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91.
Saranya G Kolandaivel P Senthilkumar K 《The journal of physical chemistry. A》2011,115(51):14647-14656
Fluoranthene and benzo[k]fluoranthene-based oligoarenes are good candidates for organic light-emitting diodes (OLEDs). In this work, the electronic structure and optical properties of fluoranthene, benzo[k]fluoranthene, and their derivatives have been studied using quantum chemical methods. The ground-state structures were optimized using the density functional theory (DFT) methods. The lowest singlet excited state was optimized using time-dependent density functional theory (TD-B3LYP) and configuration interaction singles (CIS) methods. On the basis of ground- and excited-state geometries, the absorption and emission spectra have been calculated using the TD-DFT method with a variety of exchange-correlation functionals. All the calculations were carried out in chloroform medium. The results show that the absorption and emission spectra calculated using the B3LYP functional is in good agreement with the available experimental results. Unlikely, the meta hybrid functionals such as M06HF and M062X underestimate the absorption and emission spectra of all the studied molecules. The calculated absorption and emission wavelength are more or less basis set independent. It has been observed that the substitution of an aromatic ring significantly alters the absorption and emission spectra. 相似文献
92.
Prabha R. Chatterji 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(4):435-443
Persulfate-initiated grafting of crosslinked gelatin with acrylamide in aqueous medium is investigated. the high percentages of grafting are explained as a direct consequence of the heterophase nature of grafting. Optimum reaction conditions for a high percentage of grafting together with low homopoymer yields are discussed. 相似文献
93.
B. P. Singh Prabha Parveen Saini Tejendra Gupta Parveen Garg Gaurav Kumar Indresh Pande Shailaja Pande R. K. Seth S. K. Dhawan R. B. Mathur 《Journal of nanoparticle research》2011,13(12):7065-7074
High aspect ratio multi-walled carbon nanotubes (MWCNTs) reinforced low density polyethylene (LDPE) composites were prepared by solvent casting followed by compression molding technique. Electromagnetic interference (EMI) shielding effectiveness (SE) of these composites was investigated in the frequency range of 12.4?C18 GHz (Ku-band) for the first time. The experimental results indicate that the EMI-SE of these composites is sensitive to the MWCNT loading. The average value of EMI-SE reaches 22.4 dB for 10 wt% MWCNT-LDPE composites, indicating the usefulness of this material for EMI shielding in the Ku-band. The main reason for improved SE has been attributed to significant improvement in the electrical conductivity of the composites by 20 orders of magnitude, i.e., from 10?20 for pure LDPE to 0.63 S/cm for MWCNT-LDPE, which is three order of magnitude higher than the previous reports for MWCNT-LDPE composites. Differential scanning calorimetry of the MWCNT-LDPE composites showed around 37% improvement in the crystalline contents over pure LDPE samples which resulted into enhanced thermal stability of the composites. The thermal decomposition temperature of LDPE is shifted by 40 °C on addition of 5 wt% MWCNT. The studies therefore show that these composite can be used as light weight, thermally stable EMI shielding, and antistatic material. 相似文献
94.
We present a new network simplex pivot selection rule, which we call theminimum ratio pivot rule, and analyze the worst-case complexity of the resulting network simplex algorithm. We consider networks withn nodes,m arcs, integral arc capacities and integral supplies/demands of nodes. We define a {0, 1}-valued penalty for each arc of the
network. The minimum ratio pivot rule is to select that eligible arc as the entering arc whose addition to the basis creates
a cycle with the minimum cost-to-penalty ratio. We show that the so-defined primal network simplex algorithm solves minimum
cost flow problem within O(nΔ) pivots and in O(Δ(m + n logn)) time, whereΔ is any upper bound on the sum of all arc flows in every feasible flow. For assignment and shortest path problems, our algorithm
runs in O(n
2) pivots and O(nm +n
2 logn) time. 相似文献
95.
Azaj Ansari Prabha Jayapal Gopalan Rajaraman 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(2):574-578
Metal–superoxo species are ubiquitous in metalloenzymes and bioinorganic chemistry and are known for their high reactivity and their ability to activate inert C H bonds. The comparative oxidative abilities of M–O2.− species (M=CrIII, MnIII, FeIII, and CuII) towards C H bond activation reaction are presented. These superoxo species generated by oxygen activation are found to be aggressive oxidants compared to their high‐valent metal–oxo counterparts generated by O⋅⋅⋅O bond cleavage. Our calculations illustrate the superior oxidative abilities of FeIII– and MnIII–superoxo species compared to the others and suggest that the reactivity may be correlated to the magnetic exchange parameter. 相似文献
96.
Azaj Ansari Dr. Prabha Jayapal Prof. Gopalan Rajaraman 《Angewandte Chemie (International ed. in English)》2015,54(2):564-568
Metal–superoxo species are ubiquitous in metalloenzymes and bioinorganic chemistry and are known for their high reactivity and their ability to activate inert C? H bonds. The comparative oxidative abilities of M–O2.? species (M=CrIII, MnIII, FeIII, and CuII) towards C? H bond activation reaction are presented. These superoxo species generated by oxygen activation are found to be aggressive oxidants compared to their high‐valent metal–oxo counterparts generated by O???O bond cleavage. Our calculations illustrate the superior oxidative abilities of FeIII– and MnIII–superoxo species compared to the others and suggest that the reactivity may be correlated to the magnetic exchange parameter. 相似文献
97.
Prabha Sharma 《Annals of Operations Research》2006,143(1):203-209
Optimum Communication Spanning Tree Problem is a special case of the Network Design Problem. In this problem given a graph,
a set of requirements r
ij
and a set of distances d
ij
for all pair of nodes (i,j), the cost of communication for a pair of nodes (i,j), with respect to a spanning tree T is defined as r
ij
times the length of the unique path in T, that connects nodes i and j. Total cost of communication for a spanning tree is the sum of costs for all pairs of nodes of G. The problem is to construct
a spanning tree for which the total cost of communication is the smallest among all the spanning trees of G. The problem is
known to be NP-hard. Hu (1974) solved two special cases of the problem in polynomial time. In this paper, using Hu’s result
the first algorithm begins with a cut-tree by keeping all d
ij
equal to the smallest d
ij
. For arcs (i,j) which are part of this cut-tree the corresponding d
ij
value is increased to obtain a near optimal communication spanning tree in pseudo-polynomial time.
In case the distances d
ij
satisfy a generalised triangle inequality the second algorithm in the paper constructs a near optimum tree in polynomial
time by parametrising on the r
ij
. 相似文献
98.
99.
100.
The Raman spectra of the single crystal of K2Zn(SO4)2·6H2O belonging toC
2h
5
space group in the 40–1200 cm−1 region in different scattering geometries and their spectra ofthe microcrystalline salt in the 1500-50 cm−1 region have been reported. The dynamics of the crystal has been described in terms of 186 phonon modes under the unit cell
approximation. The weak bands in the region 400–900 cm−1 have been assigned to the libratory modes of H2O molecules in contradiction to the assignments reported by Ananthanarayanan. The ambiguities existing in the literature about
the assignments ofν
2
c
andν
5
c
modes of [Zn(H2O)6]2+ have also been removed. The translatory and libratory modes of different units of the crystal have been identified and assignments
are made using farir and Raman data on various isomorphous tutton salts.
It has been inferred that both SO
4
2−
tetrahedron and [Zn(H2O)6]2+ octahedron undergo linear as well as angular distortions from their free state symmetries in the crystal. 相似文献