全文获取类型
收费全文 | 5553篇 |
免费 | 497篇 |
国内免费 | 389篇 |
专业分类
化学 | 1026篇 |
晶体学 | 59篇 |
力学 | 3472篇 |
综合类 | 73篇 |
数学 | 499篇 |
物理学 | 1310篇 |
出版年
2024年 | 5篇 |
2023年 | 28篇 |
2022年 | 98篇 |
2021年 | 226篇 |
2020年 | 158篇 |
2019年 | 92篇 |
2018年 | 114篇 |
2017年 | 153篇 |
2016年 | 209篇 |
2015年 | 159篇 |
2014年 | 201篇 |
2013年 | 328篇 |
2012年 | 199篇 |
2011年 | 269篇 |
2010年 | 220篇 |
2009年 | 268篇 |
2008年 | 282篇 |
2007年 | 332篇 |
2006年 | 338篇 |
2005年 | 288篇 |
2004年 | 284篇 |
2003年 | 244篇 |
2002年 | 182篇 |
2001年 | 207篇 |
2000年 | 216篇 |
1999年 | 177篇 |
1998年 | 142篇 |
1997年 | 137篇 |
1996年 | 131篇 |
1995年 | 113篇 |
1994年 | 90篇 |
1993年 | 92篇 |
1992年 | 81篇 |
1991年 | 75篇 |
1990年 | 48篇 |
1989年 | 40篇 |
1988年 | 43篇 |
1987年 | 42篇 |
1986年 | 30篇 |
1985年 | 21篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有6439条查询结果,搜索用时 203 毫秒
131.
Dr. Steve Y. Rhieu Dr. Aaron A. Urbas Dr. Daniel W. Bearden Dr. John P. Marino Dr. Katrice A. Lippa Dr. Vytas Reipa 《Angewandte Chemie (International ed. in English)》2014,53(2):447-450
Non‐invasive and real‐time analysis of cellular redox processes has been greatly hampered by lack of suitable measurement techniques. Here we describe an in‐cell nuclear magnetic resonance (NMR) based method for measuring the intracellular glutathione redox potential by direct and quantitative measurement of isotopically labeled glutathione introduced exogenously into living yeast. By using this approach, perturbations in the cellular glutathione redox homeostasis were also monitored as yeast cells were subjected to oxidative stress. 相似文献
132.
Dr. Liwei Zheng Xiaojuan Dai Prof. Hongmei Su Prof. Marc M. Greenberg 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13508-13515
Guanine radicals are important reactive intermediates in DNA damage. Hydroxyl radical (HO.) has long been believed to react with 2′-deoxyguanosine (dG) generating 2′-deoxyguanosin-N1-yl radical (dG(N1-H).) via addition to the nucleobase π-system and subsequent dehydration. This basic tenet was challenged by an alternative mechanism, in which the major reaction of HO. with dG was proposed to involve hydrogen atom abstraction from the N2-amine. The 2′-deoxyguanosin-N2-yl radical (dG(N2-H).) formed was proposed to rapidly tautomerize to dG(N1-H).. We report the first independent generation of dG(N2-H). in high yield via photolysis of 1 . dG(N2-H). is directly observed upon nanosecond laser flash photolysis (LFP) of 1 . The absorption spectrum of dG(N2-H). is corroborated by DFT studies, and anti- and syn-dG(N2-H). are resolved for the first time. The LFP experiments showed no evidence for tautomerization of dG(N2-H). to dG(N1-H). within hundreds of microseconds. This observation suggests that the generation of dG(N1-H). via dG(N2-H). following hydrogen atom abstraction from dG is unlikely to be a major pathway when HO. reacts with dG. 相似文献
133.
Shuman Li Alireza Azizi Steven R. Kirk Samantha Jenkins 《International journal of quantum chemistry》2020,120(19):e26361
We seek to explain why the hydrogen bond possesses unusual strength in small water clusters that account for many of the complex behaviors of water. We have investigated and visualized the donation of covalent character from covalent (sigma) to hydrogen bonds by calculating the eigenvector coupling properties of quantum theory of atoms in molecules (QTAIM), stress tensor σ ( r ), and Ehrenfest Force F ( r ) on the F ( r ) molecular graph. The next-generation three-dimensional (3-D) bond-path framework sets are presented, and only the F ( r ) bond-path framework sets reproduce the earlier finding on the coupling between covalent (sigma) and hydrogen bonds that possess a degree of covalent character. Exploration of the bond-path between the covalent (sigma) and hydrogen bond's critical points provides an explanation for the previously obtained coupling results. The directional character of the covalent (sigma) and hydrogen bonds' 3-D bond-path framework sets for the F ( r ) explains differences found in the earlier results from QTAIM and the stress tensor σ ( r ). 相似文献
134.
