全文获取类型
收费全文 | 10548篇 |
免费 | 2199篇 |
国内免费 | 782篇 |
专业分类
化学 | 4104篇 |
晶体学 | 128篇 |
力学 | 1336篇 |
综合类 | 105篇 |
数学 | 1074篇 |
物理学 | 6782篇 |
出版年
2024年 | 13篇 |
2023年 | 74篇 |
2022年 | 165篇 |
2021年 | 156篇 |
2020年 | 237篇 |
2019年 | 205篇 |
2018年 | 214篇 |
2017年 | 287篇 |
2016年 | 330篇 |
2015年 | 312篇 |
2014年 | 555篇 |
2013年 | 672篇 |
2012年 | 730篇 |
2011年 | 783篇 |
2010年 | 618篇 |
2009年 | 744篇 |
2008年 | 719篇 |
2007年 | 829篇 |
2006年 | 739篇 |
2005年 | 636篇 |
2004年 | 661篇 |
2003年 | 520篇 |
2002年 | 485篇 |
2001年 | 404篇 |
2000年 | 387篇 |
1999年 | 297篇 |
1998年 | 283篇 |
1997年 | 248篇 |
1996年 | 192篇 |
1995年 | 182篇 |
1994年 | 112篇 |
1993年 | 130篇 |
1992年 | 113篇 |
1991年 | 84篇 |
1990年 | 84篇 |
1989年 | 69篇 |
1988年 | 48篇 |
1987年 | 28篇 |
1986年 | 24篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 24篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
101.
102.
Modern trends in designing mechatronic systems call for a synergic design of the separated subsystems (mechanic, electronic parts, control modules, etc.) concurring to the overall performance. Following this point of view, this paper presents a control oriented model and a nonlinear control design for a Common Rail injection system. First a model is developed, which is tuned in a virtual simulation environment, representing the injection system in details in a reliable replication of reality. Then a sliding mode control is developed. Both the model of the injection process and of the control law are validated by a virtual detailed simulation environment. The prediction capability of the model and the control efficiency are clearly shown. 相似文献
103.
重离子治疗计划系统的构想 总被引:2,自引:1,他引:1
对重离子柬治癌的优势进行简要的回顾,并着重介绍了用于重离子放射治疗的治疗计划系统。治疗计划系统是一套软件系统,不同的硬件设施应有与其相匹配的软件系统,即治疗计划系统。在此基础上,针对兰州重离子加速器的特点提出一些关于治疗计划系统方面的构想。After a brief review concerning the advantages of heavy ions in radiotherapy, more interests are concentrated on treatment planning system (TPS) for heavy ion radiotherapy. Compared to the hardware devices such as accelerator and beam delivery system, the TPS is a set of software system, and different therapy facilities require their corresponding TPSs. Based on the specialities of the Heavy Ion Research Facility in Lanzhou (HIIRFL), some suggestions on the TPS for tumor therapy at HIRFL finally are given. 相似文献
104.
本文介绍了利用喷油脉宽大小的变化来分析电控发动机电控系统、燃油供给等系统故障的一种方法,在汽车故障检测与诊断中有着广泛的应用。 相似文献
105.
106.
Corrosion-related defects of pure iron were investigated by measuring Doppler broadening energy spectra (DBES) of positron annihilation and positron annihilation lifetime (PAL). Defect profiles of the S-parameter from DBES as a function of positron incident energy up to 30 keV (i.e. ∼1 μm depth) were analyzed. The DBES data show that S-parameter increases as a function of positron incident energy (mean depth) after corrosion, and the increase in the S-parameter is larger near the surface than in the bulk due to corrosion. Furthermore, information on defect size from PAL data as a function of positron incident energy up to 10 keV (i.e. ∼0.2 μm depth) was analyzed. In the two-state trapping model, the lifetime τ2 = 500 ps is ascribed to annihilation of positrons in voids with a size of the order of nanometer. τ1, which decreases with depth from the surface to the bulk, is ascribed to the annihilation of positrons in dislocations and three-dimensional vacancy clusters. The corroded samples show a significant increase in τ1 and the intensity I2, and near the surface the corroded iron introduces both voids and large-size three-dimensional vacancy clusters. The size of vacancy clusters decreases with depth. 相似文献
107.
考虑二阶半线性中立型差分方程给出了方程(1)的解的振动性的充分条件.所有结果推广和改进了关于中立和时滞差分方程已有结果. 相似文献
108.
Surface reconstructions of InGaAs alloys 总被引:1,自引:0,他引:1
The surface reconstructions of InxGa1−xAs alloys grown by molecular beam epitaxy on the (0 0 1) surfaces of GaAs and InAs have been studied by reflection high-energy electron diffraction and scanning tunnelling microscopy. A surface phase diagram is presented for the nominally strain-free alloy as a function of substrate temperature and alloy composition, and structural models for the commonly observed 3× reconstructions are discussed. Two new, electronically stable structural models are described that account for the transition of the InxGa1−xAs surface alloy from a c(4 × 4) to an asymmetric 3× reconstruction and that are fully consistent with all current experimental evidence. 相似文献
109.
A. Pompei 《Applied Acoustics》2006,67(5):420-431
In the present paper, we simulate focused wave fields generated by a system of plane transducers used in an immersion ultrasonic technique. The ultrasonic beam penetrates into the elastic medium through the fluid-solid boundary. A real-time computer algorithm is proposed to calculate stress components in the solid medium. It is shown that a good focusing wave structure can be provided by a pair of plane rectangular transducers, inclined with respect to each other and to the beam acoustic axis. 相似文献
110.