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21.
Basurto S García S Neo AG Torroba T Marcos CF Miguel D Barberá J Ros MB de la Fuente MR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(18):5362-5376
Several new liquid-crystalline indene and pseudoazulene systems are reported. These molecules give rise to either columnar hexagonal mesophases and/or columnar plastic phases. The unique nature of these compounds stems from their non-classical discotic structure. Although the molecules have rigid aromatic cores, they lack terminal tails and instead the polarizable atoms (S, halogens) or polar groups (CN, CO) act as unusual soft parts. On the basis of many structurally related materials, we conclude that for this type of compound molecular stacking in the solid state is a prerequisite for the appearance of a columnar mesophase, although other intermolecular interactions within the layers are also important in establishing liquid-crystalline order. The behavior reported for these mesomorphic molecules opens up new possibilities in the search for related molecular interactions that might be useful for the construction of supramolecular architectures with particular properties. 相似文献
22.
A large number of nanostructures have the potential to be used together with electrophoresis as separation media or separation additive in capillary electrophoresis, micellar electrokinetic chromatography, capillary electrochromatography, and other analytical techniques. Among those structures are nanotubes, nanocavities, nanowires, nanoposts, nanocones, nanospheres, molecular imprints, nanoparachutes (conical monodendrons), and general nanoparticles with random structures. This review is focused only on publications describing experimental works using molecular imprints, nanoposts, and nanospheres that are fabricated and applied for the purpose of separation media in electrophoresis-driven separations. The review follows an approximate chronological order in each section. As shown, the most popular are those resulting from molecular imprinting technologies. These biomimetic receptors are used in a great variety of fields, which includes electrophoresis, micellar electrokinetic chromatography, capillary electrochromatography, and other fields not reviewed in this work. A few examples of these other fields are, e.g., liquid chromatography, membranes, extractor or preconcentration techniques, immunosorbent assays, and sensing devices. The second topic scanned in the present work is the nanostructures that are used as obstacles to replace gels or polymers solutions in electrophoresis. Finally, the nascent field of nanospheres of gold and other materials as separation media is also reviewed. 相似文献
23.
Tomazela DM Gozzo FC Mayer I Engelmann FM Araki K Toma HE Eberlin MN 《Journal of mass spectrometry : JMS》2004,39(10):1161-1167
Ten homologous or isomeric singly, doubly, triply and quadruply charged cationic macrocyclic complexes I-Va, bn+ (n = 1-4) formed by the coordination of [Ru(bipy)2Cl]+ to the pyridyl N-atoms of a series of meso-(phenyl)m-(meta or para-pyridyl)n-porphyrins (m + n = 4) were transferred to the gas phase and structurally characterized by electrospray ionization (ESI) mass (MS) and tandem mass (MS/MS) spectrometry. Previously known to be stable in solution and in the solid state, I-Va, bn+ are found to constitute also a new class of stable, long-lived multiply charged gas-phase ions with spatially separated charge sites. Increasing intramolecular electrostatic repulsion from Ia, b+ to IVa, b3+ facilitates in-source and tandem collision-induced dissociation (CID). However, for the quadruply charged ions Va, b4+, electrostatic repulsion is alleviated mainly by ion pairing with the CF3SO3- counterion forming the salt clusters [Va,b/CF3SO3]3+ and [Va,b/(CF3SO3)2]2+ with reduced charge states. Ion-pairing that yields [IVa,b/CF3SO3]2+ is also observed as a minor ESI process for the triply charged ions IVa, b3+. The gaseous ions I-Va, bn+ (n = 2, 3 or 4) dissociate by sequential 'charge partitioning' with the formation of two cationic fragments by the release of [Ru(bipy)2Cl]+. The meta (a) and para (b) isomers and the positional isomers II2+ and III2+ display nearly identical ESI-MS and ESI-MS/MS spectra. ESI-MS/MS of I-Va, bn+ shows that the Ru-py(P) is, intrinsically, the weakest bond since this bond breaks preferentially upon CID. 相似文献
24.
Sandro Calogero Paolo Ganis Valerio Peruzzo Giuseppe Tagliavini Giovanni Valle 《Journal of organometallic chemistry》1981,220(1):11-20
The structures of tricyclohexyltin fluoride (I), bromide (II) and iodide (III) have been determined by X-ray analysis. Compound I crystallizes in the space group P21/m with a = 10.422(6), b = 17.238(9), c = 5.769(3) Å, β = 104.6(1)° and Z = 2. Compounds II and III crystallize in the space group Pcmn with a = 10.427(6), b = 16.914(9), c = 11.366(6) Å, Z = 4; and a = 10.400(6), b = 16.900(10), c = 11.400(4) Å, Z = 4, respectively. All three structures consist of discrete tetrahedral (cyclo-C6H11)3SnX units.The temperature dependence of the Mössbauer resonance areas has been examined in order to obtain information about the relationship between chemical structure and lattice dynamics. 相似文献
25.
