全文获取类型
收费全文 | 953篇 |
免费 | 50篇 |
国内免费 | 23篇 |
专业分类
化学 | 862篇 |
晶体学 | 4篇 |
力学 | 20篇 |
数学 | 59篇 |
物理学 | 81篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 25篇 |
2021年 | 39篇 |
2020年 | 67篇 |
2019年 | 57篇 |
2018年 | 84篇 |
2017年 | 40篇 |
2016年 | 76篇 |
2015年 | 56篇 |
2014年 | 72篇 |
2013年 | 125篇 |
2012年 | 72篇 |
2011年 | 75篇 |
2010年 | 52篇 |
2009年 | 47篇 |
2008年 | 46篇 |
2007年 | 30篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 3篇 |
1999年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有1026条查询结果,搜索用时 765 毫秒
991.
Motaharesadat Hosseini Karim Dadashi‐Noshahr Maryam Islami Ehsan Saburi Amin R. Nikpoor Amir Mellati Majid Mossahebi‐Mohammadi Fatemeh Soleimanifar Seyed E. Enderami 《先进技术聚合物》2020,31(8):1857-1864
Using stem cells to replace the lost beta cells is a hopeful strategy in the treatment of diabetic patients. Furthermore, during stem cell culture and therapy, it is a need to use a substrate to act as a supportive matrix to mimic 3D in vivo microenvironment. Therefore, in this study, human adipose‐derived stem cells were used to differentiate into insulin‐producing cells (IPCs) on a silk/polyethersulfone (PES) scaffold. After exposing to the differentiation media, 2D and 3D (silk/PES) cultured cells were gradually aggregated and formed spherical shaped clusters. The viability of cells was comparable in both 3D and 2D culture. As the results of gene expression assay in both RNA and protein level showed, the differentiation efficiency was higher in 3D culture. Furthermore, ELISA revealed that the release of C‐peptide and insulin was higher in 3D than 2D culture. It seems that silk/PES nanofibrous hybrid scaffold could provide an appropriate matrix to mimic in vivo microenvironment and therefore increases the IPC differentiation potency of stem cells. 相似文献
992.
Maryam Kaabipour Saeid Khodadoust Fatemeh Zeraatpisheh 《Journal of separation science》2020,43(5):912-919
In this work, core/shell magnetic molecularly imprinted polymer nanoparticles were synthesized for extraction and pre‐concentration of valsartan from different samples and then it was measured with high‐performance liquid chromatography. For preparation of molecularly imprinted polymer nanoparticles, Fe3O4 nanoparticles were coated with tetraethyl orthosilicate and then functionalized with 3‐(trimethoxysilyl) propyl methacrylate. In the next step, molecularly imprinted polymer nanoparticles were synthesized under reflux and distillation conditions via polymerization of methacrylic acid, valsartan (as a template), azobisisobutyronitrile and ethylene glycol dimethacrylate as cross linking. The properties of molecularly imprinted polymer nanoparticle were investigated by FTIR spectroscopy, field emission scanning electron microscopy, and X‐ray diffraction. Box‐Behnken design with the aid of desirability function was used for optimizing the effect of variables such as the amounts of molecularly imprinted polymer nanoparticles, time of sonication, pH, and volume of methanol on the extraction percentage of valsartan. According to the obtained results, the affecting variables extraction condition were set as 10 mg of adsorbent, 16 min for sonication, pH = 5.5 and 0.6 mL methanol. The obtained linear response (r2 > 0.995) was in the range of 0.005–10 µg/mL with detection limit 0.0012 µg/mLand extraction recovery was in the range of 92–95% with standard deviation less than 6% (n = 3). 相似文献
993.
Kalhor Mehdi Zarnegar Zohre Janghorban Fatemeh Mirshokraei S. Ahmad 《Research on Chemical Intermediates》2020,46(1):821-836
Research on Chemical Intermediates - In the current study, a new catalytic system based on Fe3O4 nanoparticles immobilized on zeolite-SO3H (Fe3O4@zeolite-SO3H) is introduced. In the first stage,... 相似文献
994.
Seyyedeh Masoumeh Mousavifar Hassan Kefayati Shahab Shariati 《Journal of heterocyclic chemistry》2020,57(1):157-162
A simple, economical, three-component, and one-pot synthesis of novels spiro[indoline-3,5′-pyrido[2,3-d]pyrimidine] derivatives by condensation of dimethyl acetylene dicarboxylate, isatin derivatives, and 6-amino-1,3-dimethyluracil in presence of Fe3O4@Propylsilane@Histidine[HSO4−] as an impressive catalyst via reflux and ultrasound procedure is described. The results show that ultrasound method has several advantages such as milder condition, shorter reaction time, and higher reaction yield. 相似文献
995.
