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991.
Determination of cadmium in water samples by graphite furnace atomic absorption spectrometry after cloud point extraction 总被引:3,自引:0,他引:3
The formation of a complex with 2-(5-brom-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP) and cloud point extraction have
been applied to the preconcentration of cadmium followed by its determination by graphite furnace atomic absorption spectrometry
(GFAAS) using octylphenoxypolyethoxyethanol (TritonX-114) as surfactant. The chemical variables affecting the separation were
optimized. At pH 7.0, preconcentration of only 10 mL of sample in the presence of 0.05% TritonX-114 and 2.5 × 10−6 M 5-Br-PADAP enabled the detection of 0.04 μg/L cadmium. The enrichment factor was 21 for cadmium. The regression equation
was A = 0.0439C(μg/L) + 7.2 × 10−3. The correlation coefficient was 0.9995. The precision for 10 replicate determinations at 10 μg/L Cd was 2.7% relative standard
deviation (RSD). The proposed method has been applied to the determination of cadmium in water samples.
The text was submitted by the authors in English. 相似文献
992.
A reversed-phase liquid chromatographic (RPLC) method has been developed for determination of arabinosylcytosin (Ara-C) and
its metabolite 1-β-D-arabinofuranosyluracil (Ara-U) on a 250 mm × 4.6 mm i.d., 5 μm particle, Diamonsil C18 column. The mobile phase was a mixture of 5% methanol and 95% 10 mmol L−1 phosphate buffer adjusted to pH 5.5. The flow-rate was 1.0 mL min−1 and the injection volume 20 μL. Eluting compounds were detected at 270 nm by use of an ultraviolet detector. Under these
LC conditions cyclophosphamide (CTX) and pirarubicin (THP), two other medicines given with Ara-C in clinical treatment, do
not interfere with measurement of Ara-C and Ara-U. Individual calibration plots of peak area against concentration generated
from analysis of standard solutions were used to calculate the concentrations of Ara-C and Ara-U in sample solutions. The
calibration plot was linear in the range 2.5–100 μg mL−1, the average recovery of Ara-C and Ara-U was more than 98% (RSD < 2.5%), and between-day and within-day precision, expressed as relative standard deviation (RSD), were below 4.0%. LOQ for both Ara-C and Ara-U was 2 μg mL−1. The method is rapid, simple, accurate and reproducible, and especially useful for application to patient samples. 相似文献
993.
Y Nomoto H Takai T Hirata M Teranishi T Ohno K Kubo 《Chemical & pharmaceutical bulletin》1991,39(1):86-90
A series of 1-(6,7-dimethoxy-4-quinazolinyl)piperidines carrying various 5-membered heterocycles at the 4-position was synthesized and examined for cardiotonic activity in anesthesized dogs. The (4-oxo-2-thioxo-3-imidazolindinyl)amino derivatives showed the most potent inotropic activity. Marked loss of activity was observed in the 2,4-dihydro-3-thioxo-3H-1,2,4-triazolyl, the 2,4-dihydro-3-oxo-3H-pyrazolyl and the (2,3-dihydro-2-thioxo-3H-1,3,4-thiadiazol-5-yl)amino derivatives. The synthesis and structure-activity relationships are discussed. 相似文献
994.
T. Dresch H. Kramer Y. Thurner R. Weber 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,18(4):391-397
Photodissociation of negatively charged sulfur dioxide clusters (SO2) n ? , 2≦n≦11, was investigated in the wavelength range between 458 nm and 600 nm using a tandem mass spectrometer. The spectral position of the absorption band remains unchanged, however it exhibits narrowing with increasing cluster size. The smooth evolution of the spectra shows that the clusters are composed of a dimer anion core surrounded by neutral molecules. The analysis of the fragmentation products reveals that the absorption of a photon is followed by statistical evaporation of neutrals with a mean energy loss of 0.28±0.05 eV per evaporated monomer in the large cluster limit. 相似文献
995.
H Fujita Y Sasaki H Kohno Y Ohkubo A Ambo K Suzuki M Hino 《Chemical & pharmaceutical bulletin》1990,38(8):2197-2200
Nine analogs based on a structure of Tyr-D-Arg-Phe-X (X = alkylamides or alkylhydrazide containing electron-withdrawing atoms or groups) were newly synthesized and their biological properties were examined by the opioid receptor binding properties of mu-, delta- and kappa-receptors, guinea-pig ileum (GPI) assay and analgesic activity in the tail pinch test after subcutaneous administration in mice. Analogs with X = NHCF2CF3, Sar-ol, or NH(CH2)2CN showed potent activities in the GPI and analgesic assays and high affinity for mu-receptor. An analog with X = taurinamide was found to possess 4-fold higher mu-receptor selectivity than that of [D-Ala2, MePhe4, Gly-ol5]enkephalin (DAGO). The receptor binding properties of previously reported analogs [Chem. Pharm. Bull., 33, 1528 (1985); ibid., 33, 4865 (1985); ibid., 36, 4834 (1988)] were also examined for overall discussion of the structure-activity relationships of this series of tripeptide amides. 相似文献
996.
