全文获取类型
收费全文 | 732篇 |
免费 | 17篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 40篇 |
大气科学 | 54篇 |
地球物理 | 205篇 |
地质学 | 261篇 |
海洋学 | 57篇 |
天文学 | 101篇 |
自然地理 | 35篇 |
出版年
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 21篇 |
2015年 | 15篇 |
2014年 | 17篇 |
2013年 | 37篇 |
2012年 | 8篇 |
2011年 | 29篇 |
2010年 | 43篇 |
2009年 | 41篇 |
2008年 | 29篇 |
2007年 | 32篇 |
2006年 | 26篇 |
2005年 | 27篇 |
2004年 | 22篇 |
2003年 | 19篇 |
2002年 | 26篇 |
2001年 | 16篇 |
2000年 | 8篇 |
1999年 | 17篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1983年 | 8篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1972年 | 7篇 |
1971年 | 5篇 |
1966年 | 6篇 |
1964年 | 7篇 |
1960年 | 6篇 |
1952年 | 5篇 |
1949年 | 4篇 |
1948年 | 5篇 |
排序方式: 共有753条查询结果,搜索用时 15 毫秒
121.
Gerhard Hensler 《Astrophysics and Space Science》1999,265(1-4):397-407
A two-dimensional chemodynamical model of the Milky Way Galaxy is presented that can account for the structural, kinematical,
and chemical pecularities of the galactic components in a self-consistent way. The dynamics of three stellar components and
the multi-phase interstellar medium consisting of clouds and intercloud gas are followed in detail. Mass interchange and energetic
interaction processes between the stars and the gas phases are treated simultaneously according to the astrophysical experience
including star formation, supernovae type I and II, planetary nebulae, stellar winds, evaporation and condensation, drag,
cloud collisions, heating and cooling, and stellar nucleosynthesis. These processes are coupling large ranges on temporal
and spatial scales, and allow for feedback and self-regulation mechanisms, which play a significant role in galactic evolution.
In comparison with observations the capability of the chemodynamical treatment is convincingly proved by the excellent agreement
with various observations. In addition, also well-known problems (G-dwarf problem, the discrepancy between local effective
yields, etc.), which so far could be only explained by artificial constraints, are solved in the global scenario. Here we
wish also to focus on temporal behaviours of the radial abundance gradient and abundance ratios in order to stimulate further
more specific observations and to make particular predictions which can test the validity of used model ingredients like stellar
yields.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
122.
Monthly mean surface pressure patterns in the European area are reconstructed for those winter and summer seasons of the 16th century with outstanding climatic anomalies being either widespread over Europe or remarkably intensive in some European regions. From the available documentary information about weather characteristics and their sequences, it proved possible to infer prevalent processes of lower tropospheric advection of typical air masses and to assess the position and strength of major surface pressure centres on a monthly scale. For comparison with modern pressure patterns, monthly mean sea level pressure (SLP) grids from the 20th century have been selected for seasons with similar climatic anomalies. There are broad coincidences between these pressure patterns of the 16th and the 20th centuries except for cold summer seasons. Finally, results from the 16th century are discussed in terms of circulation dynamics (different phases of the North Atlantic Oscillation (NAO) in winter, decreasing frequency of anticyclonic ridging in summer). 相似文献
123.
Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps) 总被引:52,自引:2,他引:50
Gerhard Vavra Rolf Schmid Dieter Gebauer 《Contributions to Mineralogy and Petrology》1999,134(4):380-404
Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone
(IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments
in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons
in the associated leucosomes. The primary morphology and Th-U chemistry of the zircon overgrowth in the restites show a systematic
variation apparently corresponding to the metamorphic grade: prismatic (prism-blocked) low-Th/U types in the upper amphibolite
facies, stubby (fir-tree zoned) medium-Th/U types in the transitional facies and isometric (roundly zoned) high-Th/U types
in the granulite facies. The primary crystallization ages of prograde zircons in the restites and magmatic zircons in the
leucosomes cannot be resolved from each other, indicating that anatexis in large parts of the IZ was a single and short lived
event at 299 ± 5 Ma (95% c. l.). Identical U/Pb ages of magmatic zircons from a metagabbro (293 ± 6 Ma) and a metaperidotite
(300 ± 6 Ma) from the Mafic Formation confirm the genetic context of magmatic underplating and granulite facies anatexis in
the IZ. The U-Pb age of 299 ± 5 Ma from prograde zircon overgrowths in the metasediments also shows that high-grade metamorphic
(anatectic) conditions in the IZ did not start earlier than 20 Ma after the Variscan amphibolite facies metamorphism in the
adjacent Strona–Ceneri Zone (SCZ). This makes it clear that the SCZ cannot represent the middle to upper crustal continuation
of the IZ. Most parts of zircon crystals that have grown during the granulite facies metamorphism became affected by alteration
and Pb-loss. Two types of alteration and Pb-loss mechanisms can be distinguished by cathodoluminescence imaging: zoning-controlled
alteration (ZCA) and surface-controlled alteration (SCA). The ZCA is attributed to thermal and/or decompression pulses during
extensional unroofing in the Permian, at or earlier than 249 ± 7 Ma. The SCA is attributed to the ingression of fluids at
210 ± 12 Ma, related to hydrothermal activity during the breakup of the Pangaea supercontinent in the Upper Triassic/Lower
Jurassic.
Received: 7 July 1998 / Accepted: 4 November 1998 相似文献
124.
Knittel Lukas Wichtmann Torsten Niemunis Andrzej Huber Gerhard Espino Edgar Triantafyllidis Theodoros 《Acta Geotechnica》2020,15(8):2075-2088
Acta Geotechnica - The elastic stiffness of a fine sand at small to moderate strains ( $$\varepsilon \le 2 \times 10^{-4}$$ ) has been studied based on cyclic triaxial tests on cube-shaped samples... 相似文献
125.
126.
A hydrogeological study was completed within a sub-catchment of the Zerka River drainage basin, in western Jordan. The system
is characterized by anticlinal bending with an axis trending SSW–NNE and plunging a few degrees in the SSW direction. The
anticlinal structure diverts groundwater flow towards the SSW while the strike-slipe faults cause the groundwater to diverge
where the fault is perpendicular to the groundwater flow lines, and to converge where the fault is parallel to the groundwater
flow lines. A direct relationship was found between the location of springs and the type of groundwater flow with regard to
the amount of discharge wherein large spring discharges are located in zones of converging groundwater flow lines. In areas
where faults are not abundant, the groundwater retention time in the aquifers is long and a zonation of the electrical conductivity
was detected due to mineral dissolution. By controlling groundwater flow, the anticlinal setting produces three genetic groups
of groundwater flow systems: (1) alkaline–earth alkaline water which is predominately a bicarbonate-type composition, (2)
alkaline–earth alkaline water which is predominately bicarbonate–sulfate, and (3) alkaline–earth alkaline water with a high
alkaline component. 相似文献
127.
Laboratory experiments show that dusty bodies in a gaseous environment eject dust particles if they are illuminated. We find that even more intense dust eruptions occur when the light source is turned off. We attribute this to a compression of gas by thermal creep in response to the changing temperature gradients in the top dust layers. The effect is studied at a light flux of 13 kW/m2 and 1 mbar ambient pressure. The effect is applicable to protoplanetary disks and Mars. In the inner part of protoplanetary disks, planetesimals can be eroded especially at the terminator of a rotating body. This leads to the production of dust which can then be transported towards the disk edge or the outer disk regions. The generated dust might constitute a significant fraction of the warm dust observed in extrasolar protoplanetary disks. We estimate erosion rates of about 1 kg s?1 for 100 m parent bodies. The dust might also contribute to subsequent planetary growth in different locations or on existing protoplanets which are large enough not to be susceptible to particle loss by light induced ejection. Due to the ejections, planetesimals and smaller bodies will be accelerated or decelerated and drift outward or inward, respectively. The effect might also explain the entrainment of dust in dust devils on Mars, especially at high altitudes where gas drag alone might not be sufficient. 相似文献
128.
