全文获取类型
收费全文 | 207篇 |
免费 | 9篇 |
国内免费 | 5篇 |
专业分类
化学 | 102篇 |
力学 | 13篇 |
综合类 | 2篇 |
数学 | 24篇 |
物理学 | 80篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 9篇 |
2012年 | 9篇 |
2011年 | 16篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 11篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有221条查询结果,搜索用时 31 毫秒
41.
A facile synthesis of a series of 1-alkoxyisoquinolines and (2H)-isoquinolones by an intramolecular 6-endo-dig cyclization of ortho-alkynylbenzonitriles in the presence of a catalytic amount of hydrido(dimethylphosphinous acid-κP)[hydrogen bis(dimethylphosphinito-κP)]platinum(II) in various alcohols at 65-90 °C is described for the first time. 相似文献
42.
高分子铑配合物(PYBRh)催化甲醇羰基化为乙酸和乙酸酐的动力学研究 总被引:4,自引:1,他引:4
采用2-乙烯吡啶-丁烯酮共聚物为配体,与四羰基二氯二铑形成顺二羰基铑(I)配合物(PYBRh),用于催化甲醇羰基化制备乙酸和乙酸酐的反应动力学研究。结果表明,其对反应物甲醇和一氧化碳均为零级反应,在一定范围内,对高分子铑催化剂及助催化剂碘甲烷均为一级反应,极性溶剂的加入可以提高甲醇羰基化速度。通过实验结果计算了其反应活化能,活化熵和热焓研究证明其反应机理与小分子铑催化剂相似。 相似文献
43.
A two-level additive Schwarz method for the Morley nonconforming element approximation of a nonlinear biharmonic equation 总被引:1,自引:0,他引:1
In this paper, we consider the well known Morley nonconformingelement approximation of a nonlinear biharmonic equation whichis related to the well-known two-dimensional NavierStokesequations. Firstly, optimal energy and H1-norm estimates areobtained. Secondly, a two-level additive Schwarz method is presentedfor the discrete nonlinear algebraic system. It is shown thatif the Reynolds number is sufficiently small, the two-levelSchwarz method is optimal, i.e. the convergence rate of theSchwarz method is independent of the mesh size and the numberof subdomains. 相似文献
44.
We demonstrated an all optical NOR gate operating at 10 Gb/s using a multi-wavelength mutual injection-locked Fabry-Perot laser diode (FP-LD). 相似文献
45.
Application of PSP to low density gas flows 总被引:1,自引:0,他引:1
Recently optical pressure measurement systems using pressure sensitive paints (PSP) have actively developed to measure continuous
pressure distributions on solid surfaces. However, the pressure range has been almost limited above 130 Pa (about 1 Torr)
and there is no application to lower pressure range because the pressure sensitivity seems to be not so high in that range.
In this study, we have applied three types of PSP [two types are composed by organic dye and polymer (luminophore/binder);
PtOEP/GP197 and PtTFPP/poly(TMSP), and another one is Bath-Ru adsorbed on anodized aluminum] to the rarefied gas flow mainly
lower than 130 Pa and examine those fundamental properties such as pressure sensitivity, leading to selection of the most
suitable PSP among them for the low-pressure range. Since PtTFPP/poly(TMSP) has the highest sensitivity, it is applied successfully
to the measurement of the two-dimensional pressure distribution on the surface interacting with a low density supersonic free
jet. 相似文献
46.
The absorption and emission spectra of the three isomeric cyanoanilines have been investigated. Quantum yields and decay lifetimes are reported for both fluorescence and phosphorescence processes. It is shown that the lowest energy absorption band of p-cyanoaniline consists of two distinct electronic transitions of the 1π*←1π type, whereas, in the o- and m-cyanoanilines, the lowest energy absorption band consists of a single electronic transition of the 1π*←1π type. These conditions are consistent with absorption data, emission data and kinetic analyses. The largest ?P/?F ratio is exhibited by the p-cyanoaniline and this observation is rationalized. 相似文献
47.
Rapid near-infrared Raman spectroscopy system for real-time in vivo skin measurements 总被引:1,自引:0,他引:1
A rapid dispersive-type near-infrared (NIR) Raman spectroscopy system and a Raman probe were developed to facilitate real-time, noninvasive, in vivo human skin measurements. Spectrograph image aberration was corrected by a parabolic-line fiber array, permitting complete CCD vertical binning, thereby yielding a 3.3-16-fold improvement in signal-to-noise ratio. Good quality in vivo cutaneous NIR Raman spectra free of interference from fiber fluorescence and silica Raman scattering can be acquired in less than 1 s, which greatly facilitates practical noninvasive tissue characterization and clinical diagnosis. 相似文献
48.
49.
50.
Geng Leng Guibin Lui Yong Chen Hui Yin Dezhong Dan 《Journal of separation science》2012,35(20):2796-2804
A simple, rapid, and efficient method, vortex‐assisted extraction followed by dispersive liquid–liquid microextraction (DLLME) has been developed for the extraction of polycyclic aromatic hydrocarbons (PAHs) in sediment samples prior to analysis by high performance liquid chromatography fluorescence detection. Acetonitrile was used as collecting solvent for the extraction of PAHs from sediment by vortex‐assisted extraction. In DLLME, PAHs were rapidly transferred from acetonitrile to dichloromethane. Under the optimum conditions, the method yields a linear calibration curve in the concentration range from 10 to 2100 ng g?1 for fluorene, anthracene, chrysene, benzo[k]fluoranthene, and benzo[a]pyrene, and 20 to 2100 ng g?1 for other target analytes. Coefficients of determinations ranged from 0.9986 to 0.9994. The limits of detection, based on signal‐to‐noise ratio of three, ranged from 2.3 to 6.8 ng g?1. Reproducibility and recoveries was assessed by extracting a series of six independent sediment samples, which were spiked with different concentration levels. Finally, the proposed method was successfully applied in analyses of real nature sediment samples. The proposed method extended and improved the application of DLLME to solid samples, which greatly shorten the extraction time and simplified the extraction process. 相似文献