全文获取类型
收费全文 | 2600篇 |
免费 | 867篇 |
国内免费 | 226篇 |
专业分类
化学 | 941篇 |
晶体学 | 43篇 |
力学 | 50篇 |
综合类 | 18篇 |
数学 | 60篇 |
物理学 | 2581篇 |
出版年
2024年 | 5篇 |
2023年 | 36篇 |
2022年 | 78篇 |
2021年 | 82篇 |
2020年 | 82篇 |
2019年 | 63篇 |
2018年 | 72篇 |
2017年 | 110篇 |
2016年 | 127篇 |
2015年 | 125篇 |
2014年 | 189篇 |
2013年 | 224篇 |
2012年 | 189篇 |
2011年 | 193篇 |
2010年 | 156篇 |
2009年 | 183篇 |
2008年 | 217篇 |
2007年 | 181篇 |
2006年 | 201篇 |
2005年 | 155篇 |
2004年 | 135篇 |
2003年 | 135篇 |
2002年 | 108篇 |
2001年 | 87篇 |
2000年 | 86篇 |
1999年 | 66篇 |
1998年 | 78篇 |
1997年 | 53篇 |
1996年 | 48篇 |
1995年 | 37篇 |
1994年 | 27篇 |
1993年 | 24篇 |
1992年 | 32篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有3693条查询结果,搜索用时 15 毫秒
51.
E.?V.?TsipisEmail author V.?V.?Kharton I.?A.?Bashmakov E.?N.?Naumovich J.?R.?Frade 《Journal of Solid State Electrochemistry》2004,8(9):674-680
Developments of intermediate-temperature solid oxide fuel cells (IT SOFCs) require novel anode materials with a high electrochemical activity at 800–1070 K. The polarization of cermet anodes, made of nickel, ceria and yttria-stabilized zirconia (YSZ) and applied onto a YSZ solid electrolyte, can be significantly reduced by catalytically active ceria additions, the relative role of which increases with decreasing temperature. Further improvement is observed when using Ce0.8Gd0.2O2–
(CGO) having a high oxygen ionic conductivity instead of undoped ceria, owing to enlargement of the electrochemical reaction zone. Nanocrystalline CGO powders with grain sizes of 8–35 nm were thus synthesized via the cellulose-precursor technique and introduced into Ni–CGO–YSZ cermets, and tested in contact with a (La0.9Sr0.1)0.98Ga0.8Mg0.2O3–
(LSGM) electrolyte at 873–1073 K. The results showed that the anode performance can be enhanced by additional surface activation, in particular by impregnation with a Ce-containing solution, and also by incorporation of YSZ, which probably acts as a cermet-stabilizing component. The overpotential of the surface-modified Ni–CGO (25 wt%–75 wt%) anode in a 10% H2/90% N2 atmosphere was approximately 110 mV at 1073 K with a current density of 200 mA/cm2.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003 相似文献
52.
Molecular mobility in thermotropic polyesters and side-chain polymers with different struc-ture of mesogens and spacers has been studied by dielectrical method in dilutesolutions. The results made it possible to establish the multiplicity of dielectric relaxationtransitions which reflects the small- and large-scale types of molecular motion. It was shownthat dielectric relaxation processes occurring in accordance with local mechanism (relaxationtimes 10~(-9)--10~(-7)s. and the activation energy 10--50kJ/mol) are due to the mobility of kineticchain elements of different length within a monomer units. It was found that the dielectricrelaxation process connected with a large-scale form of molecular motion (relaxation times10~(-5)--10~(-6)s. and the activation energy 100kJ/mol) did not depend on the molecular massbut was infiuenced by factors changing the conformational state of the macromolecule. It isestablished tha the cooperative reorientation mobility of associated mesogenic fragments isthe source of the large-scale process. 相似文献
53.
Here, we will show photo-induced supramolecular chirality in thin films of achiral amorphous polymers with azo groups in their side-chain. A matter of particular interest is the effect of various film thicknesses on azimuthal rotation and ellipticity of incident/transmitted polarized light. Furthermore, we investigated the temporal stability of inscribed chirality. By polarimetric measurements, we found out that the azimuthal rotation gets higher with layer thickness. In this scope, we were able to measure a very high azimuthal rotation of /μm. The inscribed chirality was stable for several days. Furthermore, we investigated the time-resolved behavior of incident and transmitted polarization ellipticities for various thicknesses. The time dependency may be explained by a two-step process: (1) fast trans-cis-isomerization resulting in photo-orientation and (2) slow photo-induced mass flow. 相似文献
54.
Hiroshi Tatewaki Tomohiro Hashimoto Kimihiko Hirao 《Theoretical chemistry accounts》1997,98(2-3):71-74
Using optimal exponents for B through Ne given by Dunning and those for Al through Ar by Woon and Dunning, d-type contracted polarization functions (2d/1d), (3d/1d), and (3d/2d) are generated from natural orbitals of atomic single and double excitation configuration interaction (SDCI) calculations,
where the numbers before and after the slash are those of the primitive and contracted Gaussian type functions. The resulting
contracted functions are tested on N2 and P2 molecules by self-consistent field and SDCI calculations, which clarify characteristics of the present polarization functions.
Received: 5 June 1997 / Accepted: 20 August 1997 相似文献
55.
