全文获取类型
收费全文 | 6565篇 |
免费 | 491篇 |
国内免费 | 507篇 |
出版年
2024年 | 18篇 |
2023年 | 129篇 |
2022年 | 127篇 |
2021年 | 158篇 |
2020年 | 176篇 |
2019年 | 215篇 |
2018年 | 178篇 |
2017年 | 193篇 |
2016年 | 196篇 |
2015年 | 195篇 |
2014年 | 224篇 |
2013年 | 346篇 |
2012年 | 201篇 |
2011年 | 259篇 |
2010年 | 203篇 |
2009年 | 311篇 |
2008年 | 338篇 |
2007年 | 350篇 |
2006年 | 380篇 |
2005年 | 329篇 |
2004年 | 325篇 |
2003年 | 290篇 |
2002年 | 245篇 |
2001年 | 229篇 |
2000年 | 217篇 |
1999年 | 184篇 |
1998年 | 151篇 |
1997年 | 157篇 |
1996年 | 153篇 |
1995年 | 103篇 |
1994年 | 145篇 |
1993年 | 112篇 |
1992年 | 111篇 |
1991年 | 96篇 |
1990年 | 78篇 |
1989年 | 63篇 |
1988年 | 56篇 |
1987年 | 53篇 |
1986年 | 42篇 |
1985年 | 44篇 |
1984年 | 36篇 |
1983年 | 29篇 |
1982年 | 19篇 |
1981年 | 21篇 |
1980年 | 11篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 7篇 |
排序方式: 共有7563条查询结果,搜索用时 14 毫秒
101.
102.
103.
Jürgen Schultze-Motel 《Vegetation History and Archaeobotany》1994,3(1):33-61
A total of 422 publications from 1991 and 1992 on archaeological remains of cultivated plants have been collected. A list is given of the finds according to species, country and age. 相似文献
104.
Lignin is a major structural polymer of secondarily thickended plant vascular tissue and fibres, imparting mechanical strength to stems and trunks and hydrophobicity to conducting vessels. Constitutive expression of a lucerne caffeic acid 3-O-methyltransferase antisense RNA in transgenic tobacco leads to a significant reduction in lignin content, particularly in the younger parts of the stems, without apparent alterations in lignin monomer composition. These observations open up the possibility of genetically manipulating plants with reduced lignin for improved processing and biomass digestibility. 相似文献
105.
Before novel transgenic plant genotypes are grown outside containment facilities and evaluated under field conditions, it is necessary to complete a risk assessment to consider the possible consequences of that release. An important aspect of risk assessment is to consider the likelihood and consequences of the transgene being transferred by cross-pollination to related species, including other crops, weeds and ruderal populations. The purpose of this report is to review the literature to assess the ease with whichBrassica napus can hybridize with related species. The evidence for hybridization is considered at three levels: a) by open pollination, b) by hand pollination and c) by the use ofin vitro ovule and embryo rescue techniques; and also examines the fertility and vigour of the F1, F2 and backcross generations. Four species are reported to hybridize withB. napus by open pollination:B. rapa andB. juncea using fully fertile parents; andB. adpressa andR. raphanistrum using a male-sterileB. napus parent. Seventeen species are reported to form hybrids (including the four species above) withB. napus when pollination is carried out manually. At least 12 of these species were unable to form F2 progeny, and eight were unable to produce progeny when the F1 was backcrossed to one of the parental species. Many factors will influence the success of hybridization under field conditions, including: distance between the parents, synchrony of flowering, method of pollen spread, specific parental genotypes used, direction of the cross and the environmental conditions. Even where there is a possibility of hybridization betweenB. napus and a related species growing in the vicinity of a release, poor vigour and high sterility in the hybrids will generally mean that hybrids and their progeny will not survive in either an agricultural or natural habitat. 相似文献
106.
M. A. Burgess 《Biodiversity and Conservation》1994,3(2):126-136
Understanding the relationships between indigenous people and their threatened economic plants can aid the conservation effort on many levels. Understanding ethnic perceptions of the taxon is critical toin situ andex situ conservation projects and enhances the accompanying educational effort. Examples are discussed from the experience of a grassroots conservation group in southwestern United States, Native Seed/SEARCH. Four levels of economic plant vulnerability are examined among 1) wild-harvested plants, 2) husbanded wild plants, 3) domesticates, and 4) wild relatives of domesticates. Legal interpretations of endangered husbanded and domestic plants are discussed, and further documentation encouraged. Genetic dynamism of threatened indigenous crops is examined and the concept of Systems Conservation (i.e. the plant/human interactive systems) is introduced. Guidelines are offered for incorporating better cultural responsibility intoex situ conservation strategies. The concept of Biocultural Restoration is introduced with an example from an O'odham community. Examples are given of ways indigenous peoples and their knowledge can assist in the conservation effort. 相似文献
107.
比较研究几种兼性和专一性CAM植物材料的PEPC同工酶表明:经自然干旱诱导,兼性CAM植物露花(Mesembryanthemumcordifolium)、长药景天(Sudumspectabile)有新的PEPC同工酶的出现,诱导前后各同工酶的天然分子量变化不大;而土三七(Sedumaizoon)则没有新的PEPC同工酶出现,但诱导后其同工酶的天然分子量有所增大。以上几种兼性CAM植物的PEPC同工酶酶谱无明显昼夜变化。专一性CAM植物的PEPC酶谱和天然分子量均较一致,亦无昼夜差异。 相似文献
108.
109.
高等植物性别分化研究的某些进展 总被引:9,自引:1,他引:8
高等植物性别分化研究的某些进展邵宏波(四平师范学院生物工程研究室吉林四平136000)关键词高等植物,性别分化,基因表达SOMEADVANCESINTHESEXUALDIFFERENTIATIONRESEARCHOFHIGHERPLANTS¥Shao... 相似文献
110.
长江三峡库区种子植物的中国特有分布 总被引:13,自引:4,他引:9
报道了分布于长江三峡库区的中国种子植物特有属及特有植物在库区的水平与垂直分布概况,对库区的特有分布的特点也进行了简要的分析和探讨。 相似文献