全文获取类型
收费全文 | 389610篇 |
免费 | 5569篇 |
国内免费 | 1781篇 |
专业分类
化学 | 211059篇 |
晶体学 | 5886篇 |
力学 | 15744篇 |
综合类 | 64篇 |
数学 | 47303篇 |
物理学 | 116904篇 |
出版年
2020年 | 3313篇 |
2019年 | 3448篇 |
2018年 | 4474篇 |
2017年 | 4573篇 |
2016年 | 7094篇 |
2015年 | 4699篇 |
2014年 | 6947篇 |
2013年 | 17067篇 |
2012年 | 13533篇 |
2011年 | 16443篇 |
2010年 | 11483篇 |
2009年 | 11197篇 |
2008年 | 15554篇 |
2007年 | 15503篇 |
2006年 | 14551篇 |
2005年 | 13150篇 |
2004年 | 11801篇 |
2003年 | 10418篇 |
2002年 | 10260篇 |
2001年 | 11315篇 |
2000年 | 8630篇 |
1999年 | 6437篇 |
1998年 | 5417篇 |
1997年 | 5297篇 |
1996年 | 5254篇 |
1995年 | 4705篇 |
1994年 | 4784篇 |
1993年 | 4664篇 |
1992年 | 5080篇 |
1991年 | 5012篇 |
1990年 | 4814篇 |
1989年 | 4637篇 |
1988年 | 4579篇 |
1987年 | 4506篇 |
1986年 | 4372篇 |
1985年 | 5820篇 |
1984年 | 5936篇 |
1983年 | 5102篇 |
1982年 | 5421篇 |
1981年 | 5079篇 |
1980年 | 4830篇 |
1979年 | 5109篇 |
1978年 | 5348篇 |
1977年 | 5316篇 |
1976年 | 5328篇 |
1975年 | 4968篇 |
1974年 | 5064篇 |
1973年 | 5271篇 |
1972年 | 3795篇 |
1971年 | 3066篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Y. Qu J.X. Zhang A. Uddin C.Y. Liu S. Yuan M.C.Y. Chan B. Bo G. Liu H. Jiang 《Applied Physics A: Materials Science & Processing》2006,82(2):305-308
Ridge-waveguide InGaAsN triple-quantum-well strain-compensated lasers grown by metal organic chemical vapor deposition were fabricated with pulsed anodic oxidation. The laser’s output power reached 145 mW in continuous-wave mode at room temperature for a 4-?m -stripe-width laser. Continuous-wave single longitudinal mode operation was maintained at a high injection current level with a wavelength of 1287.3 nm at room temperature. Single longitudinal mode operation at 1317.2 nm was achieved at twice the threshold current at 100 °C. The band gap of InGaAsN in the quantum wells at different temperatures was calculated and compared to the measured temperature-dependent laser wavelength. 相似文献
972.
The coherent inelastic processes of the type a → b, which may take place in the interaction of hadrons and γ quanta with nuclei at very high energies (the nucleus remains the same), are theoretically investigated. Analytical formulas for the effective cross-section σcoh(a→b) are obtained. 相似文献
973.
S. V. Ivanov V. V. Trachevskii O. S. Titova L. A. Zozulya 《Russian Journal of Applied Chemistry》2006,79(10):1712-1714
Experimental data demonstrate that a study of accelerated aging can enable prognostication of the working capacity and storage life of polymeric formulations used in aircraft components on the basis of changes in thermogravimetric constants of these polymeric formulations. 相似文献
974.
L. A. Gil‐Alana 《商业与工业应用随机模型》2006,22(4):385-395
This article examines the length of the cycles in the gross domestic product (GDP) real per capita series of 15 countries by means of new statistical techniques based on unit root cycles. We propose tests for unit root cycles at each of the frequencies of the process. Using this approach, we are able to approximate the number of periods per cycle. The results show that the cycles have a periodicity of approximately six years when the disturbances are white noise. However, if we permit autocorrelation, they may also occur at smaller intervals of time. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
975.
Adhesion of zein to solid substrates has been studied using surface energy profiles as indices and by adhesion mapping using
atomic force microscopy (AFM). Different plasticizers like glycerol and sorbitol have been used to form mixed films with zein
and properties of these films are studied using surface energy profiles. Comparison of the results from the different mixed
samples with those from the pure zein films showed that force mapping could identify areas rich in protein. The adhesion maps
produced were deconvoluted from sample topography and contrasted with the data obtained from contact angle measurements. A
comparison of the two methods shows that the extent of contact angle hysteresis is indicative of both hydrophobicity of the
surface as well as the force of adhesion. Mechanical properties and microstructure of zein films prepared by casting from
solutions and using Langmuir-Blodgett film technique have been investigated. Pure zein seemed brittle and exhibited an essentially
linear relationship between stress and strain. Films with plasticizer were tougher than these films. In general, mixed films
showed better mechanical properties than pure films and had higher ultimate tensile strength and increased per cent elongation.
Further, the mixed films of zein showed a higher force of adhesion compared to the pure films. 相似文献
976.
L. T. Ashchepkov D. V. Davydov 《Computational Mathematics and Mathematical Physics》2006,46(11):1910-1917
Noncooperative games of a finite number of persons with interval-valued payoff functions are considered. The concept of an equilibrium situation is introduced. A reduction of such games to deterministic noncooperative games is proposed. Properties of the reduced games are discussed. Interval antagonistic and bimatrix games are examined, and illustrative examples are considered. 相似文献
977.
A new theory of transverse susceptibility (TS) based on magnetization vector dynamics, as described by the Landau–Lifshitz equation of motion, is given. It is shown that the traditional TS experiment is, in fact, the zero-frequency limit of the ferromagnetic resonance (FMR). The importance of these results resides in the generality of the approach which allows one to find the TS for virtually any magnetic system if an expression for the magnetic free-energy density is known. Moreover, the effect of the frequency of excitatory AC field on the TS experiments and the effect of energy dissipation through the imaginary part of TS emerge coherently from the new TS model. 相似文献
978.
Necessary and sufficient conditions in constrained optimization 总被引:22,自引:0,他引:22
Additional conditions are attached to the Kuhn-Tucker conditions giving a set of conditions which are both necessary and sufficient
for optimality in constrained optimization, under appropriate constraint qualifications. Necessary and sufficient conditions
are also given for optimality of the dual problem. Duality and converse duality are treated accordingly. 相似文献
979.
V. B. Larin 《Ukrainian Mathematical Journal》1989,41(5):532-538
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 41, No. 5, pp. 615–621, May, 1989. 相似文献
980.