全文获取类型
收费全文 | 25211篇 |
免费 | 763篇 |
国内免费 | 745篇 |
专业分类
化学 | 4354篇 |
晶体学 | 861篇 |
力学 | 557篇 |
综合类 | 78篇 |
数学 | 17800篇 |
物理学 | 3069篇 |
出版年
2023年 | 87篇 |
2022年 | 225篇 |
2021年 | 192篇 |
2020年 | 180篇 |
2019年 | 619篇 |
2018年 | 663篇 |
2017年 | 453篇 |
2016年 | 395篇 |
2015年 | 413篇 |
2014年 | 823篇 |
2013年 | 1315篇 |
2012年 | 832篇 |
2011年 | 1594篇 |
2010年 | 1631篇 |
2009年 | 1905篇 |
2008年 | 1987篇 |
2007年 | 1945篇 |
2006年 | 1549篇 |
2005年 | 1115篇 |
2004年 | 1071篇 |
2003年 | 851篇 |
2002年 | 700篇 |
2001年 | 547篇 |
2000年 | 472篇 |
1999年 | 503篇 |
1998年 | 440篇 |
1997年 | 372篇 |
1996年 | 514篇 |
1995年 | 497篇 |
1994年 | 471篇 |
1993年 | 374篇 |
1992年 | 298篇 |
1991年 | 182篇 |
1990年 | 157篇 |
1989年 | 162篇 |
1988年 | 101篇 |
1987年 | 114篇 |
1986年 | 118篇 |
1985年 | 164篇 |
1984年 | 106篇 |
1983年 | 74篇 |
1982年 | 114篇 |
1981年 | 89篇 |
1980年 | 59篇 |
1979年 | 31篇 |
1978年 | 51篇 |
1977年 | 62篇 |
1976年 | 50篇 |
1974年 | 19篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Ginseng is a vastly used herbal supplement in Southeast Asian countries. Red ginseng extract enriched with Rg3 (Rg3-RGE) is a formula that has been extensively studied owing to its various biological properties. Persicaria tinctoria (PT), belonging to the Polygonaceae family, has also been reported for its anti-inflammatory properties. Ulcerative colitis (UC) is inflammation of the large intestine, particularly in the colon. This disease is increasingly common and has high probability of relapse. We investigated, separately and in combination, the effects of Rg3-RGE and PT using murine exemplary of UC induced by DSS (Dextran Sulfate Sodium). For in vitro and in vivo experiments, nitric oxide assay, qRT-Polymerase Chain Reaction (PCR), Western blot, ulcerative colitis introduced by DSS, Enzyme Linked Immunosorbent Assay (ELISA), and flow cytometry analysis were performed. The results obtained demonstrate that treatment with Rg3-RGE + PT showed synergism to suppress inflammation (in vitro) in RAW 264.7 cells via mitogen-activated protein kinase and nuclear factor κB pathways. Moreover, in C57BL/6 mice, this mixture exhibits strong anti-inflammatory effects in restoring colon length, histopathological damage, pro-inflammatory mediators, and cytokines amount, and decreasing levels of NLRP3 inflammasome (in vivo). Our results recommend that this mixture can be used for the prevention of UC as a prophylactic/therapeutic supplement. 相似文献
972.
Emanuela Colombo Rosaria Pascente Daniela Triolo Claudia Bassani Anthea De Angelis Francesca Ruffini Linda Ottoboni Giancarlo Comi Gianvito Martino Cinthia Farina 《Molecules (Basel, Switzerland)》2020,25(22)
Astrocytes greatly participate to inflammatory and neurotoxic reactions occurring in neurodegenerative diseases and are valuable pharmacological targets to support neuroprotection. Here we used human astrocytes generated from reprogrammed fibroblasts as a cellular model to study the effect of the compound Laquinimod and its active metabolite de-Laquinimod on astrocyte functions and the astrocyte–neuron interaction. We show that human iAstrocytes expressed the receptor for the inflammatory mediator IL1 and responded to it via nuclear translocation of NFκB, an event that did not occur if cells were treated with Laquinimod, indicating a direct anti-inflammatory activity of the drug on the human astrocyte. Similarly, while exposure to IL1 downregulated glial glutamate transporters GLAST and GLT1, treatment with Laquinimod supported maintenance of physiological levels of these proteins despite the inflammatory milieu. Laquinimod also induced nuclear translocation of the aryl hydrocarbon receptor (AHR), suggesting that drug action was mediated by activation of the AHR pathway. However, the drug was effective despite AHR inhibition via CH223191, indicating that AHR signaling in the astrocyte is dispensable for drug responses. Finally, in vitro experiments with rat spinal neurons showed that laquinimod did not exert neuroprotection directly on the neuron but dampened astrocyte-induced neurodegeneration. Our findings indicate that fibroblast-derived human astrocytes represent a suitable model to study astrocyte–neuron crosstalk and demonstrate indirect, partial neuroprotective efficacy for laquinimod. 相似文献
973.
