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121.
Stefan Veigel Ulrich Müller Jozef Keckes Michael Obersriebnig Wolfgang Gindl-Altmutter 《Cellulose (London, England)》2011,18(5):1227-1237
Cellulose nanofibrils were prepared by mechanical fibrillation of never-dried beech pulp and bacterial cellulose. To facilitate
the separation of individual fibrils, one part of the wood pulp was surface-carboxylated by a catalytic oxidation using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl
(TEMPO) as a catalyst. After fibrillation by a high pressure homogenizer, the obtained aqueous fibril dispersions were directly
mixed with different urea–formaldehyde-(UF)-adhesives. To investigate the effect of added cellulose filler on the fracture
mechanical properties of wood adhesive bonds, double cantilever beam specimens were prepared from spruce wood. While the highest
fracture energy values were observed for UF-bonds filled with untreated nanofibrils prepared from wood pulp, bonds filled
with TEMPO-oxidized fibrils showed less satisfying performance. It is proposed that UF-adhesive bonds can be significantly
toughened by the addition of only small amounts of cellulose nanofibrils. Thereby, the optimum filler content is largely depending
on the adhesive and type of cellulose filler used. 相似文献
122.
Ľ. Vrtoch M. Pipíška M. Horník J. Augustín J. Lesný 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(3):853-862
In order to gain biosorbent that would have the ability to bind cesium ions from water solution effectively, potassium nickel
hexacyanoferrate(II) (KNiFC) was incorporated into the mushroom biomass of Agaricus bisporus. Cesium sorption by KNIFC-modified A. bisporus biosorbent was observed in batch system, using radiotracer technique using 137Cs radioisotope. Kinetic study showed that the cesium sorption was quite rapid and sorption equilibrium was attained within
1 h. Sorption kinetics of cesium was well described by pseudo-second order kinetics. Sorption equilibrium was the best described
by Freundlich isotherm and the distribution coefficient was at interval 7,662–159 cm3 g−1. Cesium sorption depended on initial pH of solution. Cesium sorption was very low at pH0 1.0–3.0. At initial pH 11.0, maximum sorption of cesium was found. Negative effect of monovalent (K+, Na+, NH4
+) and divalent (Ca2+, Mg2+) cations on cesium sorption was observed. Desorption experiments showed that 0.1 M potassium chloride is the most suitable
desorption agent but the complete desorption of cesium ions from KNiFC-modifed biosorbent was not achieved. 相似文献
123.
Steady state analysis of a combined hybrid process consisting of a reactive distillation column, pervaporation unit, and a
distillation column is presented. This process configuration was first presented by Steinigeweg and Gmehling (2004) for the
transesterification of methyl acetate and butanol to butyl acetate and methanol. This system is characteristic for its low
reaction rate and complex phase equilibrium. Steinigeweg and Gmehling (2004) have shown that the combination of reactive distillation
and pervaporation is favourable since conversions close to 100 % can be reached with a reasonable size of the reactive section
in the reactive distillation column. The aim of this paper is to show that although high conversion can be achieved, very
complicated steady state behaviour must be expected. The presented analysis is based on mathematical modelling of a process
unit, where the steady-state analysis, including continuation and bifurcation analyses, was used. Multiple steady states were
predicted for the studied system; three steady states with conversions higher than 98 %. However, not all predicted steady
states met the maximal allowed temperature condition in the reactive section (catalyst maximal operation temperature of 393
K). The presence of multiple steady states reduces the operability and controllability of the reactive distillation column
during its start-up and during the occurrence of any variation of operating parameters because the system can be shifted from
one steady state to another one (concurrent exceeding the maximal allowed temperature) with unwanted consequences, e.g. production
loss. Therefore, design and subsequent operation of such a complicated system is an ambitious task requiring knowledge of
any possible system behaviour. 相似文献
124.
