全文获取类型
收费全文 | 45619篇 |
免费 | 757篇 |
国内免费 | 309篇 |
专业分类
测绘学 | 1249篇 |
大气科学 | 3020篇 |
地球物理 | 9276篇 |
地质学 | 15834篇 |
海洋学 | 3857篇 |
天文学 | 11074篇 |
综合类 | 116篇 |
自然地理 | 2259篇 |
出版年
2021年 | 439篇 |
2020年 | 497篇 |
2019年 | 494篇 |
2018年 | 1163篇 |
2017年 | 1039篇 |
2016年 | 1293篇 |
2015年 | 768篇 |
2014年 | 1258篇 |
2013年 | 2339篇 |
2012年 | 1411篇 |
2011年 | 1847篇 |
2010年 | 1641篇 |
2009年 | 2269篇 |
2008年 | 1871篇 |
2007年 | 1865篇 |
2006年 | 1732篇 |
2005年 | 1290篇 |
2004年 | 1301篇 |
2003年 | 1208篇 |
2002年 | 1158篇 |
2001年 | 1043篇 |
2000年 | 975篇 |
1999年 | 840篇 |
1998年 | 872篇 |
1997年 | 830篇 |
1996年 | 705篇 |
1995年 | 723篇 |
1994年 | 637篇 |
1993年 | 544篇 |
1992年 | 512篇 |
1991年 | 517篇 |
1990年 | 598篇 |
1989年 | 503篇 |
1988年 | 464篇 |
1987年 | 588篇 |
1986年 | 485篇 |
1985年 | 620篇 |
1984年 | 692篇 |
1983年 | 663篇 |
1982年 | 580篇 |
1981年 | 608篇 |
1980年 | 507篇 |
1979年 | 474篇 |
1978年 | 482篇 |
1977年 | 437篇 |
1976年 | 420篇 |
1975年 | 420篇 |
1974年 | 396篇 |
1973年 | 428篇 |
1972年 | 267篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
431.
The microstructure of lime-stabilized marine clay 总被引:2,自引:0,他引:2
The treatment of fine-grained soils with lime makes the soil system less sensitive to the changes in stress and other environmental factors. In the present investigation an attempt has been made to examine the nature of reaction products formed in a marine clay due to lime treatment using scanning electron microscopy (SEM) studies. The lime-induced microstructural changes in a marine clay have been investigated using SEM. The test results indicate that there is an overall improvement in the structure of the soil system resulting in a porous system due to the formation of new reaction products. 相似文献
432.
Robert P. Dziak Christopher G. Fox Robert W. Embley 《Marine Geophysical Researches》1991,13(3):203-208
Morphologic studies of an oceanic transform, the Blanco Transform Fault Zone (BTFZ), have shown it to consist of a series of extensional basins that offset the major strike-slip faults. The largest of the extensional basins, the Cascadia Depression, effectively divides the transform into a northwest segment, composed of several relatively short strike-slip faults, and a southeast segment dominated by fewer, longer faults. The regional seismicity distribution (m
b
4.0) and frequency-magnitude relationships (b-values) of the BTFZ show that the largest magnitude events are located on the southeast segment. Furthermore, estimates of the cumulative seismic moment release and seismic moment release rate along the southeast segment are significantly greater than that of the northwest segment. These observations suggest that slip along the southeast segment is accommodated by a greater number of large magnitude earthquakes. Comparison of the seismic moment rate, derived from empirical estimates, with the seismic moment rate determined from plate motion constraints suggests a difference in the seismic coupling strength between the segments. This difference in coupling may partially explain the disparity in earthquake size distribution. However, the results appear to confirm the relation between earthquake size and fault length, observed along continental strike-slip faults, for this oceanic transform. 相似文献
433.
Iodate (IO3−) is the predominant dissolved species of iodine in the oxygenated waters of the Mediterranean Sea. Iodide (I−) is present in significant quantities (up to 65 nM) in oxygenated waters in the photic zone and near the interface above the anoxic and saline Bannock Basin. Lesser quantities of I− (< 10 nM) are found throughout the rest of the oxic water column. An additional unidentified dissolved iodine species is present immediately above the anoxic interface.Total dissolved iodine (ΣI) increases dramatically across the seawater/brine interface. Part of this increase is undoubtedly the result of the dissolution of iodine-rich evaporites during formation of the brine bodies at the Tyro and Bannock Basins. The vertical distribution of ΣI and other dissolved chemical species (particularly PO43−) in the Bannock Basin brine, however, suggests an additional, present-day, diagenetic source of dissolved iodine to the brine. Based on the increase in the concentration of the most soluble major ions across the seawater/brine interface, 5–7 μM of the 11.5-μM increase in ΣI concentration must be attributed to diagenesis. 相似文献
434.
