全文获取类型
收费全文 | 1373篇 |
免费 | 116篇 |
国内免费 | 219篇 |
出版年
2024年 | 2篇 |
2023年 | 31篇 |
2022年 | 28篇 |
2021年 | 38篇 |
2020年 | 32篇 |
2019年 | 44篇 |
2018年 | 43篇 |
2017年 | 62篇 |
2016年 | 78篇 |
2015年 | 56篇 |
2014年 | 77篇 |
2013年 | 84篇 |
2012年 | 70篇 |
2011年 | 61篇 |
2010年 | 57篇 |
2009年 | 67篇 |
2008年 | 73篇 |
2007年 | 69篇 |
2006年 | 75篇 |
2005年 | 82篇 |
2004年 | 57篇 |
2003年 | 61篇 |
2002年 | 43篇 |
2001年 | 38篇 |
2000年 | 43篇 |
1999年 | 44篇 |
1998年 | 28篇 |
1997年 | 22篇 |
1996年 | 32篇 |
1995年 | 20篇 |
1994年 | 31篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 7篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 4篇 |
排序方式: 共有1708条查询结果,搜索用时 15 毫秒
31.
J. W. Snape A. J. Wright E. Simpson 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1984,67(2-3):143-148
Summary Three methods of estimating the numbers of genes segregating for quantitative characters using doubled haploid lines are presented. The first uses estimates of the range and genetical variance of an F1 or F2 derived population. The second adapts the genotype assay method of Jinks and Towey (1976) to F2 derived lines. The third uses the variances of an F2 derived population. Statistical problems of obtaining meaningful estimates using these methods are discussed and it is concluded that genotype assay is the best method for distinguishing between few and many genes. These methods are illustrated using data from an experiment containing doubled haploid lines of barley developed using the H. bulbosum system. 相似文献
32.
The seed coat morphology, investigated in taxa representative of the main European groups ofAconitum, are in good agreement with the current taxonomy of the genus. The seed coat microcharacteristics (warty epidermal cells) are very constant. There is a trend for the reduction of longitudinal wings on the edges concomitant with the development of ridges and transverse wings on the faces. Another morphological progression leads from smooth to rugulose and eventually to transverse wing-bearing seed faces. A working hypothesis suggests an ecological adaptative significance to these changes. 相似文献
33.
Mick Richardson 《Biochemical Systematics and Ecology》1978,6(4):283-286
A survey of 112 species of the Caryophyllales showed the presence of flavonols in all eleven families and of C-glycosylflavonoids in nine families, being absent from the Aizoaceae and Cactaceae. 18% of the species contained both classes of compound. C-glycosylflavonoids are reported for the first time in the Amaranthaceae, Basellaceae, Didieraceae, Nyctaginaceae, Phytolaccaceae, Portulacaceae and Molluginaceae. The Caryophyllaceae contained prodominantly C-glycosylflavonoids, suggesting they are the most advanced family in the order. 相似文献
34.
Leaves of greenhouse grown grasses had free protein amino acid contents of generally less than 5 % total amino acids, while field collected grasses averaged 14.7 % free protein amino acid contents. Taxonomic patterns are detectable in the total leaf amino acid profiles of grasses from both sources, those of pooids being distinguishable from those of chloridoids and panicoids, and those of danthonioids showing an intermediate pattern. Leaf profiles of Oryza, Stipeae, and Ehrharteae resemble one another, and are more like those of pooids than those of panicoids. Variations in Thr and Leu are apparently associated with differences in photosynthetic pathway. Grass leaves are generally low in total amino acid contents (2.2 ? 1.0 g % fr. wt), with Ile, Val and Met + Cys identified as the limiting essential amino acids. However, the nutritional ‘chemical scores’ of grass leaf proteins are high (75 %, based on the WHO scoring pattern). 相似文献
35.
