全文获取类型
收费全文 | 494篇 |
免费 | 35篇 |
国内免费 | 43篇 |
出版年
2023年 | 9篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 16篇 |
2019年 | 17篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 17篇 |
2014年 | 13篇 |
2013年 | 27篇 |
2012年 | 25篇 |
2011年 | 22篇 |
2010年 | 20篇 |
2009年 | 29篇 |
2008年 | 23篇 |
2007年 | 25篇 |
2006年 | 24篇 |
2005年 | 30篇 |
2004年 | 17篇 |
2003年 | 34篇 |
2002年 | 14篇 |
2001年 | 4篇 |
2000年 | 13篇 |
1999年 | 15篇 |
1998年 | 12篇 |
1997年 | 16篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 20篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1974年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有572条查询结果,搜索用时 187 毫秒
41.
42.
Triterpenoids and Flavonoids from the Leaves of Astragalus membranaceus and Their Inhibitory Effects on Nitric Oxide Production 下载免费PDF全文
Zhi‐Bin Wang Ya‐Dong Zhai Zhen‐Ping Ma Chun‐Juan Yang Rong Pan Jia‐Li Yu Qiu‐Hong Wang Bing‐You Yang Hai‐Xue Kuang 《化学与生物多样性》2015,12(10):1575-1584
Four new cycloartane triterpenes, named huangqiyegenins V and VI and huangqiyenins K and L ( 1 – 4 , resp.), together with nine known triterpenoids, 5 – 13 , and eight flavonoids, 14 – 21 , were isolated from a 70%‐EtOH extract of Astragalus membranaceus leaves. The structures of the new compounds were elucidated by detailed spectroscopic analyses, and the compounds were identified as (9β,11α,16β,20R,24S)‐11,16,25‐trihydroxy‐20,24‐epoxy‐9,19‐cyclolanostane‐3,6‐dione ( 1 ), (9β,16β,24S)‐16,24,25‐trihydroxy‐9,19‐cyclolanostane‐3,6‐dione ( 2 ), (3β,6α,9β,16β,20R,24R)‐16,25‐dihydroxy‐3‐(β‐D ‐xylopyranosyloxy)‐20,24‐epoxy‐9,19‐cyclolanostan‐6‐yl acetate ( 3 ), and (3β,6α,9β,16β,24E)‐26‐(β‐D ‐glucopyranosyloxy)‐16‐hydroxy‐3‐(β‐D ‐xylopyranosyloxy)‐9,19‐cyclolanost‐24‐en‐6‐yl acetate ( 4 ). All isolated compounds were evaluated for their inhibitory activities against LPS‐induced NO production in RAW264.7 macrophage cells. Compounds 1 – 3, 14, 15 , and 18 exhibited strong inhibition on LPS‐induced NO release by macrophages with IC50 values of 14.4–27.1 μM . 相似文献
43.
Enhancement of the innate immune response of bladder epithelial cells by Astragalus polysaccharides through upregulation of TLR4 expression 总被引:1,自引:0,他引:1
Xiaolin Yin Lei Chen Jianling Yang Zhiyan Yao Lin Wei Mingyuan Li 《Biochemical and biophysical research communications》2010,397(2):232-238
The innate host defenses at mucosal surfaces are critical in the early stages of urinary tract bacterial infection. Recent studies have shown that uroepithelial cells aid innate immune cells in fighting off infection, although the exact mechanism by which the uroepithilium participates in immunity remains unclear. TLR4 has been implicated to possess antimicrobial activities specific for bladder epithelial cells (BECs). TLR4 promotes secretion of IL-6 and IL-8, mediates inhibition of bladder epithelial cell (BEC) bacterial invasion, and mediates expulsion of uropathogenic Escherichia coli from BECs. In this study, cultured 5637 cells and Balb/C mice were treated with Astragalus polysaccharides (APS) against invading E. coli. To determine the contribution of TLR4 upregulation to immune response, TLR4 expression and bacterial colony numbers were monitored. After 24 h incubation, only 5637 cells treated with 500 μg/ml APS expressed higher levels of TLR4 compared with the untreated group. However, after 48 h, all 5637 cells treated by APS showed higher levels of TLR4 expression than the control cells. The TLR4 expression in the bladder and macrophages mice that received APS was higher than that in the controls. Bacterial colonization in 5637 cells and the bladders of mice treated with APS was significantly reduced compared with the controls. These results demonstrate that at certain concentrations, APS can induce increased TLR4 expression in vivo and in vitro. Further, TLR4 expression upregulation can enhance innate immunity during mucosal bacterial infection. The findings establish the use of APS to modulate the innate immune response of the urinary tract through TLR4 expression regulation as an alternative option for UTI treatment. 相似文献
44.
