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   9865篇
  免费   790篇
  国内免费   758篇
林业   923篇
农学   1298篇
基础科学   458篇
  1339篇
综合类   3014篇
农作物   523篇
水产渔业   617篇
畜牧兽医   2019篇
园艺   464篇
植物保护   758篇
  2024年   27篇
  2023年   128篇
  2022年   312篇
  2021年   349篇
  2020年   358篇
  2019年   348篇
  2018年   307篇
  2017年   392篇
  2016年   339篇
  2015年   439篇
  2014年   426篇
  2013年   575篇
  2012年   645篇
  2011年   713篇
  2010年   627篇
  2009年   562篇
  2008年   588篇
  2007年   555篇
  2006年   570篇
  2005年   474篇
  2004年   265篇
  2003年   182篇
  2002年   197篇
  2001年   245篇
  2000年   213篇
  1999年   192篇
  1998年   155篇
  1997年   126篇
  1996年   112篇
  1995年   119篇
  1994年   94篇
  1993年   84篇
  1992年   81篇
  1991年   84篇
  1990年   82篇
  1989年   55篇
  1988年   49篇
  1987年   35篇
  1986年   24篇
  1985年   20篇
  1984年   18篇
  1982年   12篇
  1979年   11篇
  1978年   10篇
  1976年   15篇
  1975年   11篇
  1973年   11篇
  1970年   9篇
  1968年   13篇
  1966年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Two groups of six mature brushtail possums (Trichosurus vulpeculu) were housed in two respiration chambers, and their heat production, whole body conductance and lower critical temperatures were measured under a variety of simulated weather patterns. The possums were subjected to ambient temperatures of 30, 20 and 3 degrees C. At 20 and 3 degrees C, the animals were exposed to near still air and light winds (wind speed 0.8 and 6.7 km/h), both with, and without, simulated rain every 8 hours. The lower critical temperature in near still air lies between 7 and 10 degrees C. This temperature increases by about 2, 6 and 8 degrees C respectively for a wind velocity of 6.7 km/h, simulated rain and a combination of the two factors. Weather in New Zealand, especially in the cooler part of the year, will often produce conditions below the lower critical temperature of the thermoneutral zone of possums. This will necessitate significant increases in metabolic rate and hence food consumption or mobilisation of body fat reserves, which if not sustainable will result in the death of possums. Field studies have shown that this is often the case in the wild. It is proposed that this stress may be sufficient to decrease the resistance (especially cell-mediated immunity) of some possums and allow acceleration of the disease process in those infected with Mycobacterium bovis.  相似文献   
42.
Intranuclear cisternal and vesicular structures, bound by a single membrane, were observed for the first time in some glandular "bird's eye" cells of canine circummanal gland carcinomas. The role of these intranuclear structures is not clear. It is suggested that they may be involved in cellular adaptation to an environment of nutrient deficiency, as a result of cell overcrowding.  相似文献   
43.
Bluegill absorbed 85% of 1 ppb of endrin from water within 48 hr under static exposure conditions. The absorbed radiocarbon was eliminated linearly with a half-life of about 4 weeks. Analyses of eliminated radioactivity revealed only conjugated metabolites. 12-anti-Hydroxyendrin and 12-syn-hydroxyendrin were tentatively identified by cochromatography using thin-layer chromatography/autoradiography and gas chromatography. These metabolites were also present as conjugates in the fish organs. Seventy-three percent of the absorbed radioactivity recovered from fish extracts was in the form of unchanged endrin.  相似文献   
44.
胡桃长足象是核桃果实的大害虫,为害损失很大。1975年以来,我们在四川平武地区进行了生活习性观察和防治试验,初步明确了以下几个问题。1.胡桃长足象一年一代。11月份以成虫越冬,次年4月上旬开始活动,为害果、芽、嫩枝、叶柄,5月上旬交尾产卵于果中,一般一果一粒,8月中旬产卵结束,10月陆续死亡。当年成虫6月中旬羽化,进行为害。2.成虫有假死性和向阳性,飞翔力弱,具有与核桃树芽苞相似的保护色。3.防治胡桃长足象,应抓住越冬成虫大量出现和卵孵化盛期时进行。用每毫升含孢量二至五亿的白僵菌液或50%的三硫磷乳油、50%速灭松乳剂、82%磷胺乳剂加水一千倍喷雾,效果良好。  相似文献   
45.
46.
47.
Extracts of erythroblastosis affected livers from which much of the structural protein had been removed were prepared by acid denaturation. These extracts contained complement fixing "soluble" antigen in a form which was not associated with viral or subviral particles. Ultracentrifugation can be of assistance in separating complement fixation activity from contaminating material in these extracts.  相似文献   
48.
During 1972, 333 fluff samples were tested from 13 Queensland hatcheries and assessed according to the English standards for total count, coliforms and fungi. They were also assessed as being "standard" or "substandard", using a combination of the criteria of the English system. All hatcheries had at least 2 substandard samples and all the samples from 2 hatcheries were substandard.  相似文献   
49.
将EGFPE0融合基因插入哺乳动物细胞表达载体pCI-dhfr中,构建重组质粒pCI-EGFPE0。将重组质粒转染CHO(dhfr-),在荧光显微镜下观察到少数细胞呈现绿色荧光,表明转染成功。通过MTX加压筛选后,在荧光显微镜下观察到多数细胞呈现强绿色荧光,表明重组融合蛋白EGFPE0在CHO细胞中得到大量表达。高效表达重组融合蛋白细胞克隆的获得为进一步大量制备可溶性的猪瘟病毒E0糖蛋白、制备其单抗筛选抗原表位及研究E0蛋白的生物学功能奠定基础。  相似文献   
50.
‘丰香’草莓叶片高效再生体系的建立   总被引:12,自引:0,他引:12  
 以草莓主栽品种丰香( Fragaria ×ananassa Duch ‘Toyonoka’) 叶片为外植体, 研究了影响组织培养的多个因素, 建立了高效再生体系。结果表明: MS + TDZ 1.5 mg·L - 1 + IBA 0.4 mg·L - 1培养基最适于不定芽分化。不同滤光膜(绿膜、红膜、蓝膜、黄膜) 对草莓不定芽的分化具显著效应, 绿膜和红膜对芽的分化有明显促进作用, 不定芽再生率达95%以上, 平均每个外植体再生芽数在25个以上; 而蓝膜和黄膜则不利于芽的分化。不同滤光膜光谱差异主要集中在300~700 nm, 红、绿膜在该波段光强较弱,而黄、蓝膜和荧光灯较强。暗处理4周比1、2、3周更有利于提高叶片的不定芽再生率, 此后转到光下培养, 获得的不定芽再生率可达100%。  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