全文获取类型
收费全文 | 23210篇 |
免费 | 2580篇 |
国内免费 | 6594篇 |
出版年
2024年 | 144篇 |
2023年 | 532篇 |
2022年 | 1017篇 |
2021年 | 1455篇 |
2020年 | 1250篇 |
2019年 | 1388篇 |
2018年 | 1094篇 |
2017年 | 901篇 |
2016年 | 1132篇 |
2015年 | 1692篇 |
2014年 | 2060篇 |
2013年 | 2032篇 |
2012年 | 2593篇 |
2011年 | 2298篇 |
2010年 | 1597篇 |
2009年 | 1541篇 |
2008年 | 1641篇 |
2007年 | 1423篇 |
2006年 | 1254篇 |
2005年 | 1063篇 |
2004年 | 830篇 |
2003年 | 728篇 |
2002年 | 546篇 |
2001年 | 424篇 |
2000年 | 386篇 |
1999年 | 310篇 |
1998年 | 173篇 |
1997年 | 131篇 |
1996年 | 100篇 |
1995年 | 105篇 |
1994年 | 61篇 |
1993年 | 47篇 |
1992年 | 50篇 |
1991年 | 55篇 |
1990年 | 41篇 |
1989年 | 51篇 |
1988年 | 21篇 |
1987年 | 24篇 |
1986年 | 27篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 21篇 |
1982年 | 31篇 |
1981年 | 9篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1965年 | 6篇 |
1964年 | 5篇 |
1953年 | 5篇 |
1950年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
881.
Kai‐Qing Lu Min Li Guo‐Hong Wang Lian‐Sheng Xu David K. Ferguson Anjali Trivedi Jing Xuan Ying Feng Jin‐Feng Li Gan Xie Yi‐Feng Yao Yu‐Fei Wang 《植物分类学报:英文版》2019,57(2):190-199
Members of the Chenopodiaceae are the most dominant elements in the central Asian desert. The different genera and species within this family are common in desert vegetation types. Should it prove possible to link pollen types in this family to specific desert vegetation, it would be feasible to trace vegetation successions in the geological past. Nevertheless, the morphological similarity of pollen grains in the Chenopodiaceae rarely permits identification at the generic level. Although some pollen classifications of Chenopodiaceae have been proposed, none of them tried to link pollen types to specific desert vegetation types in order to explore their ecological significance. Based on the pollen morphological characters of 13 genera and 24 species within the Chenopodiaceae of eastern central Asia, we provide a new pollen classification of this family with six pollen types and link them to those plant communities dominated by Chenopodiaceae, for example, temperate dwarf semi‐arboreal desert (Haloxylon type), temperate succulent halophytic dwarf semi‐shrubby desert (Suaeda, Kalidium, and Atriplex types), temperate annual graminoid desert (Kalidium type), temperate semi‐shrubby and dwarf semi‐shrubby desert (Kalidium, Iljini, and Haloxylon types), and alpine cushion dwarf semi‐shrubby desert (Krascheninnikovia type). These findings represent a new approach for detecting specific desert vegetation types and deciphering ecosystem evolution in eastern central Asia. 相似文献
882.
