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1.
Received July 12, 2001 / Published online February 28, 2002 相似文献
2.
3.
We introduce a new class of experiments which provide graphic insights into the propagation of acoustic waves in anisotropic media. Simply stated, we have devised a means of observing the expanding acoustic wavefront from a point disturbance in a solid. The data may be viewed as a movie or a series of snapshots. The observed wavefronts represent the group-velocity surfaces of acoustic waves, which reflect the basic elastic anisotropy of the solid. The technique has been applied to coherent acoustic waves with frequencies in the megahertz range (at ambient temperatures) and to incoherent heat pulses in the hundred-gigahertz range (at liquid-helium temperatures). In this article, we first provide a pedagogical introduction to wave propagation in elastically anisotropic media, reviewing some early methods for visualizing acoustic waves. Next, we describe the “acoustic wavefront imaging” method and give representative results in crystals and composite materials. Finally, we show how this method relates to recent advances in phonon imaging and internal diffraction of ultrasound. 相似文献
4.
Alberto García Nora Bretón Isidore Hauser 《International Journal of Theoretical Physics》1988,27(5):635-640
It is shown that any stationary axisymmetric solution to the vacuum field equations of the Jordan-Brans-Dicke (JBD) theory may be obtained from a composition of any stationary axisymmetric vacuum Einstein spacetime with the Weyl class of metrics. Thus, generating solution techniques can be used to obtain any stationary axisymmetric JBD vacuum solution. In this manner, C. B. G. McIntosh's results concerning this topic are improved upon. 相似文献
5.
Adler J Becker JJ Blaylock GT Bolton T Brient J Browder T Brown JS Bunnell KO Burchell M Burnett TH Cassell RE Coffman D Cook V Coward DH DeJongh F Dorfan DE Drinkard J Dubois GP Eigen G Einsweiler KF Eisenstein BI Freese T Gatto C Gladding G Grab C Hamilton RP Hauser J Heusch CA Hitlin DG Izen JM Kim PC Köpke L Li A Lockman WS Mallik U Matthews CG Mincer AI Mir R Mockett PM Mozley RF Nemati B Odian A Parrish L Partridge R Pitman D Plaetzer SA Richman JD Sadrozinski HF Scarlatella M Schalk TL 《Physical review letters》1989,62(16):1821-1824
6.
P. J. Hauser A. F. Schreiner J. D. Gunter W. J. Mitchell M. K. Dearmond 《Theoretical chemistry accounts》1972,24(1):78-88
MCD, electronic absorption, external heavy atom, and crystal field data are presented for the low energy region (2
E
g, 2
T
1g, 4
T
2g) and high energy region (2
T
2g, 4
T
1g) of Cr(dtp)3, Cr(dtc)3, and Cr(exan)3. At low energy, MCD intensities of 2
E(2
E
g) and 2
E(2
T
g) are as large or larger than 4
T
2g, and the MCD technique is advantageous over electronic absorption in this respect. The MCD positions of 2
E
g and 2
T
1g are nearly the same for these molecules ( 13 kK and 13.6 kK) · 4
T
2g of this region appears trigonally split ( 500 cm–1) in the MCD of dtp but to a smaller extent than in the electronic crystal spectrum of Lebedda and Palmer ( 600 cm–1). MCD did not resolve such components for exan and dtc. The higher energy region includes 2
T
2g and 4
T
1g, and the combined MCD and electronic absorption data of the three compounds taken together lead us to conclude the ordering 2
A
1(2
T
2g)<2
E(2
T
2g)<4
E(4
T
1g). The potentially useful external heavy atom affect on the solution-observed electronic 2
E and 4
E bands of Cr(dtp)3 did not shed additional light on this order of E states. Finally, it is concluded that the order of 4
T
1g and 2
T
2g cannot be decided from O
h crystal field calculations because of experimental uncertainties about choosing centers of gravity. In addition, 4
T
1g and 2
T
2g are close together so that ordering 2
E<4
E does not guarantee 2
T
2g<4
T
1g. However, it can be concluded that the ratio C/B4 is not correct, whereas the larger 7<(C/B)<8 is consistent with the data of all three molecules because of small B parameters ( 0.4). Locating OO transitions may somewhat decrease C/B and Dq.
Presented in part at the 161st American Chemical Society National Meeting, Los Angeles, California, March–April, 1971.
