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961.
In this paper, the chronoamperometry was used to study the charging processes of polyethylenedioxythiophene (PEDOT) modified electrodes in the potential range where PEDOT was in the oxidized state. The results show that the charging behaviors of the PEDOT films are well agreed with the exhausted finite diffusion model. The dependence of the capacitance values of the films on potential and concentration of solution was also studied in this potential range. 相似文献
962.
Sluszny C Yeung ES Nikolau BJ 《Journal of the American Society for Mass Spectrometry》2005,16(1):107-115
Laser desorption/ionization time-of-flight (LDI-TOF) mass spectrometry was applied for the direct analysis of cuticular waxes on intact plant tissues. Cuticular wax compounds were ionized by laser desorption in the presence of colloidal silver. Silver-adduct ions were detected on samples from Arabidopsis thaliana and from maize. Good spot-to-spot reproducibility indicated homogeneous coverage of the sample by the fine colloidal material. The results were consistent with GC-MS analyses of cuticular extracts, thus confirming the feasibility of direct analysis based on this protocol. Molecular masses of the adduct ions correspond well with the known composition of cuticular waxes. Moreover, LDI-TOF gave good estimates of the relative local abundances of a given compound. However, bias was found in cases where compounds with different ionization efficiencies were analyzed. 相似文献
963.
Verardo G Pagani E Geatti P Martinuzzi P 《Analytical and bioanalytical chemistry》2003,376(5):659-667
The composition of the surface waxes of three apple ( Malus domestica L.) cultivars ("Florina", "Golden B" and "Ozark Gold") has been studied by means of spectroscopic and GC–MS analysis of the class-fractionated mixture of components. Odd n -alkanes, mainly C27 and C29 molecules, are prevalent in the saturated fraction. Small concentrations of alkenes were also found; the C28:1 component is strongly (72%) in excess over the other 1-alkenes. Straight-chain esters (mainly of palmitic acid) of saturated primary alcohols (C18–C30) were also detected; whereas the acyl moiety is made up essentially of an even number of carbons, the alcohol counterpart does not exhibit this characteristic. Aldehydes are present (C20–C30) with the homologue patterns C26–C30 most strongly represented. Straight-chain free secondary alcohols characterize the waxes of "Florina" and "Ozark Gold"; the hydroxy function is located far from the extremity of the carbon framework. Outstanding is the presence of three alcohols with 29 carbon centres. These alcohols are accompanied by free straight-chain primary alcohols, mainly with even-numbered carbon chains in the range C26–C30. Free fatty acids are present; all of have a framework of even-numbered carbon chains mainly in the range C16–C20. C18:1 (oleic acid) is well represented. 相似文献
964.
Paula?Messina Marcela?A.?Morini Pablo?C.?SchulzEmail author 《Colloid and polymer science》2003,281(7):695-698
The hydration of micellised sodium dehydrocholate molecules was determined by viscosity measurements. It was found that there are 39 water molecules for each micellised surfactant molecule. About ten water molecules may be attributed to the hydration of the sodium carboxylate group. By assignation of two water molecules to each of the three carbonyl groups, the total hydration of a micellised sodium dehydrocholate molecule was estimated as about 16 water molecules. The remaining 23 water molecules per micellised sodium dehydrocholate molecule may be attributed to water trapped in the structure of micelles. 相似文献
965.
Jo?o L M Santos Arnaud Clausse José L F C Lima M L M F S Saraiva António O S Rangel 《Analytical sciences》2005,21(4):461-464
A new flow methodology exploiting the multi-pumping approach was developed for the spectrophotometric determination of ambroxol hydrochloride in pharmaceutical preparations. The flow manifold was implemented by using, exclusively, multiple solenoid-actuated micro-pumps, which acted simultaneously as sample insertion, solutions propelling and reagents commutation units. Linear calibration plots were obtained over an ambroxol concentration ranging from 10 to 200 mg l(-1) (r.s.d. < 0.5%, n = 15) and a sampling rate of about 60 samples per hour (flow rate = 1.92 ml min(-1), sample volume = 80 microl). 相似文献
966.
Marotta E Paradisi C Cooks RG 《Journal of the American Society for Mass Spectrometry》2005,16(7):1081-1092
The ion chemistry of the title compounds, a nonafluorobutyl methyl ether and a hydrofluoropropane, is elucidated by a combination of studies using atmospheric pressure ionization mass spectrometry and triple quadrupole mass spectrometry. In the positive ion mode, the hydrofluoroether readily forms an [M - F]+ ion, attributable to hydronium ion induced dehydrofluorination, the product of which can be further hydrated to give a protonated hydrofluoroester. By contrast, the hydrofluoropropane does not react with the hydronium ion but rather gives hydrofluoroalkenylium cations via H atom and F atom abstraction by the dioxygen radical cation. In the negative ion mode, the fluorobutyl methyl ether undergoes dissociative electron capture with O2-*, O2-*(H2O), O3-*, and NO2- to generate the fluorobutoxy anion, which can dissociate by CF2[doublebond]O loss to give the perfluorocarbanion when the precursor ions are internally excited. The hydrofluoropropane reacts readily with common atmospheric anions to form molecular complexes with F-, O2-*, and O3-* and the strongly H-bonded species, O2-*(HF) and F-(HF). Interestingly, isomeric pentafluoropropanes form in the reaction with O2-*, either O2-*(HF) or F-(HF), depending on the specific pattern of the fluoro substitution. 相似文献
967.
