全文获取类型
收费全文 | 3196篇 |
免费 | 122篇 |
国内免费 | 126篇 |
专业分类
林业 | 820篇 |
农学 | 373篇 |
基础科学 | 31篇 |
166篇 | |
综合类 | 1298篇 |
农作物 | 155篇 |
水产渔业 | 25篇 |
畜牧兽医 | 195篇 |
园艺 | 308篇 |
植物保护 | 73篇 |
出版年
2024年 | 3篇 |
2023年 | 15篇 |
2022年 | 32篇 |
2021年 | 39篇 |
2020年 | 44篇 |
2019年 | 64篇 |
2018年 | 38篇 |
2017年 | 67篇 |
2016年 | 76篇 |
2015年 | 78篇 |
2014年 | 105篇 |
2013年 | 142篇 |
2012年 | 237篇 |
2011年 | 212篇 |
2010年 | 204篇 |
2009年 | 261篇 |
2008年 | 217篇 |
2007年 | 235篇 |
2006年 | 193篇 |
2005年 | 179篇 |
2004年 | 151篇 |
2003年 | 104篇 |
2002年 | 89篇 |
2001年 | 68篇 |
2000年 | 80篇 |
1999年 | 48篇 |
1998年 | 56篇 |
1997年 | 46篇 |
1996年 | 48篇 |
1995年 | 45篇 |
1994年 | 54篇 |
1993年 | 40篇 |
1992年 | 32篇 |
1991年 | 31篇 |
1990年 | 37篇 |
1989年 | 24篇 |
1988年 | 18篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1955年 | 4篇 |
排序方式: 共有3444条查询结果,搜索用时 15 毫秒
991.
Summary Tuber characteristics of potato clones (Solanum tuberosum L.) regenerated from cultured leaf, rachis or stem pieces of cv. Desiree were assessed in field trails over three years. In the first two seasons, when the crop was grown for seed potato production, tuber numbers and the tuber yields were normally distributed and the population means of the clones were about the same as those of the controls. When 78 of the clones were grown as a ware crop in a replicated field trial there were statistically significant differences between most clones and the controls in total yield (generally lower) and ware yield (generally higher), brought about by alterations of the size distributions of tubers. In all years the population of clones had fewer scab (Streptomyces scabies) lesions than the controls. Clones with consistent differences in flesh colour and eye depth were also observed. Two out of 78 clones, in 1984, had significantly higher dry matter content. No stable decrease in susceptibility to the cyst nematode Globodera pallida was observed amongst 167 clones tested. These potato plants regenerated from explants clearly show that somaclonal variation can include agronomically relevant changes. 相似文献
992.
Genotypic and exogenous factors affecting shoot regeneration from anther callus of linseed (Linum usitatissimum L.) 总被引:1,自引:0,他引:1
Summary The objective of this study was to investigate factors affecting the regeneration capacity of linseed anther culture. Four different environmental conditions in a phytotron were tested with regard to their effects on anther donor plants of cv. Hella. Anther response and shoot regeneration from anther callus was maximal when donor plants were grown in a 16 hrs-day at 14°C day/8°C night temperature. Anthers of four linseed genotypes were cultured on different media. Maximum shoot regeneration was achieved when the induced calli were transferred onto a modified N6 medium containing zeatin (1 mg l-1). Most of the calli regenerated shoots in the second subculture on regeneration media. Shoots were rooted on modified B5 or MS media containing NAA (0.1 mg l-1). Cytological examinations of incubated anthers and root tips of regenerated plants indicated that the anther calli were derived from microspores.Abbreviations B5
Gamborg's (1975) medium
- BAP
6-benzylaminopurine
- 2,4D
dichlorophenoxyacetic acid
- N6
Chu's (1978) medium
- NAA
-naphthaleneacetic acid
- MS
Murashige & Skoog's (1962) medium
- ZEA
zeatin 相似文献
993.
Summary This paper reviews investigations into the application of protoplast fusion to the genetic and agronomic improvement of potato. Fusion studies involving Solanum tuberosum are reviewed under the categories of: fusion with wild relatives, dihaploid fusion and asymmetric strategies. The selection and characterisation of putative somatic hybrid material is identified as a critical stage in the process and certain specific aspects of this technology are identified. Future prospects for the wider uptake and integration of these techniques into breeding programmes are also discussed. 相似文献
994.
