全文获取类型
收费全文 | 56353篇 |
免费 | 983篇 |
国内免费 | 607篇 |
专业分类
测绘学 | 1357篇 |
大气科学 | 5137篇 |
地球物理 | 12000篇 |
地质学 | 20824篇 |
海洋学 | 4102篇 |
天文学 | 11050篇 |
综合类 | 106篇 |
自然地理 | 3367篇 |
出版年
2018年 | 738篇 |
2017年 | 695篇 |
2016年 | 1021篇 |
2015年 | 701篇 |
2014年 | 1023篇 |
2013年 | 2481篇 |
2012年 | 1159篇 |
2011年 | 1670篇 |
2010年 | 1434篇 |
2009年 | 2001篇 |
2008年 | 1753篇 |
2007年 | 1624篇 |
2006年 | 1742篇 |
2005年 | 1472篇 |
2004年 | 1518篇 |
2003年 | 1453篇 |
2002年 | 1454篇 |
2001年 | 1232篇 |
2000年 | 1271篇 |
1999年 | 1146篇 |
1998年 | 1094篇 |
1997年 | 1153篇 |
1996年 | 1024篇 |
1995年 | 973篇 |
1994年 | 886篇 |
1993年 | 812篇 |
1992年 | 871篇 |
1991年 | 818篇 |
1990年 | 848篇 |
1989年 | 772篇 |
1988年 | 765篇 |
1987年 | 919篇 |
1986年 | 800篇 |
1985年 | 960篇 |
1984年 | 1111篇 |
1983年 | 1141篇 |
1982年 | 1018篇 |
1981年 | 982篇 |
1980年 | 932篇 |
1979年 | 910篇 |
1978年 | 920篇 |
1977年 | 828篇 |
1976年 | 769篇 |
1975年 | 771篇 |
1974年 | 826篇 |
1973年 | 818篇 |
1972年 | 555篇 |
1971年 | 493篇 |
1970年 | 372篇 |
1969年 | 327篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
121.
The Middle Jurassic Kirkpatrick flood basalts and comagmatic Ferrar intrusions in the Transantarctic Mountains represent
a major pulse of tholeiitic magmatism related to early stages in the breakup of Gondwana. A record of the volcano-tectonic
events leading to formation of this continental flood-basalt province is provided by strata underlying and only slightly predating
the Kirkpatrick lavas. In the central Transantarctic Mountains, the lavas rest on widespread (≥7500 km2) tholeiitic pyroclastic deposits of the Prebble Formation. The Prebble Formation is dominated by lahar deposits and is an
unusual example of a regionally developed basaltic lahar field. Related, partly fault-controlled pyroclastic intrusions cut
underlying strata, and vents are represented by the preserved flanks of two small tephra cones associated with a volcanic
neck. Lahar and air-fall deposits typically contain 50–60% accidental lithic fragments and sand grains derived from underlying
Triassic – Lower Jurassic strata in the upper part of the Beacon Supergroup. Juvenile basaltic ash and fine lapilli consist
of nonvesicular to scoriaceous tachylite, sideromelane, and palagonite, and have characteristics indicating derivation from
hydrovolcanic eruptions. The abundance of accidental debris from underlying Beacon strata points to explosive phreatomagmatic
interaction of basaltic magma with wet sediment and groundwater, which appears to have occurred in particular where rising
magma intersected upper Beacon sand aquifers. Composite clasts in the lahar deposits exhibit complex peperitic textures formed
during fine-scale intermixing of basaltic magma with wet sand and record steps in subsurface fuel-coolant interactions leading
to explosive eruption.
The widespread, sustained phreatomagmatic activity is inferred to have occurred in a groundwater-rich topographic basin linked
to an evolving Jurassic rift zone in the Transantarctic Mountains. Coeval basaltic phreatomagmatic deposits of the Mawson
and Exposure Hill Formations, which underlie exposures of the Kirkpatrick Basalt up to 1500 km to the north along strike in
Victoria Land, appear to represent other parts of a regional, extension-related Middle Jurassic phreatomagmatic province which
developed immediately prior to rapid outpouring of the flood basalts. This is consistent with models which assign an important
role to lithospheric stretching in the generation of flood-basalt provinces.
Received: 28 August 1995 / Accepted: 18 April 1996 相似文献
122.
H. -U. Zimmermann 《Astrophysics and Space Science》1995,228(1-2):331-347
Results from ROSAT observations of recent supernova events are discussed in the light of a model, where the soft X-rays originate in the shock interaction of the expanding supernova ejecta with the circumstellar material, left from heavy mass loss of the progenitor object. Special attention is given to the observations of SN1993J in M81, where lightcurves and spectral measurements allow a more detailed analysis and comparison to numerical model calculations. 相似文献
123.
The testing of a synthetic aperture technique, the ETAM algorithm, is extended and its performance for CW pseudorandom signals and broadband ship noise is examined. The results show the limitations of the technique and are of special interest for operational systems development. In the CW experiments, the transmitted signal was generated with high temporal coherence, and loss of the spatial and temporal coherence of the received signal was introduced only by the medium and the stability of the towed array. In the experiments that included the pseudorandom signal and the ship noise, the temporal coherence of the transmitted signals was deliberately chosen to be poor in order to study the effects and the performance of this algorithm with broadband signals. The related experimental results show that for received signals, which have their segments over the synthesizing period highly cross-correlated, a synthetic aperture array gain was achieved that corresponds to the length of an equivalent fully populated array 相似文献
124.
125.
We study the temporal intensity variations of Mgib bright features and investigate the corresponding Hα velocity pattern.
The network bright features are well visible in the continuum, in images averaged over the duration of the observations (130 min).
We detected `flashing' bright features, which appear and disappear within two to five minutes, while the rest of the bright
features undergo small variations of either their shape and/or their intensity. A power spectrum analysis reveals a 10-min
oscillation for approximately half of the stable bright features. The 5-min oscillations are detected mainly at the network
boundaries, where stable bright features are located, while 3-min oscillations coincide with few bright features, but are
also quite intense inside the network cells. The majority of bright features are associated with Hα downflows. The downflow
is very intense at the location of `flashing' bright features. 相似文献
126.
127.
W. Goudswaard 《Geophysical Prospecting》2001,49(6):625-627
128.
129.
One zone modeling of the irregular variability of red super-giants is intended with regard to the nonlinear coupling of finite amplitude pulsation with convection. The nonlocal mixing length is employed for the evaluation of the convective flux, the turbulent pressure and the turbulent power of temperature fluctuations. The radial pulsation and the Boussinesq convection are assumed for simplicity. The one zone is defined as the layer having the entropy maximum and the minimum at the bottom and at the top, respectively. The quasi-adiabatic approximation is consistent with this definition in fixing the zone to the same mass range. The spatial derivatives are evaluated under the assumption of homologous changes with the equilibrium homologous parameters. Then, a set of 6 simultaneous first order nonlinear ordinary differential equations are obtained as the one zone representation of the irregular variability of the convective envelope. 相似文献
130.
Theoretical line ratios involving 2s
2
S - 3p
2
P, 2p
2
P - 3s
2
S, and 2p
2
S - 3d
2
D transitions inCiv between 312 and 420 Å are presented. A comparison of these with solar active region observational data obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals good agreement between theory and experiment, with discrepancies that average only 22%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on boardSkylab. The potential usefulness of theCIV line ratios as electron temperature diagnostics for the solar transition region is briefly discussed. 相似文献