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121.
During the past decade, several reports have been published that infer paleovelocity of deep-sea currents from grain-size
parameters of fine-grained sediments. Such inferences may be a gross oversimplification. Laboratory flume experiments and
theoretical treatments of suspended sediment transport indicate that particles less than 30 μm in diameter are maintained
in suspension by currents of less than 4 cm/sec. Also, there are several factors that influence sediment suspension other
than velocity, of which velocity may be one of the least important.
It is possible that coarse silt and very fine sand analyses could provide meaningful paleovelocity information; these sediments
are maintained in suspension by currents with velocities in the 1 to 15 cm/sec range. This investigation of Weddell Sea sediments
provides little encouragement for this method, however. 相似文献
122.
123.
124.
D.W. Kurtz 《Solar physics》2004,220(2):123-135
With the resounding success of helioseismology in determining the interior structure and rotation of the Sun, and in providing
unprecedented studies of the interaction of pulsation and magnetic fields in the solar atmosphere, astronomers have been delighted,
after decades of disappointing attempts, with the recent discovery of solar-like oscillations in ξ Hya, β Hyi, α Cen A and
B, η Boo, ν Ind, ζ Her, δ Eri, HD 20794, HD 160191, and others as this list is growing rapidly. There is now true seismology
of some solar-like stars. Asteroseismology also studies stars with a wide variety of interior and surface conditions. For
two decades asteroseismic techniques have been applied to many pulsating stars across the HR diagram. This review describes
some recent developments for some selected classes of pulsating stars other than the solar-like oscillators. 相似文献
125.
Ethnic Capital and Assimilation to the Great Australian (Homeownership) Dream: the early housing experience of Australia's skilled immigrants 总被引:1,自引:0,他引:1
We use the Longitudinal Survey of Immigrants to Australia, 2005–2006, to examine the housing tenure experience of skilled immigrants to Australia 6 and 18 months after arrival for relationships with ethnic capital (cultural background), visa category streams, aspects of human capital, demographics, social capital and discrimination. Homeownership experience is used to indicate integration into Australia's dominantly middle-class society. Multinomial regression analysis identifies visa entry category as the most important independent group of variables accounting for immigrants' short-term dwelling tenure, followed by aspects of human capital, family status, and the importance of ethnic capital for immigrants of both English-speaking and non-English-speaking backgrounds, and discrimination. 相似文献
126.
Ron Johnston 《Urban geography》2013,34(8):702-736
Although an innovative researcher on urban geography during the 1930s, and a prolific textbook writer thereafter, Robert Dickinson is not now recognized as one of the influential pioneers of that subfield. This paper explores why that was the case by examining his career, writings and influence, and by setting him in the context of a model of scholarly impact. [Key words: Robert Dickinson, pioneers, influence, history of urban geography.] 相似文献
127.
Ron Malega 《Urban geography》2013,34(4):530-549
This study explores Black household affluence at the metropolitan scale and suggests that metropolitan-level opportunity structures shaped rates of Black affluence for the 100 largest American metropolitan areas in 2000. I hypothesize that affluent black households favored metropolitan areas of opportunity, those places characterized by having (1) economic opportunities, (2) favorable Black–White relational standing, (3) metropolitan diversity and residential opportunities, and (4) their location in the South, which serves as a Black homeplace. Results fail to suggest evidence regarding the role of the ‘new South’ for understanding metropolitan-level rates of Black affluence. More generally, findings from this study challenge our understanding of socioeconomic stratification by investigating diversity within America’s Black community. 相似文献
128.
Nicholas Coops Andrew Loughhead Philip Ryan Ron Hutton 《International journal of geographical information science》2013,27(4):345-361
In absence of other limitations, the growth rate of a plant is dependent upon the amount of heat it receives. Each species, whether a crop, weed or disease organism, is adapted to grow at its optimum rate within a specific temperature range. Within this range, the growing degree days (GDD) is the heat accumulation above a given base temperature for a specific time period, such as a crop's growing season or phenological stage. In this paper we detail a methodology to predict GDD for synthetically generated average growing seasons derived from long term average climate data over the Australian continent. An application of these techniques has been made using the GEODATA 9 second DEM, with temperature threshold values estimated to characterize optimum growth in citrus (Citrus sinensis (L.) Osbeck). Three major determinants of the annual growth cycle of Citrus sp. were established and predicted on a spatial basis including the starting day of the growing season, the GDD for a growing season, and the time required to accumulate an arbitrarily selected 2000 GDD from the estimated starting day. When these critical environmental factors are expressed on a spatial basis, covering the Australian continent, the combination can be used to identify locations where new crop varieties can most effectively be grown to maximize fruit quality and productivity, or to extend the harvest season. Likewise, new germplasm introduced to Australia from overseas can be horticulturally assessed at sites climatically matched to the source location. 相似文献
129.
Knowing our own history? Geography department archives in the UK 总被引:1,自引:0,他引:1
The paper presents an analysis of the returns to a questionnaire survey on the state of department archives within UK departments of geography. The results of the survey are discussed in relation to recent work in geography which has examined the archive as a site for knowledge's making but seldom in its own terms as a resource for the history of geography, and studies within the archival sciences which have considered the archive as something more than a 'storehouse' for collective memory. The paper reveals that the archival record for the history of British geography is at best uneven, and in many departments non-existent, although information on departmental history is held, often as memory, by individual geographers. The paper considers the survey's implications for the future histories of British geography and addresses the nature of the UK geography department archive as resource and responsibility. 相似文献
130.
D. W. Kurtz 《Solar physics》2008,251(1-2):21-30
Stellar astronomers look on in envy at the wealth of data, the incredible spatial resolution, and the maturity of the theoretical understanding of the Sun. Yet the Sun is but one star, so stellar astronomy is of great interest to solar astronomers for its range of different conditions under which to test theoretical understanding gained from the study of the Sun. The rapidly oscillating peculiar A stars are of particular interest to solar astronomers. They have strong, global, dipolar magnetic fields with strengths in the range 1?–?25?kG, and they pulsate in high-overtone p modes similar to those in the Sun; thus they offer a unique opportunity to study the interaction of pulsation, convection, and strong magnetic fields, as is now done in the local helioseismology of sunspots. Some of them even pulsate in modes with frequencies above the acoustic cutoff frequency, in analogy with the highest frequency solar modes, but with mode lifetimes up to decades in the roAp stars, very unlike the short mode lifetimes of the Sun. They offer the most extreme cases of atomic diffusion, a small, but important ingredient of the standard solar model with wide application in stellar astrophysics. They are compositionally stratified and are observed and modelled as a function of atmospheric depth and thus can inform plans to expand helioseismic observations to have atmospheric depth resolution. Study of this unique class of pulsating stars follows the advanced state of studies of the Sun and offers more extreme conditions for the understanding of physics shared with the Sun. 相似文献