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991.
S.H. Smith 《International Journal of Multiphase Flow》1984,10(2):173-180
Two Stokes flows which are known to lead to separation are reconsidered from a more dynamic perspective, and it is found that within the region of separated flow there is an extremum for the pressure. A simple argument is presented which indicates that this is true under reasonable conditions. 相似文献
992.
The main reaction products resulting from the addition of atomic hydrogen to acetylene are shown to be ethylene, 1,3-butadiene, and benzene. The mechanism involves chain reactions of the vinyl and butadienyl radicals, which regenerate atomic hydrogen. Some of the rate parameters are estimated. 相似文献
993.
Monte Carlo selected, quasiclassical trajectories have been computed on six potential energy hypersurfaces possessing potential minima or “wells” up to 50 kJ mol?1 deep. The aim of the investigation has been to examine how vibrational energy transfer in A + BC(υ = 1) collisions is promoted by intermolecular attraction of moderate strength. Here results are reported for the mass combination mA = 20 u, mB = 1 u, mC = u. The results show that even quite slight intermolecular attraction can enhance energy transfer, as long as the attraction does not just depend on the separation of A from the center-of-mass of BC. The mean loss of vibrational energy does not depend only the well depth but also on its “location” (in particular, the difference in rBC at the minimum and in isolated BC) and on the angular anisotropy of the potential. Large transfers of energy do not occur only in complex-forming collisions; indeed, a high fraction of trajectories on all surfaces are direct but show similar transfer of energy as in the more complex trajectories on the same surface. The results of the calculations are discussed in relation to the mechanisms and rates of vibrational relaxation in collisions between radicals and between species. such as HF + HF, capable of forming hydrogen bonds. 相似文献
994.
Alan M. Kook Stanford L. Smith Ellis V. Brown 《Magnetic resonance in chemistry : MRC》1984,22(11):730-733
Hydrogen and carbon chemical shifts and H? H and C? H couplings are reported for six aminoquinolines and six aminoisoquinolines in DMSO-d6. 相似文献
995.
The tetxaacetylation of isobutene has been perfomed in AlCl3/AcCl. Treatment of the crude reaction medium with liquid ammonia yields the title compound. 相似文献
996.
Michel Talagrand 《Probability Theory and Related Fields》1998,112(4):545-563
Consider 0<α<1 and the Gaussian process Y(t) on ℝ
N
with covariance E(Y(s)Y(t))=|t|2α+|s|2α−|t−s|2α, where |t| is the Euclidean norm of t. Consider independent copies X
1,…,X
d
of Y and␣the process X(t)=(X
1(t),…,X
d
(t)) valued in ℝ
d
. When kN≤␣(k−1)αd, we show that the trajectories of X do not have k-multiple points. If N<αd and kN>(k−1)αd, the set of k-multiple points of the trajectories X is a countable union of sets of finite Hausdorff measure associated with the function ϕ(ɛ)=ɛ
k
N
/α−(
k
−1)
d
(loglog(1/ɛ))
k
. If N=αd, we show that the set of k-multiple points of the trajectories of X is a countable union of sets of finite Hausdorff measure associated with the function ϕ(ɛ)=ɛ
d
(log(1/ɛ) logloglog 1/ɛ)
k
. (This includes the case k=1.)
Received: 20 May 1997 / Revised version: 15 May 1998 相似文献
997.
In a recent paper the present authors considered the effects of small cross-flow upon the nonlinear evolution of two oblique
waves of unequal amplitude. The present analysis extends this work in two ways: (i) the cross-flow is increased to O(1) making
it of comparable magnitude to the streamwise component and (ii) by taking the long-wavelength limit of Rayleigh's equation
a whole spectrum of wave numbers can now be catered for. Thus (ii) allows a fairly general initial disturbance to be accommodated.
Another significant effect due to the presence of a whole spectrum of wave numbers is that the critical layer jump is now
forced by a quadratic, as opposed to the usual cubic, nonlinearity. Numerical solutions of the new nonlinear amplitude evolution
equation are presented for a special class of initial disturbance.
Received 7 January 1998 and accepted 15 September 1998 相似文献
998.
Donald B. Boyd David W. Smith James J. P. Stewart Erich Wimmer 《Journal of computational chemistry》1988,9(4):387-398
The monocyclic β-lactam [[4(S)-methyl-2-oxo-1-azetidinyl]thia]acetic acid was studied by the semiempirical molecular orbital methods AM1, MNDO, and MINDO/3. Using the reaction coordinate option in the program MOPAC on VAX and Cray X-MP computers, the potential energy curve was calculated for rotation of the C2-N1-S-C torsional angle in the conformationally flexible side chain while optimizing all other geometrical variables in the molecule. The trajectory taken during geometry optimization was found to be sensitive to the computer, the program version, the convergence criteria, and the degree of code optimization used in the calculation. In order to reduce the likelihood of spurious results, conformational or reaction energy hypersurfaces need to be calculated with the more precise SCF convergence and minimization criteria available in programs for MINDO/3, MNDO, and AM1 calculations. The nitrogen in the model β-lactam antibiotic is predicted to invert periodically as the dihedral angle to the exocyclic N-substituent sweeps through 360°. 相似文献
999.
Steven B. Thoma Douglas M. Smith John Boughton Reg Davies 《Particle & Particle Systems Characterization》1993,10(5):246-251
A method for the rapid on-line determination of surface area and solids content in flowing concentrated slurries using low field NMR spin-lattice relaxation measurements has been developed and demonstrated. The relationship between flow and spin-lattice relaxation time (T1) of protons in water at 20 MHz was examined using aqueous copper sulfate solutions. The ability to measure surface area and solids concentration in both stagnant (stopped flow) and flowing systems via NMR was demonstrated using several different concentrated aqueous titania and glass slurries (20 to 80 weight percent) for which the dried powder surface area was previously determined via nitrogen adsorption/BET analysis and the solids content determined gravimetrically. Surface areas were also calculated from particle size analysis and found to vary by up to an order of magnitude from the adsorption and NMR results. 相似文献
1000.
A novel NMR spectrometer is described that is uniquely versatile in its ability to accurately record broad lines by sweeping the superconducting magnetic field and to perform standard high resolution solid state NMR experiments. Broadline observation is illustrated by 27Al spectra from static samples. Such an instrument opens up many nuclei for serious study by NMR in the solid state for the first time. 相似文献