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121.
John S. Showell Henry M. Fales Edward A. Sokoloski 《Journal of mass spectrometry : JMS》1989,24(8):632-636
A series of mixtures of solid triglycerides and waxes are examined using 252Cf plasma desorption mass spectrometry. The relative abundances of diagnostic ions are found to vary with sample preparation, handling, and composition. It is proposed that the less efficiently packing, shorter chain, compounds are forced to the analysis site, i.e. the surface. This takes place at varying rates that reflect the bulk properties of the mixture as revealed by its phase diagram and thermal history. Mixtures that remain liquids during analysis show ion abundances correctly reflecting their composition. Mixtures of isotopomeric glycerides also show normal ion abundances. 相似文献
122.
Sergei V. Levchik Giovanni Camino Maria Paola Luda Luigi Costa Bruno Costes Yves Henry Emile Morel George Muller 《先进技术聚合物》1995,6(2):53-62
Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) undergoes homopolymerization on heating. Intramolecular reactions which compete with crosslinking favor the formation of cyclic structures with increasing thermal and fire resistance of the resin, whereas physical mechanical properties tend to decrease. The mechanism of thermal decomposition of TGDDM is studied by thermogravimetry, differential scanning calorimetry and thermal volatilization analysis with characterization of volatiles evolved and residue left. Thermal degradation of poly-(TGDDM) starts at 260°C with elimination of water from secondary alcoholic groups which is a typical pathway for epoxy resin degradation. Resulting unsaturations weaken bonds in the β-position and provoke the first chain breaking at allyl–amine and allyl–either bonds. With increasing temperature, saturated alkyl–ether bonds and alkyl carbon–carbon bonds are broken first, followed by the most stable alkyl–aryl bonds at T>365°C. The combustion performance of TGDDM is discussed on the basis of the thermal degradation behavior. 相似文献
123.
Turner DR Henry M Wilkinson C McIntyre GJ Mason SA Goeta AE Steed JW 《Journal of the American Chemical Society》2005,127(31):11063-11074
Four isomorphous complexes of formula [M(L)(4)(H(2)O)(2)]SO(4).2H(2)O (M = Co, 1a; Ni, 1b; Cu, 1c; Zn, 1d) have been isolated and characterized by single-crystal X-ray diffraction and neutron diffraction using the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin as well as by thermogravimetric analysis. The structures contain a discrete, strongly hydrogen-bonded water tetramer which causes a significant distortion of the metal coordination sphere in each case. Partial atomic charges and hardness analysis (PACHA) calculations reveal that the shortest hydrogen bonds are not the strongest in this constrained, cyclic solid-state structure and show that the distortion at the metal center is caused by the drive to maintain the integrity of the water tetramer. The system undergoes a disorder-order transition on slow cooling that provides insight into the nature of communication between water squares. 相似文献
124.
P. Staszczuk J. C. Bazan M. Błachnio D. Sternik N. J. Garcia 《Journal of Thermal Analysis and Calorimetry》2006,86(1):57-68
This paper presents possible applications of thermal analysis, sorptometry
and porosimetry to study physico-chemical properties of Na- and La-montmorillonite
samples, especially for determination of total surface heterogeneity. The
quasi-isothermal thermogravimetric (Q-TG) mass loss and its first derivative
(Q-DTG) curves with respect to temperature and time obtained during programmed
liquid thermodesorption under quasi-isothermal conditions have been used to
study adsorbed layers and heterogeneous properties of the Na- and La-montmorillonites.
Calculations of the desorption energy distribution functions by analytical
procedure using mass loss Q-TG and differential mass loss Q-DTG curves of
thermodesorption under quasi-isothermal conditions of polar and non-polar
liquid vapours preadsorbed on a material surface are presented. Parameters
relating to porosity of samples were determined by sorptometry, mercury porosimetry
and atomic force microscopy (AFM). From nitrogen sorption isotherms from sorptometry
and porosimetry methods, the fractal dimensions of montmorillonites have been
calculated. Moreover, a new approach is proposed to calculate fractal dimensions
of materials obtained from Q-TG curve; this is compared with values obtained
by the above methods. The total heterogeneous properties (energy distribution
function and pore-size distribution functions) of samples studied were estimated.
The radius and pore volume of the tested samples calculated on the basis of
thermogravimetry, sorptometry and porosimetry techniques were compared and
good correlations obtained. 相似文献
125.
A method is described for the determination of molybdenum down to the microgram level, in samples of soil, steels, fertilizers and pharmaceuticals. After attack with acids, this element is separated from matrix elements by extraction of its 5,5'-methylenedisalicylohydroxamic acid (MEDSHA) complex from 4M hydrochloric acid, into methyl isobutyl ketone. Molybdenum is determined by atomic-absorption spectrometry (AAS), after conversion of the Mo-MEDSHA complex into the MoSCN(-) complex in the organic phase. The detection limit is 0.03 microg/ml, with a relative standard deviation not exceeding 1.5% at a level of 2 microg/ml. The method is highly selective and suffers only from interference by tungsten. 相似文献
126.
