全文获取类型
收费全文 | 37801篇 |
免费 | 1128篇 |
国内免费 | 1049篇 |
专业分类
测绘学 | 965篇 |
大气科学 | 2909篇 |
地球物理 | 7775篇 |
地质学 | 13938篇 |
海洋学 | 3388篇 |
天文学 | 8262篇 |
综合类 | 246篇 |
自然地理 | 2495篇 |
出版年
2022年 | 292篇 |
2021年 | 481篇 |
2020年 | 464篇 |
2019年 | 504篇 |
2018年 | 919篇 |
2017年 | 888篇 |
2016年 | 1062篇 |
2015年 | 727篇 |
2014年 | 1067篇 |
2013年 | 1880篇 |
2012年 | 1356篇 |
2011年 | 1802篇 |
2010年 | 1584篇 |
2009年 | 2040篇 |
2008年 | 1722篇 |
2007年 | 1796篇 |
2006年 | 1719篇 |
2005年 | 1239篇 |
2004年 | 1159篇 |
2003年 | 1062篇 |
2002年 | 1025篇 |
2001年 | 860篇 |
2000年 | 841篇 |
1999年 | 688篇 |
1998年 | 729篇 |
1997年 | 696篇 |
1996年 | 583篇 |
1995年 | 569篇 |
1994年 | 486篇 |
1993年 | 425篇 |
1992年 | 428篇 |
1991年 | 389篇 |
1990年 | 462篇 |
1989年 | 382篇 |
1988年 | 362篇 |
1987年 | 443篇 |
1986年 | 352篇 |
1985年 | 436篇 |
1984年 | 543篇 |
1983年 | 459篇 |
1982年 | 461篇 |
1981年 | 409篇 |
1980年 | 422篇 |
1979年 | 371篇 |
1978年 | 351篇 |
1977年 | 353篇 |
1976年 | 314篇 |
1975年 | 306篇 |
1974年 | 318篇 |
1973年 | 345篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
A. A. Schreider Al. A. Schreider A. A. Bulychev J. Galindo-Zaldivar A. Maldonado G. L. Kashintsev 《Oceanology》2006,46(1):114-122
A new map of chrons for the American-Antarctic Ridge area has been compiled. Its analysis and the calculations performed showed that the seafloor spreading with respect to its axis started before 85 My B.P. The spreading directions were 115° (chrons C34-C29), 145° (chrons C29-C21), 110° (chrons C21-C5C), and 85° (chrons C5C-C1). The maximum rates of about 4 cm/year were reached earlier than 52 My B.P.; subsequently, a progressive general decrease in the spreading rate has been observed. According to our forecast, the spreading may cease in the following 3.5 My. 相似文献
262.
263.
C. Martín-Puertas M. P. Mata M. C. Fernández-Puga V. Díaz del Río J. T. Vázquez L. Somoza 《Geo-Marine Letters》2007,27(2-4):223-235
The Gulf of Cádiz area has been extensively surveyed in recent years and several gas-related fluid escape seafloor structures
have been identified. In this study, gravity cores, collected during the ANASTASYA/00 and ANASTASYA/01 cruises, on mud volcanoes,
hemipelagic sediments and dredged material from diapiric structures, have been studied. A comparative mineralogical analysis
by XRD and SEM of samples from different areas has been performed in order to determine whether there is a characteristic
mineralogy related to these fluid escape structures, and also to determine the origin of the mud matrix and constrain the
depth of the parent units. The mineralogical analysis reflects the different origins of the different units described in the
cores: hemipelagic material of the slope, clays that underlie the mud volcanoes and are discharged at the sea bottom surface,
and authigenic and diagenetic minerals possibly involved in the anaerobic oxidation of methane in the mud volcano sediments. 相似文献
264.
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
265.
266.
