全文获取类型
收费全文 | 27442篇 |
免费 | 717篇 |
国内免费 | 1575篇 |
专业分类
测绘学 | 1535篇 |
大气科学 | 2629篇 |
地球物理 | 5162篇 |
地质学 | 13256篇 |
海洋学 | 1393篇 |
天文学 | 1793篇 |
综合类 | 2440篇 |
自然地理 | 1526篇 |
出版年
2024年 | 13篇 |
2023年 | 50篇 |
2022年 | 159篇 |
2021年 | 166篇 |
2020年 | 116篇 |
2019年 | 131篇 |
2018年 | 4859篇 |
2017年 | 4142篇 |
2016年 | 2716篇 |
2015年 | 382篇 |
2014年 | 273篇 |
2013年 | 203篇 |
2012年 | 1144篇 |
2011年 | 2884篇 |
2010年 | 2205篇 |
2009年 | 2480篇 |
2008年 | 2028篇 |
2007年 | 2486篇 |
2006年 | 153篇 |
2005年 | 283篇 |
2004年 | 451篇 |
2003年 | 486篇 |
2002年 | 326篇 |
2001年 | 139篇 |
2000年 | 155篇 |
1999年 | 168篇 |
1998年 | 136篇 |
1997年 | 139篇 |
1996年 | 129篇 |
1995年 | 112篇 |
1994年 | 105篇 |
1993年 | 84篇 |
1992年 | 75篇 |
1991年 | 60篇 |
1990年 | 51篇 |
1989年 | 44篇 |
1988年 | 41篇 |
1987年 | 13篇 |
1986年 | 25篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 31篇 |
1980年 | 25篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 7篇 |
1975年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
161.
Spatial and Temporal Variations of Sound Speed at the PN Section 总被引:3,自引:0,他引:3
Gridded sound speed data were calculated using Del Grosso's formulation from the temperature and salinity data at the PN section
in the East China Sea covering 92 cruises between February 1978 and October 2000. The vertical gradients of sound speed are
mainly related to the seasonal variations, and the strong horizontal gradients are mainly related to the Kuroshio and the
upwelling. The standard deviations show that great variations of sound speed exist in the upper layer and in the slope zone.
Empirical orthogonal function analysis shows that contributions of surface heating and the Kuroshio to sound speed variance
are almost equivalent.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
162.
Tang Rongqing Wang Daoyan Zhang Xixian Egnineer Shanghai Jiao Tong University Shanghai Associate Professor Shanghai Jiao University Shanghai 《中国海洋工程》1993,(3)
- The authors have used a low-cost ROV of observation type for underice surveying of the Nen-Jiang Cross-river oil pipe line in the Da Qing oil field. The operation method, process and the safety measures for severe cold areas are presented. The fruitful tries and experience may be useful to ROV operators in severe cold areas. 相似文献
163.
Ana Luisa Rosa Yutaka Isoda Kazuyuki Uehara Tomokazu Aiki 《Journal of Oceanography》2007,63(4):573-588
Hydrographic data and composite current velocity data (ADCP and GEK) were used to examine the seasonal variations of upper-ocean
flow in the southern sea area of Hokkaido, which includes the “off-Doto” and “Hidaka Bay” areas separated by Cape Erimo. During
the heating season (April–September), the outflow of the Tsugaru Warm Current (TWC) from the Tsugaru Strait first extends
north-eastward, and then one branch of TWC turns to the west along the shelf slope after it approaches the Hidaka Shelf. The
main flow of TWC evolves continuously, extending eastward as far as the area off Cape Erimo. In the late cooling season (January–March),
part of the Oyashio enters Hidaka Bay along the shallower part of the shelf slope through the area off Cape Erimo, replacing
almost all of the TWC water, and hence the TWC devolves. It is suggested that the bottom-controlled barotropic flow of the
Oyashio, which may be caused by the small density difference between the Oyashio and the TWC waters and the southward migration
of main front of TWC, permits the Oyashio water to intrude along the Hidaka shelf slope. 相似文献
164.
本研究初步评价CHIMEHERB人工皮的治疗效果.74例,105个创面应用人工皮:供皮区47个创面,愈合时间平均为9±1.94d(天),油纱布对照为11.7±1.93d(P<0.01);14个浅Ⅱ°新鲜创面,70%在3~5d内逐渐干燥与创面紧密粘附,平均愈合时间为9.8±3.09d;11个存留上皮组织的削痂深Ⅱ°创面,平均5.7±1.7d干燥,平均愈合时间为10.55±3.09d,不需植自体皮;8个削痂刨面至脂肪组织或切痂创面4~9d更植自体皮,其存活率近乎100%,2个创面因残留坏死组织而失败;人工皮应用于16个自体皮间隙创面,除三个网状植皮和一个条状植皮创面失败外,所植自体皮都在人工皮下扩展融合,未观察到占位现象;对后期残余小创面有良好的效果.本研究结果提示人工皮对创面愈合具有有利影响.主要适用于供皮区、浅Ⅱ°新鲜创面、深Ⅱ°脱痂和削痂后存留上皮组织较多的创面、自体皮间隙创面和后期残余小创面,不适宜于深Ⅲ°新鲜创面. 相似文献
165.
166.