Yuri A. de Oliveira Só Mônica de Abreu Silva Fernando M. Carvalho Alessandra S. Kiametis Ricardo Gargano 《International journal of quantum chemistry》2020,120(11):e26194
Oxidative stress is an imbalance between the production of free radicals and the antioxidant defenses of the organism. Heart diseases, anemia, inflammation, and neurodegenerative disorders have been associated with this biological condition. Trolox is a notable antioxidant drug similar to vitamin E, and it is used to decrease the oxidative stress or repair the damage caused by it. In this work, the virtual screening technique is applied to identify compounds with antioxidant activities similar to Trolox. The antioxidant activity of these compounds was assessments by the mechanisms of hydrogen atom transfer and single electron transfer. Properties such as bond dissociation enthalpy, adiabatic ionization potential, Gibbs free reaction energy, spin density, highest occupied molecular orbital (HOMO), and GAP (HOMO-LUMO) energies, obtained from the DFT approach, point out to the predominance of the HAT mechanism for the antioxidant action of these compounds. The obtained results contribute to a better understanding of the chemical and physical properties responsible for antioxidant activity and the design of new antioxidant agents. 相似文献
135.
136.
Astaxanthin is a natural lipid-soluble and red-orange carotenoid. Due to its strong antioxidant property, anti-inflammatory, anti-apoptotic, and immune modulation, astaxanthin has gained growing interest as a multi-target pharmacological agent against various diseases. In the current review, the anti-inflammation mechanisms of astaxanthin involved in targeting for inflammatory biomarkers and multiple signaling pathways, including PI3K/AKT, Nrf2, NF-κB, ERK1/2, JNK, p38 MAPK, and JAK-2/STAT-3, have been described. Furthermore, the applications of anti-inflammatory effects of astaxanthin in neurological diseases, diabetes, gastrointestinal diseases, hepatic and renal diseases, eye and skin disorders, are highlighted. In addition to the protective effects of astaxanthin in various chronic and acute diseases, we also summarize recent advances for the inconsistent roles of astaxanthin in infectious diseases, and give our view that the exact function of astaxanthin in response to different pathogen infection and the potential protective effects of astaxanthin in viral infectious diseases should be important research directions in the future. 相似文献
137.
Xiyu Liao Zhenjun Zhu Shujian Wu Mengfei Chen Rui Huang Juan Wang Qingping Wu Yu Ding 《Molecules (Basel, Switzerland)》2020,25(22)
Pleurotus geesteranus is a promising source of bioactive compounds. However, knowledge of the antioxidant behaviors of P. geesteranus protein hydrolysates (PGPHs) is limited. In this study, PGPHs were prepared with papain, alcalase, flavourzyme, pepsin, and pancreatin, respectively. The antioxidant properties and cytoprotective effects against oxidative stress of PGPHs were investigated using different chemical assays and H2O2 damaged PC12 cells, respectively. The results showed that PGPHs exhibited superior antioxidant activity. Especially, hydrolysate generated by alcalase displayed the strongest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (91.62%), 2,2-azino-bis (3-ethylbenzothia zoline-6-sulfonic acid) (ABTS) radical scavenging activity (90.53%), ferric reducing antioxidant power, and metal ion-chelating activity (82.16%). Analysis of amino acid composition revealed that this hydrolysate was rich in hydrophobic, negatively charged, and aromatic amino acids, contributing to its superior antioxidant properties. Additionally, alcalase hydrolysate showed cytoprotective effects on H2O2-induced oxidative stress in PC12 cells via diminishing intracellular reactive oxygen species (ROS) accumulation by stimulating antioxidant enzyme activities. Taken together, alcalase hydrolysate of P. geesteranus protein can be used as beneficial ingredients with antioxidant properties and protective effects against ROS-mediated oxidative stress. 相似文献
138.
