全文获取类型
收费全文 | 179329篇 |
免费 | 2092篇 |
国内免费 | 577篇 |
专业分类
化学 | 94334篇 |
晶体学 | 2850篇 |
力学 | 7359篇 |
综合类 | 3篇 |
数学 | 20881篇 |
物理学 | 56571篇 |
出版年
2020年 | 1536篇 |
2019年 | 1691篇 |
2018年 | 2074篇 |
2017年 | 2134篇 |
2016年 | 3394篇 |
2015年 | 2076篇 |
2014年 | 3328篇 |
2013年 | 8129篇 |
2012年 | 6271篇 |
2011年 | 7550篇 |
2010年 | 5326篇 |
2009年 | 5245篇 |
2008年 | 7036篇 |
2007年 | 6998篇 |
2006年 | 6668篇 |
2005年 | 5978篇 |
2004年 | 5521篇 |
2003年 | 4966篇 |
2002年 | 4793篇 |
2001年 | 5353篇 |
2000年 | 3953篇 |
1999年 | 3051篇 |
1998年 | 2558篇 |
1997年 | 2487篇 |
1996年 | 2348篇 |
1995年 | 2196篇 |
1994年 | 2169篇 |
1993年 | 2084篇 |
1992年 | 2380篇 |
1991年 | 2297篇 |
1990年 | 2281篇 |
1989年 | 2170篇 |
1988年 | 2187篇 |
1987年 | 2183篇 |
1986年 | 2094篇 |
1985年 | 2736篇 |
1984年 | 2789篇 |
1983年 | 2453篇 |
1982年 | 2542篇 |
1981年 | 2344篇 |
1980年 | 2328篇 |
1979年 | 2463篇 |
1978年 | 2517篇 |
1977年 | 2445篇 |
1976年 | 2482篇 |
1975年 | 2392篇 |
1974年 | 2340篇 |
1973年 | 2540篇 |
1972年 | 1621篇 |
1971年 | 1333篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
131.
A. L. Apanasenko A. V. Kuznichenko Yu. B. Govyadovskii V. G. Yakunin 《Journal of Applied Spectroscopy》1991,54(3):271-276
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 438–444, March, 1991. 相似文献
132.
Yu. K. Voron'ko A. B. Kudryavtsev V. V. Osiko E. V. Sorokin 《Journal of Applied Spectroscopy》1991,55(4):953-957
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 535–540, October, 1991. 相似文献
133.
We report the results of experiments on electrically driven convection that occurs in a thin, freely suspended film of smectic A liquid crystal when an electric field is applied in the plane of the film. Convection in a vortex pattern is found above a well-defined critical voltage. The film behaves as a two-dimensional isotropic liquid: neither its thickness nor the director field are modified by the flow. We present measurements of the critical voltage at the onset of convection in two experimental configurations—one which allows the injection of charges into the film from the electrodes, and one which does not. When injection is present, the critical voltage for the onset of flow increases monotonically with increasing frequency of applied field. With no injection, there is no instability at DC and the critical voltage diverges there. The nature of the flow pattern observed at onset changes with frequency. Below a certain frequency the film flows in vortices that extend over the width of the film; above this frequency the flow is confined to two lines of smaller vortices localized along the electrodes. We present a simple discussion of the mechanisms which drive the convection. 相似文献
134.
B. P. Harlamov 《Journal of Mathematical Sciences》2006,133(3):1371-1377
An inverse process with independent positive increments is considered. For such a process, the first hitting time τx of level x as a function of x ≥ 0 is a proper process with independent positive increments. In terms of first hitting times
and their Levy measures, multidemensional distribution densities and Laplace transformations are derived. Stationary distributions
of increments of the process are investigated. Bibliography: 8 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 311, 2004, pp. 286–297. 相似文献
135.
The consequences of Ge deposition on Br-terminated Si(1 0 0) were studied with scanning tunneling microscopy at ambient temperature after annealing at 650 K. One monolayer of Br was sufficient to prevent the formation of Ge huts beyond the critical thickness of 3 ML. This is possible because Br acts as a surfactant whose presence lowered the diffusivity of Ge adatoms. Hindered mobility was manifest at low coverage through the formation of short Ge chains. Further deposition resulted in the extension and connection of the Ge chains and gave rise to the buildup of incomplete layers. The deposition of 7 ML of Ge resulted in a rough surface characterized by irregularly shaped clusters. A short 800 K anneal desorbed the Br and allowed Ge atoms to reorganize into the more energetically favorable “hut” structures produced by conventional Ge overlayer growth on Si(1 0 0). 相似文献
136.
137.
A. B. Mazo 《Fluid Dynamics》2002,37(6):913-918
Plane ideal incompressible flow in a rectangular channel partitioned by a thin permeable barrier (lattice) is considered. In flowing through the lattice the stream suddenly (jumpwise) changes direction and loses energy. The flow is assumed to be vortical; the vorticity is discontinuous on the lattice. A mathematical formulation of the problem for the stream function is proposed in the form of a nonlinear elliptic equation with coefficients discontinuous on the lattice line. A numerical solution is constructed using the finite-element iteration method. The results of the numerical simulation show how the flow velocity profile in the channel can be controlled by means of permeable barriers. 相似文献
138.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
139.
A comprehensive study of the excited electronic states of HCl is reported. Using resonance enhanced multiphoton ionization ((2 + 1) REMPI) and time-of-flight mass spectrometry (TOFMS) over 120 band systems are analyzed. Supersonic jet techniques are used to prepare rotationally cold species for laser spectroscopy in the 77 000 to 96 000 cm−1 region. At least 50 new electronic states are characterized as well as several features only tentatively assigned previously. A long vibrational progression consisting of 29 vibrational levels of the deeply bound V1Σ+(0+) valence/ion-pair state is studied. We also extend the identification and analysis to high vibrational levels of low-lying Rydberg states. The assignments of [2Πi] Rydberg state complexes are evaluated in terms of spin-orbit coupling and united-atom calculations. In several band systems, the spectra exhibit anomalous rotational line intensities and broadened linewidths which are consistent with predissociation. Multiphoton ionization with mass spectrometry permits the investigation of isotope effects as well as the appearance of fragment species associated with repulsive potential curves. 相似文献
140.