全文获取类型
收费全文 | 42917篇 |
免费 | 1976篇 |
国内免费 | 4168篇 |
专业分类
林业 | 3635篇 |
农学 | 4639篇 |
基础科学 | 3225篇 |
5463篇 | |
综合类 | 19346篇 |
农作物 | 2559篇 |
水产渔业 | 1676篇 |
畜牧兽医 | 4774篇 |
园艺 | 1372篇 |
植物保护 | 2372篇 |
出版年
2024年 | 316篇 |
2023年 | 783篇 |
2022年 | 1441篇 |
2021年 | 1560篇 |
2020年 | 1577篇 |
2019年 | 1844篇 |
2018年 | 1196篇 |
2017年 | 1957篇 |
2016年 | 2242篇 |
2015年 | 2069篇 |
2014年 | 2488篇 |
2013年 | 2555篇 |
2012年 | 3686篇 |
2011年 | 3554篇 |
2010年 | 2825篇 |
2009年 | 2600篇 |
2008年 | 2270篇 |
2007年 | 2486篇 |
2006年 | 2067篇 |
2005年 | 1613篇 |
2004年 | 1188篇 |
2003年 | 903篇 |
2002年 | 714篇 |
2001年 | 596篇 |
2000年 | 543篇 |
1999年 | 548篇 |
1998年 | 467篇 |
1997年 | 414篇 |
1996年 | 347篇 |
1995年 | 371篇 |
1994年 | 293篇 |
1993年 | 262篇 |
1992年 | 274篇 |
1991年 | 235篇 |
1990年 | 213篇 |
1989年 | 202篇 |
1988年 | 141篇 |
1987年 | 84篇 |
1986年 | 46篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1962年 | 9篇 |
1956年 | 5篇 |
1955年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A. Sambade L. Rubio S. M. Garnsey N. Costa G. W. Müller M. Peyrou J. Guerri P. Moreno † 《Plant pathology》2002,51(3):257-265
The population of sequence variants of Citrus tristeza virus (CTV) isolates of different geographic origins and pathogenicity properties was characterized by single-strand conformation polymorphism (SSCP) analysis of cDNA of the genes p18, p13, p20 and p23. The mild isolates analysed here usually yielded a SSCP profile with two DNA bands, suggestive of a predominant sequence variant, whereas the SSCP profile of the most virulent isolates contained more than two DNA bands, indicating that their viral populations are likely to be more complex. The set of SSCP profiles of the four genes allowed identification of individual isolates, but no profile characteristic of a geographic area or a biogroup was found. Sweet orange plants singly inoculated with a mild or with a severe isolate yielded the SSCP profile characteristic of each isolate, whereas the SSCP profile of plants successively inoculated with both isolates was a composite of the two individual profiles. The SSCP profile of plants singly inoculated remained constant, but the profile of doubly inoculated plants varied with time. Plants in which the SSCP profile of the severe isolate became predominant showed stem pitting, and those in which the predominant profile corresponded to the mild isolate remained symptomless. The results indicate that SSCP analysis can be used to study changes in RNA populations of doubly inoculated plants and to monitor cross-protection between mild and severe isolates. 相似文献
102.
103.
城市绿地系统对经济发展提升作用的机制——与大连市实证研究 总被引:6,自引:2,他引:6
城市绿地系统具有生态、经济、社会等多重属性 ,在城市复合系统中占有特殊的位置 ,对城市经济发展亦具有直接、间接的提升作用 :( 1 )改善城市环境质量 ,创造环境优势 ,促进城市地价及布局其间的各种经济成分增值 ;集聚外来资金和高新产业发展 ,带动整个城市产业结构优化升级。( 2 )绿地建设作为城市经济产业的有机组成部分 ,形成环境经济产业链 ,拉动其相关经济产业的发展 ,促进经济增长。 ( 3 )提高城市知名度 ,促进城市旅游业发展 ,集聚高素质人才 ,促进城市经济发展 ,本文以北方海滨城市大连为例 ,在定性分析绿地经济提升作用机制的基础上 ,建立计量经济模型 ,定量分析城市绿地系统的经济提升作用 相似文献
104.
苯磺隆·甲磺隆·氯磺隆混合物的液相色谱分析 总被引:2,自引:0,他引:2
本文以甲醇 水 冰乙酸为流动相,采用C18不锈钢柱,检测波长240nm,对苯磺隆、甲磺隆、氯磺隆混合物进行反相高效液相色谱定量分析。该方法的标准差别分别为0.081、0.013和0.013,变异系数为0.886%、0.268%和0.256%,回收率为99.39%、99.29%和99.28%,线性相关系数为苯磺隆r=0.9994、甲磺隆r=0.9992、氯磺隆r=0.9991,线性方程为苯磺隆y=1360088.17x 1389384、甲磺隆y=972186.69X-21262.8、氯磺隆y=789773.50X 86258.8。 相似文献
105.
双孢蘑菇性亲和性相关分子标记的初步筛选 总被引:4,自引:0,他引:4
以传统的形态,生理生化分析和最新的DCS-PDMA性亲和性测定方法为基础, 结合群体分离分析和RAPD技术来源于同一双孢蘑菇异核体菌株的12个不育同核原生质体个体进行分析,筛选与性亲和性相关的分子标记。研究结果表明,供试的12个不育同核原生质体个体被分成两大类性亲和性类型,其中一类(A^ )包括不育同核原生质体个体B、C、D、E、F、G、H、I、J、L,另一类(A^-)则仅仅包括不育同核原生质体个体K和M,同时筛选到一个与性亲和性相关的分子标记OPA16 1500。从而为间地利用双孢蘑菇本身特有的交配型作标记来指导杂交育种工作和进一步将性亲和性基因定位分离克隆奠定了坚实的基础。 相似文献
106.