Peter Herich Marek Fronc Jozef Koíek 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(2):159-164
Three new complexes with 3,6‐dichlorobenzene‐1,2‐dithiol (bdtCl2), namely methyltriphenylphosphonium bis(3,6‐dichlorobenzene‐1,2‐dithiolato‐κ2S,S′)cobaltate(1−), (C19H18P)[Co(C6H2Cl2S2)2], (I), bis(methyltriphenylphosphonium) bis(3,6‐dichlorobenzene‐1,2‐dithiolato‐κ2S,S′)cuprate(2−) dimethyl sulfoxide disolvate, (C19H18P)2[Cu(C6H2Cl2S2)2]·2C2H6OS, (II), and methyltriphenylphosphonium bis(3,6‐dichlorobenzene‐1,2‐dithiolato‐κ2S,S′)cuprate(1−), (C19H18P)[Cu(C6H2Cl2S2)2], (III), have been synthesized and characterized by single‐crystal X‐ray diffraction. The X‐ray structure analyses of all three complexes confirm that the four donor S atoms form a slightly distorted square‐planar coordination arrangement around the central metal atom. An interesting finding for both the CuII and CuIII complexes, i.e. (II) and (III), respectively, is that the coordination polyhedra are principally the same and differ only slightly with respect to the interatomic distances. 相似文献
125.
Methodological aspects of an off‐line combination of preparative isotachophoresis and high‐performance liquid chromatography with mass spectrometry in the analysis of biological matrices 下载免费PDF全文
This work reports on some methodological aspects of an off‐line combination of preparative ITP and HPLC with mass spectrometric detection (pITP‐HPLC‐MS) and its potential applications to the analysis of high molecular mass compounds present in complex biological matrices from the analytical chemistry perspective. Lysozyme served as the model analyte and human saliva as the complex biological matrix in this study. A mixture of five low‐molecular mass compounds was found and successfully used in the pITP experiments as discrete spacers to isolate the analyte from the interferents present in the complex biological matrix and to minimize their disturbance effect on the final MS analysis. The experiments at the pITP stage were performed in the cationic mode. On‐column conductivity detectors were used for the detection of ITP zones. Lysozyme was found in the human saliva samples using just deconvolution of the MS data after background correction. The MS data obtained from HPLC‐MS analysis of pITP fractions exhibited the great analytical potential of the combination of pITP‐HPLC‐MS resulting from the ITP clean‐up effect as well as the ITP preconcentration of the analyte present at low concentration levels in complex biological matrices. 相似文献
126.
Herein, we demonstrate that the chain-initiating dissociation of cyclohexyl hydroperoxide, CyOOH, is substantially accelerated by H-bond acceptors (e.g. Teflon), which assist O-O bond breaking by stabilising the leaving *OH radical. This is a completely new approach to boost the chain-propagating radical concentration. Indeed, up to now, literature has remained focussed on transition metal catalysis. In addition to this initiation effect, we demonstrate how inert perfluorinated compounds are also able to steer the selectivity at the molecular level, by promoting the conversion of the intermediate cyclohexyl hydroperoxide to the most desired end-product, cyclohexanone. This effect is explained by an enhanced, H-bond-assisted, hydroperoxide propagation. This hitherto overlooked hydroperoxide propagation was recently presented by us as the dominant cyclohexanone and cyclohexanol source. We herein thus confirm our previously reported autoxidation scheme, and illustrate its usefulness as a solid basis for designing new catalytic systems. 相似文献
127.
