首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4001篇
  免费   799篇
  国内免费   450篇
化学   3923篇
晶体学   65篇
力学   70篇
综合类   38篇
数学   76篇
物理学   1078篇
  2024年   9篇
  2023年   79篇
  2022年   261篇
  2021年   297篇
  2020年   305篇
  2019年   234篇
  2018年   197篇
  2017年   256篇
  2016年   326篇
  2015年   301篇
  2014年   350篇
  2013年   389篇
  2012年   358篇
  2011年   328篇
  2010年   213篇
  2009年   260篇
  2008年   186篇
  2007年   151篇
  2006年   131篇
  2005年   116篇
  2004年   88篇
  2003年   55篇
  2002年   59篇
  2001年   33篇
  2000年   41篇
  1999年   17篇
  1998年   17篇
  1997年   25篇
  1996年   23篇
  1995年   14篇
  1994年   14篇
  1993年   17篇
  1992年   10篇
  1991年   14篇
  1990年   9篇
  1989年   6篇
  1988年   7篇
  1987年   7篇
  1986年   7篇
  1985年   5篇
  1984年   9篇
  1983年   4篇
  1982年   16篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有5250条查询结果,搜索用时 312 毫秒
971.
Benzothiadiazole(BT) is an electron-deficient unit with fused aromatic core, which can be used to construct conjugated polymers for application in organic solar cells(OSCs). In the past twenty years, huge numbers of conjugated polymers based on BT unit have been developed,focusing on the backbone engineering(such as by using different copolymerized building blocks), side chain engineering(such as by using linear or branch side units), using heteroatoms(such as F, O and S atoms, and CN group), etc. These modifications enable BT-polymers to exhibit distinct absorption spectra(with onset varied from 600 nm to 1000 nm), different frontier energy levels and crystallinities. As a consequence, BT-polymers have gained much attention in recent years, and can be simultaneously used as electron donor and electron acceptor in OSCs, providing the power conversion efficiencies(PCEs) over 18% and 14% in non-fullerene and all-polymer OSCs. In this article, we provide an overview of BTpolymers for OSCs, from donor to acceptor, via selecting some typical BT-polymers in different periods. We hope that the summary in this article can invoke the interest to study the BT-polymers toward high performance OSCs, especially with thick active layers that can be potentially used in large-area devices.  相似文献   
972.
全无机钙钛矿太阳电池因其热稳定性好、载流子迁移率高,可用于制备叠层电池等优点备受关注.随着人们对全无机钙钛矿太阳电池的深入研究和制备工艺的持续优化,全无机钙钛矿太阳电池的光电转换效率已经突破19%.然而,全无机钙钛矿材料相稳定性较差,这使得实现全无机钙钛矿太阳电池在空气环境下制备和长期使用面临巨大挑战.众多科研工作者通...  相似文献   
973.
Iron is a crucial element required for the proper functioning of the body. For instance, hemoglobin is the vital component in the blood that delivers oxygen to various parts of the body. The heme protein present in hemoglobin comprises iron in the form of a ferrous state which regulates oxygen delivery. Excess iron in the body is stored as ferritin and would be utilized under iron-deficient conditions. Surprisingly, cancer cells as well as cancer stem cells have elevated ferritin levels suggesting that iron plays a vital role in protecting these cells. However, apart from the cytoprotective role iron also has the potential to induce cell death via ferroptosis which is a non-apoptotic cell death dependent on iron reserves. Apoptosis a caspase-dependent cell death mechanism is effective on cancer cells however little is known about its impact on cancer stem cell death. This paper focuses on the molecular characteristics of apoptosis and ferroptosis and the importance of switching to ferroptosis to target cancer stem cells death thereby preventing cancer relapse. To the best of our knowledge, this is the first review to demonstrate the importance of intracellular iron in regulating the switching of tumor cells and therapy resistant CSCs from apoptosis to ferroptosis.  相似文献   
974.
The use of a proper sample processing methodology for maximum proteome coverage and high-quality quantitative data is an important choice to make before initiating a liquid chromatography–mass spectrometry (LC–MS)-based proteomics study. Popular sample processing workflows for proteomics involve in-solution proteome digestion and single-pot, solid-phase-enhanced sample preparation (SP3). We tested them on both HeLa cells and human plasma samples, using lysis buffers containing SDS, or guanidinium hydrochloride. We also studied the effect of using commercially available depletion mini spin columns before SP3, to increase proteome coverage in human plasma samples. Our results show that the SP3 protocol, using either buffer, achieves the highest number of quantified proteins in both the HeLa cells and plasma samples. Moreover, the use of depletion mini spin columns before SP3 results in a two-fold increase of quantified plasma proteins. With additional fractionation, we quantified nearly 1400 proteins, and examined lower-abundance proteins involved in neurodegenerative pathways and mitochondrial metabolism. Therefore, we recommend the use of the SP3 methodology for biological sample processing, including those after depletion of high-abundance plasma proteins.  相似文献   
975.
