全文获取类型
收费全文 | 44103篇 |
免费 | 6603篇 |
国内免费 | 10849篇 |
专业分类
测绘学 | 5678篇 |
大气科学 | 5679篇 |
地球物理 | 7230篇 |
地质学 | 22992篇 |
海洋学 | 5453篇 |
天文学 | 7329篇 |
综合类 | 2973篇 |
自然地理 | 4221篇 |
出版年
2024年 | 186篇 |
2023年 | 504篇 |
2022年 | 1349篇 |
2021年 | 1566篇 |
2020年 | 1737篇 |
2019年 | 2065篇 |
2018年 | 1541篇 |
2017年 | 1935篇 |
2016年 | 1964篇 |
2015年 | 2112篇 |
2014年 | 2559篇 |
2013年 | 3018篇 |
2012年 | 2908篇 |
2011年 | 2898篇 |
2010年 | 2488篇 |
2009年 | 3088篇 |
2008年 | 3214篇 |
2007年 | 3385篇 |
2006年 | 3286篇 |
2005年 | 2795篇 |
2004年 | 2460篇 |
2003年 | 2120篇 |
2002年 | 1845篇 |
2001年 | 1523篇 |
2000年 | 1593篇 |
1999年 | 1406篇 |
1998年 | 1129篇 |
1997年 | 905篇 |
1996年 | 779篇 |
1995年 | 615篇 |
1994年 | 539篇 |
1993年 | 468篇 |
1992年 | 384篇 |
1991年 | 241篇 |
1990年 | 206篇 |
1989年 | 186篇 |
1988年 | 148篇 |
1987年 | 90篇 |
1986年 | 93篇 |
1985年 | 47篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 26篇 |
1981年 | 13篇 |
1980年 | 22篇 |
1979年 | 3篇 |
1978年 | 12篇 |
1977年 | 20篇 |
1954年 | 11篇 |
1877年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Radiative Transfer (RT) codes with image capability are a fundamental tool for preparing interferometric observations and
for interpreting visibility data. In view of the upcoming VLTI facilities, we present the first comparison of images/visibilities
coming from two 3D codes that use completely different techniques to solve the problem of self-consistent continuum RT. In
addition, we focus on the astrophysical case of a disk distorted by tidal interaction with by-passing stars or internal planets
and investigate for which parameters the distortion can be best detected in the mid-infrared using the mid-infrared interferometric
device MIDI.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
92.
Pco2 of air and seawater samples from the East China Sea(ECS) were measured in situ in autumn, 1994,Ocean currents,terrestrial fluviation,biological activities,etc.,Pco2 char-acters in air and seawater were investigated,CO2 flux and its character in the East China Sea are discussed on the basis of the Pco2 profiles of air and seawater,It was clear that the nearshore was the source of CO2;and tht the oulter sea area was the sink of CO2; and that the shelf area of the EXS is a net sink for atmospheric CO2 in autumn. 相似文献
93.
We examine possible locations for the primordial disk of the Edgeworth-Kuiper Belt (EKB), using several subsets of the known objects as markers of the total mass distribution. Using a secular perturbation theory, we find that the primordial plane of the EKB could have remained thin enough to escape detection only if it is clustered very closely about the invariable plane of the Solar System. 相似文献
94.
