全文获取类型
收费全文 | 15332篇 |
免费 | 3091篇 |
国内免费 | 474篇 |
专业分类
林业 | 940篇 |
农学 | 1449篇 |
基础科学 | 170篇 |
830篇 | |
综合类 | 5739篇 |
农作物 | 1250篇 |
水产渔业 | 702篇 |
畜牧兽医 | 4273篇 |
园艺 | 2693篇 |
植物保护 | 851篇 |
出版年
2025年 | 267篇 |
2024年 | 279篇 |
2023年 | 343篇 |
2022年 | 534篇 |
2021年 | 660篇 |
2020年 | 685篇 |
2019年 | 810篇 |
2018年 | 613篇 |
2017年 | 756篇 |
2016年 | 996篇 |
2015年 | 928篇 |
2014年 | 959篇 |
2013年 | 935篇 |
2012年 | 1198篇 |
2011年 | 1302篇 |
2010年 | 1039篇 |
2009年 | 1006篇 |
2008年 | 923篇 |
2007年 | 996篇 |
2006年 | 749篇 |
2005年 | 635篇 |
2004年 | 444篇 |
2003年 | 359篇 |
2002年 | 238篇 |
2001年 | 207篇 |
2000年 | 198篇 |
1999年 | 143篇 |
1998年 | 110篇 |
1997年 | 93篇 |
1996年 | 83篇 |
1995年 | 52篇 |
1994年 | 51篇 |
1993年 | 54篇 |
1992年 | 31篇 |
1991年 | 27篇 |
1990年 | 19篇 |
1989年 | 26篇 |
1988年 | 22篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 17篇 |
1980年 | 7篇 |
1976年 | 4篇 |
1962年 | 6篇 |
1956年 | 14篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
《Plant Production Science》2013,16(3):203-210
SummaryGenerally F1 hybrids from crosses between japonica and indica rice show variable degrees of sterility. Previous studies revealed that among the indica rice, the Aus type has sexual affinity with japonica cultivars giving higher fertility in F1 hybrids. Therefore, we made an effort to obtain higher grain yield by producing F1 hybrids between japonica and Aus-type indica. A field experiment was conducted to investigate the heterosis in these F1 hybrids for dry matter accumulation, spikelet fertility, yield and yield attributes, to find cross combinations with higher grain yield, and examined the relationships of grain yield with some agronomic characters. F1 hybrids flowered earlier than their parent cultivars. Heterosis for dry matter accumulation was positive at the panicle initiation stage, at heading and at maturity. The average heterosis for number of panicles, grain and straw yield per plant, number of spikelets per panicle and 1000-grain weight was positive. A few F1 hybrids showed positive heterosis for number of filled grains per panicle, spikelet fertility and harvest index; but the average heterosis for these traits was negative. Among the yield components, a higher number of panicles per plant and higher number of spikelet per panicle contributed to higher grain yield in F1 hybrids. A significant and positive relationship existed between spikelet fertility and grain yield per plant. The higher grain yield was attributed to higher dry matter production rather than higher harvest index in F1 hybrids, although low spikelet fertility limited yield potential in some F1 hybrids. 相似文献
22.
植物磷脂酶PLDα1与伤害信号转导密切相关,是伤害诱导内源茉莉酸(Jasmonic acid, JA)生物合成的关键酶之一。橡胶树胶乳PLDα1基因(HbPLDα1)表达的研究将有助于揭示橡胶树乳管细胞JA信号转导及其调控橡胶生物合成的机制。在EST序列的基础上,通过RACE和Genome Walking方法分别克隆了橡胶树胶乳的HbPLDα1基因及其启动子序列。HbPLDα1基因的cDNA全长为2 870 bp,包含长度为2 427 bp的完整开放阅读框(ORF),具有典型的植物PLDα蛋白保守功能域,与同属大戟科的蓖麻和麻风树的PLDα1基因亲缘关系最近。HbPLDα1基因启动子区域长为1 559 bp,除含有TATA box和CAAT box等基本顺式作用元件外,还存在JA和脱落酸等激素响应元件以及干旱胁迫等环境信号响应元件,这表明HbPLDα1基因的表达可能受激素和环境信号的调控,在橡胶树乳管细胞对激素和环境信号的响应过程中发挥重要作用。 相似文献
23.
This study sought to investigate the possible inhibition mechanism of red rice polyphenols (RRP) on pancreatic α-amylase (PA) activity. RRP showed strong inhibition against PA activity and the half-inhibitory concentration (IC50) value was 3.61 μg/mL. The fluorescence quenching of PA by RRP was a combination of static quenching and dynamic quenching. RRP could aggregate with PA and the physiochemical properties of the aggregates were closely related to the concentration of RRP. Kinetic analysis suggested that the inhibition mode of RRP on PA was reversible inhibition, which was a mixing of competitive inhibition and noncompetitive inhibition. Molecular docking speculated that RRP could form hydrogen bonds with PA by binding to the catalytic active sites (ASP197, GLU233 and ASP300) and the microenvironments of TRP58 and TRP59 were altered, thus inhibiting PA activity. 相似文献
24.