Mesorhizobium huakuii strain 7653R harbored two indigenous plasmids named pMH7653Ra and pMH7653Rb. The larger plasmid pMH7653Rb (symbiotic plasmid)
was transferred to M. huakuii HN308SR harboring three plasmids: pMHHN308a, pMHHN308b and pMHHN308c, and HN3015SR harboring three plasmids: pMHHN3015a,
pMHHN3015b and pMHHN3015c by tri-parent mating. Two stable indigenous plasmids, pMHHN308b and pMHHN308c of HN308SR, were co-eliminated
due to the introduction of pMH7653Rb, and the transconjugant was named HN308SRN14. The results implied that pMH7653Rb and
pMHHN308b, pMHHN308c were incompatible and might have been ascribed to the same incompatible group. The plasmid profiles of
transconjugant HN3015SRN14 showed that the second largest plasmid pMHHN3015b of HN3015SR was cured due to the introduction
of pMH7653Rb. The results also implied that pMH7653Rb and pMHHN3015b were incompatible. Results from plant nodulation tests
showed that pMH7653Rb could only maintain the nodulation ability in transconjugant HN308SRN14 and its nodule number was more
than that of wild strain HN308SR, but could not replace the nitrogen fixation effect of pMHHN308b and pMHHN308c. The plasmid
cured mutant HN308SRN14D harboring only pMHHN308a formed null nodules that demonstrated pMHHN308a was relevant to nodulation
ability. HN3015SRN14 harboring pMH7653Rb, pMHHN3015a and pMHHN3015c formed null nodules while HN3015SRN14D containing pMHHN3015a
and pMHHN3015c lost the nodulation ability. The plasmid replication repC-like gene sequences were detected by a polymerase chain reaction from 7653R, HN308, HN3015, HN308SRN14 and HN3015SRN14. The
repC gene sequence similarities of the strains tested attained 99%. 相似文献
45.
HaiYan Guo WeiWei Wang Ning Yang BaoLin Guo Sun Zhang RuiJing Yang Ye Yuan JunLin Yu SongNian Hu QiShi Sun Jun Yu 《中国科学:生命科学英文版》2010,53(8):992-999
Based on variable nuclear and/or organellar DNA sequences among vastly divergent species as well as morphologically indistinguishable species, DNA barcoding is widely applicable in species identification, biodiversity studies, forensic analyses, and authentication of medicinal plants. The roots of Astragalus membranaceus and A. membranaceus var. mongholica are commonly used as Radix Astragali in several Asian countries, including China, Japan, and Korea. However, in addition to the two species recorded in the Chinese Pharmacopoeia, there are twenty-three species from different genera including Astragalus, Oxytropis, Hedysarum, and Glycyrrhiza, which have been used as adulterants not only in trading markets but also by the herbal medicine industry. Therefore, a simple, reliable, and accurate classification method is important for distinguishing authentic Radix Astragali from its adulterants. In this study, we acquired data for 37 samples from four related genera within the family Fabaceae. Then we compared four candidate DNA barcoding markers using ITS, matK, rbcL, and coxI sequences from nuclear, chloroplast, and mitochondrial genomes, all commonly used for plants to identify genetic variations among genera, intraspecies, and interspecies. We observed higher divergences among genera and interspecies for ITS, which have the average Kimura 2-parameter distances of 4.5% and 14.1%, respectively, whereas matK was found to have sufficient divergence at the intraspecific level. Moreover, two indels detected in the matK sequence are useful for PCR studies in distinguishing Radix Astragali from its adulterants. This study suggests that the combined barcoding regions of ITS and matK are superior barcodes for Radix Astragali and further studies should focus on evaluating the applicability and accuracy of such combined markers for a wide range of traditional Chinese herbs. 相似文献
46.
