全文获取类型
收费全文 | 2466篇 |
免费 | 106篇 |
国内免费 | 19篇 |
专业分类
化学 | 1776篇 |
晶体学 | 17篇 |
力学 | 20篇 |
数学 | 366篇 |
物理学 | 412篇 |
出版年
2023年 | 14篇 |
2022年 | 20篇 |
2021年 | 49篇 |
2020年 | 57篇 |
2019年 | 68篇 |
2018年 | 53篇 |
2017年 | 54篇 |
2016年 | 107篇 |
2015年 | 87篇 |
2014年 | 109篇 |
2013年 | 177篇 |
2012年 | 175篇 |
2011年 | 220篇 |
2010年 | 128篇 |
2009年 | 113篇 |
2008年 | 165篇 |
2007年 | 145篇 |
2006年 | 137篇 |
2005年 | 95篇 |
2004年 | 94篇 |
2003年 | 63篇 |
2002年 | 64篇 |
2001年 | 28篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 26篇 |
1997年 | 19篇 |
1996年 | 25篇 |
1995年 | 16篇 |
1994年 | 8篇 |
1993年 | 20篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1977年 | 6篇 |
1975年 | 7篇 |
1973年 | 5篇 |
1970年 | 5篇 |
1966年 | 6篇 |
1958年 | 6篇 |
1955年 | 9篇 |
排序方式: 共有2591条查询结果,搜索用时 15 毫秒
981.
Khlyabich PP Burkhart B Thompson BC 《Journal of the American Chemical Society》2012,134(22):9074-9077
Ternary blend bulk heterojunction (BHJ) solar cells containing as donor polymers two P3HT analogues, high-band-gap poly(3-hexylthiophene-co-3-(2-ethylhexyl)thiophene) (P3HT(75)-co-EHT(25)) and low-band-gap poly(3-hexylthiophene-thiophene-diketopyrrolopyrrole) (P3HTT-DPP-10%), with phenyl-C(61)-butyric acid methyl ester (PC(61)BM) as an acceptor were studied. When the ratio of the three components was varied, the open-circuit voltage (V(oc)) increased as the amount of P3HT(75)-co-EHT(25) increased. The dependence of V(oc) on the polymer composition for the ternary blend regime was linear when the overall polymer:fullerene ratio was optimized for each polymer:polymer ratio. Also, the short-circuit current densities (J(sc)) for the ternary blends were bettter than those of the binary blends because of complementary polymer absorption, as verified using external quantum efficiency measurements. High fill factors (FF) (>0.59) were achieved in all cases and are attributed to high charge-carrier mobilities in the ternary blends. As a result of the intermediate V(oc), increased J(sc) and high FF, the ternary blend BHJ solar cells showed power conversion efficiencies of up to 5.51%, exceeding those of the corresponding binary blends (3.16 and 5.07%). Importantly, this work shows that upon optimization of the overall polymer:fullerene ratio at each polymer:polymer ratio, high FF, regular variations in V(oc), and enhanced J(sc) are possible throughout the ternary blend composition regime. This adds to the growing evidence that the use of ternary blends is a general and effective strategy for producing efficient organic photovoltaics manufactured in a single active-layer processing step. 相似文献
982.
Ali AHMAD Kashif ALI Martin BAA Petr KOVR Andrea SEMANIOV-FENOVíKOV 《数学学报(英文版)》2012,28(9):1865-1874
Let G = (V, E) be a finite, simple and undirected graph with p vertices and q edges. An (a, d)-vertex-antimagic total labeling of G is a bijection f from V (G) ∪ E(G) onto the set of consecutive integers 1, 2, . . . , p + q, such that the vertex-weights form an arithmetic progression with the initial term a and difference d, where the vertex-weight of x is the sum of the value f (x) assigned to the vertex x together with all values f (xy) assigned to edges xy incident to x. Such labeling is called super if the smallest possible labels appear on the vertices. In this paper, we study the properties of such labelings and examine their existence for 2r-regular graphs when the difference d is 0, 1, . . . , r + 1. 相似文献
983.
Evangelia Kalligiannaki Markos A. Katsoulakis Petr Plecháč Dionisios G. Vlachos 《Journal of computational physics》2012,231(6):2599-2620
In this work we propose a hierarchy of Markov chain Monte Carlo methods for sampling equilibrium properties of stochastic lattice systems with competing short and long range interactions. Each Monte Carlo step is composed by two or more sub-steps efficiently coupling coarse and finer state spaces. The method can be designed to sample the exact or controlled-error approximations of the target distribution, providing information on levels of different resolutions, as well as at the microscopic level. In both strategies the method achieves significant reduction of the computational cost compared to conventional Markov chain Monte Carlo methods. Applications in phase transition and pattern formation problems confirm the efficiency of the proposed methods. 相似文献
984.
Svagera Z Hanzlíková D Simek P Hušek P 《Analytical and bioanalytical chemistry》2012,402(9):2953-2963
Four disulfide-reducing agents, dithiothreitol (DTT), 2,3-dimercaptopropanesulfonate (DMPS), and the newly tested 2-mercaptoethanesulfonate
(MESNA) and Tris(hydroxypropyl)phosphine (THP), were investigated in detail for release of sulfur amino acids in human plasma.