ZHILONG MA GUODONG SONG DONGBO ZHAO DALU LIU XIAOLEI LIU YUXIANG DAI ZHIGANG HE DAOHAI QIAN JIAN GONG HONGBO MENG BO ZHOU TINGSONG YANG ZHENSHUN SONG 《Cytotherapy》2019,21(2):162-174
Background and aims
It has been previously verified that mesenchymal stromal cells (MSCs) have a good therapeutic effect on severe acute pancreatitis (SAP) and the potential for regeneration of damaged pancreatic tissue, but the exact molecular mechanism remains unclear. In this study, we demonstrated the therapeutic effect of bone morrow MSCs (BMSCs) on SAP, probably by targeting heme oxygenase-1 (HO-1).Methods
Six hours after SAP induction, either phosphate-buffered saline (PBS) or BMSCs were transfused into the caudal vein of rats, zinc protoporphyrin (ZnPP) was administered intraperitoneally. Pancreatic pathological scoring, serum levels of amylase and inflammatory factors, as well as levels of reactive oxygen species (ROS), malondialdehyde (MDA) and myeloperoxidase (MPO), superoxide dismutase (SOD) and catalase (CAT) activity in the pancreas were evaluated.Results
Our data showed that BMSCs significantly reduce inflammation and oxidative stress, reduce apoptosis and promote angiogenesis of damaged pancreas. Moreover, BMSCs increased the level of HO-1 in the serum and pancreatic tissue in rats with SAP. In addition, the protective effect of BMSCs was partially neutralized by the HO-1 activity inhibitor ZnPP, suggesting a key role of HO-1 in the therapeutic effect of BMSCs on SAP.Conclusions
BMSCs ameliorated SAP, probably by inducing expression of HO-1, which can exert anti-inflammatory and anti-oxidant effects, reduce apoptosis and promote angiogenesis. 相似文献883.
Yong‐Bo Hu Ru‐Jing Ren Yong‐Fang Zhang Yue Huang Hai‐Lun Cui Chao Ma Wen‐Ying Qiu Hao Wang Pei‐Jing Cui Hong‐Zhuan Chen Gang Wang 《Aging cell》2019,18(5)
Rho‐associated coiled‐coil kinase 1 (ROCK1) is proposed to be implicated in Aβ suppression; however, the role for ROCK1 in amyloidogenic metabolism of amyloid precursor protein (APP) to produce Aβ was unknown. In the present study, we showed that ROCK1 kinase activity and its APP binding were enhanced in AD brain, resulting in increased β‐secretase cleavage of APP. Furthermore, we firstly confirmed that APP served as a substrate for ROCK1 and its major phosphorylation site was located at Ser655. The increased level of APP Ser655 phosphorylation was observed in the brain of APP/PS1 mice and AD patients compared to controls. Moreover, blockade of APP Ser655 phosphorylation, or inhibition of ROCK1 activity with either shRNA knockdown or Y‐27632, ameliorated amyloid pathology and improved learning and memory in APP/PS1 mice. These findings suggest that activated ROCK1 targets APP Ser655 phosphorylation, which promotes amyloid processing and pathology. Inhibition of ROCK1 could be a potential therapeutic approach for AD. 相似文献
884.
The residues of phenothiazines and benzodiazepines in foods of animal origin are dangerous to consumers. For inspection of their abuses, this study for the first time reported on the use of a chemiluminescence array sensor for the simultaneous determination of four phenothiazines and five benzodiazepines in pig urine. Two molecularly imprinted polymers were coated in different wells of a conventional 96‐well microtiter plate as the recognition reagents. After sample loading, the absorbed analytes were initiated directly by using an imidazole enhanced bis(2,4,6‐trichlorophenyl)oxalate–hydrogen peroxide system to emit light. The assay process consisted of only one sample‐loading step prior to data acquisition, so one test was finished within 10 min. The limits of detection for the nine drugs in the pig urine were in a range of 0.1 to 0.6 pg/mL, and the recoveries from the fortified blank urine samples were in a range of 80.3 to 95%. Furthermore, the sensor could be reused six times. Therefore, this sensor could be used as a simple, rapid, sensitive and reusable tool for routine screening for residues of phenothiazines and benzodiazepines in pig urine. 相似文献
885.
