全文获取类型
收费全文 | 5756篇 |
免费 | 1006篇 |
国内免费 | 561篇 |
专业分类
化学 | 3719篇 |
晶体学 | 53篇 |
力学 | 255篇 |
综合类 | 30篇 |
数学 | 739篇 |
物理学 | 2527篇 |
出版年
2024年 | 23篇 |
2023年 | 130篇 |
2022年 | 197篇 |
2021年 | 223篇 |
2020年 | 227篇 |
2019年 | 198篇 |
2018年 | 181篇 |
2017年 | 176篇 |
2016年 | 287篇 |
2015年 | 253篇 |
2014年 | 318篇 |
2013年 | 386篇 |
2012年 | 479篇 |
2011年 | 548篇 |
2010年 | 334篇 |
2009年 | 328篇 |
2008年 | 355篇 |
2007年 | 329篇 |
2006年 | 313篇 |
2005年 | 261篇 |
2004年 | 194篇 |
2003年 | 168篇 |
2002年 | 193篇 |
2001年 | 151篇 |
2000年 | 126篇 |
1999年 | 155篇 |
1998年 | 127篇 |
1997年 | 109篇 |
1996年 | 105篇 |
1995年 | 71篇 |
1994年 | 53篇 |
1993年 | 52篇 |
1992年 | 47篇 |
1991年 | 59篇 |
1990年 | 31篇 |
1989年 | 27篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 22篇 |
1985年 | 17篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有7323条查询结果,搜索用时 15 毫秒
991.
Wenyu Sun Liusheng Hou Chuangying Dang 《Computational Optimization and Applications》2008,40(1):59-72
It is well-known that the conjugate gradient method is widely used for solving large scale optimization problems. In this
paper a modified trust-region method with Beale’s Preconditioned Conjugate Gradient (BPCG) technique is developed for solving
unconstrained optimization problems. The modified version adopts an adaptive rule and retains some useful information when
an unsuccessful iteration occurs, and therefore improves the efficiency of the method. The behavior and the convergence properties
are discussed. Some numerical experiments are reported.
This work was partially supported by Grant of the National Natural Science Foundation of China, Grant: 20040319003 of the
Doctoral Site of the Education Ministry of China, and SRG: 7001428 of City University of Hong Kong. 相似文献
992.
993.
Entanglement dynamics of anharmonic vibrations in molecule O3 is studied in terms of the linear entropy and negativity with various initial states that are, respectively, taken to be the mixed density matrices of coherent states on each normal mode. It is shown that with a suitable parameter in initial states, the entropy in one mode can be positively correlated or anti-correlated with negativity. The behavior of correlation between two entropies for two modes, negativity, and mutual entropy is discussed as well. 相似文献
994.
995.
Bismuthine was on-line trapped on tungsten coil and subsequently electrothermally vaporized for the determination by atomic fluorescence spectrometry (AFS). Several noble metals, including Pd, Rh, Pt, and Ir, were explored as permanent chemical modifier for tungsten coil on-line trapping. Investigation showed that Ir gave the best performance, in which bismuthine was on-line trapped on Ir-coated tungsten coil at 560 °C, and then released at 1550 °C for subsequent transfer to AFS by a mixture of Ar and H2. Under optimum instrumental conditions, the trapping efficiency was found to be 73 ± 3%. With 120 s (12 mL sample volume) trapping time, a limit of detection (LOD) of 4 ng L− 1 was obtained, compared to conventional hydride generation AFS (0.09 μg L− 1); the LOD can be lowered down to 1 ng L− 1 by increasing the trapping time to 480 s. The LOD was found to be better or at least comparable to literature levels involving on-line trapping and some other sophisticated instrumental methods such as ICP-MS and GF-AAS. A comprehensive interference study involving conventional hydride-forming elements and some transition metals was carried out, and the result showed that the gas phase interference from other hydride-forming elements was largely reduced, thanks to the use of on-line tungsten coil trapping. Finally, the proposed method was applied to the determination of bismuth in several biological and environmental standard reference materials, and a t-test shows that the analytical results by the proposed method have no significant difference from the certified values at the confidence level of 95%. 相似文献
996.
997.
Improving the resolution and the uniformity of AFM tip induced oxide patterns with pulsed voltages 总被引:1,自引:0,他引:1
Ziyong Shen Hui Sun Shimin Hou Xingyu Zhao Zengquan Xue 《Applied Surface Science》2004,230(1-4):340-344
Oxide line patterns were fabricated on the surface of titanium (Ti) film using atomic force microscopy (AFM) tip induced local oxidation technique. The growth behavior of the oxide under static voltages was studied. It was found the lateral growth of the oxide experienced two stages and the growth rate at the initial stage was very high. Pulsed voltages were employed and their effects on the controlling of the oxidation dynamics were examined. The results indicated that the high lateral and vertical growth rates of oxide at the initial stage could be suppressed with pulsed voltages. A minimum line width of 8 nm and highly uniform patterns were obtained with optimized voltage pulses. These results indicated that applying pulsed voltage is an effective method for improving both the resolution and the uniformity of the fabricated structures with scanning probe microscopy (SPM) tip induced local oxidation technique. 相似文献
998.
999.
1IntroductionInthispaper-wegiveasufficientconditionwhichguaranteestheg10balattractivityofthepositiveequilibriumofamu1tiplicativede1ayLogisticequation:wasproposedbyHutchinson[1]asamode1fortliegrowthofasing1especies.Equation(1.2)anditsgeneralizati0nhavereceivedandc0ntinuestoreceivegreatattenti0nssee,forexample[1,2,3,8].Inanattempttointroduceseveralenioronmentalnegativefeedbackeffects,manyau-thorshaveinvestigatedthefollowingequation[4,5,7]:However-itisn0tknownwhetherseveraleniv0ronmentalintraspe… 相似文献
1000.
浙江省是全国岛屿最多的省份,海岛为全省实现“海洋经济大省”起着重要作用。本文在分析浙江省海岛土地利用现状及其特点的基础上,指出开发利用中存在的主要问题,提出了合理开发利用的战略对策。 相似文献