全文获取类型
收费全文 | 71150篇 |
免费 | 1404篇 |
国内免费 | 659篇 |
专业分类
测绘学 | 1720篇 |
大气科学 | 5033篇 |
地球物理 | 14257篇 |
地质学 | 25344篇 |
海洋学 | 6179篇 |
天文学 | 16333篇 |
综合类 | 210篇 |
自然地理 | 4137篇 |
出版年
2022年 | 396篇 |
2021年 | 704篇 |
2020年 | 779篇 |
2019年 | 830篇 |
2018年 | 1896篇 |
2017年 | 1765篇 |
2016年 | 2242篇 |
2015年 | 1326篇 |
2014年 | 2186篇 |
2013年 | 3790篇 |
2012年 | 2289篇 |
2011年 | 3131篇 |
2010年 | 2613篇 |
2009年 | 3521篇 |
2008年 | 3262篇 |
2007年 | 3064篇 |
2006年 | 2886篇 |
2005年 | 2356篇 |
2004年 | 2256篇 |
2003年 | 2113篇 |
2002年 | 1932篇 |
2001年 | 1802篇 |
2000年 | 1721篇 |
1999年 | 1380篇 |
1998年 | 1470篇 |
1997年 | 1390篇 |
1996年 | 1101篇 |
1995年 | 1143篇 |
1994年 | 964篇 |
1993年 | 873篇 |
1992年 | 856篇 |
1991年 | 759篇 |
1990年 | 857篇 |
1989年 | 717篇 |
1988年 | 650篇 |
1987年 | 814篇 |
1986年 | 664篇 |
1985年 | 855篇 |
1984年 | 922篇 |
1983年 | 862篇 |
1982年 | 832篇 |
1981年 | 707篇 |
1980年 | 663篇 |
1979年 | 606篇 |
1978年 | 604篇 |
1977年 | 552篇 |
1976年 | 540篇 |
1975年 | 500篇 |
1974年 | 507篇 |
1973年 | 469篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
The remnant resulting from the merger of two neutron stars produces neutrinos in copious amounts. In this paper we present the neutrino emission results obtained via Newtonian, high-resolution simulations of the coalescence event. These simulations use three-dimensional smoothed particle hydrodynamics together with a nuclear, temperature-dependent equation of state and a multiflavour neutrino leakage scheme. We present the details of our scheme, discuss the neutrino emission results from a neutron star coalescence and compare them with the core-collapse supernova case where neutrino emission has been studied for several decades. The average neutrino energies are similar to those in the supernova case, but contrary to the latter, the luminosities are dominated by electron-type antineutrinos that are produced in the hot, neutron-rich, thick disc of the merger remnant. The cooler parts of this disc contain substantial fractions of heavy nuclei, which, however, do not influence the overall neutrino emission results significantly. Our total neutrino luminosities from the merger event are considerably lower than those found in previous investigations. This imposes constraints on the ability of neutron star mergers to produce a gamma-ray burst via neutrino annihilation. The neutrinos are emitted preferentially along the initial binary rotation axis, an event seen 'pole-on' would appear much brighter in neutrinos than a similar event seen 'edge-on'. 相似文献
122.
123.
M.P. Collings J.W. Dever H.J. Fraser M.R.S. McCoustra 《Astrophysics and Space Science》2003,285(3-4):633-659
The interaction of carbon monoxide (CO) with vapour-deposited water(H2O) ices has been studied using temperature programmed desorption (TPD) and Fourier transform reflection-absorption infrared
spectroscopy (FT-RAIRS) over a range of astrophysically relevant temperatures. Such measurements have shown that CO desorption
from amorphous H2Oices is a much more complex process than current astrochemical models suggest. Re-visiting previously reported laboratory
experiments (Collings et al., 2003), a rate model has been constructed to explain, in a phenomenological manner, the desorption
of CO over astronomically relevant time scales. The model presented here can be widely applied to a range of astronomical
environments where depletion of CO from the gas phase is relevant. The model accounts for the two competing processes of CO
desorption and migration, and also enables the entrapment of some of the CO in the ice matrix and its subsequent release as
the water ice crystallises and then desorbs. The astronomical implications of this model are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
124.
