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211.
212.
The dwarf nova oscillations observed in cataclysmic variable (CV) stars are interpreted in the context of a low-inertia accretor model, in which accretion on to an equatorial belt of the white dwarf primary causes the belt to vary its angular velocity. The rapid deceleration phase is attributed to propellering. Evidence that temporary expulsion rather than accretion of gas occurs during this phase is obtained from the large drop in extreme ultraviolet flux.
We show that the quasi-periodic oscillations are most probably caused by a vertical thickening of the disc, moving as a travelling wave near the inner edge of the disc. This alternately obscures and 'reflects' radiation from the central source, and is visible even in quite low inclination systems. A possible excitation mechanism, caused by winding up and reconnection of magnetic field lines, is proposed.
We apply the model, deduced largely from VW Hyi observations, to re-interpret observations of SS Cyg, OY Car, UX UMa, V2051 Oph, V436 Cen and WZ Sge. In the last of these we demonstrate the existence of a 742-s period in the light curve, arising from obscuration by the travelling wave, and hence show that the two principal oscillations are a dwarf nova oscillation and its reprocessed companion. 相似文献
We show that the quasi-periodic oscillations are most probably caused by a vertical thickening of the disc, moving as a travelling wave near the inner edge of the disc. This alternately obscures and 'reflects' radiation from the central source, and is visible even in quite low inclination systems. A possible excitation mechanism, caused by winding up and reconnection of magnetic field lines, is proposed.
We apply the model, deduced largely from VW Hyi observations, to re-interpret observations of SS Cyg, OY Car, UX UMa, V2051 Oph, V436 Cen and WZ Sge. In the last of these we demonstrate the existence of a 742-s period in the light curve, arising from obscuration by the travelling wave, and hence show that the two principal oscillations are a dwarf nova oscillation and its reprocessed companion. 相似文献
213.
Youjuan Li Brian R. Jicha Wanfeng Zhang Wen Chen Brad S. Singer Dewen Zheng Huaiyu He 《Geostandards and Geoanalytical Research》2023,47(3):657-668
The precision and accuracy of 40Ar/39Ar dates are ultimately linked to co-irradiated reference materials of known age. Here we provide new data from the SK01 sanidine, which was analysed in three different laboratories to evaluate it as a 40Ar/39Ar reference material. Aliquots of 5 mg, incrementally heated in two laboratories, yielded indistinguishable results with a weighted mean age of 27.58 ± 0.06 Ma (95% confidence level). Single-crystal step heating and single-crystal total fusion analyses of SK01 sanidine were undertaken in the third laboratory to further test the intracrystalline homogeneity. For the seven step-heating analyses, six crystals yielded nearly concordant age spectra with 40Ar/39Ar ages ranging from 26.853 ± 0.094 Ma to 26.963 ± 0.067 Ma, whereas one crystal gave an older age of 27.774 ± 0.071 Ma with a slightly discordant age spectrum. Twenty-three single-crystal total fusion analyses yielded 40Ar/39Ar ages ranging from 27.070 ± 0.108 Ma to 27.736 ± 0.062 Ma with a dispersion of ~ 3.8%. The older ages from single-crystal total fusion dates are interpreted to reflect an inherited or excess argon component in some crystals. This is an initial characterisation of the SK01 sanidine, and additional work needs to be conducted to further evaluate the age dispersion so that it can be utilised as a 40Ar/39Ar reference material. 相似文献
214.
Ayugi Brian Shilenje Zablon Weku Babaousmail Hassen Lim Kam Sian Kenny T. C. Mumo Richard Dike Victor Nnamdi Iyakaremye Vedaste Chehbouni Abdelghani Ongoma Victor 《Natural Hazards》2022,113(2):1151-1176
Natural Hazards - The ongoing global warming has caused unprecedented changes in the climate system, leading to an increase in the intensity and frequency of weather and climate extremes. This... 相似文献
215.
Katharina?MarquardtEmail author Gregory?S.?Rohrer Luiz?Morales Erik?Rybacki Hauke?Marquardt Brian?Lin 《Contributions to Mineralogy and Petrology》2015,170(4):40
Rocks consist of crystal grains separated by grain boundaries that impact the bulk rock properties. Recent studies on metals and ceramics showed that the grain boundary plane orientation is more significant for grain boundary properties than other characteristics such as the sigma value or disorientation (in the Earth’s science community more frequently termed misorientation). We determined the grain boundary character distribution (GBCD) of synthetic and natural polycrystalline olivine, the most abundant mineral of Earth’s upper mantle. We show that grain boundaries of olivine preferentially contain low index planes, in agreement with recent findings on other oxides (e.g. MgO, TiO2, Al2O3 etc.). Furthermore, we find evidence for a preferred orientation relationship of 90° disorientations about the [001] direction forming tilt and twist grain boundaries, as well as a preference for the 60° disorientation about the [100] axis. Our data indicate that the GBCD, which is an intrinsic property of any mineral aggregate, is fundamental for understanding and predicting grain boundary related processes. 相似文献
216.