C.A. Henry P.K. Diwakar D.W. Hahn 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007,62(12):1390-1398
The role of helium addition on the analyte signal enhancement in laser-induced breakdown spectroscopy for analysis of pure gaseous systems was examined using carbon and hydrogen atomic emission lines. Increased analyte response, as measured by peak-to-base and signal-to-noise ratios, was observed with increasing helium addition, with maximum enhancement approaching a factor of 7. Additional measurements revealed a significant decrease in plasma electron density with increasing helium addition. To explore the mechanisms of analyte signal enhancement, the helium emission lines were also examined and found to be effectively quenched with nitrogen addition. In consideration of the data, it is concluded that the role of metastable helium is not as important as the overall changes in plasma properties, namely electron density and laser-plasma coupling. Helium addition is concluded to affect the electron density via Penning ionization, as well as to play a role in the initial plasma breakdown processes. 相似文献
127.
MNDO and AMI calculations, including configuration interactions, were performed on cycloheptatriene (2), 1,6-methano[10]annulene (3), and the tautomeric elassovalenes (4), (5), and (6). The goal of this study is to examine these systems and assess indicators of the importance of through space (homoaromatic) interactions. It is established that the two-center energy partitioning terms are capable of detecting favorable (negative two-center term) through space interactions. In cases of cyclic conjugation (homoconjugation), it is also shown that the inclusion of CI is necessary. 相似文献
128.
Henry E. Baumgarten Richard G. Parker David L. Von Minden 《Journal of mass spectrometry : JMS》1969,2(12):1221-1237
The mass spectra of six aziridinones (α-lactams) are presented. The six aziridinones exhibit the same general fragmentation pattern, the primary processes being loss of the N-t-butyl group, loss of carbon monoxide and loss of t-butyl isocyanate. Several additional rearrangement or fragmentation processes are observed with specific α-lactams. 相似文献
129.
M. Benassi R. D. M. Garcia C. E. Siewert 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1984,35(3):308-320
Several representations of the dispersion matrix (z) basic to analytical solutions for a theory of radiative transfer that includes the effects of polarization are reported, and a method for computing the zeros of det (z) is discussed. Numerical results are given for several specific models.
Zusammenfassung Verschiedene Darstellungen der Dispersionsmatrix (z), welche grundlegende Bedeutung für die analytischen Lösungen der Theorie der Strahlungsübertragung mit Polarisation hat, werden angegeben. Eine Methode zur Berechnung der Nullstellen von det (z) wird diskutiert. Es werden numerische Ergebnisse für verschiedene Modelle angegeben.相似文献
130.
Donald R. McLaughlin Charles F. Bender Henry F. Schaefer III 《Theoretical chemistry accounts》1972,25(4):352-359
Ab initio calculations including electron correlation are reported for the water and methylene molecules as a function of geometry. A large contracted gaussian basis set is used and the multiconfiguration wave functions, optimized by the iterative natural orbital procedure, include 277 and 617 configurations for H2O and CH2 respectively. The method of selecting configurations, yielding first-order wave functions, is discussed in some detail. For H2O, the SCF geometry is r=0,942 Å, =105,8°, the correlated result is r=0,968 Å, =103,2°, and the experimental r=0,957 Å, =104,5°. The water stretching force constants, in millidynes/Å, are 8,72 (SCF), 8,75 (CI), and 8,4 (experiment). Bending force constants are 0,88 (SCF), 0,83 (CI), and 0,76 (experiment). For methylene the SCF geometry is r=1,072 Å, =129,5°, while the result from first-order wave functions is r=1,088 Å, =134°. The predicted CH2 force constants are 6,16 (SCF) and 6,13 (CI) for stretching and 0,44 (SCF) and 0,33 (CI) for bending.
Work performed under the auspices of the U.S. Atomic Energy Commision.
Supported by the grants from the Research Corporation and the University of California Committee on Research. 相似文献
Zusammenfassung Es wird über ab intito-Rechnungen mit Berücksichtigung der Elektronenkorrelation berichtet, die an Wasser- und Methylenmolekülen als Funktion der Geometrie durchgeführt worden sind. Dazu benutzt man einen großen kontrahierten Gauß-Basissatz. Die Multikonfigurationswellenfunktionen, die unter Benutzung von natürlichen Orbitalen nach der iterativen Prozedur optimiert werden, enthalten für H2O 277 Konfigurationen und für CH2 617. Die Auswahlmethode, die zu Wellenfunktionen 1. Ordnung führt, wird diskutiert. Im Falle des Wassers erhält man die SCF-Geometrie zu r=0,942 Å, =105,8°, das korrelierte Resultat ist: r=0,968 Å, =103,2° und das experimentelle r=0,957 Å, =104,5°. Für Wasser ergeben sich die Valenzkraftkonstanten (in Millidyn Å–1) 8,72 (SCF), 8,75 (CI) und 8,4 (Experiment). Die Deformationskonstanten sind 0,88 (SCF), 0,83 (CI) und 0,76 (Experiment). Im Falle des Methylens ist die SCF-Geometrie r=1,072 Å, =129,5°, während man mit Wellenfunktionen 1. Ordnung r=1,088 Å und =134° erhält. Die CH2-Kraftkonstanten werden für die Valenzschwingung zu 6,16 (SCF) und 6,13 (CI) bzw. für die Deformationsschwingung zu 0,44 (SCF) und 0,33 (CI) vorausgesagt.
Work performed under the auspices of the U.S. Atomic Energy Commision.
Supported by the grants from the Research Corporation and the University of California Committee on Research. 相似文献