全文获取类型
收费全文 | 102086篇 |
免费 | 19929篇 |
国内免费 | 41430篇 |
专业分类
测绘学 | 4062篇 |
大气科学 | 25617篇 |
地球物理 | 26301篇 |
地质学 | 57672篇 |
海洋学 | 22028篇 |
天文学 | 17758篇 |
综合类 | 4103篇 |
自然地理 | 5904篇 |
出版年
2022年 | 690篇 |
2021年 | 1251篇 |
2020年 | 2606篇 |
2019年 | 6098篇 |
2018年 | 7209篇 |
2017年 | 6876篇 |
2016年 | 7193篇 |
2015年 | 5670篇 |
2014年 | 5960篇 |
2013年 | 8225篇 |
2012年 | 6482篇 |
2011年 | 6854篇 |
2010年 | 6660篇 |
2009年 | 6861篇 |
2008年 | 5685篇 |
2007年 | 5621篇 |
2006年 | 5080篇 |
2005年 | 4337篇 |
2004年 | 4721篇 |
2003年 | 4431篇 |
2002年 | 3985篇 |
2001年 | 3548篇 |
2000年 | 3066篇 |
1999年 | 2878篇 |
1998年 | 3025篇 |
1997年 | 3065篇 |
1996年 | 2468篇 |
1995年 | 2404篇 |
1994年 | 2145篇 |
1993年 | 1991篇 |
1992年 | 1746篇 |
1991年 | 1536篇 |
1990年 | 1558篇 |
1989年 | 1334篇 |
1988年 | 1200篇 |
1987年 | 1274篇 |
1986年 | 1104篇 |
1985年 | 1245篇 |
1984年 | 1378篇 |
1983年 | 1261篇 |
1982年 | 1172篇 |
1981年 | 1093篇 |
1980年 | 956篇 |
1979年 | 894篇 |
1978年 | 827篇 |
1977年 | 793篇 |
1976年 | 716篇 |
1975年 | 711篇 |
1974年 | 685篇 |
1973年 | 751篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
锥形海山是马里亚纳弧前区非火山成因的海山。它是由俯冲的太平洋板块对仰冲板块的上推作用,地壳下的上地幔物质底辟侵入的结果。海山顶部的岩石是由蛇纹石化超镁铁质方辉橄榄岩组成。其主要矿物成分为斜方辉石、橄榄石、尖晶石、磁铁矿、蛇纹石和碳酸盐。手标本呈显晶质块状构造,薄片中呈粒状、残留状、筛网状及斑状变晶结构。岩石化学特征表现为:低Si和Al,高M/F值,含水,亏损了所有过渡金属。岩石的成因属超基性岩浆直接结晶,后经海水的参入,在热液作用下普遍发生蛇纹石化和碳酸盐化。 相似文献
994.
Study of zooplankton ecology in Zhejiang coastal upwelling system-Species distribution and diversity of zooplankton 总被引:2,自引:0,他引:2
The species distribution and diversity of zooplankton and the effects of hydrodynamic factors of Zhejiang coastal waters during the active period of upwelling are discussed.High dominance (low diversity), high biomass and short food chain were found in the landward margins of the central region of the upwelling. There were evident interactions between the distribution of zooplankton and the environmental factors. The expression of these interactions is that different ecotypes of zooplankton adapt to different hydrological situations. There is significant positive correlation between the diversity indices of zooplankton and the mean water temperature in the survey area. It is noted that the vertical distribution of Calanus sinicus indicates to a certain extent the colder water environment of the upwelling (Fig. 7, Table 2, Reference (Hargreaves, 1981). 相似文献
995.
