全文获取类型
收费全文 | 934篇 |
免费 | 8篇 |
国内免费 | 2篇 |
专业分类
化学 | 437篇 |
晶体学 | 15篇 |
力学 | 49篇 |
数学 | 128篇 |
物理学 | 315篇 |
出版年
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 10篇 |
2018年 | 27篇 |
2017年 | 29篇 |
2016年 | 30篇 |
2015年 | 13篇 |
2014年 | 34篇 |
2013年 | 46篇 |
2012年 | 56篇 |
2011年 | 46篇 |
2010年 | 46篇 |
2009年 | 67篇 |
2008年 | 57篇 |
2007年 | 53篇 |
2006年 | 54篇 |
2005年 | 28篇 |
2004年 | 41篇 |
2003年 | 21篇 |
2002年 | 18篇 |
2001年 | 22篇 |
2000年 | 36篇 |
1999年 | 24篇 |
1998年 | 30篇 |
1997年 | 21篇 |
1996年 | 11篇 |
1995年 | 17篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1936年 | 1篇 |
1935年 | 2篇 |
1919年 | 1篇 |
1914年 | 2篇 |
1913年 | 3篇 |
1912年 | 3篇 |
1911年 | 3篇 |
1909年 | 1篇 |
1892年 | 1篇 |
1888年 | 2篇 |
排序方式: 共有944条查询结果,搜索用时 15 毫秒
51.
Training American listeners to perceive Mandarin tones 总被引:1,自引:0,他引:1
Wang Y Spence MM Jongman A Sereno JA 《The Journal of the Acoustical Society of America》1999,106(6):3649-3658
Auditory training has been shown to be effective in the identification of non-native segmental distinctions. In this study, it was investigated whether such training is applicable to the acquisition of non-native suprasegmental contrasts, i.c., Mandarin tones. Using the high-variability paradigm, eight American learners of Mandarin were trained in eight sessions during the course of two weeks to identify the four tones in natural words produced by native Mandarin talkers. The trainees' identification accuracy revealed an average 21% increase from the pretest to the post-test, and the improvement gained in training was generalized to new stimuli (18% increase) and to new talkers and stimuli (25% increase). Moreover, the six-month retention test showed that the improvement was retained long after training by an average 21% increase from the pretest. The results are discussed in terms of non-native suprasegmental perceptual modification, and the analogies between L2 acquisition processes at the segmental and suprasegmental levels. 相似文献
52.
For the purpose of improving present approximations to the exchange and correlation potentials, newly derived properties of the exact exchange and correlation potentials are summarized. Present approximations are not expected to generally satisfy these properties. The summarized properties include relations at the Fermi level, low-density requirements, and a new density functional formula for computing ionization energies. © 1995 John Wiley & Sons, Inc. 相似文献
53.
54.
V. E. Egorushkin S. E. Kul’kova N. V. Mel’nikova A. N. Ponomarev 《Journal of Experimental and Theoretical Physics》2005,101(2):350-356
The dissociation of a gas molecule and the formation of a new chemical bond upon adsorption of this molecule on the surface of a transition metal are studied using the method of equations of motion. It is shown that both processes involve the formation of a mixed intermediate state during the adsorbate-substrate interaction. The dissociation is caused by a resonance growth of the vibrational mode, whereby the dissociation barrier is determined by the hybridization energy and by the frequency of electron transitions between molecular levels and the d electron energy levels of the metal in the mixed intermediate state. The resonance conditions for the formation of new surface structures are established. 相似文献
55.
Graff BA Benjaminsen IC Melås EA Brurberg KG Rofstad EK 《Magnetic resonance imaging》2005,23(9):961-966
The purpose of this study was to use dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to search for systematic intratumor heterogeneity in blood perfusion in human melanoma xenografts growing intradermally in BALB/c-nu/nu mice. Six xenografted tumors of an amelanotic human melanoma line (A-07) were included in the study. DCE-MRI was performed daily for 5 days by using spoiled-gradient recalled sequences. Tumor images of E.F (E is initial extraction fraction and F is perfusion) were produced by subjecting DCE-MRI data to Kety analysis. E.F was used as a measure of tumor blood perfusion, since comparative studies have shown that E.F is closely related to blood perfusion in A-07 tumors. The E.F images indicated that the intratumor heterogeneity in blood perfusion was similar in all investigated tumors. The blood perfusion was low in the center of the tumors and increased toward the tumor periphery in the dorsal and ventral direction by a factor of 3-4, but not in the lateral and medial direction. The magnitude of the heterogeneity increased by a factor of approximately 2 during tumor growth. In conclusion, intradermal human melanoma xenografts show significant systematic intratumor heterogeneity in blood perfusion. 相似文献
56.
