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991.
A selective Spectrophotometric method has been developed for the trace determination of copper after adsorption of its 1-phenyl-4,4,6-trimethyl(1H, 4H)-pyrimidine-2-thiol (PTPT) complex onto microcrystalline naphthalene. The complex is quantitatively adsorbed on naphthalene in the pH range 7.5–11.5, separated by filtration, dissolved in dimethylformamide (DMF) and determined spectrophotometrically at 400 nm. Beer's law is obeyed in the concentration range 2.5–37.5 g of copper in 10 ml of DMF. The molar absorptivity and Sandell's sensitivity are 1.30 × 1041 · mol–1 · cm–1 and 0.0048g cm–2, respectively. Ten replicate analyses of a solution containing 20.0 g of copper gave a mean absorbance of 0.410 with a relative standard deviation of 0.91 %. The interferences of various ions have been studied and the method has been validated by the determination of copper in various standard reference materials, beers, wines, human hair, goat liver and environmental samples.On leave from St. Stephen's College, Delhi 110 007, India 相似文献
992.
Gert Brandl Fritz Kastner Rainer Fritsch Herbert Zinner Albrecht Mannschreck 《Monatshefte für Chemie / Chemical Monthly》1992,123(11):1059-1069
Summary A procedure is described which serves to measure circular dichrograms () on line during stops of flow in liquid chromatography. Since the concentration of substrate in the spectrometer cell during the stop is not known, the differential absorption coefficients are calculated from the experimental differential absorbances A by means of UV absorption (i. e. photomultiplier voltage) data. Verifications of the procedure are obtained by its application to three substrates (Table 1), the () spectra of which were known. The present on-line technique is compared with a corresponding off-line method.The N,N-dimethylthiobenzamides1 and2 as well as the 9,10-phenanthrenequinone7 consist of interconvertible enantiomers because their planar states are destabilized by steric overcrowding of groups. The unknown dichrograms () of1, 2 and7 are obtained (Figs. 2 and 4) and discussed with reference to the helicities of these molecules.In memory of the late Professor Dr. Dr. h. c. Günther Snatzke. 相似文献
993.
A new synthetic route for the preparation of the betain-like compound (CH3N)6P4F8 from (CH3NPF3)2,N-methyl-hexamethyldisilazane andN,N-dimethyl-urea has been found. The steps of this multi-stage reaction could be rationalized to a far extent.
10. Mitteilung:Kubjacek M., Utvary K., Mh. Chem.112, 305 (1981). 相似文献
994.
In the system U–La–N a new phase of composition La2U2N5 was observed. The differaction pattern of this phase can be indexed with a tetragonal unit cell:a=8.43 Å,c=8.50 Å andc/a=1.008. The pseudocubic sub-cell withaca/2 is closely related to the CsCl-type.
Auszug aus der von der Technisch-Naturwissenschaftlichen Fakuktät der TU Wien approbierten Diplomarbait des Herrn Dipl.-Ing.J. Waldhart. 相似文献
995.
Summary A micro carbon rod atomizer has been employed for specific and quantitative bromine determinations. This Br-specific gas-chromatographic detector works by help of InBr-bands and measurement at 372.7 nm. The performance of this flame band emission detector (FBD) is demonstrated by calibration curves and the detection limits of 2 examples (ethyl bromide, ethylene dibromide), the latter being 5 and 36 ng of bromine, respectively. The reproducibility has been found to be 4.3%. An example of this detector in comparison with a thermoconductivity detector (TCD) is presented.
Verwendung einer Mikro-Graphitküvette als Br-spezifischer Detektor für die Gas-Chromatographie
Zusammenfassung Eine Mikro-Graphit-Küvette wird für spezifische quantitative Brombestimmungen nach der Indium-Methode bei 372,7 nm benützt und in Verbindung mit einem Gas-Chromatographen als Br-spezifischer Detektor eingesetzt. Die Leistungsfähigkeit dieses Detektors wird an 2 Beispielen (Äthylbromid, Dibromäthan) mit Hilfe von Eichkurven, Bestimmung von Nachweisgrenzen u. ä. demonstriert. Die Nachweisgrenzen liegen bei 5 bzw. 36 ng Brom für die 2 genannten Substanzen. Die Reproduzierbarkeit der Messungen liegt bei 4,3%. Ein Beispiel für die Registrierung eines Gemisches verschiedener Substanzen, gemessen mit dem GC + Flammen-Banden-emissions-Detektor (FBD) und zum Vergleich mit einem Wärmeleitfähigkeitsdetektor (TCD), wird dargestellt.
This research work was supported by financial help of the Bundesminister für Forschung und Technologie in Bonn (GFR). 相似文献
996.
J. Umemura 《Journal of Molecular Structure》1977,36(1):35-54
Temperature dependence of the IR spectra of crystalline propionic acid were examined in the temperature range 242–50 K. The intensities of most absorption bands increased on lowering the temperature, but some bands diminished until they disappeared at temperatures lower than about 120 K. Normal coordinate analyses indicate that the former bands are due to the stable cis dimer and the latter due to the less stable trans dimer which would be produced from the cis dimer by simultaneous proton transfer along two hydrogen bonds. 相似文献
997.