A simulation of a chronic input of petroleum into an estuarine environment was investigated using the facilities at the Marine Ecosystems Research Laboratory at the University of Rhode Island. An oil-water dispersion of No. 2 fuel oil was added to the system (twice weekly for 24 weeks) and the saturated hydrocarbons from this oil were measured in suspended material and sediments. After the initial chronic oil addition, trace amounts of hydrocarbons were detected in the sediments within two weeks, but substantial accumulation was not detected for approximately 135 days. The oil appeared to enter the sediment via the suspended material, with most of the saturated hydrocarbons associated with smaller size sediment particles (< 45 μm to > 0·3 μm). With time, the fuel oil saturated hydrocarbons in the sediments were mixed to a depth of 3 to 4 cm. Although only 12% of the total saturated hydrocarbons added to the system were found in the sediments, these hydrocarbons appear to be relatively stable and were still detectable in these sediments for at least six months after the last oil addition. 相似文献
996.
所有物体都不断地发出电磁辐射,在微波谱段内黑体的辐射量Bbb可用瑞利—金斯公式表示:Bbb=2KT/λ2。 相似文献
997.
998.
Geophysical evidence of mud diapirism on the Mediterranean Ridge accretionary complex 总被引:2,自引:0,他引:2
A. Camerlenghi M. B. Cita B. Della Vedova N. Fusi L. Mirabile G. Pellis 《Marine Geophysical Researches》1995,17(2):115-141
Mud volcanoes, mud cones, and mud ridges have been identified on the inner portion of the crestal area, and possibly on the inner escarpment, of the Mediterranean Ridge accretionary complex. Four areas containing one or more mud diapirs have been investigated through bathymetric profiling, single channel seismic reflection profiling, heat flow measurements, and coring. A sequence of events is identified in the evolution of the mud diapirs: initially the expulsion on the seafloor of gasrich mud produces a seafloor depression outlined in the seismic record by downward dip of the host sediment reflectors towards the mud conduit; subsequent eruptions of fluid mud may create a flat topped mud volcano with step-like profile; finally, the intrusion of viscous mud produces a mud cone.The origin of the diapirs is deep within the Mediterranean Ridge. Although a minimum depth of about 400 m below the seafloor has been computed from the hydrostatic balance between the diapiric sediments and the host sediments, a maximum depth, suggested by geometric considerations, ranges between 5.3 and 7 km. The presence of thermogenic gas in the diapiric sediments suggests a better constrained origin depth of at least 2.2 km.The heat flow measured within the Olimpi mud diapir field and along a transect orthogonal to the diapiric field is low, ranging between 16 ± 5 and 41 ± 6 mW m–2. Due to the presence of gas, the thermal conductivity of the diapiric sediments is lower than that of the host hemipelagic oozes (0.6–0.9 and 1.0–1.15 W m–1 K–1 respectively).We consider the distribution of mud diapirs to be controlled by the presence of tectonic features such as reverse faults or thrusts (inner escarpment) that develop where the thickness of the Late Miocene evaporites appears to be minimum. An upward migration through time of the position of the décollement within the stratigraphic column from the Upper Oligocene (diapiric sediments) to the Upper Miocene (present position) is identified. 相似文献
999.
Tetraploid induced by physical and chemical methods in Jinjiang oyster(Crassostrea rivularis) 总被引:1,自引:0,他引:1
Rong Shoubai Shi Shumei Mo Qirong Liu Shaeqiong Liang Ze Zhao Xiuzhu Tong Wangdong Li Shouwu Li Yimin 《海洋学报(英文版)》1994,13(2):275-283
TetraploidinducedbyphysicalandchemicalmethodsinJinjiangoyster(Crassostrearivularis)¥RongShoubai,ShiShumei,McQirong,LiuShaeqio... 相似文献
1000.
In this paper, the marine ship observation data sets in the seventh (October 16-December 4. 1989) and eighth (June 1-July 16, 1990) cruises of PRC -US tropical ocean and global atmosphere (TOGA) joint scientific investigation in the tropical western Pacific are used to analyze the elements such as sea surface temperature (SST), surface wind field, fluxes and net heat budget, which are important physical parameters of underlying earth's surface influencing the global mean circulation evolution on seasonal and interannual time scales. These diagnostic analyses are very beneficial to the understanding of the regional climate characteristics and the air-sea interaction mechanism, and the improving of surface flux parameterizations and regional or global climate model. 相似文献