全文获取类型
| 收费全文 | 1612篇 |
| 免费 | 48篇 |
| 国内免费 | 54篇 |
专业分类
| 化学 | 773篇 |
| 晶体学 | 12篇 |
| 力学 | 11篇 |
| 综合类 | 7篇 |
| 数学 | 454篇 |
| 物理学 | 261篇 |
| 综合类 | 196篇 |
出版年
| 2025年 | 5篇 |
| 2024年 | 17篇 |
| 2023年 | 49篇 |
| 2022年 | 171篇 |
| 2021年 | 182篇 |
| 2020年 | 93篇 |
| 2019年 | 27篇 |
| 2018年 | 16篇 |
| 2017年 | 19篇 |
| 2016年 | 25篇 |
| 2015年 | 20篇 |
| 2014年 | 33篇 |
| 2013年 | 50篇 |
| 2012年 | 50篇 |
| 2011年 | 85篇 |
| 2010年 | 64篇 |
| 2009年 | 97篇 |
| 2008年 | 75篇 |
| 2007年 | 101篇 |
| 2006年 | 65篇 |
| 2005年 | 54篇 |
| 2004年 | 51篇 |
| 2003年 | 52篇 |
| 2002年 | 47篇 |
| 2001年 | 28篇 |
| 2000年 | 31篇 |
| 1999年 | 45篇 |
| 1998年 | 19篇 |
| 1997年 | 16篇 |
| 1996年 | 22篇 |
| 1995年 | 17篇 |
| 1994年 | 15篇 |
| 1993年 | 13篇 |
| 1992年 | 13篇 |
| 1991年 | 9篇 |
| 1990年 | 4篇 |
| 1989年 | 6篇 |
| 1988年 | 2篇 |
| 1987年 | 1篇 |
| 1986年 | 8篇 |
| 1983年 | 2篇 |
| 1981年 | 1篇 |
| 1980年 | 2篇 |
| 1979年 | 4篇 |
| 1978年 | 3篇 |
| 1977年 | 2篇 |
| 1976年 | 3篇 |
排序方式： 共有1714条查询结果，搜索用时 15 毫秒
911.
Moringa oleifera (M. oleifera) leaves are rich in nutrients and antioxidant compounds that can be consumed to prevent and overcome malnutrition. The water infusion of its leaf is the easiest way to prepare the herbal drink. So far, no information is available on the antioxidant, antimutagenic, and antivirus capacities of this infusion. This study aimed to determine the composition of the bioactive compounds in M. oleifera leaf infusion, measuring for antioxidant and antimutagenic activity, and evaluating any ability to inhibit the SARS-CoV-2 main protease (Mpro). The first two objectives were carried out in vitro. The third objective was carried out in silico. The phytochemical analysis of M. oleifera leaf infusion was carried out using liquid chromatography-mass spectrometry (LC-MS). Antioxidant activity was measured as a factor of the presence of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). The antimutagenicity of M. oleifera leaf powder infusion was measured using the plasmid pBR322 (treated free radical). The interaction between bioactive compounds and Mpro of SARS-CoV-2 was analyzed via molecular docking. The totals of phenolic compound and flavonoid compound from M. oleifera leaf infusion were 1.780 ± 5.00 µg gallic acid equivalent/g (µg GAE/g) and 322.91 ± 0.98 µg quercetin equivalent/g (µg QE/g), respectively. The five main bioactive compounds involved in the infusion were detected by LC-MS. Three of these were flavonoid glucosides, namely quercetin 3-O-glucoside, kaempferol 3-O-neohesperidoside, and kaempferol 3-α-L-dirhamnosyl-(1→4)-β-D-glucopyranoside. The other two compounds were undulatoside A, which belongs to chromone-derived flavonoids, and gentiatibetine, which belongs to alkaloids. The antioxidant activity of M. oleifera leaf infusion was IC50 8.19 ± 0.005 µg/mL, which is stronger than the standard butylated hydroxytoluene (BHT) IC50 11.60 ± 0.30 µg/mL. The infusion has an antimutagenic effect and therefore protects against deoxyribonucleic acid (DNA) damage. In silico studies showed that the five main bioactive compounds have an antiviral capacity. There were strong energy bonds between Mpro molecules and gentiatibetine, quercetin, undulatoside A, kaempferol 3-o-neohesperidoside, and quercetin 3-O-glucoside. Their binding energy values are −5.1, −7.5, −7.7, −5.7, and −8.2 kcal/mol, respectively. Their antioxidant activity, ability to maintain DNA integrity, and antimutagenic properties were more potent than the positive controls. It can be concluded that leaf infusion of M. oleifera does provide a promising herbal drink with good antioxidant, antimutagenic, and antivirus capacities. 相似文献
912.
