全文获取类型
收费全文 | 364篇 |
免费 | 22篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 72篇 |
地球物理 | 102篇 |
地质学 | 112篇 |
海洋学 | 12篇 |
天文学 | 63篇 |
自然地理 | 21篇 |
出版年
2023年 | 2篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 24篇 |
2015年 | 18篇 |
2014年 | 23篇 |
2013年 | 29篇 |
2012年 | 25篇 |
2011年 | 11篇 |
2010年 | 22篇 |
2009年 | 16篇 |
2008年 | 16篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1990年 | 2篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 2篇 |
1974年 | 4篇 |
1968年 | 2篇 |
1965年 | 2篇 |
1962年 | 2篇 |
1958年 | 1篇 |
1957年 | 4篇 |
1955年 | 3篇 |
1954年 | 1篇 |
1953年 | 6篇 |
1952年 | 3篇 |
1951年 | 4篇 |
1950年 | 3篇 |
1949年 | 3篇 |
1948年 | 4篇 |
排序方式: 共有390条查询结果,搜索用时 31 毫秒
361.
362.
Pascal Willis Bruce Haines Jean-Paul Berthias Pierre Sengenes Jean-Louis Le Mouël 《Comptes Rendus Geoscience》2004,336(9):839-846
We point out an acceleration of the DORIS clock on-board the Jason satellite during passes over the South Atlantic Anomaly (SAA). When this effect is ignored in the current geodetic positioning of the DORIS stations, derived coordinates show almost linear trends in time, corresponding to anomalous horizontal and vertical velocities of the order of 1 m yr?1. We propose a simple scientific explanation of this physical phenomenon that is corroborated by direct Jason/TOPEX clock comparisons with respect to the DORIS master beacons in Kourou and Toulouse. To cite this article: P. Willis et al., C. R. Geoscience 336 (2004). 相似文献
363.
Graphitization in a high-pressure,low-temperature metamorphic gradient: a Raman microspectroscopy and HRTEM study 总被引:6,自引:0,他引:6
Olivier Beyssac Jean-Noël Rouzaud Bruno Goffé Fabrice Brunet Christian Chopin 《Contributions to Mineralogy and Petrology》2002,143(1):19-31
The graphitization of carbonaceous material (CM) in a high-pressure metamorphic gradient is characterized along a cross section in the Schistes Lustrés formation, Western Alps. Along this 25-km cross section, both the CM precursor and the host-rock lithology are homogeneous, and the prograde evolution of the pressure-temperature metamorphic conditions from the lower blueschist-facies (13 kbar, 330 °C) to the eclogite-facies (20 kbar, 500 °C) is tightly constrained by literature data. Raman microspectroscopy shows that at the micrometre scale, this process is progressive and continuous with increasing metamorphic grade, and that the structure of CM is very sensitive to temperature variations. At the nanometre scale (HRTEM), the CM is composed of a mixture of a microporous phase and an onion-ring like phase, both known as non-graphitizing under the effect of temperature at ambient pressure. The HP-LT graphitization produces structurally and microtexturally heterogeneous CM. With increasing metamorphic grade, the graphitization of the two types of CM proceeds up to the triperiodic graphite stage because of microtextural and structural changes that are specific to each type of CM. The microporous material is progressively transformed into graphite through a macroporous transitional stage. In this case, graphitization mainly occurs on the pore walls as a result of pore growth. In the case of concentric onion-ring like material, graphitization occurs in the regions with the largest radius of curvature, i.e. on the outer part of the ring. In comparison with 1-bar experiments, pressure seems to induce microtextural changes, which allows the subsequent structural modifications of the starting material. 相似文献
364.
H. GöteÖstlund H. Gorman Dorsey Claës G. Rooth 《Earth and Planetary Science Letters》1974,23(1):69-86
Radiocarbon data for 11 stations and tritium data for 16 stations in the North Atlantic Ocean from 74°N to 3°N are presented. For radiocarbon, normal errors inΔ14C are± 4‰, and in tritium,± 0.09TU or± 3%, whichever is larger. There is a remarkable, but not simply linear, correlation between oceanic bomb transients in14C and3H. The deep convective mixing in the Greenland Sea is reflected in substantial bomb tracer penetration to all depths, with residence time for the deep, cold core water that seems to be 20 to 30 years. The outflow in the bottom layer southward over the sills of the Denmark Strait and Faroe Passage carries significant tritium concentration, at least to 40°N. Complicated, but coherent, profile structures in the subtropical Atlantic suggest effects of large-scale lateral advection. In particular, a pronounced minimum in both14C and3H might be associated with the Antarctic intermediate water. 相似文献
365.
