全文获取类型
收费全文 | 20388篇 |
免费 | 1043篇 |
国内免费 | 1124篇 |
专业分类
林业 | 3160篇 |
农学 | 1844篇 |
基础科学 | 749篇 |
2802篇 | |
综合类 | 8538篇 |
农作物 | 1311篇 |
水产渔业 | 274篇 |
畜牧兽医 | 1268篇 |
园艺 | 778篇 |
植物保护 | 1831篇 |
出版年
2024年 | 97篇 |
2023年 | 327篇 |
2022年 | 550篇 |
2021年 | 628篇 |
2020年 | 640篇 |
2019年 | 741篇 |
2018年 | 522篇 |
2017年 | 778篇 |
2016年 | 936篇 |
2015年 | 709篇 |
2014年 | 957篇 |
2013年 | 1305篇 |
2012年 | 1656篇 |
2011年 | 1394篇 |
2010年 | 1159篇 |
2009年 | 1219篇 |
2008年 | 1107篇 |
2007年 | 1242篇 |
2006年 | 1039篇 |
2005年 | 861篇 |
2004年 | 718篇 |
2003年 | 568篇 |
2002年 | 468篇 |
2001年 | 428篇 |
2000年 | 367篇 |
1999年 | 303篇 |
1998年 | 252篇 |
1997年 | 198篇 |
1996年 | 180篇 |
1995年 | 195篇 |
1994年 | 155篇 |
1993年 | 150篇 |
1992年 | 135篇 |
1991年 | 135篇 |
1990年 | 123篇 |
1989年 | 93篇 |
1988年 | 78篇 |
1987年 | 59篇 |
1986年 | 27篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
981.
本文在综述了植物细胞核雄性不育和细胞质雄性不育优点和缺点基础上提出了植物杂种优势利用的一条新途径——细胞核十细胞质雄性不育,根据细胞核不育基因的显隐性、稳定性和细胞质雄性不育的稳定性不同,可以将该途径进一步分成显性细胞核+细胞质雄性不育、隐性细胞核+细胞质雄性不育、细胞核不育+生态型、细胞质雄性不育和细胞质不育+生态型细胞核雄性不育。 相似文献
982.
钟世理 《西南大学学报(自然科学版)》1987,(4)
四川狗尾草属有10种(包括1个变种),约为我国13种(包括2个变种)的77%。狼尾草属有4种,约为我国9种的44%。本文对两属的分类、分布、生态环境及经济用途等进行了描述。 相似文献
983.
984.
多年生香豌豆在黄土高原地区引种适宜性评价 总被引:6,自引:1,他引:5
多年生香豌豆从美国引种后在黄土高原大部分地区的适应性较强。结合气候相似法、模糊综合评判法以及引种栽培试验,得出多年生香豌豆的适生中心区位于气温适中的黄土高原中部呈西南~东北走向的一个狭长地带,主要包括黄土高原沟壑区、丘陵沟壑区二副区、三副区以及太行山西部山地类型。 相似文献
985.
986.
Thirty-two accessions of wild tomato (Lycopersicon spp.) germplasm were evaluated for resistance to the whiteflyBemisia argentifolii Bellows ⇐p; Perring in a greenhouse choice bioassay. Density data were recorded for the adaxial and abaxial leaf surfaces
for (i) all life stages ofB. argentifolii and (ii) types I, IV, V and VI trichomes. Individual plant selections (33 from 22 wild tomato accessions) with high resistance
were subsequently tested in the field to verify the resistance found in the greenhouse screening. Resistance was defined by
the density of all life stages of the whitefly observed on the eight leaflets sampled at nodes 5 and 7. Only type IV trichomes
had a consistent (but low) and significant negative correlation between trichome density and whitefly density for various
life stages. The highest whitefly resistance was observed inLycopersicon pennellii accessions LA 716, LA 1340 and LA 2560. The most resistantL. hirsutum f.typicum accessions were LA 1777 and LA 1353.
http://www.phytoparasitica.org posting Dec. 9, 2002. 相似文献
987.
Hypericum perforatum L. produces hyperforins, a family of antimicrobial acylphloroglucinols; and hypericins, a family of phototoxic anthraquinones exhibiting anti-microbial, anti-viral, and anti-herbivore properties in vitro. To determine whether these secondary metabolites are part of the specific plant defense systems that are mediated by methyl jasmonate or salicylic acid, we used meristem cultures to assess the effects of exposure to exogenous application of these chemical elicitors. Levels of hypericins in plant tissue increased in response to both elicitor treatments; total hypericin levels increased as much as 3.3 times control levels when treated with 200 μ
methyl jasmonate for 14 days. Increased hyperforin concentrations were detected when plantlets were treated with 1 m
salicylic acid or 50 μ
methyl jasmonate. For assessing responses to a biotic elicitor, greenhouse-grown plant materials were inoculated with the plant pathogen, Colletotrichum gloeosporioides. Levels of hypericins increased twice as much as the control when inoculated with 1 × 104 spores per ml; higher doses of spores overwhelmed the plant defenses. The elevation of hypericins and hyperforin in response to chemical and biotic elicitors suggests that these secondary metabolites are components in the inducible plant defense responses of H. perforatum. 相似文献
988.
989.
在青海湖地区的不同样地上,对甘肃棘豆、宽苞棘豆和黄花棘豆3种棘豆土壤种子库的密度进行了测定,种子密度随着植被中种群分盖度的大小而变化幅度很大,每平方80~2 220粒;同时采用四脞法对土壤种子库中的棘豆种子进行种子活力测定,其中77%的种子具有活力;用尼龙袋法测定甘肃棘豆种子在土壤种子库中的寿命,5年后埋置在土壤环境中的甘肃棘豆种子有50%的还存在,其中5%的种子具有活力;暴露在土壤表面环境中的种子有33%的种子存在;5年期间,埋置的种子和暴露在土壤表面的种子每年分别约有5%和14%的种子在发芽。 相似文献
990.
Hygienic and ecological risks connected with utilization of animal manures and biosolids in agriculture 总被引:2,自引:0,他引:2
In recent years the fate of human and animal pathogen microorganisms as a potential pollutant of the environment has been paid increased attention. Substantial quantities of these compounds and their metabolites are excreted, flushed down the drain, discarded as waste, or left over in animal feedlots. After passing to the sewer, several of these compounds are not adequately eliminated by the methods that are currently used in sewage treatment. Substantial quantities of biosolids and livestock manure end up on agricultural land. Effective sanitation of the environment, particularly of some of its special parts, which can be a source of spreading of diseases, plays an important role in prevention of infectious diseases. In this respect special attention should be paid to the disinfection of infected farm animal excrements. Sanitation of excrements should, on the one hand, ensure effective inhibition of infectious agents and, on the other hand, comply with the requirement of preserving the composition of the manure so it can be used in agricultural production. 相似文献