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101.
In our group, we work on the surface modification of cellulose nanocrystals. During this work, we have encountered reproducibility
issues when the same reactions were performed on nanocrystals from different hydrolysis batches, indicating a variable surface
composition. Given the inherent purity of the nanoparticles themselves, this issue was believed to be due to the presence
of adsorbed species at the surface of the nanocrystals blocking reactive sites. To investigate this in detail, nanocrystals
from several batches were extracted with different solvents. The effect of these extractions on the surface composition of
the nanowhiskers was investigated, followed by its effect on the Surface-Initiated Ring-Opening Polymerization (SI-ROP) of
ε-caprolactone. The extracted impurities were analysed by NMR (1H and 13C) and MS, showing a variety of adsorbed species which can be removed by solvent extraction. A Soxhlet extraction using ethanol
before the reaction was shown to be the most effective in removing adsorbed low molecular weight organic compounds produced
during the hydrolysis, resulting in improved reproducibility between reactions using nanocrystals from different batches,
as confirmed by FTIR, elemental analysis and XPS. Extraction with ethanol should thus be performed before all reaction as
these adsorbed species can be expected to interfere with all surface modification reactions. 相似文献
102.
Schenk C Kracke A Fink K Kubas A Klopper W Neumaier M Schnöckel H Schnepf A 《Journal of the American Chemical Society》2011,133(8):2518-2524
The reaction of GeBr with LiSi(SiMe(3))(3) leads to the metalloid cluster compound [(THF)(2)Li](3)Ge(14)[Si(SiMe(3))(3)](5) (1). After the introduction of a first cluster of this type, in which 14 germanium atoms form an empty polyhedron, [(THF)(2)Li](3)Ge(14)[Ge(SiMe(3))(3)](5) (2), we present here further investigations on 1 to obtain preliminary insight into its chemical and bonding properties. The molecular structure of 1 is determined via X-ray crystal structure solution using synchrotron radiation. The electronic structure of the Ge(14) polyhedron is further examined by quantum chemical calculations, which indicate that three singlet biradicaloid entities formally combine to yield the singlet hexaradicaloid character of 1. Moreover, the initial reactions of 1 after elimination of the [Li(THF)(2)](+) groups by chelating ligands (e.g., TMEDA or 12-crown-4) are presented. Collision induced dissociation experiments in the gas phase, employing FT-ICR mass spectrometry, lead to the elimination of the singlet biradicaloid Ge(5)H(2)[Si(SiMe(3))(3)](2) cluster. The unique multiradicaloid bonding character of the metalloid cluster 1 might be used as a model for reactions and properties in the field of surface science and nanotechnology. 相似文献
103.
The biochemicals utilized in the Charm MRL beta-Lactam test (8 min test) were applied to faster flowing lateral components to create a new 3 min, one-step beta-lactam test called Charm MRL-3 (Charm Sciences Inc., Lawrence, MA). This new test was validated at T&V-ILVO according to Commission Decision 2002/657/EC. The following analytical parameters were checked: test specificity, detection capability, and test robustness (impact of deviation of the test protocol, and impact of the milk composition, batch differences of reagents). Further, the suitability of the Charm MRL-3 to screen heat-treated milk or milk from animal species other than the cow was also tested. Finally, the test was integrated in the monitoring of dairy samples to check the occurrence of false-negative or false-positive results, and the test was also included in a national ring trial and an international proficiency study. The results proved that the Charm MRL-3 is a fast, simple, and reliable cows' milk test that can be used at the farm level in order to prevent tanker milk contamination, or at the entrance of the dairy plant to screen tanker milk for the presence of beta-lactam antibiotics. 相似文献
104.
Van Eenoo P Van Gansbeke W De Brabanter N Deventer K Delbeke FT 《Journal of chromatography. A》2011,1218(21):3306-3316
The use of performance enhancing drugs in sports is prohibited. For the detection of misuse of such substances gas chromatography or liquid chromatography coupled to mass spectrometry are the most frequently used detection techniques. In this work the development and validation of a fast gas chromatography tandem mass spectrometric method for the detection of a wide range of doping agents is described. The method can determine 13 endogenous steroids (the steroid profile), 19-norandrosterone, salbutamol and 11-nor-Δ9-tetrahydrocannabinol.9carboxylic acid in the applicable ranges and to detect qualitatively over 140 substances in accordance with the minimum required performance levels of the World Anti-Doping Agency in 1ml of urine. The classes of substances included in the method are anabolic steroids, β2-agonists, stimulants, narcotics, hormone antagonists and modulators and beta-blockers. Moreover, using a short capillary column and hydrogen as a carrier gas the run time of the method is less than 8min. 相似文献
105.
