全文获取类型
收费全文 | 14155篇 |
免费 | 449篇 |
国内免费 | 98篇 |
专业分类
化学 | 9268篇 |
晶体学 | 149篇 |
力学 | 324篇 |
综合类 | 1篇 |
数学 | 2337篇 |
物理学 | 2623篇 |
出版年
2023年 | 98篇 |
2022年 | 140篇 |
2021年 | 224篇 |
2020年 | 253篇 |
2019年 | 296篇 |
2018年 | 197篇 |
2017年 | 191篇 |
2016年 | 452篇 |
2015年 | 352篇 |
2014年 | 387篇 |
2013年 | 741篇 |
2012年 | 732篇 |
2011年 | 786篇 |
2010年 | 559篇 |
2009年 | 491篇 |
2008年 | 713篇 |
2007年 | 732篇 |
2006年 | 601篇 |
2005年 | 657篇 |
2004年 | 545篇 |
2003年 | 425篇 |
2002年 | 429篇 |
2001年 | 228篇 |
2000年 | 239篇 |
1999年 | 172篇 |
1998年 | 159篇 |
1997年 | 170篇 |
1996年 | 173篇 |
1995年 | 146篇 |
1994年 | 162篇 |
1993年 | 175篇 |
1992年 | 140篇 |
1991年 | 134篇 |
1990年 | 130篇 |
1989年 | 106篇 |
1988年 | 91篇 |
1987年 | 101篇 |
1986年 | 128篇 |
1985年 | 164篇 |
1984年 | 152篇 |
1983年 | 134篇 |
1982年 | 117篇 |
1981年 | 115篇 |
1980年 | 133篇 |
1979年 | 108篇 |
1978年 | 124篇 |
1977年 | 99篇 |
1976年 | 92篇 |
1975年 | 107篇 |
1974年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Two-color cross-correlation of fs-laser pulses by two-photon induced photoconductivity for near and far field optical measurements 总被引:1,自引:0,他引:1
Wolfgang Schade David L. Osborn Jan Preusser Stephen R. Leone 《Optics Communications》1998,150(1-6):27-32
Two-color two-photon induced photoconductivity in a GaAsP diffusion type photodiode is demonstrated by measuring femtosecond cross-correlation functions for widely separated wavelength pairs of 775 and 1300 nm. Results are obtained for a range of tunable wavelengths and average powers of the incident lasers by measuring the two-photon induced photocurrent as a function of the optical delay between the pulses. The temporal autocorrelation of femtosecond laser pulses in the near-field of a small diameter aluminum coated optical fiber tip is also obtained with the same photodiode method for single colors. 相似文献
182.
Applying a Lindemann like criterion obtained previously by Kierfeld et al. [J. Kierfeld, T. Nattermann, T. Hwa, Phys. Rev. B 55 (1997) 626], we estimate the magnetic field and temperature for a high-Tc superconductor, at which a topologically ordered vortex glass phase becomes unstable with respect to a disorder-induced formation of dislocations. The employed criterion is shown to be equivalent to a conventional phenomenological Lindemann criterion including the values for the numerical factors, i.e., for the Lindemann number. The positional correlation length of the topologically ordered vortex glass is calculated. 相似文献
183.
184.
Jan J. Slawianowski 《International Journal of Theoretical Physics》1998,37(1):411-420
We formulated some criticisms of the Diracequation and its Clifford-algebraic philosophy; inparticular, we show that, within a general-relativisticcontext, they seem to contain hidden action-at-distance concepts. We suggest a new model based on thefour-component Klein-Gordon equation locally invariantunder the U(2,2) gauge group. The usual Dirac equationis then obtained as a certain approximation. The geometrodynamical sector shows reasonablecorrespondence with general relativity. 相似文献
185.
Jan Weis Anders Ericsson Hans C.:Son Silander Anders Hemmingsson 《Magnetic resonance imaging》1998,16(10):1265-1272
We present a method for the quantification and correction of geometrical/intensity distortions of magnetic resonance images predominantly caused by bulk magnetic susceptibility shifts due to susceptibility heterogeneities of measured biologic tissues and shape of the object under investigation. The method includes precise and fast measurements of the static magnetic-field distribution inside the measured object and automated data processing. Magnetic-field deviations in the range −2.4; 2.6 ppm were found in the human brain at B0 = 1.5 T. For routinely used imaging parameters, with a read gradient strength of about 1 mT/m, the magnetic-field perturbations in the human brain can cause geometrical distortions up to ±4 mm and intensity changes up to ±50%. MR images corrected by the described method are suitable for planning high precision applications in neurosurgery. 相似文献
186.