Effect of gamma and ultraviolet irradiation on adventitious regeneration from in vitro cultured pear leaves 总被引:2,自引:0,他引:2
Summary Irradiation of in vitro explants and subsequent adventitious regeneration has been tested for 4 commercially important varieties of pear (Pyrus communis) with the aim to create mutants with a reduced susceptibility to fire-blight (Erwinia amylovora). The effect of gamma and ultraviolet irradiation of leaves on adventitious regeneration ability has been studied. The LD50 (50% decrease of regeneration) after gamma irradiation was genotype-dependent and was between 20 and 50 grays. The curves of regeneration showed a threshold dose underneath which none or a very slight decrease was registered. The decrease might result from cumulative events. After an ultraviolet irradiation as low as 62.5 J/m2, the leaves became crumbly and rolled up, and their metabolism seemed to be altered. The LD50 was about 125 J/m2 for all varieties and the decrease of regeneration was linear. Histological investigations showed leaves with flattened epidermal cells after ultraviolet irradiation and slack spongy parenchyma after gamma irradiation.Abbreviations Gy
grays
- J
joules
- LD
lethal dose 相似文献
995.
G. Daniel 《Plant Breeding》1993,110(3):259-261
The use of androgenetic doubled haploids in rye breeding is still limited by low regeneration rates. In this study we tested the influence of two modified MS-media on the number of reacting anthers and on plant regeneration. Picloram and 2,4-D were used as auxin components in the induction media. The highest induction rates (reacting anthers per 100 cultivated anthers) and the highest regeneration rates (number of green plants per 100 cultivated anthers) were reached on a modified MS-medium containing Picloram as auxin source, regardless of the donor plant material. The comparison of the results obtained with the single cross ‘SC 35’ which contains genes of Secale vavilovii and the true Secale cereale donor forms clearly show the genotypic influence of donor plant material on induction and regeneration ability. 相似文献
996.
The genetic determination of the plant regeneration ability of tissue cultures arising from immature embryos was studied using a ‘Chinese Spring’/‘Cheyenne’ substitution series. Plant regeneration proved to be polygenically determined. In tile current experiment the chromosomes 7B, 7D and ID were found to be effective, although the possibility of other chromosome effects cannot be excluded. 相似文献
997.
Summary The influence of cytoplasmic differences on shoot regeneration response has been investigated inB. carinata (BBCC) synthesised from reciprocal crosses betweenB. nigra (BB) andB. oleracea (CC). Mean shoot regeneration response from cotyledons of C cytoplasmic origin was twice as high as that from cotyledons with B cytoplasm. Statistical analysis of data indicated significant differences between cytoplasms, among growth regulator combinations and between cytoplasms and growth regulator interactions 相似文献
998.
Summary Shoot development through morphological transformation in spikelets occurred after segments of young unemerged orchardgrass (Dactylis glomerata L.) inflorescences were cultured on Linsmaier and Skoog's RM medium supplemented with 0, 4.52×10-4, 4.52×10-3 and 2.26×10-2 mM 2,4-dichlorophenoxyacetic acid (2,4-D) or naphthaleneacetic acid (NAA). Effects on shoot formation were better with 2,4-D than NAA in all concentrations tested. The callus initiated from the primary culture on high 2,4-D medium was reproducible, but no evidence of shoot proliferation was noted. The shoots developed into healthy plantlets after being reared on RM medium not supplemented with hormones.Contribution from South Dakota Agricultural Experiment Station Journal Article No. 1741. 相似文献
999.
B. S. Ahloowalia 《Euphytica》1982,31(3):755-759
Summary A procedure for plant regeneration from callus culture of potato, Solanum tuberosum L. is described. Calli were induced from 1–2 mm long shoot apices of potato cultivars Cara and A25/19 on half-strength Murashige and Skoog's medium (half-MS) supplemented with 3.2 mg IAA (indole-3-acetic acid), 1.0 mg kinetin (6-furfurylamino)purine], and 0.5 mg 2,4-D [2,4-dichlorophenoxy)acetic acid]/1. Sixty percent explants produced nodular calli on this medium within 30 days. Calli differentiated into shoot-primordia when subcultured on half-MS medium supplemented with 0.5 mg 2,4-D and 1.0 mg zeatin [6-(4-hydroxy-3-methybut-2 enylamino)amino purine]/1. Differentiated calli on half-MS medium without growth hormones produced complete plantlets which were cloned on the same medium and transferred into soil. 相似文献
1000.
A detailed procedure for isolated microspore culture of barley is presented along with examples of response across genotypes.
Over 30 genotypes, including winter and spring growth habit and 2-row and 6-row genotypes, have shown an essentially genotype
independent response, averaging about 10,000 embryos per 5 cm petri culture plate. The regeneration frequency, checked on
samples of 500 embryos per plate ranged from 36 to 97% with most genotypes being in the range of 70 to 90%. About 70 to 80%
of the plants regenerated have been completely fertile doubled haploids, thus eliminating the need to double the chromosome
number of plants. Many little details are critical to success of the microspore procedure and while it saves much time compared
to anther culture, greater attention to details and cleanliness is essential.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献