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Dirk Claus Benny Geypens Yvo Ghoos Paul Rutgeerts Jenny Ghyselen Keika Hoshi Geertrui Delanghe 《Journal of separation science》1997,20(2):94-98
A method is described for the analysis of volatile organic compounds in saliva and tongue coating samples. The techniue is based on an off-line preconcentration step by means of a closed-loop trapping system followed by gas chromatography-ion trap detection. With the closed-loop technique, the volatile organic compounds(VOCs) are released from the matrix and trapped on an adsorbent without interference of water. The VOCs are released from the adsorbent into the gas chromatograph by thermdesorption. After separation, identification of the compounds is performed by ion trap technology. By this technique 82 compounds could be demonstrated in saliva and tongue coating samples. The technique is also used to demonstrate the formation of volatile bacterial fermentation compounds when a protein substrate is added to tongue coating samples. It is considered a very promising tool in further research on oral malodor. 相似文献
54.
The complete molecular structure of biphenyl, characterized by 12 independent parameters, has been derived by ab initio gradient techniques using a STO -3G basis set for coplanar, perpendicular, and minimum energy conformations with the constraint of planar phenyl ring units and a C2 symmetry axis along the CC interring bond. The minimum torsional angle obtained was ? = 38.63° with torsional energy barriers of 8.59 and 10.04 kJ/mol for ? = 0° and ? = 90°, respectively. 相似文献
55.
H. Blume R. Färber N. Feldmann K. Heinloth D. Kramarczyk F. Kuckelkorn H. J. Michels J. Päsler J. P. Dowd 《Zeitschrift fur Physik C Particles and Fields》1983,16(4):283-289
The electroproduction of π0-mesons on protons has been measured with electrons of 1.7 and 2.1 GeV energy in the region of the nucleon resonances at \(W = \sqrt {(q + p)^2 } = 1,400 - 2,000MeV\) at rather low values of |q 2|=|(e?e′)2|=0.01–0.1 GeV2 but at high values of the nucleon recoil |t|=|(p?p′)2|≈0.6–2.2 GeV2 corresponding to \(\Theta _\pi ^{cm} \approx 145^ \circ - 180^ \circ\) . Up toW≈1,650 MeV the cross section for π0-production with virtual photons of |q 2|≈0.03 GeV2 is only slightly smaller than that with real photons. ForW?1,700 MeV the cross section at |q 2|≈0.03 GeV2 is on average a factor of 2 smaller than that atq 2=0 but only slightly higher than that at |q 2|≈0.3–1 GeV2. 相似文献
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Claus Harzdorf und Ottmar Steinhauser 《Fresenius' Journal of Analytical Chemistry》1966,218(2):96-104
Zusammenfassung PbClF und PbBrF werden bezüglich ihrer Fällungsbedingungen und Eignung zur Fluoridbestimmung verglichen.Für reine Lösungen sind bei Einhaltung bestimmter Fällungsbedingungen beide Methoden gleich gut geeignet. Bei der Fällung aus silicathaltigen Probelösungen, wie sie bei der Fluorbestimmung in technischen Fluoriden anfallen, liefert die PbClF-Fällung positive Fehler, während man über PbBrF sehr gute Werte erhält.Eine Arbeitsvorschrift für die Fluorbestimmung in Aluminiumfluorid und Kyrolith nach der Bleibromidfluoridmethode ist angegeben.
Summary PbClF and PbBrF have been compared with respect to their precipitation conditions and their suitability for the determination of fluoride.For pure solutions, if certain precipitation conditions are adhered to, both methods are equally well suitable. When precipitating from silicate-containing sample solutions, as they are obtained when fluorine is determined in technical fluorides, the PbClF precipitations yields positive errors, while very good values are obtained with PbBrF.A working procedure is given for the determination of fluorine in aluminium fluoride and cryolite by the lead bromide fluoride method.相似文献
58.
Improved full ab initio optimizations of the molecular structure of biphenyl in twisted minimum energy, coplanar, and perpendicular conformations by use of Poles's GAUSSIAN 82 program have been performed in the 6-31G basis set. These lead to geometries and energies of much higher reliability than our earlier STO-3G results. The torsional angle Φmin obtained now is 45.41° in close agreement with the recent experimental value of 44.4° ± 1.2°. Calculated CC distances may be converted to experimental ED rg-values by means of independently determined linear regression correlations with very high statistical confidence, although they agree better with experimental x ray data for coplanar biphenyl without this correction. Calculated intramolecular angles are very similar for both STO-3G and 6-31G basis sets. The calculated torsional energy barrier towards Φ = 90° (ΔE90) is 6.76 kJ/mol in close agreement with the experimental-31G value of 6.5 ± 2.0 kJ/mol. For coplanar biphenyl with D2h-symmetry the calculated torsional energy barrier ΔE0 is 13.26 kJ/mol which is surprisingly much higher than the experimental value of 6.0 ± 2.1 kJ/mol. This discrepancy could not be resolved by optimizations assumed for two kinds of distortions of planarity of orthohydrogens from the molecular plane of the coplanar carbon atoms. But for the twisted minimum energy conformation asymmetric bending of ortho-H atoms lead to a torsional angle Φmin = 44.74° together with a dihedral angle towards ortho-H of 1.22°, and consequently even to an increase of torsional energy barriers to ΔE0 = 13.51 and ΔE90 = 6.91 kJ/mol. 相似文献
59.
A. A. El‐Barbary M. A. Sakran A. M. El‐Madani Claus Nielsen 《Journal of heterocyclic chemistry》2005,42(5):935-941
4‐Amino‐6‐methyl‐3‐(2H)‐thioxo‐5‐(4H)‐oxo‐1,2,4‐triazine ( 1 ) was condensed with 2‐methyl (or phenyl)‐4H‐3,1‐benzoxazin‐4‐one ( 5a,b ) in boiling acetic acid to give compounds 8‐11 . Reacting 1 with chloroacetyl chloride afforded the corresponding chloroacetamido and triazinothiadiazine derivatives 12 and 13 . Condensing 2 with succinic anhydride and/or phthalic anhydride yielded compounds 14 and 15 . Benzoylation of 4‐amino‐6‐methyl‐3‐(2H)‐thioxo‐5‐(4H)‐oxo‐2‐(2,3,4,5‐tetra‐O‐acetyl‐α‐D‐glucopyra‐nosyl)‐1,2,4‐triazine ( 19 ) afforded the corresponding 4‐N,N‐dibenzoyl derivative 20 . Deblocking of the N‐2 glycoside 21 and the S‐glycoside 22 by methanolic ammonia gave compounds 23 and 24 . Acetylation of 4‐amino glycoside 25a afforded the corresponding 4‐mono‐ and 4‐diacetyl derivatives 26 and 27 . Deamination of 25a,b yielded compounds 28a,b . Methylation of compound 28b afforded the corresponding N4‐ and S‐methyl derivatives 29 and 30 . 相似文献
60.
Starting from 2-isopropylidene-1,3-dithiane, various ketene-dithioacetal-S-imides have been prepared and characterized by1H- and13C-NMR spectra.
Ketendithioacetal-S-imideKurze Mitteilung相似文献