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931.
José Luis Martínez-Hernández Marco Arnulfo Mata-Gómez Cristóbal Noé Aguilar-González Anna Ilyina 《Applied biochemistry and biotechnology》2010,160(7):2045-2053
The production of extracellular and mycelia-associated penicillin G acylase (maPGA) with Mucor griseocyanus H/55.1.1 by surface-adhesion fermentation using Opuntia imbricata, a cactus, as a natural immobilization support was studied. Enzyme activity to form 6-aminopencillanic acid (6-APA) from
penicillin G was assayed spectrophotometrically. The penicillin G hydrolysis to 6-APA was evaluated at six different times
using PGA samples recovered from the skim milk medium at five different incubation times. Additionally, the effect of varying
the penicillin G substrate concentration level on the PGA enzyme activity was also studied. The maximum reaction rate, V
max, and the Michaelis constant, K
M, were determined using the Michaelis–Menten model. The maximum levels for maPGA and extracellular activity were found to
be 2,126.50 international unit per liter (IU/l; equal to 997.83 IU/g of support) at 48 h and 755.33 IU/l at 60 h, respectively.
Kinetics of biomass production for total biomass showed a maximum growth at 60 h of 3.36 and 2.55 g/l (equal to 0.012 g of
biomass per gram of support) for the immobilized M. griseocyanus biomass. The maPGA was employed for the hydrolysis of penicillin G to obtain 6-APA in a batch reactor. The highest quantity
of 6-APA obtained was 226.16 mg/l after 40-min reaction. The effect of substrate concentration on maPGA activity was evaluated
at different concentrations of penicillin G (0–10 mM). K
M and V
max were determined to be 3.0 × 10−3 M and 4.4 × 10−3 mM/min, respectively. 相似文献
932.
Tianmin Shu Junchen Wu Ying Zou Keyin Liu Liqing Chen Tao Yi 《Frontiers of Chemistry in China》2010,5(2):184-192
A novel type of ligands contained 1,4,7,10-tetrazacyclododecane and functionalized by two azobenzene moieties grafted with
two alkyl chains was designed and synthesized. The ligands with long alkyl chains can form metallogels in the presence of
Zn2+ cations. The formation of metallogel was followed by NMR and electronic spectral detection. The morphology of the xerogels
is varied with the equivalent of Zn2+ cations and the concentration of the gel. Spectral and structural analysis indicated that the driving forces of the gel formation
were attributed to intermolecular hydrophobic interactions between alkyl chains and π-π interaction between azobenzenes. 相似文献
933.
Nearly monodispersed La3+ doped γ-Fe2O3 nanoparticles were synthesized on an ultra-large scale of about 60 g in a single reaction by a low temperature sol–gel route.
The nanoparticles were obtained by the reaction of FeCl2 and La(NO3)3 in ethanol solution with propylene oxide to form the sol, followed by the boiling of the sol solution. The La3+ doping promotes the phase transformation temperature of γ-Fe2O3 nanoparticles from 350 to 650 °C by the La3+ doping induced enhancement of phase transformation activation energy. This large scale synthesis strategy offers important
advantages over other conventional routes for the preparation of undoped and doped γ-Fe2O3 nanoparticles. These guarantee the promising application of this route in the industrial production. 相似文献
934.
Adsorption of Triton X-100 (TX-100) on silica gel has been studied as a function of temperature (308–328 K) and composition
for mixtures of water with ethanol or t-butanol. The adsorption capacity of silica gel for TX-100 decreases with increase
in alcohol content. Adsorption isotherms of TX-100 on silica gel are four-region and were analyzed using the ARIAN (adsorption
isotherm regional analysis) model. Data in regions 2, 3 and 4 were fitted to the Temkin, bilayer and reverse desorption isotherms,
respectively. The results show that adsorption of TX-100 on silica gel in water and alcohol-water binary mixtures occurs mainly
through formation of monolayer surface aggregates or low bilayer coverage.
相似文献
935.
Yuxiang Bu 《Frontiers of Chemistry in China》2010,5(3):309-324
This feature article addresses several novel aspects regarding the peptide-mediated charge migrations, including: i) radical
exchanges with tunable radical types (σ-radical versus π-radical) and electron-transfer (ET)-channel-tunable cooperative proton-coupled
ET (PCET) mechanism, including hydrogen-atom transfer (HAT), single ET-channel PCET, double ET channel PCET, and channel-type-tunable
(σ-channel versus π-channel) PCET; ii) hole hopping migration between the active groups in the side-chains and its controllability;
iii) hole hopping through stepping-stones via a solvated “hole” form; and iv) electron hopping through positively charged
groups as stepping-stones via a solvated electron state. In particular, the controllability of the ET channels (pathways and
types) and solvated-“hole”/“electron”-based relay mechanisms are mainly mentioned. Clearly, this is an important addition
to the well-documented mechanisms for charge migration in proteins. In view of the complexity of protein charge migration,
further exploration on details of the stepping-stone-based relay mechanisms, by considering the properties and structures
of the redox active centers, their intercalators, and the real surroundings, is still needed. 相似文献
936.
