全文获取类型
收费全文 | 477篇 |
免费 | 26篇 |
国内免费 | 2篇 |
专业分类
化学 | 355篇 |
晶体学 | 12篇 |
力学 | 14篇 |
数学 | 50篇 |
物理学 | 74篇 |
出版年
2024年 | 1篇 |
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 16篇 |
2017年 | 18篇 |
2016年 | 15篇 |
2015年 | 18篇 |
2014年 | 22篇 |
2013年 | 33篇 |
2012年 | 15篇 |
2011年 | 39篇 |
2010年 | 17篇 |
2009年 | 21篇 |
2008年 | 19篇 |
2007年 | 32篇 |
2006年 | 20篇 |
2005年 | 30篇 |
2004年 | 14篇 |
2003年 | 22篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有505条查询结果,搜索用时 31 毫秒
501.
Molecular Diversity - Machine learning (ML) methods have attracted increasing interest in chemistry as in all fields of science in recent years. This method is of great importance for the design of... 相似文献
502.
Ajay Kumar Sandeep Kaur Sukhvinder Dhiman Prithvi Pal Singh Gaurav Bhatia Sharad Thakur Hardeep Singh Tuli Upendra Sharma Subodh Kumar Abdulmajeed G. Almutary Abdullah M. Alnuqaydan Arif Hussain Shafiul Haque Kuldeep Dhama Satwinderjeet Kaur 《Molecules (Basel, Switzerland)》2022,27(11)
Onosma bracteata Wall. is an important medicinal and immunity-enhancing herbs. This plant is commonly used in the preparation of traditional Ayurvedic drugs to treat numerous diseases. Inspired by the medicinal properties of this plant, the present study aimed to investigate the antiproliferative potential and the primary molecular mechanisms of the apoptotic induction against human osteosarcoma (MG-63) cells. Among all the fractions isolated from O. bracteata, ethyl acetate fraction (Obea) showed good antioxidant activity in superoxide radical scavenging assay and lipid peroxidation assay with an EC50 value of 95.12 and 80.67 µg/mL, respectively. Silica gel column chromatography of ethyl acetate (Obea) fraction of O. bracteata yielded a pure compound, which was characterized by NMR, FTIR, and HR-MS analysis and was identified as 1,2-benzene dicarboxylic acid, bis (2-methyl propyl) ester (BDCe fraction). BDCe fraction was evaluated for the antiproliferative potential against human osteosarcoma MG-63, human neuroblastoma IMR-32, and human lung carcinoma A549 cell lines by MTT assay and exhibited GI50 values of 37.53 μM, 56.05 μM, and 47.12 μM, respectively. In MG-63 cells, the BDCe fraction increased the level of ROS and simultaneously decreased the mitochondria membrane potential (MMP) potential by arresting cells at the G0/G1 phase, suggesting the initiation of apoptosis. Western blotting analysis revealed the upregulation of p53, caspase3, and caspase9 while the expressions of p-NF-κB, p-Akt and Bcl-xl were decreased. RT-qPCR studies also showed upregulation in the expression of p53 and caspase3 and downregulation in the expression of CDK2, Bcl-2 and Cyclin E genes. Molecular docking analysis displayed the interaction between BDCe fraction with p53 (−151.13 kcal/mol) and CDK1 (−133.96 kcal/mol). The results of the present work suggest that the BDCe fraction has chemopreventive properties against osteosarcoma (MG-63) cells through the induction of cell cycle arrest and apoptosis via Akt/NF-κB/p53 pathways. This study contributes to the understanding of the utilization of BDCe fraction in osteosarcoma treatment. 相似文献
503.
