全文获取类型
收费全文 | 3345篇 |
免费 | 142篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 126篇 |
大气科学 | 221篇 |
地球物理 | 1188篇 |
地质学 | 1066篇 |
海洋学 | 205篇 |
天文学 | 486篇 |
综合类 | 20篇 |
自然地理 | 185篇 |
出版年
2022年 | 25篇 |
2021年 | 50篇 |
2020年 | 49篇 |
2019年 | 52篇 |
2018年 | 305篇 |
2017年 | 199篇 |
2016年 | 164篇 |
2015年 | 93篇 |
2014年 | 137篇 |
2013年 | 164篇 |
2012年 | 75篇 |
2011年 | 155篇 |
2010年 | 156篇 |
2009年 | 172篇 |
2008年 | 130篇 |
2007年 | 106篇 |
2006年 | 116篇 |
2005年 | 89篇 |
2004年 | 88篇 |
2003年 | 86篇 |
2002年 | 73篇 |
2001年 | 52篇 |
2000年 | 50篇 |
1999年 | 33篇 |
1998年 | 46篇 |
1997年 | 36篇 |
1996年 | 53篇 |
1995年 | 37篇 |
1994年 | 33篇 |
1993年 | 41篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 26篇 |
1989年 | 32篇 |
1988年 | 26篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 27篇 |
1984年 | 23篇 |
1983年 | 28篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1980年 | 24篇 |
1979年 | 23篇 |
1978年 | 27篇 |
1977年 | 25篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1973年 | 17篇 |
1971年 | 21篇 |
排序方式: 共有3497条查询结果,搜索用时 93 毫秒
41.
Influence of the solar radiation (electromagnetic and corpuscular - solar wind) on the motion of the interplanetary dust particle is investigated. The ratio time of inspiralling toward the Sun: time of inspiralling neglecting the change of mass of the particle is presented as a function of initial eccentricities. 相似文献
42.
Reports
Regional Seas and Sustainable Development Results of an International Workshop 相似文献43.
New observations of the umbral limb-darkening are presented. We find a real and significant decrease in the umbra/photosphere intensity ratio towards the limb. This result contrasts the findings of previous authors and we believe this to be the first time such a decrease is reported. Our conclusion is based on broad band pinhole photometer intensity observations of 22 large sunspots covering the spectral region 0.387–2.35 m. The data are selected from measurements on approximately 600 days during the last 15.5 yr. The application of the limb-darkening data to the study of the temperature stratification in the umbra is briefly discussed. The observations confirm the suggestion that the umbra/photosphere intensity ratio seems to be a linear function of the phase in the solar cycle. 相似文献
44.
Series of white light heliograms and oft- and on-band H filtergrams have been obtained, with an average spatial resolution of 1, to study the flare active McMath region 15403 on 11 July, 1978. A great number of accurate heliographic positions were determined for the umbrae, the white light flare patches and several bright H flare knots, as well as along the principal zero filament and an arch prominence. Using the measured heliographic coordinates of these objects their motions could be analyzed in some detail. The velocities of several different objects could be deduced from the coordinates. Since the heliocentric angle of the region was about 45°, the variation in apparent heliographic coordinates also enabled some variations in heights to be determined.It is pointed out that the flare when fully developed, consisted almost entirely of loops. The zero filament which was activated prior to the flare ran between two umbrae of common penumbra and opposite polarity, one belonging to an old, the other to a new spot group. The white light flare developed on both sides of the filament where it passed between these two umbrae; it was also the place where the flare started. Observational evidence appears to indicate that the erupted filament re-formed from below.An indication has been found that there was a link between the motion of some umbrae and the major flare occurrence. 相似文献
45.
Pavel Voráček 《Astrophysics and Space Science》1982,81(1-2):85-94
Four situations are shown where the Schwarzschild metric cannot be used or is subject to unsurmountable problems. The first is the question of a metric useful for PPN-formalism checking different gravitational theories. The second problem occurs in connection with Mach's principle, when the flatness of the spacetime inside a massive hollow sphere is a generally accepted solution. The metrical discontinuity on the same spherical shell is a third problem. The fourth one is the anisotropy of the mass-energy of a test particle in the gravitational field. Three principles for solution are proposed:
- The space is not dilated, but rather contracted, in the gravitational field; then the measurement-rods are shorter and measured distances have greater magnitudes.
