全文获取类型
收费全文 | 5234篇 |
免费 | 249篇 |
国内免费 | 349篇 |
专业分类
林业 | 322篇 |
农学 | 330篇 |
基础科学 | 145篇 |
603篇 | |
综合类 | 2085篇 |
农作物 | 321篇 |
水产渔业 | 399篇 |
畜牧兽医 | 1076篇 |
园艺 | 157篇 |
植物保护 | 394篇 |
出版年
2024年 | 12篇 |
2023年 | 40篇 |
2022年 | 100篇 |
2021年 | 132篇 |
2020年 | 126篇 |
2019年 | 175篇 |
2018年 | 116篇 |
2017年 | 182篇 |
2016年 | 212篇 |
2015年 | 205篇 |
2014年 | 242篇 |
2013年 | 252篇 |
2012年 | 399篇 |
2011年 | 487篇 |
2010年 | 460篇 |
2009年 | 404篇 |
2008年 | 356篇 |
2007年 | 368篇 |
2006年 | 312篇 |
2005年 | 232篇 |
2004年 | 178篇 |
2003年 | 130篇 |
2002年 | 106篇 |
2001年 | 95篇 |
2000年 | 87篇 |
1999年 | 75篇 |
1998年 | 41篇 |
1997年 | 35篇 |
1996年 | 36篇 |
1995年 | 35篇 |
1994年 | 18篇 |
1993年 | 19篇 |
1992年 | 33篇 |
1991年 | 25篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1973年 | 2篇 |
1956年 | 4篇 |
1955年 | 5篇 |
排序方式: 共有5832条查询结果,搜索用时 15 毫秒
11.
RT-PCR及RFLP分析技术对鸡传染性支气管炎病毒的诊断和S1基因分型的研究 总被引:4,自引:0,他引:4
本研究使用分别扩增整个S1糖蛋白基因 (引物A)和S1糖蛋白基因N_端高变区Ⅰ (引物B)的 2对引物对 3个IBV标准株M41、Connecticut、Arkansas及 5个地方分离株 (C60 ,D41A ,D41B ,A112 1,A1171)进行RT_PCR扩增。用引物A时 ,有 5个IBV毒株扩增到目的片段 (172 0bp) ;用引物B时 ,所有 8个IBV毒株均得到与预计大小相符的目的产物 (2 2 8bp)。对 172 0bp的PCR产物用限制性内切酶HaeⅢ进行酶切 ,结果得出 3个不同的RFLP图谱 ,其中M41、Connecticut、D41B具有相同的HaeⅢ酶切图谱。Arkansas和D41A则分别具有互不相同的图谱 ;对 2 2 8bp的PCR产物进行DdeⅠ、RsaⅠ限制性内切酶消化 ,根据它们的RFLP图谱 ,8个IBV毒株可分为 5个基因型。综合 2对引物的PCR产物的RFLP分析结果 ,8个IBV毒株可分为 7个基因型 ,分型的结果与传统的血清学方法吻合。本研究建立的方法和技术具有快速、简单、特异、灵敏等优点 ,为现场流行毒株的定型(基因型 /血清型 )及其S1基因变异的跟踪研究以及更有效防制传染性支气管炎奠定了基础。 相似文献
12.
13.
E. Ubels 《European journal of plant pathology / European Foundation for Plant Pathology》1979,85(3):143-150
The construction and application is described of a polystyrol humidity box in which wheat leaves, while continuing to function as parts of living plants, can be tested for their reactions toSeptoria spp. in an atmosphere nearly saturated with water, as is required for successful infection. The method is simple, accurate ans inexpensive.Samenvatting Voor dit doel is een z.g. vochtdoos geconstrueerd (Fig. 1A). Het te toetsen blad wordt daar doorheen geleid en in de doos geïnoculeerd met een druppel conidiën-suspensie van de schimmel. Onder het blad staat wat water in de doos (Fig. 1B). Na afsluiting ontstaat in de doos de hoge luchtvochtigheid van bijna 100% die nodig is voor de infectie. Dit wordt op deze wijze eenvoudig en goedkoop gerealiseerd. De bladeren die zo worden getoetst blijven onbeschadigd functioneren aan de plant. Na enkele dagen kan de doos worden geopend en kan de symptoom-ontwikkeling worden afgewacht en gevolgd (Fig. 3A, 3B en 4). De methode leent zich voor nauwkeurig werk en vereist zeer weinig infectiemateriaal. De Technische en Fysische Dienst voor de Landbouw (TFDL), Wageningen, ontwierp en construeerde een statief voor het gebruik van de vochtdozen in serie (Fig. 2). 相似文献
14.
Although the molluscicide Frescon is a strong neurotoxin to the Lymnaea stagnalis central nervous system in vitro, it is probable that the exposure of the whole animal to this molluscicide fails to result in central nervous system abnormalities: Frescon does not appear to reach the brain in sufficient quantity to disrupt its normal activity. However, only those Frescon analogs found to be neurotoxic were molluscicidal, suggesting some related mode, if not site, of action. Frescon and its analogs may act by affecting excitable tissues other than the nervous system (e.g., the snail musculature) by altering certain functional and/or structural membrane properties. 相似文献
15.
