全文获取类型
收费全文 | 836篇 |
免费 | 26篇 |
国内免费 | 3篇 |
专业分类
化学 | 590篇 |
晶体学 | 4篇 |
力学 | 18篇 |
数学 | 72篇 |
物理学 | 181篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 16篇 |
2018年 | 11篇 |
2017年 | 24篇 |
2016年 | 22篇 |
2015年 | 25篇 |
2014年 | 26篇 |
2013年 | 56篇 |
2012年 | 31篇 |
2011年 | 44篇 |
2010年 | 23篇 |
2009年 | 22篇 |
2008年 | 39篇 |
2007年 | 42篇 |
2006年 | 48篇 |
2005年 | 41篇 |
2004年 | 33篇 |
2003年 | 19篇 |
2002年 | 18篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1964年 | 8篇 |
1960年 | 4篇 |
排序方式: 共有865条查询结果,搜索用时 15 毫秒
1.
B. Sanjeeva Rao M. Ramakrishna Murthy 《Journal of Polymer Science.Polymer Physics》1989,27(6):1187-1194
Electron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ-irradiated in air at room temperature and recorded at room temperature and at liquid-nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least-squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10-line spectra are assigned to the chain radicals CH3? CH? CH2 ~ and/or ~ CH2? CH? CH2 ~. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the Cα? Cβ bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption. 相似文献
2.
J.S. Yadav B.V. Subba Reddy V. Sunitha K. Srinivasa Reddy K.V.S. Ramakrishna 《Tetrahedron letters》2004,45(42):7947-7950
Aryl amines react with endocyclic ene-carbamates such as tert-butyl 2,3-dihydro-1H-1-pyrrolecarboxylate and tert-butyl 1,2,3,4-tetrahydro-1-pyridinecarboxylate, on the surface of montmorillonite KSF clay under mild conditions to afford the corresponding 3-aminopropylhexahydropyrrolo[3,2-c]quinoline or 4-aminobutyloctahydrobenzo[h][1,6]naphthyridine derivatives in excellent yields with moderate diastereoselectivity. 相似文献
3.
The K-shell X-ray fluorescence cross sections are determined experimentally for 10 elements such as Pb, Hg, Ir, W, Lu, Tm,
Dy, Tb, Gd and Nd at excitation energy of 661.6 keV associated with γ-rays of 137Cs radioisotope. The technique employed involves the measurement of total intensity of fluorescent K X-rays that follow the
photoeffect absorption of a known flux of γ-rays using a well type Nal(Tl) detector. The obtained results are compared with the available theoretical values and other
measured values. 相似文献
4.
Richard A. Cairncross Jeffrey G. Becker Shri Ramaswamy Ryan O'Connor 《Applied biochemistry and biotechnology》1996,131(1-3):774-785
Management of moisture penetration and hydrolytic degradation of polylactide (PLA) is extremely important during the manufacturing,
shipping, storage, and end-use of PLA products. Moisture transport, crystallization, and degradation, in PLA have been measured
through a variety of experimental techniques including size-exclusion chromatography, differential scanning calorimetry, and
X-ray diffraction. Quartz crystal microbalance and dynamic vapor sorption experiments have also been used to measure moisture
sorption isotherms in PLA films with varying crystallinity. A surprising result is that, within the accuracy of the experiments,
crystalline and amorphous PLA films exhibit identical sorption isotherms. 相似文献
5.
6.
7.
Excess enthalpies (H
E
) for mixtures of cyclohexanone with propan-1-ol. propan-2-ol, butan-1-ol, butan-2-ol and 2-methyl propan-1-ol at 298.15 K
have been measured over the entire composition range. All mixed endothermically with the maximum values ofH
E
occurring at equimole fraction. Comments about the molecular interactions contributing to the excess enthalpies of a cyclic
ketone + an alcohol are made on the basis of these results. 相似文献
8.
The phase diagram for the ternary system deca glycerol dioleate(DGD)/heptane/water was established at 25 °C. In this phase diagram it was seen that the reverse micellar solution phase extends in its area until the water content reaches 35–45 wt%, at which a liquid crystalline phase begins to appear. On the basis of the experimental results of specific conductivity, viscosity, etc. for the samples containing a definite amount of DGD (0,1 M), and varying relative amounts of heptane and water, the mechanism of the transition of reverse micellar structures to liquid crystalline phase is discussed. 相似文献
9.
A highly sensitive and selective spectrofluorimetric method for the determination of 0.05-2.00 mug germanium is described. Germanium is treated with chromotropic acid at pH 2.5 and the resultant anionic complex is extracted as an ion pair with rhodamine into toluene. Addition of butanol to the organic extract releases the fluorescent dye and facilitates its measurement at 570 nm after exciting at 540 nm. The method provides a detection limit of 0.003 mug ml(-1) and is virtually free from interference from extraneous ions. The relative standard deviaiton is 2.9% for ten determinations of 1.0 mug germanium. The method has been applied to the determination of germanium in various ores, minerals and rock samples. 相似文献
10.
A total synthesis of d-(+)-biotin is described starting from d-(+)-glucosamine using acyliminium chemistry. 相似文献