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991.
992.
Heinrich B Tserkovnyak Y Woltersdorf G Brataas A Urban R Bauer GE 《Physical review letters》2003,90(18):187601
A long-range dynamic interaction between ferromagnetic films separated by normal-metal spacers is reported, which is communicated by nonequilibrium spin currents. It is measured by ferromagnetic resonance and explained by an adiabatic spin-pump theory. In such a resonance the spin-pump mechanism of spatially separated magnetic moments leads to an appreciable increase in the resonant linewidth when the resonance fields are well apart, and results in a dramatic linewidth narrowing when the resonant fields approach each other. 相似文献
993.
Sun PZ Seland JG Cory D 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,161(2):168-173
Pulsed gradient spin echo (PGSE) experiments can be used to measure the probability distribution of molecular displacements. In homogeneous samples this reports on the molecular diffusion coefficient, and in heterogeneous samples, such as porous media and biological tissue, such measurements provide information about the sample's morphology. In heterogeneous samples however background gradients are also present and prevent an accurate measurement of molecular displacements. The interference of time independent background gradients with the applied magnetic field gradients can be removed through the use of bipolar gradient pulses. However, when the background gradients are spatially non-uniform molecular diffusion introduces a temporal modulation of the background gradients. This defeats simple bipolar gradient suppression of background gradients in diffusion related measurements. Here we introduce a new method that requires the background gradients to be constant over coding intervals only. Since the coding intervals are typically at least an order of magnitude shorter than the storage time, this new method succeeds in suppressing cross-terms for a much wider range of heterogeneous samples. 相似文献
994.
K. Kossert M. Camen F. Wissmann J. Ahrens J.R.M. Annand H.-J. Arends R. Beck G. Caselotti P. Grabmayr O. Jahn P. Jennewein M.I. Levchuk A.I. L'vov J.C. McGeorge A. Natter V. Olmos de León V.A. Petrun'kin G. Rosner M. Schumacher B. Seitz F. Smend A. Thomas W. Weihofen F. Zapadtka 《The European Physical Journal A - Hadrons and Nuclei》2003,16(2):259-273
Differential cross-sections for quasi-free Compton scattering from the proton and neutron bound in the deuteron have been
measured using the Glasgow/Mainz photon tagging spectrometer at the Mainz MAMI accelerator together with the Mainz [48]cm
;SPMOslash; × [64]cm NaI(Tl) photon detector and the G?ttingen SENECA recoil detector. The data cover photon energies ranging from [200]MeV
to [400]MeV at θLAB
γ = 136.2°. Liquid deuterium and hydrogen targets allowed direct comparison of free and quasi-free scattering from the proton. The neutron
detection efficiency of the SENECA detector was measured via the reaction p(γ,π+
n). The “free” proton Compton scattering cross-sections extracted from the bound proton data are in reasonable agreement with
those for the free proton which gives confidence in the method to extract the differential cross-section for free scattering
from quasi-free data. Differential cross-sections on the free neutron have been extracted and the difference of the electromagnetic
polarizabilities of the neutron has been determined to be αn - βn = 9.8±3.6(stat)+2.1
-1.1(syst)±2.2(model) in units of [10-4]fm
3. In combination with the polarizability sum αn + βn = 15.2±0.5 deduced from photoabsorption data, the neutron electric and magnetic polarizabilities, αn = 12.5±1.8(stat)+1.1
-0.6(syst)±1.1(model) and βn = 2.7±1.8(stat)+0.6
-1.1(syst)±1.1(model) are obtained. The backward spin polarizability of the neutron was determined to be γ(n)
π = (58.6±4.0)×10-4
fm
4.
Received: 21 August 2002 / Accepted: 16 October 2002 / Published online: 11 February 2003
RID="a"
ID="a"Part of the Doctoral Thesis.
RID="b"
ID="b"Present address: Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig.
RID="a"
ID="a"Part of the Doctoral Thesis.
RID="b"
ID="b"Present address: Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig.
RID="c"
ID="c"Part of the Habilitation Thesis.
RID="d"
ID="d"e-mail: schumacher@physik2.uni-goettingen.de
Communicated by Th. Walcher 相似文献
995.
Meyer JC Paillet M Michel T Moréac A Neumann A Duesberg GS Roth S Sauvajol JL 《Physical review letters》2005,95(21):217401
Using electron diffraction on freestanding single-walled carbon nanotubes, we have determined the structural indices (n,m) of tubes in the diameter range from 1.4 to 3 nm. On the same freestanding tubes, we have recorded Raman spectra of the tangential modes and the radial breathing mode. For the smaller diameters (1.4-1.7 nm), these measurements confirm previously established radial breathing mode frequency versus diameter relations and would be consistent with the theoretically predicted proportionality to the inverse diameter. However, for extending the relation to larger diameters, either a yet unexplained environmental constant has to be assumed, or the linear relation has to be abandoned. 相似文献
996.
Seland JG Bruvold M Anthonsen H Brurok H Nordhøy W Jynge P Krane J 《Magnetic resonance imaging》2005,23(2):353-354
We have used combined D-T1 and T1-T2 correlation experiments to explore water compartments in rat heart tissue (myocardium). The results show that two main compartments can be identified, which we assign to extracellular (ec) and intracellular (ic) water. The exchange rate of water across the cell membrane was found to be on the order of 0.1 Hz. In addition, the T1-T2 correlation measurements indicate that the ic compartment contain two T2 populations. 相似文献
997.
[reaction: see text] A Ru-catalyzed tandem alkyne-enone coupling/Michael addition reaction is reported. It provides an efficient, atom-economic entry to 4-methylene-2,6-cis-tetrahydropyrans from simple, readily available homopropargylic alcohols and beta,gamma-unsaturated enones in good yields. Further functionalization of the resultant vinylsilane leads to the synthesis of either geometrically defined trisubstituted alkene exocyclic to the 2,6-cis-dihydropyran. 相似文献
998.
999.
The recognition of isolated words and words in sentences: individual variability in the use of sentence context 总被引:2,自引:0,他引:2
Estimates of the ability to make use of sentence context in 34 postlingually hearing-impaired (HI) individuals were obtained using formulas developed by Boothroyd and Nittrouer [Boothroyd and Nittrouer, J. Acoust. Sco. Am. 84, 101-114 (1988)] which relate scores for isolated words to words in meaningful sentences. Sentence materials were constructed by concatenating digitized productions of isolated words to ensure physical equivalence among the test items in the two conditions. Isolated words and words in sentences were tested at three levels of intelligibility (targeting 29%, 50%, and 79% correct). Thus, for each subject, three estimates of context ability, or k factors, were obtained. In addition, auditory, visual, and auditory-visual sentence recognition was evaluated using natural productions of sentence materials. Two main questions were addressed: (1) Is context ability constant for speech materials produced with different degrees of clarity? and (2) What are the relations between individual estimates of k and sentence recognition as a function of presentation modality? Results showed that estimates of k were not constant across different levels of intelligibility: k was greater for the more degraded condition relative to conditions of higher word intelligibility. Estimates of k also were influenced strongly by the test order of isolated words and words in sentences. That is, prior exposure to words in sentences improved later recognition of the same words when presented in isolation (and vice versa), even though the 1500 key words comprising the test materials were presented under degraded (filtered) conditions without feedback. The impact of this order effect was to reduce individual estimates of k for subjects exposed to sentence materials first and to increase estimates of k for subjects exposed to isolated words first. Finally, significant relationships were found between individual k scores and sentence recognition scores in all three presentation modalities, suggesting that k is a useful measure of individual differences in the ability to use sentence context. 相似文献
1000.