全文获取类型
收费全文 | 31442篇 |
免费 | 6960篇 |
国内免费 | 5528篇 |
专业分类
测绘学 | 1587篇 |
大气科学 | 584篇 |
地球物理 | 1607篇 |
地质学 | 22798篇 |
海洋学 | 11901篇 |
天文学 | 25篇 |
综合类 | 4283篇 |
自然地理 | 1145篇 |
出版年
2024年 | 149篇 |
2023年 | 714篇 |
2022年 | 856篇 |
2021年 | 945篇 |
2020年 | 879篇 |
2019年 | 987篇 |
2018年 | 726篇 |
2017年 | 777篇 |
2016年 | 883篇 |
2015年 | 1015篇 |
2014年 | 2416篇 |
2013年 | 1589篇 |
2012年 | 2453篇 |
2011年 | 2455篇 |
2010年 | 1931篇 |
2009年 | 2143篇 |
2008年 | 2040篇 |
2007年 | 1601篇 |
2006年 | 1677篇 |
2005年 | 1508篇 |
2004年 | 1353篇 |
2003年 | 1329篇 |
2002年 | 1219篇 |
2001年 | 1215篇 |
2000年 | 1078篇 |
1999年 | 1003篇 |
1998年 | 1160篇 |
1997年 | 1114篇 |
1996年 | 915篇 |
1995年 | 956篇 |
1994年 | 821篇 |
1993年 | 829篇 |
1992年 | 783篇 |
1991年 | 838篇 |
1990年 | 628篇 |
1989年 | 481篇 |
1988年 | 38篇 |
1987年 | 44篇 |
1986年 | 43篇 |
1985年 | 63篇 |
1984年 | 31篇 |
1983年 | 32篇 |
1982年 | 33篇 |
1981年 | 21篇 |
1980年 | 23篇 |
1979年 | 17篇 |
1976年 | 10篇 |
1948年 | 14篇 |
1946年 | 8篇 |
1942年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
YaoDaquan ZhaiHongtao 《中国地震研究》2005,19(1):35-42
In order to determine the degree of returning-to-zero of temperatures of deformed calcite, a series of rock-breaking experiments were designed to test calcite-rich limestone samples under fixed confining pressures and different temperatures. The consolidated deformed samples in their initial state were observed under a microscope and the microscopic indicators in different zero-returning states were put forward, thus providing a microscopic foundation for evaluation of reliability of dating values of deformation in calcite. At last, the correction of dating values of deformation for samples whose temperature has not yet returned to zero is discussed. 相似文献
72.
9月15日上午,峄山省级地质公园揭碑开园仪式在邹城市峄山举行。山东省国土资源厅领导及济宁市、邹城市有关领导和部门负责同志出席了揭碑开园仪式,并参观游览了峄山地质公园。峄山省级地质公园位于邹城市市区东南部,总面积约80平方千米。主要包括“七山一水”为主的自然地质景观和人文历史景观。作为主要标志、第一高峰的峄山,海拔582.8米,素有“邹鲁灵秀”、“岱南奇观”之美誉,被誉为“神州怪石第一山”、“天下第一奇山”。区内纵横交错的花岗岩节理,直插天表的花岗岩奇峰, 相似文献
73.
Silicon limitation on primary production and its destiny in Jiaozhou Bay, China——Ⅳ:Study on cross-bay transect from estuary to ocean 总被引:1,自引:0,他引:1
The authors analyzed the data collected in the Ecological Station Jiaozhou Bay from May 1991 to November 1994, including 12
seasonal investigations, to determine the characteristics, dynamic cycles and variation trends of the silicate in the bay.