Shahin Zarre Zeinab KhodaeiZahra Karamali Vahid NiknamMassoud Mirmasoumi 《Biochemical Systematics and Ecology》2007
Isoenzyme electrophoresis was employed to examine the relationships of 21 individuals representing four populations of Astragalus gossypinus complex as well as 20 individuals representing five populations of Astragalus persicus complex. A total of 27 bands from three enzyme systems (superoxide dismutase, esterase, and peroxidase) were obtained. UPGMA clustering method resulted in two distinct clusters for different populations corresponding to the two species complexes analysed. In both species, populations distributed on Alborz mountain range in northern Iran form separated clusters from those distributed on Zagros mountain range in the West. The results also show that both species complexes exhibit a high diversity based on Shannon–Weaver diversity index (H′) compared with other species of Astragalus reported previously. The mean number of bands per each presumed isoenzyme ranges from 2.14 to 3.57. The value of Euclidean distance ranges from 1.251 to 3.152. Our data suggest that both species should be circumscribed wider than that treated by most taxonomists, and several taxonomic names should be reduced under synonymy of the corresponding species. 相似文献
47.
描述了产于中国新疆的黄耆属(Astragalus)丁字毛类群2新种,即额尔齐斯黄耆(Astragalus eerqisiensis Z.Y.Chang,L. R. Xu & D.Podlech)和沙地黄耆(A.shadiensis L. R. Xu,Z.Y.Chang & D.Podlech).其中,额尔齐斯黄耆仅见于新疆布尔津县的额尔齐斯河流域,与哈巴河黄耆(A.habaheensis)近缘,区别在于前者小叶菱形、倒卵形或椭圆形,长15~25(30)mm,宽(3)7~12(15)mm,旗瓣长20~22(25)mm,翼瓣顶端2裂;沙地黄耆产于新疆托克逊县东北部,散生于沙地荒漠,形态上与变异黄耆(A. variabilis Bunge ex Maxim.)接近,区别在于小叶5~7(9)枚而非11~19枚,旗瓣在中部收缩,植株全体被灰色毛而呈灰色.2新种均系中国特有种,其中额尔齐斯黄耆隶属于乌拉尔组(A. Sect.Helmia Bunge),沙地黄耆隶属于旱生组[A. Sect.Craccina(Stev.)Bunge]. 相似文献
48.
In this study, morphological alterations, biomass growth, and secondary metabolite production of genetically transformed hairy
roots ofPanax ginseng C. A. Meyer, were evaluated after administration of plant growth regulators. The addition of benzylamino purine and kinetin
to the culture media increased biomass formation and phenolic compound biosynthesis in the hairy roots. α-Naphthaleneacetic
acid and indole-3-butyric acid inhibited hairy root growth, however, low concentrations of indole-3-acetic acid slightly increased
hairy root growth. Low concentrations of 2,4-Dichlorophenoxyacetic acid profoundly inhibited growth of hairy roots. The addition
of plant growth regulators, such as auxin, did not increase total phenolic compounds in hairy roots that did not contain gibberellic
acid and cytokinins. Callus formation was induced in cultures suspended in liquid medium amended with benzylamino purine and
kinetin. Hairy roots regenerated from these calluses exhibited an active growth pattern with extensive lateral branching in
non-amended medium, similar to the growth pattern of the original hairy roots. 相似文献
49.
The quality of pharmaceutical products such as ginseng is important for ensuring consumer safety and efficacy. Ginseng is
an expensive herb, and adulteration with other cheaper products may occur. Quality assurance of ginseng is needed since many
of its commercial products now come in various formulations such as capsules, powder, softgels and tea. Thus traditional means
of authentication via smell, taste or physical appearance are hardly reliable. Herbs like ginseng tend to exhibit characteristic
infrared fingerprints due to their different chemical constituents. Here we report for the first time a rapid means of distinguishing
American and Asian ginsengs from two morphological fakes – sawdust and Platycodon grandiflorum, via pattern differences and principal component analysis of their infrared spectra. Our results show that ginseng can be
distinguished from both sawdust and Platycodon grandiflorum, hence there is a potential of using infrared spectroscopy as a novel analytical technique in the authentication of ginseng. 相似文献
50.
Subhrojit SenShali Chen Biao FengYuexiu Wu Edmund LuiSubrata Chakrabarti 《Phytomedicine》2011,18(13):1110-1117