全文获取类型
收费全文 | 82580篇 |
免费 | 14979篇 |
国内免费 | 22622篇 |
专业分类
化学 | 58950篇 |
晶体学 | 2824篇 |
力学 | 5691篇 |
综合类 | 2302篇 |
数学 | 13207篇 |
物理学 | 37207篇 |
出版年
2024年 | 196篇 |
2023年 | 1009篇 |
2022年 | 2642篇 |
2021年 | 2737篇 |
2020年 | 2883篇 |
2019年 | 2758篇 |
2018年 | 2559篇 |
2017年 | 3428篇 |
2016年 | 3075篇 |
2015年 | 3986篇 |
2014年 | 4826篇 |
2013年 | 6402篇 |
2012年 | 6798篇 |
2011年 | 7412篇 |
2010年 | 6593篇 |
2009年 | 6714篇 |
2008年 | 7436篇 |
2007年 | 6759篇 |
2006年 | 6470篇 |
2005年 | 5469篇 |
2004年 | 4310篇 |
2003年 | 3281篇 |
2002年 | 3188篇 |
2001年 | 3107篇 |
2000年 | 3112篇 |
1999年 | 2025篇 |
1998年 | 1203篇 |
1997年 | 991篇 |
1996年 | 1017篇 |
1995年 | 907篇 |
1994年 | 886篇 |
1993年 | 759篇 |
1992年 | 753篇 |
1991年 | 551篇 |
1990年 | 513篇 |
1989年 | 484篇 |
1988年 | 419篇 |
1987年 | 338篇 |
1986年 | 347篇 |
1985年 | 284篇 |
1984年 | 244篇 |
1983年 | 222篇 |
1982年 | 163篇 |
1981年 | 135篇 |
1980年 | 122篇 |
1979年 | 121篇 |
1978年 | 55篇 |
1977年 | 56篇 |
1974年 | 62篇 |
1973年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
We prove the existence of global smooth solutions near a given steady state of the hydrodynamic model of the semiconductors
in a bounded domain with physical boundary conditions. The steady state and the doping profile are permitted to be of large
variation but the initial velocity must be small. Two cases are considered. In the first one the problem is three-dimensional,
the boundary conditions are insulating and the steady state velocity vanishes. In the second one, the problem is one-dimensional,
the boundary is of contact type and the steady state velocity does not vanish. 相似文献
54.
55.
Uhm H.S. Lee P.H. Kim Y.I. Kim J.H. Chang H.Y. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(4):628-635
A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data 相似文献
56.
WANG Zhong HONG Haitao XIAO Hai SUN Changku MENG Yan YE Shenghua 《Chinese Journal of Lasers》1997,6(5):435-440
1.IntroductionAbsolutedistancemeasurementisfarfromanewtopic.However,itisstillafieldstimulatinggreatinterestsnowadaysduetoitSimportantroleinmanufacturingandassembly['J.SincethegreatsuccessachievedbyMichelsonandBenoitwhentheyfirstdevelopedaninterferometertodeterminethestandardmeterintermsofthemonochromaticredcadmiumline,theopticinterferometerhasbeenprovedtobeoneofthemostpreciseandefficientwayindisplacementmeasurementbecauseofitshighdiscriminationandsimplestructure.However,thetraditionalinterfe… 相似文献
57.
ZHAO Shan-Rong CHEN Kai-Xian JIANG Hua-Liang WANG Qin-Mi JI Ru-YunShanghai Institute of Materia Medica Chinese Academy of Sciences Shanghai China 《中国化学》1997,15(1):84-89
We have used quantum mechanical method to study the transition states(TSs) of uridine phosphorolysis reaction. Comparing the four different reaction pathways and the five transition states obtained, we conclude that enzymatic uridine phosphorolysis takes place mainly according to acid-catalyzed SN2 mechanism. The proposed reaction pathway is consistent with many experimental results. 相似文献
58.
本文利用统计计量学方法对山西省农民家庭消费水平和消费结构的变化及原因进行了实证分析。建立了山西省农民人均消费的消费函数和山西省农民总消费支出与食品、衣着、住房、日用品、燃料及文化生活服务支出的关系模型,并通过模型分析解释了农民的消费结构,也为决策者提供一些有效的参考资料。 相似文献
59.
60.