全文获取类型
收费全文 | 207099篇 |
免费 | 854篇 |
国内免费 | 534篇 |
专业分类
化学 | 99463篇 |
晶体学 | 2887篇 |
力学 | 10716篇 |
综合类 | 20篇 |
数学 | 29755篇 |
物理学 | 65646篇 |
出版年
2019年 | 2298篇 |
2018年 | 4565篇 |
2017年 | 4950篇 |
2016年 | 4842篇 |
2015年 | 2377篇 |
2014年 | 4034篇 |
2013年 | 7658篇 |
2012年 | 8532篇 |
2011年 | 8770篇 |
2010年 | 7132篇 |
2009年 | 7022篇 |
2008年 | 6866篇 |
2007年 | 6880篇 |
2006年 | 6166篇 |
2005年 | 9319篇 |
2004年 | 8643篇 |
2003年 | 6609篇 |
2002年 | 4976篇 |
2001年 | 5252篇 |
2000年 | 3774篇 |
1999年 | 2978篇 |
1998年 | 2707篇 |
1997年 | 2520篇 |
1996年 | 2292篇 |
1995年 | 2084篇 |
1994年 | 2043篇 |
1993年 | 2055篇 |
1992年 | 2225篇 |
1991年 | 2518篇 |
1990年 | 2436篇 |
1989年 | 2480篇 |
1988年 | 2348篇 |
1987年 | 2351篇 |
1986年 | 2160篇 |
1985年 | 2692篇 |
1984年 | 2697篇 |
1983年 | 2339篇 |
1982年 | 2386篇 |
1981年 | 2286篇 |
1980年 | 2087篇 |
1979年 | 2417篇 |
1978年 | 2573篇 |
1977年 | 2657篇 |
1976年 | 2798篇 |
1975年 | 2571篇 |
1974年 | 2505篇 |
1973年 | 2678篇 |
1972年 | 2190篇 |
1971年 | 1997篇 |
1970年 | 1873篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The determination of the sensitivity of the acoustical characteristics of vibrating systems with respect to the variation of the design parameters predicting these characteristics is a necessary and important step of the acoustic design and optimization process. Acoustic design sensitivity analysis includes the computation and evaluation of the sensitivity information required for this procedure. In this study, a boundary element code performing the sensitivity analysis of the acoustic pressure by using the matrix sensitivities with respect to different design variables has been developed. The effect of the precision of boundary element discretization on the acoustic pressure sensitivity is examined via this code. The formulation is applied to a multi-source system and the dimension sensitivity analysis of near field pressures of two-dilating-spherical source is performed. The last application is devoted to a real sound source: a washing machine sitting on the floor. Sensitivity of the field pressures to the machine’s dimensions (size), surface velocity and frequency is examined on the bases of the boundary element model of the machine and half-space condition. The impacts of these variables are compared; and a limiting speed for the machine responding both the acoustical and operational requirements is determined. 相似文献
942.
A.I. Veinger A.G. Zabrodskii T.V. Tisnek S.I. Goloshchapov 《Solid State Communications》2005,133(7):455-458
The first observation of low-temperature magnetoresistance (MR) of interference nature in the case of a light doping is reported. The MR occurs in n- and p-type Ge samples at a frequency of 10 GHz at temperatures below 30 K in weak magnetic fields on the background of the classical MR effect associated with electrons in different valleys (n-Ge) and with heavy and light holes (p-Ge). 相似文献
943.
Methods for accelerometer unit calibration are usually based on sufficiently strict requirements on the knowledge of the gravity orientation with respect to the unit (of the order of fractions of an arc minute). But it is not always possible to know the orientation with such high accuracy. In the present paper, we consider an approach to accelerometer unit calibration for whose implementation it suffices to have rough angular information (of the order of tens of arc minutes). We use a guaranteeing approach to calculate optimal schemes calibration experiments and propose an iterative scheme of calibration. 相似文献
944.
K. Migléczi Gy. Somorjai M. Pátfalusi G. Tóth Gy. Horváth I. Hazai 《Chromatographia》2004,60(1):S67-S74
GYKI-16084 – (+)-(R)-2-{3-(benzo[1,4]dioxan-2-yl-methylamino)-1-propyl}-3(2H)-pyridazinone hydrochloride – is a new drug candidate for the treatment of benign prostatic hyperplasia. In our study the major metabolites formed in the rat and dog were isolated from dog and rat urine, then their structures were elucidated by means of MS and NMR. A two stage solid phase extraction (SPE) procedure and a semi-preparative HPLC method were developed utilizing various mechanisms of separation. The major metabolites proved to be isomeric glucuronides of the benzodioxane moiety hydroxylated at positions 6 or 7 and {2-(2-carboxyethyl)-3(2H)-pyridazinone}. 相似文献
945.
946.
A. I. Kolesnikov I. A. Kaplunov I. V. Talyzin S. A. Tret’yakov O. V. Gritsunova E. Yu. Vorontsova 《Crystallography Reports》2008,53(7):1144-1149
A computer simulation and measurements of the light transmittance of germanium and paratellurite crystals of different thickness
were used to show that, at scattering probabilities of photons comparable to their absorption probabilities, the standard
methods for calculating light extinction coefficients on the basis of the Bouguer law lead to rough errors in estimation of
the optical quality of a material. 相似文献
947.
A mathematical model of the formation of primary grown-in microdefects on the basis of dissociation diffusion is presented.
Cases of “vacancy-oxygen” (V + O) and “carbon-interstitial” (C + I) interaction near the crystallization front are considered
for dislocation-free Si single crystals grown by the floating-zone and Czochralski methods. The approximate analytical expressions
obtained by setting 1D and 2D temperature fields in a crystal are in good agreement with the heterogeneous mechanism of formation
of grown-in microdefects. 相似文献
948.
The types of quartz textures found in a large collection of multiphase rocks from different regions of the earth are analyzed. Crystallographic textures of granulite, amphibolite, slate, and gneiss samples are measured, classified, and compared with the similar textures of monomineral rocks. 相似文献
949.
950.