The purpose of this study was to evaluate the potential of a newly modified cyclodextrin derivative, water-soluble β-cyclodextrin–epichlorohydrin (β-CD), as an effective drug carrier to enhance the poor solubility and bioavailability of galangin (GAL), a poorly water-soluble model drug. In this regard, inclusion complexes of GAL/β-CDP were prepared. UV-VIS spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), X-ray crystallography (XRD), zeta potential analysis, particle size analysis, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) were applied to characterize the synthesized GAL/β-CD. Michigan Cancer Foundation-7 (MCF-7; human breast cancer cells) and rat embryo fibroblast (REF; normal cells) were employed to examine the in vitro cytotoxic effects of GAL/β-CD using various parameters. The dye-based tests of MTT and crystal violet clearly exhibited that GAL/β-CD-treated cells had a reduced proliferation rate, an influence that was not found in the normal cell line. The cells’ death was found to follow apoptotic mechanisms, as revealed by the dye-based test of acridine orange/ethidium bromide (AO/EtBr), with the involvement of the mitochondria via caspase-3-mediated events, as manifested by the Rh 123 test. We also included a mouse model to examine possible in vivo toxic effects of GAL/β-CD. It appears that the inclusion complex does not have a significant influence on normal cells, as indicated by serum levels of kidney and liver enzymatic markers, as well as thymic and splenic mass indices. A similar conclusion was reached on the histological level, as manifested by the absence of pathological alterations in the liver, kidney, thymus, spleen, heart, and lung.  相似文献   
976.
HCV全基因组培养细胞的比较蛋白组学研究   总被引:1,自引:0,他引:1  
利用比较蛋白质组技术研究了转染丙型肝炎病毒(Hepatitis C virus, HCV)全基因组的人肝癌细胞系Huh7细胞模型中蛋白质表达谱的变化, 建立了Huh7-HCV的双向凝胶电泳蛋白质表达图谱和数据库. 通过双向凝胶电泳分离和图像分析, 对表达差异2倍以上蛋白质点进行了胶内酶解和MALDI-TOF MS鉴定. 得到包括与细胞骨架蛋白、细胞周期、凋亡和信号转导等相关的14个蛋白质, 并且用Western blot验证了热休克蛋白70的蛋白质组研究结果. 利用HCV全基因组培养系统, 采用蛋白质组学技术, 为研究HCV病毒和宿主细胞相互作用提供了新的实验数据, 为深入研究HCV病毒复制和分子致病机理奠定了基础.  相似文献   
977.
978.
From the dried vines of Aspidopterys obcordata Hemsl, five new polyoxypregnane glycosides, named obcordatas J–N (1–5), were obtained. Their structures were fully elucidated and characterized by HRESIMS and extensive spectroscopic data. In addition, all of the new compounds were screened for their antinephrolithiasis activity in vitro. The results showed that compounds 1–3 have prominent protective effects on calcium oxalate crystal-induced human kidney 2 (HK-2) cells, with EC50 values ranging from 6.72 to 14.00 μM, which is consistent with the application value of A. obcordata in folk medicine for kidney stones.  相似文献   
979.
王藜  徐苗  应磊  刘烽  曹镛 《高分子学报》2008,(10):993-997
以PC[70]BM(phenyl C71-butyric acid methyl ester)取代PC[60]BM(phenyl C61-butyric acid methyl ester)作为电子受体材料,以MEH-PPV(poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene])为电子给体材料,制成了本体异质结(bulk heterojunction,BHJ)聚合物太阳能电池.MEH-PPV/PC[70]BM器件在AM1.5G(80 mW/cm2)模拟太阳光的光照条件下得到了3.42%的能量转换效率,短路电流值达到了6.07 mA/cm2,开路电压0.85 V,填充因子为53%.通过紫外可见吸收光谱和外量子效率的研究,发现PC[70]BM作为电子受体,对扩大光谱的吸收范围和增加活性层的吸收系数有明显的作用.同时比较了不同溶剂对该体系器件性能的影响.通过原子力显微镜(AFM)、光暗导I-V曲线等研究,分析了1,2-二氯苯有利于给体相和受体相的微相分离和载流子的传输的原因.  相似文献   
980.
This study evaluated the effect of grape seed-derived monomer, dimeric, and trimeric procyanidins on rat pheochromocytoma cell line (PC12) cells and in a zebrafish Parkinson’s disease (PD) model. PC12 cells were cultured with grape seed-derived procyanidins or deprenyl for 24 h and then exposed to 1.5 mm 1-methyl-4-phenylpyridinium (MPP+) for 24 h. Zebrafish larvae (AB strain) 3 days post-fertilization were incubated with deprenyl or grape seed-derived procyanidins in 400 µM 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for 4 days. The results showed that the procyanidin dimers procyanidin B1 (B1), procyanidin B2 (B2), procyanidin B3 (B3), procyanidin B4 (B4), procyanidin B1-3-O-gallate (B1-G), procyanidin B2-3-O-gallate (B2-G), and the procyanidin trimer procyanidin C1 (C1) had a protective effect on PC12 cells, decreasing the damaged dopaminergic neurons and motor impairment in zebrafish. In PC12 cells and the zebrafish PD model, procyanidin (B1, B2, B3, B4, B1-G, B2-G, C1) treatment decreased the content of reactive oxygen species (ROS) and malondialdehyde (MDA), increased the activity of antioxidant enzymes glutathione peroxidase (GSH-Px), catalase (CAT), and superoxide dismutase (SOD), and upregulated the expression of nuclear factor-erythroid 2-related factor (Nrf2), NAD(P)H: quinone oxidoreductase 1 (NQO1), and heme oxygenase-1 (HO-1). These results suggest that in PC12 cells and the zebrafish PD model, the neuroprotective effects of the procyanidins were positively correlated with their degree of polymerization.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号