Photometric observations of Pluto in the BVR filter system were obtained in 1999 and in 1990-1993, and observations in the 0.89-μm methane absorption band were obtained in 2000. Our 1999 observations yield lightcurve amplitudes of 0.30 ± 0.01, 0.26 ± 0.01, and 0.21 ± 0.02 and geometric albedos of 0.44 ± 0.04, 0.52 ± 0.03, and 0.58 ± 0.02 in the B, V, and R filters, respectively. The low-albedo hemisphere of Pluto is slightly redder than the higher albedo hemisphere. A comparison of our results and those from previous epochs shows that the lightcurve of Pluto changes substantially through time. We developed a model that fully accounts for changes in the lightcurve caused by changes in the viewing geometry between the Earth, Pluto, and the Sun. We find that the observed changes in the amplitude of Pluto’s lightcurve can be explained by viewing geometry rather than by volatile transport. We also discovered a measurable decrease since 1992 of ∼0.03 magnitudes in the amplitude of Pluto’s lightcurve, as the model predicts. Pluto’s geometric albedo does not appear to be currently increasing, as our model predicts, although given the uncertainties in both the model and the measurements of geometric albedo, this result is not firm evidence for volatile transport. The maximum of methane-absorption lightcurve occurs near the minimum of the BVR lightcurves. This result suggests that methane is more abundant in the brightest regions of Pluto. Pluto’s phase coefficient exhibits a color dependence, ranging from 0.037 ± 0.01 in the B filter to 0.032 ± 0.01 in the R filter. Pluto’s phase curve is most like those of the bright, recently resurfaced satellites Triton and Europa. Although Pluto shows no strong evidence for volatile transport now (unlike Triton), it is important to continue to observe Pluto as it moves away from perihelion. 相似文献
95.
李毅心 《成都信息工程学院学报》2006,21(2):206-209
积件技术是教学软件发展的方向,探讨了用Power Builder前台结合SQL Server关系数据库后台进行多媒体教学积件管理的应用模式,并结合具体教学示例,进行了分析说明。 相似文献
96.
97.
Groundbased radio observations indicate that Jupiter's ammonia is globally depleted from 0.6 bars to at least 4-6 bars relative to the deep abundance of ∼3 times solar, a fact that has so far defied explanation. The observations also indicate that (i) the depletion is greater in belts than zones, and (ii) the greatest depletion occurs within Jupiter's local 5-μm hot spots, which have recently been detected at radio wavelengths. Here, we first show that both the global depletion and its belt-zone variation can be explained by a simple model for the interaction of moist convection with Jupiter's cloud-layer circulation. If the global depletion is dynamical in origin, then important endmember models for the belt-zone circulation can be ruled out. Next, we show that the radio observations of Jupiter's 5-μm hot spots imply that the equatorial wave inferred to cause hot spots induces vertical parcel oscillation of a factor of ∼2 in pressure near the 2-bar level, which places important constraints on hot-spot dynamics. Finally, using spatially resolved radio maps, we demonstrate that low-latitude features exceeding ∼4000 km diameter, such as the equatorial plumes and large vortices, are also depleted in ammonia from 0.6 bars to at least 2 bars relative to the deep abundance of 3 times solar. If any low-latitude features exist that contain 3-times-solar ammonia up to the 0.6-bar ammonia condensation level, they must have diameters less than ∼4000 km. 相似文献
98.
Brian Warner Patrick A. Woudt 《Monthly notices of the Royal Astronomical Society》2006,367(4):1562-1576
We present new observations of the rapid oscillations in the dwarf nova VW Hyi, made late in outburst. These dwarf nova oscillations (DNOs) increase in period until they reach 33 s, when a transition to a strong 1st harmonic and weak fundamental takes place. After further period increase, the 2nd harmonic appears; often all three components are present simultaneously. This 1:2:3 frequency suite is similar to what has been seen in some neutron star and black hole X-ray binaries, but has not previously been seen in a cataclysmic variable. When studied in detail, the fundamental and 2nd harmonic vary similarly in phase, but the 1st harmonic behaves independently, though keeping close to twice the frequency of the fundamental. The fundamental period of the DNOs, as directly observed or inferred from the harmonics, increases to ∼100 s before the oscillation disappears as the star reaches quiescence. Its maximum period is close to that of the 'longer-period' DNOs observed in VW Hyi. The quasi-periodic oscillations (QPOs), which have fundamental periods 400–1000 s, behave in the same way, showing 1st and 2nd harmonics at approximately the same times as the DNOs. We explore some possible models. One in which the existence of the 1st harmonic is due to the transition from viewing a single accretion region to viewing two regions, and the rate of accretion on to the primary is modulated at the frequency of the 1st harmonic, as in the 'beat frequency model', can generate the suite of DNO frequencies observed. But the behaviour of the QPOs is not yet understood. 相似文献
99.
100.