全文获取类型
收费全文 | 1437篇 |
免费 | 61篇 |
国内免费 | 5篇 |
专业分类
化学 | 1019篇 |
晶体学 | 7篇 |
力学 | 35篇 |
综合类 | 1篇 |
数学 | 157篇 |
物理学 | 284篇 |
出版年
2022年 | 13篇 |
2021年 | 18篇 |
2020年 | 22篇 |
2019年 | 25篇 |
2018年 | 21篇 |
2017年 | 15篇 |
2016年 | 27篇 |
2015年 | 36篇 |
2014年 | 29篇 |
2013年 | 55篇 |
2012年 | 84篇 |
2011年 | 91篇 |
2010年 | 45篇 |
2009年 | 33篇 |
2008年 | 75篇 |
2007年 | 101篇 |
2006年 | 97篇 |
2005年 | 82篇 |
2004年 | 81篇 |
2003年 | 56篇 |
2002年 | 55篇 |
2001年 | 30篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 24篇 |
1994年 | 20篇 |
1993年 | 10篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1975年 | 14篇 |
1974年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有1503条查询结果,搜索用时 15 毫秒
11.
12.
E. J. Dean 《Journal of Optimization Theory and Applications》1992,75(3):471-486
The method of quasilinearization for nonlinear two-point boundary-value problems is an application of Newton's method to a nonlinear differential operator equation. Since the linear boundary-value problem to be solved at each iteration must be discretized, it is natural to consider quasilinearization in the framework of an inexact Newton method. More importantly, each linear problem is only a local model of the nonlinear problem, and so it is inefficient to try to solve the linear problems to full accuracy. Conditions on size of the relative residual of the linear differential equation can then be specified to guarantee rapid local convergence to the solution of the nonlinear continuous problem. If initial-value techniques are used to solve the linear boundary-value problems, then an integration step selection scheme is proposed so that the residual criteria are satisfied by the approximate solutions. Numerical results are presented that demonstrate substantial computational savings by this type of economizing on the intermediate problems.This work was supported in part by DOE Contract DE-AS05-82-ER13016 and NSF Grant RII-89-17691 and was part of the author's doctoral thesis at Rice University. It is a pleasure to thank the author's thesis advisors, Professor R. A. Tapia and Professor J. E. Dennis, Jr. 相似文献
13.
H. De Witte A. N. Andreyev S. Dean S. Franchoo M. Huyse O. Ivanov U. Köster W. Kurcewicz J. Kurpeta A. Plochocki K. Van de Vel J. Van de Walle P. Van Duppen 《The European Physical Journal A - Hadrons and Nuclei》2005,23(2):243-247
A new measurement of the 200Fr -decay half-life, with improved accuracy compared to previous measurements, has been carried out at the Isolde-CERN on-line mass separator. A half-life of 49(4) ms has been obtained, which is substantially different from earlier literature values. For the 196At daughter decay, a half-life of 389(54) ms and an branching ratio b = 94(5)% were measured. In addition, the half-lives of 201, 203, 205Fr and 197,199At are reported. 相似文献
14.
Dean W. Robinson 《Optics Communications》1978,27(2):281-286
This paper reports the observation of 337 μm and 311 μm stimulated emission from HCN in which the (1110)?(0400) inversion has been established by photopumping of HCN and by chemical pumping with reactions between CN and H2 or saturated hydrogen-rich organic compounds. Similarities in output pulse behavior between the discharge and chemical versions of the HCN laser are suggestive that the pumping mechanism in the discharge is the chemical reaction, CN + H2 → HCN2 + H. The well-known inefficiency of this laser is then due to the fact that the reaction is a slow one and its exothermicity does not match the energy of the upper lasing level, but depends for inversion on (randomizing) relaxation into (1110) among others. Substantial improvements in the power of the HCN laser cannot be made from this route. 相似文献
15.
