全文获取类型
收费全文 | 480186篇 |
免费 | 5706篇 |
国内免费 | 1495篇 |
专业分类
化学 | 250097篇 |
晶体学 | 7864篇 |
力学 | 21717篇 |
综合类 | 36篇 |
数学 | 54786篇 |
物理学 | 152887篇 |
出版年
2021年 | 4183篇 |
2020年 | 4665篇 |
2019年 | 5223篇 |
2018年 | 6773篇 |
2017年 | 7005篇 |
2016年 | 9925篇 |
2015年 | 5859篇 |
2014年 | 9609篇 |
2013年 | 22650篇 |
2012年 | 17241篇 |
2011年 | 20691篇 |
2010年 | 15070篇 |
2009年 | 14971篇 |
2008年 | 18460篇 |
2007年 | 18259篇 |
2006年 | 17005篇 |
2005年 | 14983篇 |
2004年 | 13878篇 |
2003年 | 12435篇 |
2002年 | 12227篇 |
2001年 | 14484篇 |
2000年 | 10923篇 |
1999年 | 8452篇 |
1998年 | 6977篇 |
1997年 | 6803篇 |
1996年 | 6435篇 |
1995年 | 5748篇 |
1994年 | 5594篇 |
1993年 | 5299篇 |
1992年 | 6210篇 |
1991年 | 6330篇 |
1990年 | 6067篇 |
1989年 | 6054篇 |
1988年 | 5813篇 |
1987年 | 5929篇 |
1986年 | 5578篇 |
1985年 | 7140篇 |
1984年 | 7197篇 |
1983年 | 5862篇 |
1982年 | 6055篇 |
1981年 | 5878篇 |
1980年 | 5582篇 |
1979年 | 6119篇 |
1978年 | 6154篇 |
1977年 | 6253篇 |
1976年 | 6091篇 |
1975年 | 5666篇 |
1974年 | 5542篇 |
1973年 | 5583篇 |
1972年 | 3934篇 |
排序方式: 共有10000条查询结果,搜索用时 90 毫秒
771.
Institute of Automated Control Systems and Radioelectronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 1, pp. 94–105, January, 1989. 相似文献
772.
Ultrasonic longitudinal velocity and adsorption have been measured in ceramic superconductors YBa2Cu3Oy with various porosity and also in BiSrCaCu2Oy. A velocity drop of about 400 ppm was found at Tc only in the measurements on cooling. The magnitude of the velocity drop is anomalously large compared with the value expected from the thermodynamics. A hysteresis of velocity with respect to temperature was observed in all the samples studied. It is suggested that some structural change at pore size level is responsible for this phenomenon. 相似文献
773.
774.
Summary The meaning of linear absorbing boundary conditions for periodic water waves in elliptical approaches is discussed. It is
found that the direction of propagation of the waves must be known for reliable boundary conditions and that the energy dissipation
of waves running parallel to a boundary in general cannot be modelled in the framework of a linear theory.
Work presented at the Euromech Colloquium 240 on ?Dispersive waves in dissipative fluids?, Bologna, August 30–September 2,
1988. 相似文献
775.
In an effort to clarify the role of controlled oxygen exposure in the synthesis of LaBa2Cu3Oy samples which achieve zero resistivity above 90 K, we have prepared samples of La(1+x)Ba(2–x)Cu3Oy with x approximately equal to 0 and with y varying between 6.22 and 7.00. We find that for large values of y, 6.88相似文献
776.
Summary We have estimated and measured the daily thermal expansion of an oceanographic platform. This has been found negligible as
far as the calibration of a satellite altimeter is concerned. 相似文献
777.
The reactions of 2,3,6,11-tetrahydroanthra[2,1-d]isothiazole-3,6,11-trione with dimethyl sulfate, benzyl chloride, and allyl bromide afforded the corresponding 2-alkyl-2,3,6,11-tetrahydroanthra[2,1-d]isothiazole-3,6,11-triones and 3-(alkoxy)-6,11-dihydroanthra[2,1-d]isothiazole-6,11-diones. The reactions of 2,3,6,11-tetrahydroanthra[2,1-d]isothiazole-3,6,11-trione and its S-oxide with a formaldehyde—secondary amine system yielded 2-[(alkylamino)methyl]-2,3,6,11-tetrahydroanthra[2,1-d]isothiazole-3,6,11-triones and 2-[(alkylamino)methyl]-3,6,11-trioxo-2,3,6,11-tetrahydroanthra[2,1-d]isothiazole 1-oxides, respectively. 相似文献
778.
779.
Using the DFT/B3LYP method with a 6-31G(d) basis set, the structure, normal vibration frequencies, and the absolute band intensities in the IR spectra of the chlorin molecule and its four symmetric isotopomers have been calculated. Scaling of the force field by the Pulay method in independent and natural coordinates has been carried out. A method for obtaining effective force fields without using experimental data on the fundamental vibration frequencies is proposed. By comparing the vibration modes and constructing special matrices, complete assignment of the fundamental frequencies of porphin and chlorin has been carried out. It has been shown that the majority of porphin macroring vibrations upon pyrrolenine ring hydrogenation are frequency-characteristic and only 12 vibrations change considerably. A frequency correlation with regard for the mode transition between chlorin and all its isotopomers under consideration has been established. Comparative analysis of the force fields of porphin and chlorin in dependent natural coordinates has revealed the unique nonlocal character of the change in force constants of the macroring upon hydrogenation of one pyrrolenine ring. Modeling of the IR spectra of chlorin and its isotopomers has been performed. Assignment and interpretation of the normal vibrations of the molecules under consideration have been carried out. 相似文献
780.
Random copolymers of poly{(methacrylamide)-co-(vinyl trimethoxysilane)} and poly{(methacrylic acid)-co-(vinyl trimethoxysilane)} were synthesized via a free radical polymerization reaction. Acid catalyzed sol-gel process of tetraethylorthosilicate (TEOS) with aforementioned polymers in the presence of methyl xanthine class of alkaloid like caffeine resulted in the formation of highly transparent monoliths. Solvent extraction of the template leaves behind the recognition sites intact with high selectivity towards the print molecule. The ionic and non-specific adsorptions, which are considered to be the main disadvantages of the molecularly imprinted polymers (MIP), are prevented to a considerable extent by the end capping of surface silanol groups. The template binding efficiencies of MIP were determined by HPLC analysis. 相似文献