Crystals of Csx(NH4)1?xLiSO4 (0.39≤x≤1.0) solid solutions are grown and investigated using polarized light microscopy and measurements of the birefringence in the temperature range 100–530 K. The (x-T) phase diagram of the Csx(NH4)1?xLiSO4 solid solutions is constructed. It is demonstrated that, upon substitution of ammonium for cesium in the CsLiSO4 crystal, the phase transition temperature gradually increases to such a degree that the ferroelastic phase can exist at room temperature. The triple point of intersection of the Pmcn, P21cn, and P1121/n phase boundaries is determined. It is established that the introduction of ammonium in small amounts has an unusually strong effect on the refractive properties and character of the ferroelastic phase transition in the CsLiSO4 crystal. 相似文献
57.
The influence of the water concentration in the water—n-octane—sodium dodecyl sulfate—n-pentanol microemulsions on the polarity index I
1/I
3, the efficiency of formation of the fluorescent probe (pyrene) excimers I
ex/I
m, and the conductivity of the system in a wide interval of water—oil ratios was studied. Analysis of changes in the polarity index shows that in all types of the microemulsions pyrene is solubilized in the hydrophobic part of the water—oil interface between the surfactant hydrocarbon radicals. Depending on the water—oil ratio, the site of its localization changes, and the effective permittivity of the medium eff varies from 5 to 11. Variations of the conductivity and polarity index allow one to observe three structures in the mucroemulsion, viz., water—oil, bicontinual region, and oil—water. Variation of the I
ex/I
m ratio reveals only the transition from the water—oil microemulsion to the oil—water microemulsion. 相似文献
58.
S. V. Mel’nikova S. V. Misyul’ A. F. Bovina M. L. Afanas’ev 《Physics of the Solid State》2000,42(2):345-349
Single-crystal plates of different sections of the (NH4)3ScF6 crystal have been investigated by polarization-optical microscopy and X-ray diffraction over a wide temperature range, including the temperatures of two known phase transitions and the third transition found recently. It is established that the symmetry of 5 phases changes in the following sequence: $\begin{gathered} O_h^5 - Fm3m(Z = 4) \leftrightarrow C_{2h}^5 - {{P12_1 } \mathord{\left/ {\vphantom {{P12_1 } {n1}}} \right. \kern-0em} {n1}}(Z = 2) \leftrightarrow C_{2h}^3 - {{I12} \mathord{\left/ {\vphantom {{I12} {m1}}} \right. \kern-0em} {m1}} \\ (Z = 16) \leftrightarrow C_i^1 - I\bar 1(Z = 16) \\ \end{gathered} $ . 相似文献
59.
I. K. Kamilov A. G. Gamzatov A. M. Aliev A. B. Batdalov Sh. B. Abdulvagidov O. V. Mel’nikov O. Yu. Gorbenko A. R. Kaul’ 《Journal of Experimental and Theoretical Physics》2007,105(4):774-781
We have measured the resistivity, magnetoresistance, and thermopower of ceramic manganite samples La1 ? x Ag y MnO3 (y ≤ x) doped with silver as functions of temperature (4.2–350 K) and magnetic field (up to 26 kOe). A metal-insulator phase transition is observed in all investigated samples at temperatures close to room temperature. The behavior of the resistivity and thermopower in the high-temperature paramagnetic region is interpreted using the concept of small radius polaron; the activation energy decreases with increasing doping level. The resistivity in the low-temperature ferromagnetic region is approximated by the expression ρFM(T) = ρ0 + AT 2 + BT 4.5 presuming the existence of electron-electron and electron-magnon interactions. A resistivity minimum and a strong magnetoresistive effect are observed at low temperatures. The latter effect is associated with scattering of charge carriers at grain boundaries, which are antiferromagnetically ordered relative to one another. The temperature dependence of thermopower in the magnetically ordered phase is described in the framework of a model taking into account the drag of charge carriers by magnons. 相似文献
60.
Photolysis of the alkylperoxy radicals ≡SiOCH2OO and ≡SiOCH2CH2OO grafted onto an activated surface of silica was found to be accompanied by photochemical radical chain reactions. 相似文献