全文获取类型
收费全文 | 177篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 9篇 |
地球物理 | 26篇 |
地质学 | 88篇 |
海洋学 | 33篇 |
天文学 | 12篇 |
自然地理 | 12篇 |
出版年
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 13篇 |
2013年 | 16篇 |
2012年 | 2篇 |
2011年 | 3篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 12篇 |
2007年 | 6篇 |
2006年 | 1篇 |
2005年 | 8篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有187条查询结果,搜索用时 15 毫秒
71.
An analysis of the New Zealand whale stranding record by M. W. Bradyn. Science and Research Series 29. ISSN 0113–3713, ISBN 0–478–01278–6. Available from Department of Conservation, Wellington. Price: $15.00. Fish quality control by computer vision, edited by L. F. Pau and R. Olafsson. Published by Marcel Dekker, Inc. 相似文献
72.
Samantha J. Penny Christopher J. Conselice 《Monthly notices of the Royal Astronomical Society》2008,383(1):247-257
We present the result of a photometric and Keck low-resolution imaging spectrometer (LRIS) spectroscopic study of dwarf galaxies in the core of the Perseus Cluster, down to a magnitude of M B =−12.5 . Spectra were obtained for 23 dwarf-galaxy candidates, from which we measure radial velocities and stellar population characteristics from absorption line indices. From radial velocities obtained using these spectra, we confirm 12 systems as cluster members, with the remaining 11 as non-members. Using these newly confirmed cluster members, we are able to extend the confirmed colour–magnitude relation for the Perseus Cluster down to M B =−12.5 . We confirm an increase in the scatter about the colour–magnitude relationship below M B =−15.5 , but reject the hypothesis that very red dwarfs are cluster members. We measure the faint-end slope of the luminosity function between M B =−18 and −12.5, finding α=−1.26 ± 0.06 , which is similar to that of the field. This implies that an overabundance of dwarf galaxies does not exist in the core of the Perseus Cluster. By comparing metal and Balmer absorption line indices with α-enhanced single stellar population models, we derive ages and metallicities for these newly confirmed cluster members. We find two distinct dwarf elliptical populations: an old, metal-poor population with ages ∼8 Gyr and metallicities [Fe/H] < −0.33 , and a young, metal-rich population with ages <5 Gyr and metallicities [Fe/H] > −0.33 . Dwarf galaxies in the Perseus Cluster are therefore not a simple homogeneous population, but rather exhibit a range in age and metallicity. 相似文献
73.
G. V. Gibbs M. B. Boisen F. C. Hill O. Tamada R. T. Downs 《Physics and Chemistry of Minerals》1998,25(8):574-584
The topological properties of the electron density distributions for more than 20 hydroxyacid, geometry optimized molecules
with SiO and GeO bonds with 3-, 4-, 6- and 8-coordinate Si and Ge cations were calculated. Electronegativities calculated
with the bond critical point (bcp) properties of the distributions indicate, for a given coordination number, that the electronegativity
of Ge (∼1.85) is slightly larger than that of Si (∼1.80) with the electronegativities of both atoms increasing with decreasing
bond length. With an increase in the electron density, the curvatures and the Laplacian of the electron density at the critical
point of each bond increase with decreasing bond length. The covalent character of the bonds are assessed, using bond critical
point properties and electronegativity values calculated from the electron density distributions. A mapping of the (3, −3)
critical points of the valence shell concentrations of the oxide anions for bridging SiOSi and GeOGe dimers reveals a location
and disposition of localized nonbonding electron pairs that is consistent with the bridging angles observed for silicates
and germanates. The bcp properties of electron density distributions of the SiO bonds calculated for representative molecular
models of the coesite structure agree with average values obtained in X-ray diffraction studies of coesite and danburite to
within ∼5%.
Received: 18 August 1997 / Revised, accepted: 19 February 1998 相似文献
74.
Shigeho Sueno Shigeru Matsuura G. V. Gibbs M. B. Boisen Jr. 《Physics and Chemistry of Minerals》1998,25(5):366-377
Two new protoamphibole-type amphiboles with space group type Pnmn, have been found in nature: protoferro-anthophyllite (Fe0.80Mn0.20)2 (Fe0.98Mg0.02)5 (Si4O11)2(OH)2, and protomangano-ferro-anthophyllite, (Mn0.70Fe0.30)2 (Fe0.82Mg0.18)5 (Si4O11)2(OH)2. Protoferro-anthophyllite (PFA) occurs in pegmatites at both Gifu Prefecture, Japan and at Cheyenne Mountain, El Paso County, Colorado, USA. Protomangano-ferro-anthophyllite, (PMFA) occurs in pegmatites at Fukushima Prefecture and in a Mn mine at Tochigi Prefecture, Japan. Structure determinations of the two amphiboles show that both are isostructural with the synthetic fluorian-amphibole, protoamphibole (= protofluorian-lithian-anthophyllite). A calculation of the procrystal electron density distributions, the bond paths and the bond critical point properties of PFA, PMFA, grunerite and protoamphibole indicates that the M4 cation in these amphiboles is 4-coordinated. A calculation of the electron density distributions at the Becke3LYP/6-311G(2d,p) level for model silicate tetrahedra for these amphiboles and anthophyllite reveals that the value of the electron density at the bond critical points, ρ(r c ), for the SiO(nbr) bonds is larger, on average (0.93 e/Å3), than that for the SiO(br) bonds (0.90 e/Å3). The observed SiO bond lengths decrease linearly with increasing ρ(r c ) while the magnitudes of the curvatures of ρ(r c ) both perpendicular and parallel to the bonds and the Laplacian of ρ(r c ) each increases. These trends are associated with an increase in the electronegativity of the Si cation, a possible increase in the covalent character of the SiO bond and a tendency for SiO(nbr) bonds to be involved in wider OSiO angles than SiO(br) bonds. It is possible, if not likely, that protoanthophyllite has often been misidentified as anthophyllite. 相似文献
75.