Hydrodynamic and sediment transport measurements from instrumentation deployed during a 54-day winter period at two sites on the Louisiana inner shelf are presented. Strong extratropical storms, with wind speeds of 7.8 to 15.1 m s-1, were the dominant forcing mechanism during the study. These typically caused mean oscillatory flows and shear velocities about 33% higher than fair weather (averaging 12.3 and 3.2 cm s-1 at the landward site, and 11.4 and 2.7 cm s-1 at the seaward site, respectively). These responses were coupled with mean near-bottom currents more than twice as strong as during fair weather (10.3 and 7.5 cm s-1 at the landward and seaward sites, respectively). These flowed in approximately the same direction as the veering wind, causing a net offshore transport of fine sand. Weak storms were responsible for little sediment transport whereas during fair weather, onshore sand transport of approximately 25-75% of the storm values appears to have occurred. This contradicts previous predictions of negligible fair-weather sediment movement on this inner shelf. 相似文献
167.
A high-resolution seismic survey covering more than 2,000 km2 has revealed the processes responsible for the slope morphology and channel sedimentation across the forearc slope-basin
of the Kurile Arc–NE Japan Arc collision zone, offshore from Tokachi (Hokkaido, Japan). The dominant slope contours parallel
the trench but, in the middle and lower reaches of the southern slope, contours are convex-shaped with an offshore trend.
This sector of the slope is traversed diagonally by the Hiroo submarine channel. The offshore-trending convex contours and
the channel course have developed through the interplay of tectonic and sedimentary processes, including the development of
anticlines, anticline-induced lobe sedimentation and channel avulsion. In its upper reaches, the channel is restricted by
a topographic low associated with NNW–SSE-trending anticlines which developed within the upper and middle slope sectors during
late Miocene uplift. The uplift timing and trend of these anticlines indicate that they resulted from collision, the channel
sedimentology and slope morphology of the middle and lower slopes having been influenced by Pliocene uplift of NE–SW-trending
anticlines. The trends of these anticlines parallel those of the Kurile Trench. The Pliocene and early Pleistocene strata
of the middle and lower slopes consist of ponded lobe sediments deposited along the palaeo-Hiroo submarine channel on the
landward side of the anticlines. As a lobe pile accumulated, the channel thalweg shifted to the north of the stack, allowing
the channel to bypass the topographic high formed by the growing stack. Thick levee deposits built up along the channel course
during the late Pleistocene and Holocene. These levees, along with the Pliocene and early Pleistocene lobes, are reflected
in the present-day sigmoid-shaped, convex offshore-trending contours. Thus, the interplay of subduction- and collision-related
anticlines, tectonic-related channel ponding, and avulsion has contributed to the slope morphology of the southern Kurile
Trench. 相似文献
168.
东海温度锋的分布特征及其季节变异 总被引:8,自引:4,他引:8
根据1934-1988年东海水文观测资料,重点分析东海温度锋的分布特征及其季节变异,并结合近期中日黑潮合作调查研究成果,初步探讨温度锋季节变异和水团演变的关系,所得主要结论是:(1)东海不仅常年存在浙闽沿岸锋,东海北部陆架锋和黑潮锋,而且、春、夏两季,在东海南部还出现一条东海中部出架锋。(2)江海温度锋季节变化的特点是:冬季,锋的宽度和强度皆是表层最强,夏季,表层温度锋仅出现在浙江近岸小范围海域。 相似文献
169.
Characterization of interface roughness of rippled sand off Fort Walton Beach, Florida 总被引:1,自引:0,他引:1
As part of the environmental characterization to model acoustic bottom scattering during the high-frequency sediment acoustics experiment (SAX99), fine-scale sediment roughness of a medium sand was successfully measured within a 600 /spl times/ 600-m area by two methods: stereo photography and a technique using a conductivity system. Areal coverage of the two methods, representing approximately 0.16 m/sup 2/ of the sea floor, was comparable, resulting in the depiction and quantification of half-meter wavelength sand ripples. Photogrammetric results were restricted to profiles digitized at 1-mm intervals; sediment conductivity results generated gridded micro-bathymetric measurements with 1- to 2-cm node spacing. Roughness power spectra give similar results in the low-spatial-frequency domains where the spectra estimated from both approaches overlap. However, spectra derived from higher resolution photogrammetric results appear to exhibit a multiple-power-law fit. Roughness measurements also indicate that spectrum changes as a function of time. Application of statistical confidence bounds on the power spectra indicates that roughness measurements separated by only 1-2 m may be spatially nonstationary. 相似文献
170.
Remote estimation of surficial seafloor properties through the application Angular Range Analysis to multibeam sonar data 总被引:2,自引:2,他引:2
The variation of the backscatter strength with the angle of incidence is an intrinsic property of the seafloor, which can
be used in methods for acoustic seafloor characterization. Although multibeam sonars acquire backscatter over a wide range
of incidence angles, the angular information is normally neglected during standard backscatter processing and mosaicking.
An approach called Angular Range Analysis has been developed to preserve the backscatter angular information, and use it for
remote estimation of seafloor properties. Angular Range Analysis starts with the beam-by-beam time-series of acoustic backscatter
provided by the multibeam sonar and then corrects the backscatter for seafloor slope, beam pattern, time varying and angle
varying gains, and area of insonification. Subsequently a series of parameters are calculated from the stacking of consecutive
time series over a spatial scale that approximates half of the swath width. Based on these calculated parameters and the inversion
of an acoustic backscatter model, we estimate the acoustic impedance and the roughness of the insonified area on the seafloor.
In the process of this inversion, the behavior of the model parameters is constrained by established inter-property relationships.
The approach has been tested using a 300 kHz Simrad EM3000 multibeam sonar in Little Bay, NH. Impedance estimates are compared
to in situ measurements of sound speed. The comparison shows a very good correlation, indicating the potential of this approach for
robust seafloor characterization. 相似文献