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331.
The development of microplasmas for spectrochemical analysis by optical methods is discussed. Recent achievements in miniaturization are highlighted, especially for three types of plasmas, namely high-frequency plasmas, dc-discharges and microwave plasmas. The potentials of each of these groups of plasmas as sources for atomic emission spectrometry are discussed. Literature citations and experiments indicate that the plasmas are also very useful as atom reservoirs for atomic absorption spectrometry. Methods of sampling, including feeding with gas chromatography effluents, the use of electrothermal vaporization, and the evolution of gaseous species (as shown for the case of Hg vapor), are discussed as prominent interfaces to make use of these sources for elemental analysis. 相似文献
332.
C. Dubourdieu N. Didier O. Thomas J. P. Sénateur N. Valignat Y. Rebane T. Kouznetsova A. Gaskov J. Hartmann B. Stritzker 《Analytical and bioanalytical chemistry》1997,357(8):1061-1065
Some YBa2Cu3O7-δ films and heterostructures prepared by Chemical Vapor Deposition (CVD) were analyzed in our laboratories by EPMA-EDX or WDX,
RBS, SNMS and AES. It was found that in some cases the results of composition analysis can significantly deviate from each
other. At least two main reasons for these deviations exist: the different lateral resolution and the application of different
reference samples for the calibration.
Received: 3 June 1996 / Revised: 14 October 1996 / Accepted: 16 October 1996 相似文献
333.
The laser-induced charge-transfer cross section for Li3+ + H collisions is calculated using the perturbation approach of Copelang and Tang, and is compared to the collision-induced cross section. The validity of perturbation theory and the use of simple criteria based on the Landau-Zener formula to extend the usefulness of the theory are examined. 相似文献
334.
The site of preferred nucleophilic attack on XC6H5Cr(CO)3 complexes is more influenced by the conformation of the Cr(CO)3 group than by the nature of X substituent. This is supported both by experimental and theoretical results. 相似文献
335.
Hauchard C Pépin C Rowntree P 《Langmuir : the ACS journal of surfaces and colloids》2005,21(20):9154-9165
The adsorption of Fe(CO)(5) onto Au(111)/mica and C(4), C(8), C(12), and C(16) SAMs/Au(111)/mica surfaces has been studied using infrared spectroscopy to elucidate the coverage-dependent structures of these films and the intermolecular couplings that determine the form of the spectra. For all substrates, the first layer is composed of molecules physisorbed with one axial and two equatorial carbonyl groups directed toward the substrate; subsequent layers are preferentially oriented with the C(3) molecular axis aligned perpendicular to the substrate (i.e., one axial carbonyl group directed toward the substrate). The axial vibrational band systematically shifts to higher frequencies with increasing surface coverage because of the effects of intermolecular coupling of the quasiparallel transition dipole moments. The strong effects of dipolar coupling are also witnessed by the trends of the band positions when the distance to the image plane is systematically varied using highly organized self-assembled organic substrates; no band shifts are observed when dilute Fe(CO)(5) is embedded in Xe matrixes under identical experimental conditions. The as-deposited films are structurally stable below 125 K on Au(111)/mica surfaces and below 100 K on the organic self-assembled monolayers. The instability of the films above these temperatures demonstrates that the as-adsorbed films do not form thermodynamically well-defined phases but are structurally metastable. The results presented herein and in the companion paper provide a consistent framework to interpret the spectroscopy of these systems that resolves outstanding issues concerning these films and provides a structural model that explains the dynamic properties of these films during exposure to low-energy electron beams. 相似文献
336.
337.
Appleby I Boulton LT Cobley CJ Hill C Hughes ML de Koning PD Lennon IC Praquin C Ramsden JA Samuel HJ Willis N 《Organic letters》2005,7(10):1931-1934
Two methods to produce (2S)-5-amino-2-(1-n-propyl-1H-imidazol-4-ylmethyl)-pentanoic acid were investigated. Diastereoisomeric salt resolution, using the quinidine salt, gave the desired intermediate in 98% ee and 33% yield. Asymmetric hydrogenation of various substrates gave high conversions, with up to 83% ee. Integration of these two approaches via asymmetric hydrogenation of a quinidine salt substrate followed by crystallization provided the desired intermediate in 94% ee and 76% yield. 相似文献
338.
Kótai László Gács István Kazinczy Béla Sajó István E. Sreedhar B. 《Transition Metal Chemistry》2003,28(3):292-295
The theoretical investigation on the distribution of chemical species obtainable as a function of the temperature of the aqueous solutions of metal complexes containing a basic ligand, altogether with the solubility relationship of the compounds to be formed, offers a simple means of planning the preparation of various types of complexes, double and single salts of the central metal cation and onium type compounds of protonated ligand of the central ion and the anion. 相似文献
339.
Denise Baudry Michel Ephritikhine Hugh Felkin Yves Dromzee Yves Jeannin 《Journal of organometallic chemistry》1984,272(3):403-409
Bis(triphenylphosphine)(η-cyclohexa-1,3-diene)rhenium trihydride, (Ph3P)2(η-C6H8)ReH3 (I) crystallises in the space group C2/c with cell dimensions a 22.76(2), b 10.14(1) c 29.813(6) Å, β 97.69(8)°. The final refinement of 126 variables using 1580 non-zero reflections resulted in a final R value of 0.064. In spite of uncertainties in some of the atomic positions, the structure of I is compatible with a trihydrido diene compound with a distorted pentagonal bipyramidal configuration, rather than with a dihydrido cyclohexenyl compound having an “agostic” CH ? Re interaction. The factors which govern the structure of the complexes (Ph3P)2(η-1,3-diene)ReH3 are discussed. 相似文献
340.
Atomic layer deposition in nanometer-level replication of cellulosic substances and preparation of photocatalytic TiO2/cellulose composites 总被引:4,自引:0,他引:4
Kemell M Pore V Ritala M Leskelä M Lindén M 《Journal of the American Chemical Society》2005,127(41):14178-14179
TiO2 replicas of filter paper with nanometer-level accuracy were prepared by atomic layer deposition of thin conformal TiO2 coating, followed by a removal of the paper by air-anneal at 450 degrees C. Photocatalytic anatase TiO2/cellulose composites were also made by leaving the paper intact. The TiO2 films were deposited from Ti(OMe)4 and H2O at 150-250 degrees C. The photocatalytic activity of the TiO2/cellulose composite was verified by photocatalytic reduction of Ag(I) from an aqueous solution to Ag nanoparticles on the TiO2 surface. The TiO2/cellulose composites are mechanically more stable than the free-standing TiO2 replicas and are therefore potentially suitable as lightweight, high surface area photocatalysts. 相似文献