全文获取类型
收费全文 | 494073篇 |
免费 | 5368篇 |
国内免费 | 1471篇 |
专业分类
化学 | 251735篇 |
晶体学 | 7276篇 |
力学 | 22712篇 |
综合类 | 12篇 |
数学 | 68839篇 |
物理学 | 150338篇 |
出版年
2020年 | 2462篇 |
2018年 | 11253篇 |
2017年 | 12079篇 |
2016年 | 8713篇 |
2015年 | 4866篇 |
2014年 | 5504篇 |
2013年 | 17416篇 |
2012年 | 17127篇 |
2011年 | 28142篇 |
2010年 | 17181篇 |
2009年 | 16957篇 |
2008年 | 25009篇 |
2007年 | 28493篇 |
2006年 | 15010篇 |
2005年 | 20732篇 |
2004年 | 15779篇 |
2003年 | 14132篇 |
2002年 | 11988篇 |
2001年 | 12317篇 |
2000年 | 9639篇 |
1999年 | 7542篇 |
1998年 | 6202篇 |
1997年 | 5996篇 |
1996年 | 6126篇 |
1995年 | 5643篇 |
1994年 | 5247篇 |
1993年 | 5047篇 |
1992年 | 5651篇 |
1991年 | 5501篇 |
1990年 | 5148篇 |
1989年 | 4994篇 |
1988年 | 5266篇 |
1987年 | 4988篇 |
1986年 | 4781篇 |
1985年 | 6876篇 |
1984年 | 7009篇 |
1983年 | 5740篇 |
1982年 | 6367篇 |
1981年 | 6267篇 |
1980年 | 6046篇 |
1979年 | 6138篇 |
1978年 | 6290篇 |
1977年 | 6141篇 |
1976年 | 6135篇 |
1975年 | 5957篇 |
1974年 | 5688篇 |
1973年 | 5993篇 |
1972年 | 3520篇 |
1971年 | 2642篇 |
1968年 | 2661篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
P. David J. Hartfiel H. Janszen R. von Mutius J. Arvieux L. Farvacque B. Berthier B. Bonin J. C. Lugol 《Zeitschrift für Physik A Hadrons and Nuclei》1987,326(4):367-372
The excitation function of the fission probability P E E x) for238U has been measured in the reaction238U(α, α′ f) at 480 MeV bombarding energy. The reaction mechanism of this reaction is discussed for excitation energies belowB nf , the threshold for second chance fission, and aboveB nf up toE x =37 MeV. In comparing with results from fission induced by photons and by particle transfer reactions the (α, α′f) reaction gives too low values for the fission probabilityP f at excitation energies well aboveB nE . The role of the quasi-elastic knock-out process in this reaction is discussed. 相似文献
142.
J. H. Eberly 《Laser Physics》2006,16(6):921-926
We examine the application of Schmidt mode analysis to pure-state entanglement. Several examples permitting exact analytic calculation of Schmidt eigenvalues and eigenfunctions are included, as well as evaluation of the associated degree of entanglement. 相似文献
143.
T. Kumita Y. Kamiya M. Babzien I. Ben-Zvi K. Kusche I. V. Pavlishin I. V. Pogorelsky D. P. Siddons V. Yakimenko T. Hirose T. Omori J. Urakawa K. Yokoya D. Cline F. Zhou 《Laser Physics》2006,16(2):267-271
Thomson scattering of high-power laser and electron beams is a good test of electrodynamics in the high-field region. We demonstrated production of high-intensity X-rays in the head-on collision of a CO2 laser and 60-MeV electron beams at Brookhaven National Laboratory, Accelerator Test Facility. The energy of an X-ray photon was limited at 6.5 keV in the linear (lowest order) Thomson scattering, but the nonlinear (higher order) process produces higher energy X-rays. We measured the angular distribution of the high-energy X-rays and confirmed that it agrees with theoretical predictions. 相似文献
144.
