全文获取类型
收费全文 | 129118篇 |
免费 | 7294篇 |
国内免费 | 3909篇 |
出版年
2023年 | 1277篇 |
2022年 | 1471篇 |
2021年 | 2930篇 |
2020年 | 2995篇 |
2019年 | 3798篇 |
2018年 | 3359篇 |
2017年 | 2512篇 |
2016年 | 3047篇 |
2015年 | 4867篇 |
2014年 | 8973篇 |
2013年 | 10267篇 |
2012年 | 6725篇 |
2011年 | 8217篇 |
2010年 | 5858篇 |
2009年 | 6137篇 |
2008年 | 6561篇 |
2007年 | 6742篇 |
2006年 | 5124篇 |
2005年 | 4669篇 |
2004年 | 3670篇 |
2003年 | 3279篇 |
2002年 | 2856篇 |
2001年 | 2062篇 |
2000年 | 1753篇 |
1999年 | 1688篇 |
1998年 | 1531篇 |
1997年 | 1343篇 |
1996年 | 1377篇 |
1995年 | 1596篇 |
1994年 | 1498篇 |
1993年 | 1394篇 |
1992年 | 1284篇 |
1991年 | 1196篇 |
1990年 | 1042篇 |
1989年 | 1021篇 |
1988年 | 948篇 |
1987年 | 915篇 |
1986年 | 698篇 |
1985年 | 1312篇 |
1984年 | 1849篇 |
1983年 | 1322篇 |
1982年 | 1583篇 |
1981年 | 1381篇 |
1980年 | 1136篇 |
1979年 | 1065篇 |
1978年 | 722篇 |
1977年 | 685篇 |
1976年 | 643篇 |
1974年 | 484篇 |
1973年 | 504篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
4.
Insights into the discrepant luminescence for BaSiO3:Eu2+ phosphors prepared by solid‐state reaction and precipitation reaction methods 下载免费PDF全文
Jiao Xu Yang Zhao Jingjing Chen Zhiyong Mao Yanfang Yang Dajian Wang 《Luminescence》2017,32(6):957-963
Two synthesis routes, solid‐state reaction and precipitation reaction, were employed to prepare BaSiO3:Eu2+ phosphors in this study. Discrepancies in the luminescence green emission at 505 nm for the solid‐state reaction method sample and in the yellow emission at 570 nm for the sample prepared by the precipitation reaction method, were observed respectively. A detail investigation about the discrepant luminescence of BaSiO3:Eu2+ phosphors was performed by evaluation of X‐ray diffraction (XRD), photoluminescence (PL)/photoluminescence excitation (PLE), decay time and thermal quenching properties. The results showed that the yellow emission was generated from the BaSiO3:Eu2+ phosphor, while the green emission was ascribed to a small amount of Ba2SiO4:Eu2+ compound that was present in the solid‐state reaction sample. This work clarifies the luminescence properties of Eu2+ ions in BaSiO3 and Ba2SiO4 hosts. 相似文献
5.
Marco Dogs Bernd Wemheuer Laura Wolter Nils Bergen Rolf Daniel Meinhard Simon Thorsten Brinkhoff 《Systematic and applied microbiology》2017,40(6):370-382
Macroalgae harbour specific microbial communities on their surface that have functions related to host health and defence. In this study, the bacterial biofilm of the marine brown alga Fucus spiralis was investigated using 16S rRNA gene amplicon-based analysis and isolation of bacteria. Rhodobacteraceae (Alphaproteobacteria) were the predominant family constituting 23% of the epibacterial community. At the genus level, Sulfitobacter, Loktanella, Octadecabacter and a previously undescribed cluster were most abundant, and together they comprised 89% of the Rhodobacteraceae. Supported by a specific PCR approach, 23 different Rhodobacteraceae-affiliated strains were isolated from the surface of F. spiralis, which belonged to 12 established and three new genera. For seven strains, closely related sequences were detected in the 16S rRNA gene dataset. Growth experiments with substrates known to be produced by Fucus spp. showed that all of them were consumed by at least three strains, and vitamin B12 was produced by 70% of the isolates. Since growth of F. spiralis depends on B12 supplementation, bacteria may provide the alga with this vitamin. Most strains produced siderophores, which can enhance algal growth under iron-deficient conditions. Inhibiting properties against other bacteria were only observed when F. spiralis material was present in the medium. Thus, the physiological properties of the isolates indicated adaption to an epiphytic lifestyle. 相似文献
6.