This paper presents an investigation on the enhancement of the barrier properties of paperboard and paper. Microfibrillar
cellulose (MFC) and shellac were deposited on the fibre based substrates using a bar coater or a spray coating technique.
The air, oxygen and water vapour permeability properties were measured to quantify the barrier effect of the applied coatings.
In addition, the mechanical properties were determined and image analysis of the structure was performed to examine the coating
adhesion. The air permeance of the paperboard and papers was substantially decreased with a multilayer coating of MFC and
shellac. Furthermore, for the MFC and shellac coated papers, the oxygen transmission rate decreased several logarithmic units
and the water vapour transmission rate reached values considered as high barrier in food packaging (6.5 g/m2 24 h). The analysis of mechanical and morphological properties indicated good adhesion between the coating and the base substrate. 相似文献
937.
S. Masoud Hosseini A. R. Moghadassi D. Henneke Ali Elkamel 《Journal of Thermal Analysis and Calorimetry》2010,101(1):113-118
Changes in the thermal conductivities of paraffin and mono ethylene glycol (MEG) as a function of β-SiC nanoparticle concentration
and size was studied. An enhancement in the effective thermal conductivity was found for both fluids (i.e., both paraffin
and MEG) upon the addition of nanoparticles. Although an enhancement in thermal conductivity was found, the degree of enhancement
depended on the nanoparticle concentration in a complex way. An increase in particle-to-particle interactions is thought to
be the cause of the enhancement. However, the enhancement became muted at higher particle concentrations compared to lower
ones. This phenomenon can be related to nanoparticles interactions. An improvement in the thermal conductivities for both
fluids was also found as the nanoparticle size shrank. It is believed that the larger Brownian motion for smaller particles
causes more particle-to-particle interactions, which, in turn, improves the thermal conductivity. The role that the base-fluid
plays in the enhancement is complex. Lower fluid viscosities are believed to contribute to greater enhancement, but a second
effect, the interaction of the fluid with the nanoparticle surface, can be even more important. Nanoparticle-liquid suspensions
generate a shell of organized liquid molecules on the particle surface. These organized molecules more efficiently transmit
energy, via phonons, to the bulk of the fluid. The efficient energy transmission results in enhanced thermal conductivity.
The experimentally measured thermal conductivities of the suspensions were compared to a variety of models. None of the models
proved to adequately predict the thermal conductivities of the nanoparticle suspensions. 相似文献
938.
The Becke3LYP density functional was used to study structural and thermodynamic parameters of bivalent zinc cation complexes
with selected substrates and ACE inhibitors (H2O/OH−, neutral forms of captopril, zofenoprilat, omapatrilat, CH3CONHCH3, and N-terminal anions of captopril, zofenoprilat, omapatrilat, enalaprilat, perindoprilat, trandolaprilat, and fosinoprilat). The
combination of DFT and the conductor-like polarizable continuum model (CPCM) were employed to compute the Gibbs interaction
energies (ΔG) between Zn2+ and the selected ACE inhibitors for dielectric media with ɛ = 5 (to simulate the protein environment) and for water media (ɛ = 78.39) for comparison purposes. The results show that ΔG is sensitive to the dielectric constant of the environment and that lower dielectric medium favors the binding of inhibitors
to the zinc cation. 相似文献
939.
Michito Shiotsuka Naoki Nishiko Yasushi Tsuji Noboru Kitamura Satoru Onaka Katsuya Sako 《Transition Metal Chemistry》2010,35(2):129-135
A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh3)–Au–C≡C}2-phen, has been synthesized from Au(PPh3)Cl (PPh3 = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh3)–Au–C≡C}2-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed 3
π–π* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline,
3,8-bis{(PPh3)–Au–C≡C}2-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh3)–Au–C≡C}-phen, and 3-ethynylphenanthroline, 3-{(PPh3)–Au–C≡C}-phen was observed. The absorption bands assignable to the π–π*(C≡Cphen) transition and phosphorescent emission assignable to the metal-perturbed 3
π–π* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT. 相似文献
940.
Ya-juan Wang Jun Guo Hui Chen Zhi-hua Shan 《Journal of Thermal Analysis and Calorimetry》2010,99(1):295-300
The thermal stability of sheepskin collagen cross-linked with chrome sulfate and mimosa (MI)–oxazolidine (OZ), respectively,
had been researched in this experiment. All samples’ shrinkage temperatures (T
s) are determined by a special T
s-testing-apparatus and denaturation temperatures (T
d) are determined by the differential scanning calorimetry. The relations between the modified collagens containing moisture
and their hydrothermal stability, T
s or T
d, were studied. The results show that the cross linking agents can enhance the thermal stability of modified collagen whose
T
s are 109.8 and 110.6 °C for collagen treated with chrome and MI–OZ, respectively. When the samples contain 25–71.9% moisture
for chrome leather and 20–71.1% for leather treated with MI–OZ, the hydrothermal stability will decrease with the increase
of moisture. It was found that the difference between T
s and T
d of collagen modified by chrome is more obvious than that of collagen modified with MI–OZ. And when the moisture of chrome
leather exceeds 55%, T
d cannot express thermal stability of modified collagen as a substitute for T
s, and the moisture is 40% for leather tanned with MI–OZ. 相似文献