J. Brian Balta Matthew E. Sanborn Arya Udry Meenakshi Wadhwa Harry Y. McSween 《Meteoritics & planetary science》2015,50(1):63-85
The fall and recovery of the Tissint meteorite in 2011 created a rare opportunity to examine a Martian sample with a known, short residence time on Earth. Tissint is an olivine‐phyric shergottite that accumulated olivine antecrysts within a single magmatic system. Coarse olivine grains with nearly homogeneous cores of Mg# >80 suggest slow re‐equilibration. Many macroscopic features of this sample resemble those of LAR 06319, including the olivine crystal size distribution and the presence of evolved oxide and olivine compositions. Unlike LAR 06319, however, no magmatic hydrous phases were found in the analyzed samples of Tissint. Minor and trace element compositions indicate that the meteorite is the product of closed‐system crystallization from a parent melt derived from a depleted source, with no obvious addition of a LREE‐rich (crustal?) component prior to or during crystallization. The whole‐rock REE pattern is similar to that of intermediate olivine‐phyric shergottite EETA 79001 lithology A, and could also be approximated by a more olivine‐rich version of depleted basaltic shergottite QUE 94201. Magmatic oxygen fugacities are at the low end of the shergottite range, with log fO2 of QFM‐3.5 to ‐4.0 estimated based on early‐crystallized minerals and QFM‐2.4 estimated based on the Eu in pyroxene oxybarometer. These values are similarly comparable to other depleted shergottites, including SaU 005 and QUE 94201. Tissint occupies a previously unsampled niche in shergottite chemistry: containing olivines with Mg# >80, resembling the enriched olivine‐phyric shergottite LAR 06319 in its crystallization path, and comparable to intermediate olivine‐phyric shergottite EETA 79001A, depleted olivine‐phyric shergottite DaG 476, and depleted basaltic shergottite QUE 94201 in its trace element abundances and oxygen fugacity. The apparent absence of evidence for terrestrial alteration in Tissint (particularly in trace element abundances in the whole‐rock and individual minerals) confirms that exposure to the arid desert environment results in only minimal weathering of samples, provided the exposure times are brief. 相似文献
217.
Dai Aiguo Huang Danqing Rose Brian E. J. Zhu Jian Tian Xiangjun 《Climate Dynamics》2020,54(11):4515-4543
Climate Dynamics - Equilibrium climate sensitivity (ECS) refers to the total global warming caused by an instantaneous doubling of atmospheric CO2 from the pre-industrial level in a climate system.... 相似文献
218.
Abstract The design of a spar buoy, employed as one component of a current monitoring system deployed during 1980 in Davis Strait, and some of its response characteristics to ocean waves are presented. The buoy was 36.5 ft (11.13 m) in length with upper and lower masts 0.5ft (15.2 cm) in diameter and buoyancy hulls, centrally located, 2 ft (61.0 cm) in diameter. Power for the system was supplied from lead‐acid batteries in a ballast tank on the lower end. Telemetry electronics were located in a 1‐ft (30.5‐cm) diameter case on the upper end, below the antenna. The buoy weighed about 1,635 lb (746kg) and could be man‐handled at sea with relatively light lifting equipment. It had a damped period of 16s and a significant heave response of about 62% of the significant wave height of the forcing spectrum. Scale model tests indicated that the buoy would be operational in heavy sea swell up to about 20ft in height with pitching angles of less than 10° off vertical. Observations at sea have shown that the buoy followed swell waves better than the 62% heave response figure would imply and had negligible pitching motions except during severe storms. The design was judged to be successful in providing a stable base for VHF transmission and is recommended for use in other applications. 相似文献
219.
J. de Grandpré J.W. Sandilands J.C. McConnell S.R. Beagley P.C. Croteau M.Y. Danilin 《大气与海洋》2013,51(4):385-431
Abstract An important objective of middle atmosphere global climate modelling is the development of the capability of predicting the response of the middle atmosphere to natural or anthropogenic perturbations. To achieve this, a comprehensive chemistry package interactively coupled with radiative and dynamical modules is required. This paper presents preliminary results obtained with a photochemistry module which has been incorporated in the Canadian Middle Atmosphere Model (CMAM). The module contains 42 species including necessary oxygen, hydrogen, nitrogen, chlorine, bromine and methane oxidation cycle species. Photochemical balance equations are solved on‐line throughout the middle atmosphere at every dynamical time step. A full diurnal cycle is simulated with photolysis rates provided by a look‐up table. The chemistry solver is a mass conserving, fully implicit, backward difference scheme which currently uses less than 10% of the GCM run time. We present the results obtained from short integrations and compare them with UARS measurements. The model ozone distribution appears in quantitative agreement with observations showing peak values near 10 ppmv and confined to the 35‐km region. The abundance of nitrogen, chlorine, bromine oxides and their respective contributions to the overall ozone budget is realistic. The study illustrates the capability of the model to simulate middle atmosphere photochemistry for the disparate conditions occurring throughout the region. 相似文献
220.
Brian Warner 《Astrophysics and Space Science》1995,226(2):187-211
Photometric properties of known and suspected members of the SU UMa subclass of dwarf novae are tabulated and discussed. The precessing disc model of superoutbursts gives a satisfactory quantitative explanation of the periods of superhumps and their changes during superoutburst. The systems such as WZ Sge and HV Vir that have very long intervals between superoutbursts are deduced to be beyond the orbital period minimum, and have degenerate secondaries. The systems such as V1159 Ori that have extremely short recurrence times have high rates of mass transfer and are the equivalent of the Z Cam subclass that occurs at longer orbital periods.A simplified analytical approach to the theory of accretion discs is able to explain the correlations between normal and superoutburst recurrence times. It also explains the slope of the plateau region of superoutbursts, and why the slope is shallower in the very short recurrence time systems. 相似文献