全文获取类型
收费全文 | 219617篇 |
免费 | 5253篇 |
国内免费 | 3112篇 |
专业分类
化学 | 97859篇 |
晶体学 | 3243篇 |
力学 | 13344篇 |
综合类 | 283篇 |
数学 | 36118篇 |
物理学 | 77135篇 |
出版年
2022年 | 1213篇 |
2021年 | 1590篇 |
2020年 | 1806篇 |
2019年 | 1754篇 |
2018年 | 11116篇 |
2017年 | 11860篇 |
2016年 | 6929篇 |
2015年 | 3045篇 |
2014年 | 3125篇 |
2013年 | 5915篇 |
2012年 | 10326篇 |
2011年 | 19790篇 |
2010年 | 12204篇 |
2009年 | 12331篇 |
2008年 | 16552篇 |
2007年 | 20006篇 |
2006年 | 5153篇 |
2005年 | 11506篇 |
2004年 | 7417篇 |
2003年 | 6840篇 |
2002年 | 4613篇 |
2001年 | 4711篇 |
2000年 | 3719篇 |
1999年 | 2828篇 |
1998年 | 2176篇 |
1997年 | 2093篇 |
1996年 | 2127篇 |
1995年 | 1788篇 |
1994年 | 1636篇 |
1993年 | 1431篇 |
1992年 | 1782篇 |
1991年 | 1747篇 |
1990年 | 1563篇 |
1989年 | 1406篇 |
1988年 | 1392篇 |
1987年 | 1413篇 |
1986年 | 1218篇 |
1985年 | 1489篇 |
1984年 | 1457篇 |
1983年 | 1036篇 |
1982年 | 1066篇 |
1981年 | 1015篇 |
1980年 | 907篇 |
1979年 | 1134篇 |
1978年 | 1145篇 |
1977年 | 1088篇 |
1976年 | 1036篇 |
1975年 | 888篇 |
1974年 | 901篇 |
1973年 | 880篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The object of this note is to prove the followingTheorem Let{a_n}and{b_n}be sequences of real numbers such that0<∑∑a_n~2<+∞and0<∑b_n~2<+∞.Then we have the inequalitysum from m=1 to∞sum from n=1 to∞a_mb_n/m+n<{sum from n=1 to∞(π-θ/n~(1/2)a_n~2}~1/2{sum from n=1 to∞(π-θ/n~(1/2)b_n~2}~1/2 (1)whereθ=3/2~(1/2)-1=1.121320343. 相似文献
132.
133.
J Szeman H Ueda J Szejtli E Fenyvesi Y Machida T Nagai 《Chemical & pharmaceutical bulletin》1987,35(1):282-288
134.
This paper reports that the growth of RuOx(110) thin layer growth on Ru(0001)
has been investigated by means of scanning tunnelling microscope (STM). The STM
images showed a domain structure with three rotational domains of RuOx(110)
rotated by an angle of 120℃.
The as-grown RuOx(110) thin layer is expanded from the bulk-truncated
RuOx(110) due to the large mismatch between RuOx(110) and the
Ru(0001) substrate. The results also indicate that growth of RuOx(110)
thin layer on the Ru(0001) substrate by oxidation tends first to formation
of the Ru-O (oxygen) chains in the [001] direction of RuOx(110). 相似文献
135.
L. Tong Y. Tian Q. Y. Wang Y. S. Ling 《International Journal of Infrared and Millimeter Waves》2006,27(9):1307-1314
The paper introduces a special system calibration technology in s-parameters measurement of microwave and millimeter wave
devices. The 8-term errors module is built by analyzing the signals flowing in the measurement system. Then the calibration
technology using non-standard kits is designed on the base. Finally, the experiment using the calibration technology is introduced. 相似文献
136.
V. Yu. Baranovskii L. L. Yasina M. V. Motyakin I. I. Aliev S. Shenkov M. Dimitrov N. Lambov A. M. Wasserman 《Polymer Science Series A》2006,48(12):1304-1309
Partially water-swellable polymer networks were synthesized on the basis of poly(acrylic acid) and various macrodiisocyanates. Hydrophilic and hydrophobic local regions were revealed in swollen networks (hydrogels) by means of the spin probe technique. The local mobility in hydrophobic regions depends on the macrodiisocyanate structure; however, it is substantially lower than that in hydrophilic regions for all gels. It was assumed that the presence of hydrophobic and hydrophilic regions and the difference in their local dynamics must have a substantial effect on the pharmacokinetics of release of drugs immobilized in these hydrogels. 相似文献
137.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献
138.
The quantitative rainbow schlieren deflectometry (RSD) technique was applied to measure temperature and oxygen concentration in an axisymmetric hydrogen gas-jet diffusion flame burning in quiescent air at fuel jet exit Reynolds number of 70. Schlieren measurements were compared with conventional measurements using a thermocouple and a gas-sampling probe. Good agreement between the two measurement techniques was achieved on the fuel-lean side of the flame. 相似文献
139.
This study addresses the problem of the automatic flow regime identification in two-phase flows in pipes. A novel wavelet transform-based approach is proposed and validated using time series of differential pressure fluctuations. The experimental data on the differential pressure measured in a vertically installed Venturi meter for air-water flow were analyzed and found to be appropriate for flow regime identification. The wavelet spectrum of the measured signal is shown to characterize the flow patterns completely, and the vector of the wavelet variances is proposed as the characteristic vector for use in an on-line flow regime identification system. 相似文献
140.
Three new cytotoxic polyacetylenes, PQ-1 (1), PQ-2 (2) and PQ-3 (3), have been isolated from Panax quinquefolium. The structures of these acetylenes were determined by analyses of their 1H-1H and 1H-13C COSY spectra. All these compounds exhibited strong cytotoxic activities against leukemia cells (L 1210) in tissue culture. 相似文献