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211.
Electrospray ionization mass spectrometry of terrestrial humic substances and their size fractions 总被引:2,自引:0,他引:2
Electrospray ionization mass spectrometry (ESI-MS) was used to evaluate the average molecular mass of terrestrial humic substances, such as humic (HA) and fulvic (FA) acids from a soil, and humic acid from a lignite (NDL). Their ESI mass spectra, by direct infusion, gave average molecular masses comparable to those previously obtained for aquatic humic materials. The soil HA and FA were further separated in size-fractions by preparative high performance size exclusion chromatography (HPSEC) and analyzed with ESI-MS by both direct infusion and a further on-line analytical HPSEC. Unexpectedly, their average molecular mass was only slightly less than for the bulk sample and, despite different nominal molecular size, did not substantially vary among size-fractions. The values increased significantly (up to around 1200 Da) after on-line analytical HPSEC for the HA bulk sample, at both pH 8 and 4, and for the HA size-fractions when pH was reduced from 8 to 4. It was noticed that HA size-fractions at pH 8 were separated by on-line HPSEC in further peaks showing average masses which progressively increased with elution volume. Furthermore, when the HA and NDL bulk samples were sequentially ultracentrifuged at increasing rotational speed, their supernatants showed mass values which were larger than bulk samples and increased with rotational speed. These variations in mass values indicate that the electrospray ionization is dependent on the composition of the humic molecular mixtures and increases when their heterogeneity is progressively reduced. It is suggested that the dominance of hydrophobic compounds in humic supramolecular associations may inhibit the electrospray ionization of hydrophilic components. Our results show that ESI-MS is reasonably applicable to humic substances only after an extensive reduction of their chemical complexity. 相似文献
212.
Natural cellulose fibres comprise several non-cellulose compounds and cationic trash which cause problems during different adsorption processes such as dying, printing, final fiber finishing and coating. Therefore the pre-treatment (classical NaOH or environmental friendly enzymatic treatment, demineralisation) is the most important step in cellulose textile prefinishing-cleaning. An appropriate way to describe the success of different processes in fiber pre-treatment which result in distinct surface charge is the determination of electrokinetic properties-zetapotential (ZP) of fibers and textile materials. The zetapotential was determined by streaming potential measurements as a function of the pH and the surfactant concentration in the liquid phase.Cellulose fibers in an aqueous medium are negatively charged due to their characteristic carbonyl and hydroxyl groups. The degradation and removal of specific hydrophobic non-cellulose compounds which cover the primary wall of the cellulose polymer change the surface charge.The ZP is mainly influenced by waxes, their removal decreases the negative ZP. This result is obtained by the classical chemical process as well as by an environmentally friendly enzymatic treatment.Our results indicate that the progress of textile treatment and purification is reflected by the zetapotential of the fabrics. This method enables the estimation of the process'es progress and the interaction between components of the liquid phase and the fibre surface. 相似文献
213.