NDEA Pre-Doctoral Fellow. 相似文献
Zusammenfassung In der vorliegenden Arbeit werden folgende Meßergebnisse mitgeteilt; MCD, elektronische Absorption, Einfluß eines äußeren schweren Atoms sowie Kristallfelddaten für den Bereich niedriger Energie (2 E g, 2 T 1g, 4 T 2g) und den Bereich hoher Energie (2 T 2g, 4 T 1g) von Cr(dtp)3, Cr(dtc)3 und Cr(exan). Bei niedriger Energie sind die MCD-Intensitäten von 2 E(2 E g) und 2 E(2 T 1g) genau so groß, oder größer als 4 T 2g, und die MCD-Technik bietet Vorteile gegenüber der elektronischen Absorptionsmethode. Die MCD-Werte von 2 E g und 2 T 1g sind für die genannten Moleküle etwa gleich ( 13 kK und 13,6 kK). 4 T 2g dieses Gebietes erscheint trigonal aufgespalten ( 500 cm–1) bei MCD von dtp, aber in einem geringeren Maß als im elektronischen Kristallspektrum von Lebedda und Palmer ( 600 cm–1) MCD löste solche Komponenten bei exan und dtc nicht auf. Der Bereich höherer Energie enthält 2 T 2g und 4 T 1g, und aus der Kombination von Daten der MCD-Methode sowie der elektronischen Absorption schlossen wir auf die Anordnung 2 A 1g(2 T 2g)<2 E(2 T 2g)<4 E(4 T 1g). Der möglicherweise nützliche Effekt eines äußeren schweren Atoms auf die in Lösung beobachteten elektronischen 2 E- und 4E-Banden von Cr(dtp)3 brachte bezüglich dieser Anordnung der E-Zustände nichts Neues. Weiterhin wird gefolgert, daß die Ordnung von 4 T 1g und 2 T 2g nicht aus O h-Kristallfeldberechnungen entschieden werden kann, da experimentelle Unsicherheiten bezüglich der Wahl von Schwerpunkten bestehen. Außerdem liegen 4 T 1g und 2 T 2g nahe zusammen, sodaß aus der Anordnung 2 E<4 E nicht notwendig 2 T 2g<4 T 1g folgt. Es kann jedoch gefolgert werden, daß das Verhältnis C/B4 nicht korrekt ist, während 7<(C/B)<8 konsistent mit den Daten aller drei Moleküle ist, da die B-parameter klein sind (0,4). Die Vokalisierung der OO-Übergänge könnten C/B und Dq etwas erniedrigen.
Presented in part at the 161st American Chemical Society National Meeting, Los Angeles, California, March–April, 1971.
NDEA Pre-Doctoral Fellow. 相似文献
7.
The enantiomers of adrenaline, noradrenaline, ephedrine and pseudoephedrine were separated by capillary electrophoresis on a micromachined device. Detection was carried out with a new two-electrode amperometric detector, eliminating the need for individual counter and reference electrodes. Separation of the isomers was achieved by employing carboxymethyl-beta-cyclodextrin as chiral selector in the buffer, partly with the additional inclusion of the crown ether 18-crown-6. Plate numbers of up to 20,000, chiral resolutions of 2.5 and detection limits of the order of 10(-7) M were achieved. All separations were completed in less then 3 min. 相似文献
8.
We have synthesized two forms of erbium tetracyanoplatinates, Er2[Pt(CN)4]3.21H2O (red form) and Er2[Pt(CN)4]2.SO4.11.5H2O (yellow form), and determined their crystal structures by X-ray diffraction. While the red form crystallizes in the orthorhombic space group Pbcn, with a = 15.4848(3) A, b = 13.8186(2) A, c = 19.07820(10) A, alpha = beta = gamma = 90 degrees, and Z = 4, the yellow form precipitates in the tetragonal space group I4cm, with a = b = 14.321(2) A, c = 13.338(3) A, alpha = beta = gamma = 90 degrees, and Z = 4. Both forms show [Pt(CN)4]2- chains but differ markedly in color and morphology. This is due to the incorporation of sulfate ions in the latter modification, leading to an increased Pt-Pt distance. The observed optical absorption and emission behavior of the title compounds is correlated with the Pt-Pt distances. 相似文献
9.
We have used the oscillating peroxidase-oxidase (PO) reaction as a model system to study how oscillatory dynamics may affect the influence of toxic reaction intermediates on enzyme stability. In the peroxidase-oxidase reaction reactive intermediates, such as hydrogen peroxide, superoxide, and hydroxyl radical are formed. Such intermediates inactivate many cellular macromolecules such as proteins and nucleic acids. These reaction intermediates also react with peroxidase itself to form an inactive enzyme. The fact that the PO reaction shows bistability between an oscillatory and a steady state gives us a unique possibility to compare such inactivation when the system is in one of these two states. We show that inactivation of peroxidase is slower when the system is in an oscillatory state, and using numerical simulations we provide evidence that oscillatory dynamics lower the average concentration of the reactive intermediates. 相似文献
10.
Baltrusaitis RM Becker JJ Blaylock GT Brown JS Bunnell KO Burnett TH Cassell RE Coffman D Cook V Coward DH Cui H Del Papa C Dorfan DE Duncan AL Einsweiler KF Eisenstein BI Fabrizio R Gladding G Grancagnolo F Hamilton RP Hauser J Heusch CA Hitlin DG Köpke L Mockett PM Moss L Mozley RF Nappi A Odian A Partridge R Perrier J Plaetzer SA Richman JD Roehrig JR Russell JJ Sadrozinski HF Scarlatella M Schalk TL Schindler RH Seiden A Sleeman JC Spadafora AL Thaler JJ Toki W Unno Y Villa F Wattenberg A 《Physical review letters》1985,55(17):1723-1726