全文获取类型
收费全文 | 496篇 |
免费 | 13篇 |
国内免费 | 36篇 |
专业分类
林业 | 36篇 |
农学 | 44篇 |
基础科学 | 10篇 |
44篇 | |
综合类 | 191篇 |
农作物 | 62篇 |
水产渔业 | 36篇 |
畜牧兽医 | 74篇 |
园艺 | 40篇 |
植物保护 | 8篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 5篇 |
2017年 | 5篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 20篇 |
2013年 | 27篇 |
2012年 | 28篇 |
2011年 | 46篇 |
2010年 | 35篇 |
2009年 | 35篇 |
2008年 | 48篇 |
2007年 | 43篇 |
2006年 | 27篇 |
2005年 | 22篇 |
2004年 | 11篇 |
2003年 | 19篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 17篇 |
1999年 | 15篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有545条查询结果,搜索用时 46 毫秒
51.
本文研究了中棉(Gossypium arboreum race sinense)与纳尔逊氏棉(G. nelsonii Fryx) 种间杂种F1的一些形态性状的遗传变异及花粉母细胞减数分裂的染色体行为。杂种一代呈筒形,全株密集如毡的绒毛,叶片缺刻浅,似纳尔逊氏棉。除第一朵花为闭花外,其余均为开放花,呈玫瑰红色。少数花药退化成托叶状。减数分裂中期I的染 相似文献
52.
Oz Barazani Azat Atayev Bakhtiyor Yakubov Vladimir Kostiukovsky Konstantin Popov Avi Golan-Goldhirsh 《Genetic Resources and Crop Evolution》2003,50(4):383-389
Seedlings of Pistacia vera L. developed from seeds of two separate populations in Turkmenistan, Kepele and Agachli, were evaluated for their growth potential and genetic polymorphism. Plant growth rate as well as random amplified polymorphic DNA (RAPD) analysis showed distinct differences between the two populations. In plant height growth rate, 17 Agachli accessions were 1.3 times higher on average than that of 10 accessions of Kepele (significant at p = 0.046) and 1.2 times higher for trunk diameter growth rate (p = 0.062). Cluster analysis divided most accessions into two main genetic groups according to their geographic origin. The Agachli group was further divided into two subgroups. One Kepele accession (K4), was genetically different from the rest and clustered on a separate outgroup. Two Agachli accessions (A12 and A17) were outside the two main populations clusters. Accessions K9 and K10 from Kepele were exceptional and were clustered in each of the two Agachli's subgroups, indicating a close genetic relationship between the two populations. In addition, high similarity values (0.58–1.00) and small genetic distances reflect plausible gene flow between Kepele and Agachli, which are 100 Km apart. Mantel test revealed significant relationship between the RAPD and the morphological traits matrices, pointing to the genetic basis for the measured differences in the growth rate. Growing the accessions on the same plot, under similar conditions enabled the evaluation of genotypic differences. The combination of morphological traits and molecular markers will further assist in preservation of genetic variability and cultivation of useful genotypes of P. vera L. 相似文献
53.
Italy has been used as a country for estimating genetic erosion in crops. It was possible to compare early surveys (from the
1920s to the 1950s), especially on wheats, with results of later missions in the 1980s and 1990s. In the early years, a relatively
high genetic erosion was observed (13.2% p.a.). From the 1950s until the 1980s erosion rates between 0.48 and 4% p.a. were
estimated. In the little island of Favignana there was an erosion rate of 12.2% p.a. leading to the extinction of the last
wheat landraces of this island. There have been no significant differences in erosion rates between field- and garden-crops
though there has been the impression that garden crops are better preserved over the long run. Interestingly extinction rates
of wild plants (0.13% in the Mediterranean) come close to the average erosion rates of crop plants in the area.
1Dedicated to Erna Bennett on the occasion of her 80th birthday
2Lecture presented during the XVIIth Congress of EUCARPIA in Tulln, Austria, 2004 相似文献
54.
M.?K.?RanaEmail author V.?P.?Singh K.?V.?Bhat 《Genetic Resources and Crop Evolution》2005,52(8):989-997
Genetic diversity in 24 advanced breeding lines of cotton was studied by using six amplified fragment length polymorphism
(AFLP) primer-pairs and 14 morphological characters. The six selected AFLP primer-pairs generated a total of 535 amplification
products, of which 460 were found to be polymorphic resulting in 85.9% polymorphism. The observed genetic distances using
AFLP markers ranged from 30% to 87% with an average of 34%. A wide range of variability was observed for all the morphological
traits studied. The range in taxonomic distance was from 0.60 to 2.77. Most of the lines could be clustered in two major clusters
in both the analyses. But the correlation coefficient between the pair-wise distances estimated from AFLPs and the average
taxonomic distances estimated from morphological characters was found to be 0.04. UPGMA cluster analysis revealed inconsistencies
in the clustering patterns, as the co-phenetic correlation coefficient between the dendrograms for morphological and AFLP
data indicated a poor fit for the two data types. From combined information, genotypes ‘RST-12’, ‘H 1226’, ‘P 348’, ‘KDCAKD’,
‘CISV 24’ and ‘H1222’ were found to be distinct from rest of the material. 相似文献
55.
