全文获取类型
收费全文 | 1289篇 |
免费 | 268篇 |
国内免费 | 192篇 |
专业分类
化学 | 476篇 |
晶体学 | 1篇 |
力学 | 164篇 |
综合类 | 19篇 |
数学 | 93篇 |
物理学 | 996篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 41篇 |
2021年 | 32篇 |
2020年 | 41篇 |
2019年 | 41篇 |
2018年 | 35篇 |
2017年 | 36篇 |
2016年 | 44篇 |
2015年 | 47篇 |
2014年 | 70篇 |
2013年 | 83篇 |
2012年 | 78篇 |
2011年 | 100篇 |
2010年 | 76篇 |
2009年 | 100篇 |
2008年 | 79篇 |
2007年 | 100篇 |
2006年 | 96篇 |
2005年 | 71篇 |
2004年 | 74篇 |
2003年 | 60篇 |
2002年 | 51篇 |
2001年 | 49篇 |
2000年 | 33篇 |
1999年 | 26篇 |
1998年 | 36篇 |
1997年 | 26篇 |
1996年 | 31篇 |
1995年 | 20篇 |
1994年 | 29篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有1749条查询结果,搜索用时 531 毫秒
1.
2.
建立了一个四组分一维混合模型,对电子束注入大气产生大尺度等离子体的过程进行了数值模拟.结果表明了能量为140keV、流强为50mA/cm2的注入电子束,可以产生线度为0.5m,密度为1012cm-3量级的大气环境下等离子体.电子束所伴随的空间电荷效应由于等离子体的产生会很快消失,不影响后续的等离子体产生过程.电子束注入流强主要影响产生等离子体的密度,而电子束能量则同时影响其空间线度和密度.
关键词:
电子束
碰撞
电离 相似文献
3.
A sample of 1233 events is used to study the general characteristics of {}^{16}O-Em interactions at 4.5 A GeV/c. Multiplicity and angular distributions of slow particles and correlations among them are discussed. The present data are compared with the corresponding results from the interactions of other projectiles at the same energy and also the same projectile at different energies. The results indicate that black particle production is independent of the energy and mass of the projectile, but for grey particles it is dependent on the mass of projectile. 相似文献
4.
Investigation of the mean free path of projectile fragments produced in 16O-Em collision at 60 A GeV
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Results are presented for an investigation of the mean free path of projectile fragments with charge 3≤Z≤8, produced by 60 A GeV {}^{16}O in nuclear emulsion. No dependence of mean free path on the distance from the point of the fragment emission is observed and our result is consistent with the nonexistence of anomalons. 相似文献
5.
J. R. Lindle W. W. Bewley I. Vurgaftman J. R. Meyer J. L. Johnson M. L. Thomas W. E. Tennant 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):558
A self-referencing, optical modulation technique was used to measure the negative luminescence efficiencies of an array of mid-wave infrared HgCdTe photodiodes with cutoff wavelength 4.6 μm as a function of sample temperature. The internal efficiency at a wavelength of 4 μm was 93% at 295 K, and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction >50 K at room temperature and >30 K at 240 K. Moreover, the reverse-bias saturation current density was only 0.13 A/cm2. The measured transmission and emission spectra were simulated using empirical HgCdTe absorption formulas from the literature. 相似文献
6.
7.
一种改进的计算探测器校正因子的相关抽样方法 总被引:1,自引:0,他引:1
对于小尺寸探测器处于大块介质的情形, 在探测器的校正因子的Monte Carlo模拟中, 存在两个难题: 一是由于探测器尺寸很小粒子难以到达探测器并发生碰撞; 二是两个随机变量比值难以达到要求精度. 本文使用经过改进的粒子碰撞自动重要抽样方法, 再结合相关抽样方法, 解决了这两个难题, 并在MCNP-4C程序平台上加以实现. 除了粒子碰撞自动重要抽样以外, 还选用了其他3种方法: 直接模拟、区域分裂、强迫碰撞+Dxtran球分别与相关抽样方法结合, 对一个简化的探测器校正因子计算模型进行了计算. 实际计算结果表明, 相关抽样方法无论与哪种方法结合, 都起到了提高相关量计算效率的作用; 而它与粒子碰撞自动重要抽样结合, 比其他方法具有明显的优越性. 相似文献
8.
A convergent-barrel (CB) cold spray nozzle was designed through numerical simulation. It was found that the main factors influencing significantly particle velocity and temperature include the length and diameter of the barrel section, the nature of the accelerating gas and its pressure and temperature, and the particle size. Particles can achieve a relatively low velocity but a high temperature under the same gas pressure using a CB nozzle compared to a convergent-divergent (CD) nozzle. The experiment results with Cu powder using the designed CB nozzle confirmed that particle deposition can be realized under a lower gas pressure with a CB nozzle. 相似文献
9.
Kirk L. Shanahan 《Thermochimica Acta》2006,441(2):210-214
Dr. E. Storms has published a Letter [E. Storms, Comment on papers by K. Shanahan that propose to explain anomalous heat generated by cold fusion, Thermochim. Acta, 2006] in which he argues that in a sequence of recent papers, the apparent excess heat signal claimed by Dr. Shanahan to arise from a calibration constant shift is actually true excess heat. In particular he proposes that the mechanisms proposed that foster the proposed calibration constant shifts cannot occur as postulated for several reasons. As well, he proposes Shanahan has ignored the extant data proving this. Because this Letter may lend unwarranted support to acceptance of cold fusion claims, these erroneous arguments used by Storms need to be answered. 相似文献
10.
A direct central collision of two identical bodies of revolution is studied. A nonstationary mixed boundary-value problem with an unknown moving boundary is formulated. Its solution is represented by a series in term of Bessel functions. An infinite system of Volterra equations of the second kind for the unknown expansion coefficients is derived by satisfying the boundary conditions. The basic characteristics of the collision process are determined depending on the curvature of the frontal surface of the bodies 相似文献