Antonio Salatino 《Molecules (Basel, Switzerland)》2022,27(14)
Propolis has gained wide popularity over the last decades in several parts of the world. In parallel, the literature about propolis composition and biological properties increased markedly. A great number of papers have demonstrated that propolis from different parts of the world is composed mainly of phenolic substances, frequently flavonoids, derived from plant resins. Propolis has a relevant role in increasing the social immunity of bee hives. Experimental evidence indicates that propolis and its components have activity against bacteria, fungi, and viruses. Mechanisms of action on bacteria, fungi, and viruses are known for several propolis components. Experiments have shown that propolis may act synergistically with antibiotics, antifungals, and antivirus drugs, permitting the administration of lower doses of drugs and higher antimicrobial effects. The current trend of growing resistance of microbial pathogens to the available drugs has encouraged the introduction of propolis in therapy against infectious diseases. Because propolis composition is widely variable, standardized propolis extracts have been produced. Successful clinical trials have included propolis extracts as medicine in dentistry and as an adjuvant in the treatment of patients against COVID-19. Present world health conditions encourage initiatives toward the spread of the niche of propolis, not only as traditional and alternative medicine but also as a relevant protagonist in anti-infectious therapy. Production of propolis and other apiary products is environmentally friendly and may contribute to alleviating the current crisis of the decline of bee populations. Propolis production has had social-economic relevance in Brazil, providing benefits to underprivileged people. 相似文献
913.
Anna Tesei Michela Cortesi Martina Bedeschi Noemi Marino Giacomo Rossino Roberta Listro Daniela Rossi Pasquale Linciano Simona Collina 《Molecules (Basel, Switzerland)》2022,27(14)
Different pathological conditions, including viral infections and cancer, can have a massive impact on the endoplasmic reticulum (ER), causing severe damage to the cell and exacerbating the disease. In particular, coronavirus infections, including SARS coronavirus-2 (SARS-CoV-2), responsible for COVID-19, cause ER stress as a consequence of the enormous amounts of viral glycoproteins synthesized, the perturbation of ER homeostasis and the modification of ER membranes. Therefore, ER has a central role in the viral life cycle, thus representing one of the Achilles’ heels on which to focus therapeutic intervention. On the other hand, prolonged ER stress has been demonstrated to promote many pro-tumoral attributes in cancer cells, having a key role in tumor growth, metastasis and response to therapies. In this report, adopting a repurposing approach of approved drugs, we identified the antiplatelet agent ticlopidine as an interferent of the unfolded protein response (UPR) via sigma receptors (SRs) modulation. The promising results obtained suggest the potential use of ticlopidine to counteract ER stress induced by viral infections, such as COVID-19, and cancer. 相似文献
914.
Graham J. Moore Harry Ridgway Konstantinos Kelaidonis Christos T. Chasapis Irene Ligielli Thomas Mavromoustakos Joanna Bojarska John M. Matsoukas 《Molecules (Basel, Switzerland)》2022,27(15)
Angiotensin receptor blockers (ARBs) used in the treatment of hypertension and potentially in SARS-CoV-2 infection exhibit inverse agonist effects at angiotensin AR1 receptors, suggesting the receptor may have evolved to accommodate naturally occurring angiotensin ‘antipeptides’. Screening of the human genome has identified a peptide (EGVYVHPV) encoded by mRNA, complementary to that encoding ANG II itself, which is an inverse agonist. Thus, opposite strands of DNA encode peptides with opposite effects at AR1 receptors. Agonism and inverse agonism at AR1 receptors can be explained by a receptor ‘switching’ between an activated state invoking receptor dimerization/G protein coupling and an inverse agonist state mediated by an alternative/second messenger that is slow to reverse. Both receptor states appear to be driven by the formation of the ANG II charge-relay system involving TyrOH-His/imidazole-Carboxylate (analogous to serine proteases). In this system, tyrosinate species formed are essential for activating AT1 and AT2 receptors. ANGII is also known to bind to the zinc-coordinated metalloprotease angiotensin converting enzyme 2 (ACE2) used by the COVID-19 virus to enter cells. Here we report in silico results demonstrating the binding of a new class of anionic biphenyl-tetrazole sartans (‘Bisartans’) to the active site zinc atom of the endopeptidase Neprilysin (NEP) involved in regulating hypertension, by modulating humoral levels of beneficial vasoactive peptides in the RAS such as vasodilator angiotensin (1–7). In vivo and modeling evidence further suggest Bisartans can inhibit ANG II-induced pulmonary edema and may be useful in combatting SARS-CoV-2 infection by inhibiting ACE2-mediated viral entry to cells. 相似文献
915.
This paper, “Multivariate Dynamic Modeling for Bayesian Forecasting of Business Revenue,” proposes a novel Bayesian approach based on dynamic linear models to share information from different sectors, LSG (Local Store Group), and item category, through the use of auxiliary information (the discount information). The authors demonstrate the feasibility of parallel computing with multiple item categories, making the Bayesian method highly scalable. The proposed method in the paper should have wide applicability in inventory and revenue management. We suggest in this discussion potential areas for further development. 相似文献
916.
