全文获取类型
收费全文 | 33289篇 |
免费 | 6049篇 |
国内免费 | 8083篇 |
专业分类
测绘学 | 1740篇 |
大气科学 | 7476篇 |
地球物理 | 8601篇 |
地质学 | 16582篇 |
海洋学 | 3889篇 |
天文学 | 1620篇 |
综合类 | 3683篇 |
自然地理 | 3830篇 |
出版年
2024年 | 109篇 |
2023年 | 462篇 |
2022年 | 1350篇 |
2021年 | 1566篇 |
2020年 | 1374篇 |
2019年 | 1485篇 |
2018年 | 1753篇 |
2017年 | 1646篇 |
2016年 | 1899篇 |
2015年 | 1491篇 |
2014年 | 1939篇 |
2013年 | 1773篇 |
2012年 | 1738篇 |
2011年 | 1796篇 |
2010年 | 1895篇 |
2009年 | 1913篇 |
2008年 | 1673篇 |
2007年 | 1642篇 |
2006年 | 1388篇 |
2005年 | 1257篇 |
2004年 | 1005篇 |
2003年 | 1009篇 |
2002年 | 995篇 |
2001年 | 944篇 |
2000年 | 1155篇 |
1999年 | 1648篇 |
1998年 | 1388篇 |
1997年 | 1474篇 |
1996年 | 1214篇 |
1995年 | 1153篇 |
1994年 | 1020篇 |
1993年 | 890篇 |
1992年 | 712篇 |
1991年 | 522篇 |
1990年 | 365篇 |
1989年 | 389篇 |
1988年 | 327篇 |
1987年 | 225篇 |
1986年 | 194篇 |
1985年 | 130篇 |
1984年 | 107篇 |
1983年 | 85篇 |
1982年 | 85篇 |
1981年 | 67篇 |
1980年 | 51篇 |
1979年 | 36篇 |
1978年 | 18篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1958年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
PALEOSOLSOFSANDYLANDSANDENVIRONMENTALCHANGESINTHEWESTERNPARTOFNORTHEASTPLAINOFCHINAWESTERNDURINGHOLOCENE¥QiuShanwen(裘善文)LiQus... 相似文献
62.
本文应用了最新取得的“五统一”区域重力成果,并经过对浅表松散槽(如下辽河断陷,大岩体等)的密度亏损进行补偿改正后,求取了全省的区域重力场及其垂向二次导数,计算了莫氏面等深度图。在分析区域重力场及其垂向二次导数异常特征和莫氏面起伏特征的基础上,划分出辽宁深部构造的基本格局。从平面上探讨了深部构造与地形地势、地质构造及矿产分布的关系,从剖面上剖析了辽宁省地壳分层的宏观特征 相似文献
63.
THE SIMULATED STORAGE CAPACITY OF FLOOD AND WATERLOGGING IN THE TYPICAL AGRICULTURAL REGION IN JIANGHAN PLAIN 总被引:2,自引:0,他引:2
1INTRODUCTIONJianghanPlainisoneoftheimportantbasesofChina′sagriculturalproductivitylocatedinthemiddleChangjiangRivervalleyofcentralChina.TheJianghanplainapproximately6.6×104km2inareaandover30millioninpopulationistherenowned“countryoffishandrice"in… 相似文献
64.
In this paper, we idealize the actual solar atmosphere as a multi-isothermal-layer system so as to obtain the energy transmittance of the linear Alfvén wave that propagates through such a system in presence of a uniform oblique magnetic filed. The results indicate that the two-layer model is essentially different to the three-layer one. In the two-layer model, the temperature jump acts as a high pass filter. In the three-layer model, resonant transfer will take place and the transmittance undergoes oscillation as the trigonometric function terms dominate its behavior. For actual solar atmosphere, the result reveals that the lower parts of solar atmosphere are more suitable for those Alfvén waves with period of seconds to transfer their energy. 相似文献
65.
Boli basin, between Yishu fracture belt and Dunmi fracture belt, is the biggest Mesozoic coal basin in the east of Heilongjiang Province. Now it is a fault - fold remnant basin. The basin' s shape is generally consistent with the whole distribution of the cover folds, an arc protruding southwards. The basement of the basin can be divided into three fault blocks or structural units. The formation and evoluation of the basin in Mesozoic was determined by the basement fault blocks' displacement features rusulted from by the movement of the edge faults and the main basement faults. 相似文献
66.
67.
本文分析了国外用于测定度盘分划改正的几种方法,并分析了固定角距法的优点和不足之处;详细叙述了组合固定角距法测定对径改正的原理和计算公式;并且讨论了两对显微镜之间夹角变化以及显微镜比例尺变化对对径改正的影响,给出了相应的修正方法。用固定角距法所测的对径改正精度可达±0″.009。 相似文献
68.
69.
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
70.
北天山东段康古尔塔格带是晚古生代塔里木板块和准噶尔板块碰撞的结果。它是一条复杂的、强烈的高应变带.并具有独特的变形机制、应变序列以及构造变形。本文运用构造-地层研究方法对该碰撞带的构造特征加以分析和研究。 相似文献