974.
Hui Sun Yun-Feng Zhang Hui-Xia Huo Peng-Wei Guan Chao-Chao Wang Hui-Na Yao 《Natural product research》2020,34(14):2030-2036
AbstractTwo new benzophenone glycosides, aquilarisides A (1) and B (2), together with six known analogues (3-8) were isolated from the pericarps of Aquilaria yunnanensis S. C. Huang. Their structures were elucidated on the basis of 1D and 2D NMR and mass spectroscopic analyses, and the absolute configuration of compound 1 was determined by experimental and calculated electronic circular dichroism (ECD) spectra. Anti-inflammatory activities of all compounds 1–8 were evaluated for their inhibitory activities against lipopolysaccharide (LPS)-stimulated induced nitric oxide (NO) production in RAW 264.7 cells using the Griess assay. Compound 2 indicated a weak inhibition of NO production. 相似文献
975.
Dayu Zhou Chunying Jiang Chenghao Fu Ping Chang Bin Yang Jiadi Wu 《Natural product research》2020,34(6):893-897
AbstractThis study aims to isolate the potential antiproliferative and cytotoxic compounds from ginkgo biloba sarcotestas (GBS) and investigates the underlying mechanism in human MDA-MB-231 and mouse 4T-1 triple-negative breast cancer cells. Our results showed that 2-Hydroxy-6-tridecylbenzoic acid was isolated by cytotoxicity-guided fractionation where different fractions were assessed using MTT assay against MDA-MB-231 and 4T-1 cells. Colony formation assay showed that 2-Hydroxy-6-tridecylbenzoic acid significantly inhibited cell proliferation. The inhibition was associated with the enhancement of cytochrome P450 (CYP) 1B1 expression in a dose- and time-dependent manner and no significant change of CYP1A1 expression by qPCR and Western blot assays in MDA-MB-231 and 4T-1 cells. The mechanism was further demonstrated by the activation of aryl hydrocarbon receptor (AhR) pathway with the upregulation of AhR, AhR nuclear translocator (ARNT) and AhR-dependent xenobiotic response elements (XRE) activity. These findings may have implications for development of anticancer agents containing 2-Hydroxy-6-tridecylbenzoic acid as functional additives. 相似文献
976.
《Arabian Journal of Chemistry》2020,13(1):431-443
Crystalline orthorhombic Bi2WO6 powders were synthesized by a hydrothermal method from aqueous solutions of Bi(NO3)3·5H2O and Na2WO4·2H2O over a range of three selected pH values (2.0, 5.0 and 7.0), using NaOH as precipitating agent. The as-prepared catalysts were characterized by XRD, BET, FE-SEM, TEM, XPS and UV-vis spectroscopy. The effect of pH-synthesis on crystallinity, morphologies, surface area and optical absorption properties, were investigated. Although the pH has a marked influence on morphology, the nature of the precipitating agent (NaOH or TEA) also influences the morphology and surface structure composition, as it is observed in the present work. Three different probe molecules were used to evaluate the photo-catalytic properties under two illumination conditions (UV and Visible): Methyl Orange and Rhodamine B were chosen as dye substrates and Phenol as a transparent substrate. The photo-catalytic activities are strongly dependent not only on the pH used in the synthesis but also on the nature of the chosen substrate in assessing the photo-catalytic activities. Results were compared with those obtained when using TiO2(P25, Evonik) in the same experimental conditions. The photo-catalytic activity of one of the synthesised samples has been evaluated by exposing a mixture of Rhodamine B and Phenol in water, to different illumination conditions. Our results provide new evidences about the issue of whether dyes are suitable substrates to assess the activity of a photo-catalyst. 相似文献
977.