G. Fritz St. Lauble R. Befurt K. P. Peters E.-M. Peters F. H. G. von Schnering 《无机化学与普通化学杂志》1993,619(9):1494-1511
Formation of Organosilicon Compounds. 110. Reactions of (Cl3Si)2CCl2 and its Si-methylated Derivatives as well as of (Cl3Si)2CHCl, (Cl3Si)2C(Cl)Me and Me2CCl2 with Silicon (Cu cat.) The reactions of (Cl3Si)2CCl2 1 , its Si-methylated derivatives (Me3Si)2CCl2 8 , Me3Si? CCl2? SiMe2Cl 9 , (ClMe2Si)2CCl2 10 , Me3Si? CCl2? SiMeCl2 11 , Cl2MeSi? CCl2? SiCl3 12 as well as of (Cl3Si)2CHCl 38 , (Cl3Si)2CClMe 39 and of Me2CCl2 with Si (Cu cat.) in a fluid bed reactor ( 38 and 39 also in a stirred solid bedreactor) arc presented. While (Cl3Si)2CCl2 1 yields C(SiCl3)4 2 the 1,1,3,3-tetrachloro-2,2,4,4-tetrakis(trichlorsilyl)-1,3-disilacyclobutane Si6C2Cl16 3 and the related C-spiro linked disilacyclobutanes Si8C3Cl20 4 , Si10C4Cl24 5 , Si12C5Cl28 6 , Si14C6Cl32 7 this type of compounds is not obtained starting from the Si-methylated derivatives 8, 9, 10, 11 They Produce a number of variously Si-chlorinated and -methylated tetrasila- and trisilamethanes. However, Cl2MeSi? CCl2? SiCl3 12 forms besides of Si-chlorinated trisilamethanes also the disilacyclobutanes Si6C2Cl15Me 34 and cis- and trans Si6C2Cl14Me2 35 as well as the spiro-linked disilacyclobutanes Si8C3Cl19Me 36 , Si8C3Cl18Me2 37 . (Cl3Si)2CHCl 38 mainly yields HC(SiCl3)3 31 and also the disilacyclobutanes cis- and trans-(Cl3Si)HC(SiCl2)2CH(SiCl3) 41 and (Cl3Si)2C(SiCl2)2CH(SiCl3) 45 the 1,3,5-trisilacyclohexane [Cl3Si(H)C? SiCl2]3 44 as well as [(Cl3Si)2CH]2SiCl2, and (Cl3Si)2CClMe 39 mainly yields (Cl3Si)2C?CH2and (Cl3Si)2besides of HC(SiCl3)3, MeC(SiCl3)3and (Cl3Si)3C? SiCl2Me.,. Me2CCl2 59 mainly yields Me(Cl)C?CH2, Me2CHCl and HCl2Si? CMe2? SiCl3, besides of Me2C(SiCl3)2 and Me2C(SiCl2H)2 Compound 3 crystallizes triclinically in the space group P1 (Nr. 2) mit a = 900,3, b = 914,0, c = 855,3 pm, α = 116,45°, β = 101,44°, γ = 95,86° and one molecule per unit cell. Compound 4 crystallizes monoclinically in thc space group C2/c (no. 15) with a = 3158.3,b = I 103.7, c = 2037.4 pm, β = 1 16.62° and 8 molecules pcr unit cell. The disilacyclobutane ring of compound 3 is plane, showing a mean distance of d (Si-C) =19 1.8 pm and the usual deformations of endocyclic angles: αSi = 94,2°> 85,8° = αC.The spiro-linked disilacyclobutane rings of compound 4 are slightly folded by a mean angle of (19.0°). Their mean distances were found to be d (Si? C) = 190.4 pm relating to the central carbon atom and 192.0 pm to the outer ones, respectively. The deformations of endocyclic angles: αSi = 93,9°> 84,4° = αC are comparable to those of compound 3. 相似文献
214.
Summary Good agreement between the impurity levels in a batch of a related impurity of ranitidine were obtained by CE and HPLC. A solution of the impurity was positioned on the CE autosampler and analysed sequentially. The extent of degradation was monitored by loss of main peak and the formation of two principal degradation products. It was found that after 9.25 hours only 2% area/area of the original impurity remained. Buffering of the sample solution to pH 7 was shown to minimise this degradation.Unattended in-situ stability testing of an solution of the impurity in water was performed by CE. 相似文献
215.
The natural lignin of Allochruza paniculata and Glycyrrhiza glabra is studied by catalytic hydrogenolysis. Three types of lignin structural units are present: guaiacyl, syringyl, and p-coumaryl, which are characteristic of annual and perennial herbaceous plants. The structure of DLA from these plants is confirmed by UV, IR and PMR spectra. 相似文献
216.
