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   16792篇
  免费   968篇
  国内免费   1207篇
林业   1425篇
农学   1563篇
基础科学   1059篇
  2577篇
综合类   4732篇
农作物   1330篇
水产渔业   886篇
畜牧兽医   3682篇
园艺   640篇
植物保护   1073篇
  2024年   48篇
  2023年   200篇
  2022年   466篇
  2021年   562篇
  2020年   556篇
  2019年   562篇
  2018年   438篇
  2017年   584篇
  2016年   575篇
  2015年   706篇
  2014年   713篇
  2013年   909篇
  2012年   1166篇
  2011年   1187篇
  2010年   970篇
  2009年   925篇
  2008年   1031篇
  2007年   957篇
  2006年   804篇
  2005年   748篇
  2004年   509篇
  2003年   513篇
  2002年   589篇
  2001年   559篇
  2000年   431篇
  1999年   327篇
  1998年   202篇
  1997年   154篇
  1996年   167篇
  1995年   150篇
  1994年   141篇
  1993年   118篇
  1992年   117篇
  1991年   95篇
  1990年   97篇
  1989年   90篇
  1988年   65篇
  1987年   62篇
  1986年   28篇
  1985年   40篇
  1984年   34篇
  1983年   33篇
  1981年   25篇
  1980年   18篇
  1978年   21篇
  1977年   19篇
  1976年   28篇
  1974年   20篇
  1973年   22篇
  1972年   22篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
羊肚菌研究进展   总被引:29,自引:1,他引:29  
综述了近年来羊肚菌营养成分、有效成分,培养技术,以及细胞学、生物化学和分子生物学等方面的研究进展。  相似文献   
62.
姬松茸与双孢蘑菇不同菌株的RAPD扩增研究   总被引:6,自引:1,他引:6  
以4个姬松茸菌株和2个双孢蘑菇菌株为材料,用20个随机引物对它们进行RAPD扩增,通过对供试菌株遗传相似系数的估算和系统聚类分析,构建姬松茸和双孢蘑菇遗传相关树状聚类图谱,结果表明,进行RAPD扩增的20个随机引物中,有12个能产生三种带型,当遗传相似系数升至0.8713时,这6个菌株被分为3类,第一类为菌株18和26,第二类为菌株13和12,第三类为菌株33和45。  相似文献   
63.
Rice dwarf virus isolates were collected from several locations in Japan, the Philippines, China, Nepal and Korea. Genomic dsRNA segment profiles in polyacrylamide gel electrophoresis differed among the isolates. There were less differences in the profiles between isolates from Japan and Korea than in those between these two Countries and others. Nucleic acid hybridization was used to examine the extent of genomic variation. Full-length cDNAs to all genomic segments encoding non-structural proteins (S4, S6, S9, S10, S11 and S12) were synthesized from two Japanese isolates, and were used for dot-blot hybridization. Hybridizations using probes generated from the full-length cDNA clones failed to differentiate isolates from different geographical areas. However, cDNA probes covering a variable region of S12 were able to distinguish Japanese and Korean isolates from those of other countries. Phylogenetic tree analysis based on the amino acid sequence of P12 encoded by S12 grouped Japanese and Korean isolates together. The Chinese isolates from two different locations (Yunnan and Fujian) were closely related to each other, and were the most distantly related to Japanese and Korean isolates.  相似文献   
64.
大豆疫病的种子处理技术研究   总被引:2,自引:0,他引:2  
本试验用不同浓度的瑞毒锰锌、杀毒矾和克露进行大豆种子处理试验,结果表明,500ppm瑞毒锰锌对大豆疫病具有很好的治疗作用,而用杀毒矾以种子重量0.4—0.5%的剂量闷种,能显著地抑制大豆疫霉菌的侵入  相似文献   
65.
 分析植物酸性转化酶基因的保守区序列,设计一对PCR引物,以君子兰基因组DNA为模板,采用PCR方法扩增出长约500 bp的DNA片段,克隆入pGEM-TEasy载体,测序结果表明获得君子兰酸性转化酶基因家族的一个成员CMCW1,该基因片段长518 bp,不含内含子,编码172个氨基酸。其序列已在GenBank中登记(登记号为AY151269)。在GenBank中进行同源性检索的结果表明,该成员编码的氨基酸与其它植物细胞壁酸性转化酶编码的氨基酸同源性较高。  相似文献   
66.