7.
Ehsan Ullah Mughal Amina Sadiq Shahzad Murtaza Hummera Rafique Muhammad Naveed Zafar Tauqeer Riaz Bilal Ahmad Khan Abdul Hameed Khalid Mohammed Khan 《Bioorganic & medicinal chemistry》2017,25(1):100-106
The present study describes efficient and facile syntheses of varyingly substituted 3-thioaurones from the corresponding 3-oxoaurones using Lawesson’s reagent and phosphorous pentasulfide. In comparison, the latter methodology was proved more convenient, giving higher yields and required short and simple methodology. The structures of synthetic compounds were unambiguously elucidated by IR, MS and NMR spectroscopy. All synthetic compounds were screened for their inhibitory potential against in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. Molecular docking studies were also performed in order to examine their binding interactions with AChE and BChE human proteins. Both studies revealed that some of these compounds were found to be good inhibitors against AChE and BChE. 相似文献
8.
9.
Maria Weinert Tharakeswari Selvakumar Travis S. Tierney Kambiz N. Alavian 《Journal of visualized experiments : JoVE》2015,(96)
Degeneration of mesencephalic dopaminergic (mesDA) neurons is the pathological hallmark of Parkinson’s diseae. Study of the biological processes involved in physiological functions and vulnerability and death of these neurons is imparative to understanding the underlying causes and unraveling the cure for this common neurodegenerative disorder. Primary cultures of mesDA neurons provide a tool for investigation of the molecular, biochemical and electrophysiological properties, in order to understand the development, long-term survival and degeneration of these neurons during the course of disease. Here we present a detailed method for the isolation, culturing and maintenance of midbrain dopaminergic neurons from E12.5 mouse (or E14.5 rat) embryos. Optimized cell culture conditions in this protocol result in presence of axonal and dendritic projections, synaptic connections and other neuronal morphological properties, which make the cultures suitable for study of the physiological, cell biological and molecular characteristics of this neuronal population. 相似文献
10.
Botrytis allii andCollectotrichum dematium are onion pathogens which can infect in the field and cause decay in storage. Some phenolics can hinder development of these fungi, but the effect of cytokinins is not clear. Cytokinins (kinetin or 6-benzyladenine) or phenolics (caffeic or chlorogenic acids) were added to agar at concentrations of 0 to 10–3 M. Cultures were continuously irradiated with fluorescent light or maintained in the dark for 6 days. On unamended media, final mycelial elongation was 45 or 17.8 mm and sporulation was 28 or 10.6 × 104 spores/ml forBotrytis andColletotrichum, respectively. ForBotrytis, mycelial elongation was slightly (5%) but significantly increased and sporulation increased by 21% by incubation on phenolics as compared to cytokinins. Mycelial extension ofColletotrichum was not affected by amendment. Sporulation ofColletotrichum on kinetin was 16 to 28% greater than on the other amendments. As amendments concentration increased elongation of mycelia of both fungi decreased. Sporulation ofBotrytis increased by 60% as amendment concentration increased from 0 to 10–5 M and then decreased 25% at 10–3 M. As amendment concentration increased from 0 to 10–3 M, sporulation ofColletotrichum increased by 45%. Incubation in light increased mycelial extension 3 to 17% forBotrytis andColletotrichum respectively, and sporulation was increased approximately 78% for both fungi. These compounds do not appear to inhibit development of theseBotrytis orColletotrichum species in culture. 相似文献