月季切花乙烯受体ETR1 cDNA克隆及其序列分析* 总被引:6,自引:0,他引:6
根据乙烯受体基因ETR1 保守区设计引物, 分别以瓶插寿命差异显著的月季切花品种‘德克萨斯’和‘维亚蒂’为材料, 通过RT-PCR 从花瓣中扩增出了797 bp 的cDNA 片段, 它编码265 个氨基酸。测序和序列分析表明,‘德克萨斯’重组质粒中插入片段的核苷酸序列之间完全相同, 命名为pRT-ETR1。而‘维亚蒂’所获得的重组质粒中插入片段的核苷酸和氨基酸序列之间存在差异, 同源性分别为85. 2 %和92. 1 % , 分别命名为pRV-ETR1-V4 和pRV-ETR1-V5。pRV2 ETR12V5 的核苷酸和氨基酸序列与‘德克萨斯’pRT2 ETR1 的同源性均达99 %以上; pRV-ETR1-V4 中的核苷酸和氨基酸序列与‘德克萨斯’pRT-ETR1 的同源性分别为85. 0 %和92. 5 %。上述插入片段与桃、苹果、天竺葵、拟南芥等植物的ETR1相应区域高度同源, 其氨基酸同源性均大于90 %。 相似文献
107.
Henk-jan Schoonbeek Johannes G.M. van Nistelrooy Maarten A. de Waard 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(9):1003-1011
The role of multiple ATP-binding cassette (ABC) and major facilitator superfamily (MFS) transporter genes from the plant pathogenic fungus Botrytis cinerea in protection against natural fungitoxic compounds was studied by expression analysis and phenotyping of gene-replacement mutants. The expression of 11 ABC (BcatrA–BcatrK) and three MFS genes (Bcmfs1, Bcmfs2 and Bcmfs4) was studied. All genes showed a low basal level of expression, but were differentially induced by treatment with cycloheximide and the plant defence compounds camptothecin, eugenol, psoralen, resveratrol and rishitin. The latter compounds induced expression of BcatrB at a high level. Eugenol was more toxic to BcatrB gene-replacement mutants than to the control isolates. Eugenol also caused an instantaneous increase in mycelial accumulation of the fungicide fludioxonil, a known substrate of BcatrB. However, there was no difference in virulence between the wild-type and BcatrB gene-replacement mutants on Ocimum basilicum, a plant known to contain eugenol. The results indicate that BcatrB is a transporter of lipophilic compounds, such as eugenol, but its role in virulence remains uncertain. 相似文献
108.
109.
TATSUYA INAMURA 《Weed Biology and Management》2003,3(1):1-7
The loss of final tuber weight of Eleocharis kuroguwai Ohwi by shading during the early tuber formation period (TFP) is overcome by exposure to unshaded daylight thereafter (late TFP). In the present study, the growth parameters that contribute to the dry matter increase (DMI) per day of tubers in the late TFP were examined. DMI of the tuber during the late TFP was determined by that of the whole plant and the ratio of the DMI of the tuber to that of the whole plant during this period. The ratio of the DMI of the tuber to that of the whole plant during the late TFP was significantly correlated with the DMI of the whole plant during the first 14 days of the late TFP. During the late TFP after the exposure to unshaded daylight, DMI of the whole plant correlated with the surface area of the stem (SAS) and net assimilation ratio (NAR), and the SAS correlated with the stem dry weight (DW) and specific stem-surface area (SSA). SSA negatively influenced NAR, but NAR was increased by unshading. During the late TFP after shading, the effect of the decrease of the stem DW due to shading on the DMI of the whole plant was mitigated by the large SAS and high NAR. These results indicate that the growth parameters that contribute to the DMI of tuber during the late TFP after exposure to unshaded daylight are SAS and NAR just after unshading, and SSA during this period. 相似文献
110.
棉花黄萎病菌致病型的AFLP分析 总被引:16,自引:0,他引:16
选用41个棉花黄萎病菌(Verticillium dahliae)代表菌系,在温室条件下,对4个棉花品种鄂荆1号(感)、中棉所12(耐)、文-5(抗)和唐棉2号(抗)进行致病性测定,结果可将供试菌系分为落叶型与非落叶型2类。选取8对AFLP引物PCR扩增的结果中,统计带型稳定、清晰且有多态性的条带,共169条作系统聚类分析,将上述菌系分为2大类,第一类为非落叶型菌系,包括10个非落叶型菌系和1个过渡菌系;第二类为30个落叶型菌系。根据聚类分析建立树状图,发现菌系与地理来源存在一定的相关性,而依据菌系致病力强弱分类则相关关系不大。选用25对EcoRⅠ和MseⅠ引物组合,对供试的41个V.dahliae进行AFLP扩增,筛选到2对引物E64(GACTGCGTACCAATTCGAC)、M53(GATGAGTCCTGAGTAACCG)和E49(GACTGCGTACCAATTCCAG)、M65(GAT-GAGTCCTGAGTAAGAG),能分别扩增出433bp和110bp2条仅为V.dahliae非落叶型菌系独有的特异片段,可将落叶型与非落叶型菌系分开,这2条特异片段被命名为EM433和EM110。 相似文献