全文获取类型
收费全文 | 2266篇 |
免费 | 107篇 |
国内免费 | 39篇 |
专业分类
测绘学 | 95篇 |
大气科学 | 177篇 |
地球物理 | 870篇 |
地质学 | 767篇 |
海洋学 | 164篇 |
天文学 | 175篇 |
综合类 | 14篇 |
自然地理 | 150篇 |
出版年
2022年 | 15篇 |
2021年 | 24篇 |
2020年 | 54篇 |
2019年 | 35篇 |
2018年 | 65篇 |
2017年 | 55篇 |
2016年 | 91篇 |
2015年 | 80篇 |
2014年 | 76篇 |
2013年 | 129篇 |
2012年 | 105篇 |
2011年 | 127篇 |
2010年 | 114篇 |
2009年 | 130篇 |
2008年 | 105篇 |
2007年 | 76篇 |
2006年 | 72篇 |
2005年 | 46篇 |
2004年 | 51篇 |
2003年 | 53篇 |
2002年 | 39篇 |
2001年 | 57篇 |
2000年 | 37篇 |
1999年 | 38篇 |
1998年 | 38篇 |
1997年 | 39篇 |
1996年 | 32篇 |
1995年 | 25篇 |
1994年 | 19篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1990年 | 26篇 |
1989年 | 21篇 |
1988年 | 20篇 |
1987年 | 20篇 |
1986年 | 23篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1983年 | 31篇 |
1982年 | 26篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1979年 | 24篇 |
1978年 | 23篇 |
1977年 | 17篇 |
1976年 | 20篇 |
1975年 | 19篇 |
1973年 | 20篇 |
1972年 | 16篇 |
1971年 | 15篇 |
排序方式: 共有2412条查询结果,搜索用时 328 毫秒
21.
Gravitational spreading of mountain ridges displays primary disequilibrium of flysch mountain areas of the Czech Carpathians.
The progression of various types of mass movements is a product of long-term ridge disintegration and is predisposed by the
geological structure of the area and the upper Tertiary-Quaternary morphogenesis of the mountain area. Deep-seated slope deformations
are spatially interconnected by the occurrence of some other types of slope deformations (e.g. debris flows, debris slides,
slumps, rock avalanches, etc.), which pose a considerable risk for the existence of human society. An important causative
factor in these dynamically developing hazardous processes is, among other factors, the way in which land has been used in
the last three centuries. Therefore, the occurrence of various types of slope deformations is studied in terms of their relation
to deep-seated gravitational deformations and in terms of other limiting factors (structural geological, morphological and
climatic factors, manmade impacts, etc.). The paper presents several case studies of slope deformations (Velká Čantoryje Mt,
Lysá hora Mt, Ropice Mt and Smrk Mt) in the area of the Outer Carpathians within the territory of the Czech Republic and also
adverts to some consequences in terms of the socioeconomic structure of the landscape. 相似文献
22.
M. Čadež 《Pure and Applied Geophysics》1960,47(1):172-182
Zusammenfassung Man beobachtet Antizyklonen, die als Folge einer Konzentration von Kaltluftmasssen auf ein kleineres Gebiet gedeutet werden können. Die Konzentration der Kaltluft ist durch die Umwandlung der kinetischen Energie der Kaltluft in potentielle Energie oder durch die Wärmezufuhr der kalten Luft bedingt. Solche Antizyklonen bilden sich oft in Berggebieten, da dort wegen der grossen äusseren Reibung die erwähnte Umwandlung der Energie beschleunigt wird. Wie gross solche antizyklogenetischen Effekte sein können, ist berechnet.
Summary The origin of some anticyclones can be explained as a consequence of the concentration of the cold air on a smaler area. The concentration of the cold air is caused by a transformation of the kinetic energy of the cold air into the potential energy or by the heating of the cold air. Such anticyclones often appear in mountain regions where the transformation of the mentioned energy is more intense. The intensity of such anticyclogenetical effects is evaluated.相似文献
23.
