全文获取类型
收费全文 | 132461篇 |
免费 | 24758篇 |
国内免费 | 12073篇 |
专业分类
化学 | 106031篇 |
晶体学 | 1381篇 |
力学 | 6739篇 |
综合类 | 622篇 |
数学 | 13890篇 |
物理学 | 40629篇 |
出版年
2024年 | 354篇 |
2023年 | 2056篇 |
2022年 | 3600篇 |
2021年 | 3901篇 |
2020年 | 5008篇 |
2019年 | 5959篇 |
2018年 | 4243篇 |
2017年 | 3792篇 |
2016年 | 7586篇 |
2015年 | 7709篇 |
2014年 | 8539篇 |
2013年 | 10818篇 |
2012年 | 11561篇 |
2011年 | 11052篇 |
2010年 | 8728篇 |
2009年 | 8477篇 |
2008年 | 8585篇 |
2007年 | 7360篇 |
2006年 | 6591篇 |
2005年 | 5884篇 |
2004年 | 4737篇 |
2003年 | 3882篇 |
2002年 | 4486篇 |
2001年 | 3438篇 |
2000年 | 3151篇 |
1999年 | 2442篇 |
1998年 | 1849篇 |
1997年 | 1739篇 |
1996年 | 1748篇 |
1995年 | 1432篇 |
1994年 | 1282篇 |
1993年 | 1094篇 |
1992年 | 987篇 |
1991年 | 850篇 |
1990年 | 724篇 |
1989年 | 564篇 |
1988年 | 493篇 |
1987年 | 399篇 |
1986年 | 381篇 |
1985年 | 359篇 |
1984年 | 239篇 |
1983年 | 169篇 |
1982年 | 151篇 |
1981年 | 121篇 |
1980年 | 117篇 |
1979年 | 92篇 |
1978年 | 70篇 |
1977年 | 74篇 |
1976年 | 67篇 |
1973年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
Piaoping Yang Jianfeng Yu Zhenlü Wang Qingsheng Liu Tonghao Wu 《Reaction Kinetics and Catalysis Letters》2004,83(2):275-282
Mg-Al, Zn-Al and Ni-Al hydrotalcite-like compounds with high crystallinity were synthesized by using the decomposing property
of urea at high temperature. The crystallinity and the regularly of the samples were much preferable to those synthesized
by other methods.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
292.
Z. J. Yu L. J. Liu R. X. Zhuo 《Journal of polymer science. Part A, Polymer chemistry》2003,41(1):13-21
The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by 1H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (Mw) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (Mw/Mn)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with Mw = 12,100 and Mw/Mn = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in Mw of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003 相似文献
293.
294.
295.
296.
Summary Vezetéknév 相似文献
297.
The properties of pulsed laser vapor doping on p-Si(1 0 0) with a KrF (248 nm) excimer pulsed laser (248 nm) and BCl3 gas are reported in this paper. The doped samples are characterized by the resistance measured using a four-probe method, since the sheet resistance changes with the carrier concentration of the sample. The doping effects with the variation of laser energy density, pulse number, and the pressure of BCl3 were investigated in terms of the sheet resistance. In this way, the optimized parameters were obtained and used for the positive heavy doping on p-Si(1 0 0) and p-Si(1 1 1). Then, using a square mesh under the above conditions, an image doping was completed. Finally, the metal–semiconductor Ohmic contacts were realized by plating Ag and Cu films on the doped surface. 相似文献
298.
H. -Q. Liu 《manuscripta mathematica》1995,87(1):159-166
This article was processed by the author using the IATEX style filecljourl from Springer-Verlag. 相似文献
299.
A hybrid finite-element method, combining ideas from a modified method of characteristics and the streamline diffusion method, delivers accurate solutions to the advection–diffusion equation. An error analysis for the case of tensorial diffusion shows that the lowest-order version of the scheme, which allows one to use a symmetric linear solvers at each time step, possesses first-order accuracy in time and space. Numerical experiments demonstrate the scheme's ability to model advection-dominated transport of solute plumes without distorting sharp fronts. © 1995 John Wiley & Sons, Inc. 相似文献
300.
The growth mechanism of the peritectic η phase involving the peritectic reaction and peritectic transformation in Cu-70%Sn alloy was investigated under directional
solidification. The results show that a major growth mechanism in thickening of the peritectic η-layer is not the peritectic reaction but the peritectic transformation. The transformation temperature and isothermal time
play crucial roles in determining the volume fraction and the thickness of the peritectic η phase. With the increase of the temperature and isothermal time, the volume fraction of the peritectic η phase increases. The regressed data show that the relationship between the thickness of η phase (Δx) and the transformation temperature (T) meets the following equation In Δx=6.5−1673 1 / T. Additionally, there exists a relationship between the thickness of the η phase (Δx) and the isothermal time (t) at the 9 mm solidification distance below the peritectic reaction interface, Δx=0.72t
1/2, which is consistent with the theoretical model.
Supported by the National Science Foundation of China (Grant No. 50395102) 相似文献