全文获取类型
收费全文 | 57295篇 |
免费 | 5663篇 |
国内免费 | 4161篇 |
专业分类
化学 | 40123篇 |
晶体学 | 831篇 |
力学 | 2465篇 |
综合类 | 349篇 |
数学 | 5919篇 |
物理学 | 17432篇 |
出版年
2023年 | 571篇 |
2022年 | 974篇 |
2021年 | 1305篇 |
2020年 | 1390篇 |
2019年 | 1526篇 |
2018年 | 1182篇 |
2017年 | 1208篇 |
2016年 | 1954篇 |
2015年 | 1948篇 |
2014年 | 2288篇 |
2013年 | 3571篇 |
2012年 | 4555篇 |
2011年 | 4826篇 |
2010年 | 3348篇 |
2009年 | 3180篇 |
2008年 | 4014篇 |
2007年 | 3638篇 |
2006年 | 3494篇 |
2005年 | 3156篇 |
2004年 | 2719篇 |
2003年 | 2149篇 |
2002年 | 2138篇 |
2001年 | 1618篇 |
2000年 | 1349篇 |
1999年 | 945篇 |
1998年 | 661篇 |
1997年 | 613篇 |
1996年 | 671篇 |
1995年 | 537篇 |
1994年 | 579篇 |
1993年 | 520篇 |
1992年 | 450篇 |
1991年 | 390篇 |
1990年 | 316篇 |
1989年 | 264篇 |
1988年 | 267篇 |
1987年 | 195篇 |
1986年 | 188篇 |
1985年 | 293篇 |
1984年 | 195篇 |
1983年 | 178篇 |
1982年 | 181篇 |
1981年 | 149篇 |
1980年 | 135篇 |
1978年 | 119篇 |
1977年 | 129篇 |
1976年 | 132篇 |
1975年 | 137篇 |
1974年 | 129篇 |
1973年 | 146篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
External difference families (EDFs) are a type of new combinatorial designs originated from cryptography. In this paper, some
earlier ideas of recursive and cyclotomic constructions of combinatorial designs are extended, and a number of classes of
EDFs and disjoint difference families are presented. A link between a subclass of EDFs and a special type of (almost) difference
sets is set up. 相似文献
182.
Myung-Soon Lee 《Applied Surface Science》2006,252(14):5019-5025
We prepared high quality Au(1 1 1) film on Si wafer through the spin coating and thermal decomposition of a gold ink, spin-coated-and-fired (SCAF) Au film. The X-ray measurements, XRD and pole-figure analysis, showed that the SCAF Au film has a (1 1 1) out-of-plane orientation with a random in-plane orientation. In order to confirm the chemical activity of the SCAF Au film, we demonstrate the formation of patterned structures with the film by using soft lithography technique. The chemical activities of this physically stable SCAF Au film to the alkanethiols were at least equivalent those of physically deposited the Au films. The possibility of the mass production of micro patterned structure with the SCAF Au film was also demonstrated over the wide region on Si wafer by the microcontact lithography. These suggest that the Au film will help the easy fabrication of various nanosized devices on Si wafer and other substrates. 相似文献
183.
Young Hee Geum Young Ik Kim Kang Sup Lee 《Journal of Applied Mathematics and Computing》2007,25(1-2):109-118
A parametric boundary equation is established for the principal period-2 bulb in the cubic Mandelbrot set. Using its geometry, an efficient escape-time algorithm which reduces the construction time for the period-2 bulbs in the cubic Mandelbrot set is introduced and the implementation graphic results display the fascinating fractal beauty 相似文献
184.
A high-performance liquid chromatographic procedure was developed for the quantitation of homoharringtonine in plasma. Harringtonine was used as an internal standard, and 1 ml of sample was required. The single-step extraction with dichloromethane resulted in almost 100% recovery for homoharringtonine and harringtonine. Analysis was performed on a reversed-phase CN column with amperometric detection. Chromatography was completed in 12 min. At an oxidation potential of +1.0 V, the detection limit was 1 ng/ml at a signal-to-noise ratio of 2. The mean analytical recovery for homoharringtonine was 99.5%. The within-run precision and between-run precision were both less than 11%. The method is equally applicable for plasma or serum, and it has been demonstrated to be applicable for study of the pharmacokinetics of homoharringtonine in patients suffering from acute non-lymphocytic leukaemia. 相似文献
185.
186.
金属薄板中Lamb波波速与静应力关系的理论研究 总被引:2,自引:1,他引:1
本研究基于各向同性金属材料在静压力作用下产生各向异性的事实,从固体中超声波的非线性理论出发,得到了在一定应力下固体的等效的二阶弹性常数,再利用各向异性板中的Lamb波理论推得了在静应力作用下与应力平行和垂直方向的Lamb波的频散方程,讨论了金属薄板中Lamb波波速与静应力的关系。 相似文献
187.
188.
This study investigates a holographic recording effect of biphotonic polarization gratings (BPGs) written on dye-doped liquid crystal (DDLC) films. One linearly polarized green light (λG = 514.5 nm) and a polarization-modulated interference pattern formed by two mutually coherent orthogonal (±45° with respect to the polarization of the green light) polarized red lights simultaneously excite the DDLC films to generate a BPG. The formation of BPGs depends primarily on the dichroism of the dye molecules and a sequence of mechanisms: photoisomerization, anisotropic adsorption and inhibition of dye adsorption. The cis-isomer absorbance-modulated distribution associated with the red polarization-modulation pattern induces the dye adsorption-modulated pattern, in turn, yielding the permanent BPG which generates a modulated twisted nematic (TN) structure pattern in the sample. It is found that each BPG is verified to be electrically switchable and thermally erasable. The switching time is in the order of milliseconds. Additionally, the recording time to form a BPG decreases with increasing intensity of the green pump beam. 相似文献
189.
190.
K.E. Lee T.L. Phan N.D. Ha M.H. Phan S.C. Yu C.O. Kim 《Journal of magnetism and magnetic materials》2006
Influences of oxygen-partial pressure and annealing on the electrical and magnetic properties of CoFeAlO thin films were systematically investigated by means of resistivity, permeability, magnetization and ferromagnetic resonance (FMR) measurements. It was found that, with increasing oxygen-partial pressure or under annealing, the electrical resistivity of the film increased and the magnetic softness decreased, which is attributed to the microstructural change of the film. Interestingly, an as-deposited Co45.30Fe20.65Al19.34O14.71 film was found to exhibit an inverted hysteresis loop with negative coercivity, and this peculiar phenomenon disappeared upon effects of oxygen-partial pressure and annealing. It was also found that the as-deposited films owned a narrow FMR line width that increased with increasing oxygen-partial pressure or under annealing. 相似文献