High-performance liquid chromatographic fractionation and characterization of fulvic acid 总被引:1,自引:0,他引:1
High-performance immobilized metal ion affinity chromatography (HP-IMAC) was used to fractionate humic substances (HS) based on their affinity for the immobilized copper(II) ion using acidic and glycine eluents. The work was carried out with two naturally occurring aqueous fulvic acids and commercially available Suwannee River fulvic acid. The IMAC-fractionated HS were then characterized by reversed-phase high-performance liquid chromatography (RP-HPLC) and size exclusion chromatography. The results showed that the affinity HS fraction eluted first using an acidic pH=2 eluent exhibited a relatively high hydrophilic character, whereas the fraction eluted later using a glycine eluent exhibited both a higher hydrophobic character and larger molecular size. On the other hand, the HS fraction with no affinity for the immobilized copper had low molecular size. The affinity of the HS fraction for copper(II) increased with increasing molecular weight. Based on the composite results of three different HS, it is evident that strong relationships exist between affinity, molecular weight, and hydrophilic/hydrophobic properties during the HP-IMAC fractionation. The results presented here have significance for understanding the nature of chemical interactions at the molecular level between dissolved organic matter and trace metals. IMAC, coupled with other liquid chromatographic strategies, is a promising tool for chemical fractionation and characterization of HS. 相似文献
217.
K. Turdumambetov Z. Bekmuratov D. A. Rakhimov M. Kh. Malikova 《Chemistry of Natural Compounds》2007,43(1):1-4
Structures of glucofructans isolated from Cousinii radians roots were studied by methylation, periodate oxidation, and IR and 13C NMR spectroscopies. It was found that fructofuranose units were bonded to each other by inulin-type β-(2→1)-gylcoside bonds.
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Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 3–5, January–February, 2007. 相似文献
218.
A simple solid-phase extraction (SPE) procedure with an octadecyl bonded phase silica (C18) was developed for clean-up of the fungicide thiram from aqueous solutions containing high concentrations of humic substances, for future studies of thiram adsorption onto solid humic substances or soils. Suspensions of humic acids and soil, in aqueous 0.01 M CaCl2 solution, were prepared and used as samples. These extracts were spiked with thiram and immediately applied to a C18-SPE cartridge. Thiram was eluted with chloroform and its concentration measured by spectrophotometry at 283 nm. Non-spiked aqueous extracts (blanks) and a control sample of thiram in 0.01 M CaCl2 aqueous solution were also prepared and submitted to the same SPE procedure. The results show that humic substances are extensively retained by the C18 cartridge but are not eluted with CHCl3. Recoveries of 100-104% were obtained for thiram in the presence of humic substances. The SPE procedure described in this work is an efficient clean-up step to remove the interference of humic substances absorbance and to be coupled to any spectrophotometric or HPLC-UV method, usually used for thiram analysis in food extracts. 相似文献
219.
M. K. Turovskaya T. M. Prokop’eva E. A. Karpichev A. E. Shumeiko M. L. Kostrikin V. A. Savelova I. V. Kapitanov A. F. Popov 《Theoretical and Experimental Chemistry》2006,42(5):295-302
The reactivity of α-nucleophilic groups in functional detergents is comparable with those for analogous compounds which do
not form micelles. Methods are proposed for the modification of surface active compounds to produce supernucleophilic systems
for the decomposition of organophosphorus compounds. A new functional detergent — 1-cetyl-3-(2-hydroxyiminoethyl)imidazolium
chloride-is the most powerful of the investigated surface active reagents capable of achieving half lives for the decomposition
of 4-nitrophenyl diethyl phosphonate and 4-nitrophenyl diethyl phosphate of ≤2 and 14 s respectively.
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Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 288–294, September–October, 2006. 相似文献
220.
Summary An isocratic liquid chromatography method for assay and purity control of erythromycin is presented. Erythromycin A is separated
from all its potential impurities, except erythromycin D. The selectivity depends on the pore size of the poly(styrene-divinylbenzene)
stationary phase. Wide pore PLRP-S 8 μm 1000 ? shows the best selectivity. The column is heated at 70°C. The mobile phase
is acetonitrile-2-methyl-2-propanol-0.2 M potassium phosphate buffer pH 9.0-water (3:16.5:5:75.5). The flow rate is 2 ml/min.
UV detection is performed at 215 nm. The total analysis time is about 30 min. The method was used to compare official standards. 相似文献