全文获取类型
收费全文 | 39299篇 |
免费 | 855篇 |
国内免费 | 424篇 |
专业分类
测绘学 | 869篇 |
大气科学 | 2545篇 |
地球物理 | 7489篇 |
地质学 | 14766篇 |
海洋学 | 3922篇 |
天文学 | 8544篇 |
综合类 | 88篇 |
自然地理 | 2355篇 |
出版年
2022年 | 341篇 |
2021年 | 552篇 |
2020年 | 637篇 |
2019年 | 696篇 |
2018年 | 1287篇 |
2017年 | 1223篇 |
2016年 | 1405篇 |
2015年 | 763篇 |
2014年 | 1265篇 |
2013年 | 2259篇 |
2012年 | 1439篇 |
2011年 | 1813篇 |
2010年 | 1609篇 |
2009年 | 1997篇 |
2008年 | 1703篇 |
2007年 | 1749篇 |
2006年 | 1671篇 |
2005年 | 1057篇 |
2004年 | 1043篇 |
2003年 | 975篇 |
2002年 | 1005篇 |
2001年 | 836篇 |
2000年 | 790篇 |
1999年 | 648篇 |
1998年 | 664篇 |
1997年 | 585篇 |
1996年 | 533篇 |
1995年 | 500篇 |
1994年 | 536篇 |
1993年 | 430篇 |
1992年 | 424篇 |
1991年 | 429篇 |
1990年 | 446篇 |
1989年 | 334篇 |
1988年 | 333篇 |
1987年 | 414篇 |
1986年 | 329篇 |
1985年 | 510篇 |
1984年 | 507篇 |
1983年 | 443篇 |
1982年 | 437篇 |
1981年 | 371篇 |
1980年 | 388篇 |
1979年 | 344篇 |
1978年 | 352篇 |
1977年 | 301篇 |
1976年 | 280篇 |
1975年 | 289篇 |
1974年 | 247篇 |
1973年 | 265篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
John T. Bowen 《The Professional geographer》2006,58(3):249-265
The article analyzes patterns in the distribution of manufacturing job losses that have been certified as trade‐induced by the U.S. Department of Labor. Spatial patterns in the likelihood of job loss are examined in the United States for the period from 1994 to 2002, with particular emphasis on county‐level patterns in New England. The findings demonstrate that the pattern of losses was correlated with measures of economic vitality and competitiveness including per capita income, educational attainment, occupational structure, and inventiveness. These results suggest that trade‐induced deindustrialization is borne most heavily by places ill‐equipped to compete in a more open, integrated international economy. 相似文献
932.
The U.S. and U.K. literatures have discussed “food deserts,” reflecting populated, typically urban, low‐income areas with limited access to full‐service supermarkets. Less is known about supermarket accessibility within Canadian cities. This article uses the minimum distance and coverage methods to determine supermarket accessibility within the city of Edmonton, Canada, with a focus on high‐need and inner‐city neighborhoods. The results show that for 1999 both of these areas generally had higher accessibility than the remainder of the city, but six high‐need neighborhoods had poor supermarket accessibility. We conclude by examining potential reasons for differences in supermarket accessibility between Canadian, U.S., and U.K. cities. 相似文献
933.
Robert Gilbert Sarah Crookshanks Kyle R. Hodder John Spagnol Roland B. Stull 《Journal of Paleolimnology》2006,35(4):737-745
Severe rainfall in mid October, 2003 produced the largest floods in almost a century of record on rivers in the Cordillera
of southwestern British Columbia. Sediment deposited in Lillooet Lake as a result of this event is clearly distinguished by
stratigraphy, colour, texture, magnetic properties, and organic content. Each of these physical properties is related to the
lacustrine processes, especially turbid underflow, that distributed the sediment through the lake. The flood, which lasted
less than a week, delivered 8–12 times the amount of sediment that accumulates in most entire years in the deepest, central
parts of the lake. Recognition of events of this type in the stratigraphic record offers a means of assessing the changing
nature of extreme hydroclimatic events, and their relation to more ubiquitous, lower-energy processes. 相似文献
934.
