全文获取类型
收费全文 | 6681篇 |
免费 | 383篇 |
国内免费 | 38篇 |
专业分类
测绘学 | 173篇 |
大气科学 | 714篇 |
地球物理 | 1755篇 |
地质学 | 2607篇 |
海洋学 | 359篇 |
天文学 | 1166篇 |
综合类 | 28篇 |
自然地理 | 300篇 |
出版年
2024年 | 21篇 |
2023年 | 33篇 |
2022年 | 47篇 |
2021年 | 128篇 |
2020年 | 142篇 |
2019年 | 112篇 |
2018年 | 309篇 |
2017年 | 323篇 |
2016年 | 427篇 |
2015年 | 311篇 |
2014年 | 365篇 |
2013年 | 523篇 |
2012年 | 414篇 |
2011年 | 382篇 |
2010年 | 361篇 |
2009年 | 379篇 |
2008年 | 260篇 |
2007年 | 222篇 |
2006年 | 207篇 |
2005年 | 163篇 |
2004年 | 176篇 |
2003年 | 134篇 |
2002年 | 139篇 |
2001年 | 107篇 |
2000年 | 92篇 |
1999年 | 77篇 |
1998年 | 85篇 |
1997年 | 101篇 |
1996年 | 58篇 |
1995年 | 71篇 |
1994年 | 68篇 |
1993年 | 47篇 |
1992年 | 31篇 |
1991年 | 35篇 |
1990年 | 61篇 |
1989年 | 30篇 |
1988年 | 21篇 |
1987年 | 42篇 |
1986年 | 31篇 |
1985年 | 41篇 |
1984年 | 43篇 |
1983年 | 36篇 |
1982年 | 42篇 |
1981年 | 42篇 |
1980年 | 21篇 |
1979年 | 27篇 |
1978年 | 23篇 |
1977年 | 23篇 |
1975年 | 19篇 |
1973年 | 24篇 |
排序方式: 共有7102条查询结果,搜索用时 0 毫秒
991.
Sébastien Darchen 《Urban geography》2016,37(2):202-222
In this paper, I question whether agglomerations of video game companies in Australia function as clusters (spatially bound) or rather as communities (not spatially bound). The two case studies included in the analysis are the main agglomerations of video companies in Australia—Brisbane and Melbourne. The data have been collected through 21 semi-structured interviews performed between 2012 and 2014. The main findings are as follows: (1) the primary reason that video game companies come together is to share tacit knowledge and skilled labour; (2) these agglomerations do not have the attributes of “creative clusters”; and (3) new technologies enable experienced game developers to operate at the geographic periphery of the main agglomeration of developers. Therefore, to paint a more accurate picture of why some video game companies are successful—beyond simply positive externalities associated with co-localization—I propose the term “networked communities.” This recognizes that social networks at varying scales (local, national, international) are being developed by video game firms in order to thrive and reach a global audience. 相似文献
992.
The discrimination between distinct remote compressions and multiple local stress deviations within a single compressive stress field has been carried out in the central-eastern Iberian Chain, by using structural criteria, computing palaeostress directions, identifying and ‘filtering’ stress deviations, and analysing time relationships. A probabilistic analysis based on a systematic comparison of real and expected frequencies of coexistence of two compressions is applied by means of the χ 2 Test. This allows us to identify those tectonic compressions that behave as independent events from the probabilistic point of view. The results suggest that among five initially defined compression directions only three can be considered as representative of distinct (although partially superposed) externally applied intraplate stress fields: Iberian s.l. (NE-SW), Betic s.l. (NW-SE), and Pyrenean (N-S to NNE-SSW). 相似文献
993.
Thérèse Encrenaz 《Astronomy and Astrophysics Review》1999,9(3-4):171-219
Summary. The exploration of Jupiter, the closest and biggest giant planet, has provided key information about the origin and evolution
of the outer Solar system. Our knowledge has strongly benefited from the Voyager and Galileo space missions. We now have a
good understanding of Jupiter's thermal structure, chemical composition and magnetospheric environment.
