全文获取类型
收费全文 | 68篇 |
免费 | 3篇 |
国内免费 | 7篇 |
专业分类
化学 | 40篇 |
力学 | 1篇 |
数学 | 15篇 |
物理学 | 22篇 |
出版年
2021年 | 1篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2014年 | 1篇 |
2013年 | 2篇 |
2011年 | 6篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 3篇 |
2007年 | 4篇 |
2006年 | 1篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1942年 | 1篇 |
1934年 | 1篇 |
1932年 | 2篇 |
1927年 | 1篇 |
1908年 | 1篇 |
排序方式: 共有78条查询结果,搜索用时 46 毫秒
61.
Rodney G. Downey Michael R. Fellows Venkatesh Raman 《Discrete Applied Mathematics》2000,100(3):155-167
An irredundant set of vertices V′V in a graph G=(V,E) has the property that for every vertex uV′, N[V′−{u}] is a proper subset of N[V′]. We investigate the parameterized complexity of determining whether a graph has an irredundant set of size k, where k is the parameter. The interest of this problem is that while most “k-element vertex set” problems are NP-complete, several are known to be fixed-parameter tractable, and others are hard for various levels of the parameterized complexity hierarchy. Complexity classification of vertex set problems in this framework has proved to be both more interesting and more difficult. We prove that the k-element irredundant set problem is complete for W[1], and thus has the same parameterized complexity as the problem of determining whether a graph has a k-clique. We also show that the “parametric dual” problem of determining whether a graph has an irredundant set of size n−k is fixed-parameter tractable. 相似文献
62.
63.
A. Dias Tavares Jr. A. M. Borges C. E. Fellows C. A. Massone 《Applied physics. B, Lasers and optics》1994,59(6):645-648
This work reports the role some additives have in pre-ionizing a N2 TE UV laser (337.1 nm). The modifications in both stimulated radiation characteristics and excitation-pulse period prove the different ionizing power of each element. The laser operating without a pre-ionizing wire device and with N2 plus different additives was able to generate pulses with a temporal width of the same order than those obtained when it was operating with N2 and a pre-ionizing wire device. Also, a relation between ionization efficiency and interelectrode distance has been established allowing the prediction of conditions for optimum laser-pulse width generation. 相似文献
64.
B. Oliveira dos Santos C. E. Fellows J. B. de Oliveira e Souza C. A. Massone 《Applied physics. B, Lasers and optics》1986,41(4):241-244
A 3% efficiency, crossed-field type, N2 laser (337.1 nm) has been developed, based on very low inductance circuits (coaxial configuration) and a careful selection of their resonance frequencies. 相似文献
65.
K G Allen J MacGee M E Fellows P A Tornheim K R Wagner 《Journal of chromatography. A》1984,309(1):33-42
Fatty acids were analyzed by a new method which involved their isolation from hexane extracts of serum or brain tissue in aqueous potassium hydroxide (10 microliter) and methylation directly in this solution with methyl iodide. The resulting fatty acid methyl esters were partitioned into ethylene chloride (25 microliter) and were quantitated by gas-liquid chromatography. The procedure was documented by comparison with conventional methylation reactions on serum fatty acids. This method, which avoids thin-layer chromatography and which measures individual free fatty acid concentrations in 20-mg brain tissue samples, should be of particular value for examining regional free fatty acids in brain following ischemia and trauma. 相似文献
66.
Tertiary amine local anesthetics cause a time- and dose-dependent, reversible increase in insulin binding sites in cultured chick embryo fibroblasts. Incubation of fibroblasts with 0.2 mM dibucaine for 3 h at 37 degrees C results in a twofold to threefold increase in insulin binding, with an increase in average number of binding sites (Ka = 3.0 X 10(7) M-1) from 9 X 10(3) per cell. Trypsin or ethyleneglycoltetraacetic acid (EGTA) alone increases insulin binding twofold to threefold, but fails to further increase 125I-insulin binding in cells pretreated with dibucaine. Transformation of chick embryo fibroblasts with Rous sarcoma virus causes a threefold to fivefold increase in insulin binding, which is not further increased by incubation with dibucaine. As demonstrated by transmission electron microscopy, dibucaine and trypsin also induce changes in the cytoskeleton of chick embryo fibroblasts, characterized by disorganization and disappearance of microfilament and microtubule bundles. These alterations are accompanied by gross morphologic changes, including rounding of cells and appearance of numerous ruffles and blebs on the cell surface. These observations are consistent with the hypothesis that expression of surface receptors in cultured chick embryo fibroblasts is related to the organization and disorganization of cytoskeletal structures. 相似文献
67.
68.
Comprehensive and systematic optical activation studies of Si-implanted GaN grown on sapphire substrates have been made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×1013 to 5×1015 cm−2 at room temperature. The samples were proximity cap annealed from 1250 to 1350 °C with a 500-Å-thick AlN cap in a nitrogen environment. The results of photoluminescence measurements made at 3 K show a very sharp neutral-donor-bound exciton peak along with a sharp donor-acceptor pair peak after annealing at 1350 °C for 20 s, indicating excellent implantation damage recovery. The results also indicate the AlN cap protected the implanted GaN layer very well during high temperature annealing without creating any significant anneal-induced damage. This observation is consistent with the electrical activation results for these samples. 相似文献
69.
Pressure-induced line shift coefficients have been measured for more than 200 rovibrational lines of NH3 perturbed by O2 at room temperature (T = 295 K) in some branches of the ν2, 2ν2, and ν4 bands. These lines with J values ranging from 1 to 13 are located in the spectral range 800-1800 cm−1. Experiments were made with a high-resolution Fourier transform spectrometer. The treatment of vibration-rotation lines includes interference effects caused by the overlapping of lines. The O2 pressure-induced shift coefficients have been derived from the non-linear least-squares multi-pressure fitting technique. The results illustrate a vibrational dependence of line shifts with vibrational quantum number. Most of the measured shifts are negative in the ν4 band. They are positive for the ν2 and 2ν2 bands. The measured shift coefficients are compared with previous measurements and with those calculated from a semiclassical theory based upon the Robert-Bonamy formalism extended to the case of symmetric top molecule with inversion motion. The predictions are generally in satisfactory agreement with the experimental data. Analyses of measured and predicted results illustrate that these shifts mainly originate from the isotropic part of the intermolecular potential. 相似文献
70.
N. P. Pimentel C. E. Fellows A. M. Borges C. A. Massone 《Applied physics. B, Lasers and optics》1992,55(5):433-436
In this paper the ionizing role of isobutane (iso-C4H10) in the operation of a N2TE UV laser is analyzed. Laser pulse width value modifications, different laser wavelengths generated in the 2+ system and voltage pulse period modifications are analysed in order to show that isobutane, in very reduced quantities, generates a preionizing effect that can be higher than that produced by a conventional wire preionization system. 相似文献