全文获取类型
收费全文 | 31731篇 |
免费 | 435篇 |
国内免费 | 392篇 |
专业分类
化学 | 2284篇 |
晶体学 | 53篇 |
力学 | 300篇 |
综合类 | 129篇 |
数学 | 1012篇 |
物理学 | 1706篇 |
综合类 | 27074篇 |
出版年
2024年 | 35篇 |
2023年 | 126篇 |
2022年 | 332篇 |
2021年 | 345篇 |
2020年 | 471篇 |
2019年 | 388篇 |
2018年 | 351篇 |
2017年 | 326篇 |
2016年 | 422篇 |
2015年 | 634篇 |
2014年 | 1804篇 |
2013年 | 1402篇 |
2012年 | 1961篇 |
2011年 | 2297篇 |
2010年 | 1843篇 |
2009年 | 2096篇 |
2008年 | 2316篇 |
2007年 | 2490篇 |
2006年 | 2094篇 |
2005年 | 1762篇 |
2004年 | 1522篇 |
2003年 | 1467篇 |
2002年 | 1283篇 |
2001年 | 1093篇 |
2000年 | 802篇 |
1999年 | 578篇 |
1998年 | 421篇 |
1997年 | 344篇 |
1996年 | 278篇 |
1995年 | 214篇 |
1994年 | 187篇 |
1993年 | 136篇 |
1992年 | 121篇 |
1991年 | 108篇 |
1990年 | 109篇 |
1989年 | 111篇 |
1988年 | 83篇 |
1987年 | 63篇 |
1986年 | 56篇 |
1985年 | 22篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 14篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1972年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
本文针对国内高校尤其是工科院校学生培养中普遍存在的教学环节设置低年级专业渗透不够、高年级研究性不足的问题,提出开设贯穿于四年的工科学生培养专业研究实践教学模式。文章阐述了工科大学专业研究实验的研究性与专业化思想,在此基础上提出应根据学生在学习过程中所处的不同学习阶段有侧重的选择实验项目,以期帮助学生理解基础课程与专业课程之间的知识关联、形成统一的学科知识体系,满足后续工作、科研的需求的同时培养他们对于专业的感情。文章在此基础上,依据所提出的教学模式给出了相应的教学实验示例。旨在为应用工程类专业学生培养提供一种新的教学思路和教学模式,调动学生主观能动性的同时推进学研结合。 相似文献
982.
Sha Xia Dan Wang Nian-Ke Chen Dong Han Xian-Bin Li Hong-Bo Sun 《Annalen der Physik》2020,532(3):1900318
Defects play a central role in controlling the electronic properties of two-dimensional (2D) materials and realizing the industrialization of 2D electronics. However, the evaluation of charged defects in 2D materials within first-principles calculation is very challenging and has triggered a recent development of the WLZ (Wang, Li, Zhang) extrapolation method. This method lays the foundation of the theoretical evaluation of energies of charged defects in 2D materials within the first-principles framework. Herein, the vital role of defects for advancing 2D electronics is discussed, followed by an introduction of the fundamentals of the WLZ extrapolation method. The ionization energies (IEs) obtained by this method for defects in various 2D semiconductors are then reviewed and summarized. Finally, the unique defect physics in 2D dimensions including the dielectric environment effects, defect ionization process, and carrier transport mechanism captured with the WLZ extrapolation method are presented. As an efficient and reasonable evaluation of charged defects in 2D materials for nanoelectronics and other emerging applications, this work can be of benefit to the community. 相似文献
983.
离子通道可以有效抑制电子束在等离子体环境内传输过程中的径向扩散,已有工作研究了离子通道对电子束的影响,但离子通道建立过程和暂态特性研究则更有助于理解和利用离子通道在电子束长程传输中的作用。本文利用PIC方法对离子通道的时空分布进行二维模拟,并基于单粒子理论推导出描述离子通道振荡的解析模型,对上述两种模型的结果相互校验。上述模型的计算结果表明,在长程传输过程中,相对论电子束在等离子体内部建立的离子通道是持续周期振荡的,电子束密度、电子束初始半径以及环境等离子体密度都会对离子通道的振荡规律产生影响,针对不同的等离子体环境选择合适的电子束参数可以有效提高离子通道的稳定性,进而提升传输过程中电子束的束流质量。 相似文献
984.
985.
A method is reviewed for conversion of a microphone signal into calibrated Sound Pressure Level (SPL) units. The method follows American National Standards Institute (ANSI) standard for S1.4 SPL meters and requires an accurate SPL meter and an accurate calibration sound source for conversion. Accuracy and validation data from test signals and human phonation are provided. The results indicate that under typical speech conditions, an absolute accuracy of plus or minus 1.6 dB (type I SPL meter) can be obtained with a miniature head-mounted microphone. 相似文献
986.
M. S. T. Piza 《Journal of statistical physics》1997,89(3-4):581-603
We consider a polymer model on ℤ
+
d
where to each edgee is associated a random variable v(e). A polymer configuration is represented by a directed pathr and has a weight exp[-β ∑
e
∈r
ν(e)], withβ=1/T the inverse temperature. We extend some rigorous results that have been obtained for the ground state of this model to finite
temperatures. In particular we obtain some upper and lower bounds on sample-to-sample free energy fluctuations, and also rigorous
scaling inequalities between the exponents describing free energy fluctuations and transversal displacements of polymer configurations 相似文献
987.
光学介质表面波度的计算机模型 总被引:2,自引:1,他引:2
任一光学介质表面波度对光散射具有不可忽视的影响.本文对用激光轮廓仪所测物体表面曲线进行研究,运用傅里叶级数和最小二乘法拟合光学介质表面波形形态分布,建立了光学介质表面波度的计算机一维模型. 相似文献
988.
989.
Electron Spin Resonance (ESR) spectra of gamma irradiated methylacrylamide-2-acrylamido-2-methyl-propanesulphonic acid (MA-AMPS) are recorded to identify the radical species formed during the irradiation of the copolymer. The ESR spectrum observed for irradiated MA-AMPS copolymer at liquid nitrogen temperature (LNT) (77 r K) is an asymmetric triplet; while the spectrum observed at room temperature (RT) is a quintet. The intensity distribution of both the spectra deviated appreciably from the expected theoretical values. Computer simulations are employed to analyze the ESR spectra observed at different temperatures. The triplet spectrum observed at LNT is simulated to be a superposition of component spectra arising from macroradicals of the type~CH 2 - \dot {\rm C} H-CH 2 ~ (I), radicals of the type \dot {\rm C} H 2 SO 3 H (II), and peroxy radicals (III). In contrast, the RT spectrum is simulated to be a superposition of component spectra arising due to radicals I, II, III together with the component quartet assigned to methyl radicals ( \dot {\rm C} H 3 ). The formation of such free radicals in irradiated copolymer is discussed. 相似文献
990.
The angular distribution of atoms sputtered from germanium under 1–20 keV Ar+ ion bombardment (normal incidence) has been studied experimentally and using computer simulations. A collector technique combined with Rutherford backscattering to analyze the distribution of collected material was used. In addition, the surface topography was under control. It was found that the experimental angular distribution of sputtered atoms (E 0=3–10 keV) could be approximated by the function cos n θ with n≈ 1.65. Such a high value of n is connected with the surface scattering of ejected atoms and a noticeable contribution of backscattered ions to the formation of the sputter flux (the mass effect). The target surface was found to be practically flat even at ion fluencies ~1018 ions/cm2. The results obtained are compared with data from the literature, including our recent data on Si sputtering. 相似文献