全文获取类型
收费全文 | 22916篇 |
免费 | 232篇 |
国内免费 | 130篇 |
专业分类
测绘学 | 354篇 |
大气科学 | 1203篇 |
地球物理 | 4357篇 |
地质学 | 8997篇 |
海洋学 | 2231篇 |
天文学 | 5267篇 |
综合类 | 42篇 |
自然地理 | 827篇 |
出版年
2022年 | 263篇 |
2021年 | 431篇 |
2020年 | 394篇 |
2019年 | 461篇 |
2018年 | 939篇 |
2017年 | 864篇 |
2016年 | 879篇 |
2015年 | 365篇 |
2014年 | 765篇 |
2013年 | 1287篇 |
2012年 | 897篇 |
2011年 | 1089篇 |
2010年 | 1054篇 |
2009年 | 1212篇 |
2008年 | 1039篇 |
2007年 | 1217篇 |
2006年 | 1060篇 |
2005年 | 565篇 |
2004年 | 533篇 |
2003年 | 539篇 |
2002年 | 559篇 |
2001年 | 508篇 |
2000年 | 409篇 |
1999年 | 333篇 |
1998年 | 323篇 |
1997年 | 329篇 |
1996年 | 254篇 |
1995年 | 262篇 |
1994年 | 236篇 |
1993年 | 182篇 |
1992年 | 208篇 |
1991年 | 183篇 |
1990年 | 199篇 |
1989年 | 190篇 |
1988年 | 157篇 |
1987年 | 183篇 |
1986年 | 171篇 |
1985年 | 205篇 |
1984年 | 198篇 |
1983年 | 197篇 |
1982年 | 188篇 |
1981年 | 173篇 |
1980年 | 162篇 |
1979年 | 182篇 |
1978年 | 158篇 |
1977年 | 142篇 |
1976年 | 133篇 |
1975年 | 136篇 |
1974年 | 125篇 |
1973年 | 165篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
V. I. Ferronsky S. A. Denisik S. V. Ferronsky 《Celestial Mechanics and Dynamical Astronomy》1996,64(3):167-183
The physical meaning of the terms of the potential and kinetic energy expressions, expanded by means of the density variation function for a nonuniform self-gravitating sphere, is discussed. The terms of the expansions represent the energy and the moment of inertia of the uniform sphere, the energy and the moment of inertia of the nonuniformities interacting with the uniform sphere, and the energy of the nonuniformities interacting with each other. It follows from the physical meaning of the above components of the energy structure, and also from the observational fact of the expansion of the Universe that the phase transition, notably, fusion of particles and nuclei and condensation of liquid and solid phases of the expanded matter accompanied by release of energy, must be the physical cause of initial thermal and gravitational instability of the matter. The released kinetic energy being constrained by the general motion of the expansion, develops regional and local turbulent (cyclonic) motion of the matter, which should be the second physical effect responsible for the creation of celestial bodies and their rotation. 相似文献
102.
103.
104.
L. I. Onuora 《Astrophysics and Space Science》1987,136(1):11-15
The inflationary unvierse model predicts the density parameter 0 to be 1.0 with the cosmological constant 0 usually taken to be zero, whereas observational estimates give 00.2 and 010-57 cm–2. It was found, however, that the observed variation of angular diameter with redshift for extragalactic radio sources could be interpreted in terms of a low density universe with linear size evolution of the sources for either an inflationary model with 0 or an open model with =0. 相似文献
105.
Observations made by the differential method in the H line have revealed longperiod (on a timescale of 40 to 80 min) line-of-sight velocity oscillations which increase in amplitude with distance from the centre to the solar limb and, as we believe, give rise to prominence oscillations. As a test, we present some results of simultaneous observations at the photospheric level where such periods are absent.Oscillatory processes in the solar chromosphere have been studied by many authors. Previous efforts in this vein led to the detection of shortperiod oscillations in both the mass velocities and radiation intensity (Deubner, 1981). The oscillation periods obtained do not, normally, exceed 10–20 min (Dubov, 1978). More recently, Merkulenko and Mishina (1985), using filter observations in the H line, found intensity fluctuations with periods not exceeding 78 min. However, the observing technique they used does not exclude the possibility that those fluctuations were due to the influence of the Earth's atmosphere. It is also interesting to note that in spectra obtained by Merkulenko and Mishina (1985), the amplitude of the 3 min oscillations is anomalously small and the 5 min period is altogether absent, while the majority of other papers treating the brightness oscillations in the chromosphere, do not report such periods in the first place. So far, we are not aware of any other evidence concerning the longperiod velocity oscillations in the chromosphere on a timescale of 40–80 min.Longperiod oscillations in prominences (filaments) in the range from 40 to 80 min, as found by Bashkirtsev et al. (1983) and Bashkirtsev and Mashnich (1984, 1985), indicate that such oscillations can exist in both the chromosphere and the corona (Hollweg et al., 1982).In this note we report on experimental evidence for the existence of longperiod oscillations of mass velocity in the solar chromosphere. 相似文献
106.
107.
L. I. Chetverikov 《Mathematical Geology》1991,23(1):33-40
This paper considers the present state of mathematical geology. Three directions are recognized: applied, theoretical, and mathematical. Applied mathematical geology includes formal use of mathematics to solve problems and computer processing of data. Success is achieved by a correspondence of mathematical methods used to the nature of geological data. This correspondence can be demonstrated by purely mathematical means. Theoretical mathematical geology uses mathematics as a language of geology; however, a number of methodological problems must be solved: formalization of initial geological concepts and creation of a strict conceptual basis, substantiation of initial principles of mathematical simulation, creation of theoretical geological models, problems of elementary and coincidence in geology, and methodological substantiations of possibilities of any mathematical model to approximate geological models. The essense and significance of these problems are considered. The main task of mathematical geology is to prove its correspondence to the nature of the geological objects studied, geological data obtained, and geological problems solvable. Finally, the main problems of mathematical geology are not so much mathematical as geological and methodological. 相似文献
108.
I. A. Hassanien 《Astrophysics and Space Science》1991,175(1):135-147
Unsteady two-dimensional flow of a viscous incompressible and electrical-conducting fluid through a porous medium bounded by two infinite parallel plates under the action of a transverse magnetic field is presented when there is time-varying suction at the plates. The lower plate is at rest while the upper plate is oscillating in its own plane about a constant mean velocity. Expressions for the velocity, fluctuating parts of the velocity, amplitude, and phase of the skin-friction are obtained. The flow phenomenon has been characterized by the parametersK (permeability of the porous medium),N(magnetic parameter) (frequency parameter), andA(variable suction parameter) and the role of these parameters on the flow characteristics has been studied. 相似文献
109.
Quasi-steady high-temperature current sheets are an energy source during the main or hot phase of solar flares. Such sheets are shown to be stabilized with respect to the tearing instability by a small transverse component of magnetic field existing in the sheets. 相似文献
110.
A. O. Allakhverdiyev O. H. Guseinov F. K. Kasumov I. M. Yusifov 《Astrophysics and Space Science》1986,121(1):21-44
A new way of choosing of the calibrators for constructing (D)-dependence of supernova remnants (SNR) is suggested. A knowledge of the distance of an SNR is not sufficient to consider it as a calibrator. It is shown that neither more accurate determination of distance to calibrators, nor an increase in their number, nor an increase in the precision of the remnant angular size and radio flux determination can lead to a considerable improvement of simple (D)-dependence which is suggested in the given work.For remnants with small surface brightnesses there is no (D)-dependence at all. The most accurate remnant distances currently known, are given: these are liable to change only after a large amount of additional observational data accurately compiled. 相似文献