76.
Recovery of polluted ecosystems: the case for long-term studies 总被引:6,自引:0,他引:6
Hawkins SJ Gibbs PE Pope ND Burt GR Chesman BS Bray S Proud SV Spence SK Southward AJ Langston WJ 《Marine environmental research》2002,54(3-5):215-222
Recovery of marine ecosystems from pollution has tended to receive less attention than the study of new or continuing impacts, but such studies are important in charting recovery from acute incidents and following legislation to deal with chronic contamination. Recovery is inevitably a long-term process, and where such studies have been made they are often too short-lived. Interest quickly wanes following an acute incident and governmental bodies rapidly switch to new legislative priorities for chronic inputs. We review three case studies: recovery of dogwhelk populations after local extinction by tributyl tin leachates from anti-fouling paints; recovery of rocky shore communities from oil spills; and recovery of estuarine ecosystems from industrial and urban development. We then make some generalisations about recovery processes before making a plea for long-term studies of polluted areas. 相似文献
77.
M. B. Boisen Jr. G. V. Gibbs M. S. T. Bukowinski 《Physics and Chemistry of Minerals》1994,21(5):269-284
A simulated annealing technique was used to search for global and local minimum energy structures of a potential energy model for silica. The model is based on ab initio SCF MO calculations on the disilicic acid molecule, H6Si2O7. Starting with 4 SiO2 units, with the atoms randomly distributed in the unit cell, 23 distinct silica tetrahedral framework structures were found, with a variety of space group symmetries and cell dimensions. Despite the assumption of P 1 space group symmetry for the starting structure, only 7 of the local minimum energy structures were found to possess triclinic symmetry with the remainder exhibiting symmetries ranging from P c to
to within 0.001 Å. Although the interaction potential for the disilicic acid molecule has a single minimum energy SiO bond length and SiOSi angle, the local minimum energy structures exhibit angles that range between 105° and 180° and bond lengths that range between 1.55 and 1.68 Å. The correlation observed for coesite and the other silica polymorphs between SiO bond length and fs(O) is reproduced. The generated structures show a wide variety of coordination sequences, ring sizes and framework densities, the later ranging from 19.8 to 35.5 Si/1000 Å3. The energies of these structures correlate with their framework densities, particularly for higher energy structures. 相似文献
78.
Ronald J. Gibbs 《Marine Chemistry》1986,18(2-4)
The transport of metals from rivers through the estuaries to the oceans is, to a large extent, carried out by small particles. These small particles coagulate when they are exposed to small amounts of salt water. The coagulation process segregates the particles and their associated metals in different size flocs. To understand further the process that was found to occur in the Chesapeake Bay, laboratory simulation experiments have been conducted on these natural materials in which the turbulence and salinity was controlled. The metals studied were Cd, Cr, Cu, Fe, Pb, Ni, Mn and Zn. In these laboratory simulation experiments, the concentration of the various metals was different in the various size flocs. This experiment demonstrated that segregation of the metals does occur due to the coagulation of natural sediments by seawater. 相似文献
79.
80.
Cheryl?L.?DoughtyEmail author J.?Adam?Langley Wayne?S.?Walker Ilka?C.?Feller Ronald?Schaub Samantha?K.?Chapman 《Estuaries and Coasts》2016,39(2):385-396
The climate change-induced expansion of mangroves into salt marshes could significantly alter the carbon (C) storage capacity of coastal wetlands, which have the highest average C storage per land area among unmanaged terrestrial ecosystems. Mangrove range expansion is occurring globally, but little is known about how these rapid climate-driven shifts may alter ecosystem C storage. Here, we quantify current C stocks in ecotonal wetlands across gradients of marsh- to mangrove-dominance, and use unique chronological maps of vegetation cover to estimate C stock changes from 2003 to 2010 in a 567-km2 wildlife refuge in the mangrove-salt marsh ecotone. We report that over the 7-yr. period, total wetland C stocks increased 22 % due to mangrove encroachment into salt marshes. Newly established mangrove stands stored twice as much C on a per area basis as salt marsh primarily due to differences in aboveground biomass, and mangrove cover increased by 69 % during this short time interval. Wetland C storage within the wildlife refuge increased at a rate of 2.7 Mg C ha?1 yr.?1, more than doubling the naturally high coastal wetland C sequestration rates. Mangrove expansion could account for a globally significant increase of terrestrial C storage, which may exert a considerable negative feedback on warming. 相似文献