There is still debate about the nature of the heating source responsible for the high thermospheric temperatures (precipitating
particles and/or gravity waves). The measurement of elemental abundance ratios (C/H, N/H, S/H) gives strong support to the
“nucleation” formation model, according to which giant planets formed from the accretion of an initial core and the collapse
of the surrounding gaseous protosolar nebula. The D/H and He/He ratios are found to be representative of their protosolar value. The helium abundance, in contrast, appears to be slightly
depleted in the outer envelope with respect to the protosolar value; this departure is interpreted as an evolutionary effect,
due to the condensation of helium droplets in the liquid hydrogen ocean inside Jupiter's interior.
The cloud structure of Jupiter, characterized by the belt-zone system, is globally understood; also present are specific features
like regions of strong infrared radiation (“hot spots”), colder regions (“white ovals”) and the Great Red Spot (GRS). Clouds
were surprisingly absent at the hot spot corresponding to the Galileo probe entry site, and the water abundance measured there
was strongly depleted with respect to the solar O/H value. This probably implies that hot spots are dry, cloud-free regions
of subsidence, while “normal” air, rich in condensibles, is transported upward by convective motions. As a result, the Jovian
meteorology, still based on Halley-type cells, seems to be much more complex than a simple zone-belt system. The nature of
the GRS, a giant anticyclonic storm, colder and higher than its environment, has been confirmed by the Galileo observations,
but its internal structure appears to be very complex.
Strong winds, probably driven by the Jovian internal source, were measured at deep tropospheric levels. The troposphere might
be statically stable at pressures higher than 18 bars, but the extent of this putative radiative layer is still unknown.
Received 23 November 1998 相似文献
994.
Light element nucleosynthesis is an important chapter of nuclear astrophysics. Specifically, the rare and fragile light nuclei
Lithium, Beryllium and Boron (LiBeB) are not generated in the normal course of stellar nucleosynthesis (except 7Li) and are, in fact, destroyed in stellar interiors. This characteristic is reflected in the low abundance of these simple
species. Up to recently, the most plausible interpretation was that Galactic Cosmic Rays (GCR) interact with interstellar
CNO to form LiBeB. Other origins have been also identified: primordial and stellar (7Li) and supernova neutrino spallation (7Li and 11B). In contrast, 9Be, 10B and 6Li are pure spallative products. This last isotope presents a special interest since the 6Li/7Li ratio has been measured recently in a few halo stars offering a new constraint on the early galactic evolution of light
elements. Optical measurements of the beryllium and boron abundances in halo stars have been achieved by the 10 meter KECK
telescope and the Hubble Space Telescope. These observations indicate a quasi linear correlation between Be and B vs Fe, at
least at low metallicity, which, at first sight, is contradictory to a dominating GCR origin of the light elements which predicts
a quadratic relationship. As a consequence, the theory of the origin and evolution of LiBeB nuclei has to be refined. Aside
GCRs, which are accelerated in the general interstellar medium (ISM) and create LiBeB through the break up of CNO by fast
protons and alphas, Wolf-Rayet stars (WR) and core collapse supernovae (SNII) grouped in superbubbles could produce copious
amounts of light elements via the fragmentation in flight of rapid carbon and oxygen nuclei colliding with H and He in the
ISM. In this case, LiBeB would be produced independently of the interstellar medium chemical composition and thus a primary
origin is expected. These different processes are discussed in the framework of a galactic evolutionary model. More spectroscopic
observations (specifically of O, Fe, Li, Be, B) in halo stars are required for a better understanding of the relative contribution
of the various mechanisms. Future tests on the injection and acceleration of nuclei by supernovae and Wolf Rayet relying on
gamma-ray line astronomy will be invoked in the perspective of the European INTEGRAL satellite.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
995.
The advent of new and better instruments in space has resulted in a considerable increase in the number of solar gamma-ray events (GRE) detected. In this paper, we analyze available SMM/GRS and GRANAT/PHEBUS data on the hard X-ray and gamma-ray events, and their associations with solar proton events (SPE) at the Earth's orbit, for the observation period of 1980–1995. About 58% of the GREs under study were found to be SPE-related ones. Size (frequency) distributions have been obtained, for the first time, for the events with different types of emissions (bremsstrahlung, narrow GR lines, positron annihilation line, neutron capture line, SPEs, etc.). We discuss the possible relationships between size distributions implied by the parameter correlation. The distribution for GR events turns out to be generally harder than that for X-ray bursts. The GREs involving energetic particles in space are shown to have a harder frequency distribution in comparison with that for GREs without detectable SPEs. There is also a tendency for the GREs with highest fluences to be related with SPEs. Finally, no correlation seems to exist between the GRL fluence and maximum flux of >10 MeV protons near the Earth. 相似文献
996.
