全文获取类型
收费全文 | 277篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
化学 | 206篇 |
力学 | 5篇 |
数学 | 28篇 |
物理学 | 53篇 |
出版年
2023年 | 2篇 |
2022年 | 11篇 |
2021年 | 15篇 |
2020年 | 17篇 |
2019年 | 13篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 14篇 |
2015年 | 6篇 |
2014年 | 17篇 |
2013年 | 23篇 |
2012年 | 15篇 |
2011年 | 15篇 |
2010年 | 7篇 |
2009年 | 15篇 |
2008年 | 16篇 |
2007年 | 11篇 |
2006年 | 6篇 |
2005年 | 15篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1991年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1916年 | 2篇 |
排序方式: 共有292条查询结果,搜索用时 31 毫秒
241.
A classification of full algebras of matrices is given. All such algebras are permutation-isomorphic to block lower-triangular matrices with corresponding subdiagonal blocks being either zero-blocks or full. Two full algebras are isomorphic if and only if they are permutation-isomorphic. A one-to-one correspondence is provided between the full algebras and transitive directed graphs. It is also proven that such algebras, if endowed with a lattice order, can be almost f- or d-algebras only if they are diagonal. 相似文献
242.
Khosravi Raouf Rabiei Saeed Khaki Mohammad Safaei Mohammad Reza Goodarzi Marjan 《Journal of Thermal Analysis and Calorimetry》2021,145(4):1949-1967
Journal of Thermal Analysis and Calorimetry - Analyzing microchannel heat sinks (MCHS) in terms of the second thermodynamic law is useful, and it is necessary to examine MCHSs in terms of... 相似文献
243.
Javan Mohamed Mehdi Enina Yulianna 《International Journal of Theoretical Physics》2021,60(5):1742-1756
International Journal of Theoretical Physics - The behavior of the spatial and angular Goos-Hänchen (GH) shifts for the reflected and transmitted probe light beams is theoretically... 相似文献
244.
An open metal site framework named UTSA‐16 was synthesized and modified as a high‐capacity adsorbent for reversible CO2 capture. Partial substitution of intrinsic Co2+ sites of UTSA‐16 with Ni2+ centres was realized in the molar composition range 0–75% Ni with the aim of increasing CO2 uptake. Synthesized bimetallic Nix‐UTSA‐16 (x = 0, 20, 50, 75) materials were characterized using various techniques to assess the influence of chemical composition on CO2 binding affinity and any subsequent physical change in morphology, crystal size and porosity on the total uptake. Experimental isotherm adsorption studies showed the following trend for CO2 adsorption capacity employing the Nix‐UTSA‐16 series: Ni20‐UTSA‐16 > UTSA‐16 > Ni50‐UTSA‐16 > Ni75‐UTSA‐16. According to the dynamic breakthrough CO2 profiles measured for a mixture of CO2 and CH4 (15/85 molar ratio), Ni20‐UTSA‐16 exhibited 2 times the breakthrough time with 1.5 times the loading capacity at 75 Nml min?1 feed flow rate, compared to the parent UTSA‐16. In addition, the Ni20‐UTSA‐16 bimetallic metal–organic framework exhibited lower isosteric heat of adsorption compared to UTSA‐16 (ΔHave = 28.54 versus 46.85 kJ mol?1). As a result, more than 95% of its capacity was restored by applying a partial vacuum for only 1 h at room temperature without involving any other time‐ and energy‐consuming regenerative step. 相似文献
245.
Marjan Matvejchuk 《International Journal of Theoretical Physics》1999,38(8):2065-2093
We characterize measures on hyperbolic logicsassociated to von Neumann algebras acting in a spacewith an indefinite metric. An analog to the Gleasontheorem is proved. 相似文献
246.
Manuel D. N. T. Oliveira Fernando A. F. Ferreira Guillermo O. Pérez-Bustamante Ilander Marjan S. Jalali 《The Journal of the Operational Research Society》2017,68(9):985-997
The 2008 global financial crisis and its aftermath have shown the ability to predict bankruptcy to be a vital management skill and that the methodologies used for that purpose should be as close to reality as possible. This study aims to develop a multiple criteria system to predict bankruptcy in small- and medium-sized enterprises (SMEs). It combines cognitive mapping with the measuring attractiveness by a categorical based evaluation technique (MACBETH), resulting in a more complete and transparent process for evaluating SMEs and their risk of bankruptcy. What differentiates this framework is the fact that it is based on information obtained directly from managers and bank analysts who deal with this type of adversity on a daily basis. The results highlight the importance of financial and strategic aspects, among others, and demonstrate how cognitive mapping can improve the understanding of the decision situation at hand, while MACBETH facilitates the calculation of trade-offs among evaluation criteria. 相似文献
247.