M. Čadež 《Pure and Applied Geophysics》1963,54(1):182-189
Résumé Dans cette étude l'explication de la formation des nuages Ac tra part de la supposition que l'air dans ce type de nuages est plus froid que l'air environnant, ce qui provoque certains courants convectifs dans la région du nuage. Ces courants ressemblent à ceux qui sont supposés par la théorie thermoconvective actuelle. D'après notre avis se trouvent des courants descendants audessous des petits nuages qui composent l'Ac tra, et les petits nuages qui forment l'Ac tra sont des corps séparés dont la température est moindre que la température de l'air environnant: c'est pour cela qu'ils tombent. Au contraire, d'après la théorie thermoconvective actuelle, l'air audessous de petits nuages monte et dans la distribution de la température des discontinuités n'existent pas.
Rapport présenté le 26 Avril 1962 à la Xème Assemblée Générale de laSocietà Italiana di Geofisica e Meteorologia (26–28 Avril 1962) 相似文献
Summary In this paper the explanation of the formation of clouds Ac tra is based on the assumption that the air in the cloud is colder than the surrounding air, causing convective currents in the region of the cloud. These currents are not unlike those assumed by the existing thermoconvective theory. According to the author's view there are descending currents under the cloudlets of which the Ac tra is made, and these cloudlets are separate bodies at a lower temperature than that of the surrounding air, so that the cloudlets fall. On the contrary, according to the existing thermoconvective theory, the air under the cloudlets rises and there are no discontinuities in the distribution of the temperature.
Rapport présenté le 26 Avril 1962 à la Xème Assemblée Générale de laSocietà Italiana di Geofisica e Meteorologia (26–28 Avril 1962) 相似文献
24.
Karel Kučera 《Studia Geophysica et Geodaetica》1966,10(4):411-421
Summary In [1] the author has put forward a three-direction method, a general way of adjustment of angular observations in incomplete
sets by the method of extending into angular combinations, and the definition of mean weightP
*. In this article the question is dealt with as a whole. In the three-direction methods>3 triangulation directions are measured in direction triplets 123, 234, 345,… …,s12, while in the method of measuring single angles at the station they are measured in angles 12, 23, 34, 45, …,s1. The advantage of transition from angles to direction triplets rests, besides in saving 31% of pointings, above all in certain
possibility of elimination of the horizontal refraction, which follows from this. The treatise of the relation between the
method of measurement and the refraction is not included into this article, as it would go beyond its scope. The fact that
adjusted directions, with the exception of the stations having four directions, are not of equal weight, is proper not only
to the three-direction method. The non-equality of weights is even more conspicuous in the method of measuring single angles
at the station, and it appears already at the stations having four directions. In author's view the homogeneity of observation
elements is more important than the homogeneity of weights from the point of view of adjustment at the station; therefore
the direction triplets ought not to exist abreast with the angles in one programme, and especially the number of observations
ought to be constant at one station with adjusted direction of homogeneous mean weight in the net.
This transition from angles to direction triplets could also provoke a comment that simultaneous visibility of three adjoining
directions occurs less often than of two such directions. The author adds to this that nowadays the causes of this phenomenon,
following from unsuitable technique, must be eliminated. It is just air limpidity that ought to define the visibility, not
unsufficient or everywhere equal intensity of light of reflectors, or too long sides of the triangulation net. Recent approach
to this problem requires simultaneous visibility of all directions during most of the days of observation. In connection with
the out-of=date technique, the methods of angular observation often have one unfavourable character: they are the cause of
the accumulation of observations of “always visible” directions. The supposed merit of angles thus turns into their imperfection.
Адрес: Politickych vězňů 12, Praha 1-Nové Město 相似文献
Адрес: Politickych vězňů 12, Praha 1-Nové Město 相似文献
25.