Tectonic setting of the Azores Plateau deduced from a OBS survey 总被引:1,自引:0,他引:1
Miranda J.M. Mendes Victor L.A. Simões J.Z. Luis J.F. Matias L. Shimamura H. Shiobara H. Nemoto H Mochizuki H. Hirn A. Lépine J.C. 《Marine Geophysical Researches》1998,20(3):171-182
The studies of Azores seismicity generally show shocks with either normal faulting or right-lateral strike-slip along the ESE direction, compatible with a eastward relative motion of the Eurasian (EU) relative to the African (AF) plate. However, the 1 January 1980 earthquake was interpreted as a clear left-lateral strike-slip shock along the N150E direction. This pattern is difficult to explain in terms of the relative motion between the EU, AF and North American (NA) plates: all available models for the present day movement of this triple junction fail to explain the regional variability in the stress conditions of the area. Here we present data from a 34-day long Ocean Bottom Seismograph array deployment. We show that the seismicity is distributed along a band aligned with the island chain itself, and is concentrated along several faults with an approximate N150E strike, cutting the Azores plateau in all the area covered by the OBS network. The combination of these new results with other geophysical data permits us to conclude that the tectonic setting of the Azores plateau is characterised by the existence of two sets of faults, in the N120E and N150E directions, defining several crustal blocks, whose relative motion accommodates the interaction of the three megaplates. The deformation of these tectonic blocks is probably driven by the shear between the EU and AF plates. This model explains well the spatial variability of the stress conditions in the Azores domain, the combination of dextral and sinistral strike slip mechanisms and the observed seismotectonics of the Azores islands. 相似文献
997.
J.-J. Cornée J. Butterlin P. Saint-Marc J.-P. Rehault C. Honthaas A. Laurenti-Ribaud C. Chaix M. Villeneuve Y. Anantasena 《Geo-Marine Letters》1998,18(1):34-39
In December 1995 we dredged early Miocene coral-reef carbonates and early/middle Pliocene slope carbonates outcropping on
the submerged Rama Ridge. This indicates that some of the Banda Sea Ridges were present during early Miocene times. Subsequent
major tectonic subsidence occurred between middle Miocene and early Pliocene times. These results concur with the hypothesis
of a relatively recent age for the North Banda Sea basement.
Received: 5 March 1997 / Revision received: 23 October 1997 相似文献
998.
Based on the analysis of geological, technical and hydrometeorological conditions of the coastal part of the Arctic offshore, a concept of its hydrocarbon resource development is submitted. 相似文献
999.
--A tensiometric method (Wilhelmy plate) is used to study Wood's metal dynamic wettability on specially prepared surfaces of quartz single crystals at low velocities of immersion (2 to 16 wm/s). After correction for buoyancy, the force exerted on the plate by the molten metal is used to derive the unit work of wetting n cos where n is the Wood's metal surface tension and is the interfacial contact angle. Tests at different temperatures (85, 120 and 200°C) show that below 120°C, viscosity effects cannot be neglected. At an immersion/emersion rate of 2 wm/s, n cos is in the range 0.417-0.444 N/m at 120°C, and 0.432-0.458 N/m at 200°C. These figures allow the conversion of injection pressures into capillary diameters during Wood's metal injection tests. The method is promising since it may be used in porous materials to check the sensitivity of the unit work of wetting n cos to parameters such as roughness and mineralogy, which are known to vary in a wide range within the pores and cracks of rocks. 相似文献
1000.
A method to construct a nomogram of the daytime mixed-layer-height evolution is presented. The nomogram will be specific for a given location and land surface type and is intended to be an easy tool to achieve a general understanding of mixed-layer behaviour. Also it is a pedagogical graphical one-pager that displays the bulk of data that controls the evolution of the mixed layer. Nomograms from northern, central and southern Europe are presented and discussed. Comparison with data from two sites shows good agreement although the nomograms overestimated the mixing height when it was low. 相似文献