Gallo D. G. Kidd W. S. F. Fox P. J. Karson J. A. Macdonald K. Crane K. Choukroune P. Seguret M. Moody R. Kastens K. 《Marine Geophysical Researches》1984,6(2):159-185
During the Fall of 1979, a manned submersible program, utilizing DSRV ALVIN, was carried out at the intersection of the East Pacific Rise (EPR) with the Tamayo Transform boundary. A total of seven dives were completed in the vicinity of the EPR/Tamayo intersection depression and documented the geologic relationships that characterize the juxtaposition of these types of plate boundaries. The young volcanic terrain of the EPR axis can be traced into and across the Tamayo Transform valley but becomes buried by sedimentary talus that is being shed from sediment scarps along the unstable sediment slope that defines the north side of the intersection depression. Within 4 km of the transform boundary, the dominant trend (000°) of the fissures and faults that disrupt the rise-generated volcanics is markedly oblique to the regional direction of sea floor spreading (120°). Since no evidence was found to suggest that these structures accommodate significant amounts of strike-slip displacement, they are taken to reflect a distortion of the EPR extensional tectonic regime by a transform generated shear couple. The floor of the Tamayo Transform valley in this area is inundated by mass-wasted sediment, and the principal transform displacement zone is characterized at the surface by a narrow (<1.5 km) interval of fault scarps in sediment that trends parallel with the transform valley. Extrapolated to the west, this zone links with zones of transform deformation investigated during earlier submersible studies (CYAMEX and Pastouret, 1981). Evidence of low-level hydrothermal discharge was seen at one locality on the EPR axis and at another 8 km west of the axis at the edge of the zone of transform deformation. 相似文献
435.
The wavemaking capability and energy absorbing characteristics of a single submerged body, constrained to move horizontally in a surge mode, are examined. The body possesses both a vertical axis of symmetry and a horizontal plane of symmetry and is ‘thin’ in the sense that the body draft is small compared to the length. The behaviour of a single body subject to a constraint being placed upon the amplitude of its displacement and the properties of an array of interacting identical devices are also discussed. 相似文献
436.
437.
Abstract. Benthic metabolism and standing stocks were investigated in the deep Red Sea between 21o and 27o N, Activity was assessed by the determination of respiration rates with a shipboard method and by calculating oxygen consumption from the activity in the electron transport system. We attempted to compare results from different latitudes within the warm Red Sea and with data from cold Atlantic environments. Our investigations were part of an environmental risk assessment to evaluate future mining of metalliferous sediments from the Atlantis II Deep. 相似文献
438.
Framvaren, a super-anoxic fjord in southern Norway, contains 7–8 mmoll−1 of sulphide and a total carbonate concentration of 18.5 mmol kg−1 in the bottom water. The chemistry of calcium has been studied, considering sources, biogenic and chemical processes and sedimentary sinks. Calcium associated with the bacteria biomass at the redox interface (18m depth) appears to be the primary source of dissolved calcium in the deep, anoxic water. Excess calcium and high total carbonate cause supersaturation of calcite, which is precipitated chemogenically. Calcite (and presumably some aragonite) is identified both in sediment trap material and the bottom sediments below the depth of supersaturation. 相似文献
439.
On the analysis of catch and effort data 总被引:1,自引:0,他引:1
440.
Methods developed earlier, based on hydration numbers for individual ionic species, have been extended to the calculation of ionic activity coefficients in aqueous systems of two electrolytes MX and NX2 with a common unhydrated anion (X−). The data required include the mean activity coefficients of MX and NX2 in the mixtures, together with the osmotic coefficient. The procedure is illustrated by a calculation of γNa, γMg, and γCl in a mixture of NaCl and MgCl2 closely approximating the composition of seawater with salinity of 35‰. 相似文献