全文获取类型
收费全文 | 72620篇 |
免费 | 2661篇 |
国内免费 | 3208篇 |
专业分类
测绘学 | 2283篇 |
大气科学 | 6303篇 |
地球物理 | 13681篇 |
地质学 | 30567篇 |
海洋学 | 6681篇 |
天文学 | 13339篇 |
综合类 | 1227篇 |
自然地理 | 4408篇 |
出版年
2022年 | 903篇 |
2021年 | 1270篇 |
2020年 | 1236篇 |
2019年 | 1360篇 |
2018年 | 4495篇 |
2017年 | 4157篇 |
2016年 | 3308篇 |
2015年 | 1397篇 |
2014年 | 1937篇 |
2013年 | 2784篇 |
2012年 | 2986篇 |
2011年 | 4942篇 |
2010年 | 4410篇 |
2009年 | 4831篇 |
2008年 | 4098篇 |
2007年 | 4649篇 |
2006年 | 2326篇 |
2005年 | 1857篇 |
2004年 | 1758篇 |
2003年 | 1915篇 |
2002年 | 1690篇 |
2001年 | 1330篇 |
2000年 | 1158篇 |
1999年 | 1082篇 |
1998年 | 991篇 |
1997年 | 1018篇 |
1996年 | 838篇 |
1995年 | 818篇 |
1994年 | 722篇 |
1993年 | 628篇 |
1992年 | 568篇 |
1991年 | 525篇 |
1990年 | 523篇 |
1989年 | 497篇 |
1988年 | 443篇 |
1987年 | 460篇 |
1986年 | 470篇 |
1985年 | 547篇 |
1984年 | 587篇 |
1983年 | 578篇 |
1982年 | 532篇 |
1981年 | 488篇 |
1980年 | 471篇 |
1979年 | 432篇 |
1978年 | 391篇 |
1977年 | 400篇 |
1976年 | 361篇 |
1975年 | 371篇 |
1974年 | 352篇 |
1973年 | 384篇 |
排序方式: 共有10000条查询结果,搜索用时 84 毫秒
771.
Mussel Periostracum from Deep-Sea Redox Communities as a Microbial Habitat: 3. Secondary Inhabitants
Abstract. Vacated microborings in periostracum of live mussels of the Florida Escarpment redox community (depth of 3266 m) become a habitat for a prolific secondary microbiota consisting of a variety of prokaryotic and a few eukaryotic organisms. Periostracum surface is also colonized by diverse microorganisms, dominated by presumed chemolithotrophic bacteria with stacks of intracellular lamellae. Unlike sheltered microflora within borings, the surface community is heavily grazed upon by numerous archaeogastropods and ciliates. 相似文献
772.
In mammals, the induction of cytochrome P4501A forms by chlorinated dibenzo-p-dioxins, chlorinated dibenzofurans, and halogenated biphenyls is under control of a soluble protein known as the Ah (aromatic hydrocarbon) receptor. Little is known about the presence and properties of the Ah receptor in other vertebrate and invertebrate species. In these studies, we sought evidence for an Ah receptor in the liver or liver-equivalent of 20 species of marine and freshwater animals, using the photoaffinity ligand 2-azido-3-[125I] iodo-7,8-dibromodibenzo-p-dioxin (N3[125I]Br2DD). Specific labeling of cytosolic proteins by N3[125I]Br2DD was observed in seven species of teleost and elasmobranch fish, in PLHC-I fish hepatoma cells, and in beluga whales. No specifically labeled proteins were found in cytosol from two species of agnathan fish nor in any of nine invertebrate species representing eight classes of four phyla. The presence or absence of specifically labeled polypeptides corresponds with the inducibility of cytochrome P4501A and sensitivity to the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related planar halogenated aromatic hydrocarbons in many of these groups. Thus, Ah receptor function may have arisen early invertebrate evolution and has been conserved from elasmobranch and teleost fish to mammals. 相似文献
773.
F. E. Grousset J. L. Joron P. E. Biscaye C. Latouche M. Treuil N. Maillet J. C. Faugères E. Gonthier 《Geo-Marine Letters》1988,8(1):25-34
Data obtained from mineralogical and geochemical analyses of piston and gravity cores, recovered from an area off Lisbon (Portugal) to the Alboran Sea (Mediterranean), serve as a basis for better understanding the past 18,000 years of hydrological exchanges at Gibraltar. Tracers used in this study are smectite, kaolinite, Ta, Th, La. One of the primary sources of particles both into and out of the Mediterranean is the Guadalquivir River. These particles are transported back into the Atlantic in the Mediterranean outflow water, and deposited along the Iberian slope. No evidence for reversal of this outflow current was found in those cores, since 18,000 years B.P. 相似文献
774.
775.
Detection of buried targets using a synthetic aperture sonar 总被引:1,自引:0,他引:1
Piper J.E. Commander K.W. Thorsos E.I. Williams K.L. 《Oceanic Engineering, IEEE Journal of》2002,27(3):495-504
This paper presents observations of buried target detections made using a 20-kHz synthetic aperture sonar. At grazing angles below the critical angle, surprisingly high signal-to-noise detections were made of cylindrical targets buried at depths of 15 and 50 cm. During a separate set of measurements, buried spheres were clearly seen at steep grazing angles, but were generally not seen below the critical angle. Since scattering from wave-generated sand ripples may contribute to detections at grazing angles below critical angle, the information available on the ripple fields is discussed and used in acoustic backscatter simulations for the buried spheres. Lack of information on the ripple height precludes a definitive explanation for the absence of buried sphere detections at subcritical grazing angles. 相似文献
776.
The autonomous underwater glider "Spray" 总被引:4,自引:0,他引:4
A small (50-kg, 2-m long) underwater vehicle with operating speeds of 20-30 cm/s and ranges up to 6000 km has been developed and field tested. The vehicle is essentially an autonomous profiling float that uses a buoyancy engine to cycle vertically and wings to glide horizontally while moving up and down. Operational control and data relay is provided by GPS navigation and two-way communication through ORBCOMM low-Earth-orbit satellites. Missions are envisioned with profile measurements repeated at a station or spaced along a transect. The initial instrument complement of temperature, conductivity, and pressure sensors was used to observe internal waves and tides in the Monterey underwater canyon 相似文献
777.
778.
The Solomon Sea Plate was widely developed during late Oligocene, separating the proto-West Melanesian Arc from the proto-Trobriand Arc. Spreading in the Bismarck Sea and in the Woodlark Basin resulted from interaction between the Pacific and Australian Plates, specifically from the collision of the proto-West Melanesian Arc with north New Guinea, which occurred after arc reversal. This model explains the extensive Miocene, Pliocene, and Quaternary volcanism of the Papua New Guinea mainland as it related to southward subduction of the Trobriand Trough. Our interpreted plate motions are concordant with the geological evidence onshore and also with complex tectonic features in the Solomon Sea Basin Region. 相似文献
779.
780.
To improve resolution of seismic-reflection profiles in continental slope water depths of 900 to 1500 m, a single hydrophone
was towed about 150 m off the bottom to receive reflected signals from a surface-towed sparker sound source. That deep-towed
hydrophone data show that valleys which appear V-shaped in records from a surface-towed hydrophone are flat-bottomed, and
that subbottom reflections from an erosional unconformity can be much better resolved. The data produced by this technique
are very hepful when used in conjunction with records from conventional surface-towed seismic-profiling equipment. 相似文献