全文获取类型
收费全文 | 422篇 |
免费 | 15篇 |
国内免费 | 114篇 |
专业分类
551篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 8篇 |
2019年 | 17篇 |
2018年 | 3篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 31篇 |
2011年 | 31篇 |
2010年 | 20篇 |
2009年 | 16篇 |
2008年 | 15篇 |
2007年 | 31篇 |
2006年 | 38篇 |
2005年 | 36篇 |
2004年 | 30篇 |
2003年 | 24篇 |
2002年 | 26篇 |
2001年 | 18篇 |
2000年 | 14篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有551条查询结果,搜索用时 0 毫秒
111.
112.
113.
Neil Carrier 《Ethnos》2013,78(3):415-437
This article examines the enormous variety evident in the ‘social life’ of Kenyan khat (miraa) and the role of this variety in the creation and manipulation of value. The article, after a discussion of the literature on value and its relevance to miraa, describes variables used in distinguishing the many different types of miraa, describes how consumers associate themselves with certain varieties and suggests why some varieties are more valued – culturally and economically – than others. The article then looks at the international trade in miraa, and how value is manipulated as exporters – well positioned to exploit different ‘fields of value’ – blend different varieties together to ensure a decent financial reward. It concludes by emphasising that understanding miraa requires an appreciation of its complex particularity. 相似文献
114.
Koichi Tanaka 《Entomologia Experimentalis et Applicata》1999,90(3):279-287
The virulence of Nilaparvata lugens Stål (Homoptera: Delphacidae) to a resistant variety of rice, Oryza sativa L., is suggested to be under polygenic control. To determine whether the virulence of N. lugens is a quantitative character that has continuous distribution or a threshold character that has a few discontinuous phenotypic forms and is determined by some underlying continuous variable, I examined the frequency distribution of honeydew excretion that has been used as a measure of ability of attacking the rice plants, and the relationship between honeydew excretion and the oviposition rate of N. lugens females using a japonica rice line Saikai 190 which has a resistance gene Bph 1. The frequency distribution in honeydew excretion significantly differed from the normal distribution, but two distributions below and above 10 mg honeydew excretion for two days did not significantly deviate from normality, suggesting a bimodal distribution. There were significant differences in the proportion of females ovipositing and the number of eggs deposited between the female groups that excreted 0–10 mg honeydew and more than 20 mg honeydew. Within these female groups, however, the reproductive performances were not different. Thus, virulence of N. lugens can be analyzed as a threshold character that has two distinct phenotypes, virulent and avirulent. I estimated the heritabilities of the virulence of N. lugens by parent-offspring regression using the percentage of virulent females in a full-sib family. The estimates of heritability were 0.41 on Saikai 190 and 0.55 on ASD7, carrying the bph 2 gene. These results show that the N. lugens population has substantial genetic variation in virulence. The regression coefficients on female and male parents were similar, suggesting similar genetic contributions by both parents. When the parental families were examined on Saikai 190 and the progeny on ASD7, the regression coefficient approached zero. There may be a low genetic correlation between virulences to the two varieties. 相似文献
115.
W. Link 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,79(5):713-717
Summary To increase the level and stability of yield in faba beans (Vicia faba L.), heterosis must be exploited. Hybrids are not available because of the instability of male sterility. Synthetic varieties can and should be bred. Thus, we studied the reproductive behavior of this partially allogamous, insect-pollinated crop. Autofertility (AF) and the rate of cross-fertilization (C) were measured in 36 inbred lines and 28 crosses in F1, F2, and F3 generations for 3 years at Hohenheim, Stuttgart, FRG. Heterozygosity strongly increased AF and decreased C. AF was negatively correlated with C. AF varied from 1% to 98%, and C varied from 7% to 82%. Heritability for both characters was high. For an optimum exploitation of heterosis, breeders should utilize lines with high C as variety components. It is often labor-intensive to multiply such lines, due to low AF. Hence, breeders tend to use autofertile lines with rather limited C. We showed that even in this case about 50% of the total heterosis, which equals a yield increase of at least 25% over the inbred line level, is realized. An increase in yield stability due to heterogeneity will occur simultaneously. 相似文献
116.
117.
Identification of a set of RFLP probes for subspecies differentiation in Oryza sativa L. 总被引:2,自引:0,他引:2
H-R. Qian J-Y. Zhuang H-X. Lin J. Lu K-L. Zheng 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,90(6):878-884
Sixty-eight indica-japonica tester-differentiating RFLP probes were tested in seven indica and seven japonica varieties of rice (Oryza sativa L.) with four enzyme digestions (EcoRI, EcoRV, HindIII and DraI). Twenty-one DNA clones were isolated as indica-japonica subspecies-differentiating probes. A set of 13 probes was established as core probes for subspecies differentiation and a pooled blotting analysis was carried out to facilitate the application of RFLP in rice genetics and breeding practice. A dendrogram of 12 wide-compatibility varieties was constructed based on RFLPs detected by 13 core probes with single enzyme digestions. It was speculated that most RFLPs of indica-japonica differentiating probes were generated by insertions/deletions, which may be of great significance for the origin and differentiation of subspecies in Oryza sativa L. 相似文献
118.
以中国传统名花──洛阳牡丹330个品种为研究材料,采用模糊数学方法构造项目、类目反应表,建立专家打分系统.在此基础上构造评估模型,并对每个品种进行评估.采用方差分析及参数估计的方法将330个品种划分为4等:其中Ⅰ等(优)含16个品种,为大家共认的珍稀品种;Ⅱ等(良)含51个品种,为牡丹的上等品种;Ⅲ等(一般)含231个品种;Ⅳ等(差)含32个品种.本研究较科学地解决了洛阳牡丹品种种质资源的定量评估及等级划分问题,为牡丹品种的计算机管理、信息交流、选种育种、市场销售提供了定量依据. 相似文献
119.
描述了在中国安徽发现的水晶兰属一新变种:霍山水晶兰Monotropa uniflora L.var.huoshanensis X.L.Zhao。该变种与原变种水晶兰M.uniflora L.相似,但本变种的花梗有褐色长柔毛,成熟时蒴果果柄弯曲向下而易区别。 相似文献
120.
S. S. Karataglis 《Plant Systematics and Evolution》1989,163(1-2):13-20
A native population ofAegilops cylindrica was encountered for the first time in Greece in 1980 (near Kastoria, NW. Greece), completely isolated and at a great distance from its main distribution area. There are morphological and chromosomal, but no protein and esterase pattern differences from otherAe. cylindrica populations. This justifies the recognition of a new variety: var.kastorianum. Our comparative and karyotypic observations support the view thatAe. caudata var.polyathera and not var.caudata (typica) is the possible donor of genome C of the new variety. 相似文献