全文获取类型
收费全文 | 77880篇 |
免费 | 523篇 |
国内免费 | 114篇 |
专业分类
化学 | 41323篇 |
晶体学 | 1260篇 |
力学 | 3284篇 |
综合类 | 1篇 |
数学 | 7908篇 |
物理学 | 24741篇 |
出版年
2022年 | 629篇 |
2021年 | 872篇 |
2020年 | 965篇 |
2019年 | 1103篇 |
2018年 | 1596篇 |
2017年 | 1686篇 |
2016年 | 2148篇 |
2015年 | 1024篇 |
2014年 | 1721篇 |
2013年 | 3332篇 |
2012年 | 2896篇 |
2011年 | 3277篇 |
2010年 | 2638篇 |
2009年 | 2634篇 |
2008年 | 2996篇 |
2007年 | 2875篇 |
2006年 | 2767篇 |
2005年 | 2432篇 |
2004年 | 2238篇 |
2003年 | 2073篇 |
2002年 | 2135篇 |
2001年 | 2234篇 |
2000年 | 1625篇 |
1999年 | 1255篇 |
1998年 | 1129篇 |
1997年 | 1045篇 |
1996年 | 896篇 |
1995年 | 832篇 |
1994年 | 815篇 |
1993年 | 815篇 |
1992年 | 869篇 |
1991年 | 947篇 |
1990年 | 881篇 |
1989年 | 921篇 |
1988年 | 818篇 |
1987年 | 768篇 |
1986年 | 740篇 |
1985年 | 866篇 |
1984年 | 964篇 |
1983年 | 820篇 |
1982年 | 837篇 |
1981年 | 749篇 |
1980年 | 704篇 |
1979年 | 770篇 |
1978年 | 893篇 |
1977年 | 914篇 |
1976年 | 811篇 |
1975年 | 778篇 |
1974年 | 792篇 |
1973年 | 766篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
A sequential injection methodology for the spectrophotometric determination of calcium, magnesium and alkalinity in water samples is proposed. A single manifold is used for the determination of the three analytes, and the same protocol sequence allows the sequential determination of calcium and magnesium (the sum corresponds to the water hardness). The determination of both metals is based on their reaction with cresolphtalein complexone; mutual interference is minimized by using 8-hydroxyquinoline for the determination of calcium and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) for the determination of magnesium. Alkalinity determination is based on a reaction with acetic acid, and corresponding color change of Bromcresol Green. Working ranges of 0.5 - 5 mg dm(-3) for Ca, 0.5 - 10 mg dm(-3) for Mg, and 10 - 100 mg HCO3- dm(-3), for alkalinity have been achieved. The results for water samples were comparable to those of the reference methods and to a certified reference water sample. RSDs lower than 5% were obtained, a low reagent consumption and a reduced volume of effluent have been accomplished. The determination rate for calcium and magnesium is 80 h(-1), corresponding to 40 h(-1) per element, while 65 determinations of alkalinity per hour could be carried out. 相似文献
62.
63.
The operating principles, design, and characteristics of an ion source with a cold magnetron cathode and magnetic plasma compression are described. The source is intended for the injector of a linear proton accelerator. 相似文献
64.
O. Martio 《Journal of Mathematical Analysis and Applications》2003,286(2):524-539
Some boundary properties of nonparametric surfaces with finite area are proved. 相似文献
65.
We investigate a new interpretation for the Navier-Stokes corrections to the hydrodynamic equation of asymmetric interacting particle systems. We consider a system that starts from a measure associated with a profile that is constant along the drift direction. We show that under diffusive scaling the macroscopic behavior of the process is described by a nonlinear parabolic equation whose diffusion coefficient coincides with the diffusion coefficient of the hydrodynamic equation of the symmetric version of the process. 相似文献
66.
Results of experimental investigations of the volt-brightness characteristics, frequency dependences of brightness, and the
directional radiation pattern of electroluminescent MSDM, MSCM, and MSDCM emitters, where M stands for the first transparent
and second nontransparent electrodes, S is a semiconductor, D is a thin-film dielectric, and C is a silicone-based composite
liquid dielectric with a powdered segnetoelectric filler, developed on conventional “smooth” and rough glass substrates are
presented. It is shown that electroluminescent structures on rough surfaces have a brightness approximately two times higher
than that of similar structures developed on a “smooth” substrate.
Ul’yanovsk State University, 42, L. Tolstoi St., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 64, No. 4, pp. 507–512, July–August, 1997. 相似文献
67.
68.
R. Grac M. Pugnet J.H. Collet B. Lambert C. De Matos H. L'Haridon A. Le Corre J.O. White 《Superlattices and Microstructures》1997,22(4):505-509
We report new results on the diffraction properties of photoinduced gratings in InGaAs/InGaAsP MQW structures. The original feature of this device is that the QWs are enclosed in an asymmetric Fabry–Perot microcavity in order to increase the diffraction efficiency. We observe oscillations in the diffraction efficiency due to resonant effects in the microcavity. The experimental spectra are compared with theory. Diffraction efficiency at 1.55 μm attains a maximum value of 2.7% at a write beam fluence of 260 μ J cm−2, and then decreases at higher fluences. We explain this phenomenon by an absorption saturation at high excitation. 相似文献
69.
O. A. Dubovskii 《Physics of the Solid State》1998,40(11):1937-1941
Solutions of the dispersion equations for polariton states in finite one-dimensional crystals of arbitrary length are obtained.
The appearance and evolution of the radiative and nonradiative polariton branches are traced as the length varies from two
monomers to limiting values, above which the spectrum no longer undergoes significant changes. The dependences of the frequencies
and radiative widths on the polariton wave vector are found for various orientations of the dipole moment of the quantum transition.
The evolution of superradiance as the length of the crystal increases is traced. Some previously unknown significant features
of the polariton spectrum are noted particularly the damping of the branch traditionally termed nonradiative as a consequence
of emission from the end faces.
Fiz. Tverd. Tela (St. Petersburg) 40, 2136–2140 (November 1998) 相似文献
70.
T. B. Anders W. Jachmann A. O. Barut 《Zeitschrift fur Physik C Particles and Fields》1992,56(4):561-563
The polarization asymmetries related to usual polarizations combine at least 4 different helicity amplitudes. The introduction of ±45° inclined transverse polarizations allows us to obtain the complete set of new polarization asymmetries combining only up to 3 helicity amplitudes. There are no further polarization asymmetries depending on a smaller number of helicity amplitudes. These expressions are most economical to determine the helicity amplitudes from observed data. Some of them are suitable to study especially the spin-flip effects. We give a complete Table of all such polarization asymmetries. 相似文献