The tape stripping technique is an experimental method frequently used for reconstruction of the in-depth distribution of various topically administered substances within the horny layer of human skin, e.g., compounds contained in sunscreens. Titanium dioxide (TiO2) nanoparticles (25–200 nm in diameter) are one such compound. Optical techniques which apply blue light are found to be suitable for reconstruction. However, the presence of particles affects the light propagation within the skin and therefore causes incorrect determination of strip thickness, leading to an improper reconstructed distribution of nanoparticle concentration revealed from the experimental data. This study evaluates the errors emerging from the use of blue (400 nm) and NIR (800 nm) radiation and finds the use of longer wavelength light more advantageous. Particles of different diameters are considered, and it is revealed that the application of small particles (25–60 nm) results in the lowest rate of error. 相似文献
145.
The synthesis of rigid spirocyclic bislactams derived from pyroglutamic acid has been established. 相似文献
146.
Critical problems of the present approach of electrolytes for Solid Oxide Fuel Cells (SOFCs) for commercialization are discussed.
Major progress is expected from the development of materials based on the “SEA (Single Element Arrangement)” concept. The
galvanic cell consists in this case basically of a single chemically homogeneous compound, which functions as electrodes at
high and low activity and as electrolyte at intermediate activities of the electroactive component.
In view of the large structural flexibility of the chemical nature of the constitutents, we explored perovskite (ABO3)-type compounds to be used as SEAs for SOFCs. Results of studies on Pr-substituted LSGM and Fe-substituted SrSnO3 perovskite-type oxides are presented. For instance, SrSn1-xFexO3-δ with x=0.1 exhibits p and n-type electronic conduction at the cathode and anode sides of the SOFC, respectively, while oxide
ion conduction prevails at intermediate oxygen partial pressures. The SEA concept is also applicable for other devices in
the field of Ionics. 相似文献
147.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
148.
R. A. Ganeev A. I. Ryasnyanskii M. K. Kodirov Sh. R. Kamalov V. A. Li R. I. Tugushev T. Usmanov 《Technical Physics》2002,47(8):991-995
Nonlinear optical parameters (nonlinear refractive indices and nonlinear absorption coefficients) of solutions of polyvinylpyrrolidone doped by cobalt to various concentrations are measured at the lasing and second-harmonic wavelengths of a picosecond Nd:YAG laser (λ=1064 and 532 nm, respectively, and τ=35 ps). Data on optical limitation in these solutions are presented. The absence of nonlinear absorption in the IR spectral range and its significant effect in the visible range are demonstrated. Optical limitation at a wavelength of 1064 nm is related to defocusing, whereas at 532 nm, this effect is caused by two-photon absorption and partially by inverse saturated absorption and defocusing. Nonlinear optical parameters of metal-polymer complexes are reported. 相似文献
149.
B. Dubrulle F. Hersant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):379-386
We generalize an analogy between rotating and stratified shear flows. This analogy is summarized in Table 1. We use this analogy
in the unstable case (centrifugally unstable flow vs. convection) to compute the torque in Taylor-Couette configuration, as a function of the Reynolds number. At low Reynolds
numbers, when most of the dissipation comes from the mean flow, we predict that the non-dimensional torque G = T/ν2
L, where L is the cylinder length, scales with Reynolds number R and gap width η, G = 1.46η3/2(1 - η)-7/4
R
3/2. At larger Reynolds number, velocity fluctuations become non-negligible in the dissipation. In these regimes, there is no
exact power law dependence the torque versus Reynolds. Instead, we obtain logarithmic corrections to the classical ultra-hard (exponent 2) regimes: G = 0.50
. These predictions are found to be in excellent agreement with avail-able experimental data. Predictions for scaling of velocity
fluctuations are also provided.
Received 7 June 2001 and Received in final form 7 December 2001 相似文献
150.
Inventiones mathematicae - 相似文献