After protein precipitation with trichloroacetic acid (TCA), the plasma supernatant was treated with methyl, ethyl, or propyl
chloroformate via the well-proven derivatization–extraction technique and the products were subjected to gas chromatographic–mass
spectrometric (GC–MS) analysis. All the tested agents proved to be rapid and effective reducing agents for the assay of plasma
thiols. When compared with DTT, the novel reducing agents DMPS, MESNA, and THP provided much cleaner extracts and improved
analytical performance. Quantification of homocysteine, cysteine, and methionine was performed using their deuterated analogues,
whereas other analytes were quantified by means of 4-chlorophenylalanine. Precise and reliable assay of all examined analytes
was achieved, irrespective of the chloroformate reagent used. Average relative standard deviations at each analyte level were
≤6%, quantification limits were 0.1–0.2 μmol L−1, recoveries were 94–121%, and linearity was over three orders of magnitude (r
2 equal to 0.997–0.998). Validation performed with the THP agent and propyl chloroformate derivatization demonstrated the robustness
and reliability of this simple sample-preparation methodology. 相似文献
985.
986.
Emanuel Makrlík Petr Vaňura Pavel Selucký 《Central European Journal of Chemistry》2012,10(5):1495-1499
From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium C+(aq) + 1·Na+(nb) <=>1·C+ (nb) + Na+(aq) taking place in the two-phase water-nitrobenzene system (C+ = methylammonium, ethylammonium, propylammonium, ethanolammonium, diethanolammonium, triethanolammonium, cation TRIS+, hydrazinium, hydroxylammonium; 1 = benzo-18-crown-6; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the 1·C+ cationic complex species in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: triethanolammonium < propylammonium < ethylammonium, diethanolammonium < methylammonium < ethanolammonium < cation TRIS+ < hydrazinium < hydroxylammonium. 相似文献
987.
Fryčák P Jirkovský J Ranc V Bednář P Havlíček V Lemr K 《Journal of mass spectrometry : JMS》2012,47(6):720-726
Atmospheric pressure chemical ionization is known for producing unusual artifacts of the ionization process in some cases. In this work, processes occuring in atmospheric pressure chemical ionization/MS of orotic acid that afforded ions accompanying protonated and deprotonated orotic acid molecules in the spectra were studied. Two processes ran in parallel in the ion source: decarboxylation of neutral orotic acid and collision-induced dissociation of its protonated or deprotonated form. A procedure discerning pre-ionization decomposition and post-ionization dissociation by manipulating ion source parameters was proposed. Experiments with isotopically labeled solvents confirmed ion-molecule reactions of the product of collision-induced dissociation of protonated orotic acid with solvent molecules in the ion source and even under vacuum in the ion trap. 相似文献
988.
Luk Fojt Petr Klapetek Ludk Strak Vladimír Vetterl 《Micron (Oxford, England : 1993)》2009,40(8):918-922
Atomic force microscopy was used to distinguish changes in morphology of bacteria induced by 50 Hz 10 mT magnetic field exposure. It is known that alternating magnetic field exposure causes decrease of viability of different bacterial strains. Previously we found that the viability of rod-like bacteria exposed to magnetic field decreased twice more in comparison with the spherical ones. Motivated by this fact we carried out this study with bacterial cells of both shapes. We used Escherichia coli (rod-like) and Paracoccus denitrificans (spherical) bacteria. As a result we have not observed any change in bacterial morphology neither of rod-like nor of spherical bacteria after 1 h, 50 Hz and 10 mT magnetic field exposure. 相似文献
989.
The information about molecular structure coded in the optical spectra must often be deciphered by complicated computational procedures. A combination of spectral modeling with the molecular dynamic simulations makes the process simpler, by implicit accounting for the inhomogeneous band broadening and Boltzmann averaging of many conformations. Ideally, geometries of studied systems can be deduced by a direct confrontation of such modeling with the experiment. In this work, the comparison is enhanced by restrictions to molecular dynamics propagations based on the Raman and Raman optical activity spectra. The methodology is introduced and tested on model systems comprising idealized H(2)O(2), H(2)O(3) molecules, and the alanine zwitterion. An additional gradient term based on the spectral overlap smoothed by Fourier transformation is constructed and added to the molecular energy during the molecular dynamics run. For systems with one prevalent conformation the method did allow to enrich the Boltzmann ensemble by a spectroscopically favored structure. For systems with multiconformational equilibria families preferential conformations can be selected. An alternative algorithm based on the comparison of the averaged spectra with the reference enabling iterative updates of the conformer probabilities provided even more distinct distributions in shorter times. It also accounts for multiconformer equilibria and provided realistic spectra and conformer distribution for the alanine. 相似文献
990.
Emanuel Makrlík Petr Vaňura Jan Budka 《Monatshefte für Chemie / Chemical Monthly》2009,287(1):583-585