The results indicated that the rivers around Jiaozhou Bay provided abundant supply of silicate to the bay. The silicate concentration
there depended on river flow variation. The horizontal variation of silicate concentration on the transect showed that the
silicate concentration decreased with distance from shorelines. The vertical variation of it showed that silicate sank and
deposited on the sea bottom by phytoplankton uptake and death, and zooplankton excretion. In this way, silicon would endlessly
be transferred from terrestrial sources to the sea bottom. The silicon took up by phytoplankton and by other biogeochemical
processes led to insufficient silicon supply for phytoplankton growth. In this paper, a 2D dynamic model of river flow versus
silicate concentration was established by which silicate concentrations of 0.028–0.062 μmol/L in seawater was yielded by inputting
certain seasonal unit river flows (m3/s), or in other words, the silicate supply rate; and when the unit river flow was set to zero, meaning no river input, the
silicate concentrations were between 0.05–0.69 μmol/L in the bay. In terms of the silicate supply rate, Jiaozhou Bay was divided
into three parts. The division shows a given river flow could generate several different silicon levels in corresponding regions,
so as to the silicon-limitation levels to the phytoplankton in these regions. Another dynamic model of river flow versus primary
production was set up by which the phytoplankton primary production of 5.21–15.55 (mgC/m2·d)/(m3/s) were obtained in our case at unit river flow values via silicate concentration or primary production conversion rate.
Similarly, the values of primary production of 121.98–195.33 (mgC/m2·d) were achieved at zero unit river flow condition. A primary production conversion rate reflects the sensitivity to silicon
depletion so as to different phytoplankton primary production and silicon requirements by different phytoplankton assemblages
in different marine areas. In addition, the authors differentiated two equations (Eqs. 1 and 2) in the models to obtain the
river flow variation that determines the silicate concentration variation, and in turn, the variation of primary production.
These results proved further that nutrient silicon is a limiting factor for phytoplankton growth.
This study was funded by NSFC (No. 40036010), and the Director's Fund of the Beihai Sea Monitoring Center, the State Oceanic
Administration. 相似文献
74.
章仲根 《广东海洋大学学报》2004,24(5):13-18
宁波商帮是我国十大商帮之一 ,百年经久不衰 ,究其原因是宁波商帮受到独特的宁波城市文化熏陶。宁波得天独厚的海洋优势 ,造就了有悠久历史凝结和中外文化交融的宁波海洋文化。海洋文化是一种先进的文化 ,具有大海的许多秉性 :大度、创新、包容。宁波城市文化把中国传统的儒家文化和宁波海洋文化很好地结合起来。正是这种独特的宁波城市文化 ,才哺育出顽强开拓、勇于创新 ,克勤克俭、脚踏实地 ,注重团队、和衷共济的“宁波商帮精神”。 相似文献
75.
1 INTRODUCTIONThe South China Sea (SCS) is a semi-enclosedmarginal sea in western North Pacific Ocean withvery complex topography and is the important pas-sage connecting the Pacific and Indian Oceans. Ithas great impact to the global climate and a greatinterest of many oceanography researchers. Twodominant surface hydrographic and circulation fea-tures in the northern SCS are a strong fresh waterexpansion and a warm and high-salinity seawaterintrusion such as the SCS Diluted Water… 相似文献
76.
WEIHai-quan JINBo-lu LIUYong-shun 《东北亚地学研究》2004,7(1):28-35
A number of different lahars have been recognized from a systematic survey of a mapping project. The high setting temporamre feature of the deposits indicates a relationship between the lahar and the Millennium eruption event of Tianchi Volcano. The lahars caused a dramatic disaster. Recognize of the huge avalanche scars and deposits around Tianchi Volcano imply another highly destructive hazard. Three types of different texture of the avalanche deposits have been recognized. There was often magma mixing processes during the Millennium eruption of Tianchi Volcano, indicating a mixing and co-eruption regime of the eruption. 相似文献
77.
78.
79.
80.
大别山麓前寒武纪变质岩分布区,具片麻状构造的花岗岩类分布较广。周家塆岩体即为一例。前人主要依据片麻理发育程度,以类比的声法,将这些片麻状花岗岩时代定为“大别-吕梁期”或“晋宁期”,而将周家塆岩体定为燕山早期花岗岩侵入体。这些结论,均缺乏同位素年龄数据佐证,有的也不切合地质实际,因而谬误不少。 相似文献