全文获取类型
收费全文 | 4854篇 |
免费 | 169篇 |
国内免费 | 42篇 |
专业分类
化学 | 2891篇 |
晶体学 | 28篇 |
力学 | 110篇 |
数学 | 971篇 |
物理学 | 702篇 |
无线电 | 363篇 |
出版年
2023年 | 40篇 |
2022年 | 101篇 |
2021年 | 120篇 |
2020年 | 106篇 |
2019年 | 118篇 |
2018年 | 107篇 |
2017年 | 79篇 |
2016年 | 168篇 |
2015年 | 128篇 |
2014年 | 158篇 |
2013年 | 267篇 |
2012年 | 286篇 |
2011年 | 326篇 |
2010年 | 210篇 |
2009年 | 182篇 |
2008年 | 301篇 |
2007年 | 237篇 |
2006年 | 239篇 |
2005年 | 246篇 |
2004年 | 223篇 |
2003年 | 156篇 |
2002年 | 157篇 |
2001年 | 54篇 |
2000年 | 54篇 |
1999年 | 69篇 |
1998年 | 56篇 |
1997年 | 46篇 |
1996年 | 79篇 |
1995年 | 41篇 |
1994年 | 35篇 |
1993年 | 32篇 |
1992年 | 36篇 |
1991年 | 36篇 |
1990年 | 16篇 |
1989年 | 20篇 |
1988年 | 19篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 23篇 |
1984年 | 31篇 |
1982年 | 35篇 |
1981年 | 31篇 |
1980年 | 12篇 |
1979年 | 22篇 |
1978年 | 31篇 |
1977年 | 19篇 |
1976年 | 25篇 |
1974年 | 15篇 |
1973年 | 14篇 |
1972年 | 10篇 |
排序方式: 共有5065条查询结果,搜索用时 15 毫秒
131.
OR Luca JD Blakemore SJ Konezny JM Praetorius TJ Schmeier GB Hunsinger VS Batista GW Brudvig N Hazari RH Crabtree 《Inorganic chemistry》2012,51(16):8704-8709
Nonplatinum metals are needed to perform cost-effective water reduction electrocatalysis to enable technological implementation of a proposed hydrogen economy. We describe electrocatalytic proton reduction and H(2) production by two organometallic nickel complexes with tridentate pincer ligands. The kinetics of H(2) production from voltammetry is consistent with an overall third order rate law: the reaction is second order in acid and first order in catalyst. Hydrogen production with 90-95% Faradaic yields was confirmed by gas analysis, and UV-vis spectroscopy suggests that the ligand remains bound to the catalyst over the course of the reaction. A computational study provides mechanistic insights into the proposed catalytic cycle. Furthermore, two proposed intermediates in the proton reduction cycle were isolated in a representative system and show a catalytic response akin to the parent compound. 相似文献
132.
A conformational switching of bis(zinc octaethylporphyrin) was observed, for the first time, in a Langmuir-Schaefer film as a consequence of appropriate host-guest interactions. The spectral changes are completely reversible and the high sensitivity (~20ppb) and specificity for aromatic amines open up interesting prospects of this functional material as a performing sensor for amines. 相似文献
133.
E Bellido I Ojea-Jiménez A Ghirri C Alvino A Candini V Puntes M Affronte N Domingo D Ruiz-Molina 《Langmuir : the ACS journal of surfaces and colloids》2012,28(33):12400-12409
Atomic force microscopy is shown to be an excellent lithographic technique to directly deposit nanoparticles on graphene by capillary transport without any previous functionalization of neither the nanoparticles nor the graphene surface while preserving its integrity and conductivity properties. Moreover this technique allows for (sub)micrometric control on the positioning thanks to a new three-step protocol that has been designed with this aim. With this methodology the exact target coordinates are registered by scanning the tip over the predetermined area previous to its coating with the ink and deposition. As a proof-of-concept, this strategy has successfully allowed the controlled deposition of few nanoparticles on 1 μm(2) preselected sites of a graphene surface with high accuracy. 相似文献
134.