Chiang E. I. Lovering J. R. Millis R. L. Buie M. W. Wasserman L. H. Meech K. J. 《Earth, Moon, and Planets》2003,92(1-4):49-62
We review ongoing efforts to identify occupants of mean-motion resonances(MMRs) and collisional families in the Edgeworth–Kuiper belt. Directintegrations of trajectories of Kuiper belt objects (KBOs) reveal the 1:1(Trojan), 5:4, 4:3, 3:2 (Plutino), 5:3, 7:4, 9:5, 2:1 (Twotino), and 5:2 MMRsto be inhabited. Apart from the Trojan, resonant KBOs typically have largeorbital eccentricities and inclinations. The observed pattern of resonanceoccupation is consistent with resonant capture and adiabatic excitation bya migratory Neptune; however, the dynamically cold initial conditions priorto resonance sweeping that are typically assumed by migration simulationsare probably inadequate. Given the dynamically hot residents of the 5:2 MMRand the substantial inclinations observed in all exterior MMRs, a fraction ofthe primordial belt was likely dynamically pre-heated prior to resonancesweeping. A pre-heated population may have arisen as Neptune gravitationallyscattered objects into trans-Neptunian space. The spatial distribution of Twotinosoffers a unique diagnostic of Neptune's migration history. The Neptunian Trojanpopulation may rival the Jovian Trojan population, and the former's existence isargued to rule out violent orbital histories for Neptune. Finally, lowest-order seculartheory is applied to several hundred non-resonant KBOs with well-measured orbitsto update proposals of collisional families. No convincing family is detected. 相似文献
125.
D. H. Lumb A. Finoguenov R. Saxton B. Aschenbach P. Gondoin M. Kirsch I. M. Stewart 《Experimental Astronomy》2003,15(2):89-111
We describe measurements of the mirror vignetting in the XMM-Newton Observatory made in-orbit, using observations of SNR G21.5-09
and SNR 3C58 with the EPIC imaging cameras. The instrument features that complicate these measurements are briefly described.
We show the spatial and energy dependences of measured vignetting, outlining assumptions made in deriving the eventual agreement
between simulation and measurement. Alternate methods to confirm these are described, including an assessment of source elongation
with off-axis angle, the surface brightness distribution of the diffuse X-ray background, and the consistency of Coma cluster
emission at different position angles. A synthesis of these measurements leads to a change in the XMM calibration data base,
for the optical axis of two of the three telescopes, by in excess of 1 arcmin. This has a small but measureable effect on
the assumed spectral responses of the cameras for on-axis targets.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
126.
A major difficulty in remote sensing is handling the many data from sensors aboard aircraft and satellites. In this paper we identify an optimal procedure for sampling remotely sensed data before their storage or on their retrieval. The procedure depends on spatial correlation in the scene and uses kriging to estimate values that have been lost. An example in which data from an airborne multispectral scanner could be diminished to only about one tenth without serious loss of precision illustrates the method. 相似文献
127.
We report multi-frequency and multi-epoch radio continuum observations with multi-spatial resolution for the low-luminosity active galactic nucleus (LLAGN) NGC 266. In the centimetre regime, we find diffuse components with Very Large Array (VLA) observations, and a variable compact core with a rising spectrum with Very Long Baseline Array (VLBA) observations. Although the spectral index of the rising spectrum is consistent with the prediction of the simple advection-dominated accretion flow (ADAF) model, the observed radio power is slightly high compared with that of the model prediction. A spectral break at centimetre-to-millimetre wavelengths is inferred from the upper limits of flux densities from Nobeyama Millimetre Array (NMA) and James Clerk Maxwell Telescope (JCMT) data at millimetre and submillimetre wavelengths, respectively. More complicated considerations are required for the theoretical model to interpret such observed radio properties. 相似文献
128.
129.
It is shown how the hard X-ray burst count rate and itse-folding ime can be used to estimate the minimum magnetic fieldB
min required in a flare magnetic reconnection site for the burst to be interpreted in terms of a thick target model. Application of the method to data from the Solar Maximum Mission (HXRBS) indicates absolute minimum fields well in excess of 100 G, and impossibly high values for some reconnection geometries. 相似文献
130.