全文获取类型
收费全文 | 485篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 30篇 |
地球物理 | 72篇 |
地质学 | 153篇 |
海洋学 | 26篇 |
天文学 | 107篇 |
综合类 | 1篇 |
自然地理 | 102篇 |
出版年
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 11篇 |
2013年 | 17篇 |
2012年 | 12篇 |
2011年 | 19篇 |
2010年 | 13篇 |
2009年 | 19篇 |
2008年 | 25篇 |
2007年 | 26篇 |
2006年 | 20篇 |
2005年 | 14篇 |
2004年 | 18篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1970年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有500条查询结果,搜索用时 15 毫秒
1.
Estela M. Reynoso † Simon Johnston Anne J. Green Bärbel S. Koribalski 《Monthly notices of the Royal Astronomical Society》2006,369(1):416-424
We have observed the supernova remnant (SNR) G290.1−0.8 in the 21-cm H i line and the 20-cm radio continuum using the Australia Telescope Compact Array (ATCA). The H i data were combined with data from the Southern Galactic Plane Survey to recover the shortest spatial frequencies. In contrast, H i absorption was analysed by filtering extended H i emission, with spatial frequencies shorter than 1.1 kλ. The low-resolution ATCA radio continuum image of the remnant shows considerable internal structure, resembling a network of filaments across its 13-arcmin diameter. A high-resolution ATCA radio continuum image was also constructed to study the small-scale structure in the SNR. It shows that there are no structures smaller than ∼17 arcsec, except perhaps for a bright knot to the south, which is probably an unrelated object. The H i absorption study shows that the gas distribution and kinematics in front of SNR G290.1−0.8 are complex. We estimate that the SNR probably lies in the Carina arm, at a distance 7 (±1) kpc. In addition, we have studied nearby sources in the observed field using archival multiwavelength data to determine their characteristics. 相似文献
2.
3.
4.
Abstract. Anaerobic metabolism in the central and marginal portions of the mantle of Mercenaria mercenaria was compared. Anaerobic succinate accumulation was more rapid in the central region. This difference may be due to higher phosphoenolpyruvate carboxykinase activity in the central region. Thus, the central region is more specialized for anaerobic metabolism and the marginal region more for net shell growth. The original rate of succinate accumulation in the mantle is similar in isolated mantles and intact clams, suggesting that mantle succinate production does not require translocation of precursors from other tissues. However, in intact clams, the rate of succinate accumulation in the central region of the mantle slows after four hours. The reduced rate is probably caused by reducing the metabolic rate. Succinate accumulation and shell dissolution are slower in freshly collected clams than in clams that had been stored anaerobically. The difference may be due to induction of PEPCK synthesis during storage. Shell derived calcium did not accumulate in the mantle and, therefore did not alter the intracellular calcium concentration in the mantle. 相似文献
5.
6.
7.
In mammals, the induction of cytochrome P4501A forms by chlorinated dibenzo-p-dioxins, chlorinated dibenzofurans, and halogenated biphenyls is under control of a soluble protein known as the Ah (aromatic hydrocarbon) receptor. Little is known about the presence and properties of the Ah receptor in other vertebrate and invertebrate species. In these studies, we sought evidence for an Ah receptor in the liver or liver-equivalent of 20 species of marine and freshwater animals, using the photoaffinity ligand 2-azido-3-[125I] iodo-7,8-dibromodibenzo-p-dioxin (N3[125I]Br2DD). Specific labeling of cytosolic proteins by N3[125I]Br2DD was observed in seven species of teleost and elasmobranch fish, in PLHC-I fish hepatoma cells, and in beluga whales. No specifically labeled proteins were found in cytosol from two species of agnathan fish nor in any of nine invertebrate species representing eight classes of four phyla. The presence or absence of specifically labeled polypeptides corresponds with the inducibility of cytochrome P4501A and sensitivity to the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related planar halogenated aromatic hydrocarbons in many of these groups. Thus, Ah receptor function may have arisen early invertebrate evolution and has been conserved from elasmobranch and teleost fish to mammals. 相似文献
8.
Sediment supply and pre-existing shoreline morphology are crucial factors in controlling coastal changes due to sea-level rise. Using examples from both southeast and northeast Ireland, it can be shown that sea-level change may trigger a sequence of events which leads to both static and dynamic shoreline equilibrium. Cliff erosion and longshore sediment movement in east Co. Wexford has led to injection of sediment onto the shelf, and the growth, under both wave and tide regimes, of linear offshore shoals. These shoals now control the pattern of shoreline erosion and provide a template for possible stepwise evolution of the coast under any future sea-level rise. In contrast, the nearby coast of south Co. Wexford comprises a series of coarse clastic barriers moving monotonously onshore, via overwash processes. Here the behavior of the barrier is conditioned by the antecedent morphology of both the beach face and stream outlet bedforms. Finally, the rock platform coast of Co. Antrim presents a far more resistant shoreline to incident marine processes, yet even here there is strong evidence of present process control over so-called ‘raised’ platforms and embayments. It is concluded that coastal sediment supply and dynamics, together with coastal morphology and its interaction with waves, present a far more complex variety of sea-level indicators than is normally acknowledged. 相似文献
9.
Parnell PE 《Marine environmental research》2003,55(4):293-311
The effects of sewage discharge on algal populations and the quality of Hawai'ian coastal waters were investigated. Two outfalls were studied. One discharges primary treated sewage and the other discharges secondary treated sewage but are otherwise similar. This enabled comparisons of the effects of these different levels of treatment on the water quality and algal productivity of receiving waters. Plumes were followed and repeatedly sampled in a time-series manner. Rhodamine dye was used as a conservative tracer to compare the dilution behavior of the plume constituents MRP, NO(3)+NO(2), NH(4), Silicate, TDP, TDN, total bacteria, PC, and PN. Rates of initial dilution ranged from two to almost three orders of magnitude, and were in reasonable agreement with engineering model predictions. Dilution of plume constituents approximated that of Rhodamine until background concentrations were reached, typically within 10 min of discharge. Chl a concentrations did not increase through time in the primary sewage plume but did increase up to 30% in the secondary sewage plume. However, rates of far-field dilution were so rapid that the increase could not have been due to algal growth. The increase was attributed to the plume mixing with a water mass whose relative chl a concentrations were greater. Rates of secondary dilution ranged from 2 to 3 orders of magnitude resulting in total dilutions of 10(5)-10(6) within 3 h of discharge. These rates of secondary dilution were much greater than model predictions. From a nutrient standpoint, secondary treatment exhibited no advantages over primary treatment because dilutions were so rapid. 相似文献
10.
R. J. Johnston 《GeoJournal》1997,42(1):9-16
In those parts of their discipline which can be categorised as spatial analysis, geographers have focused attention on distance as a key variable, and have paid little attention to bounded spaces and territoriality strategies. In a rapidly restructuring world, in which distance is becoming increasingly irrelevant as an influence on many forms of behaviour, territoriality remains an important aspect of the manipulation of space for economic, social, political and cultural purposes: in the terminology of Hagerstrands classic model, while the coupling and capability constraints on interaction are weakening, the authority constraint remains strong. 相似文献