全文获取类型
收费全文 | 491篇 |
免费 | 26篇 |
国内免费 | 5篇 |
专业分类
化学 | 355篇 |
晶体学 | 10篇 |
力学 | 23篇 |
数学 | 30篇 |
物理学 | 104篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 16篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 20篇 |
2016年 | 32篇 |
2015年 | 32篇 |
2014年 | 33篇 |
2013年 | 57篇 |
2012年 | 33篇 |
2011年 | 51篇 |
2010年 | 30篇 |
2009年 | 29篇 |
2008年 | 23篇 |
2007年 | 22篇 |
2006年 | 12篇 |
2005年 | 15篇 |
2004年 | 10篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 7篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有522条查询结果,搜索用时 15 毫秒
131.
M. Samee M. Gadwal Shrikrishina D. Sartale Vikas L. Mathe Habib M. Pathan 《Electrochemistry communications》2009,11(8):1711-1713
The patterned Co layers deposited on the scratched Cu surfaces were investigated with the use of the scanning electron microscopy. Patterned cobalt thin films were electrochemically deposited from the cobalt sulfate bath at room temperature. Pattering of cobalt was carried out by simple means of substrate scratching. Gentle scratching induces a direct pattering of cobalt from vertical to horizontal. The prepared pattered films were characterized for their structural, surface morphological and compositional properties by means of X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. X-ray diffraction studies reveal that the films are of cobalt. From the SEM images fabrication of patterns of cobalt is apparent. This work demonstrates a novel approach for obtaining patterned cobalt for many technological applications. 相似文献
132.
Mazaahir?KidwaiEmail author Poonam?Mothsra Vikas?Bansal Ritu?Goyal 《Monatshefte für Chemie / Chemical Monthly》2006,137(9):1189-1194
Summary. Elemental iodine is used as an efficient catalyst for the synthesis of 2,4,5-triarylimidazoles in excellent yields via condensation of benzoin, ammonium acetate, and aromatic aldehydes. This is a simple, one-pot, high yielding technique using
cheap, non-toxic iodine in catalytic amounts. 相似文献
133.
Vikas Vikram Singh Abdel Lisser 《Journal of Optimization Theory and Applications》2018,178(3):998-1013
We consider a two-player random bimatrix game where each player is interested in the payoffs which can be obtained with certain confidence. The payoff function of each player is defined using a chance constraint. We consider the case where the entries of the random payoff matrix of each player jointly follow a multivariate elliptically symmetric distribution. We show an equivalence between the Nash equilibrium problem and the global maximization of a certain mathematical program. The case where the entries of the payoff matrices are independent normal/Cauchy random variables is also considered. The case of independent normally distributed random payoffs can be viewed as a special case of a multivariate elliptically symmetric distributed random payoffs. As for Cauchy distribution, we show that the Nash equilibrium problem is equivalent to the global maximization of a certain quadratic program. Our theoretical results are illustrated by considering randomly generated instances of the game. 相似文献
134.
Raghunath B. Toche Muddassar A. Kazi Shivaraj P. Patil Shrikant B. Kanawade Madhukar N. Jachak 《Journal of fluorescence》2010,20(5):1129-1137
Series of quinolone C3-substituted pyrazolines, isoxazolines, pyridines and pyrimidines were synthesized in good yields by the cyclocondensation
reactions of 1, 2-unsaturated ketones and hydrazines, hydroxylamine hydrochloride and dimedone respectively. The quinolone
derivatives (3, 5 and 7) were synthesized and further studied for their photophysical properties. High absorption and quantum
yield are found for N1-phenyl and C3,4-dimethoxy substituents on phenyl ring (3h). Energy optimization by PM6 methods showed high stability required for selection
of suitable candidates to be use as future blue emitters. 相似文献
135.
Anna N. Gidd Madhukar D. Bhand Gavisiddappa S. Gokavi 《Transition Metal Chemistry》1995,20(4):367-368
Summary The complementary reaction between TlI and AuCl
inf4
sup–
was studied in a 3.0 mol dm–3 HCl medium. The active species of oxidant and reductant were found to be HAuCl4 and TlCl
inf2
sup–
, respectively. A mechanism involving these reactive species is proposed, in agreement with the results obtained. 相似文献
136.
The role of nuclear degrees of freedom in modifying the electron or exciton transfer rates between molecules is investigated. In addition to the usual Franck-Condon overlap factors which arise from the overlaps of initial and final vibrational states, we discuss a dependence of the transfer integral upon nuclear motions, a dependence which has been often cited, but nearly always ignored, in the usual dynamical theories of transfer processes. We show, within a Bom-Oppenheimer treatment, that the transfer integral dependence upon librational, rotational and vibrational modes can profoundly change both the rate itself and its functional dependences (upon temperature, upon orientation, etc.). Using a simple cosine form for the dependence of the transfer integral upon the modifying nuclear mode and a simple displaced-oscillator transformation, we obtain a closed-form solution for the transfer rate, which includes a new overlap factor arising from the dependence of the transfer integral upon nuclear coordinates. Some general remarks about the role of this dependence are made, and applications to particular transfer systems are briefly discussed. 相似文献
137.
Mazaahir Kidwai Poonam Mothsra Vikas Bansal Ritu Goyal 《Monatshefte für Chemie / Chemical Monthly》2006,120(5):1189-1194
Elemental iodine is used as an efficient catalyst for the synthesis of 2,4,5-triarylimidazoles in excellent yields via condensation of benzoin, ammonium acetate, and aromatic aldehydes. This is a simple, one-pot, high yielding technique using
cheap, non-toxic iodine in catalytic amounts. 相似文献
138.