Closely-spaced 3.5 kHz seismic profiles were collected over the north-easterly trending ridge and swale system 50 km east-southeast of Atlantic City, New Jersey. They yield information on the Late Quaternary depositional history of the area, and on the origin of the ridge system. Four of the sub-bottom reflectors identified were sufficiently persistent to warrant investigation and interpretation. These reflectors, which have been cored, lithologically identified, and radiocarbon dated, are stratigraphically higher than the reflectors dealt with by the majority of previous studies. The upper three reflectors are definitely mid- and post-Wisconsin in age and present a record of the most recent glacial cycle. The upper three units associated with the observed reflectors appear to exert a pronounced influence on the bathymetry. The gently corrugated ridge system of Holocene sand is formed over the regionally flat-lying upper unit, an Early Holocene lagoonal silty clay. The characteristically flat, broad depressions of the area are floored by this lagoonal material. Locally, however, marine scour has cut through the silty clay into an underlying unit of unconsolidated fine Pleistocene sand. Several stages of trough development appear to be represented. After penetrating the lagoonal clay, troughs are initially narrow, but when incised through the sand into a lower, Pleistocene, silty-clay unit, the troughs become notably wider. As downcutting is inhibited by the lower clay, the upper clay is undercut as the trough widens in a fashion similar to a desert blowout.
The sub-bottom reflectors indicate that ridge development on the central shelf has involved aggradation as well as erosion. Some ridges seem to have grown by vertical and lateral accretion from small cores. The internal structure of other ridges suggests that they formed by the coalescence of several small ridges. Others appear to have undergone appreciable lateral migration.
The ridges appear to be in a state of continuing adjustment to the hydraulic regime of the deepening post-Pleistocene water column. 相似文献
267.
Environmental concern for the deep-sea ecosystem is increasing as contaminants, originating from anthropogenic activities, have been detected in deep-sea biota. However, little is known on the xenobiotics metabolising capability of deep-sea fauna. In this study, the deep-sea amphipod Eurythenes gryllus was selected as sentinel species to measure the total oxyradical scavenging capacity (TOSC). Individuals of E. gryllus were sampled at 2000 m depth in the Arctic Ocean. The TOSC assay was measured on the cytosolic fraction and the soluble fraction (3 kDa) of the digestive gland and on the cell-free haemolymph toward peroxyl, hydroxyl and peroxynitrite radicals according to the method of Winston et al. [Free Radical Biology and Medicine 24 (3) (1998) 480] and Regoli and Winston [Toxicology and Applied Pharmacology 156 (1999) 96]. These results provide the first baseline data set for total antioxidant capacity in a deep-sea amphipod. 相似文献
268.
Lorenzo Ciannelli Richard D. Brodeur Gordon L. Swartzman Sigrid Salo 《Deep Sea Research Part II: Topical Studies in Oceanography》2002,49(26):6109-6126
The waters around the Pribilof Islands, in the southeast Bering Sea, are a main nursery area for age-0 pollock. Each summer, the islands are surrounded by a well-mixed inshore region, separated from a stratified offshore region by a frontal zone. To study the spatial distribution of age-0 pollock around this frontal structure in relation to physical and biological factors that are likely to influence it, such as advection, age-0 pollock feeding, and predation, samples were collected during September of four consecutive years, 1994–97, along two transects. Samples collected included water column hydrography and currents, acoustic backscatter, and groundfish predator density.Our analysis suggested that different mechanisms may be involved in controlling age-0 pollock distribution north and south of the islands. On the shelf area north of the islands, high age-0 pollock density was significantly associated with areas of high potential for growth only in years or portions of the frontal transect in which predator numbers were relatively low, indicating the importance of predation in controlling fish distribution in this area. In contrast, south of the islands, age-0 pollock distribution was associated more with prey availability, which appeared to be determined by vertical spatial overlap between predators and prey. Moreover, south of the islands, the stronger geostrophic currents, typical of the slope region, were more likely to affect the overall standing biomass of juvenile pollock, by constantly advecting fish away from the area. 相似文献
269.
270.