全文获取类型
收费全文 | 8602篇 |
免费 | 275篇 |
国内免费 | 129篇 |
专业分类
测绘学 | 165篇 |
大气科学 | 710篇 |
地球物理 | 2005篇 |
地质学 | 3022篇 |
海洋学 | 797篇 |
天文学 | 1239篇 |
综合类 | 37篇 |
自然地理 | 1031篇 |
出版年
2022年 | 33篇 |
2021年 | 115篇 |
2020年 | 153篇 |
2019年 | 156篇 |
2018年 | 202篇 |
2017年 | 195篇 |
2016年 | 242篇 |
2015年 | 200篇 |
2014年 | 260篇 |
2013年 | 473篇 |
2012年 | 283篇 |
2011年 | 409篇 |
2010年 | 375篇 |
2009年 | 475篇 |
2008年 | 400篇 |
2007年 | 407篇 |
2006年 | 341篇 |
2005年 | 293篇 |
2004年 | 282篇 |
2003年 | 300篇 |
2002年 | 240篇 |
2001年 | 200篇 |
2000年 | 221篇 |
1999年 | 164篇 |
1998年 | 149篇 |
1997年 | 132篇 |
1996年 | 144篇 |
1995年 | 131篇 |
1994年 | 124篇 |
1993年 | 101篇 |
1992年 | 100篇 |
1991年 | 68篇 |
1990年 | 97篇 |
1989年 | 78篇 |
1988年 | 85篇 |
1987年 | 94篇 |
1986年 | 84篇 |
1985年 | 110篇 |
1984年 | 131篇 |
1983年 | 122篇 |
1982年 | 105篇 |
1981年 | 77篇 |
1980年 | 57篇 |
1979年 | 71篇 |
1978年 | 67篇 |
1977年 | 61篇 |
1976年 | 61篇 |
1975年 | 69篇 |
1974年 | 55篇 |
1973年 | 68篇 |
排序方式: 共有9006条查询结果,搜索用时 15 毫秒
31.
32.
33.
Trace metal-binding proteins in marine molluscs and crustaceans 总被引:1,自引:0,他引:1
Some marine invertebrates, such as the American oyster, Crassostrea virginica, the blue crab, callinectes sapidus and the American lobster, Homarusamericanus, concentrate trace metals in their tissues. The occurrence of metallothionein, a low molecular weight, sulfur-containing metal-binding protein, has been correlated with elevated levels of trace metals in these organisms. It is our hypothesis that, whilst metallothioneins are involved in the sequestration of elevated levels of trace metals, they primarily function in regulating normal metal metabolism. In this paper we describe recent field and laboratory experiments designed to examine how oysters, blue crabs and lobsters manage accumulated cadmium, copper and zinc. The possible rôles of metallothionein, as well as the tissue distribution of metals, are emphasized. Metallothioneins were found in all animals we examined; concentrations of metallothioneins and the the amount of bound trace metals are related to time of exposure. We have also demonstrated that the laboratory developed metallothionein models for blue crabs and lobsters may be useful in predicting the partitioning of trace metals in animals living in environments polluted with trace metals. 相似文献
34.
35.
It is shown that the values of pK1C and pK2C for carbonic acid, pKB for boric acid and the ionic product of water, pKw, in sea water may be explained on the basis of their determination in 0.7 Mw sodium chloride and the formation of the following ion-pairs: NaSO4?, MgSO4, CaSO4, MgCO3, CaCO3, MgHCO3+, CaHCO3+, MgOH+, HSO4?, MgB(OH)4+ and CaB(OH)4+. On the whole the calculated stability constants are lower than those given by Garrels and Thompson (1962). 相似文献
36.
Robert D. Moore Leroy M. Dorman Chin-Yen Huang David L. Berliner 《Marine Geophysical Researches》1981,4(4):451-477
We describe the design and construction of an ocean bottom seismometer configured as a computer, based on an Intersil IM6100 microprocessor plus appropriate peripheral devices. The sensors consist of triaxial 1 Hz seismometers and a hydrophone, each sensor channel being filtered prior to digitizing so that typical noise spectra are whitened. Digital data are recorded serially on magnetic tape. The instrument is placed on the ocean bottom by allowing it to fall freely from just below the surface. An acoustic system allows precise determination of instrument position, acoustic recall, and transmission of operational information to the surface. Release from an expendable anchor is accomplished by redundant pyrotechnic bolts which can be fired by acoustic command or by precision timers.The operational flexibility provided by the micro-computer, which executes the DEC PDP8/E instruction set, enables optimum use of the 6-hr recording capacity (at 128 samples/second/channel) in the context of the particular experiment being performed.
相似文献
相似文献
37.
38.
Multi-AUV Control and Adaptive Sampling in Monterey Bay 总被引:3,自引:0,他引:3
Edward Fiorelli Naomi Ehrich Leonard Pradeep Bhatta Derek A. Paley Ralf Bachmayer David M. Fratantoni 《Oceanic Engineering, IEEE Journal of》2006,31(4):935-948
Operations with multiple autonomous underwater vehicles (AUVs) have a variety of underwater applications. For example, a coordinated group of vehicles with environmental sensors can perform adaptive ocean sampling at the appropriate spatial and temporal scales. We describe a methodology for cooperative control of multiple vehicles based on virtual bodies and artificial potentials (VBAP). This methodology allows for adaptable formation control and can be used for missions such as gradient climbing and feature tracking in an uncertain environment. We discuss our implementation on a fleet of autonomous underwater gliders and present results from sea trials in Monterey Bay in August, 2003. These at-sea demonstrations were performed as part of the Autonomous Ocean Sampling Network (AOSN) II project 相似文献
39.
40.
David K. Rea 《Marine Geophysical Researches》1976,2(4):291-313
The axis of the East Pacific Rise is defined by a topographic block about 15 km wide and 300 to 350 m high which is flanked by abyssal hills 100 to 200 m high and 3 to 5 km wide. These hills often are tilted such that their steep slopes face the axis. An empirical model explaining these features combines axial extrusion to form the central block and rotational faulting to lower the shoulders of the axial block to the regional depth and tilt them outward.The axial block is offset about 10 km left-laterally at 10.0°S and a similar amount right-laterally at 11.5°S. Offsets (or lack of offsets) of young magnetic anomalies indicate that these axial displacements occurred between 1.7 and 0.9 m.y. ago and 0.7 m.y. ago and the present in the north and south. respectively. These small axial offsets are interpreted to be the result of either brief episodes of asymmetric see-floor spreading or discrete jumps in the site of spreading activity. Both axial shifts were to the west; a unidirectional sequence of such shifts occurring at the above rate of one per million years would be difficult to differentiate from true regional asymmetric spreading and might explain that phenomenon on other medium-to fast-spreading rises.Reconnaissance data from the east flank of the East Pacific Rise indicate that spreading activity began on that part of the rise between the 9°S and 13.5°S fracture zones approximately 8.2 m.y. ago when the site of crustal accretion jumped westward from the now dormant Galapagos Rise. Slope change in crust approximately 2 and 6 m.y. old imply faster spreading rates between about 6 and 2 m.y. ago than either before or after that time. Identification and correlation of anomaly 3 allows an estimate of about 90 mm/y for this higher east flank spreading rate. Since 1.7 m.y. ago spreading rates have averaged about 80 mm/y to the west and 77 mm/y to the east. 相似文献