Ghesquière B Goethals M Van Damme J Staes A Timmerman E Vandekerckhove J Gevaert K 《Rapid communications in mass spectrometry : RCM》2006,20(19):2885-2893
Nitrated tyrosines are easily converted into their aminotyrosine equivalents by a reduction step. We here show that this conversion can be exploited to readily discern 3-aminotyrosine peptides in a background of non-nitrated peptides. Furthermore, aminotyrosine peptides are more stable in single mass spectrometry (MS) mode rendering peptide mass maps easier to interpret. One significant caveat of both 3-nitrotyrosine and 3-aminotyrosine peptides is their lack of efficient fragmentation upon collision-induced dissociation (CID) which, in the case of the latter peptides, also produces unexpected, deviating isotopic patterns of fragment ions containing the aminotyrosine residue. The net result is that sequence database searching becomes daunting as the correct peptide is frequently missed since insufficient and/or inaccurate peptide fragments are used. We show that a simple acetylation step, blocking all amines (including aminotyrosine), produces peptides that undergo extensive backbone fragmentation by CID and are thus easily identifiable in databases. Our procedure is additionally illustrated by doubling the number of nitration events mapped in tetranitromethane-nitrated bovine serum albumin (BSA) as compared to a direct analysis of the nitrated peptides using the same amount of material. In conclusion, we here illustrate that this two-step process, heme-mediated reduction and acetylation, can be used for more efficient characterization of protein-bound nitrated tyrosines. 相似文献
128.
Mydlová J Fedurcová A Lehotay J Krupcík J Májek P Armstrong DW He BL Cotton FA 《Journal of separation science》2006,29(17):2594-2599
In this paper, an HPLC method is used to determine the enantiomerization barrier of 2,3-pentadienedioic acid enantiomers. The racemate of 2,3-pentadienedioic acid was separated by HPLC on a chiral CHIROBIOTIC T column with a 90:10 (100:0.5:0.5 MeOH/HOAc/TEA)/H2O mobile phase. Peak areas of enantiomers prior to (A(+)0, A(-)0) and after the separation (A(+), A(-)), were used for calculation of the rate constants and the enantiomerization barrier, as determined by computer-assisted peak deconvolution of the peak clusters on the chromatograms. The kinetic equation for irreversible reactions was used to determine the apparent enantiomerization rate constants and the interconversion energy barrier. The dependence of the apparent enantiomerization barrier (deltaG1(app), deltaG-1(app)) on temperature was used to determine the apparent activation enthalpy (deltaH1(app), deltaH(-1)app) and entropy (deltaS1(app), deltaS-1(app)) for the interconversion of 2,3-pentadienedioic acid enantiomers, where the coefficients 1 and -1 designate the interconversions (+) --> (-) and (-) --> (+), respectively. 相似文献
129.
Nuclear-spin relaxation is considered in a molecular system undergoing two types of dynamic processes: asymmetric-top small-step rotational diffusion and discrete multisite local jumps. The two processes are assumed to be uncorrelated. Time correlation functions for relevant rank-two interactions and corresponding spectral density functions are derived for a general relation between the characteristic rate constants. In addition, limiting cases of fast and slow local motions and of some specific jump conditions are also investigated. 相似文献
130.
L’ubica Triščíková Ivan Potočňák Jozef Chomič Peter Baran 《Transition Metal Chemistry》2006,31(4):504-515
The new mixed-valence mixed-metal complex Cu(py)6Cu2Ag2(CN)6 (py = pyridine) possesses a three dimensional polymeric crystal structure. The Cu(I) atom is tetrahedrally coordinated by
two nitrogen atoms of pyridine molecules, by one nitrogen atom of the dicyanoargentate anion and by one carbon atom of the
cyano group. Both the dicyanoargentate anion and the cyano group bridge the Cu(I) atom with neighboring Cu(II) atoms. These
are hexacoordinated in the form of an elongated tetragonal bipyramid. The equatorial plane is formed by two nitrogen atoms
from two pyridine molecules and two nitrogen atoms from bridging cyano groups. Axial positions are occupied by nitrogen atoms
of the bridging [Ag(CN2]− anions. Correlation between structures of the title compound and seven other dicyanoargentates with their i.r. spectra has
been studied. The coordination mode of [Ag(CN2]− anions in compounds Cu8-xAgx(tn)3(CN)10 x = 0.25, Cu(3-Mepy)2Ag2(CN)4, Cu(py)2Ag2(CN)4 and Cu(py)4Ag2(CN)4 (tn is 1,3-diaminopropane, 3-Mepy is 3-methylpyridine) is predicted based on this correlation. 相似文献