Muhammad Arif Rahim Ullah Maaz Ahmad Ahmad Ali Zahid Ullah Mohammad Ali Fakhria A. Al-Joufi Muhammad Zahoor Hassan Sher 《Molecules (Basel, Switzerland)》2022,27(11)
Biologically synthesized silver nanoparticles are emerging as attractive alternatives to chemical pesticides due to the ease of their synthesis, safety and antimicrobial activities in lower possible concentrations. In the present study, we have synthesized silver nanoparticles (AgNPs) using the aqueous extract of the medicinal plant Euphorbia wallichii and tested them against the plant pathogenic bacterium Xanthomonas axonopodis, the causative agent of citrus canker, via an in vitro experiment. The synthesized silver nanoparticles were characterized by techniques such as UV-Vis spectroscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis and transmission electron microscopy. Moreover, the plant species were investigated for phenolics, flavonoids and antioxidant activity. The antioxidant potential of the extract was determined against a DPPH radical. The extract was also evaluated for phenolic compounds using the HPLC technique. The results confirmed the synthesis of centered cubic, spherical-shaped and crystalline nanoparticles by employing standard characterization techniques. A qualitative and quantitative phytochemical analysis revealed the presence of phenolics (41.52 mg GAE/g), flavonoids (14.2 mg QE/g) and other metabolites of medicinal importance. Different concentrations (1000 µg/mL to 15.62 µg/mL—2 fold dilutions) of AgNPs and plant extract (PE) alone, and both in combination (AgNPs-PE), exhibited a differential inhibition of X. axanopodis in a high throughput antibacterial assay. Overall, AgNPs-PE was superior in terms of displaying significant antibacterial activity, followed by AgNPs alone. An appreciable antioxidant potential was recorded as well. The observed antibacterial and antioxidant potential may be attributed to eight phenolic compounds identified in the extract. The Euphorbia wallichii leaf-extract-induced synthesized AgNPs exhibited strong antibacterial activity against X. axanopodis, which could be exploited as effective alternative preparations against citrus canker in planta in a controlled environment. In addition, as a good source of phenolic compounds, the plant could be further exploited for potent antioxidants. 相似文献
504.
Arif Akhundov Dima Bardin Lida Kalinovskaya Tord Riemnann 《Fortschritte der Physik》1996,44(5):373-482
We give an exhaustive presentation of the semi-analytical approach to the model independent leptonic QED corrections to deep inelastic neutral current lepton-nucleon scattering. These corrections include photonic bremsstrahlung from and vertex corrections to the lepton current of the order φ(α) with soft photon exponentiation. A common treatment of these radiative corrections in several variables — leptonic, hadronic, mixed, Jaquet-Blondel variables — has been developed and double differential cross sections are calculated. In all sets of variables we use some structure functions, which depend on the hadronic variables and which do not have to be defined in the quark parton model. The remaining numerical integrations are twofold (for leptonic variables) or onefold (for all other variables). For the case of hadronic variables, all phase space integrals have been performed analytically. Numerical results are presented for a large kinematical range, covering fixed target as well as collider experiments at HERA or LEP⊗LHC, with a special emphasis on HERA physics. 相似文献
505.
Atta M. Arif Alan H. Cowley Robert M. Kren Donald L. Westmoreland 《Heteroatom Chemistry》1990,1(1):117-122
The phosphenium ion [(i-Pr2N)CIP]+ (1) reacts with crotonaldehyde dimethylhydrazone (2) to afford a product with a C3NP ring system (4) . The reaction of 1 with acetone azine (3) results in a novel tricyclic compound (6) which features a C2N2P2 and two C2N2P rings. The structures of 4 and 6 were established by X-ray crystallography. Compound 4 , C12H26AlCl3N3OP, crystallizes in the monoclinic space group P21/n with Z = 4, a = 15.400(6), b = 14.442(4), c = 9.206(3) Å, and β = 93.33(3)°. Compound 6 , C12H22Al2Cl6N4O2P2, crystallizes in the triclinic group P1 with Z = 1, a = 8.556(1), b = 9.782(1), c = 8.119(1) Å, α = 94.48(1), β = 104.97(1), and γ = 78.35(1)°. 相似文献