New directions for research identified during the final plenary discussion of the Sixth Symposium on the Biology of Terrestrial Isopods included: locating enzymes buffering pleon fluids during excretion of ammonia and the use of isopods in ecotoxicology including how they adapt to or tolerate high contaminant levels; how they interact with free living and endosymbiotic microbiota and how Wolbacchia avoids the immune response of isopods. New analyses of mating behaviour raised questions concerning mate choice while new microsatellite techniques may help resolve issues of multiple paternity and sperm competition. In relation to their ecology and biogeography new questions included how does the ability to learn the location of high quality food patches in spatially heterogeneous environments and the existence of an Allee effect, influence the population biology of isopods in the field and how do patterns of invasion and colonisation vary between species with different motility and life history strategies? 相似文献
56.
本文根据扫描电镜观察,时稻胚发生过程及胚表面构件的形态作了描述,并对文献中存在的稻胚结构构件名称的混乱情况进行了查核。从而发现历来稻胚形态描述上与事实不符之处,如广为流传的 Juliano 论文中的图将胚芽鞘和侧鳞误以为外胚叶;容启东、星川清亲等将侧鳞误为腹鳞;《水稻的生长发育》和《稻的生长》等的中译本,则将侧鳞误为胚芽鞘等等。本文还提出了胚的结构及各构件的合理命名。 相似文献
57.
Alpaca fibers have some distinct properties such as softness and warmth, which have not been fully understood in combination
with the fiber internal structures. In the present investigation, the internal structures of alpaca fibers have been closely
examined under the scanning electron microscope (SEM), especially in the longitudinal direction. The results showed that numerous
pigment granules reside loosely inside pockets in brown and dark-brown alpaca fibers. These pigment granules were mainly distributed
inside the cortical cells, the medullation regions as well as underneath the cuticles. Their size in the brown alpaca fibers
was smaller and more uniformly round than in the dark-brown fibers. These granules in colored alpaca fibers loosen the bundle
of cortical cells, providing many crannies in the fibers which may contribute to the superior flexibility, warmth and softness
of the fibers. Moreover, there are no heavy metal elements found in the granules. The mordant hydrogen peroxide bleaching
employed could eliminate the pigment granules and create many nano-volumes for further dyeing of fibers into more attractive
colors. 相似文献
58.
蒙古冰草居群遗传多样性研究 总被引:15,自引:0,他引:15
应用居群生物学原理及方法,对分布于中国不同地区的35个蒙古冰草(Agropyron mongolicum Keng)居群的形态学性状进行了分析。结果表明,蒙古冰草居群在形态学性状上具有丰富的遗传多样性(H′=1.7779)。在遗传多样性的分布上,居群间虽存在一定程度的遗传变异(9.15%),但遗传多样性主要集中在居群内部(90.85%),这种居群内遗传变异大于居群间遗传变异是由蒙古冰草异花、风媒传粉的外繁育系统所决定的。我国蒙古冰草居群在各个分布区的遗传多样性程度也不同,从大到小依次为陕西地区(H′=1.8627)、宁夏地区(H′=1.8332)、内蒙古地区(H′=1.7232)、新疆地区(H′=1.6453)、甘肃地区(H′=1.6436);陕西与宁夏地区的蒙古冰草居群主要采集于毛乌素沙漠南缘地区,其数量占分析居群数的68.6%。因此,对于分布于毛乌素沙漠南缘地区的蒙古冰草居群,无论从研究还是利用的角度都应给予较大关注。另外,还讨论了居群在物种定义上的意义,并提出了我国蒙古冰草居群的保护策略。 相似文献
59.
60.
木粉加入量对木/塑复合材料性能影响的研究 总被引:18,自引:0,他引:18
研究了聚丙烯与木粉以不同比率复合而成的材料的物理力学性能和复合形态特征。结果表明:不同混合比率的聚丙烯与木粉进行复合后所得的复合材料,除冲击强度有所降低外,其它力学性能均比纯聚丙烯的有较大幅度的提高。木粉表面的酯化处理可以改善木塑界面之间的相容性和复合材料的均匀性。在木塑复合过程中木塑之间发生镶嵌现象使木塑之间产生物理结合。 相似文献