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931.
V. A. Dlugunovich V. A. Zaitseva S. A. Sergeichik O. V. Tsaryuk 《Journal of Applied Spectroscopy》2001,68(6):1020-1025
Results of laboratory simulation experiments on the influence of H2SO4 solutions on the optical characteristics of the radiation reflected from Rhododendron smirnovii leaves illuminated at an angle of 55° by He–Ne laser radiation ( = 0.63 m) linearly polarized in the plane of incidence are presented. The coefficients of correlation between the optical characteristics of the reflected radiation, the concentration of the acid, and the pigment composition of the leaves have been calculated. It is shown that the influence of acidic stresses on the polarization characteristics of the radiation reflected from a leaf manifests itself indirectly as changes in the concentration of chlorophyll a and chlorophyll b and changes in their ratio in the leaf when observation is performed at angles of 50–60°. 相似文献
932.
Jacek Goc Alina Dudkowiak Zygmunt Gryczyński Ignacy Gryczyński Bogumil Zelent Danuta Frąckowiak 《Journal of fluorescence》2001,11(1):53-63
Polarized absorption and fluorescence spectra of bacteriochlorophyll c and green photosynthetic bacterium Prostheecochloris aestuarii cells and cell fragments embedded in stretched polymer film were measured. In pigment samples the artificial oligomers of bacteriochlorophyll c (with absorption about 750 nm) and other forms of this pigment and bacteriopheophytin (with absorption at 670 nm) were present. In bacteria samples, embedded in polymer, oligomers were in high degree disaggregated and as a result the absorption about 670 nm was observed. Previously for similar sets of samples the decay of fluorescence excited only at one wavelength was analyzed on three exponential components, but exact lifetime values of these components for various samples were different. The aim of present paper was to check if these differences occur because of various contributions to decay from three well defined forms or if they were related to the existence of several pigment forms with slightly different lifetimes. The global analysis of data obtained for various excitation and observation wavelengths of fluorescence were done. From this analysis it follows that the second situation occurs. For a model system containing artificial oligomers the largest component of decay has a 4 of about 0.183 ns or 0.136 ns depending on observation wavelength. For the bacteria sample, in which the emission at 680 nm is the superposition from various pigments, global analysis done for various excitation wavelengths shows also that the values differ depending on the regions of fluorescence observation. From polarized spectra, it follows that in the model system the pigments absorbing at 670 nm are randomly distributed whereas oligomers are highly oriented. In bacteria fragments absorbing at 670 nm pigment molecules can be divided into two groups: one oriented along the axis of film stretching and the second practically randomly distributed. In living organisms, under some conditions, small amount of 670 nm pigments can be present and can work as excitation energy traps or as antenna transferring the excitation. Present results show that the role of various pools of 670 nm absorbing pigments can be different because of their differing orientation. 相似文献
933.
Mauro C. Beltrametti Andrew J. Sommese 《Transactions of the American Mathematical Society》2000,352(7):3045-3064
Let be a very ample line bundle on a connected complex projective manifold of dimension . Except for a short list of degenerate pairs , and there exists a morphism expressing as the blowup of a projective manifold at a finite set , with nef and big for the ample line bundle . The projective geometry of is largely controlled by the pluridegrees for , of . For example, , where is the genus of a curve section of , and is equal to the self-intersection of the canonical divisor of the minimal model of a surface section of . In this article, a detailed analysis is made of the pluridegrees of . The restrictions found are used to give a new lower bound for the dimension of the space of sections of . The inequalities for the pluridegrees, that are presented in this article, will be used in a sequel to study the sheet number of the morphism associated to .
934.
935.
936.
《Fiber and Integrated Optics》2007,26(3):135-146
We investigate the accuracy of a Gaussian approach (GA) developed to estimate the performance of a direct-detection optical receiver with arbitrary optical and electrical filtering and in the presence of partially polarized noise due to polarization-dependent loss (PDL). The accuracy is assessed by comparison of the performance estimates obtained from the GA with the estimates obtained from a rigorous method (RM) based on the calculation of the moment-generating function of the current at the optical receiver output.
We show that the GA has a good accuracy when considering the variation of the optical filter bandwidth, extinction ratio, degree of polarization of the noise (DOP), and angle between signal and noise polarizations. However, it fails to predict the receiver sensitivity within 2 dB of the RM when DOP is greater than 0.7 and signal and noise polarizations are orthogonal in the Jones space.
Nevertheless, it is shown that the GA provides receiver sensitivity estimates with good accuracy in most cases of long-haul optical communication systems influenced by PDL, where the typical average DOP is below 0.15. Due to its simplicity, shorter computation time, and good accuracy, the GA is a good tool to assess the performance of such optical systems. 相似文献
We show that the GA has a good accuracy when considering the variation of the optical filter bandwidth, extinction ratio, degree of polarization of the noise (DOP), and angle between signal and noise polarizations. However, it fails to predict the receiver sensitivity within 2 dB of the RM when DOP is greater than 0.7 and signal and noise polarizations are orthogonal in the Jones space.
