全文获取类型
收费全文 | 1405篇 |
免费 | 32篇 |
国内免费 | 15篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 136篇 |
地球物理 | 372篇 |
地质学 | 598篇 |
海洋学 | 111篇 |
天文学 | 159篇 |
综合类 | 3篇 |
自然地理 | 57篇 |
出版年
2021年 | 12篇 |
2018年 | 25篇 |
2017年 | 14篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 34篇 |
2013年 | 40篇 |
2012年 | 33篇 |
2011年 | 52篇 |
2010年 | 37篇 |
2009年 | 49篇 |
2008年 | 54篇 |
2007年 | 36篇 |
2006年 | 46篇 |
2005年 | 38篇 |
2004年 | 34篇 |
2003年 | 31篇 |
2002年 | 47篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 16篇 |
1998年 | 27篇 |
1997年 | 16篇 |
1996年 | 19篇 |
1995年 | 23篇 |
1993年 | 19篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1976年 | 15篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 17篇 |
1970年 | 11篇 |
1959年 | 15篇 |
1956年 | 12篇 |
1954年 | 13篇 |
1948年 | 16篇 |
1943年 | 11篇 |
1941年 | 11篇 |
排序方式: 共有1452条查询结果,搜索用时 31 毫秒
121.
Using paleoclimate proxy-data to select optimal realisations in an ensemble of simulations of the climate of the past millennium 总被引:1,自引:0,他引:1
Hugues Goosse Hans Renssen Axel Timmermann Raymond S. Bradley Michael E. Mann 《Climate Dynamics》2006,27(2-3):165-184
We present and describe in detail the advantages and limitations of a technique that combines in an optimal way model results and proxy-data time series in order to obtain states of the climate system consistent with model physics, reconstruction of past radiative forcing and proxy records. To achieve this goal, we select among an ensemble of simulations covering the last millennium performed with a low-resolution 3-D climate model the ones that minimise a cost function. This cost function measures the misfit between model results and proxy records. In the framework of the tests performed here, an ensemble of 30 to 40 simulations appears sufficient to reach reasonable correlations between model results and reconstructions, in configurations for which a small amount of data is available as well as in data-rich areas. Preliminary applications of the technique show that it can be used to provide reconstructions of past large-scale temperature changes, complementary to the ones obtained by statistical methods. Furthermore, as model results include a representation of atmospheric and oceanic circulations, it can be used to provide insights into some amplification mechanisms responsible for past temperature changes. On the other hand, if the number of proxy records is too low, it could not be used to provide reconstructions of past changes at a regional scale. 相似文献
122.
Storglaciären in northernmost Sweden has the world's longest ongoing continuous mass-balance record, starting in 1946. To extend this mass-balance record, we have reconstructed summer (bS) and winter (bW) mass balances separately back to the mass balance year 1780/81 with annual resolution. We used tree-ring data for bS and a set of circulation indices, based on the sea-level pressure, for bW. Both proxies have correlation coefficients with respective mass balance components of ca. 0.7. The reconstructed net balance (bN) of Storglaciären was well correlated to the observations during 1946-1980 (r = 0.8, p < 0.05). Our reconstruction agrees well with previously obtained results of northern Sweden glacier variability, where the predominantly positive bN years between 1890 and 1910 correspond to the well documented post-Little Ice Age advance of Storglaciären. Furthermore, the results suggest that bS, as a function of summer temperatures, is more important than bW in determining the bN, which is contrary to glaciers in the maritime parts of western Scandinavia. In general, bN has been negative over the last 220 yr, suggesting a predomination of continental conditions over northern Sweden. However, the influence of bW increased in the late twentieth century, indicating a shift to a more oceanic climate regime. 相似文献
123.
Peter Brack Hans Rieber Roland Mundil Wolfgang Blendinger Florian Maurer 《Swiss Journal of Geoscience》2007,100(3):327-348
The depositional architecture and the geometric relationships between platform-slope deposits and basinal sediments along
with paleontological evidence indicate the time interval of the younger Anisian Reitziites reitzi ammonoid zone to largely represent the main stage of platform aggradation at the Cernera and Bivera/Clapsavon carbonate platforms.