§1Introduction Asweknow,Backlundtransformation[1-3]isaverypowerfulwayforfindingnonline evolutionequations.Inrecentdecades,Painlevéanalysis[4]hasbecomeaverypopu methodtoobtainBacklundtransformation.Inreference[5],fordevelopingthetheory Painlevéanalysis,AndrewPickeringintroduceanewexpansionvariableZwhichsatisf thefollowingRicattiSystem:Zx=1-AZ-BZ2,Zt=-C+(AC+Cx)Z-(D-BC)Z2.(1.Astheapplicationofthenewexpansionvaraible,thepotentialfifth-orderMKd equation(PMKdV5)-vxt+(vxxxxx-10k2v2… 相似文献
978.
Callicarpalongissima has been used as a Yao folk medicine to treat arthritis for years in China, although its active anti-arthritic moieties have not been clarified so far. In this study, two natural phenolic diterpenoids with anti-rheumatoid arthritis (RA) effects, rosmanol and carnosol, isolated from the medicinal plant were reported on for the first time. In type II collagen-induced arthritis DBA/1 mice, both rosmanol (40 mg/kg/d) and carnosol (40 mg/kg/d) alone alleviated the RA symptoms, such as swelling, redness, and synovitis; decreased the arthritis index score; and downregulated the serum pro-inflammatory cytokine levels of interleukin 6 (IL-6), monocyte chemotactic protein 1 (MCP-1), and tumor necrosis factor α (TNF-α). Additionally, they blocked the activation of the Toll-like receptor 4 (TLR4)/nuclear factor κB (NF-κB)/c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) pathways. Of particular interest was that when they were used in combination (20 mg/kg/d each), the anti-RA effect and inhibitory activity on the TLR4/NF-κB/MAPK pathway were significantly enhanced. The results demonstrated that rosmanol and carnosol synergistically alleviated RA by inhibiting inflammation through regulating the TLR4/NF-κB/MAPK pathway, meaning they have the potential to be developed into novel, safe natural combinations for the treatment of RA. 相似文献
979.
活性艳红X-3B(C.I.ReactionRed 2)是一种单偶氮染料,其应用范围广泛,可用于棉、粘纤、涤/棉、锦纶、蚕丝、羊毛、锦/粘等织物的染色和丝绸的印花,因此其废水量大且色度深。目前染料废水的生物处理方法脱色效果差、占地面积大、处理周期长,传统的物理法和化学法也存在着成本高、不能彻底矿化染料分子等缺点。近年来发展起来的光化学处理染料废水的方法及各种光化学组合技术日益受到人们关注,但其中使用的普通紫外灯存在使用寿命短、启动慢、发光不稳定、电极材料易损等缺点[1],致使光化学方法处理废水的成本很高。本文利用微波产生的高频… 相似文献
980.
活性炭纤维电极生成羟基自由基降解酸性红B 总被引:18,自引:0,他引:18
分别采用具有吸附催化性能的活性炭纤维(ACF)作为阳极和阴极对水中偶氮染料酸性红B (ARB)的电化学降解情况进行了系统研究. 研究表明两种体系均可较好降解ARB, 可达到色度完全去除, 但ACF作为阴极电芬顿对有机物的矿化程度远远高于以ACF作为阳极时的矿化程度, 其TOC去除率达到70%, 高于阳极体系的30% TOC去除率. 通过电子自旋捕集技术(ESR)检测两种反应体系中产生的活性中间体, 发现在两种体系中均有高活性的羟基自由基生成, ACF阴极体系中产生的羟基自由基的量远远高于阳极体系产生量, 这是阴极体系有机物矿化效果较好的根本原因. 还对电流强度和初始pH的影响进行了研究, 并对两个体系反应机理进行了讨论. 相似文献