全文获取类型
收费全文 | 11534篇 |
免费 | 547篇 |
国内免费 | 86篇 |
专业分类
化学 | 7935篇 |
晶体学 | 48篇 |
力学 | 323篇 |
数学 | 1408篇 |
物理学 | 1463篇 |
无线电 | 990篇 |
出版年
2023年 | 117篇 |
2022年 | 127篇 |
2021年 | 230篇 |
2020年 | 244篇 |
2019年 | 269篇 |
2018年 | 193篇 |
2017年 | 160篇 |
2016年 | 364篇 |
2015年 | 319篇 |
2014年 | 404篇 |
2013年 | 633篇 |
2012年 | 830篇 |
2011年 | 900篇 |
2010年 | 473篇 |
2009年 | 404篇 |
2008年 | 795篇 |
2007年 | 794篇 |
2006年 | 745篇 |
2005年 | 675篇 |
2004年 | 586篇 |
2003年 | 508篇 |
2002年 | 429篇 |
2001年 | 128篇 |
2000年 | 123篇 |
1999年 | 116篇 |
1998年 | 103篇 |
1997年 | 112篇 |
1996年 | 138篇 |
1995年 | 98篇 |
1994年 | 79篇 |
1993年 | 59篇 |
1992年 | 58篇 |
1991年 | 68篇 |
1990年 | 70篇 |
1989年 | 45篇 |
1988年 | 36篇 |
1987年 | 32篇 |
1986年 | 49篇 |
1985年 | 65篇 |
1984年 | 67篇 |
1983年 | 44篇 |
1982年 | 53篇 |
1981年 | 39篇 |
1980年 | 57篇 |
1979年 | 35篇 |
1978年 | 45篇 |
1977年 | 49篇 |
1976年 | 41篇 |
1975年 | 37篇 |
1974年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 685 毫秒
941.
942.
Let GK denote a graph G whose edges can fail and with a set K ? V specified. Edge failures are independent and have known probabilities. The K-terminal reliability of GK, R(GK), is the probability that all vertices in K are connected by working edges. A factoring algorithm for computing network reliability recursively applies the formula R(GK) = piR(GK * ei) + qiR(GK - ei) where GK * ei is GK, with edge ei contracted, GK - ei is GK with ei deleted and pi ? 1 - qi is the reliability of edge ei. Various reliability-preserving reductions can be performed after each factoring operation in order to reduce computation. A unified framework is provided for complexity analysis and for determining optimal factoring strategies. Recent results are reviewed and extended within this framework. 相似文献
943.
We develop a kinetic model for the exchange of tritium and deuteriumbetween tritium-containing heavy water and deuterated chloroform in a two-phase liquid system, catalyzed by hydroxide ion (sodium hydroxide). For the exchange reaction yielding tritiated chloroform andheavy water, the measured equilibrium constant is 0.518 at 25–45°C, independent of temperature. The rate constant (for the controlling step, deuteron abstraction from chloroform) is 0.22 L/mol s at 25°C, 0.72 at 35°C, and 2.0 at 45°C, corresponding to an activation energy of 87 kJ/mol. Comparison is made with literature data, and effects of mass transfer on the apparent rate constant are discussed. 相似文献
944.
945.
946.
We extend earlier representation results for monetary risk measures on Orlicz
hearts. Then we give general conditions for such risk measures to be Gateaux-differentiable,
strictly monotone with respect to almost sure inequality, strictly convex modulo translation,
strictly convex modulo comonotonicity, or monotone with respect to different stochastic
orders. The theoretical results are used to analyze various specific examples of risk measures.
We thank Andreas Hamel and Michael Kupper for fruitful discussions and helpful comments. P. Cheridito has been supported by
NSF Grant DMS-0642361, a Rheinstein Award and a Peek Fellowship. T. Li has been supported by a Marshall Scholarship and a
Merage Fellowship. 相似文献
947.
Kevin P. Cole David Mitchell M. Austin Carr James R. Stout Matthew D. Belvo 《Tetrahedron: Asymmetry》2009,20(11):1262-1266
A route for the synthesis of (S,S)-7-amino-5-methyl-5H-dibenzo[b,d]azepin-6(7H)-one hydrochloride is disclosed. The synthesis includes a Friedel–Crafts alkylation to form the seven-membered ring and a highly efficient classical resolution. Additional studies on the enantiopure material showed the amine to be highly resistant to racemization, which led us to investigate the unexpected stability. We propose that the inherent axial chirality contained in the dibenzazepinone works to produce an interesting chirality transfer mechanism, which accounts for the observed robustness of the stereocenter. This previously unrecognized stereochemical element exists within this specific class of molecules, and they should be drawn in a manner which displays the axial chirality. 相似文献
948.
949.
950.
Goldberger Ary L. Kobalter Kevin Bhargava Valmik 《IEEE transactions on bio-medical engineering》1986,(9):874-876
Daily neutrophil counts show considerable variability in normal subjects. The dynamics of these apparently erratic fluctuations have not been characterized. We hypothesized that this variability might reflect the kind of 1/f-like (inverse power-law) spectrum seen in other physiologic processes. Fast Fourier transform analysis of neutrophil count data over 64 consecutive days from four previously reported normal volunteers showed a good fit (r = 0.84; p 0.001) to the predicted power-law regression line (y = ?1.14x ?1.05). Further characterization of normal and pathologic neutrophil spectra may have diagnostic value. 相似文献