium (Se), glutathione peroxidase (GPx), superoxide dismutase (SOD), alanine aminotransferase (ALT), malondiaoldehyde (MDA) and nitric oxide (NO) levels in blood and liver were measured. RESULTS:The level of Se,GPx and SOD activities were obviously higher(P<0.05)but ALT activity,MDA and NO2-/NO3- levels were remarkably lower(P<0.05)in Se-SPC treated groups than those in CCl4 groups,and effects of high dose Se-SPC on Se,GPx,MDA and NO2-/NO3- were even more significant(P<0.01).Under the same dose of Se or protein,effects of all selected targets in Se-SPC groups were more efficient than those in SPC groups and inorganic-Se groups.Furthermore,Se levels had a positive correlation with GPx activity(r=01705),which had negative correlation with levels of MDA,NO2-/NO3- and ALT(r=-0.629,r=-0.336,r=-0.457,respectively), and positive correlations between ALT activity and MDA or NO2-/NO3- level were found (r=0.519,r=0.641). CONCLUSION:These results indicated that Se-SPC may attenuate liver injury of mice induced by CCl4 through its anti-inflammatory action and enhancing selenoenzyme expression.  相似文献   
57.
AIM: The purpose of the present study was to explore the relationship between interleukin-6 mRNA expression and endometriosis. METHODS: Using the rat model, IL-6 mRNA expression in the endometrium was examined by RT-PCR. RESULTS: The expression of IL-6 mRNA in control rats did not change at 2, 4, 6 and 8 weeks after sham operation (P>0.05), but in model rats it gradually increased at 2, 4, 6 and 8 weeks after endometriosis (P<0.01). The expression of IL-6 mRNA in uterine endometrium with endometriosis was lower than in endometriotic tissue, but higher than in endometrium from healthy controls. CONCLUSION: The IL-6 mRNA expression may contribute to the development of endometriosis . The increase in IL-6 mRNA expression may promote the implantation and growth of endometriotic tissue.  相似文献   
58.
The abnormality of the central noradrenergic system in Alzheimer's disease has two cases: decrease or increase. The former is easy to be understood, because it is resulted from the outstanding forfeit of the noradrenergic neurons in the nucleus locus ceruleus (nLC); but the noradrenalin concentration does not change and enen increase, it seems to disagree with the loss of the noradrenergic neurons in the nLC. This article put emphasis on it, enumerated the related evidence and analyzed the possible causes. At present time, the drugs to increase noradrenalin is used mostly in clinic. This paper summarized it and put forth our own opinions.  相似文献   
59.
60.
 根据普通生物学和血清学特性,长豇豆病毒病的病原被鉴定为黑眼豇豆花叶病毒(Blackeye cowpea mosaic virus,Bl CMV)、豇豆蚜传花叶病毒(Cowpea aphidborne mosaic virus,CABMV)和黄瓜花叶病毒(Cucumbermosaic virus,CMV)。  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