全文获取类型
收费全文 | 2290篇 |
免费 | 82篇 |
国内免费 | 15篇 |
专业分类
测绘学 | 74篇 |
大气科学 | 184篇 |
地球物理 | 458篇 |
地质学 | 825篇 |
海洋学 | 156篇 |
天文学 | 431篇 |
综合类 | 7篇 |
自然地理 | 252篇 |
出版年
2023年 | 10篇 |
2021年 | 26篇 |
2020年 | 34篇 |
2019年 | 31篇 |
2018年 | 52篇 |
2017年 | 33篇 |
2016年 | 60篇 |
2015年 | 55篇 |
2014年 | 61篇 |
2013年 | 136篇 |
2012年 | 59篇 |
2011年 | 104篇 |
2010年 | 96篇 |
2009年 | 122篇 |
2008年 | 115篇 |
2007年 | 101篇 |
2006年 | 103篇 |
2005年 | 91篇 |
2004年 | 92篇 |
2003年 | 88篇 |
2002年 | 91篇 |
2001年 | 64篇 |
2000年 | 53篇 |
1999年 | 62篇 |
1998年 | 59篇 |
1997年 | 31篇 |
1996年 | 27篇 |
1995年 | 28篇 |
1994年 | 32篇 |
1993年 | 33篇 |
1992年 | 22篇 |
1991年 | 23篇 |
1990年 | 28篇 |
1989年 | 34篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 29篇 |
1983年 | 25篇 |
1982年 | 19篇 |
1981年 | 34篇 |
1980年 | 26篇 |
1979年 | 17篇 |
1977年 | 14篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1974年 | 15篇 |
1973年 | 9篇 |
1970年 | 8篇 |
排序方式: 共有2387条查询结果,搜索用时 93 毫秒
21.
Laurie S. Balistrieri David M. Borrok W. Ian Ridley 《Geochimica et cosmochimica acta》2008,72(2):311-328
Fractionation of Cu and Zn isotopes during adsorption onto amorphous ferric oxyhydroxide is examined in experimental mixtures of metal-rich acid rock drainage and relatively pure river water and during batch adsorption experiments using synthetic ferrihydrite. A diverse set of Cu- and Zn-bearing solutions was examined, including natural waters, complex synthetic acid rock drainage, and simple NaNO3 electrolyte. Metal adsorption data are combined with isotopic measurements of dissolved Cu (65Cu/63Cu) and Zn (66Zn/64Zn) in each of the experiments. Fractionation of Cu and Zn isotopes occurs during adsorption of the metal onto amorphous ferric oxyhydroxide. The adsorption data are modeled successfully using the diffuse double layer model in PHREEQC. The isotopic data are best described by a closed system, equilibrium exchange model. The fractionation factors (αsoln-solid) are 0.99927 ± 0.00008 for Cu and 0.99948 ± 0.00004 for Zn or, alternately, the separation factors (Δsoln-solid) are −0.73 ± 0.08‰ for Cu and −0.52 ± 0.04‰ for Zn. These factors indicate that the heavier isotope preferentially adsorbs onto the oxyhydroxide surface, which is consistent with shorter metal-oxygen bonds and lower coordination number for the metal at the surface relative to the aqueous ion. Fractionation of Cu isotopes also is greater than that for Zn isotopes. Limited isotopic data for adsorption of Cu, Fe(II), and Zn onto amorphous ferric oxyhydroxide suggest that isotopic fractionation is related to the intrinsic equilibrium constants that define aqueous metal interactions with oxyhydroxide surface sites. Greater isotopic fractionation occurs with stronger metal binding by the oxyhydroxide with Cu > Zn > Fe(II). 相似文献
22.
23.