Bwalya A. Witika Pedzisai A. Makoni Larry L. Mweetwa Pascal V. Ntemi Melissa T. R. Chikukwa Scott K. Matafwali Chiluba Mwila Steward Mudenda Jonathan Katandula Roderick B. Walker 《Molecules (Basel, Switzerland)》2020,25(24)
The current COVID-19 pandemic has tested the resolve of the global community with more than 35 million infections worldwide and numbers increasing with no cure or vaccine available to date. Nanomedicines have an advantage of providing enhanced permeability and retention and have been extensively studied as targeted drug delivery strategies for the treatment of different disease. The role of monocytes, erythrocytes, thrombocytes, and macrophages in diseases, including infectious and inflammatory diseases, cancer, and atherosclerosis, are better understood and have resulted in improved strategies for targeting and in some instances mimicking these cell types to improve therapeutic outcomes. Consequently, these primary cell types can be exploited for the purposes of serving as a “Trojan horse” for targeted delivery to identified organs and sites of inflammation. State of the art and potential utilization of nanocarriers such as nanospheres/nanocapsules, nanocrystals, liposomes, solid lipid nanoparticles/nano-structured lipid carriers, dendrimers, and nanosponges for biomimicry and/or targeted delivery of bioactives to cells are reported herein and their potential use in the treatment of COVID-19 infections discussed. Physicochemical properties, viz., hydrophilicity, particle shape, surface charge, composition, concentration, the use of different target-specific ligands on the surface of carriers, and the impact on carrier efficacy and specificity are also discussed. 相似文献
917.
The global emergency caused by COVID-19 makes the discovery of drugs capable of inhibiting SARS-CoV-2 a priority, to reduce the mortality and morbidity of this disease. Repurposing approved drugs can provide therapeutic alternatives that promise rapid and ample coverage because they have a documented safety record, as well as infrastructure for large-scale production. The main protease of SARS-CoV-2 (Mpro) is an excellent therapeutic target because it is critical for viral replication; however, Mpro has a highly flexible active site that must be considered when performing computer-assisted drug discovery. In this work, potential inhibitors of the main protease (Mpro) of SARS-Cov-2 were identified through a docking-assisted virtual screening procedure. A total of 4384 drugs, all approved for human use, were screened against three conformers of Mpro. The ligands were further studied through molecular dynamics simulations and binding free energy analysis. A total of nine currently approved molecules are proposed as potential inhibitors of SARS-CoV-2. These molecules can be further tested to speed the development of therapeutics against COVID-19. 相似文献
918.
Low levels of micronutrients have been associated with adverse clinical outcomes during viral infections. Therefore, to maximize the nutritional defense against infections, a daily allowance of vitamins and trace elements for malnourished patients at risk of or diagnosed with coronavirus disease 2019 (COVID-19) may be beneficial. Recent studies on COVID-19 patients have shown that vitamin D and selenium deficiencies are evident in patients with acute respiratory tract infections. Vitamin D improves the physical barrier against viruses and stimulates the production of antimicrobial peptides. It may prevent cytokine storms by decreasing the production of inflammatory cytokines. Selenium enhances the function of cytotoxic effector cells. Furthermore, selenium is important for maintaining T cell maturation and functions, as well as for T cell-dependent antibody production. Vitamin C is considered an antiviral agent as it increases immunity. Administration of vitamin C increased the survival rate of COVID-19 patients by attenuating excessive activation of the immune response. Vitamin C increases antiviral cytokines and free radical formation, decreasing viral yield. It also attenuates excessive inflammatory responses and hyperactivation of immune cells. In this mini-review, the roles of vitamin C, vitamin D, and selenium in the immune system are discussed in relation to COVID-19. 相似文献
919.
920.
A novel magnetic photocatalyst MoS2-SrFe12O19 was successfully synthesized via a facile and reliable hydrothermal method. Flower-shaped nanospheres MoS2 was compactly decorated with hexagon nanoplate SrFe12O19, which formed a new p-n heterojunction. The superiority of this heterojunction structure has validated by characterizations and spectroscopic technique. Importantly, the MoS2-SrFe12O19 composite presents remarkable photocatalytic activity for the degradation of organic dyes (RhB and MB), far exceeding those for the pure MoS2 and SrFe12O19. In particular, the degradation rate of RhB reached to 96.5% after only 120 min photocatalytic reaction for the composite MoS2-SrFe12O19 (10 wt%). Based on the experiments and mechanism research, this magnetic photocatalyst can facilitate the separation of photogenerated electron-hole pairs, inhibit the recombination and prolong lifespan of charge. It is attributed to its unique composite structure and intimate interfacial contact, which can obtain a higher light utilization and electron transit path. In addition, MoS2-SrFe12O19 can be rapidly separated (5–10 seconds) and recycled under an external magnetic field, which verifies the satisfactory magnetism and reusability of the composite (Ms = 10.1 emu g–1, Mr = 3.5 emu g–1, Hci = 1407.7 Oe). Overall, this work provides a new insight for the recyclable photocatalytic systems with multi-functionalities. 相似文献