全文获取类型
收费全文 | 11791篇 |
免费 | 448篇 |
国内免费 | 47篇 |
专业分类
化学 | 7758篇 |
晶体学 | 76篇 |
力学 | 259篇 |
数学 | 1995篇 |
物理学 | 2198篇 |
出版年
2023年 | 94篇 |
2022年 | 131篇 |
2021年 | 164篇 |
2020年 | 230篇 |
2019年 | 239篇 |
2018年 | 149篇 |
2017年 | 145篇 |
2016年 | 423篇 |
2015年 | 378篇 |
2014年 | 361篇 |
2013年 | 608篇 |
2012年 | 678篇 |
2011年 | 781篇 |
2010年 | 483篇 |
2009年 | 407篇 |
2008年 | 635篇 |
2007年 | 564篇 |
2006年 | 545篇 |
2005年 | 515篇 |
2004年 | 442篇 |
2003年 | 388篇 |
2002年 | 377篇 |
2001年 | 233篇 |
2000年 | 214篇 |
1999年 | 192篇 |
1998年 | 146篇 |
1997年 | 162篇 |
1996年 | 161篇 |
1995年 | 137篇 |
1994年 | 137篇 |
1993年 | 135篇 |
1992年 | 113篇 |
1991年 | 88篇 |
1990年 | 93篇 |
1989年 | 71篇 |
1988年 | 73篇 |
1987年 | 72篇 |
1986年 | 91篇 |
1985年 | 85篇 |
1984年 | 73篇 |
1983年 | 69篇 |
1982年 | 70篇 |
1981年 | 59篇 |
1980年 | 83篇 |
1978年 | 77篇 |
1977年 | 71篇 |
1976年 | 60篇 |
1975年 | 68篇 |
1974年 | 57篇 |
1973年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Stefan A. Maier 《Optical and Quantum Electronics》2006,38(1-3):257-267
The controlled squeezing of electromagnetic energy into nanometric volumes via surface plasmon-polariton excitations in plasmonic nanoresonators is analyzed using the concept of an effective electromagnetic mode volume V eff, while taking careful account of the plasmon-polariton dispersion and the electromagnetic energy stored in the metal. Together with the quality factor Q of the cavity resonance, this enables a comparison with dielectric optical cavities, where V eff is limited by diffraction. For a Fabry–Perot type planar metallic cavity, a one-dimensional analytic model as well as a three-dimensional finite-difference time-domain simulation reveal that V eff is not bounded by diffraction, and that Q/V eff increases for decreasing cavity size. In this picture, matter–plasmon interactions can be quantified in terms of Q and V eff, and a resonant cavity model for the enhancement of spontaneous Raman scattering is presented. 相似文献
12.
13.
14.
Kristin Fischer Silvio Prause Stefan Spange Frank Cichos Christian Von Borczyskowski 《Journal of Polymer Science.Polymer Physics》2003,41(11):1210-1218
Solvent‐dependent ultraviolet–visible (UV–vis) absorption and Stokes shifts including strong hydrogen‐bond‐donating (HBD) solvents such as 2,2,2‐trifluoroethanol and 1,1,1,3,3,3‐hexafluoro‐2‐propanol of two coumarine dyes (Co 151 and Co 153) were analyzed with multiple‐square analyses of linear solvation energy relationships and the Kamlet–Taft solvent parameter set to α (HBD capacity), β (hydrogen‐bond‐accepting capacity), and π* (dipolarity/polarizability). The UV–vis absorption and emission spectra of Co 151 and Co 153 were measured when adsorbed on various polysaccharides such as different cellulose batches, carboxymethylcelluloses with different degrees of substitution, and chitine. As a result of this evaluation, Co 153 is recommended as an alternative UV–vis probe for evaluating the dipolarity/polarizability of cellulose and cellulose derivates. Multiple adsorption of Co 153 on Linters cellulose took place indicating a wide‐surface polarity distribution, which makes the determination of a rigid polarity parameter questionable. Thus, fluorescence measurements of adsorbed Co 153 are suitable to detect inhomogenities on a surface but not for the determination of empirical polarity parameters. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1210–1218, 2003 相似文献
15.
