全文获取类型
收费全文 | 45757篇 |
免费 | 10372篇 |
国内免费 | 2033篇 |
专业分类
化学 | 47519篇 |
晶体学 | 434篇 |
力学 | 928篇 |
综合类 | 51篇 |
数学 | 3275篇 |
物理学 | 5955篇 |
出版年
2023年 | 174篇 |
2022年 | 335篇 |
2021年 | 460篇 |
2020年 | 1513篇 |
2019年 | 2816篇 |
2018年 | 1238篇 |
2017年 | 909篇 |
2016年 | 3678篇 |
2015年 | 3817篇 |
2014年 | 3795篇 |
2013年 | 4642篇 |
2012年 | 3750篇 |
2011年 | 3072篇 |
2010年 | 3349篇 |
2009年 | 3327篇 |
2008年 | 2976篇 |
2007年 | 2345篇 |
2006年 | 1984篇 |
2005年 | 2100篇 |
2004年 | 1850篇 |
2003年 | 1694篇 |
2002年 | 2303篇 |
2001年 | 1634篇 |
2000年 | 1474篇 |
1999年 | 537篇 |
1998年 | 192篇 |
1997年 | 170篇 |
1996年 | 180篇 |
1995年 | 135篇 |
1994年 | 152篇 |
1993年 | 126篇 |
1992年 | 119篇 |
1991年 | 100篇 |
1990年 | 109篇 |
1989年 | 86篇 |
1988年 | 94篇 |
1987年 | 64篇 |
1986年 | 72篇 |
1985年 | 99篇 |
1984年 | 71篇 |
1983年 | 70篇 |
1982年 | 51篇 |
1981年 | 48篇 |
1980年 | 48篇 |
1979年 | 35篇 |
1977年 | 40篇 |
1976年 | 40篇 |
1975年 | 36篇 |
1974年 | 50篇 |
1973年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
221.
This work reports a new synthetic approach for single‐phase TiO2 nanomaterials by solvothermal treatment of titanium tetrachloride in acetone at 80–110 °C. Small, uniform, and yet size‐tunable (5–10 nm) anatase titania nanocrystallites were obtained using a low concentration of TiCl4 in acetone (i.e., at molar ratios of TiCl4/acetone ≤ 1:15) in the temperature range of 80–110 °C, while rutile nanofibers were synthesized using a high concentration of TiCl4 (e.g., TiCl4/acetone = 1:10) at 110 °C. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
222.
Y.T. Chen S.U. Jen Y.D. Yao J.M. Wu G.H. Hwang T.L. Tsai Y.C. Chang A.C. Sun 《Journal of magnetism and magnetic materials》2006
Co50Fe50 films with thickness varying from 100 to 500 Å were deposited on a glass substrate by sputtering process, respectively. Two kinds of CoFe films were studied: one was the as-deposited film, and the other the annealed film. The annealing procedure was to keep the films at 400 °C for 5 h in a vacuum of 5×10−6 mbar. From the X-ray study, we find that the as-deposited film prefers the CoFe(1 1 0) orientation. Moreover, the body-centered cubic (bcc) CoFe(1 1 0) line is split into two peaks: one corresponding to the ordered body-centered tetragonal (bct) phase, and the other, the disordered bcc phase. After annealing, the peak intensity of the ordered bct phase becomes much stronger, while that of the disordered bcc phase disappears. The annealing has also caused the ordered CoFe(2 0 0) line to appear. When the amount of the ordered bct phase in Co50Fe50 is increased, the saturation magnetization (Ms) and coercivity (Hc) become larger, but the electrical resistivity (ρ) decreases. From the temperature coefficient of resistance (TCR) measurement, we learn that the bct grains in the CoFe film start to grow at temperature 82 °C. 相似文献
223.
Wally L. Chang Kurt C. Frisch Kaneyoshi Ashida 《Journal of polymer science. Part A, Polymer chemistry》1989,27(11):3637-3649
The anionic polymerization of ?-caprolactam (CLM) has been shown to proceed at high reaction rate when catalyzed by metallic lactamates and initiated by acyllactams. The role of initiator and catalyst concentration on the process of ?-caprolactam anionic polymerization has been explored, with the aim of selecting the most suitable experimental conditions for reaction injection molding (RIM). The overall polymerization rates and physical properties for reaction injection molding of star-shaped nylon 6 homopolymer have been studied by the quasi-adiabatic process. In order to model the actual rapid molding conditions, time vs. temperature reaction profiles were measured, and the relative rates of polymerization subsequently determined from these data. 相似文献
224.
225.
226.
227.
228.
This paper studied the cost allocation for the unfunded liability in a defined benefit pension scheme incorporating the stochastic phenomenon of its returns. In the recent literature represented by Cairns and Parker [Insurance: Mathematics and Economics 21 (1997) 43], Haberman [Insurance: Mathematics and Economics 11 (1992) 179; Insurance: Mathematics and Economics 13 (1993) 45; Insurance: Mathematics and Economics 14 (1994) 219; Insurance: Mathematics and Economics 14 (1997) 127], Owadally and Haberman [North American Actuarial Journal 3 (1999) 105], the fund level is modeled based on the plan dynamics and the returns are generated through several stochastic processes to reflect the current realistic economic perspective to see how the contribution changed as the cost allocation period increased. In this study, we generalize the previous constant value assumption in cost amortization by modeling the returns and valuation rates simultaneously. Taylor series expansion is employed to approximate the unconditional and conditional moments of the plan contribution and fund level. Hence the stability of the plan contribution and the fund size under different allocation periods could be estimated, which provide valuable information adding to the previous works. 相似文献
229.
230.