R. G. DAVIES K. L. BORATYSKI 《Biological journal of the Linnean Society. Linnean Society of London》1979,12(2):95-165
A quantitative comparison of the classifications of 24 species of male Diaspididae by principal component and principal coordinate analysis was extended to allow the comparison of classifications based on selected subsets of the 101 available characters. It was shown that subsets of 25–28 characters could be chosen numerically and used to construct classifications that resembled very closely the classification based on the reference set of characters. The conclusions are discussed in relation to other views on character-weighting and in relation to classifications of the Diaspididae based on traditional taxonomic characters provided by the females. 相似文献
36.
Anton Weber 《Plant Systematics and Evolution》1977,127(2-3):201-216
Within the genusLoxonia
Jack, currently regarded as monotypic, three species are recognized:L. hirsuta
Jack (Sumatra, Mentawai-Islands, Java, Borneo, Anambas-Islands, Malay Peninsula),L. discolor
Jack (Sumatra) andL. burttiana
A. Weber, spec. nova (Borneo). [Key with English translation p. 203.] There is evidence thatL. discolor is the most primitive species within the genus, the two others being derived from it.
Teil V der Beiträge zur Morphologie und Systematik derKlugieae undLoxonieae (Gesneriaceae). 相似文献
37.
本文综述了外生菌根的形态学和解剖学特征,评价了这些特征用于外生菌根分类的价值,同时指出各种类型的形态学特征和解剖学特征与其营养吸收的关系。这些特征包括了菌根的颜色类型及变化、形状及分枝方式、外伸菌丝的多少及特征、根状菌索有无及分化、菌核有无及特征、菌套内外表面的菌丝排列及分化,菌套的切面特征,丹宁层厚度及分化、哈氏网的菌丝排列及厚度等。较详细阐述了100多年来,人们为外生菌根分类所作出的种种努力,并对各种分类方式作了简单的评价。 相似文献
38.
H. Walter Lack 《Plant Systematics and Evolution》1979,131(1-2):35-52
Three species of the genusPicris L. are native in Tropical Africa:P. abyssinica
Sch. Bip. (Ethiopia),P. xylopoda
Lack, spec. nova (Nigeria, Ethiopia) andP. humilis DC. (Senegal, Mali). There are indications that the two perennial species,P. abyssinica andP. xylopoda, are related to and have evolved from a primitive Central Asiatic stock in a manner parallel to many African species ofCrepis L.P. humilis, on the other hand, is a small annual plant with a high number of derived characters. The introduced species of European origin growing south of the Sahara are briefly mentioned. 相似文献
39.
40.
Lilian I. B. Stedille Juliano P. Gomes Newton C. F. da Costa Roseli L. da Costa Bortoluzzi Adelar Mantovani 《Restoration Ecology》2020,28(5):1213-1224
Monitoring successional advancement is a complex field involving a constant search for applied ecological indicators which facilitate monitoring of secondary forests for both active and passive restoration. In this study, the authors investigate the successional advancement of floristics and tree structure within Araucaria Forest (AF) fragments under passive restoration in a context where exotic tree plantations (mainly Pinus L. genus) dominate the landscape. The ecological indicators used were floristic dissimilarity (β‐diversity inferences), indicator species, ecological groups of species, basal area, and species abundance distribution (SAD) models (α‐diversity inferences). A total of 182 tree species belonging to 91 genera and 43 botanical families were identified. A high β diversity was verified for which each site has indicator species (for the locations CD—Dicksonia sellowiana; CO—Cryptocarya aschersoniana; and PG—Pinus taeda), where pioneer species contributed to much of the abundance. Different SAD models are useful for describing passive restoration sites in exotic tree plantation landscapes, namely Lognormal, Mandelbrot, and Zipf. SAD models together with basal area, taxonomic group (e.g. Myrtaceae assemblage), and tree abundance in ecological groups are strategic ecological indicators for monitoring successional advancement in AF. 相似文献