Stefan Richter William T. Ross Carl Sundberg 《Proceedings of the American Mathematical Society》2004,132(8):2361-2365
In this paper, we refine a result of Nagel, Rudin, and Shapiro (1982) concerning the zeros of holomorphic functions on the unit disk with finite Dirichlet integral.
16.
This paper presents a new generic Evolutionary Algorithm (EA) for retarding the unwanted effects of premature convergence. This is accomplished by a combination of interacting generic methods. These generalizations of a Genetic Algorithm (GA) are inspired by population genetics and take advantage of the interactions between genetic drift and migration. In this regard a new selection scheme is introduced, which is designed to directedly control genetic drift within the population by advantageous self-adaptive selection pressure steering. Additionally this new selection model enables a quite intuitive heuristics to detect premature convergence. Based upon this newly postulated basic principle the new selection mechanism is combined with the already proposed Segregative Genetic Algorithm (SEGA), an advanced Genetic Algorithm (GA) that introduces parallelism mainly to improve global solution quality. As a whole, a new generic evolutionary algorithm (SASEGASA) is introduced. The performance of the algorithm is evaluated on a set of characteristic benchmark problems. Computational results show that the new method is capable of producing highest quality solutions without any problem-specific additions. 相似文献
17.
18.
Time-resolved electron transport studies on InGaAs/GaAs-QWIPs 总被引:1,自引:0,他引:1
S. Steinkogler H. Schneider R. Rehm M. Walther P. Koidl P. Grant R. Dudek H. C. Liu 《Infrared Physics & Technology》2003,44(5-6):355-361
Due to the short internal response time, quantum-well infrared photodetectors (QWIPs) are interesting for high-speed applications such as heterodyne spectroscopy or laser pulse monitoring. We studied the photocurrent transients of InGaAs/GaAs-QWIPs after irradiation with infrared laser pulses of 250 fs duration. The excitation wavelength of about 9 μm matches the peak wavelength of the QWIP structure. The photocurrent transient consists of two different dynamical components, representing the fast photoionization in the quantum-wells and the slow injection current that compensates the remaining space charge. The investigations of the different components as a function of temperature and bias voltage were performed on a nanosecond time-scale. The experimental separation of the two photocurrent contributions allows us to determine the photoconductive gain. The Fourier transform of the photocurrent transient was compared with other experimental methods including heterodyne detection and microwave rectification. The quantitative agreement between these different measurement techniques is excellent. 相似文献
19.
20.
Stefan Pitsch Sebastian Wendeborn Ramanarayanan Krishnamurthy Armin Holzner Mark Minton Martin Bolli Christian Miculca Norbert Windhab Ronald Micura Michael Stanek Bernhard Jaun Albert Eschenmoser 《Helvetica chimica acta》2003,86(12):4270-4363
Pyranosyl‐RNA (‘p‐RNA’ ) is an oligonucleotide system isomeric to natural RNA and composed of the very same building blocks as RNA. Its generational, chemical, and informational properties are deemed to be those of an alternative nucleic acid system that could have been a candidate in Nature's evolutionary choice of the molecular basis of genetic function. We consider the study of the chemistry of p‐RNA as etiologically relevant in the sense that knowledge of its structural, chemical, and informational properties on the chemical level offers both a perspective and reference points for the recognition of specific structural assets of the RNA structure that made it the (supposedly) superior system among possible alternatives and, therefore, the system that became part of biology as we know it today. The paper describes the chemical synthesis of β‐d‐ (and L )‐ribopyranosyl‐(4′→2′)‐oligonucleotide sequences, presents a resume of their structural and chemical properties, and cautiously discusses what we may and may not have learned from the pyranosyl isomer of RNA with respect to the conundrum of RNA's origin. 相似文献