全文获取类型
收费全文 | 477篇 |
免费 | 15篇 |
专业分类
测绘学 | 38篇 |
大气科学 | 41篇 |
地球物理 | 93篇 |
地质学 | 131篇 |
海洋学 | 30篇 |
天文学 | 105篇 |
自然地理 | 54篇 |
出版年
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 17篇 |
2014年 | 18篇 |
2013年 | 23篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 12篇 |
2009年 | 22篇 |
2008年 | 19篇 |
2007年 | 32篇 |
2006年 | 30篇 |
2005年 | 21篇 |
2004年 | 18篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 17篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 15篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有492条查询结果,搜索用时 15 毫秒
1.
J. Zhang D. B. Williams J. I. Goldstein R. S. Clarke 《Meteoritics & planetary science》1990,25(3):167-175
Abstract— Characterization of the microstructural features of the metal of the Santa Catharina meteorite was performed using a variety of electron optical techniques. Sample USNM#6293 is chemically homogeneous on the micron scale and has a Ni content of 28.2 wt.%. Its microstructure is similar to that of the Twin City ataxite and contains clear taenite II, i.e., fcc taenite with domains of tetrataenite, < 10 nm in size. Sample USNM#3043 is a more typical Santa Catharina specimen with dark and light regions as observed with the light optical microscope. The dark regions are inhomogeneous and contain 45–50 wt.% Ni and 7–12 wt.% O. The light regions are homogeneous and contain 35 wt.% Ni and no detectable oxygen. The microstructure is that of cloudy zone, i.e., islands of tetrataenite, ~20 nm in size, in a honeycomb matrix. The honeycomb phase contains Ni rich oxide in the dark regions and contains metal, fcc taenite, in the light regions. The original metal structure of USNM#3043 is cloudy zone which formed during cooling into the low temperature miscibility gap of the Fe-Ni phase diagram. The dark regions were developed from the metal by selective corrosion of the honeycomb structure, transforming it into Ni containing oxides, possibly non-stoichiometric Fe2NiO4 while retaining the tetrataenite islands. Using the results of this study, many of the existing discrepancies concerning the microstructure of Santa Catharina can be explained. 相似文献
2.
The Bloomington meteorite, a 67.8 gram veined, brecciated chondrite, fell during the summer of 1938 in Bloomington, Illinois. Its olivine, orthopyroxene and metal compositions (fo69, en74 and Fe52 Ni48 respectively) and its texture identify it as a brecciated LL6 chondrite of shock facies d. Shock melt glasses occur in Bloomington as sparse melt pockets and veins in clasts and as isolated masses in the black, clast-rich matrix. The vein glasses chemically resemble bulk LL-group chondrites and thus appear to reflect total melting of the host meteorite. The melt pocket and matrix glasses, like those described previously in L-group chondrites, have more varied compositions and are typically enriched in normative plagioclase. All glasses that we analyzed in Bloomington have FeO/MgO and Na/Al ratios similar to those of LL-group chondrites, indicating that melting of this meteorite involved neither a significant change in the oxidation state of iron nor loss of sodium to a vapor phase. Bloomington is a monomict breccia whose components formed in place as a result of a single episode of shock and attendant melting. 相似文献
3.
4.
5.
6.
7.
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
8.
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
9.
10.