Low-energy CAD product-ion spectra of various molecular species of phosphatidylserine (PS) in the forms of [M−H]− and [M−2H+Alk]− in the negative-ion mode, as well as in the forms of [M+H]+, [M+Alk]+, [M−H+2Alk]+, and [M−2H+3Alk]+ (where Alk=Li, Na) in the positive-ion mode contain rich fragment ions that are applicable for structural determination.
Following CAD, the [M−H]− ion of PS undergoes dissociation to eliminate the serine moiety (loss of C3H5NO2) to give a [M−H−87]− ion, which equals to the [M−H]− ion of a phoshatidic acid (PA) and give rise to a MS3-spectrum that is identical to the MS2-spectrum of PA. The major fragmentation process for the [M−2H+Alk]− ion of PS arises from primary loss of 87 to give rise to a [M−2H+Alk−87]− ion, followed by loss of fatty acid substituents as acids (RxCO2H, x=1,2) or as alkali salts (e. g., RxCO2Li, x=1,2). These fragmentations result in a greater abundance of [M−2H+Alk−87−R2CO2H]− than [M−2H+Alk−87−R1CO2H]− and a greater abundance of [M−2H+Alk−87−R2CO2Li]− than [M−2H+Alk−87−R1CO2Li]−; while further dissociation of the [M−2H+Alk−87−R2(or 1)CO2Li]− ions gives a preferential formation of the carboxylate anion at sn-1 (R1CO2−) over that at sn-2 (R2CO2−). Other major fragmentation process arises from differential loss of the fatty acid substituents as ketenes (loss of Rx′CH=CO, x=1,2). This results in a more prominent [M−2H+Alk−R2′CH=CO]− ion than [M−2H+Alk−R1′CH=CO]− ion. Ions informative for structural characterization of PS are of low abundance in the MS2-spectra of both the [M+H]+ and the [M+Alk]+ ions, but are abundant in the MS3-spectra. The MS2-spectrum of the [M+Alk]+ ion contains a unique ion corresponding to internal loss of a phosphate group probably via the fragmentation processes involving
rearrangement steps. The [M−H+2Alk]+ ion of PS yields a major [M−H+2Alk−87]+ ion, which is equivalent to an alkali adduct ion of a monoalkali salt of PA and gives rise to a greater abundance of [M−H+2Alk−87−R1CO2H]+ than [M−H+2Alk−87−R2CO2H]+. Similarly, the [M−2H+3Alk]+ ion of PS also yields a prominent [M−2H+3Alk−87]+ ion, which undergoes consecutive dissociation processes that involve differential losses of the two fatty acyl substituents.
Because all of the above tandem mass spectra contain several sets of ion pairs involving differential losses of the fatty
acid substituents as ketenes or as free fatty acids, the identities of the fatty acyl substituents and their positions on
the glycerol backbone can be easily assigned by the drastic differences in the abundances of the ions in each pair. 相似文献
968.
Joeng-Shein Chen Harald Berndt Günther T?lg 《Fresenius' Journal of Analytical Chemistry》1992,344(12):526-534
Summary Various possibilities for the determination of trace impurities in high-purity iron by atomic spectrometry were investigated in detail. For Ba, Bi, Cd, Co, Cr, Cu, Mn, Ni, Pb, Ti and V, flame AAS, furnace AAS and ICP-OES were firstly evaluated in terms of their power of detection. Detection limits in the g/g-range could be achieved by direct determination. For determination in the ng/g-range a removal of iron by a solvent extraction technique prior to the instrumental measurement was required. The power of detection of direct determination, and of combined procedures were compared with regard to routine applicability and a minimization of systematic errors. 相似文献
969.
The cycloaddition reaction of N-ethoxycarbonyl-1H-azepine with 2,5-dimethoxycarbonyl-3,4-diphenylcyclopentadienone gave anti-endo [4+2]π and exo [6+4]π cycloadducts. These structures were fully identified by X-ray crystallographic techniques. Mechanism for their cycloaddition reactions are also discussed. 相似文献
970.
Mechanism of Thermal Dehydration of Sodium Dihydrogenphosphate The thermal dehydration of sodium dihydrogenphosphate (P1) to sodium cyclotriphosphate (CP3) and sodium polyphosphate, the so-called Maddrell's salt (MS), is controlled by nucleation and crystallization of CP3 and MS, respectively. The wellknown influence of various formation conditions on the CP3:MS product ratio is caused by amorphous and crystalline intermediate phases and their ability to form CP3 or MS nuclei. On seeding P1 with CP3 or MS the dehydration proceeds structure-controlled via dihydrogendiphosphate to pure CP3 or pure MS. The particularities of thermal dehydration of crystalline sodium dihydrogendiphosphate, and also the dehydration and reorganization of sodium phosphate glasses (Na:P = 1:1) with different mean chain lengths, under formation of CP3 or MS are described. 相似文献