Mjelde Rolf Fjellanger Jan Petter Digranes Per Kodaira Shuichi Shimamura Hideki Shiobara Hajime 《Marine Geophysical Researches》1997,19(1):81-96
A 140 km long wide-angle seismic profile has been acquired by use of 6 Ocean Bottom Seismographs across the Jan Mayen Ridge, North Atlantic. The profile was acquired twice; once with a traditionally tuned standard source and secondly with a somewhat smaller source tuned on the first bubble pulse. Analysis of the frequency content of the data reveals that the single-bubble source within the 10-15 Hz frequency range generates a signal with a level about 5 db above that of the standard source. These differences can partly be related to differences in airgun depth. The higher output level for these frequencies enables the single-bubble source to resolve intra-crustal structures with a higher degree of certainty, when compared to the data acquired by use of the standard source array. The standard source seems to generate slightly more energy for frequencies around 6 Hz, probably due to the use of a large 1200 in/sup3 gun in this array. These low frequencies a re of importance for mapping of lower crustal and upper mantle structures, and it is recommended that this is taken into account when seismic sources for mapping of deep crustal and upper mantle structures are designed. 相似文献
26.
Sheet flow and suspension of sand in oscillatory boundary layers 总被引:1,自引:0,他引:1
after revisionTime-dependent measurements of flow velocities and sediment concentrations were conducted in a large oscillating water tunnel. The measurements were aimed at the flow and sediment dynamics in and above an oscillatory boundary layer in plane bed and sheet-flow conditions. Two asymmetric waves and one sinusoidal wave were imposed using quartz sand with D50 = 0.21 mm. A new electro-resistance probe with a large resolving power was developed for the measurement of the large sediment concentrations in the sheet-flow layer. The measurements revealed a three layer transport system consisting of a pick-up/deposition layer, an upper sheet flow layer and a suspension layer.In the asymmetric wave cases the total net transport was directed “onshore” and was mainly concentrated in the thin sheet flow layer (< 0.5 cm) at the bed. A small net sediment flux was directed “offhore” in the upper suspension layer. The measured flow velocities, sediment concentrations and sedimenl fluxes showed a good qualitative agreement with the results of a (numerical) 1DV boundary-layer flow and transport model. Although the model did not describe all the observed processes in the sheet-flow and suspension layer, the computational results showed a reasonable agreement with measured net transport rates in a wide range of asymmetric wave conditions. 相似文献
27.
In order to prevent the generation of spurious free sub- and superharmonics of random waves in a laboratory channel, the control signal for the wave board has to be derived according to a higher-order wave theory. An expression for this control signal has been derived with the perturbation method of multiple scales. It is much less complex and requires less computation time than the expressions obtained from the full second-order theory. The new method for second-order subharmonics was verified experimentally for waves with bichromatic and continuous first-order spectra. The data were analysed with the complex-harmonic principal-component analysis to reduce the influence of noise. 相似文献
28.
Jan Kohlmeyer 《Marine Ecology》1984,5(4):329-378
Abstract. Marine Ascomycetes, Basidiomycetes and Deuteromycetes were collected in tropical and subtropical regions (Australia, Belize, Fiji, Hawaii, Marshall Islands, Mexico, New Zealand, Palau, Thailand), and the known range of distribution for these fungi was extended. Exclusively tropical are 27 taxa, 9 are probably restricted to the tropics also, and 11 are cosmopolitan. Distribution maps are given for 5 taxa. New species (4), varieties (3), and combinations (2) of Ascomycetes are proposed, and keys to the taxa of Halosarpheia and Lulworthia are presented. Most of the species are decomposers of mangrove parts or of detritus in sandy beaches. Nine new host plants were found. Marine Ascomycetes were discovered for the first time living in shells of foraminifera. 相似文献
29.
30.
Modest observations and numerical experiments were conducted to investigate circulation and brackish water dispersal in a
coastal lagoon southwest of Taiwan. The Chi-Ku Lagoon, partially shielded from the sea by a string of sandbar barriers with
two entrances among them, receives modest and episodic runoff from Chi-Ku Stream. Flood and ebb tidal streams entering and
leaving the two entrances are found to converge and diverge in a flow stagnation area inside the lagoon. Under weak wind conditions,
brackish water is preferentially retained in the flow stagnation area. Besides the observations, scenario runs using a three-dimensional
numerical model also indicate strong modulation by monsoon winds. Both summer southwest monsoon and winter northeast monsoon
reduce brackish water retention; the latter is found to be more effective.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献