梨自交不亲和强度不同品种花柱S糖蛋白含量的差异 总被引:12,自引:2,他引:12
提取梨( Pyrus) 自交不亲和强度不同品种花柱可溶性蛋白质, 应用等电聚焦电泳法在凝胶板上分离出S 糖蛋白, 用图像解析法进行定量。结果表明, 花柱总S 糖蛋白含量因品种而异, 自交不亲和强、弱及自交亲和的品种每1 1048577;g 花柱可溶性蛋白中含总S 糖蛋白分别为1048578;1. 3 ng 、0. 7 ~ 0. 9 ng、 0. 7 ng 。不同的S 基因所表达的S 糖蛋白量差异显著, 即使是同一S 基因所对应的S 糖蛋白量也因品种而异。 相似文献
16.
ZHANG Yu-xia YU Lun-yin LIU Ming-qiu ZHANG Zheng-bin TANG Zhi-jiao XIA Dong WANG Ming 《园艺学报》2002,18(1):32-35
AIM:To investigate the protein expression of cyclin D2 and p16 in proliferation and differentiation of cultured cardiac myocytes.METHODS:One-day-old Sparague-Dawley rats were used. Cardiac myocytes(CM) were collected by a trypsin-dispersal method and cultured. Cell growth line and fluorescence activated cell sorting (FACS) were used to investigate the proliferation of CM. Ultra-thin sections were made to observe the ultrastructure of CM under transmission electron microscope. The expression of cyclin D2 and p16 in CM were measured using immunocytochemistry and image analysis.RESULTS:①Results of cell growth line and FACS analysis showed that cultured CM could proliferate in the first 3 cultured days, but the ability decreased quickly, concomitant with differentiation. CM was obseved quiescent in cell cycle three days later. The ultrastructure of CM showed the large amount of myofilaments and mitochondrion. ②The protein expression of cyclin D2 in 3,4,5 day CM group was 0.89 times(P<0.05),0.80 times (P<0.05) and 0.56 times (P<0.01) of that in 1 day group, respectively. The expression of p16 in CM was increased during the culture process, 2,3,4,5 day group were 1.63 times, 1.72 times, 1.99 times and 2.84 times (P<0.01) of that in 1 day group, respectively.CONCLUSION:Cultured neonatal rat cardiac myocytes could proliferate during the first 3 days after incubation, but the ability of proliferation decreased, from the fourth day, concomitant with differentiation. Cyclin D2 and p16 play the key roles in CM postnatal development. Downregulation of cyclin D2 and upregulation of p16 may induce CM differentiation. 相似文献
17.
18.
昆虫病原线虫rDNA多态性分析 总被引:1,自引:0,他引:1
本文对国内外昆虫病原线虫斯氏属和异小杆属的47个品系进行rDNA—ITS PCR—RFLP分析,研究其DNA多态性,并构建了分子系统发育树状图。各品系的ITS区无明显的长度差异,PCR—RFLP分析将47个品系分为斯氏属和异小杆属两大类,两属线虫又分别分为11组和4组。所得结果丰富了ITS PCR—RFLP图谱库,为弄清我国的昆虫病原线虫与国外种类的分子系统发育关系及未定名线虫的鉴定提供重要依据,同时为筛选适合的线虫种类防治害虫奠定基础。 相似文献
19.
Eiko E. Kuramae Alexandre L. Buzeto Maisa B. Ciampi Nilton L. Souza 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(4):391-395
Fungi isolated in Brazil, from lettuce, broccoli, spinach, melon and tomato, were identified as Rhizoctonia solani. All lettuce isolates anastomosed with both AG 1-IA and IB subgroups and all isolates from broccoli, spinach, melon and tomato anastomosed with AG 4 subgroup HG-I, as well as with subgroups HG-II and HG-III. DNA sequence analyses of ribosomal internal transcribed spacers showed that isolates from lettuce were AG 1-IB, isolates from tomato and melon were AG 4 HG-I, and isolates from broccoli and spinach were AG 4 HG-III. The tomato isolates caused stem rot symptoms, the spinach, broccoli and melon isolates caused hypocotyl and root rot symptoms on the respective host plants and the lettuce isolates caused bottom rot. This is the first report on the occurrence in Brazil of R. solani AG 4 HG-I in tomato and melon, of AG 4 HG-III in broccoli and spinach and of AG 1-IB in lettuce. 相似文献
20.
Anthropogenic influences on potential fire spread in a pyrogenic ecosystem of Florida, USA 总被引:1,自引:1,他引:1
Fire has historically been an important ecological factor maintaining southeastern U.S. vegetation. Humans have altered natural
fire regimes by fragmenting fuels, introducing exotic species, and suppressing fires. Little is known about how these alterations
specifically affect spatial fire extent and pattern. We applied historic (1920 and 1943) and current (1990) GIS fuels maps
and the FARSITE fire spread model to quantify the differences between historic and current fire spread distributions. We held
all fire modeling variables (wind speed and direction, cloud cover, precipitation, humidity, air temperature, fuel moistures,
ignition source and location) constant with exception of the fuel models representing different time periods. Model simulations
suggest that fires during the early 1900's burned freely across the landscape, while current fires are much smaller, restricted
by anthropogenic influences. Fire extent declined linearly with patch density, and there was a quadratic relationship between
fire extent and percent landscape covered by anthropogenic features. We found that as little as 10 percent anthropogenic landcover
caused a 50 percent decline in fire extent. Most landscapes (conservation or non-conservation areas) are now influenced by
anthropogenic features which disrupt spatial fire behavior disproportionately to their actual size. These results suggest
that land managers using fire to restore or maintain natural ecosystem function in pyrogenic systems will have to compensate
for anthropogenic influences in their burn planning.
This revised version was published online in May 2005 with corrections to the Cover Date.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献