全文获取类型
收费全文 | 241篇 |
免费 | 20篇 |
专业分类
化学 | 165篇 |
晶体学 | 7篇 |
力学 | 12篇 |
数学 | 11篇 |
物理学 | 66篇 |
出版年
2023年 | 7篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 17篇 |
2012年 | 22篇 |
2011年 | 28篇 |
2010年 | 12篇 |
2009年 | 15篇 |
2008年 | 19篇 |
2007年 | 13篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 8篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1973年 | 1篇 |
1943年 | 1篇 |
1930年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有261条查询结果,搜索用时 15 毫秒
1.
Toshiro Watanabe Tapan Kumar Mazumder Shiro Nagai Keisuke Tsuji Shigeru Terabe 《Analytical sciences》2003,19(1):159-161
A micellar electrokinetic chromatography (MEKC) method was developed for estimating the angiotensin-I converting enzyme (ACE) inhibitory activity by separating the hippuric acid liberated in the ACE reaction mixture in the presence of an inhibitor, captopril. The hippuric acid was successfully separated and detected by MEKC with a 25 mM sodium dodecyl sulfate solution in a 25 mM phosphate-50 mM borate buffer at pH 7.0; the total analysis took about 5 min. A good linear relationship was observed between the inhibitor and the peak area of hippuric acid release. No significant difference in the ACE inhibitory activity (IC50) of captopril (an antihypertensive medicine) or autolyzed-mushrooms (functional foods) was observed between the conventional method and the MEKC method. The MEKC method was found to be a useful technique for a rapid assay of the ACE inhibitory activity. 相似文献
2.
This paper deals with the small-angle neutron scattering (SANS) investigation on solution-quenched PH13-8 Mo stainless steel.
From the nature of the variation of the functionality of the profiles for varying specimen thickness and also from the transmission
electron microscopy (TEM), it has been established that the small-angle scattering signal predominantly originates from the
block-like metallic carbide precipitates in the specimen. The contribution due to double Bragg reflection is not significant
in the present case. The single scattering profile has been extracted from the experimental profiles corresponding to different
values of specimen thickness. In order to avoid complexity and non-uniqueness of the multi-parameter minimization for randomly
oriented polydisperse block-like precipitate model, the data have been analyzed assuming randomly oriented polydisperse cylindrical
particle model with a locked aspect ratio. 相似文献
3.
Koushik Saha Benson Joseph Rongala Ramalakshmi Dr. R. S. Anju Dr. Babu Varghese Prof. Sundargopal Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(23):7871-7878
Thermolysis of [Cp*Ru(PPh2(CH2)PPh2)BH2(L2)] 1 (Cp*=η5‐C5Me5; L=C7H4NS2), with terminal alkynes led to the formation of η4‐σ,π‐borataallyl complexes [Cp*Ru(μ‐H)B{R‐C=CH2}(L)2] ( 2 a – c ) and η2‐vinylborane complexes [Cp*Ru(R‐C=CH2)BH(L)2] ( 3 a – c ) ( 2 a , 3 a : R=Ph; 2 b , 3 b : R=COOCH3; 2 c , 3 c : R=p‐CH3‐C6H4; L=C7H4NS2) through hydroboration reaction. Ruthenium and the HBCC unit of the vinylborane moiety in 2 a – c are linked by a unique η4‐interaction. Conversions of 1 into 3 a – c proceed through the formation of intermediates 2 a – c . Furthermore, in an attempt to expand the library of these novel complexes, chemistry of σ‐borane complex [Cp*RuCO(μ‐H)BH2L] 4 (L=C7H4NS2) was investigated with both internal and terminal alkynes. Interestingly, under photolytic conditions, 4 reacts with methyl propiolate to generate the η4‐σ,π‐borataallyl complexes [Cp*Ru(μ‐H)BH{R‐C=CH2}(L)] 5 and [Cp*Ru(μ‐H)BH{HC=CH‐R}(L)] 6 (R=COOCH3; L=C7H4NS2) by Markovnikov and anti‐Markovnikov hydroboration. In an extension, photolysis of 4 in the presence of dimethyl acetylenedicarboxylate yielded η4‐σ,π‐borataallyl complex [Cp*Ru(μ‐H)BH{R‐C=CH‐R}(L)] 7 (R=COOCH3; L=C7H4NS2). An agostic interaction was also found to be present in 2 a – c and 5 – 7 , which is rare among the borataallyl complexes. All the new compounds have been characterized in solution by IR, 1H, 11B, 13C NMR spectroscopy, mass spectrometry and the structural types were unequivocally established by crystallographic analysis of 2 b , 3 a – c and 5 – 7 . DFT calculations were performed to evaluate possible bonding and electronic structures of the new compounds. 相似文献
4.
