全文获取类型
收费全文 | 2487篇 |
免费 | 110篇 |
国内免费 | 14篇 |
专业分类
测绘学 | 48篇 |
大气科学 | 164篇 |
地球物理 | 1120篇 |
地质学 | 685篇 |
海洋学 | 104篇 |
天文学 | 386篇 |
综合类 | 4篇 |
自然地理 | 100篇 |
出版年
2021年 | 41篇 |
2020年 | 33篇 |
2019年 | 34篇 |
2018年 | 81篇 |
2017年 | 106篇 |
2016年 | 114篇 |
2015年 | 92篇 |
2014年 | 108篇 |
2013年 | 133篇 |
2012年 | 78篇 |
2011年 | 73篇 |
2010年 | 102篇 |
2009年 | 96篇 |
2008年 | 80篇 |
2007年 | 72篇 |
2006年 | 54篇 |
2005年 | 37篇 |
2004年 | 46篇 |
2003年 | 46篇 |
2002年 | 61篇 |
2001年 | 39篇 |
2000年 | 35篇 |
1999年 | 26篇 |
1998年 | 36篇 |
1997年 | 24篇 |
1996年 | 41篇 |
1995年 | 27篇 |
1994年 | 36篇 |
1993年 | 29篇 |
1992年 | 30篇 |
1991年 | 24篇 |
1990年 | 29篇 |
1989年 | 20篇 |
1988年 | 31篇 |
1987年 | 30篇 |
1986年 | 32篇 |
1985年 | 23篇 |
1984年 | 32篇 |
1983年 | 32篇 |
1982年 | 42篇 |
1981年 | 30篇 |
1980年 | 26篇 |
1979年 | 37篇 |
1978年 | 28篇 |
1977年 | 28篇 |
1975年 | 24篇 |
1974年 | 25篇 |
1973年 | 24篇 |
1972年 | 28篇 |
1971年 | 27篇 |
排序方式: 共有2611条查询结果,搜索用时 31 毫秒
21.
The Barra Nova inlet, in south Portugal, is known to migrate progressively southeastwards under wave action. The morphodynamics
of this system during a representative year suggests that this long-term evolution is dependent on a seasonal behavior of
the tidal inlet which can be described through a three-stage model of post-storm, transition and extended fair-weather conditions.
Processes involved in this evolution indicate that the historical migration of the Barra Nova is not dependent on the longshore
drift forcing constricting the channel on the updrift coast, but rather on the adjustment of the system to a major erosion
of the downdrift coast during short storm events. 相似文献
22.
A comparative analysis of spotless and spot group flares recorded at Hvar and Kanzelhöhe Observatories during the 21st cycle of solar activity is presented. The rate of occurrence of two-ribbon flares was found to be significantly higher for the spotless flares. In comparison with spot group flares of corresponding H importance, the soft X-ray peak values have been systematically lower for the spotless flares. The highest peak values and the energy released in soft X-rays was found for flares with a H ribbon protruding over a major spot umbra. It was found that the effective plasma temperatures in spotless flares have been considerably lower than the temperatures in spot group flares. 相似文献
23.
Igor Vrišer 《GeoJournal》1996,38(2):151-156
An important state sector developed in Slovenian agriculture under communism and although it accounted for a less than a tenth of the agricultural area it assumed a major role in supplying food to the urban markets; also in providing raw material to the food processing industry and for exporting. In the context of the transition to a market economy legislation has been enacted that provides for denationalisation and the restructuring of enterprises. This threatens the survival of the state sector and creates problems for the food market because the private farmers are not yet well-organised to provide an alternative supply. The government is committed by the legislation already passed but is anxious to avoid marketing problems. 相似文献
24.
Recently a method has been suggested to analyze the chaotic behaviour of a conservative dynamical system by numerical analysis of the fundamental frequencies. Frequencies and amplitudes are determined step by step. As the frequencies are not generally orthogonal, a Gramm-Schmidt orthogonalization is made and for each new frequency the old amplitudes of previously determined frequencies are corrected. For a chaotic trajectory variations of the frequencies and amplitudes determined over different time periods are expected. The change of frequencies in such a calculation is a measure of the chaoticity of the trajectory. While amplitudes are corrected, the frequencies (once determined) are constant. We suggest here simple linear corrections of frequencies for the effect of other close frequencies. The improvement of frequency determination is demonstrated on a model case. This method is applied to the first fifty numbered asteroids. 相似文献
25.
