全文获取类型
收费全文 | 8326篇 |
免费 | 247篇 |
国内免费 | 41篇 |
专业分类
化学 | 5821篇 |
晶体学 | 40篇 |
力学 | 209篇 |
数学 | 1107篇 |
物理学 | 1437篇 |
出版年
2023年 | 43篇 |
2022年 | 47篇 |
2021年 | 66篇 |
2020年 | 93篇 |
2019年 | 99篇 |
2018年 | 72篇 |
2017年 | 61篇 |
2016年 | 183篇 |
2015年 | 152篇 |
2014年 | 174篇 |
2013年 | 370篇 |
2012年 | 460篇 |
2011年 | 532篇 |
2010年 | 284篇 |
2009年 | 233篇 |
2008年 | 516篇 |
2007年 | 546篇 |
2006年 | 548篇 |
2005年 | 474篇 |
2004年 | 427篇 |
2003年 | 367篇 |
2002年 | 346篇 |
2001年 | 149篇 |
2000年 | 106篇 |
1999年 | 66篇 |
1998年 | 82篇 |
1997年 | 100篇 |
1996年 | 133篇 |
1995年 | 126篇 |
1994年 | 105篇 |
1993年 | 145篇 |
1992年 | 96篇 |
1991年 | 78篇 |
1990年 | 96篇 |
1989年 | 74篇 |
1988年 | 64篇 |
1987年 | 65篇 |
1986年 | 52篇 |
1985年 | 90篇 |
1984年 | 81篇 |
1983年 | 57篇 |
1982年 | 87篇 |
1981年 | 90篇 |
1980年 | 69篇 |
1979年 | 70篇 |
1978年 | 68篇 |
1977年 | 50篇 |
1976年 | 69篇 |
1975年 | 47篇 |
1973年 | 36篇 |
排序方式: 共有8614条查询结果,搜索用时 406 毫秒
991.
992.
W. M. R. Dirkx W. E. Van Mol R. J. A. Van Cleuvenbergen F. C. Adams 《Fresenius' Journal of Analytical Chemistry》1989,335(7):769-774
Summary A reproducible and interference-free method is presented for simultaneous determination of individual tri-, di- and monoalkyltin species present in aqueous systems. The ionic methyltin and butyltin compounds are extracted from water into pentane as diethyldithiocarbamate complexes at pH 5. The organic phase is then evaporated to dryness under reduced pressure, after which derivatization withn-pentyl (Pe) Grignard reagent is carried out in a microvolume ofn-octane to form pentylated alkyltin compounds R
n
SnPe(4-n) (R = Methyl, Me or Butyl, Bu). The quantitation is subsequently performed by gas chromatography with quartz furnace atomic absorption spectrometric detection (GC-AAS). Absolute detection limits range between 0.16 ng and 0.40 ng Sn for the various organotin species, allowing speciation in natural water down to the 4-10 ng 1–1 level.
Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday 相似文献
Speziation von organischen Zinnverbindungen in Wasser durch GC/AAS
Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday 相似文献
993.
R F Adams 《Journal of chromatography. A》1974,95(2):189-212
994.
n-C3H7ONO was photolyzed with 366 nm radiation at ?26, ?3, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yields of C2H5CHO, C2H5ONO, and CH3CHO were measured as a function of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?1 = 0.38 ± 0.04 independent of temperature. The n-C3H7O radicals can react with NO by two routes The n-C3H7O radical can decompose via or react with O2 via Values of k4/k2 ? k4b/k2 were determined to be (2.0 ± 0.2) × 1014, (3.1 ± 0.6) × 1014, and (1.4 ± 0.1) × 1015 molec/cm3 at 55, 88, and 120°C, respectively, at 150-torr total pressure of N2. Values of k6/k2 were determined from ?26 to 88°C. They fit the Arrhenius expression: For k2 ? 4.4 × 10?11 cm3/s, k6 becomes (2.9 ± 1.7) × 10?13 exp{?(879 ± 117)/T} cm3/s. The reaction scheme also provides k4b/k6 = 1.58 × 1018 molec/cm3 at 120°C and k8a/k8 = 0.56 ± 0.24 independent of temperature, where 相似文献
995.
996.
Both the multiphoton absorption and the luminescence brightness of osmium tetroxide induced by absorption of temporally smooth CO2 10P(20) laser pulses of 10 and 40 ns FWHM have been measured for pressures in the range 6.7 to 200 Pa. A dependence of these phenomena on laser pulse length is observed. Comparison of the luminescence brightness to the average excitation shows that the distribution of the multiphoton excitation depends on the laser pulse intensity for the two pulse lengths studied.Issued as AECL Contribution No. 8806 相似文献
997.
Steven W. Beyerlein Rainer K. Cossmann Horst.J. Richter 《International Journal of Multiphase Flow》1985,11(5):629-641
In vertical bubbly flow, the bubbles are not distributed evenly across the flow section. Several investigators have observed a wall-skewed bubble concentration profile in a vertical upward flow. This paper presents an analysis that predicts this type of bubble distribution by incorporating into the equation of motion a lateral force due to the relative velocity of the two phases and the eddy diffusivity of the liquid. Comparison of analysis and experiment shows good agreement. 相似文献
998.
999.
1000.
With quasicommutative n-square complex matrices A1,…,As and s-square hermitian G=(gij), relationships are given between the image of a linear transformation on n being positive definite and the action of H on generalized inertial decompositions of n. 相似文献