- The potential energy is to be related to a potential level where a stationary observer is placed and the general relativistic potential must be used.
- A new metric must be introduced which is distinct from the Schwarzschild metric, so that the space in the gravitational field is warped isotropically.
46.
Summary The estimation of the theoretical magnitude for deep foci based on the vertica component of medium-period PKIKP waves, Earth model PREM and source spectra is presented. The given graphs are valid for period T ranging from 1·6 s to 10 s, source depth of 25 km to 600 km and distance range of 16 500 km to 19 800 km. A simplified method of representing calibration curves is used. 相似文献
47.
Climatic characteristics are affected by various systematic and occasional impacts: besides the changes in the observing system (locations of the stations of the meteorological network, instruments, observing procedures), the possible local-scale and global natural and antropogenic impacts on climatic conditions should be taken into account. Apart from the predictability problems, the phenomenological analysis of the climatic variability and the determination of past persistent climatic anomalies are significant problems, among other aspects, as evidence of the possible anomalous behavior of climate or for climate impact studies. In this paper, a special technique for the identification of such shifts in the observational series is presented. The existence of these significant shorter or longer term changes in the mean characteristics for the properly selected adjoining periods of time is the necessary condition for the formation of any more or less unidirectional climatic trends. Actually, the window technique is based on a complete set of orthogonal functions. The sensitivity of the proposed model on its main parameters is also investigated. This method is applied for hemispheric and Hungarian data series of the mean annual surface temperature.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program 相似文献
48.
Summary The Banach theorem is applied to the Lagrange planetary equation for the semimajor axis of a geostationary satellite orbit to estimate the stability of near-geostationary satellite orbits. To achieve a graveyard (disposal) orbit, which will not interfere (=cross) the initial geostationary orbit, the geostationary semi-major axis ag have to be increased at least by 50 km. Numerical results for a variety of graveyard orbits show that the increase of ag by about 100 km will yield sufficiently stable orbits (accounting for the Earth's gravitational perturbations only) during the next 150 years.Dedicated to the 75th Birthday of Professor Academician Tibor Kolbenheyer 相似文献
49.
J. Zahradník M. Antonini G. Grünthal J. Janský D. Procházková E. Schmedes A. Špičak J. Zedník 《Pure and Applied Geophysics》1990,133(1):53-71
The main shock of the West-Bohemian earthquake swarm, Czechoslovakia, (magnitudem=4.5, depthh=10 km) exhibits an irregular areal distribution of macroseismic intensities 6° to 7° MSK-64. Four lobes of the 6° isoseismal are found and the maximum observed intensity is located at a distance of 8 km from the instrumentally determined epicentre. This distribution can be explained by the energy flux of the directS wave generated by a circular source, the hypocentral location and focal mechanism of which are taken from independent instrumental studies. The theoretical intensity, which is assumed to be logarithmically proportional to the integrated squared ground-motion velocity (i.e.,I=const+log v
2
(t)dt), fits the observed intensity with an overall root-mean-square error less than 0.5°. It is important that the present intensity data can also be equally well explained by the isotropic source. The fit was attained by means of a horizontally layered model though large fault zones and an extended sedimentary basin suggest a significant lateral heterogeneity of the epicentral region. The results encourage a broader application of the simple modelling technique used. 相似文献
50.
A new method to determine semi-analytical solutions of one-dimensional contaminant transport problem with nonlinear sorption is described. This method is based on operator splitting approach where the convective transport is solved exactly and the diffusive transport by finite volume method. The exact solutions for all sorption isotherms of Freundlich and Langmuir type are presented for the case of piecewise constant initial profile and zero diffusion. Very precise numerical results for transport with small diffusion can be obtained even for larger time steps (e.g., when the Courant-Friedrichs-Lewy (CFL) condition failed). 相似文献