全文获取类型
收费全文 | 287957篇 |
免费 | 1486篇 |
国内免费 | 448篇 |
专业分类
化学 | 130926篇 |
晶体学 | 4470篇 |
力学 | 16786篇 |
综合类 | 10篇 |
数学 | 44844篇 |
物理学 | 92855篇 |
出版年
2020年 | 2008篇 |
2019年 | 2567篇 |
2018年 | 11108篇 |
2017年 | 11763篇 |
2016年 | 8367篇 |
2015年 | 3020篇 |
2014年 | 4393篇 |
2013年 | 8683篇 |
2012年 | 10638篇 |
2011年 | 18970篇 |
2010年 | 12588篇 |
2009年 | 12939篇 |
2008年 | 16965篇 |
2007年 | 20091篇 |
2006年 | 6855篇 |
2005年 | 11463篇 |
2004年 | 8458篇 |
2003年 | 8231篇 |
2002年 | 6480篇 |
2001年 | 5756篇 |
2000年 | 4449篇 |
1999年 | 3172篇 |
1998年 | 2736篇 |
1997年 | 2774篇 |
1996年 | 2714篇 |
1995年 | 2311篇 |
1994年 | 2411篇 |
1993年 | 2306篇 |
1992年 | 2592篇 |
1991年 | 2722篇 |
1990年 | 2626篇 |
1989年 | 2701篇 |
1988年 | 2622篇 |
1987年 | 2643篇 |
1986年 | 2492篇 |
1985年 | 3125篇 |
1984年 | 3214篇 |
1983年 | 2693篇 |
1982年 | 2655篇 |
1981年 | 2622篇 |
1980年 | 2424篇 |
1979年 | 2821篇 |
1978年 | 2793篇 |
1977年 | 2902篇 |
1976年 | 2934篇 |
1975年 | 2719篇 |
1974年 | 2654篇 |
1973年 | 2807篇 |
1972年 | 2125篇 |
1971年 | 1978篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
921.
D.A. Garanin E.M. Chudnovsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):3-7
We compute the width and shape of the EPR and tunneling resonances due to dislocations in Mn12 acetate crystals. Uncorrelated dislocations produce the Gaussian shape of resonances while dislocations bound in pairs produce
the Lorentzian shape. We stress that the uniaxial spin Hamiltonian together with crystal defects can explain the totality
of experimental data on Mn12.
Received 2 August 2001 / Received in final form 15 March 2002 Published online 17 September 2002 相似文献
922.
R. Adhikari A. Sil A. Raychaudhuri 《The European Physical Journal C - Particles and Fields》2002,25(1):125-130
We present a solution of the solar neutrino deficit using three flavors of neutrinos and R-parity non-conserving supersymmetry. In this model, in vacuum, the is massless and unmixed, mass and mixing being restricted to the - sector only, which we choose in consistency with the requirements of the atmospheric neutrino anomaly. The flavor changing
and flavor diagonal neutral currents present in the model and the three-flavor picture together produce an energy dependent
resonance-induced - mixing in the sun. This mixing plays a key role in the new solution to the solar neutrino problem. The best fit to the solar
neutrino rates and spectrum (1258-day SK and 241-day SNO data) requires a mass square difference of eV2 in vacuum between the two lightest neutrinos. This solution cannot accommodate a significant day-night effect for solar neutrinos
nor CP violation in terrestrial neutrino experiments.
Received: 26 December 2001 / Revised version: 16 February 2002 / Published online: 26 July 2002 相似文献
923.
N. S. Smirnova 《Journal of Mathematical Sciences》1991,55(3):1741-1746
We consider theoretical seismographs of a wave field passing through an elastic layer with high propagation velocity. We note the presence of a low-frequency part of the seismogram for longitudinal waves. It is shown that the propagation time of low-frequency vibrations is equal to that of longitudinal disturbances screened by the layer.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, AN SSSR, Vol. 173, pp. 134–141, 1988. 相似文献
924.
N. L. Vekshin 《Journal of Applied Spectroscopy》1991,54(1):17-22
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 1, pp. 26–32, January, 1991. 相似文献
925.