Dr. N. N. Mozgova S. N. Nenasheva A. V. Efimov Dr. Yu. S. Borodaev Dr. Y. Moëlo 《Mineralogy and Petrology》1992,46(2):137-153
Summary A second confirmed occurrence of wittite, one of the four known Pb-Bi-Se-sulfosalts, has been found in the Nevskoe tin deposit (Eastern Siberia). Microprobe analyses of wittite show pronounced variation of Se content (from 9.5 to 16.5 wt. %), due to S --> Se substitution; Pb and Bi contents vary from 29 and 43%, up to 34 and 46%, respectively. Minor elements are also present: Sb up to 1.5%, Ag up to 1.3 %, and Cu (0 to 0.2%). Comparison of microprobe data of wittite from Nevskoe and Falun, on the one hand, and cannizzarite from different deposits on the other hand, indicate that Ag is incorporated in the wittite/cannizzarite structure through the substitution 2 Pb -> Bi + Ag. Conversely, Ag substraction gives a constant Bi/(Bi + Pb) atomic ratio, independent of the Se/(Se+"S) ratio, and close to 55.1%. Se-rich wittite is compositionally very close to proudite and weibullite. X-ray powder and electron microdiffraction patterns are given; the incommensurate structure agrees with the 7H/12Q match along , like in wittite from Falun. Nevskoe wittite is close to Pb8Bi10(S, Se)23, but the 7H/12Q match requires the formula Pb11.61Bi14.26S33, with about 3% of the Pb atoms in the Q layer replaced by Bi atoms and vacancies (p). Taking into account all microprobe data, the general formula developed is: Pb11.61–2x0.13Agx(Bi14.26+x-ySby)(S1–zSez)33 with x and y 0.86 at., and z 0.45. At Nevskoe, associated bismuthinite contains from 5 to 12% Se, with minor Sb, Pb and Cu. Se-rich cosalite contains from 4 to 8% Se, with Sb from 2.7 to 5.3%, and minor Ag and Cu. Wittite in contact with cosalite clearly shows a relative Se-enrichment, that could be due to the pseudo-hexagonal sub-lattice of this incommensurate structure, very similar to the Bi2(Se, Te, S)3 sheet in the tetradymite series. According to microprobe data, there is a continuous change from Se-free cannizzarite to Se-rich wittite. Therefore, the validity of wittite as a specific mineral species appears questionable, and more accurate crystallographic studies on this incommensurate series are necessary.
Wittite avec Cosalite et Bismuthinite Séléniferes du Gisement d'Etain de Hevskoe (District de Magadan, Russie)
Resume Une seconde occurrence de wittite, l'un des quatre sulfosels de Pb-Bi-Se cormus, a été trouvée daps le gisement d'étain de Nevskoe (Sibérie Orientale). Son analyse á la microsonde électronique montre une forte variation de la teneur en sélénium (de 9,5 á 16,5%), qui se substitue au soufre; les teneurs en Pb et Bi varient de 29 à 43 et 34 á 46%, respectivement. On note la présence de Sb (, 1,5%), Ag ( 1,3%) et Cu (< 0,2%). La comparaison des analyses de wittite de Nevskoe et Falun, et de cannizzarite de différents gisements, montre que Bans cette série l'argent est incorporé suivant la substitution 2 Pb Bi + Ag. Après soustraction de Ag, le rapport atornique Bi/(Bi + Pb) corrigé apparaït constant, proche de 55,1%, et indépendant du rapport Se/(S + Se). La wittite la plus riche en Se est chimiquement très proche de la proudite et de la weibullite. Son diagramme de poudre aux rayons X ainsi que son étude en microdiffraction électronique sont présentés; la structure, de type incommensurable, s'accorde aver un ajustement selon le rapport 7H/12Q suivant , comme dans la wittite de Falun. La formule de la wittite de Nevskoe est proche de Pb8Bi10(S, Se)23, mais l'ajustement 7H/12Q demande la formule Pb11.61Bi14.26S33, avec environ 3% des sites à Pb du feuillet Q remplacés par des atomes de Bi et des sites vacants (). La prise en compte de l'ensemble des analyses conduit á la formule développée générale: Pb11.61-2x0.13Agx(Bi14,26+x–ySby)-(S1 –zSez)33 avec x et y 0,86 at., et z 0,45. A Nevskoe, la bismuthinite associée contient de 5 à 12% Se, avec Sb, Pb et Cu mineurs. La cosalite contient de 4 a 8% Se, 2,7 á 5,3% Sb, avec Ag et Cu mineurs. Lá où wittite et cosalite sont en contact étroit, la wittite montre clairement un enrichissement relatif en Se, qui pourrait etre du au sousréseau pseudo-hexagonal de cette structure incommensurable, très proche du feuillet Bi2(Se, Te, S)3 présent dans la série de la tétradymite. Les analyses à la microsonde indiquant une continuité chimique de la cannizzarite sans Se à la wittite 1a plus riche en Se, la validité de la wittite en tant qu'espéce spécifique apparaït discutable. Mais le caractère incommensurable de cette série demande une etude cristallographique plus détaillée.相似文献
366.