Kubra Kahremanoglu Ezgi Rana Temel Tamara Ecem Korkut Atakan Arda Nalbant Bersu Batu Azer Caner Durucan Murvet Volkan Ezel Boyaci 《Journal of separation science》2020,43(9-10):1925-1933
Recently the connection between oxidative stress and various diseases, including cancer and Alzheimer's, attracts notice as a pathway suitable for diagnostic purposes. 8‐Oxo‐deoxyguanosine and 8‐oxo‐deoxyadenosine produced from the interaction of reactive oxygen species with DNA become prominent as biomarkers. Several methods have been developed for their determination in biofluids, including solid‐phase extraction and enzyme‐linked immunosorbent assays. However, still, there is a need for reliable and fast analytical methods. In this context, solid‐phase microextraction offers many advantages such as flexibility in geometry and applicable sample volume, as well as high adaptability to high‐throughput sampling. In this study, a solid‐phase microextraction method was developed for the determination of 8‐oxo‐deoxyguanosine and 8‐oxo‐deoxyadenosine in biofluids. The extractive phase of solid‐phase microextraction consisted of hydrophilic–lipophilic balanced polymeric particles. In order to develop a solid‐phase microextraction method suitable for the determination of the analytes in saliva and urine, several parameters, including desorption solvent, desorption time, sample pH, and ionic strength, were scrutinized. Analytical figures of merit indicated that the developed method provides reasonable interday and intraday precisions (<15% in both biofluids) with acceptable accuracy. The method provides a limit of quantification for both biomarkers at 5.0 and 10.0 ng/mL levels in saliva and urine matrices, respectively. 相似文献
139.
Dongmei Zhang Bulei Wang Yajuan Sun Changhao Wang Somnath Mukherjee Cheng Yang Yashao Chen 《Macromolecular bioscience》2020,20(6)
Burn wound healing remains a challenging health problem worldwide due to the lack of efficient and precise therapy. Inherent oxidative stress following burn injury is importantly responsible for prolonged inflammation, fibrotic scar, and multiple organ failure. Herein, a bioinspired antioxidative defense system coupling with in situ forming hydrogel, namely, multiresponsive injectable catechol‐Fe3+ coordination hydrogel (MICH) matrix, is engineered to promote burn‐wound dermal repair by inhibiting tissue oxidative stress. This MICH matrix serves as the special traits of “Fe‐superoxide dismutases,” small molecular antioxidant (vitamin E), and extracellular matrix (ECM) in alleviating cellular oxidative damage, which demonstrates precise scavenging on reactive oxygen species (ROS) of different cellular locations, blocking lipid peroxidation and cell apoptosis. In in vivo burn‐wound treatment, this MICH promptly integrates with injured surrounding tissue to provide hydration microenvironment and physicochemical ECM for burn wounds. Importantly, the MICH matrix suppresses tissue ROS production, reducing the inflammatory response, prompting re‐epithelization and neoangiogenesis during wound healing. Meanwhile, the remodeling skin treated with MICH matrix demonstrates low collagen deposition and normal dermal collagen architecture. Overall, the MICH prevents burn wound progression and enhances skin regeneration, which might be a promising biomaterial for burn‐wound care and other disease therapy induced by oxidative stress. 相似文献
140.
Michaela Kohlov Susana Rocha Clia Gomes Amorim Alberto de Nova Araújo Alice Santos‐Silva Petr Solich Maria Conceio Branco da Silva Montenegro 《Macromolecular bioscience》2020,20(7)
The reduction of free radicals by bioactive membranes used for hemodialysis treatment is an important topic due to the constant rise of oxidative stress‐associated cardiovascular mortality by hemodialysis patients. Therefore, it is urgent to find an effective solution that helps to solve this problem. Polysulfone membranes enriched with α‐lipoic acid, α‐tocopherol, and with both components are fabricated by spin coating. The antioxidant properties of these membranes are evaluated in vitro by determining the lipid‐peroxidation level and the total antioxidant status of the blood plasma. The biocompatibility is assessed by quantifying the protein adsorption, platelet adhesion, complement activation, and hemolytic effect. All types of membranes show in vitro antioxidant activity and a trend to reduce oxidative stress in vivo; the best results show membranes prepared with a combination of both compounds and prove to be nonhemolytic and hemocompatible. Moreover, the membrane specific separation ability for the main waste products is not affected by antioxidants incorporation. 相似文献