Kinshuk Dasgupta D. Sen T. Mazumdar R. K. Lenka R. Tewari S. Mazumder J. B. Joshi S. Banerjee 《Journal of nanoparticle research》2012,14(3):728
For the first time, bamboo-shaped multiwalled carbon nanotubes, having diameter of the order of 50 nm, have been grown on
carbon black in a fluidized bed in bulk amount. The activation energy for the synthesis of the product was found out to be
around 33 kJ/mol in the temperature range of 700−900 °C. The carbon nanotubes were separated from the carbon black by preferential
oxidation of the later, the temperature of which was determined by thermogravimetry. The transmission electron microscopy
revealed different features of the nanotubes such as “Y” junction, bend, and catalyst filling inside the nanotubes. Small
angle neutron scattering was performed on the nanotubes synthesized at different temperatures. The data were fitted into a
suitable model in order to find out the average diameter, which decreases with increase in synthesis temperature. The Monte
Carlo simulation predicts the same behavior. Based on the above observations, a possible growth mechanism has been predicted.
The oscillation in carbon saturation value inside the catalyst in the fluidized bed has been indicated as the responsible
factor for the bamboo-shaped structure. 相似文献
5.
Michael Koch Karthikeyan Perumal Dr. Olivier Blacque Dr. Jai Anand Garg Dr. Ramanathan Saiganesh Dr. Senthamaraikannan Kabilan Prof. Dr. Kallupattu Kuppusamy Balasubramanian Dr. Koushik Venkatesan 《Angewandte Chemie (International ed. in English)》2014,53(25):6378-6382
Design of highly efficient phosphorescent emitters based on metal‐ and heavy atom‐free boron compounds has been demonstrated by taking advantage of the singlet fission process. The combination of a suitable molecular scaffold and appropriate electronic nature of the substituents has been utilized to tailor the phosphorescence emission properties in solution, neat solid, and in doped PMMA thin films. 相似文献
6.
AC Conduction and Time–Temperature Superposition Scaling in a Reduced Graphene Oxide–Zinc Sulfide Nanocomposite 下载免费PDF全文
Koushik Chakraborty Poulomi Das Sankalpita Chakrabarty Dr. Tanusri Pal Dr. Surajit Ghosh 《Chemphyschem》2016,17(10):1518-1523
We report, herein, the results of an in depth study and concomitant analysis of the AC conduction [σ′(ω): f=20 Hz to 2 MHz] mechanism in a reduced graphene oxide–zinc sulfide (RGO–ZnS) composite. The magnitude of the real part of the complex impedance decreases with increase in both frequency and temperature, whereas the imaginary part shows an asymptotic maximum that shifts to higher frequencies with increasing temperature. On the other hand, the conductivity isotherm reveals a frequency‐independent conductivity at lower frequencies subsequent to a dispersive conductivity at higher frequencies, which follows a power law [σ′(ω)∝ωs] within a temperature range of 297 to 393 K. Temperature‐independent frequency exponent ′s′ indicates the occurrence of phonon‐assisted simple quantum tunnelling of electrons between the defects present in RGO. Finally, this sample follows the “time–temperature superposition principle”, as confirmed from the universal scaling of conductivity isotherms. These outcomes not only pave the way for increasing our elemental understanding of the transport mechanism in the RGO system, but will also motivate the investigation of the transport mechanism in other order–disorder systems. 相似文献
7.
