全文获取类型
收费全文 | 282篇 |
免费 | 15篇 |
专业分类
化学 | 218篇 |
晶体学 | 11篇 |
力学 | 3篇 |
数学 | 8篇 |
物理学 | 57篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 15篇 |
2021年 | 18篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 16篇 |
2016年 | 16篇 |
2015年 | 10篇 |
2014年 | 23篇 |
2013年 | 19篇 |
2012年 | 20篇 |
2011年 | 23篇 |
2010年 | 9篇 |
2009年 | 11篇 |
2008年 | 18篇 |
2007年 | 13篇 |
2006年 | 9篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有297条查询结果,搜索用时 15 毫秒
51.
The matrix isolation technique has been combined with infrared spectroscopy and theoretical calculations to explore the reaction of (CH3)2Zn with O3 over a range of time scales. Upon twin jet deposition, an initial cage pair complex was observed, along with formation of the novel H3COZnCH3 species. Subsequent UV irradiation destroyed the complex and greatly increased the yield of H3COZnCH3. An extensive set of bands were seen for this molecule, and (18)O spectroscopic data were obtained as well. The identification of this species was supported by theoretical calculations at the B3LYP/6-311++g(d,2p) level. Merged jet deposition led to a very different set of products, including H2CO, CH3OH and C2H6, identifications that were confirmed by (18)O substitution. In addition, a new variable length concentric deposition technique was developed to permit study of the time scales between twin (relatively short) and merged (relatively longer) reaction times. Mechanistic inferences for this reaction are discussed. 相似文献
52.
Priya K. Patel 《Molecular Crystals and Liquid Crystals》2016,634(1):41-49
A novel thermotropically mesomorphic, meta-substituted nitro group of chalconyl ester series, RO-C6H4-COO-C6H3-(NO2)-CO-CH=CH-C6H4OC12H25(n) (para) is synthesized and studied with an aim to establish the relation between molecular structure and the mesomorphism with reference to changing molecular flexibility in presence of nitro lateral group. Novel homologous series consist of thirteen homologs (C1–C18) whose mesomorphism commences from C5 homolog as enantiotropic nematogenic with absence of smectic property, even in the monotropic condition. Transition temperatures of novel substances were determined by an optical polarizing microscope, equipped with a heating stage (POM). Textures of a nematic phase are threaded or Schlieren. N-I transition curve exhibited narrow, sharp and short odd-even effect; with deviating trend in a phase diagram. Analytical, spectral and thermal data confirmed the molecular structures of homologs. Thermal stability for nematic is 182.89°C, whose mesophase lengths minimum to maximum ranges from 17°C to 45°C and it is an upper middle ordered melting type series. Group efficiency order for nematic is series 1 > series Y > series X, as derived from comparative study of structurally similar analogous series. 相似文献
53.
Umezawa N Kalia RK Nakano A Vashista P Shimojo F 《The Journal of chemical physics》2007,126(23):234702
We have investigated the decomposition and chemisorption of a 1,3,5-trinitro-1,3,5-triazine (RDX) molecule on Al(111) surface using molecular dynamics simulations, in which interatomic forces are computed quantum mechanically in the framework of the density functional theory (DFT). The real-space DFT calculations are based on higher-order finite difference and norm-conserving pseudopotential methods. Strong attractive forces between oxygen and aluminum atoms break N-O and N-N bonds in the RDX and, subsequently, the dissociated oxygen atoms and NO molecules oxidize the Al surface. In addition to these Al surface-assisted decompositions, ring cleavage of the RDX molecule is also observed. These reactions occur spontaneously without potential barriers and result in the attachment of the rest of the RDX molecule to the surface. This opens up the possibility of coating Al nanoparticles with RDX molecules to avoid the detrimental effect of oxidation in high energy density material applications. 相似文献
54.
Priya Malpani Kishore Thapliyal Nasir Alam Anirban Pathak Venkatakrishnan Narayanan Subhashish Banerjee 《Annalen der Physik》2019,531(11)
Quantum phase properties of photon added and subtracted displaced Fock states (and their limiting cases) are investigated from a number of perspectives, and it is shown that the quantum phase properties are dependent on the quantum state engineering operations performed. Specifically, the analytic expressions for quantum phase distributions and angular Q distribution as well as measures of quantum phase fluctuation and phase dispersion are obtained. The uniform phase distribution of the initial Fock states is observed to be transformed by the unitary operation (i.e., displacement operator) into non‐Gaussian shape, except for the initial vacuum state. It is observed that the phase distribution is symmetric with respect to the phase of the displacement parameter and becomes progressively narrower as its amplitude increases. The non‐unitary (photon addition/subtraction) operations make it even narrower in contrast to the Fock parameter, which leads to broadness. The photon subtraction is observed to be a more powerful quantum state engineering tool in comparison to the photon addition. Further, one of the quantum phase fluctuation parameters is found to reveal the existence of antibunching in both the engineered quantum states under consideration. Finally, the relevance of the engineered quantum states in the quantum phase estimation is also discussed. 相似文献
55.
