全文获取类型
收费全文 | 11074篇 |
免费 | 875篇 |
国内免费 | 1193篇 |
专业分类
化学 | 7343篇 |
晶体学 | 201篇 |
力学 | 181篇 |
综合类 | 45篇 |
数学 | 274篇 |
物理学 | 5098篇 |
出版年
2023年 | 94篇 |
2022年 | 156篇 |
2021年 | 121篇 |
2020年 | 135篇 |
2019年 | 161篇 |
2018年 | 186篇 |
2017年 | 206篇 |
2016年 | 322篇 |
2015年 | 269篇 |
2014年 | 341篇 |
2013年 | 887篇 |
2012年 | 516篇 |
2011年 | 587篇 |
2010年 | 504篇 |
2009年 | 725篇 |
2008年 | 643篇 |
2007年 | 733篇 |
2006年 | 663篇 |
2005年 | 584篇 |
2004年 | 535篇 |
2003年 | 478篇 |
2002年 | 424篇 |
2001年 | 373篇 |
2000年 | 366篇 |
1999年 | 369篇 |
1998年 | 317篇 |
1997年 | 263篇 |
1996年 | 276篇 |
1995年 | 292篇 |
1994年 | 241篇 |
1993年 | 195篇 |
1992年 | 256篇 |
1991年 | 165篇 |
1990年 | 99篇 |
1989年 | 90篇 |
1988年 | 98篇 |
1987年 | 70篇 |
1986年 | 48篇 |
1985年 | 52篇 |
1984年 | 44篇 |
1983年 | 32篇 |
1982年 | 36篇 |
1981年 | 26篇 |
1980年 | 27篇 |
1979年 | 27篇 |
1978年 | 15篇 |
1976年 | 22篇 |
1975年 | 15篇 |
1974年 | 15篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
131.
Selenomethionine contents of NIST wheat reference materials 总被引:1,自引:0,他引:1
Values of the total selenium and selenomethionine (Semet) content of four wheat-based reference materials have been obtained by gas chromatography-stable isotope dilution mass spectrometry methods. The total Se method is an established one, and the results obtained with it are consistent with previously-assigned values. The Semet method (previously reported by our laboratory) is based on reaction with CNBr. Our data indicate that the four wheat samples (wheat gluten, durum wheat, hard red spring wheat, and soft winter wheat), though having a 30-fold range in total Se content, all have about 45% of their total Se values in the form of selenomethionine. Investigation of the CNBr-based method suggests that additional experiments are needed to verify that all selenomethionine in the wheat samples is accounted for, but also indicates that the values obtained are within 15% of the true values. As the form in which Se occurs in foods and dietary supplements is important from a nutritional perspective, adding information about Se speciation to total Se values in appropriate reference materials makes these materials more valuable in relevant analytical work. 相似文献
132.
毛细管电泳质谱联用技术及其应用 总被引:9,自引:0,他引:9
本文介绍了用于毛细管电泳质谱联用仪器的多种接口技术,描述了CZE,CIEF,CGE,MEKC和CITP等毛细管电泳技术和四极质谱,离子阱质谱,傅 叶变换离子回旋共振质谱,飞行时间质谱,磁质谱,解吸质谱等联用的现状及发展前景,对近年来CE-MS在酶解产物。蛋白质和肽,核苷酸,药物及代谢产物等领域中的应用作了详细述评。 相似文献
133.
V. K. Turchaninov N. N. Chipanina T. N. Aksamentova M. S. Sorokin V. A. Pestunovich 《Russian Chemical Bulletin》1998,47(2):231-236
Five ionization potentials for thesp,ac andsp, sp conformers of (acetylthiomethyl)trifluorosilane MeC(O)SCH2SiE3 and six ionization potentials for the same conformers of (benzoylthiomethyl)trifluorosilane PhC(O)CH2SiF3 were calculated by the semiempirical AM1 method. The resulting values are in good agreement with the data of photoelectron
spectroscopy only for thesp.ac conformers. The structure of the preferred conformer of (acetylthiomethyl)trifluorosilane was confirmed by measurement of
its dipole moment in the gas phase. The influence of the long-range inductive effect (field effect) on the energy of nonbonding
electrons of the carbonyl oxygen atom in the series of acetic acid derivatives was observed.
For Part 9, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 236–241, February, 1998. 相似文献
134.