Abstract— The weak and reversible binding of the antifungal drug, griseofulvin (GF), to calf thymus DNA has been demonstrated by difference spectroscopy and the quenching of the fluorescence of GF by DNA observed. The value of K n was determined to be 800 M -1 by fluorescence quenching titration. Adenosine and guanosine also exhibit difference spectra with GF and quench GF fluorescence indicating that they may be the site of both binding and energy transfer. The in vitro photosensitization of DNA by griseofulvin is shown to occur. It is proposed that the clinically observed in vivo photosensitizing action of griseofulvin may result from binding followed by excitation energy transfer and that this may also be important in the antifungal activity of the drug. 相似文献
997.
J. J. Zhang L. G. Ge X. L. Zhang Y. J. Dai H. L. Chen L. P. Mo 《Journal of Thermal Analysis and Calorimetry》1999,58(2):269-278
The thermal decomposition of Zn[NFA]25H2O (NFA=C16H18FN3O3, norfloxacin) and its kinetics were studied under non-isothermal conditions in air by TG-DTG and DTA methods. The intermediate and residue for each decomposition were identified from the TG curve. The non-isothermal kinetic data were analyzed by means of the Achar method and the Madhusudanan-Krishnan-Ninan (MKN) method. The possible reaction mechanisms were investigated by comparing the kinetic parameters. The kinetic equation for the second stage can be expressed as d/dt=Aexp(–E/RT)(1–).This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
998.
WADOOD Y. HAMAD 《Cellulose (London, England)》1997,4(1):51-56
Wood-pulp fibres are recognized as concentrically-layered, laminated composite tubes of structural reinforcing material, the
cellulose microfibrils, embedded in a cementing matrix of hemicellulose and lignin. When the single fibres are subjected to
cyclic mechanical action, their morphological behaviour is characterized by the fatigue growth of micro-voids and surface
damage which individually and collectively give rise to stress concentrations, and eventually crack development. The progressive
damage phenomena, evinced by the surface imaging and optical sectioning techniques through utilizing confocal laser scanning
microscopy, are understood to be consequences of the cumulative material micromechanical degradation and subsequent microstructural
breakdown of the cellulose microfibrillar framework. This structural breakdown is believed to effect the fibrillation and
flexibilization of the fibres
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
999.
J. H. Shan L. Fan S. Y. Huo J. J. Zhu H. M. Liu S. G. Shen 《Journal of the Iranian Chemical Society》2007,4(4):476-480
A spectrophotometric study of the kinetics and mechanism of the oxidation of malic acid (Mal) by chromium(VI) catalyzed by 2,2′-bipyridyl (bpy) in aqueous acidic medium was conducted in a temperature range of ~298 to 313 K. This reaction was found to be pseudo-first order with respect to Cr(VI) and first order with respect to malic acid. Under the conditions of the pseudo-first order ([Mal]o ? [Cr(VI)]o), the observed rate constant (k obs) increased with the increase in [H+] and [bpy]. There was a weak negative salt effect. Based on the experimental results, a possible reaction mechanism for this oxidation catalyzed by bpy is proposed. The rate equation derived from this mechanism can explain all the experimental phenomena. 相似文献
1000.
S. G. Wang Y.X. Qiu E. Neumann H. J. Deiseroth W. H. Eugen Schwarz 《无机化学与普通化学杂志》2003,629(10):1718-1730
About 60 molecular species composed of up to 10 mercury atoms and of oxygen atoms and/or of some other elements or groups (such as halogen, OH2, OH, H, alkali, NO3) have been investigated quantum chemically. Different density functional approaches and the ab initio SCF‐MP2 method were applied, comparing different basis sets and different atomic core sizes. It is important not to treat the Hg 5s, p, d as inactive core shells, and to use sufficiently many polarization functions. The shape of the 〉O‐Hg‐Hg‐O〈 units is not favorable concerning the formation of lattices composed of HgI, O and OH only. Despite its bulkiness, the OHgHgO units can easily come into contact with each other and then disproportionate. This is prevented in the so‐called ternary M‐HgI oxides by the embedded oxometallate (oxoacidic) anions. Furthermore, the HgI and HgII oxide bond energies are less favorable towards the stability of HgI oxo compounds, as compared to Hg halidic or oxoacidic compounds. Both points are not promising concerning the search for HgI oxides/hydroxides, although the preparation of such compounds, including spacer groups, by topochemical reactions can still not be excluded. So far, experimental efforts towards the synthesis of such a new class of compounds have only demonstrated that HgII is strictly preferred over HgI in the formation of solids of binary Hg‐O or ternary A‐Hg‐O composition (A = electropositive metal such as alkali, in contrast to M = transition or semi‐metal). This is so even if compounds containing ‘electron rich Hgδ— atoms’ (i.e. A‐Hg amalgams) are oxidized under mild conditions. 相似文献