R. Németh 《Journal of statistical physics》1991,63(1-2):419-424
We calculate the site occupation probabilities of one-dimensional lattice gas models within the canonical and grand canonical ensembles. The appearing differences do not vanish if we increase the system size keeping the site energies discrete. In this way one can explain the surprising numerical results of Barszczak and Kutner. This effect in the single-site occupation number disappears in higher dimensions. 相似文献
926.
Water suppression by diffusive attenuation was used to measure Brix in intact cellular tissue of apple and strawberry. Given
the signal-to-noise ratio, the correlation for apple was established without repeated acquisition, so this protocol should
also be useful for rapid, on-line measurements at low spectrometer frequencies. Water suppression by theT
1-Null method fails with cellular tissue because of the considerable variation in the longitudinal relaxation times of vacuolar
and cytoplasmic water. 相似文献
927.
Velislava A Ignatova Sven Van Den Berghe Steven Van Dyck Vladimir N Popok 《Microscopy and microanalysis》2006,12(5):432-437
The oxide scales of AISI 304 formed in boric acid solutions at 300 degrees C and pH = 4.5 have been studied using X-ray photoelectron spectroscopy (XPS) depth profiling. The present focus is depth profile quantification both in depth and chemical composition on a molecular level. The roughness of the samples is studied by atomic force microscopy before and after sputtering, and the erosion rate is determined by measuring the crater depth with a surface profilometer and vertical scanning interferometry. The resulting roughness (20-30 nm), being an order of magnitude lower than the crater depth (0.2-0.5 microm), allows layer-by-layer profiling, although the ion-induced effects result in an uncertainty of the depth calibration of a factor of 2. The XPS spectrum deconvolution and data evaluation applying target factor analysis allows chemical speciation on a molecular level. The elemental distribution as a function of the sputtering time is obtained, and the formation of two layers is observed-one hydroxide (mainly iron-nickel based) on top and a second one deeper, mainly consisting of iron-chromium oxides. 相似文献
928.
M. G. Voronkov E. A. Grebneva O. M. Trofimova A. I. Albanov N. F. Chernov N. N. Chipanina 《Russian Journal of General Chemistry》2006,76(12):1851-1853
Reaction of tetrafluorosilane with tris(2-hydroxyethyl)-and tris(2-trimethylsiloxyethyl)amine results in formation of 1-fluorosilatrane and fluorosilatrane in 75 and 53% yield, respectively. Reaction of tetrafluorosilane with bis(2-trimethylsiloxyethyl)amine and its N-methyl derivative leads to the hitherto unknown 1,1-difluoroquasisilatranes (N → Si) F2Si(OCH2CH2)2NR (R = H, Me) containing donor-acceptor bond N → Si and pentacoordinate silicon atom. The structure of the synthesized compounds was proved by 1H, 13C, 15N, 19F, 29Si NMR and IR spectroscopy. 相似文献
929.
A. A. Lamberov E. V. Dement’eva Kh. Kh. Gil’manov S. R. Egorova N. V. Romanova 《Russian Journal of Applied Chemistry》2006,79(9):1453-1457
The effect of the paste molding pressure on the physicomechanical and texture characteristics of catalysts was studied. An indirect criterion is suggested to evaluate the molding pressure in industrial extruders, whose optimal value ensures good physicomechanical properties of the catalysts and kinetic control over the catalyzed reaction. The results obtained were verified in paste molding on various industrial extruders, and this enabled the optimal choice of the molding equipment. 相似文献
930.
This paper proposes a new method that extends the efficient global optimization to address stochastic black-box systems. The
method is based on a kriging meta-model that provides a global prediction of the objective values and a measure of prediction
uncertainty at every point. The criterion for the infill sample selection is an augmented expected improvement function with
desirable properties for stochastic responses. The method is empirically compared with the revised simplex search, the simultaneous
perturbation stochastic approximation, and the DIRECT methods using six test problems from the literature. An application
case study on an inventory system is also documented. The results suggest that the proposed method has excellent consistency
and efficiency in finding global optimal solutions, and is particularly useful for expensive systems. 相似文献