Jing Wang Fengjuan Song Yongling Ai Shanwen Hu Zhizhou Huang Wenying Zhong 《Luminescence》2019,34(2):205-211
In this study, we developed a novel simple fluorescence resonance‐energy transfer (FRET) system between two‐color CdTe quantum dots (QDs) assisted by cetyltrimethylammonium bromide (CTAB). Mercaptopropionic (MPA)‐capped CdTe QDs serving as both donors and acceptors were successfully synthesized by changing the refluxing time in aqueous solution. CTAB micelles formed in water and minimized the distance between the donors and acceptors significantly by electrostatic interactions, improving FRET efficiency. Several factors that affected the fluorescence spectra of the FRET system were investigated. The prepared FRET system was feasible as an effective fluorescent probe to detect Hg(II) in aqueous solution. At pH 7.0, a linear relationship between the quenched fluorescence intensity of orange‐emitting acceptors (QDs(A)) and Hg(II) concentration was acquired in the range 5–250 nmol/L with a detection limit of 1.95 nmol/L. The developed method showed excellent analytical performance for Hg(II) with high sensitivity and acceptable selectivity, reproducibility and stability. This finding indicated that the method has a promising potential application for environmental monitoring. This study demonstrated the great promise of QDs for expedient, low‐cost and high‐sensitivity detection of Hg(II). 相似文献
886.
887.
Hanyu Huo Yue Chen Jing Luo Xiaofei Yang Xiangxin Guo Xueliang Sun 《Liver Transplantation》2019,9(17)
Solid polymer electrolytes as one of the promising solid‐state electrolytes have received extensive attention due to their excellent flexibility. However, the issues of lithium (Li) dendrite growth still hinder their practical applications in solid‐state batteries (SSBs). Herein, composite electrolytes from “ceramic‐in‐polymer” (CIP) to “polymer‐in‐ceramic” (PIC) with different sizes of garnet particles are investigated for their effectiveness in dendrite suppression. While the CIP electrolyte with 20 vol% 200 nm Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particles (CIP‐200 nm) exhibits the highest ionic conductivity of 1.6 × 10?4 S cm?1 at 30 °C and excellent flexibility, the PIC electrolyte with 80 vol% 5 µm LLZTO (PIC‐5 µm) shows the highest tensile strength of 12.7 MPa. A sandwich‐type composite electrolyte (SCE) with hierarchical garnet particles (a PIC‐5 µm interlayer sandwiched between two CIP‐200 nm thin layers) is constructed to simultaneously achieve dendrite suppression and excellent interfacial contact with Li metal. The SCE enables highly stable Li plating/stripping cycling for over 400 h at 0.2 mA cm?2 at 30 °C. The LiFePO4/SCE/Li cells also demonstrate excellent cycle performance at room temperature. Fabricating sandwich‐type composite electrolytes with hierarchical filler designs can be an effective strategy to achieve dendrite‐free SSBs with high performance and high safety at room temperature. 相似文献
888.
Wei Wang Kun Lv Ji‐Rui Wang Jing Zhou Jian‐Qiang Gu Guo‐Xin Zhou Zhi‐Hong Xu 《Entomological Research》2019,49(3):113-122
In the present study, partial sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene of 22 island populations of the springtail Homidia socia in the Thousand Island Lake were sequenced. Across all sequences, 37 haplotypes were identified for the 510‐bp mitochondrial (mt) DNA COI gene. Haplotype 2 was the most common, and was distributed in the most of the 22 island populations. Haplotype diversity ranged from 0.065 to 0.733, and the total genetic diversity was 0.56216. The genetic characteristics of the 22 island populations were analyzed using the fixation index and gene flow, with values of 0.00043–0.94900 and 0.02703–703.72540, respectively. Comparison between (island area and isolations) with population genetic diversity revealed that there were no significant correlations between them, except for a significant correlation between the number of haplotypes and island area. Mantel tests showed that there was no significant correlation between geographic distance and genetic distance among various groups. All the results indicated that there were no obvious relationships between island characteristics and the genetic diversity of the springtails. We consider that the low dispersal capacity of springtails and the island patches surrounded by water in the Thousand Island Lake are the major factors affecting the genetic diversity of H. socia. 相似文献
889.