Summary Direct measurements of the thermal plasma parameters in the topside ionosphere reveal variations of the plasmasphere boundary in the dusk sector. The ACTIVE satellite's near-polar orbits at altitudes of 500 – 1800 km around winter solstice 1989 were used to study the bulge region of the plasmasphere during intervals with different levels of geomagnetic agitation. The narrow, sharply defined trough in electron concentration corresponding to the plasmapause under quiet conditions situated at L = 6 – 7 moved to lower L-values with increasing geomagnetic activity. This narrow trough can be found in all main ion constituents. During periods of moderate geomagnetic activity, following the onset of a weak magnetic storm, a portion of the plasmaspheric bulge region was separated from the main plasmaspheric body. This can be seen in the outer ionosphere as an inner narrow trough at lower L-value. Troughs in light ions need no longer coincide with this in electron concentration. He+ is the most sensitive constituent reflecting the dusk sector plasmaspheric situation at this altitude.Dedicated to the Memory of Professor Karel P 相似文献
26.
In an earlier paper Arp, Bi, Chu and Zhu investigated various quasar samples and recognized a periodicity of remarkable degree in them. Their conclusion was that the existence of such a periodicity is a counterevidence against the cosmological origin of quasar redshifts. Since this question is of great importance in a cosmological context, here we reanalyze some of the samples together with a galaxy sample of the pencil-beam survey of Broadhurstet al. Our result is that on the plane of cosmological parameters (0, 0) there is a non-negligible region where two quasar samples and the galaxy sample are simultaneously fairly periodic. Pure periodicity is still compatible with cosmological principles, at least on length scales much longer than the period length. So the regularities can fit into a cosmological context. 相似文献
27.
28.
Miroslav Krs František Novák Marta Krsová Petr Pruner Jiří Jansa 《Studia Geophysica et Geodaetica》1993,37(4):382-400
Summary This study is a follow up of the investigation of some magnetic properties and metastability of greigite in samples obtained from Miocene claystones in the Kruné hory (Erzgebirge) Piedmont basins (Bohemia). Three different methods of upgrading the smythite were applied; the magnetic properties of the concentrates are compared. The thermal conversion of smythite sets in at 200°C while greigite converts at 250°C. The first intermediate products to be formed are iron sulphides, marcasite clearly dominating over pyrite and pyrrhotite. Apart from a Fe3+ sulphate with a composition of Fe2(SO4)3, oxidation of these sulphides gives rise to -Fe2O3. The result of the subsequent decomposition of the mentioned sulphate is the formation of -Fe2O3, which retains the sulphate structure. The final product of the thermal decomposition at 800°C is -Fe2O3. In the smythite concentrate the conversion to Fe3+ sulphate and -Fe2O3 is about twice as intensive as in greigite. No direct conversion to -Fe2O3 was found. During the thermal process self-reversals of remanence were observed, in various samples as many as four reversals in the temperature interval from 340 to 590°C. The occurrences of self-reversals of remanence were only observed at high degrees of thermal demagnetization, of the order of 10–2 down to 10–3 in the temperature interval of sulphide origin (below 400°C), and of the order of 10–4 down to 10–6 in the temperature interval of Fe-oxides origin (above 400°C).Presented at the 3rd Conference on New Trends in Geomagnetism, Castle of Smolenice, Czechoslovakia, June 22–29, 1992 相似文献
29.
Gojko Djurašević 《Astrophysics and Space Science》1993,206(2):207-218
The paper is devoted to the actual problematics in the determination of orbital and physical parameters of active CB on the basis of the interpretation of photometric observations. One solves the problem in two stages: by obtaining a synthetic light curve in the case when the parameters of the corresponding CB model (Djuraevi, 1992a) are given a priori (direct problem) and by determining the parameters of the given model for which the best fit between the synthetic light curve and the observations is achieved (inverse problem) (Djuraevi, 1992b). In this paper, the above procedure is applied to a particular case of an interpretation of CB light curves AU Ser and RV Corvi. 相似文献
30.
Gojko Djurašević 《Astrophysics and Space Science》1993,206(1):129-144
The author considers the current problematics in the determination of the orbital and physical parameters for active close binaries (CB) of W Ser type based on the interpretation of photometric observations. In the particular case one analyses the light curves of CB RX Cas in the framework of the accretion-disc model explained in the second paper of this series (Djuraevi, 1992a). The change of the light curves with that of the system's physical-activity phase is analysed and the orbital and physical parameters of the system are determined for the maximum, minimum and the transition regime of the physical activity by applying the inverse-problem method described in the third paper of the series (Djuraevi, 1992b). In the paper a graphical illustration of the solutions obtained is also given. 相似文献