Published and new U-Pb age data of zircons from volcaniclastic layers bracketing the stratigraphic interval of platform growth
constrain the duration of platform evolution to a time span shorter than 1.8±0.7m.y., probably in the order of 0.5-1m.y.,
reflecting fast rates of vertical platform aggradation exceeding 500 m/m.y. In the range of growth potentials for shallow-water
carbonate systems estimated in relation to the time span of observation, this high rate is in agreement with values for short
intervals of 105-106yrs (e.g., Schlager 1999).
After drowning, the platforms at Cernera and Bivera/Clapsavon were blanketed by thin pelagic carbonates. On the former platform
flanks the draping sediments in places comprise red nodular pelagic limestones (Clapsavon Limestone) similar in facies to
the Han Bulog Limestones occurring elsewhere in Middle Triassic successions of the Mediterranean Tethys. The drowning of vast
areas of former carbonate platforms possibly triggered the onset of bottom-water circulation in adjacent basins as suggested
by the abrupt transition from laminated to bioturbated pelagic nodular limestones in the Buchenstein Formation which occurred
close to the time of initial platform submergence. During the Late Ladinian the topographic features of the drowned platforms
were onlapped by rapidly deposited, predominantly clastic successions including coarse breccias and volcanic rocks sealing
and preserving the peculiar stratigraphic setting. 相似文献
124.
Nathan Roche Steve Eales & Hans Hippelein 《Monthly notices of the Royal Astronomical Society》1998,295(4):946-958
We investigate the angular correlation function, ο(θ), of the galaxies detected in the 2.1-μm K ' band in 17 fields (101.5 arcmin2 in total), each containing a z ∼1.1 radio galaxy. There is a significant detection of galaxy clustering at a limit of K ∼20, with a ο(θ) amplitude similar to that estimated by Carlberg et al. at K =21.5. The ο(θ) amplitudes of these K -limited samples are higher than expected from the faint galaxy clustering in the blue and red passbands, but consistent with a pure luminosity evolution model if clustering is stable (ε=0) and the correlation function of early-type galaxies is steeper than that of spirals.
We do not detect a significant cross-correlation between the radio galaxies and the other galaxies in these fields. The upper limits on the cross-correlation are consistent with a mean clustering environment of Abell class 0 for z ∼1.1 radio galaxies, similar to that observed for radio galaxies at z ∼0.5, but would argue against an Abell class 1 or richer environment. As Abell 0 clustering around the radio galaxies would not significantly increase the ο(θ) amplitude of galaxies in these fields, stable clustering with a steep ξ( r ) for E/S0 galaxies appears to remain the most likely interpretation of the ο(θ) amplitude.
At K ≤20, the number of galaxy–galaxy pairs of 2–3 arcsec separation exceeds the random expectation by a factor of 2.15±0.26. The excess of close pairs is comparable to that previously reported for R -band data, and consistent with a ∼(1+ z )2 evolution of the galaxy merger rate. 相似文献
We do not detect a significant cross-correlation between the radio galaxies and the other galaxies in these fields. The upper limits on the cross-correlation are consistent with a mean clustering environment of Abell class 0 for z ∼1.1 radio galaxies, similar to that observed for radio galaxies at z ∼0.5, but would argue against an Abell class 1 or richer environment. As Abell 0 clustering around the radio galaxies would not significantly increase the ο(θ) amplitude of galaxies in these fields, stable clustering with a steep ξ( r ) for E/S0 galaxies appears to remain the most likely interpretation of the ο(θ) amplitude.
At K ≤20, the number of galaxy–galaxy pairs of 2–3 arcsec separation exceeds the random expectation by a factor of 2.15±0.26. The excess of close pairs is comparable to that previously reported for R -band data, and consistent with a ∼(1+ z )
125.
The application of kriging-based geostatistical algorithms to integrate large-scale seismic data calls for direct and cross variograms of the seismic variable and primary variable (e.g., porosity) at the modeling scale, which is typically much smaller than the seismic data resolution. In order to ensure positive definiteness of the cokriging matrix, a licit small-scale coregionalization model has to be built. Since there are no small-scale secondary data, an analytical method is presented to infer small-scale seismic variograms. The method is applied to estimate the 3-D porosity distribution of a West Texas oil field given seismic data and porosity data at 62 wells. 相似文献
126.