Nevertheless, it is shown that the GA provides receiver sensitivity estimates with good accuracy in most cases of long-haul optical communication systems influenced by PDL, where the typical average DOP is below 0.15. Due to its simplicity, shorter computation time, and good accuracy, the GA is a good tool to assess the performance of such optical systems. 相似文献
937.
F. Russo G. Carapella V. Granata N. Martucciello G. Costabile 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(1):61-66
The magnetoresistance of several Ferromagnet/Normal
metal/Ferromagnet spin-valve type structures has been investigated using Al
as normal spacer layer. A magnetoresistance ratio up to 4.1% at room
temperature and 5.7% at 0.3 K is found for the sandwich with both Co
layers, while slightly lower signals are found for the structures involving
CoFe and NiFe layers. The magnetoresistance dependence for Co/Al/Co,
Co/Al/CoFe and Co/Al/NiFe on the spacer layer thickness exhibits the
familiar non monotonic behaviour with second peak slightly larger than the
one reported for Cu based pseudo spin valves. At cryogenic temperatures,
preliminary results on the onset of spin switch effects in Co/Al/Co and the
full spin switch effect in Co/Nb/Co are also reported here. 相似文献
938.
X. W. Zhang J. B. Xia 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):263-268
The electronic structure, spin splitting energies, and g factors of
paramagnetic In1-xMnxAs nanowires under magnetic and electric
fields are investigated theoretically including the sp-d exchange
interaction between the carriers and the magnetic ion. We find that the
effective g factor changes dramatically with the magnetic field. The spin
splitting due to the sp-d exchange interaction counteracts the
Zeeman spin splitting. The effective g factor can be tuned to zero by the
external magnetic field. There is also spin splitting under an electric
field due to the Rashba spin-orbit coupling which is a relativistic effect.
The spin-degenerated bands split at nonzero kz (kz is the wave
vector in the wire direction), and the spin-splitting bands cross at
kz = 0, whose kz-positive part and negative part are symmetrical. A
proper magnetic field makes the kz-positive part and negative part of
the bands asymmetrical, and the bands cross at nonzero kz. In the
absence of magnetic field, the electron Rashba coefficient increases almost
linearly with the electric field, while the hole Rashba coefficient
increases at first and then decreases as the electric field increases. The
hole Rashba coefficient can be tuned to zero by the electric field. 相似文献
939.
Investigation of Near-Field Imaging Characteristics of Radial Polarization for Application to Optical Data Storage 总被引:4,自引:0,他引:4
Wan-Chin Kim No-Cheol Park Yong-Joong Yoon Hyun Choi Young-Pil Park 《Optical Review》2007,14(4):236-242
Radially polarized incident light can generate a more confined longitudinal electric field on a focal plane in near-field
(NF) optics than focusing circularly polarized light. Using this phenomenon, it is feasible to reduce beam spot size on storage
media to increase the areal density of optical data storage. A radially polarized beam generates a beam spot which is 20%
more confined on the 1st surface of medium than that of circularly polarized light. However, the peak intensity of total electric
field sharply decreases and its transverse component is much more dominant inside the media stack. This confirms that radially
polarized optics can be a candidate not for an NF recording system but for an NF read-only memory (ROM) system. Potentially,
the results could be useful to understand the effect of radial and circular polarizations inside and outside medium for various
applications of NF optics. 相似文献
940.
A. N. Useinov L. R. Tagirov R. G. Deminov Y. Zhou G. Pan 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):187-192
We investigated the mean-free path effects
on the magnetoresistance of ferromagnetic nanocontacts.
For most combinations of parameters the magnetoresistance
monotonously decreases with increasing the contact cross-section.
However, for a certain choice of parameters the calculations show
non-monotonous behavior of the magnetoresistance
in the region in which the diameter of the contact becomes
comparable with the mean-free path of electrons.
We attribute this effect to different conduction
regimes in the vicinity of the nanocontact: ballistic for electrons of
one spin projection, and simultaneously diffusive for the other.
Furthermore, at certain combinations of spin asymmetries
of the bulk mean-free paths in a heterocontact, the
magnetoresistance can be almost constant,
or may even grow as the contact diameter increases.
Thus, our calculations suggest a way to search
for combinations of material parameters,
for which high magnetoresistances can be achieved
not only at the nanometric size of the contact, but also at much
larger cross-sections of nanocontacts which can be
easier for fabriaction with current technologies.
The trial calculations of the magnetoresistance with material parameters
close to those for the Mumetal-Ni heterocontacts agree satisfactorily
with the available experimental data. 相似文献