FT-IR and Raman spectroscopic study of hydrated rubidium (cesium) borates and alkali double borates 总被引:1,自引:0,他引:1
Zhu Lixia Yue Tao Wang Jiang Gao Shiyang 《Russian Journal of Inorganic Chemistry》2007,52(11):1786-1792
FT-IR and Raman spectra of five hydrated alkali borates and five hydrated alkali double borates have been recorded at room
temperature in the range 400 to 4000 cm−1, and analyzed. Fundamental vibrational modes have been identified and assignments tentatively made in comparison with the
work of Janda and Heller, and Li Jun.
The text was submitted by the authors in English. 相似文献
135.
136.
Enhancement of electronic excitation energy transfer in the colloidal crystals of colloidal silica suspensions doped with fluorescent dyes 总被引:1,自引:0,他引:1
Kiyoshi Shibata Hiroshi Kimura Akira Tsuchida Tsuneo Okubo 《Colloid and polymer science》2006,285(2):127-133
The efficiency of electronic excitation energy transfer from photo-excited rhodamine 110 (Rh110, energy donor) to rhodamine B (RhB, energy acceptor) in an exhaustively deionized colloidal silica suspension has been studied. This colloidal suspension shows Bragg reflection due to the formation of colloidal crystals and the Bragg-peak wavelength is controllable by the volume fraction of the silica spheres. When the Bragg-peak wavelength matches with the fluorescence band of Rh110, a depletion was observed in the Rh110 fluorescence spectrum. This means the fluorescence of Rh110 is partially trapped due to the Bragg reflection inside the crystal lattice. In the coexistence of RhB, the enhancement of RhB fluorescence intensity was observed. These facts clearly indicate the trapped photon energy of Rh110 is efficiently transferred to RhB within the colloidal crystals. The quantitative measurements showed that the enhancement of the transfer efficiency is 20% (or slightly more) in the present experimental conditions. 相似文献
137.
138.
冠醚化二苯甲酮的合成及其光物理行为 总被引:1,自引:0,他引:1
本文报道采用在多聚磷酸中酰化的方法,合成了冠醚化二苯甲酮1~8。它们与叔胺类共用可能被用作光引发剂。为此,用紫外光谱详细研究了这些化合物及其络合后的光物理行为。还提及化合物3和4作为紫外吸收剂的可能性。 相似文献
139.
Modified modeling of the effect of pH and viscosity on the mass transfer in hydrophobic hollow fiber membrane contactors 总被引:3,自引:0,他引:3
This paper studied the effect of pH and the viscosity of feed solution on the mass transfer in two different specifications of hydrophobic hollow fiber membrane contactors. Experimental results showed that the pH of the feed had a significant effect on the rate of mass transfer, the flux and the removal efficiency of easily ionized volatile compounds (VCs), such as ammonia. In unbuffered feed solutions, both the resistance of membrane and the resistance of feed side were affected by the pH of feed and both of them had contributions to the overall mass transfer. A model, , was proposed to predict the effect of pH and gave good agreement with the experimental data for the two contactors. The relationship between viscosities and the mass transfer coefficient could be described by . Based on our experiments, the change of the viscosities in the concentration range of ammonia from 50 to 10,000 mg l−1 caused about 3–4% variation of the mass transfer coefficients. Moreover, it may be more suitable to use the equilibrium concentrations of volatile species instead of the total concentrations of VCs to estimate mass transfer coefficients, removal efficiency and flux. Experimental results also revealed that the choice of the pH of feed might be one of the most crucial factors for removing easily ionized VCs, such as ammonia, from water and wastewater. 相似文献
140.
Yu.?V.?PleskovEmail author M.?D.?Krotova V.?G.?Ralchenko A.?V.?Khomich R.?A.?Khmelnitskii 《Russian Journal of Electrochemistry》2005,41(3):304-309
The photocurrent and photopotential for undoped polycrystalline diamond film electrodes prepared by chemical vapor deposition and annealed in vacuum at 1500–1640°C are measured. The metal-like samples (annealed at 1630°C) have a negligible photosensitivity. Judging from the positive sign of the photopotential and the cathodic direction of the photocurrent, the material under study formally behaves as a p-type semiconductor. The photoeffects are presumably caused by structure defects, in particular, the dislocations in diamond crystallites formed close to intercrystalline boundaries during the high-temperature annealing.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 343–349.Original Russian Text Copyright © 2005 by Pleskov, Krotova, Ralchenko, Khomich, Khmelnitskii. 相似文献