Heravi Majid M. Janati Fatemeh Zadsirjan Vahideh 《Monatshefte für Chemie / Chemical Monthly》2020,151(4):439-482
Monatshefte für Chemie - Chemical Monthly - The Knoevenagel condensation reaction is a prominent organic reaction commonly being utilized in the total synthesis of natural and biologically... 相似文献
996.
Masoumeh Vafaei-Nezhad Ghiasi Reza Shafiei Fatemeh 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2020,94(4):772-777
Russian Journal of Physical Chemistry A - This research aimed at exploring the stabilities of the conformers of 2-methoxy-2-oxo-1,3,2-dioxaphosphorinane and its methylthio and methylselenyl analogs... 相似文献
997.
Let \(\mathfrak{A }\) be a Banach \(*\) -algebra and let \(\varphi \) be a nonzero self-adjoint character on \(\mathfrak{A }\) . For a \(*\) -representation \(\pi \) of \(\mathfrak{A }\) on a Hilbert space \(\mathcal{H }\) , we introduce and study strong \(\varphi \) -amenability of \(\pi \) in terms of certain states on the von Neumann algebra of bounded operators on \(\mathcal{H }\) . We then give some characterizations of this notion in terms of certain positive functionals on \(\mathfrak{A }\) . We finally investigate some hereditary properties of strong \(\varphi \) -amenability of Banach algebras. 相似文献
998.
Fatemeh Vahdati Rad Mohammad Reza Housaindokht Razieh Jalal Hossein Eshtiagh Hosseini Asma Verdian Doghaei Sadegh Sadeghi Goghari 《Journal of fluorescence》2014,24(4):1225-1234
Blocking the division of tumor cells by small-molecules is currently of great interest for the design of new antitumor drugs. The interaction of a new metal complex with DNA was investigated through several techniques. Absorption spectroscopy and gel electrophoresis studies on the interaction of the Cu-complex of (2a-4mpyH)2 [Cu(pyzdc)2 (H2O)2].6 H2O with DNA have shown that this complex can bind to CT-DNA with binding constant 3.99?×?105 M?1. The cyclic voltammetry (CV) responses of the metal complex in the presence of CT-DNA have shown that the metal complex can bind to CT-DNA through partial intercalation mode and this is consistent with molecular docking analysis, quenching process and thermal denaturation experiments. The cytotoxicity of this complex has been evaluated by MTT assay. The results of cell viability assay on DU145 cell line revealed that the metal complex had cytotoxic effects. 相似文献
999.
The effects of a running gravitational coupling and the entropic force on future singularities are considered. Although it is expected that the quantum corrections remove the future singularities or change the singularity type, treating the running gravitational coupling as a function of energy density is found to cause no change in the type of singularity but causes a delay in the time that a singularity occurs. The entropic force is found to replaces the singularity type $II\, \hbox {by} \overline{III} (a=\hbox {const.}, H=\hbox {const.}, \dot{H} \rightarrow \infty , p \rightarrow \infty , \rho \rightarrow \infty )$ which differs from previously known type $III$ and to remove the $w$ -singularity. We also consider an effective cosmological model and show that the types $I$ and $II$ are replaced by the singularity type $III$ . 相似文献
1000.
Mahmoud Roushani Zahra Saedi Yar Mohammad Baghelani Fatemeh Hamdi 《International journal of environmental analytical chemistry》2013,93(15):1586-1603
ABSTRACTIn this paper, a novel, simple, selective and effective solid phase extraction method based on ion-imprinted polymer (IIP) technology and flame atomic absorption spectrometry (FAAS) for separation and pre-concentration of trace amounts of titanium (IV) ions was reportd?. It was obtained by precipitation polymerisation by using 2-(2,4-dihydroxyphenyl)-3,5,7-trihydroxychromen-4-one titanium (IV) complex abbrivated as Ti(IV)-(morin), as the template molecule. After polymerisation, leaching the polymer in HNO3 (50% (v/v) solution caused formation cavities in the polymer. Characterisation studies of the ?Ti(IV)-imprinted polymer (Ti-IP) was performed by FT-IR, UV-Vis and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) techniques and then, the effective factors on extraction were optimised. A sensitive response to Ti(IV) within a concentration range between 0.01 and 4.0 μg mL?1 was achieved under the optimum conditions. A total of 10.0 ng mL?1 and 80.0 mg g?1 were obtained as limit of detection (LOD, 3Sb/m) and maximum adsorption capacity, respectively. The relative standard deviation (RSD) for eight replicates detections of 0.2 μg mL?1 of Ti(IV)? was found to be 2.8%. By this method, pre-concentration factor (PF) of 100 was obtained. Successfully applying this method in the water and standard samples, reasonable results were obtained for the extraction and pre-concentration of the titanium ions. 相似文献