Band structure calculations at the level of LMTO-ASA provide insight into the electronic structure of BaV10O15 and the origin of the structural phase transition. A crystal orbital Hamiltonian population/integrated crystal orbital Hamiltonian population analysis provides evidence that the crystallographic phase transition is driven by V-V bond formation. As well, the energy bands near the Fermi level are very narrow, <1 eV, consistent with the fact that the observed insulating behavior can be due to electron localization via either Mott-Hubbard correlation and/or Anderson disorder. The partial solid solution, BaV10−xTixO15, was examined to study the effect of Ti-doping at the V sites on the structure and electronic transport properties. In spite of the non-existence of “BaTi10O15”, the limiting x=8, as indicated by a monotonic increase in the cell volume and systematic changes in properties. This limit may be due to the difficulty of stabilizing Ti2+ in this structure. For x=0.5 both the first order structural phase transition and the magnetic transition at 40 K are quenched. The samples obey the Curie-Weiss law to x=3 with nearly spin only effective moments along with θ values which range from −1090 K (x=0.5) to −1629 K (x=3). For x>3 a very large, ∼2×10−3 emu/mol, temperature independent (TIP) contribution dominates. Conductivity measurements on sintered, polycrystalline samples show semiconducting behavior for all compositions. Activation energies for Mott hopping derived from high temperature data range from ∼0.1 eV for x=0-1 and fall to a plateau of 0.06 eV for x=3-7. Low temperature data for x=3, 5 and 7 show evidence for Mott variable range hoping (VRH) with a T1/4 law and in one case between 5 and 17 K, a Efros-Shklovskii correlated hopping, T1/2 law, was seen, in sharp contrast to BaV10O15 where only the E-S law was observed up to 75 K. Seebeck coefficients are small (<35 μV/K), positive, roughly TIP and increase with increasing x up to x=5. This may point to a Heikes hopping of holes but a simple single carrier model is impossible. The compositions for x>3 are remarkable in that local moment behavior is lost, yet a metallic state is not reached. The failure of this system to be driven metallic even at such high doping levels is not fully understood but it seems clear that disorder induced carrier localization plays a major role. 相似文献
998.
Piotr Kujawa Annie Audibert‐Hayet Joseph Selb Franoise Candau 《Journal of Polymer Science.Polymer Physics》2004,42(9):1640-1655
Multisticker associative polyelectrolytes of acrylamide (≈86 mol %) and sodium 2‐acrylamido‐2‐methylpropanesulfonate (≈12 mol %), hydrophobically modified with N,N‐dihexylacrylamide groups (≈2 mol %), were prepared with a micellar radical polymerization technique. This process led to multiblock polymers in which the length of the hydrophobic blocks could be controlled through variations in the surfactant‐to‐hydrophobe molar ratio, that is, the number of hydrophobes per micelle (NH). The rheological behavior of aqueous solutions of polymers with the same molecular weight and the same composition but with two different hydrophobic block lengths (NH = 7 or 3 monomer units per block) was investigated as a function of the polymer concentration with steady‐flow, creep, and oscillatory experiments. The critical concentration at the onset of the viscosity enhancement decreased as the length of the hydrophobic segments in the polymers increased. Also, an increase in the NH value significantly enhanced the thickening ability of the polymers and affected the structure of the transient network. In the semidilute unentangled regime, the behavior of the polymer with long hydrophobic segments (NH = 7) was studied in detail. The results were well explained by the sticky Rouse theory of associative polymer dynamics. Finally, the viscosity decreased with an increase in the temperature, mainly because of a lowering of the sample relaxation time. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1640–1655, 2004 相似文献
999.
近红外(NIR)光谱技术可用于表征氯仿体系中反胶团增溶水的能力. 对于C12-s-C12•2Br (s=2, 3, 4, 5, 6, 8)系列, 不论体系是否含有NaBr电解质, 由于具有较短联接链的表面活性剂易形成较大的反胶团, 其增溶水的能力随着联接链长度增加而降低. 与未含NaBr电解质的体系相比, 当体系中存在NaBr电解质时所形成的反胶团增溶水能力降低. 相似文献
1000.
《Electroanalysis》2006,18(1):35-43
A new method is presented for the determination of electrochemically labile iron in estuarine and coastal seawater. The method is based on differential pulse anodic stripping voltammetry (DPASV) at a rotating silver‐alloy disk electrode. The voltammetric parameters include a plating potential of ?1.5 V and an activation potential of ?5 V for 10s; the seawater is at the original sample pH. The main finding is the presence of a peak for low nmol L?1 levels of iron at ?0.55 V ascribed to elemental iron deposited on the bare silver alloy electrode. The peak increased linearly with the iron concentration between <1 and 14 nmol L?1 using a 900 s plating time. At higher concentrations an additional iron peak appeared at ?0.7 V which was also found to increase linearly with the iron concentration but at a higher concentration range from ca. 15 to 90 nmol L?1 using a 300 s plating time. The second peak was ascribed to iron deposited on iron. Additions of chelating agents (EDTA and a siderophore) to seawater caused the iron peak to be masked indicating that this method is suitable for iron speciation as only the electrochemically labile fraction is determined. The detection limit was 0.3 nmol L?1 using a 900 s plating time. The method was used to determine iron in the range of 5 to 50 nmol L?1 in samples from the Mersey estuary near Liverpool and its potential use for in situ monitoring was demonstrated by using it to monitor labile iron (at 2–3 nmol L?1) over a period of 4 days at 1 h intervals in coastal waters in the Trondheim fjord, Norway. 相似文献