Marjan Motiei Luis Pleno de Gouveia Tom opík Robert Vícha David koda Jaroslav Císa Reza Khalili Eva Domincov Bergerov Luk Münster Haojie Fei Vladimír Sedlaík Petr Sha 《Molecules (Basel, Switzerland)》2021,26(7)
The alkaline milieu of chronic wounds severely impairs the therapeutic effect of antibiotics, such as rifampicin; as such, the development of new drugs, or the smart delivery of existing drugs, is required. Herein, two innovative polyelectrolyte nanoparticles (PENs), composed of an amphiphilic chitosan core and a polycationic shell, were synthesized at alkaline pH, and in vitro performances were assessed by 1H NMR, elemental analysis, FT-IR, XRD, DSC, DLS, SEM, TEM, UV/Vis spectrophotometry, and HPLC. According to the results, the nanostructures exhibited different morphologies but similar physicochemical properties and release profiles. It was also hypothesized that the simultaneous use of the nanosystem and an antioxidant could be therapeutically beneficial. Therefore, the simultaneous effects of ascorbic acid and PENs were evaluated on the release profile and degradation of rifampicin, in which the results confirmed their synergistic protective effect at pH 8.5, as opposed to pH 7.4. Overall, this study highlighted the benefits of nanoparticulate development in the presence of antioxidants, at alkaline pH, as an efficient approach for decreasing rifampicin degradation. 相似文献
248.
Amir Jouya Talaei Nahid Zarei Anwarul Hasan Samir Haj Bloukh Zehra Edis Niusha Abbasi Gamasaee Marjan Heidarzadeh Mohammad Mahdi Nejadi Babadaei Koorosh Shahpasand Majid Sharifi Keivan Akhatri Suliman Khan Menzghou Xue Mojtaba Falahati 《Arabian Journal of Chemistry》2021,14(2):102923
The interaction of nanoparticles with biological systems can provide useful information about their therapeutic applications. The aluminum nanoparticles (Al2O3 NPs) were synthesized by laser ablation technique and well-characterized by different methods. Fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular docking studies were employed to evaluate the effect of Al2O3 NPs on the protein structure. Growth inhibitory and apoptotic effects of the Al2O3 NPs against K562 cancer cells and lymphocyte cells were assessed using [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT), flow cytometry, and real time polymerase chain reaction (PCR) assays. The antipathogenic activity of Al2O3 NPs against a diverse range of Gram-negative and Gram-positive pathogens was explored through a disk diffusion method. The characterization techniques determined that the Al2O3 NPs were successfully synthesized in the nanoscales. Intrinsic, 1-anilino-8-naphthalenesulfonate (ANS) and acrylamide fluorescence spectroscopy studies disclosed that Al2O3 NPs can partially change the tertiary structure of human serum albumin (HSA), whereas CD spectroscopy investigation depicted that the secondary structure of HSA remained intact. Molecular docking investigation also manifest that the Al2O3 nano-clusters preferably bind to electrostatic residues. Al2O3 NPs exhibited promising and selective anticancer features through reactive oxygen species (ROS) production, apoptosis induction, and elevation of Bax/Bcl-2 mRNA ratio. Furthermore, the Al2O3 NP showed a remarkable antibacterial activity against both Gram-negative and Gram-positive pathogens. In conclusion, it may be suggested that the synthesized Al2O3 NPs can be integrated in the development of anticancer and antipathogenic agents. 相似文献
249.
A ring R is (weakly) nil clean provided that every element in R is the sum of a (weak) idempotent and a nilpotent. We characterize nil and weakly nil matrix rings over abelian rings. Let R be abelian, and let n ∈ ?. We prove that M n (R) is nil clean if and only if R/J(R) is Boolean and M n (J(R)) is nil. Furthermore, we prove that R is weakly nil clean if and only if R is periodic; R/J(R) is ?3, B or ?3 ⊕ B where B is a Boolean ring, and that M n (R) is weakly nil clean if and only if M n (R) is nil clean for all n ≥ 2. 相似文献
250.