全文获取类型
收费全文 | 251854篇 |
免费 | 4935篇 |
国内免费 | 3301篇 |
专业分类
测绘学 | 6698篇 |
大气科学 | 18699篇 |
地球物理 | 52711篇 |
地质学 | 87008篇 |
海洋学 | 20861篇 |
天文学 | 55482篇 |
综合类 | 977篇 |
自然地理 | 17654篇 |
出版年
2021年 | 2213篇 |
2020年 | 2563篇 |
2019年 | 2827篇 |
2018年 | 2925篇 |
2017年 | 2645篇 |
2016年 | 5396篇 |
2015年 | 4147篇 |
2014年 | 6856篇 |
2013年 | 14139篇 |
2012年 | 6198篇 |
2011年 | 7261篇 |
2010年 | 6412篇 |
2009年 | 9044篇 |
2008年 | 7888篇 |
2007年 | 7234篇 |
2006年 | 9530篇 |
2005年 | 7535篇 |
2004年 | 7456篇 |
2003年 | 6935篇 |
2002年 | 6568篇 |
2001年 | 5890篇 |
2000年 | 5871篇 |
1999年 | 5180篇 |
1998年 | 5203篇 |
1997年 | 4994篇 |
1996年 | 4643篇 |
1995年 | 4390篇 |
1994年 | 4075篇 |
1993年 | 3817篇 |
1992年 | 3601篇 |
1991年 | 3572篇 |
1990年 | 3739篇 |
1989年 | 3496篇 |
1988年 | 3286篇 |
1987年 | 3832篇 |
1986年 | 3391篇 |
1985年 | 4206篇 |
1984年 | 4716篇 |
1983年 | 4387篇 |
1982年 | 4300篇 |
1981年 | 3907篇 |
1980年 | 3629篇 |
1979年 | 3502篇 |
1978年 | 3471篇 |
1977年 | 3272篇 |
1976年 | 3035篇 |
1975年 | 2953篇 |
1974年 | 2911篇 |
1973年 | 3070篇 |
1972年 | 2022篇 |
排序方式: 共有10000条查询结果,搜索用时 3 毫秒
361.
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
362.
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
363.
B. D. F. Methley 《The Photogrammetric Record》1994,14(83):793-803
A case is made for the development of an inexpensive and portable data capturing unit which could be used with existing mirror stereoscopes and which could provide an accuracy sufficient for most digital map databases. The results of simulation experiments to test the accuracy of the system are presented. 相似文献
364.
Abstract— A whole rock sample from the H3 chondrite Sainte Rose, which was discovered in 1983, was dated with the 40Ar-39Ar technique. From the K/Ca spectrum and from an analysis of the 39Ar recoil effect we conclude that this meteorite has at least two distinguishable K-carriers: a low temperature, high-K/Ca, fine-grained carrier with a typical grain size of about 2 μm and a high temperature, low-K/Ca, more coarse-grained carrier. The K-Ar clocks of both were started 4.40 ± 0.01 Ga ago. 相似文献
365.
366.
The restricted problem of 2 + 2 bodies when one of the infinitesimal masses is further acted upon by the light pressure of the two primaries, is considered. The stationary solutions of this problem are found out. A short discussion is devoted to the stability of these solutions. 相似文献
367.
Perspectives for the Radio-Optical Telescope 54/32/2.6 are given for scientific research in radioastronomy. Its characteristics and potential scientific fields are summarized in the frame of the present French-Armenian collaboration. A 3-phase upgrade plan including a detailed technical evaluation of the antenna is presented.Published in Astrofizika, Vol. 38, No. 4, pp. 645–648, October–December, 1995. 相似文献
368.
We have studied the influence of the magnetic helicity on solar particle propagation using the IMF data observed by the HELIOS spacecraft in the range 0.31–0.95 AU, during eight solar proton events. For this, we have derived power and helicity spectra of the turbulence of the magnetic field during the time of the events. These are used to compute the particle pitch-angle scattering coefficients according to the quasi-linear theory (QLT) treatment of particle propagation in turbulent magnetic fields. The results show that in all the cases the helicity effects are negligible and the particle's mean free paths deduced from the pitch-angle diffusion coefficients are the same regardless of whether or not helicity effects are included in the calculations. The computed mean free paths are quite different in each case.Deceased 10 April, 1995. 相似文献
369.
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
370.
K. A. van der Hucht 《Astronomy and Astrophysics Review》1992,4(2):123-159
Summary Recent literature on Population I Wolf-Rayet star research extending from the Milky Way to blue compact dwarf galaxies is reviewed, broken down into inventory, basic parameters and galactic distribution, atmospheres, binaries, intrinsic variability, mass loss, enrichment and evolution. Also the incidence of Wolf-Rayet stars with variable non-thermal radio emission, excess X-ray fluxes, and episodic/periodic IR excesses is reviewed. These phenomena appear to be associated with wind-wind interaction in wide long-period WR+OB binaries and with wind-compact object interaction in WR+c binaries, with orbit sizes of the order of magnitude of the WR radio photosphere sizes or larger. 相似文献