I. D. L. Foster T. M. Mighall H. Proffitt D. E. Walling P. N. Owens 《Journal of Paleolimnology》2006,35(4):881-895
We present 137Cs profiles for three low lying coastal lagoons in Southwest England that show a decline in activity with sediment depth.
137Cs inventories are lower than expected by comparison with local reference inventories despite the fact that sampling was undertaken
in the deep-water zone of each lake where sediment and 137Cs focusing would be expected. At all three locations, lake sediment 7Be and unsupported 210Pb (210Pbun) inventories are not significantly lower than the local reference inventory. 137Cs inventories in the study cores range from 38 to 95% of local reference inventories. The standing water level and mud: water
interface at two sites are below maximum tide level and, at all three sites, salinity increases significantly in the water
columns between low and high tide and in the pore waters of the underlying sediments. We suggest that the difference in hydrostatic
pressure between sea level and standing water levels in the lagoons forces salt water up through the sediment column and that
monovalent cations (especially Na+ and K+) replace 137Cs on exchange sites leading to the upward migration and loss of 137Cs. Rising sea levels may therefore contribute to remobilisation and release of 137Cs to the aquatic environment from the sediments of coastal lagoons. 相似文献
935.
Miriam Dühnforth Andreas G. N. Bergner Martin H. Trauth 《Journal of Paleolimnology》2006,36(3):281-294
The Nakuru-Elmenteita basin in the Central Kenya Rift, contains two shallow, alkaline lakes, Lake Nakuru (1770 m above sea level) and Lake Elmenteita (1786 m). Ancient shorelines and lake sediments at 1940 m suggest that these two lakes formed a single large and deep lake as a result of a wetter climate during the early Holocene. Here, we used a hydrological model to compare the precipitation–evaporation balance during the early Holocene to today. Assuming that the Nakuru-Elmenteita basin was hydrologically closed, as it is today, the most likely climate scenario includes a 45% increase in mean-annual precipitation, a 0.5°C decrease in air temperature, and an increase of 9% in cloud coverage from the modern values. Compared to the modeling results from other East African lake basins, this dramatic increase in precipitation seems to be unrealistic. Therefore, we propose a significant flow of water from the early Holocene Lake Naivasha in the south towards the Nakuru-Elmenteita basin to compensate the extremely negative hydrological budget of this basin. Since we did not find any field evidence for a surface connection, as often proposed during the last 70 years, the hydrological deficit of the Nakuru-Elmenteita basin could have also been compensated by a subsurface water exchange. 相似文献
936.
This study investigates the extent to which people's views on the causes and preventability of earthquake damage might be influenced by their degree of exposure to hazard as well as what information they have been given about the hazard. The results show that the provision of hazard zoning information influences judgements on preventability and causes of damage, but this effect depends on the degree of hazard faced by residents. In low hazard zones, information leads to the view that causes are manageable, whereas in high hazard zones information may induce a degree of fatalism. The use of public information in risk management needs to take into account the degree of risk faced by the recipients. 相似文献
937.
On the Social Lives of Maps and the Politics of Diagrams: A story of power, seduction, and disappearance 总被引:1,自引:0,他引:1
John Pickles 《Area》2006,38(3):347-350
938.
939.
K. W. Helen Lau Keith E. Louden Sharon Deemer Jeremy Hall John R. Hopper Brian E. Tucholke W. Steven Holbrook Hans Christian Larsen † 《Geophysical Journal International》2006,167(1):157-170
New multichannel seismic reflection data were collected over a 565 km transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350 km of the profile: (1) continental crust; (2) transitional basement and (3) oceanic crust. Continental crust thins over a wide zone (∼160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastwards beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landwards by a basement high that may consist of serpentinized peridotite and seawards by a pair of basement highs of unknown crustal origin. Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle, although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landwards of magnetic anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ∼138 Ma (Valanginian) in the south (southern Newfoundland Basin) to ∼125 Ma (Barremian–Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins. 相似文献