HeinzD. Roth 《Helvetica chimica acta》2006,89(12):2847-2860
Chemically induced dynamic nuclear polarization (CIDNP) observed during electron transfer (ET) reactions of tertiary amines such as DABCO ( 1 ) or Et3N ( 2 ) with a wide range of electron acceptors support the involvement of amine radical‐cations (e.g., 1. + or 2. + ) as key intermediates. Radical ions such as 2. + may be deprotonated, generating neutral aminoalkyl radicals (e.g., 2. ). When generated by reaction with an electron acceptor of energetically low triplet state such as naphthalene (1Naph*), the resulting pair 2. + /Naph.? reacts mostly by reverse electron transfer (RET) from triplet pairs populating the naphthalene triplet state. 相似文献
56.
Use of intermittent jets to enhance flux in crossflow filtration 总被引:1,自引:0,他引:1
This paper deals with the influence of a new flow unsteadiness on the permeate fluxes in crossflow filtration. A pneumatically controlled valve generates intermittent jets from the main flow, causing the formation of large vortices moving downstream along the tubular membrane. The main results of the numerical calculation of such flows are given. The experimental study was carried out by filtering a bentonite suspension through an ultrafiltration mineral membrane. Time evolutions of flux were achieved in steady and unsteady operating conditions. Results concerning the influence and limits of the nozzle to tube diameter ratio and the jet velocities are discussed. The applicability of such an unsteady flow is examined with a view to effects on energy consumption and possible viscosity effects. 相似文献
57.
The reaction of electroreduction of platinum(II) aquachloride complexes on a negatively charged dropping mercury electrode is used to determine specific features of interpretation of experimental data in the case of parallel conversion of several forms of a reactant, connected with the manner of introducing a correction for the concentration polarization. The difference in the charges of species undergoing simultaneous reduction gives rise to ambiguity when analyzing kinetic data on the dependence of current on the supporting-electrolyte concentration at constant electrode charge. A new self-consistent technique for deducing model parameters (ratio between reactant discharge rate constants) is proposed. 相似文献
58.
An equation for a polarization curve of a hydrophobized electrode is proposed for electrosynthesis of a soluble electroactive product in an inner-kinetic mode. The equation contains the concentration of the target product (TP) in an explicit form. The shape of the curve depends on the biquadratic root of the TP concentration and the square root of the ratio between exchange currents of the side and target reactions. 相似文献
59.
Express detection of nonylphenol in water samples by fluorescence polarization immunoassay 总被引:6,自引:0,他引:6
Yakovleva JN Lobanova AY Shutaleva EA Kourkina MA Mart'ianov AA Zherdev AV Dzantiev BB Eremin SA 《Analytical and bioanalytical chemistry》2004,378(3):634-641
The development of express method for detection of endocrine-disrupting chemicals (EDC) such as alkylphenols is required for ecological monitoring. Several attempts have been made to produce antibodies against 4-nonylphenol (NP) in recent years. This work describes the production of new antibodies against NP and also summarizes the characterization of antibodies obtained earlier. Three approaches used to produce alkylphenol-specific antibodies are compared; these are based on: 1. omega-(4-hydroxyphenyl)nonanoic or omega-(4-hydroxyphenyl)heptanoic acid NP derivatives designed to mimic the linear NP isomer; 2. 4-aminophenol, which potentially mimics various substituted phenolic compounds with different side-chain structures at position 4 of the benzene ring; and 3. a mixture of branched NP isomers, conjugated to the carrier protein via a benzene ring by the Mannich reaction, and expected to be the closest mimic of NP structure by preserving its natural alkyl moiety.Fluorescence polarization immunoassays based on different combinations of antibody and labeled antigen for screening detection of NP were developed and structural aspects of assay sensitivity and specificity were investigated. The assays based on the antisera raised against omega-(4-hydroxyphenyl)nonanoic acid and NP conjugate via Mannich reaction are capable of express detection of NP with detection limit of 7 microg mL(-1 )and assay dynamic range of 18-300 microg mL(-1). 相似文献
60.
Theodorus J.M. de Bruin Karoly Vekey Yves Gimbert Anne Milet 《Journal of organometallic chemistry》2006,691(20):4281-4288
The influence of carbon-carbon triple bond polarization on the regiochemistry of the Pauson-Khand reaction has been studied with the B3LYP functional. The regiochemistry determining step of this reaction, i.e., olefin insertion leading to cobaltacycle formation, has been examined with ethylene as the olefin and propyne, methyl 2-butynoate, and methyl propiolate as the acetylenes. From this study, it has been concluded that, in absence of overwhelming steric effects of an acetylene substituent, the regiochemistry is influenced by the polarization of the acetylenic bond, which arises from the different substituents. The initial C-C bond is preferentially formed with the acetylenic carbon that has the greater electron density: with propyne, this leads to a cyclopentenone having the methyl group in the α-position; with methyl 2-butynoate, to a cyclopentenone with the CO2Me in the β-position; with methyl propiolate, which is virtually unpolarized in the complex, to a cyclopentenone with the CO2Me in the α-position (a result of steric effects). These theoretical results are concordant with those observed experimentally with norbornene. The question of axial versus equatorial reactive positions for the coordinated olefin is also addressed and a kinetic simulation is presented. 相似文献