全文获取类型
收费全文 | 233007篇 |
免费 | 1996篇 |
国内免费 | 800篇 |
专业分类
化学 | 116824篇 |
晶体学 | 3996篇 |
力学 | 10757篇 |
综合类 | 1篇 |
数学 | 25503篇 |
物理学 | 78722篇 |
出版年
2020年 | 1787篇 |
2019年 | 2043篇 |
2018年 | 2719篇 |
2017年 | 2651篇 |
2016年 | 3913篇 |
2015年 | 2389篇 |
2014年 | 3967篇 |
2013年 | 10072篇 |
2012年 | 7529篇 |
2011年 | 9392篇 |
2010年 | 6684篇 |
2009年 | 6628篇 |
2008年 | 8701篇 |
2007年 | 8734篇 |
2006年 | 8271篇 |
2005年 | 7491篇 |
2004年 | 6918篇 |
2003年 | 6111篇 |
2002年 | 6060篇 |
2001年 | 7091篇 |
2000年 | 5372篇 |
1999年 | 4235篇 |
1998年 | 3563篇 |
1997年 | 3472篇 |
1996年 | 3293篇 |
1995年 | 3008篇 |
1994年 | 2951篇 |
1993年 | 3042篇 |
1992年 | 3151篇 |
1991年 | 3332篇 |
1990年 | 3084篇 |
1989年 | 3027篇 |
1988年 | 3066篇 |
1987年 | 2955篇 |
1986年 | 2800篇 |
1985年 | 3808篇 |
1984年 | 4005篇 |
1983年 | 3198篇 |
1982年 | 3410篇 |
1981年 | 3336篇 |
1980年 | 3230篇 |
1979年 | 3335篇 |
1978年 | 3422篇 |
1977年 | 3350篇 |
1976年 | 3448篇 |
1975年 | 3141篇 |
1974年 | 3150篇 |
1973年 | 3194篇 |
1972年 | 2235篇 |
1971年 | 1849篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector. 相似文献
102.
We have simultaneously used adsorption isotherm volumetry and Fourier transform infrared spectroscopy in order to take the investigations on amorphous ice structure a step further, especially concerning porosity and annealing-induced modifications. We have studied surface reorganization during annealing and found that the number of surface sites decreases before crystallization, their relative ratios being different for amorphous and crystalline ice. We also present results confirming that ice can have a large specific surface area and nevertheless be non-microporous. 相似文献
103.
P.A. Sinclair 《Discrete Mathematics》2004,286(3):177-184
Let G be a connected graph with minimum degree at least 3. We prove that there exists an even circuit C in G such that G−E(C) is either connected or contains precisely two components one of which is isomorphic to a 1-bond. We further prove sufficient conditions for there to exist an even circuit C in a 2-connected simple graph G such that G−E(C) is 2-connected. As a consequence of this, we obtain sufficient conditions for there to exist an even circuit C in a 2-connected graph G for which G−E(C) is 2-connected. 相似文献
104.
105.
Svitlana P. Rogovchenko 《Journal of Mathematical Analysis and Applications》2003,279(1):121-134
In this paper, we are concerned with a class of nonlinear second-order differential equations with a nonlinear damping term. Passage to more general class of equations allows us to remove a restrictive condition usually imposed on the nonlinearity, and, as a consequence, our results apply to wider classes of nonlinear differential equations. Two illustrative examples are considered. 相似文献
106.
Silica@copper (SiO2@Cu) core–shell nanoparticles were synthesized and well characterized by XRD, TEM, AFM, XPS, UV/Vis, TGA–MS, and ICP–AES techniques. The synthesized SiO2@Cu core–shell nanoparticles were employed as catalysts for the conjugate addition of amines to α,β‐unsaturated compounds in water to obtain β‐amino carbonyl compounds in excellent yields in shorter reaction times. Furthermore, the catalyst works well for hetero‐Michael addition reactions of heteroatom nucleophiles such as thiols to α,β‐unsaturated compounds. As the reaction is performed in water, it allows for easy recycling of the catalyst with consistent activity. 相似文献
107.
108.
V. P. Ershov D. A. Kas’yanov V. I. Rodchenkov D. A. Sergeev 《Crystallography Reports》2008,53(2):339-343
The growth of the isolated (100) face of a KDP crystal at exposure of the phase boundary to the initial ultrasound field and a standing acoustic wave has been investigated. A significant growth response of this face, exposed to sound normally along the acoustic axis in the near zone of a piston-like half-wave vibrator with f = 20 kHz and tangentially in the pulsed two-frequency (f = 600 and 900 kHz) standing-wave mode, has been revealed. It is shown that the mechanisms of mass exchange enhancement in these acoustic modes are different. The results obtained show a fundamental possibility of controlling crystal growth and dissolution by varying the parameters of inhomogeneous acoustic field. 相似文献
109.
A. P. Voronov G. N. Babenko V. M. Puzikov A. D. Roshal’ V. I. Salo 《Crystallography Reports》2008,53(4):708-712
The features of doping of KDP crystals with cerium ions and organocerium complexes with alizarin complexon and arsenazo III have been investigated. It is established that “direct” doping by introducing cerium salts into the initial solution cannot be implemented. The effect of organometallic complexes of cerium on the crystal growth has been studied. Organocerium complexes predominantly enter the prismatic or pyramidal growth sectors. It is shown that the complex arsenazo III + Ce blocks the growth of the prismatic sector. Cerium-doped KDP crystals exhibit a photoluminescence band peaking at the wavelength λmax= 350 nm. 相似文献
110.
K. Morigaki K. Takeda H. Hikita C. Ogihara P. Roca i Cabarrocas 《Journal of Non》2008,354(19-25):2131-2134
Our model for light-induced defect creation in hydrogenated amorphous silicon is applied to its kinetics, i.e., the growing curve of light-induced dangling bond density as a function of illumination time, which is fitted to a stretched exponential function. Two parameters β and τ involved in the function are estimated as functions of saturated dangling bond density in terms of our model. These are compared with two experimental results, i.e., our results obtained from ESR measurements and Shimakawa et al.’s results obtained from photoconductivity measurements. The saturated dangling bond density is also measured as a function of the generation rate of free carriers. The experimental results are compared with calculated results and discussed. 相似文献