Val M. Runge Mark A. Osborne Michael L. Wood Samuel M. Wolpert Eddie Kwan Dean M. Kaufman 《Magnetic resonance imaging》1987,5(6):421-430
The angle between the straight axial plane and the orbito-meatal line was measured in 156 consecutive magnetic resonance examinations. Inconsistent head positioning caused this angle to vary by as much as 44 degrees. Careful positioning of the patient by the technologist can minimize this variability, leading potentially to improved image interpretation. To assess the merit of a standardized orientation for MR examinations of the head, straight axial and tilted axial MR scans were compared in 34 patients. The tilted images were obtained parallel to the orbito-meatal line and were found to be superior for visualization of the cerebellum. When correlative x-ray CTs are available or when an abnormality in the posterior fossa is suspected, tilted axial MR scans should be employed. 相似文献
16.
17.
P.J. Dean 《Journal of luminescence》1979,21(1):75-83
Comparative measurements have been made of optical absorption and photoluminescence of refined undoped and Cu in-diffused ZnTe single crystals. Strong increases in a bound exciton BE line near 2.375 eV previously identified with the electrically dominant point defect acceptor ‘a’, with binding energy EA ? 149 meV, suggests that this acceptor is substitutional CuZn. Similarly strong increases in a relatively broad band at slightly higher energy suggests the simultaneous incorporation of shallow donors, possibly interstital CuI. These findings indicate that intrinsic defects such as VZn neither control the Fermi level in refined ZnTe nor produce shallow acceptors with EA ? 250 meV, contrary to much previous speculation. 相似文献
18.
分别采用514 nm绿光、488 nm蓝光和390 nm紫外光作为敏化光,633 nm红光作为记录光,详细研究了敏化光波长对氧化(Fe,Ni):LiNbO3晶体全息记录性能的影响.结果表明:随着敏化光波长的逐渐减小,氧化(Fe,Ni):LiNbO3晶体的非挥发全息记录性能逐渐优化,390 nm紫外光是这三种敏化光中最优的敏化光.考虑敏化光的吸收,为了在双中心全息记录中获得最优的性能,应当选择合适波长的敏化光:一方面短波长敏化光能有效地敏化深中心;另一方面短波长敏化光的吸收太强(如对光折变效应无用的基质吸收),不能沿厚度方向有效地敏化晶体,所以实际上需折衷考虑,并从理论上给予了解释. 相似文献
19.
径向双折射滤波器的超分辨性能研究 总被引:1,自引:3,他引:1
超分辨技术因其可以超越经典的衍射极限而为人们所熟知.并且.在光存储和共焦扫描成像系统中有着广泛的应用。把由两个偏振器和一个圆对称的双折射元件组成的径向双折射滤波器引入超分辨技术,借助琼斯算法推导出其光瞳函数的表达式。由分析得出通过改变径向双折射滤波器中偏振器的偏振方向和双折射元件的主轴之间的夹角,即可实现光学系统的横向超分辨或轴向超分辨。同时对评价该器件超分辨性能的参量第一零点比、斯特尔比和旁瓣强度抑制比做了详细的讨论。该滤波器用于超分辨技术的优点在于其制作不涉及相位的变化而比较简单,且费用比较低。缺点是旁瓣能量过高,但可以通过采用共焦系统来抑制。 相似文献
20.
Arytenoid Cartilage Dislocation: A 20-year Experience 总被引:2,自引:0,他引:2
Adam D. Rubin Mary J. Hawkshaw Cheryl A. Moyer Carole M. Dean Robert T. Sataloff 《Journal of voice》2005,19(4):687-701
SUMMARY: Arytenoid cartilage dislocation is an infrequently diagnosed cause of vocal fold immobility. Seventy-four cases have been reported in the literature to date. Intubation is the most common origin, followed by external laryngeal trauma. Decreased volume and breathiness are the most common presenting symptoms. We report on 63 patients with arytenoid cartilage dislocation treated by the senior author (RTS) since 1983. Significantly more posterior than anterior dislocations were represented. Although reestablishing joint mobility is difficult, endoscopic reduction should be considered to align the heights of the vocal processes. This process may result in significant voice improvement even long after the dislocation. Strobovideolaryngoscopy, laryngeal electromyography, and laryngeal computed tomography (CT) imaging are helpful in the evaluation of patients with vocal fold immobility to help distinguish arytenoid cartilage dislocation from vocal fold paralysis. Familiarity with signs and symptoms of arytenoid cartilage dislocation and current treatment techniques improves the chances for optimal therapeutic results. 相似文献