Methacrylate monolithic stationary phases were produced in fused-silica chips by UV initiation. Poly(butyl methacrylate-co-ethylene dimethacrylate) (BMA) and poly(lauryl methacrylate-co-ethylene dimethacrylate) (LMA) monoliths containing 30, 35 and 40% monomers were evaluated for the separation of peptides under gradient conditions. The peak capacity was used as an objective tool for the evaluation of the separation performance. LMA monoliths of the highest density gave the highest peak capacities (≈40) in gradients of 15 min and all LMA monoliths gave higher peak capacities than the BMA monoliths with the same percentage of monomers. Increasing the gradient duration to 30 min did not increase the peak capacity significantly. However, running fast (5 min) gradients provides moderate peak capacities (≈20) in a short time. Due to the system dead volume of 1 μL and the low bed volume of the chip, early eluting peptides migrated over a significant part of the column during the dwell time under isocratic conditions. It was shown that this could explain an increased band broadening on the monolithic stationary phase materials used. The effect is stronger with BMA monoliths, which partly explains the inferior performance of this material with respect to peak capacity. The configuration of the connections on the chip appeared to be critical when fast analyses were performed at pressures above 20 bar. 相似文献
106.
Lemaire S Houpis I Wechselberger R Langens J Vermeulen WA Smets N Nettekoven U Wang Y Xiao T Qu H Liu R Jonckers TH Raboisson P Vandyck K Nilsson KM Farina V 《The Journal of organic chemistry》2011,76(1):297-300
Diastereoselective hydrogenation of 2'-deoxy-2'-exo-methyleneuridine was carried out under homogeneous conditions using a low loading of a chiral Rh catalyst. This, coupled with improvements in the synthesis of the substrate, allowed the smooth pilot plant preparation of the title compound on >10 kg scale. 相似文献
107.
de Graaf AJ Mastrobattista E van Nostrum CF Rijkers DT Hennink WE Vermonden T 《Chemical communications (Cambridge, England)》2011,47(24):6972-6974
This communication describes a novel and fast reaction to substitute the living chain end after Atom Transfer Radical Polymerization (ATRP) by an azide functionality. The reaction is catalyzed by the ATRP catalyst at room temperature in aqueous solution and can be followed by a 'click' reaction using again the same catalyst. 相似文献
108.
Medium-resolution spectra of the N2 b1Πu-X1Σg+ band system were recorded by 1 + 1 multiphoton ionization. In the spectra we found different linewidths for transitions to different vibrational levels in the b 1Πu state: Δν0 = 0.50 ± 0.05 cm−1, Δν1 = 0.28 ± 0.02 cm−1, Δν2 = 0.65 ± 0.06 cm−1, Δν3 = 3.2 ± 0.5 cm−1, Δν4 = 0.60 ± 0.07 cm−1, and Δν5 = 0.28 ± 0.02 cm−1. From these linewidths, predissociation lifetimes τν were obtained: τ0 = 16 ± 3 ps, τ1 > 150 ps, τ2 = 10 ± 2 ps, τ3 = 1.6 ± 0.3 ps, τ4 = 9 ± 2 ps, and τ5 > 150 ps. Band origins and rotational constants for the b 1Πuν = 0 and 1 levels were determined for the 14N2 and 14N15N molecules. 相似文献
109.
Ewin F. Van Dishoeck Peter N.Th. Van Velzen Wim J. Van Der Hart 《Chemical physics letters》1979,62(1):135-138
The photodissociation spectra of the molecular ions of some cycloalkanes are compared with those of the corresponding acyclic alkanes and alkenes. It is shown that the molecular ions of cyclohexane and cycloheptane are cyclic whereas the cyclopentane ring opens upon ionisation. This conclusion is supported by a study of the charge-transfer equilibria: C6D12± + C6H12 ? C6D12 + C6H12±, C5D10± + C5H10 ? C5D10 + C5H10±. It is furthermore shown that the maxima in the photodissociation spectra of the molecular ions of saturated hydrocarbons correspond to different dissociation processes. 相似文献
110.
Biorthogonal Smooth Local Trigonometric Bases 总被引:3,自引:0,他引:3
In this paper we discuss smooth local trigonometric bases. We present two generalizations of the orthogonal basis of Malvar
and Coifman-Meyer: biorthogonal and equal parity bases. These allow natural representations of constant and, sometimes, linear
components. We study and compare their approximation properties and applicability in data compression. This is illustrated
with numerical examples. 相似文献