Inhomogeneous substrate analysis using EM300 backscatter imagery 总被引:2,自引:0,他引:2
Backscatter reflectivity from multibeam echo-sounders provides a powerful tool to efficiently characterize seafloor substrates. A comprehensive EM300 bathymetric and backscatter survey has been completed of Cook Strait, in central New Zealand. This paper presents a detailed analysis of the realtime corrections applied to the raw EM300 multibeam data and additional corrections required to compute angular variations of the backscatter strength. The corrections, including the local absorption coefficient, the influence of seafloor topography and sound refraction in the water column, are determined for different Cook Strait seafloor substrates. Modifying MB-System software code, we extracted the backscatter signal parameters in order to quantify the raw backscatter strength and apply additional processing. Profiles of backscatter strength versus incidence angle were computed for a variety of sites characterized by flat seafloor and homogeneous substrates, and for which ground-truth data were available. For each homogeneous site, different but characteristic backscatter profiles are observed that can be interpreted in terms of sediment facies. To analyze heterogeneous substrates, we present a statistical technique, based on a 3-dimensional distribution of (incidence angle, backscatter strength) couples that preserves geological information of the substrate components. This analysis, using backscatter data acquired on a submarine volcano, north of New Zealand, clearly differentiates soft sediments and lava flows within a heterogeneous substrate. 相似文献
24.
25.
Laurence P. Madin Stephen M. Bollens Erich Horgan Mari Butler Jeffrey Runge Barbara K. Sullivan Grace Klein-Macphee Edward Durbin Ann G. Durbin Donna Van Keuren Stphane Plourde Ann Bucklin M. Elizabeth Clarke 《Deep Sea Research Part II: Topical Studies in Oceanography》1996,43(7-8)
Hydroids are typically attached, benthic cnidarians that feed on a variety of small prey. During sampling on Georges Bank in spring 1994, we found huge numbers of hydroids suspended in the plankton. They fed on young stages of copepods that are an important prey for fish, as well as on young fish themselves. Two independent methods were used to estimate feeding rates of the hydroids; both indicate that the hydroids are capable of consuming from 50% to over 100% of the daily production of young copepods. These results suggest that hydroids can have a profound effect on the population dynamics of zooplankton and young fish on Georges Bank. 相似文献
26.
Alkylphenolic compounds are present in estuarine and marine environments. They are moderately bioaccumulative, and oestrogenic to fish following three week, in vivo, exposures. The effects of prolonged exposure are, as yet, unclear. Sand goby (Pomatoschistus minutus) were exposed to measured concentrations of 4-tert-octylphenol (OP) in a 28-day, dose-ranging study, and a six month temporal response study. Following 28-days exposure to measured 31+/-6 or 101+/-47 microg l(-1) OP (mean+/-SD), immature male sand goby showed elevated vitellogenin (VTG) mRNA expression. Plasma alkali-labile phosphate concentrations were elevated in both sexes and were higher in females than males. Although measured OP concentrations were variable, they were significantly different for each treatment and a range of concentration-dependent effects were observed. The LC(50) for chronic OP exposure (8 weeks) was 29+/-6 microg l(-1), and both sexes demonstrated concentration and duration dependent increases in VTG mRNA expression. Exposure to 28+/-20 microg l(-1) OP (median+/-95% CI) for 6 months inhibited development of male nuptial colouration and sperm duct glands. These findings are discussed in relation to environmental concentrations of alkylphenols and ecological concerns. 相似文献
27.
28.
Here we report the results of the first molecular enzymological study of fish UDP-glucuronosyltransferase (UDPGT). UDPGT activities of plaice liver microsomes were greatest for planar phenols and there was low but measurable conjugation of bilirubin, testosterone and androsterone. A highly purified preparation was isolated which possessed activities towards 1-naphthol, bilirubin and testosterone, containing several molecular weight species of Mr 52–56 kDa. On immunoblot analysis these proteins cross-reacted with a polyspecific anti-rat UDPGT antibody, suggesting that a number of plaice UDPGT isoforms with epitopes in common with the corresponding rat enzymes had been purified. 相似文献
29.
30.