AIM: To explore interaction and biological behaviour changes of two kinds of cells-blastocysts and hepatocarcinoma cells in the same microenvironment. METHODS:The models of mouse blastocysts co-cultured with human hepatocarcinoma cell lines were established, then biological behaviours and mutual effects of the two kinds of cells in co-culture system were observed. RESULTS: Compared with control group, hepatocarcinoma cells with differently invasive and metastatic potential significantly enhanced the rates of blastocyst hatchment , attachment and outgrowth(P<0.05). There was no significant difference in those among hepatocarcinoma cells co-cultured groups (P>0.05). The blastocyst hatched and attached to hepatocarcinoma cells with differently invasive and metastatic potential. Then, differential trophoblasts invaded hepatocarcinoma cells. The clear-cut interfaces were gradually formed between both sides. Hepatocarcinoma cells on interface showed changes of growth direction and cell shapes and did not invade blastocysts. CONCLUSIONS: Hepatocarcinoma cells promoted blastocyst development. Blastocysts implanted and invaded hepatocarcinoma cells with differently invasive and metastatic potential in vitro, which indicate that blastocyst implantation in vitro does not relate with the kinds and differential level of interactional cells and the low selectivity maybe relate with high adaptability of early life.  相似文献   
67.
68.
桃树根癌病防治技术探讨   总被引:8,自引:0,他引:8  
桃树根癌病是公认最难防治的土传细菌病害之一。在对该病进行较系统研究的基础上,采用多种抗菌药剂、多种方法进行了室内、外药敏测定与防治试验,显示出异菌氰、次氯酸钠、乙蒜素、妥布霉素、环丙沙星、庆大霉素及其混用对防治桃树根癌病菌有明显防效。  相似文献   
69.
1案情2003年3月23日锡盟正镶白旗改良站从通辽市科左后旗查金台牧场购入26头西门塔尔牛 (其中3头种公牛 ) ,用汽车从科尔沁区运抵锡盟正镶白旗羊场 ,并与2002年11月从通辽科左后旗查金台牧场购入的10头牛混群饲养。24日下午起 ,新购进牛陆续发病 ,至31日病牛已达26头 (新购和原购的牛都有 ) ,旗兽医站接到疫情报告后即派兽医人员到羊场调查情况 ,并采取了相应措施。兽医人员初步诊断为某一类病 ,于是向旗、盟畜牧局和政府上报疫情。并采取病料送自治区兽医站检验诊断 ,确诊为某一类传染病。2处罚经自治区动物防疫监督检验所调查取证 ,这是一…  相似文献   
70.
Essential oils are widely used in the pharmaceutical, food and cosmetic industries, and many plant essential oils have shown that they have positive effects on broilers nutrition. This experiment was conducted to study the effects of orally administered different dosages of carvacrol essential oils on intestinal barrier function in broiler chickens. A total of eighty 28‐day‐old (1.28 ± 0.15 kg) ROSS 308 broilers were randomly allocated to four groups of 20 replicates each, with one chicken per replicate per cage, and all were fed with the same diet. Four experimental groups were orally administered 0, 200, 300 or 400 μl carvacrol essential oils at 18:00 hr every day during the 2‐week experimental period. As a result of which, the gene expression of the occludin, claudin‐1, claudin‐5, ZO‐1 and ZO‐2 in intestinal mucosa of small intestine (p < 0.05) and the goblet cell content in small intestine epithelium (p < 0.05) were significantly increased; test subjects with 300 or 400 μl carvacrol essential oils reduced the microbial counts of Salmonella spp. and Escherichia coli in the intestines (p < 0.05); Essential oils administration also significantly increased activity of the sucrase (p < 0.05) and lactase (p < 0.05) in intestinal mucosa. In conclusion, the carvacrol essential oils have positive effects on growth performance and intestinal barriers function of broilers; those effects may be related to the dosage, as administration of 300 or 400 μl was more effective than that of 200 μl.  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