127.
128.
This paper presents the results of a detailed structural analysis of the northern Nijar and southern Vera basins with special emphasis on the evolution of the regional stress field and the associated timing of movement of the Serrata, Gafarillos and Palomares strike-slip fault zones. These major fault zones control the Neogene deformation of the SE Internal Betic Cordilleras in Spain. Detailed stress analysis on Neogene sediments of the Vera and Nijar basins shows a strike-slip regime with NW–SE-oriented subhorizontal maximum principal stress (σ1) during Tortonian and earliest Messinian times. Under the influence of this stress field, dextral displacement along the N090E-trending Gafarillos fault zone resulted in deformation of the sediments of the southern Sorbas and northeastern Nijar basins. During the early Messinian a clock-wise rotation of the stress field occurred. Stress analysis in rocks with late–early Messinian up to Quaternary ages in the Nijar and Vera basins indicates a strike-slip regime with N–S-oriented subhorizontal maximum principal stress (σ1). Under the influence of this stress field the main activity along the N010E-striking Palomares strike-slip fault zone took place, resulting in deformation of the Neogene sediments of the southeastern Vera basin and culminating in a maximum sinistral displacement of more than 20 km. At the same time the stress field was not suitably oriented to exert a large shear component on the Gafarillos fault zone, which activity ended after the earliest Messinian. Fault and outcrop patterns of syntectonic Neogene sediments in the Vera basin show that displacement along the Palomares fault zone decreased at the end of the Middle Miocene although minor displacement phases may still have occurred during the Late Miocene and possibly even Pliocene. From the Middle Miocene onward, deformation in the Nijar basin was controlled by sinistral displacement along the N040E-trending Serrata strike-slip fault zone. 相似文献
129.
Dunite samples have been deformed non-coaxially at high temperatures and pressures. In samples which were deformed by translation glide on {Okl}[100], olivine [100] = Z-axes rotated toward the maximum extensile-strain axis. In samples which were partly or completely recrystallized syntectonically the new olivine grains attained preferred orientations with [010] = X and [100] = Z parallel to the maximum and least principal compressive stress axes, respectively. These results may be used for kinematic and dynamic analysis of naturally deformed dunites and peridotites. 相似文献
130.
Eberhard Seidel Martin Okrusch Hans Kreuzer Helmut Raschka Wilhelm Harre 《Contributions to Mineralogy and Petrology》1981,76(3):351-361
The uppermost unit of the Cretan nappe system consists of ophiolites on the top, and an ophiolitic mélange at the base.Among the various constituents of the mélange, there are slices of low-P/high-T metamorphics. They form a variegated series consisting of tholeiitic ortho-amphibolites, para-amphibolites, andalusite and sillimanite-cordierite-garnet bearing mica schists, calcsilicate rocks, and marbles. The metamorphic sequence is locally intruded by early tectonic magmatites of gabbroic, dioritic and granitic composition. Critical mineral assemblages lead to a maximum temperature of about 700° C reached during metamorphism, at a total pressure of 4–5 kilobars. K — Ar dating on 6 hornblendes, 7 biotites and 1 muscovite yielded cooling ages of 75–66 m.y. and confirmed earlier results according to which the metamorphism and related magmatism took place in Late Cretaceous times.In order to evaluate the age relationships between the hightemperature metamorphics within the ophiolitic mélange and the ophiolites, hornblendes from ultramafic and mafic rocks of the ophiolite complex were dated by the K — Ar method. Hornblende from one schistose hornblendite forming a constituent of the ophiolites proper yielded 156 m.y. and thus provides a middle Jurassic minimum age for the formation of this piece of oceanic lithosphere. Four hornblendes of calc-alkaline gabbrodiorite dikes within the ophiolite complex gave distinctly lower K — Ar dates of about 140 m.y.. The dikes probably intruded after the detachment of the ophiolites in an island-arc or continental-margin environment.As a consequence, the high-temperature metamorphics and related intrusives in the ophiolitic mélange of Crete are genetically unrelated to the overlying ophiolites. The paleogeographic position of the crystalline terrane, slices of which are now incorporated into the ophiolitic mélange is still open to discussion. 相似文献