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801.
Chloroacetyl chloride is studied by gas-phase electron diffraction at nozzle-tip tempera- tures of 18, 110 and 215°C. The molecules exist as a mixture of anti and gauche confor- mers with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ is found to be 0.770 (0.070), 0.673 (0.086) and 0.572 (0.086) at 18, 110 and 215°C, respectively. These values correspond to an energy difference with estimated standard deviation ΔEo = Eog -Eoa = 1.3 ± 0.4 kcal mol?1 and an entropy difference ΔSo = Sog -Soa = 0.7 ± 1.1 cal mol?1 K?1. Certain of the diffraction results permit the evaluation of an approximate torsional potential function of the form 2V = V1(1 - cos φ) + V2(1 - cos 2φ) + V3(1 - cos 3φ); the results are V1 = 1.19 ± 0.33, V2 = 0.56 ± 0.20 and V3 = 0.94 ± 0.12, all in kcal mol?1. The results for the distance (ra), angle (∠α) and r.m.s. amplitude parameters obtained at the three temperatures are entirely consistent. At 18°C the more important parameters are, with estimated uncertainties of 2σ, r(C-H) = 1.062(0.030) Å, r(CO) = 1.182(0.004) Å, r(C-C) = 1.521(0.009) Å. r(CO-Cl) = 1.772(0.016) Å, r(CH2-Cl) = 1.782(0.018) Å, ∠C-C-0 = 126.9(0.9)°, ∠CH2-CO-C1 = 110.0(0.7)°,∠CO-CH2-C1 = 112.9(1–7)°, ∠H-C-H = 109.5° (assumed), ∠φ (gauche torsion angle relative to 0° for the anti form) = 116.4(7.7)°, δ (r.m.s. amplitude of torsional vibration in the anti conformer) == 17.5(4.2)°. 相似文献
802.
Grunwaldt G Haebel S Spitz C Steup M Menzel R 《Journal of photochemistry and photobiology. B, Biology》2002,67(3):177-186
Fluorescein isothiocyanate (FITC)-myoglobin conjugates were synthesized with a binding stoichiometry of one to three fluorophores per protein. FITC binding sites were determined by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). Five lysine residues and the N-terminal amino group were identified as preferential binding sites. The ground and excited-state absorption spectra and the fluorescence decay of the conjugates in the native and denatured state of the carrier protein were analyzed. For comparison, unbound FITC and FITC covalently bound to a polysaccharide (dextran) were studied. For FITC, FITC-dextran and the FITC-myoglobin conjugates, only one FITC absorption peak was obtained in the ground state spectrum. Similarly, the excited state absorption (ESA) spectra of unbound FITC and of FITC-dextran showed only one single maximum whereas two maxima were detected for the native FITC-myoglobin conjugates. One of these sub-bands disappeared following urea treatment of the conjugate. We conclude that ESA measurements of extrinsic fluorophores on proteins can be used to monitor different micro-environments of the fluorophore and to distinguish between different conformational states of the labeled protein. This method can be a useful tool for analysing coexisting protein conformations. 相似文献
803.
804.
805.
Jussi Behrndt Hagen Neidhardt Paul N. Racec Ulrich Wulf 《Journal of Differential Equations》2008,244(10):2545-2577
The main objective of this paper is to give a rigorous treatment of Wigner's and Eisenbud's R-matrix method for scattering matrices of scattering systems consisting of two selfadjoint extensions of the same symmetric operator with finite deficiency indices. In the framework of boundary triplets and associated Weyl functions an abstract generalization of the R-matrix method is developed and the results are applied to Schrödinger operators on the real axis. 相似文献
806.
This paper presents two new dynamic hysteresis models obtained from the Bouc–Wen model by incorporating position and acceleration information. On the one hand, the model employing position information is rate-independent and it is able to reproduce some kind of double hysteretic loops unable to be reproduced with the original Bouc–Wen model. On the other hand, the model employing acceleration information is insensitive to linear time-scale variations. Moreover, a classification of the BIBO-stable models has been derived for both position and acceleration cases. Double hysteretic loops have been experimentally reported in shape-memory alloys, reinforced concrete structures, wood structures and lightweight steel shear wall structures. The proposed hysteretic models represent a prominent use in the field of structural dynamics and earthquake engineering because they can capture the nonlinear dynamics of the materials and structures presented earlier when they are subjected to dynamic loads as earthquake excitations. 相似文献
807.
Claudia S. Neuhaus Gisela Gabernet Christian Steuer Katharina Root Jan A. Hiss Renato Zenobi Gisbert Schneider 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(6):1688-1692
A computational technique based on a simulated molecular evolution protocol was employed for anticancer peptide (ACP) design. Starting from known ACPs, innovative bioactive peptides were automatically generated in computer‐assisted design–synthesize–test cycles. This design algorithm offers a viable strategy for the generation of novel peptide sequences, without requiring a priori structure–activity knowledge. Sequence morphing and activity improvement were achieved through iterative amino acid variation and selection. Results show that not only the interaction of ACPs with the target membrane is important for their anticancer activity, but also the degree of peptide dimerization, which was corroborated by temperature profiling and electrospray mass spectrometry. 相似文献
808.
Dr. Suvendu Sekhar Mondal Alex Kreuzer Dr. Karsten Behrens Prof. Dr. Gisela Schütz Prof. Hans-Jürgen Holdt Dr. Michael Hirscher 《Chemphyschem》2019,20(10):1311-1315
Quantum sieving of hydrogen isotopes is experimentally studied in isostructural hexagonal metal-organic frameworks having 1-D channels, named IFP-1, −3, −4 and −7. Inside the channels, different molecules or atoms restrict the channel diameter periodically with apertures larger (4.2 Å for IFP-1, 3.1 Å for IFP-3) and smaller (2.1 Å for IFP-7, 1.7 Å for IFP-4) than the kinetic diameter of hydrogen isotopes. From a geometrical point of view, no gas should penetrate into IFP-7 and IFP-4, but due to the thermally induced flexibility, so-called gate-opening effect of the apertures, penetration becomes possible with increasing temperature. Thermal desorption spectroscopy (TDS) measurements with pure H2 or D2 have been applied to study isotope adsorption. Further TDS experiments after exposure to an equimolar H2/D2 mixture allow to determine directly the selectivity of isotope separation by quantum sieving. IFP-7 shows a very low selectivity not higher than S=2. The selectivity of the materials with the smallest pore aperture IFP-4 has a constant value of S≈2 for different exposure times and pressures, which can be explained by the 1-D channel structure. Due to the relatively small cavities between the apertures of IFP-4 and IFP-7, molecules in the channels cannot pass each other, which leads to a single-file filling. Therefore, no time dependence is observed, since the quantum sieving effect occurs only at the outermost pore aperture, resulting in a low separation selectivity. 相似文献
809.
810.
Hagen S Barfod R Fehrmann R Jacobsen CJ Teunissen HT Ståhl K Chorkendorff I 《Chemical communications (Cambridge, England)》2002,(11):1206-1207
Barium-promoted cobalt catalysts supported on carbon exhibit higher ammonia activities at synthesis temperatures than the commercial, multipromoted iron catalyst and also a lower ammonia inhibition. 相似文献