The objective of this study was to characterize the flavonoid compounds found in the different grain parts of common and tartary buckwheat, and to determine the contribution of these flavonoids to the antioxidant properties of buckwheat. Eight flavonoid compounds were quantified and their antioxidant activity determined by FRAP, DPPH, and ABTS assays. Of the flavonoid compounds identified rutin was the most abundant, particularly in tartary buckwheat, in which it comprised approximately 90% of total flavonoid content. Flavan-3-ols were detected in common but not tartary buckwheat, and quercetin was detected only in tartary buckwheat. Flavonoid content—in particular, levels of rutin, orientin, and/or epicatechin gallate—was found to influence the total antioxidant activity of buckwheat. Results from this study indicate that antioxidant activity is not only closely associated with flavonoid content, but that different flavonoids contribute differently to the total antioxidant activity of common and tartary buckwheat. 相似文献
25.
Karim Hosni Kamel Msada Mouna Ben Tarit Olfa Ouchikh Monem Kallel Brahim Marzouk 《Industrial Crops and Products》2008,27(3):308-314
The essential oils obtained by hydrodistillation from the aerial parts of Tunisian native Hypericum perfoliatum L. (sect. Drosocarpium Spach.) and Hypericum tomentosum (sect. Adenosepalum Spach.) were analyzed by GC and GC–MS. Thirty-two compounds were identified in the essential oils of H. perfoliatum with α-pinene (13.1%), allo-aromadendrene (11.4%), germacrene-D (10.6%), n-octane (7.3%), α-selinene (6.5%) and β-selinene (5.5%) as main constituents. Sixty-seven components were identified in the oil of H. tomentosum with menthone (17.0%), n-octane (9.9%), β-caryophyllene (5.3%), α-pinene (5.2%), lauric acid (4.1%) and β-pinene (3.7%) as the most abundant components. Both oils were characterized by the presence of many components which could have numerous applications in food, pharmaceutical and perfume industries. 相似文献
26.
This study aimed to investigate the application of microbubble technology for delaying banana ripening. A preparation of 1-MCP designed for use as a form of aqueous micro bubble (MBs) solutions was formulated. Banana fruit were immersed in 500 nL L−1 of aqueous 1-MCP microbubbles (1-MCP-MBs) or fumigated with 500 nL L−1 1-MCP, then stored at 25 °C for 8 days. 1-MCP-MBs were more effective in delaying postharvest ripening than conventional 1-MCP fumigation. 1-MCP-MBs reduced the respiration rate and ethylene production compared to the control and 1-MCP fumigated fruit. Moreover, 1-MCP-MBs delayed yellowing and maintained firmness of banana fruit during storage. These results indicate that 1-MCP-MBs can be used as an alternative method for delaying the postharvest ripening of banana fruit, and its application for other commodities needs to be further elucidated. 相似文献
27.
28.
Three abortigenic Indian isolates of equine herpesvirus-1 (EHV-1) (Tohana, Hisar and Bikaner), along with two exotic abortigenic
isolates (AB4 and V592) and another EHV-1 isolate (Jind) obtained from a case of perinatal foal mortality, were studied for
variability. For this purpose, PCR and restriction endonuclease (RE) digestion techniques were used simultaneously as a DNA
fingerprinting system. Nine different regions of EHV-1 virus were amplified by PCR using primer pairs specific for the regions
and the products obtained from these regions were subsequently subjected to various restriction endonucleases to further assess
the variability in the number of RE sites as well as in their positions. No difference was observed in all the four abortigenic
isolates in terms of the size of different PCR products amplified by all the nine primer pairs, except for primer pairs ‘E’
and ‘C’. PCR products obtained with primer pair E revealed that Tohana and Bikaner isolates were most similar while Hisar
isolate was like V592 isolate. However, the PCR product obtained from Jind isolate had a size between the PCR products of
Hisar and Tohan/Bikaner isolates. The primer pair ‘C’ used to amplify the region between 1151 to 3679 in ‘Gene 1,2,3’ clearly
differentiated the EHV-1 isolate obtained from a case of perinatal foal mortality from isolates obtained from abortion cases.
This primer pair needs to be exploited more extensively for use as a potential marker for differentiating the EHV-1 isolates,
mainly the abortion cases from perinatal foal mortality ones. Restriction endonuclease studies done with PCR product of all
the isolates with various primer pairs did not reveal any changes in the position or number of RE sites present in the products
amplified, indicating no variation in different RE sites within the amplified PCR products. However, this study clarified
that all the Indian isolates belonged to the IP group of EHV-1. 相似文献
29.
30.
为研究显花植物自交不亲和的分子机理,以无籽沙糖橘为试材,克隆无籽沙糖橘花粉S1基因的cDNA和DNA全长序列,命名为CrS1-1,该基因cDNA和DNA全长均为450 bp。半定量PCR分析结果表明,该基因在花粉中特异表达。Real-time PCR分析表明,该基因在无籽沙糖橘自花授粉72h表达量达到最大,而无籽沙糖橘×有籽沙糖橘异花授粉72 h的表达量最低。 相似文献