We use a recently proposed metric, termed the point-to-set correlation functions, to probe the molecular weight dependence of the relevant static length scales in glass-forming oligomeric chain liquids of 4, 5, 8, and 10 repeat units. In agreement with the results for simple, monatomic fluids, we find that static length scales of the oligomers increase monotonically when the temperature is lowered towards the glass transition temperature of the fluid. More interestingly, the static length scale increases with increasing chain length. Within the bounds of error in our simulations, the static length scale appears to scale as the radius of gyration of the oligomer, but with a prefactor, which is much larger than unity and which grows with the temperature. The preceding behavior contrasts with the length scales extracted from the radial distribution function of the oligomer system, which is practically independent of the chain length. 相似文献
135.
Antonio Galdámez Fernanda López-Vergara Patricia Barahona Victor Manríquez Ricardo E. ávila 《Journal of Solid State Electrochemistry》2012,16(2):697-702
The new solid solutions AgPbSb1 − x
Bi
x
S3 were prepared by solid state reactions. The phases were characterized by powder X-ray diffractions (XRD), scanning electron
microscopy, and thermal analysis. The XRD patterns of different members (x = 0.5, 0.7, 0.8, and 1.0) are consistent with pure phases crystallizing in the cubic PbS-type structure. The electrical characterization
was carried out using ac impedance spectroscopy and dc methods. The temperature dependence of the dc conductivity shows typical
semiconductor Arrhenius behavior. The impedance measurements were performed in the frequency range of 0.1 Hz to 10 MHz and
at the temperature range of 15 °C to 350 °C. The ac conductivity conforms to Jonscher’s universal power law. The frequency
dependence of the dielectric permittivity follows the normal dielectric material behavior, and the relaxation is thermally
activated. The frequency and temperature dependences of the electrical data are found to follow Summerfield scaling formalism. 相似文献
136.
137.
John A. Pojman Jason Willis Dionne Fortenberry Victor Ilyashenko Akhtar M. Khan 《Journal of polymer science. Part A, Polymer chemistry》1995,33(4):643-652
Several properties of propagating fronts of addition polymerization were studied. A power function could be fit to the velocity dependence on initiator concentration, but not with the exponents predicted by current models or in agreement with other published work. Bubbles from the volatile by-products of initiator decomposition were found to affect the front velocity and curvature. The front velocity for triethylene glycol dimethacrylate polymerization was found to depend linearly on temperature over a moderate range. The conversion of methacrylic acid in fronts varied greatly with initiator type and concentration. Benzoyl peroxide produced much lower conversion than t-butyl peroxide, but fronts with tBPO propagated slower. A dual initiator system of BPO and tBPO produced rapidly propagating fronts with good conversion but the contribution of each initiator to the velocity was not additive. The possibility of chain branching was considered. The apparent molecular weight distributions were very broad, often trimodal, and found to depend on initiator type and concentration as well as the tube diameter. The temperature profiles were measured and found to be very sharp for BPO and broader for tBPO but both had front temperatures in excess of 200°C, indicating a high ceiling temperature. © 1995 John Wiley & Sons, Inc. 相似文献
138.
Weiss VU Subirats X Pickl-Herk A Bilek G Winkler W Kumar M Allmaier G Blaas D Kenndler E 《Electrophoresis》2012,33(12):1833-1841
During infection, enteroviruses, such as human rhinoviruses (HRVs), convert from the native, infective form with a sedimentation coefficient of 150S to empty subviral particles sedimenting at 80S (B particles). B particles lack viral capsid protein 4 (VP4) and the single-stranded RNA genome. On the way to this end stage, a metastable intermediate particle is observed in the cell early after infection. This subviral A particle still contains the RNA but lacks VP4 and sediments at 135S. Native (150S) HRV serotype 2 (HRV2) as well as its empty (80S) capsid have been well characterized by capillary electrophoresis. In the present paper, we demonstrate separation of at least two forms of subviral A particles on the midway between native virions and empty 80S capsids by CE. For one of these intermediates, we established a reproducible way for its preparation and characterized this particle in terms of its electrophoretic mobility and its appearance in transmission electron microscopy (TEM). Furthermore, the conversion of this intermediate to 80S particles was investigated. Gas-phase electrophoretic mobility molecular analysis (GEMMA) yielded additional insights into sample composition. More data on particle characterization including its protein composition and RNA content (for unambiguous identification of the detected intermediate as subviral A particle) will be presented in the second part of the publication. 相似文献
139.
