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111.
The crystal structure of α-methanol at 15K has been determined from neutron powder diffraction measurements. The structure is orthorhombic, space group P212121. The molecular geometry is found to be very similar to that in the gas phase, but the methyl group no longer has ideal 3-fold symmetry. The crystal is formed by infinite hydrogen-bonded chains of molecules with adjacent chains ‘pointing’ in opposite directions. The O-H … O hydrogen bonds are almost linear. No phase intermediate between the low temperature α-phase and the high temperature β-phase was found, but a new, metastable phase was discovered. 相似文献
112.
113.
114.
M.J.D. Powell 《Numerische Mathematik》1994,68(1):107-128
Summary.
Let be a function from to that has
square
integrable second derivatives and let be the thin plate spline
interpolant
to at the points in
. We seek
bounds on the error when is in the convex
hull of
the interpolation points or when is close to at least one of
the
interpolation points but need not be in the convex hull. We find, for example,
that, if is inside a triangle whose vertices are any three
of the
interpolation points, then is bounded above by a
multiple of ,
where is the length of the longest side of the triangle and
where the
multiplier is independent of the interpolation points. Further, if
is any
bounded set in that is not a subset of a single straight
line, then we
prove that a sequence of thin plate spline interpolants converges to
uniformly on . Specifically, we require , where
is now the least upper bound on the numbers and where ,
, is
the least Euclidean
distance from to an interpolation point. Our method of
analysis applies
integration by parts and the Cauchy--Schwarz inequality to the scalar product
between second derivatives that occurs in the variational calculation of thin
plate spline interpolation.
Received November 10, 1993 / Revised version received March 1994 相似文献
115.
The title compound was obtained in crystalline form suitable for X-ray structure determination. It forms crystals in the monoclinic space group P21/c with two centrosymmetric molecules in a unit cell of dimensions, a = 10.888(1) Å, b = 10.182(2) Å, c = 17.929(4) Å, β = 104.33(1)°. The central Mo2Cl2(O2C)2P2 core has effectively C2h-symmetry with the following principal dimensions: MoMo = 2.091(1) Å, MoCl = 2.405 Å, MoP = 2.566(2) Å, MoO(av.) = 2.103[4] Å, MoMoP = 104.38(7)°, and MoMoCl = 116.23(8)°. 相似文献
116.
117.
M. J. D. Powell 《Mathematical Programming》1977,12(1):141-147
Davidon [1] provides a variable metric algorithm for minimization calculations that achieves quadratic termination without any line searches by a method that uses positive definite second derivative approximations. We give a new and elementary proof of these termination properties. It shows the great freedom allowed by the algorithm in the choice of search directions and it explains the effect of a restart procedure. 相似文献
118.
A.L.S. Angelis G. Basini H.-J. Besch R. Breedon L. Camilleri T.J. Chapin R.L. Cool P.T. Cox C. von Gagern C. Grosso-Pilcher D. Hanna J.T. Linnemann C.B. Newman R.B. Nickerson N. Phinney S.H. Pordes K. Powell J.M. Yelton 《Physics letters. [Part B]》1982,116(5):379-382
The invariant cross sections for π0 meson production in alpha—alpha and alpha—proton collisions at the ISR were meas- ured up to transverse momenta of and , respectively. These measurements are compared with π0 production in pp collisions at the same values of nucleon, and the variation of the nuclear A-dependence with pT is determined. 相似文献
119.
M. J. D. Powell 《Mathematical Programming》1988,42(1-3):171-180
An unusual form of the maximum entropy problem is considered, that includes simple bound constraints on the Fourier coefficients of the required image, as well as nonnegativity conditions on the image intensities. The algorithm avoids mixing these constraints by introducing a parameter into the objective function that is adjusted by an outer iteration. For each parameter value an inner iteration solves a large optimization calculation, whose constraints are just the simple bounds, by a combination of the conjugate gradient procedure and an active set method. An important feature is the ability to make many changes to the active set at once. The outer iteration includes a test for inconsistency of all the given constraints. The algorithm is described, a proof of convergence is given, and there are some second-hand remarks on numerical results. 相似文献
120.
J. L. Bailly W. Bartl F. Bruyant W. M. Bugg C. Caso R. Contri H. Dibon R. Di Marco B. Epp A. Ferrando F. Fontanelli P. Girtler A. Gurfu E. L. Hart P. Herquet J. Hrubec Y. Iga E. Kisteney S. Kitamura J. M. Kohli H. Kohno J. C. Marin M. Markytan I. S. Mittra L. Montanet G. Neuhofer Y. Petrovykh R. Plano B. Poljakov P. Porth B. Powell B. Pylgroms T. Rodrigo A. H. Rogers J. Salicio S. Squarcia P. Stamer V. Stopchenko K. Sudhakar U. Trevisan C. Willmott T. Yamagata V. Yarba EHS-RCBC Collaboration Bombay-CERN-Genova-Innsbruck-Japan UG-Madrid-Mons-Rutgers-Serpukhov-Tennessee-Vienna Collaboration 《Zeitschrift fur Physik C Particles and Fields》1984,22(2):119-124
The intermediate and forward gamma detectors of EHS are used to reconstructπ°'s produced by 360 GeV/cpp interactions in the Rapid Cycling Bubble Chamber (RCBC). Using thepp forwardbackward symmetry, the inclusiveπ° production cross section is obtainedσ π°=(132±11) mb. The averageπ° multiplicity is determined as a function of the charged particle multiplicity. The (1?x) dependence is given for differentp T regions. 相似文献