Marcos J Pascual JA de la Torre X Segura J 《Journal of mass spectrometry : JMS》2002,37(10):1059-1073
A fast and sensitive method for the comprehensive screening of anabolic agents and other banned doping substances using gas chromatography/tandem mass spectrometry (GC/MS/MS) with an external ionization ion trap mass spectrometer is presented. The method takes advantage of the resolving power of MS/MS to eliminate background interferences, thus speeding up the chromatographic analysis. For each compound, different fragmentation reactions were studied and their collision energies optimized to obtain the best sensitivity in terms of their signal-to-noise ratio (S/N). A dramatic reduction in overall analysis time was achieved compared with other common approaches. More than 50 substances could finally be monitored in less than 7.4 min with detection limits (S/N >3) lower than 0.5 ng ml(-1) for most of the compounds with special sensitivity requirements according to the International Olympic Committee (IOC). A validation procedure for qualitative analysis was performed. The selectivity of the method showed that no interfering peaks were observed at the retention time of the analytes. Good intermediate precision, below 25% for most of the compounds, and robustness were observed. The optimized method was successfully applied to analyse more than 100 real human urine samples with optimum sensitivity and specificity rates. 相似文献
26.
Jos Luis Lpez Marcos Mandado Ana M. Graa Ricardo A. Mosquera 《International journal of quantum chemistry》2002,86(2):190-198
The atomic and bond properties of a series of alkanenitriles were calculated in order to analyze the transferability of the CN, methyl, and methylene groups. The calculations were carried out using the atoms in molecules (AIM) theory on RHF/6‐31++G**// RHF/6‐31G** wave functions obtained for compounds CN–R (R ranging from H to C11H23). Linear correlations between L(Ω) and N(Ω) were used to establish N(CH2) and N(CH3) nearly transferable values. Average values and maximum differences to the mean value of several properties were used for classifying the CN group. It shows a transferable behavior along the CN–R series for R>Et. The methyl group presents specific properties when R<Pr. The methylene groups can be classified considering both their position with respect to the end of the chain and the position with respect to the CN group. The atomic energy displays a dependence on the molecular size. Although this behavior does not allow to consider this property as transferable, both the ab initio total electronic molecular energies and the experimental heats of formation can be fitted, by linear regression analysis, as a function of the number of methylene groups. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 相似文献
27.
Computerized analytical instruments of late 70's and 80's are facing rapid technological obsolescence, although they are often retaining good analytical performances. Responsibility is to be attributed to the fast advance in computer technology, which is leaving little or no back-compatibility with old standards and data formats. Rejuvenation may be reached by simple hardware and software modifications, to allow data exchange with modern PC's and LIMS. Two typical case histories for spectrometric instrumentation of late 70's are then presented and discussed in a general fashion. 相似文献
28.
Mandado M Mosquera RA Van Alsenoy C 《Physical chemistry chemical physics : PCCP》2005,7(18):3290-3296
The presence of intramolecular hydrogen bond (IHB) in beta-hydroxyethylperoxy and beta-hydroxyethoxy radicals was investigated using the QTAIM topological study on UB3LYP/6-311++G(2d,2p) charge densities. Only one of the two conformers of beta-hydroxyethylperoxy radical which were previously considered to present IHB displays a bond critical point (BCP) associated to an IHB. Furthermore, the atomic energies and electron populations indicate no evidence of IHB in the second conformer. Nevertheless, very small differences in molecular energies were obtained using several one-step and multi-step methods (G3, G3B3) between both conformers. No BCP is found between the hydroxyl hydrogen and the oxygen in the most stable conformer or in the transition state for the dissociation path of beta-hydroxyethoxy radical. However, a BCP is formed in the last steps of this path, thereby yielding H-bonded products. 相似文献
29.
30.
A new reagentless system for sulphite (or sulphur dioxide) determination is reported based on the use of an organic conducting polymer, polyaniline, and its absorbance variation at 550 nm, depending on the sulphite concentration. After chemical polymerisation of aniline a very thin film of polyaniline is obtained. Although the response is not fully reversible, each film can be used for at least 10 measurements for low analyte concentrations (up to 0.5 mg l−1) and five measurements for higher sulphite concentrations. Moreover, the reproducibility, ease of preparation and low cost of the films, permit the use of a new disposable system for each measurement. When the change in absorbance at 550 nm was measured for 210 s (stabilisation time), the system showed a linear response, which ranged from 0.025 to 1.50 mg l−1 of sulphite. A theory with regard to the reaction mechanism between the polyaniline films and sulphite is also proposed. The system was applied to sulphite determination in wine samples and the results were in agreement with those obtained by the Official Method of Analysis (iodometric titration). 相似文献