Philippe Léone Charlotte Doussier-Brochard Gilles André Yves Moëlo 《Physics and Chemistry of Minerals》2008,35(4):201-206
Mn2+Sb2S4, a monoclinic dimorph of clerite, and benavidesite (Mn2+Pb4Sb6S14) show well-individualized single chains of manganese atoms in octahedral coordination. Their magnetic structures are presented
and compared with those of iron derivatives, berthierite (Fe2+Sb2S4) and jamesonite (Fe2+Pb4Sb6S14). Within chains, interactions are antiferromagnetic. Like berthierite, MnSb2S4 shows a spiral magnetic structure with an incommensurate 1D propagation vector [0, 0.369, 0], unchanged with temperature.
In berthierite, the interactions between identical chains are antiferromagnetic, whereas in MnSb2S4 interactions between chains are ferromagnetic along c-axis. Below 6 K, jamesonite and benavidesite have commensurate magnetic structures with the same propagation vector [0.5, 0, 0]:
jamesonite is a canted ferromagnet and iron magnetic moments are mainly oriented along the a-axis, whereas for benavidesite, no angle of canting is detected, and manganese magnetic moments are oriented along b-axis. Below 30 K, for both compounds, one-dimensional magnetic ordering or correlations are visible in the neutron diagrams
and persist down to 1.4 K. 相似文献
367.
Amandine Cozic Eric Viollier Jean-François Chiffoleau Joël Knoery Emmanuelle Rozuel 《Estuaries and Coasts》2008,31(6):1063-1071
Concentrations of volatile hydrogen sulfide (H2S), carbonyl sulfide (OCS), methane thiol (MeSH), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS) in the Seine estuary
(France) were investigated in spring 2005 using samples collected from the first meter beneath the surface. Levels of dissolved
metals (Ag, Cd, Cu, Zn, Ni, Co, Pb), suspended particulate matter, and particular organic carbon were also assessed. Maximum
concentrations were 0.80 nM for H2S, 0.64 nM for OCS, 3.06 nM for MeSH, 11.06 nM for DMS, and 1.18 nM for DMDS, and different features were observed for the
five volatile reduced sulfur compounds (VRSCs). Experiments were conducted to determine silver–VRSC conditional stability
constants. Major interactions were observed between H2S and Ag, which may partially account for the absence of volatile H2S at the lowest salinities. OCS, MeSH, and DMS did not interact with Ag, as revealed by their insignificant K′ values. Variations in concentrations along the salinity gradient may be explained by the influence of phytoplanktonic compounds. 相似文献
368.
369.
We analyze the Wolf number daily series WN (1849 to present) as well as two other related series characterizing solar activity. Our analysis consists in computing the
amplitude of a given Fourier component in a sliding time window and examining its long-term evolution. We start with the well-known
27.03- and 27.6-day periods and observe strong decadal variations of this amplitude as well as a sharp increase of the average
value starting around 1905. We then consider a packet of 31 lines with periods from 25.743 to 28.453 days, which is shown
to be a better representation of the synodic solar rotation. We first examine the temporal evolution of individual lines,
then the energy of the packet. The energy of the packet increases sharply at the beginning of the 20th century, leading by
more than two decades the well-known increase of the Wolf number. The nonaxisymmetry of sunspots increases before the total
increase of activity and may be considered as a precursor. We discuss briefly and tentatively this observation in terms of
solar dynamo theory. 相似文献
370.
Lewis SE Schaffelke B Shaw M Bainbridge ZT Rohde KW Kennedy K Davis AM Masters BL Devlin MJ Mueller JF Brodie JE 《Marine pollution bulletin》2012,65(4-9):280-291
Herbicide residues have been measured in the Great Barrier Reef lagoon at concentrations which have the potential to harm marine plant communities. Monitoring on the Great Barrier Reef lagoon following wet season discharge show that 80% of the time when herbicides are detected, more than one are present. These herbicides have been shown to act in an additive manner with regards to photosystem-II inhibition. In this study, the area of the Great Barrier Reef considered to be at risk from herbicides is compared when exposures are considered for each herbicide individually and also for herbicide mixtures. Two normalisation indices for herbicide mixtures were calculated based on current guidelines and PSII inhibition thresholds. The results show that the area of risk for most regions is greatly increased under the proposed additive PSII inhibition threshold and that the resilience of this important ecosystem could be reduced by exposure to these herbicides. 相似文献