全文获取类型
收费全文 | 8108篇 |
免费 | 1200篇 |
国内免费 | 1745篇 |
专业分类
测绘学 | 111篇 |
大气科学 | 244篇 |
地球物理 | 893篇 |
地质学 | 4743篇 |
海洋学 | 1224篇 |
天文学 | 2149篇 |
综合类 | 369篇 |
自然地理 | 1320篇 |
出版年
2024年 | 32篇 |
2023年 | 109篇 |
2022年 | 323篇 |
2021年 | 340篇 |
2020年 | 318篇 |
2019年 | 369篇 |
2018年 | 307篇 |
2017年 | 295篇 |
2016年 | 282篇 |
2015年 | 345篇 |
2014年 | 347篇 |
2013年 | 416篇 |
2012年 | 372篇 |
2011年 | 389篇 |
2010年 | 333篇 |
2009年 | 595篇 |
2008年 | 490篇 |
2007年 | 538篇 |
2006年 | 588篇 |
2005年 | 447篇 |
2004年 | 454篇 |
2003年 | 486篇 |
2002年 | 396篇 |
2001年 | 334篇 |
2000年 | 339篇 |
1999年 | 291篇 |
1998年 | 312篇 |
1997年 | 208篇 |
1996年 | 149篇 |
1995年 | 149篇 |
1994年 | 148篇 |
1993年 | 96篇 |
1992年 | 98篇 |
1991年 | 54篇 |
1990年 | 54篇 |
1989年 | 29篇 |
1988年 | 25篇 |
1987年 | 29篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 25篇 |
1983年 | 32篇 |
1982年 | 33篇 |
1981年 | 40篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A. R. King K. Schenker U. Kolb M. B. Davies 《Monthly notices of the Royal Astronomical Society》2001,321(2):327-332
We show that the usual picture of supersoft X-ray binary evolution as driven by conservative thermal time-scale mass transfer cannot explain the short orbital periods of RX J0537.7–7034 (3.5 h) and 1E 0035.4–7230 (4.1 h). Non-conservative evolution may produce such periods, but requires very significant mass loss, and is highly constrained. 相似文献
42.
43.
Francesca Matteucci Antonio Pipino 《Monthly notices of the Royal Astronomical Society》2005,357(2):489-496
We have studied the effects of a hypothetical initial generation containing very massive stars [ M > 100 M⊙ , pair-creation supernovae] on the chemical and photometric evolution of elliptical galaxies. To this purpose, we have computed the evolution of a typical elliptical galaxy with luminous mass of the order of 1011 M⊙ and adopted chemical evolution models already tested to reproduce the main features of ellipticals. We have tested several sets of yields for very massive zero-metallicity stars: these stars should produce quite different amounts of heavy elements than lower-mass stars. We found that the effects of Population III stars on the chemical enrichment is negligible if only one or two generations of such stars occurred, whereas they produce quite different results from the standard models if they continuously formed for a period not shorter than 0.1 Gyr. In this case, the results are at variance with the main observational constraints of ellipticals such as the average [〈α/ Fe〉* ] ratio in stars and the integrated colours. Therefore, we conclude that if Population III stars ever existed they must have been present for a very short period of time and their effects on the following evolution of the parent galaxy must have been negligible. This effect is minimum if a more realistic model with initial infall of gas rather than the classic monolithic model is adopted. Ultimately, we conclude that there is no need to invoke a generation of very massive stars in ellipticals to explain their chemical and photometric properties. 相似文献
44.
Measurements of salinity perturbations in a partially mixed estuary have been used to evaluate the usefulness of an inductive salinometer and to determine some of the characteristics of the salinity perturbations. The salinometer performed satisfactorily under most conditions. Although internal wave like effects were present, the turbulence fluctuations were dominant. The salinity fluctuations and the turbulent fluxes and were found to behave in a manner similar to the density fluctuations in a thermally stratified atmospheric boundary layer and a laboratory open channel flow. A quadrant analysis suggested that the contribution of each quadrant to the turbulent flux changed with Ri. The turbulence parameters ν and cγ were found to decrease and increase respectively as Ri increases. 相似文献
45.
M. G. Abrahamyan 《Astrophysics》2004,47(4):555-567
The equilibrium of elliptical Riemann disks with a polytropic equation of state and their evolution under the influence of viscosity and gravitational radiation inside spheroidal halos with a relative surface mass density k. The evolutionary trajectory of a disk inside a halo with k<0.5, which is analogous to the evolution of an isolated disk, differs from that of a disk inside a denser halo. 相似文献
46.
47.
48.
V. Castellani S. Degl'Innocenti P. G. Prada Moroni 《Monthly notices of the Royal Astronomical Society》2001,320(1):66-72
We compare theoretical stellar models for main sequence (MS) stars with the Hipparcos data base for the Hyades cluster to give a warning against the uncritical use of available theoretical scenarios and to show how formal MS fittings can be fortuitous if not fictitious. Moreover, we find that none of the current theoretical scenarios appears able to account for an observed mismatch between theoretical predictions and observations of the coolest Hyades MS stars. Finally, we show that current theoretical models probably give too faint He burning luminosities unlike the case of less massive He burning models, with degenerate progenitors, which have been suggested to suffer the opposite discrepancy. 相似文献
49.
50.
The biomass of macro- and interstitial fauna on clean and wrack-covered beaches in Western Australia
Anton McLachlan 《Estuarine, Coastal and Shelf Science》1985,21(4):587-599
The benthic faunal spectrum including bacteria, protozoans, meiofauna, wrack epifauna and macrofauna, was quantitatively surveyed on two modally reflective, moderate energy, Western Australian beaches. The more exposed beach had coarser sand, no intertidal macrofauna and a poor interstitial fauna. The less exposed beach had a large deposit of wrack totalling 161 kg m?1 dry mass concentrated on the lower shore. The amphipod Allorchestes compressa was abundant in the fresh wrack comprising most of the macrofauna. There were also fairly abundant small epifauna on the wrack. Dry biomass of macrofauna, epifauna, meiofauna, protozoans and bacteria was 0, 0, 15, 4 and 180 g m?1 on the more exposed beach and 160, 3, 112, 9 and 901 g m?1 on the less exposed beach with wrack. On the latter beach there was an inverse correlation between meiofaunal densities and the densities of protozoans and bacteria, suggesting grazing by the former on the latter. On both beaches meiofauna was concentrated in the mid- to upper beach, protozoans near the surface and bacteria in the mid- to lower beach. It is estimated that bacteria are responsible for most of the secondary production on both beaches. 相似文献