Reactivity studies of oxo-Mo(IV) complexes, Tp(iPr)MoO{2-OC(6)H(4)C(O)R-κ(2)O,O'} (R = Me, Et, OMe, OEt, OPh, NHPh), containing chelated hydrogen-bond donor/acceptor phenolate ligands are reported. Hydrolysis/oxidation of Tp(iPr)MoO(2-OC(6)H(4)CO(2)Ph-κ(2)O,O') in the presence of methanol yields tetranuclear [Tp(iPr)MoO(μ-O)(2)MoO](2)(μ-OMe)(2) (1), while condensation of Tp(iPr)MoO{2-OC(6)H(4)C(O)Me-κ(2)O,O'} and methylamine gives the chelated iminophenolate complex, Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe-κ(2)O,N} (2), rather than the aqua complex, Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe-κO}(OH(2)). The oxo-Mo(IV) complexes are readily oxidized by dioxygen or hydrogen peroxide to the corresponding cis-dioxo-Mo(VI) complexes, Tp(iPr)MoO(2){2-OC(6)H(4)C(O)R}; in addition, suitable one-electron oxidants, e.g., [FeCp(2)]BF(4) and [N(C(6)H(4)Br)(3)][SbCl(6)], oxidize the complexes to their EPR-active (g(iso) ≈ 1.942) molybdenyl counterparts (3, 4). Molybdenyl complexes such as Tp(iPr)MoOCl{2-OC(6)H(4)C(O)R} (5) and Tp(iPr)MoOCl(2) also form when the complexes react with chlorinated solvents. The ester derivatives (R = OMe, OEt, OPh) react with propylene sulfide to form cis-oxosulfido-Mo(VI) complexes, Tp(iPr)MoOS{2-OC(6)H(4)C(O)R}, that crystallize as dimeric μ-disulfido-Mo(V) species, [Tp(iPr)MoO{2-OC(6)H(4)C(O)R}](2)(μ-S(2)) (6-8). The crystal structures of [Tp(iPr)MoO(μ-O)(2)MoO](2)(μ-OMe)(2), Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe}, Tp(iPr)MoOCl{2-OC(6)H(4)C(O)NHPh}·{2-HOC(6)H(4)C(O)NHPh}, and [Tp(iPr)MoO{2-OC(6)H(4)C(O)R}](2)(μ-S(2)) (R = OMe, OEt) are reported. 相似文献
140.
Goy-López S Juárez J Alatorre-Meda M Casals E Puntes VF Taboada P Mosquera V 《Langmuir : the ACS journal of surfaces and colloids》2012,28(24):9113-9126
Gold nanoparticles (Au NPs) from 5 to 100 nm in size synthesized with HAuCl(4) and sodium citrate were complexed with the plasma protein human serum albumin (HSA). Size, surface charge, and surface plasmon bands of the Au NPs are largely modified by the formation of a protein corona via electrostatic interactions and hydrogen bonding as revealed by thermodynamic data. Negative values of the entropy of binding suggested a restriction in the biomolecule mobility upon adsorption. The structure of the adsorbed protein molecules is slightly affected by the interaction with the metal surface, but this effect is enhanced as the NP curvature decreases. Also, it is observed that the protein molecules adsorbed onto the NP surface are more resistant to complete thermal denaturation than free protein ones as deduced from the increases in the melting temperature of the adsorbed protein. Differences in the conformations of the adsorbed protein molecules onto small (<40 nm) and large NPs were observed on the basis of ζ-potential data and FTIR spectroscopy, also suggesting a better resistance of adsorbed protein molecules to thermal denaturing conditions. We think this enhanced protein stability is responsible for a reduced formation of HSA amyloid-like fibrils in the presence of small Au NPs under HSA fibrillation conditions. 相似文献