Priya Gupta David Noone Joseph Galewsky Colm Sweeney Bruce H. Vaughn 《Rapid communications in mass spectrometry : RCM》2009,23(16):2534-2542
This study demonstrates the application of Wavelength‐Scanned Cavity Ring‐Down Spectroscopy (WS‐CRDS) technology which is used to measure the stable isotopic composition of water. This isotopic water analyzer incorporates an evaporator system that allows liquid water as well as water vapor to be measured with high precision. The analyzer can measure HO, HO and HD16O content of the water sample simultaneously. The results of a laboratory test and two field trials with this analyzer are described. The results of these trials show that the isotopic water analyzer gives precise, accurate measurements with little or no instrument drift for the two most common isotopologues of water. In the laboratory the analyzer has a precision of 0.5 per mil for δD and 0.1 per mil for δ18O which is similar to the precision obtained by laboratory‐based isotope ratio mass spectrometers. In the field, when measuring vapor samples, the analyzer has a precision of 1.0 per mil for δD and 0.2 per mil for δ18O. These results demonstrate that the isotopic water analyzer is a powerful tool that is appropriate for use in a wide range of applications and environments. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
56.
Priya Arora Krishan Kumar R. K. Moudgil 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(4):76
We have studied spin-resolved correlations in the warm-dense homogeneous electron gas by determining the linear density and spin-density response functions, within the dynamical self-consistent mean-field theory of Singwi et al. The calculated spin-resolved pair-correlation function g σ σ′(r) is compared with the recent restricted path-integral Monte Carlo (RPIMC) simulations due to Brown et al. [Phys. Rev. Lett. 110, 146405 (2013)], while interaction energy E int and exchange-correlation free energy F xc with the RPIMC and very recent ab initio quantum Monte Carlo (QMC) simulations by Dornheim et al. [Phys. Rev. Lett. 117, 156403 (2016)]. g ↑↓(r) is found to be in good agreement with the RPIMC data, while a mismatch is seen in g ↑↑(r) at small r where it becomes somewhat negative. As an interesting result, it is deduced that a non-monotonic T-dependence of g(0) is driven primarily by g ↑↓(0). Our results of E int and F xc exhibit an excellent agreement with the QMC study due to Dornheim et al., which deals with the finite-size correction quite accurately. We observe, however, a visible deviation of E int from the RPIMC data for high densities (~8% at r s = 1). Further, we have extended our study to the fully spin-polarized phase. Again, with the exception of high density region, we find a good agreement of E int with the RPIMC data. This points to the need of settling the problem of finite-size correction in the spin-polarized phase also. Interestingly, we also find that the thermal effects tend to oppose spatial localization as well as spin polarization of electrons. 相似文献
57.
Manandhar Suman Sankhe Runali Priya Keerthi Hari Gangadhar Kumar B. Harish Mehta Chetan H. Nayak Usha Y. Pai K. Sreedhara Ranganath 《Molecular diversity》2022,26(5):2793-2811
Molecular Diversity - Wnt signaling pathway is an evolutionarily conserved pathway responsible for neurogenesis, axon outgrowth, neuronal polarity, synapse formation, and maintenance.... 相似文献
58.
59.
The oxidation of alcohols to aldehydes using stoichiometric 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) in CH(2)Cl(2) at room temperature is a highly selective process favoring reaction at the carbinol center best able to accommodate a positive charge. The oxidation of aldehydes to carboxylic acids by 1 in wet acetonitrile is also selective; the rate of the process correlates with the concentration of aldehyde hydrate. A convenient and high yield method for oxidation of alcohols directly to carboxylic acids has been developed. 相似文献
60.
Naked eye detection of nitric oxide release from nitrosothiols aided by gold nanoparticles 总被引:1,自引:0,他引:1
In this work we have demonstrated that nitric oxide can be monitored spectrophotometrically using cyclodextrin encapsulated ferrocene. The detection course showed the colour change from yellow to blue which can be detected with the naked eye. Also we describe the catalytic effect of gold nanoparticles in enhancing nitric oxide release from S-nitrosothiols. 相似文献