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241.
We report the temperature dependence of electrical resistance (R) and thermopower (S) of clathrate Cs8Sn44 under high pressure up to 1.2 GPa. We observe a reversible gap widening, prominent relaxation effect of R, irreversible increase of |S| under high pressure. We also find that the power factor S2σ (σ: electrical conductivity) reaches a maximum at pressure of 0.3 GPa. Comparison of the experimental results with band structure calculations suggests that the intrinsic vacancy in the clathrate structure of Cs8Sn44 plays an important role in transport properties under high pressure. Measurements on Cs8Zn4Sn42, a clathrate which has defects other than vacancies, are compared with Cs8Sn44. The results indicate that replacing Sn by Zn has similar effect as the intrinsic vacancy on S. 相似文献
242.
O. S. Kushnir A. A. Bevz O. G. Vlokh L. F. Lutsiv-Shumskii 《Optics and Spectroscopy》2002,93(6):930-933
On the basis of a complex null-polarimetric method, the natural birefringence and the rotation of the optical indicatrix in crystals of deuterated triglycinesulfate are measured in the temperature range of 300–340 K. The temperature-dependent behavior of the optical parameters is shown to be close to that observed previously in triglycinesulfate crystals. Changes in them upon the ferroelectric phase transition can be accounted for by the spontaneous quadratic electro-optic effect, with the values of the electro-optic coefficients being larger by a factor of 1.4 than in triglycinesulfate crystals. 相似文献
243.
F.F. Karpeshin J. da Providência C. Providência J. da Providência Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):319-326
Two types of extreme collective motion, large-amplitude many-phonon vibration of the ionic core and rotation of the cluster
with high angular momenta, are considered. The interplay between vibration and collective motion towards fission is discussed.
A new mechanism of formation and rupture of the neck is proposed which is based on the Franck-Condon principle, and accounts
for the interplay between vibration and fission. Under rotation, the change of the shape of the cluster and a phase transition
from axially symmetric to triaxial ellipsoid are predicted. For studying the effects, vibrational motion can be induced by
laser radiation. Rotational motion may arise in collisions of clusters.
Received 26 April 2001 and Received in final form 15 October 2001 相似文献
244.
Transpiration is a technique in which extra non-physical normal flows are created on an aerofoil surface in order to form a new streamline pattern such that the surface streamlines no longer follow the aerofoil surface under inviscid flow. The transpiration model is an important technique adopted in aerofoil design either to avoid mesh regeneration when aerofoil profile co-ordinates are adjusted or to find shape corrections in inverse design methods. A first-order approximation (with respect to the normal streamline displacement) to the transpiration model is commonly adopted; it is shown that this can be a poor approximation especially in regions of high curvature. In this paper more accurate approximations are developed to address this problem and improve the accuracy. 相似文献
245.
Trace pollutants analysis in soil by a time-resolved laser-induced breakdown spectroscopy technique 总被引:5,自引:0,他引:5
A. Ciucci V. Palleschi S. Rastelli R. Barbini F. Colao R. Fantoni A. Palucci S. Ribezzo H. J. L. van der Steen 《Applied physics. B, Lasers and optics》1996,63(2):185-190
The results of a joint experiment of IFAM-Pisa and ENEA-Frascati for the detection of traces of pollutants in soil by a time-resolved laser-induced spectroscopy technique are reported. Using samples of soil with known pollutants' concentration [Geochemical Exploration Reference (GXR) silicate from US Geological Survey], we were able to estimate the sensitivity of this Laser-Induced Breakdown Spectroscopy (LIBS) technique to be of the order of some parts per million for a vast class of metallic pollutants, including extremely dangerous soil pollutants such as copper, lead and chromium.ENEA guest with HC&M fellowship 相似文献
246.
247.
Juan F García-Reyes Pilar Ortega-Barrales Antonio Molina-Díaz 《Analytical sciences》2007,23(4):423-428
A combined approach based on solid-phase optosensing and multicommutation principles has been applied to develop a method for the simultaneous analysis of two pharmaceuticals (naproxen and salicylic acid) in biological fluids. The multicommuted flow-through optosensor was based on direct native fluorescence measurements of both analgesics using a non-polar sorbent (C18 silica gel) as a solid sensing zone. The flow system was controlled by Java-written home-made software and designed using three-way solenoid valves for an independent automated manipulation of sample and carrier solutions. Using an optimized sampling time, the method was calibrated in the range of 1 - 25 and 5 - 200 ng mL(-1). The obtained detection limits were 0.3 and 1.3 ng mL(-1) for naproxen and salicylic acid, respectively, with RSD (%) values of better than 2% for both analytes. The proposed methodology was successfully applied to urine, serum and pharmaceutical preparations. Recovery percentages ranging from 96.1 to 104% were obtained for both analytes. 相似文献
248.
Summary Two polyampholyte copolymers based on sodium-2-acrylamido-2-methylsulfonate (NaAMPS) and methacryloyloxyethyltrimethylammonium
chloride (MADQUAT) have been prepared either in homogeneous solution or by an inverse microemulsion polymerization technique.
The copolymer microstructure was shown to depend on the method of preparation. The microemulsion polymerization yields copolymers
with a monomer sequence distribution not far from random while those obtained by polymerization in solution have a strong
tendency to alternation. The aqueous-solution properties of the two samples have been investigated by viscometry. The results
show that the charge distribution along the copolymer chain affects considerably its conformation, in good agreement with
recent theoretical studies.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994 相似文献
249.
C. Saragovi F. Labenski S. M. Duhalde S. Acebal R. Venegas 《Hyperfine Interactions》1994,91(1):765-769
Clay fractions of a Mollisol sample as is, treated with ammonium oxalate (AO), with dithionite-citrate-bicarbonate (DCB) and with dithionite-ethilene-diamine-tetraacetic acid (D-EDTA) methods, were studied. Illite-montmorillonites together with hematites, goethites and maghemites, all of the AI-substituted and with a wide range of sizes, were identified. It is found that the AO attack extracts little iron, whereas the other two attacks extract the magnetic signal. Furthermore, the DCB attack facilitates the reduction of the Fe3+ ions, while the D-EDTA method does not. Instead, this attack extracts more clay mineral Fe ions. A comparison with large grain soil samples is made. 相似文献
250.
G. F. R. Ellis 《General Relativity and Gravitation》1992,24(10):1047-1068
This paper gives a covariant formalism enabling investigation of the possibility of change of signature in classical General Relativity, when the geometry is that of a Robertson-Walker universe. It is shown that such changes are compatible with the Einstein field equations, both in the case of a barotropic fluid and of a scalar field. A criterion is given for when such a change of signature should take place in the scalar field case. Some examples show the kind of resulting exact solutions of the field equations. 相似文献