Synthesis of five-, six-, seven-, eight-, and nine-membered cyclic α-hydrazino acids from a common starting material ‘diethylmalonate’ with 26, 16, 34, 13.5, and 13.33% overall yields is described. Sequential allylation or homoallylation and electrophilic amination followed by cyclization gave the desired rings. The methyl esters of eight- and nine-membered rings were synthesized by RCM and the corresponding free acids were generated after hydrolysis in the presence of 1 M BBr3 solution in DCM. 相似文献
8.
We present a novel mechanism of pattern formation behind a flat interface during directional solidification of peritectic alloys. It is shown through computational modeling that irregular oscillatory thermosolutal convection can develop in the vertical Bridgman system, even with bottom seeding and bottom cooling. The coupling of the flow oscillation near the interface with solidification leads to ordered layered structures in the solidified crystal, which agree closely with earlier experimental results. 相似文献
9.
Yao‐Rong Zheng Hai‐Bo Yang Prof. Dr. Koushik Ghosh Liang Zhao Dr. Peter J. Stang Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(29):7203-7214
The self‐organization of multicomponent supramolecular systems involving a variety of two‐dimensional (2 D) polygons and three‐dimensional (3 D) cages is presented. Nine self‐organizing systems, SS1 – SS9 , have been studied. Each involves the simultaneous mixing of organoplatinum acceptors and pyridyl donors of varying geometry and their selective self‐assembly into three to four specific 2 D (rectangular, triangular, and rhomboid) and/or 3 D (triangular prism and distorted and nondistorted trigonal bipyramidal) supramolecules. The formation of these discrete structures is characterized using NMR spectroscopy and electrospray ionization mass spectrometry (ESI‐MS). In all cases, the self‐organization process is directed by: 1) the geometric information encoded within the molecular subunits and 2) a thermodynamically driven dynamic self‐correction process. The result is the selective self‐assembly of multiple discrete products from a randomly formed complex. The influence of key experimental variables ‐ temperature and solvent ‐ on the self‐correction process and the fidelity of the resulting self‐organization systems is also described. 相似文献
10.
The mechanism of action of inosine-uridine nucleoside hydrolase has been investigated by long-term molecular dynamics (MD) simulation in TIP3P water using stochastic boundary conditions. Five MD studies have been performed with enzyme substrate complex (E.S), enzyme substrate complex with protonated His241 (EH.S), enzyme transition state complex (E.TS), enzyme transition state complex with protonated His241 (EH.TS), and His241Ala transition state complex E(H241A).TS. Special attention has been given to the role of His241, which has been considered as the general acid catalyst to assist departure of the leaving nucleobase on the basis of its location in the active site in the X-ray crystal structure (). Yet on the basis of the location in the active site, Tyr229 is closer to the aniline ring of pAPIR as compared to His241. On initiation of MD simulations, His241 does not approach the nucleobase in the structures of EH.S, E.S, EH.TS, and E.TS. In the solvated enzyme, Tyr229, which is a member of the hydrogen bonding network inosine O2'.Asp14.His241.Tyr229.inosine N7, serves as a proton source to the leaving nucleobase. The loss of significant activity of His241Ala mutant is shown to be related to the disruption of the above hydrogen bonded network and the distancing of Tyr229 from inosine N7. The structures of the enzyme complexes with substrate or TS are not visibly altered on protonation of His241, a most unusual outcome. The bell-shaped pH dependence upon pK(app)'s of 7.1 and 9.1 may be attributed to the necessity of the dissociation of Asp10 or Asp15 and the acid form of Tyr229, respectively. In TS, the residue Ile81 migrated closer, whereas Arg233 moved away from the nucleobase. The probability of ribooxocarbenium ion stabilization by Asn168 and Asp14 is discussed. The Asp14-CO(2)(-) is hydrogen bonded to the ribose 2'-OH for 96% of the MD simulation time. Nucleophilic addition of water138 to ribooxocarbenium ion is suggested to be assisted by the proton shuttle from water138 --> Asp10 --> Asp15 --> water pool. An anticorrelation motion between Tyr229-OH and Asn168-OD1 in EH.S and E.S is observed. The relationship of this anticorrelated motion to mechanism, if any, deserves further exploration, perhaps the formation of a near attack conformation. 相似文献