A. Krushelnitsky D. Reichert G. Hempel V. Fedotov H. Schneider L. Yagodina A. Schulga 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,138(2):244-255
Superslow backbone dynamics of the protein barstar and the polypeptide polyglycine was studied by means of a solid-state MAS 1D exchange NMR method (time-reverse ODESSA) that can detect reorientation of nuclei carrying anisotropic chemical shift tensors. Experiments were performed on carbonyl 13C in polyglycine (natural abundance) and backbone 15N nuclei in uniformly 15N-enriched barstar within a wide range of temperatures in dry and wet powders for both samples. Two exchange processes were observed in the experiments: molecular reorientation and spin diffusion. Experimental conditions that are necessary to separate these two processes are discussed on a quantitative level. It was revealed that the wet protein undergoes molecular motion in the millisecond range of correlation times, whereas in dry protein and polyglycine molecular reorientations could not be detected. The correlation time of the motion in the wet barstar at room temperature is 50-100 ms; the activation energy is about 80 kJ/mol. Previously, protein motions with such a long correlation time could be observed only by methods detecting chemical exchange in solution (e.g., hydrogen exchange). The application of solid-state MAS exchange spectroscopy provides new opportunities in studying slow biomolecular dynamics that is important for the biological function of proteins. 相似文献
187.
The cerebral involvement of a 13-yr-old boy with Wilson's disease was serially evaluated during the first 18 mo of D-penicillamine treatment. An ultra-low-field magnetic resonance imaging (ULF MRI) system, operating at 0.02 T, with computerized image processing was used. The half-yr period prior to the clinical diagnosis was set, the patient had showed poor school performance, emotional lability, deteriorating handwriting, progressively slow, gross, and fine motor functions, and a fixed rigid smile. No overt signs of liver disease were found. With D-penicillamine treatment (1–1.5 g/d) a continuous improvement was seen. The pretreatment MRI investigation showed pronounced pathological transformation in the basal ganglia. However, changes were seen also in most other parts of the brain indicating diffuse involvement. During treatment the computerized MR images became gradually more normal. The current magnetic resonance imaging system with computerized image processing is a sensitive and simple method for evaluation of subtle parenchymal changes of the brain. 相似文献
188.
R. Wordel M. Baier G. Schneider F. E. Wagner V. E. Antonov E. G. Ponyatovsky Yu. Kopilovskii E. F. Makarov 《Hyperfine Interactions》1990,54(1-4):891-894
Hydrides of iron and cobalt prepared at pressures between 4.0 and 9.5 GPa were studied by57Fe Mössbauer spectroscopy at 4.2 K. Iron hydride was found to be nearly stoichiometric FeH. The two iron sites in its dhep lattice have hyperfine fields of 33.8 and 28.8 T. Practically the same results were found for the deuteride. In hep ε-CoHx, the hyperfine fields decrease with hydrogen content by about 6% betweenx=0 andx=0.5. In all studied hydrides the electron densities at the57Fe nuclei are smaller than in the pure metals. 相似文献
189.
We extend a model for layered high-temperature superconductors to systems with two CuO2 layers per unit cell and two interlayer spacings with different physical properties. The carriers are assumed to occupy Fermi liquid states, forming narrow tight-binding bands. The layers are coupled by weak interlayer-hopping matrix elements between adjacent sheets, as well as by an attractive interaction between carriers in neighboring layers in addition to an on-site intralayer coupling. We solve the Gorkov equations for this model to obtain the critical temperature and the density of states of the oneparticle excitations from the superconducting condensate, and discuss various parameter regimes concerning the coupling between the two layers. We compare our results with current experimental findings for high-temperature superconductors. The presence of two CuO2 layers leads to multi-peak features in the superconducting density of states, as has been observed in recent tunneling measurements. 相似文献
190.