全文获取类型
收费全文 | 1215篇 |
免费 | 37篇 |
国内免费 | 8篇 |
专业分类
化学 | 670篇 |
晶体学 | 8篇 |
力学 | 70篇 |
数学 | 115篇 |
物理学 | 397篇 |
出版年
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 6篇 |
2019年 | 20篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 23篇 |
2015年 | 25篇 |
2014年 | 35篇 |
2013年 | 40篇 |
2012年 | 82篇 |
2011年 | 91篇 |
2010年 | 53篇 |
2009年 | 56篇 |
2008年 | 66篇 |
2007年 | 71篇 |
2006年 | 65篇 |
2005年 | 57篇 |
2004年 | 38篇 |
2003年 | 38篇 |
2002年 | 31篇 |
2001年 | 26篇 |
2000年 | 30篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 9篇 |
1994年 | 15篇 |
1993年 | 28篇 |
1992年 | 19篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1972年 | 5篇 |
1970年 | 7篇 |
1969年 | 8篇 |
排序方式: 共有1260条查询结果,搜索用时 78 毫秒
11.
The UV light irradiation of isoniazid (I) in methanol four products, isonicotinic acid (II), isonicotinamide (III), N, N′-bis(isonicotinic acid)hydrazide (IV) and isonicotinaldehyde isonicotinyl hydrazone (V), in ethanol three products, (III), (IV) and acetaldehyde isonicotinyl hydrazone (VI) were isolated and identified. Also, the photoreaction mechanism of isoniazid in methanol and ethanol were discussed. 相似文献
12.
13.
Denote bymi(G) the number of maximal independent sets ofG. This paper studies the setS(k) of all graphsG withmi(G) = k and without isolated vertices (exceptG K
1) or duplicated vertices. We determineS(1), S(2), andS(3) and prove that |V(G)| 2
k–1
+k – 2 for anyG inS(k) andk 2; consequently,S(k) is finite for anyk.
Supported in part by the National Science Council under grant NSC 83-0208-M009-050 相似文献
14.
The effects of three-dimensionality on the turbulence producing near-wall structures over a rotating disk are examined using hydrogen bubble visualization. Laser Doppler anemometry measurements of the tangential and radial velocities indicate the flow to resemble that of an infinite disk. It was found that the crossflow acts to reduce vertical mixing during the turbulence ejection events, thus reducing the efficiency of the boundary layer in producing shear stress.This research has been sponsored by the Department of Energy Office of Basic Energy Sciences through Grants DE-FG03-86ER13608 and DE-FG03-93ER12309. 相似文献
15.
16.
For a stochastic matrix (Q
ij
T
)
i,j=1
M
withQ
ij
T
exp(–U(ij)/T) at the off-diagonal positions, we develop an algorithm to evaluate the asymptotic convergence rate of all eigenvalues ofQ
ij
T
asT 0 using Ventcel's optimal graphs. As an application we can compare the convergence rates of some random updating schemes used in image processing.This research was partially supported by the National Science Council, Taiwan and Air Force Office of Scientific Research Contract No. F49620 S5C 0144, and was completed while Tzuu-Shuh Chiang was visiting the Center for Stochastic Processes, Department of Statistics, University of North Carolina, Chapel Hill, NC 27599-3260, USA. 相似文献
17.
18.
19.
The suitability of blue light-emitting diodes as radiation sources in molecular absorption spectroscopy was evaluated. Electronic as well as spectral considerations are discussed. A transducer based on a blue light-emitting diode and a photodiode is described which yields direct absorbance readings by passing the photocurrent to an integrated circuit logarithmic converter. The performance of this device was tested for commonly used spectrophotometric procedures for Cr, Mn, Zn, Fe and Cl and compared with conventional molecular absorption spectroscopy. Also investigated was the application of the transducer as a detector in flow-injection analysis. 相似文献
20.
Ta Chi Chiang Quang-Tho Pham Alain Guyot 《Journal of polymer science. Part A, Polymer chemistry》1977,15(9):2173-2191
Constant-composition copolymers of methyl methacrylate and vinylidene chloride produced by radical copolymerization are studied by 1H-NMR at 60 and 250 MHz. The different methods of the literature for the derivation of reactivity ratios from either the copolymer composition or the sequence average lengths, or even the diad distribution, are applied but lead to rather dispersed results. A new graphical method is proposed, based on the use of peculiar values of the triad distribution functions. It allows us to detect a penultimate effect for the vinylidene chloride-rich region. In the same range, a change in tacticity of the diads and triads on the methylmethacrylate sequences, as compared with homopolymers, is observed; it suggests that the anomaly is caused by the competition of the depropagation reaction. 相似文献