Bhargav Shreevatsa Chandan Dharmashekara Vikas Halasumane Swamy Meghana V. Gowda Raghu Ram Achar Vivek Hamse Kameshwar Rajesh Kumar Thimmulappa Asad Syed Abdallah M. Elgorban Salim S. Al-Rejaie Joaquín Ortega-Castro Juan Frau Norma Flores-Holguín Chandan Shivamallu Shiva Prasad Kollur Daniel Glossman-Mitnik 《Molecules (Basel, Switzerland)》2021,26(22)
NAD(P)H:quinone acceptor oxidoreductase-1 (NQO1) is a ubiquitous flavin adenine dinucleotide-dependent flavoprotein that promotes obligatory two-electron reductions of quinones, quinonimines, nitroaromatics, and azo dyes. NQO1 is a multifunctional antioxidant enzyme whose expression and deletion are linked to reduced and increased oxidative stress susceptibilities. NQO1 acts as both a tumor suppressor and tumor promoter; thus, the inhibition of NQO1 results in less tumor burden. In addition, the high expression of NQO1 is associated with a shorter survival time of cancer patients. Inhibiting NQO1 also enables certain anticancer agents to evade the detoxification process. In this study, a series of phytobioactives were screened based on their chemical classes such as coumarins, flavonoids, and triterpenoids for their action on NQO1. The in silico evaluations were conducted using PyRx virtual screening tools, where the flavone compound, Orientin showed a better binding affinity score of −8.18 when compared with standard inhibitor Dicumarol with favorable ADME properties. An MD simulation study found that the Orientin binding to NQO1 away from the substrate-binding site induces a potential conformational change in the substrate-binding site, thereby inhibiting substrate accessibility towards the FAD-binding domain. Furthermore, with this computational approach we are offering a scope for validation of the new therapeutic components for their in vitro and in vivo efficacy against NQO1. 相似文献
139.
An efficient diethyl ether-based soxhlet protocol to quantify faecal sterols from catchment waters 总被引:2,自引:0,他引:2
A study was conducted to evaluate the efficiency and reproducibility of a diethyl ether-based soxhlet extraction procedure for faecal sterols occurring from catchment waters. Water samples spiked with a mixture of faecal sterols were filtered and analytes were extracted using the diethyl ether-based soxhlet method and the Bligh and Dyer chloroform extraction process. For diethyl ether-based soxhlet extraction procedure, solvent extracts were saponified with 100 microL of 10% KOH in methanol (100 degrees C/120 min) and then acidified with 60 microL of 6M HCl. Lipid contents were extracted by ethanol (0.5 mL) from the saponification products. The lipid extracts were then reacted with 100 microL of bis(trimethyl)trifluoroacetamide (BSTFA) containing 1% trimethyl chlorosilane (100 degrees C/60 min) to form the trimethylsilyl (TMS) derivatives. The derivatised extracts were then analyzed by gas chromatography-mass spectrometry. For sterol concentrations ranging from 35 to 175 microg mL(-1), the soxhlet-based extraction process yielded the following recovery efficiencies for coprostanol (101%), epicoprostanol (97%), cholesterol (97%), dihydrocholesterol (97%) and 5alpha-cholestane (111%), whereas the Bligh and Dyer process yielded recoveries of 32, 41, 0, 36 and 51%, respectively. The results suggested that the diethyl ether-based soxhlet extraction method was more efficient and reproducible than the Bligh and Dyer chloroform extraction process for the analyses of trace levels of faecal sterols from water samples. Moreover, it was revealed that the diethyl ether-based soxhlet extraction method used less solvent and was logistically easier. 相似文献
140.
Shilpa Raina Vikas Sharma Zahid Nabi Sheikh Navneet Kour Shashank K. Singh Ali Zari Talal A. Zari Hesham F. Alharby Khalid Rehman Hakeem 《Molecules (Basel, Switzerland)》2022,27(7)
The current study was conducted to examine the in vitro anticancer potential of Cordia dichotoma (bark, leaves, pulp and seed). The plant material was collected from UT of J&K and methodical bioassays were carried out on ten human cancer cell lines (Michigan Cancer Foundation-7 (MCF-7), M.D. Anderson-Metastatic Breast (MDA-MB-231), Neuroblastoma-2a (N2A), SH-SY5Y, U-251, HCT-116, SW-620, A-549, MIA PaCa-2, Panc-1) from five different origins (breast, CNS, colon, lung, pancreas) respectively. Methanolic extracts were produced and fractions were then obtained from the extracts and evaluated for cytotoxicity. Mechanistic assays, HPLC, and GCMS profiling were performed on the highest active fraction. The Sulforhodamine B (SRB) assay determined the in vitro cytotoxicity. The findings revealed that the bark portion had in vitro cytotoxicity against the A-549 human lung cancer cell line. To our knowledge, this is the first study to show that the plant’s bark has anticancer properties and induced chromatin condensation, confirmed cell death via ROS generation, and significantly decreased colony formation in A-549 cell line from lung origin in a dose-dependent manner. Furthermore, HPLC and GCMS investigations indicated the presence of a number of bioactive molecules such as gallic acid (144,969.86) uV*sec, caffeic acid (104.26) uV*sec, ferulic acid (472.87) uV*sec, vanillic acid (13,775.39) uV*sec, palmitic acid (18.34%), cis vaccenic acid (28.81%), etc. and one of the compounds was reported for the first time from the bark. As a result of its promising efficacy, it may become an essential cancer chemopreventive or chemotherapeutic medication for patients with lung carcinoma. 相似文献