Sven Petersen Peter M. Herzig Thomas Kuhn Leander Franz Mark D. Hannington Thomas Monecke 《Marine Georesources & Geotechnology》2013,31(3):175-193
ABSTRACT From September to October 2002, shallow drilling, using the submersible (5 m) Rockdrill of the British Geological Survey and the German R/V Sonne revealed critical information on the subsurface nature of two distinct hydrothermal systems in the New Ireland fore-arc and the Manus Basin of Papua New Guinea. Drilling at Conical Seamount significantly extends the known surface extent of the previously discovered vein-style gold mineralization (up to 230 g/t Au) at this site. Drilling the conventional PACMANUS volcanic-hosted massive sulfide deposit recovered complexly textured massive sulfide with spectacular concentrations of gold in several core sections including 0.5 m @ 28 g/t Au, 0.35 m @ 30 g/t Au, and 0.20 m @ 57 g/t Au. Shallow drilling is a fast and cost efficient method that bridges the gap between surface sampling and deep (ODP) drilling and will become a standard practice in the future study of seafloor hydrothermal systems and massive sulfide deposits. 相似文献
129.
Impact of loading displacements on SLR-derived parameters and on the consistency between GNSS and SLR results 总被引:5,自引:4,他引:1
Krzysztof Sośnica Daniela Thaller Rolf Dach Adrian Jäggi Gerhard Beutler 《Journal of Geodesy》2013,87(8):751-769
Displacements of the Earth’s surface caused by tidal and non-tidal loading forces are relevant in high-precision space geodesy. Some of the corrections are recommended by the international scientific community to be applied at the observation level, e.g., ocean tidal loading (OTL) and atmospheric tidal loading (ATL). Non-tidal displacement corrections are in general recommended not to be applied in the products of the International Earth Rotation and Reference Systems Service, in particular atmospheric non-tidal loading (ANTL), oceanic and hydrological non-tidal corrections. We assess and compare the impact of OTL, ATL and ANTL on SLR-derived parameters by reprocessing 12 years of SLR data considering and ignoring individual corrections. We show that loading displacements have an influence not only on station long-term stability, but also on geocenter coordinates, Earth Rotation Parameters, and satellite orbits. Applying the loading corrections reduces the amplitudes of annual signals in the time series of geocenter and station coordinates. The general improvement of the SLR station 3D coordinate repeatability when applying OTL, ATL and ANTL corrections are 19.5 %, 0.2 % and 3.3 % respectively, w.r.t. the solutions without loading corrections. ANTL corrections play a crucial role in the combination of optical (SLR) and microwave (GNSS, VLBI, DORIS) space geodetic observation techniques, because of the so-called Blue-Sky effect: SLR measurements can be carried out only under cloudless sky conditions—typically during high air pressure conditions, when the Earth’s crust is deformed, whereas microwave observations are weather-independent. Thus, applying the loading corrections at the observation level improves SLR-derived products as well as the consistency with microwave-based results. We assess the Blue-Sky effect on SLR stations and the consistency improvement between GNSS and SLR solutions when ANTL corrections are included. The omission of ANTL corrections may lead to inconsistencies between SLR and GNSS solutions of up to 2.5 mm for inland stations. As a result, the estimated GNSS–SLR coordinate differences correspond better to the local ties at the co-located stations when applying ANTL corrections. 相似文献
130.
Christian Hirt Martin Schmitz Uwe Feldmann-Westendorff Gerhard Wübbena Cord-Hinrich Jahn Günter Seeber 《GPS Solutions》2011,15(2):149-159
The method of geometric-astronomical leveling is presented as a suited technique for the validation of GNSS (Global Navigation
Satellite System) heights. In geometric-astronomical leveling, the ellipsoidal height differences are obtained by combining
conventional spirit leveling and astronomical leveling. Astronomical leveling with recently developed digital zenith camera
systems is capable of providing the geometry of equipotential surfaces of the gravity field accurate to a few 0.1 mm per km.
This is comparable to the accuracy of spirit leveling. Consequently, geometric-astronomical leveling yields accurate ellipsoidal
height differences that may serve as an independent check on GNSS height measurements at local scales. A test was performed
in a local geodetic network near Hanover. GPS observations were simultaneously carried out at five stations over a time span
of 48 h and processed considering state-of-the-art techniques and sophisticated new approaches to reduce station-dependent
errors. The comparison of GPS height differences with those from geometric-astronomical leveling shows a promising agreement
of some millimeters. The experiment indicates the currently achievable accuracy level of GPS height measurements and demonstrates
the practical applicability of the proposed approach for the validation of GNSS height measurements as well as the evaluation
of GNSS height processing strategies. 相似文献