全文获取类型
收费全文 | 1163篇 |
免费 | 156篇 |
国内免费 | 166篇 |
专业分类
测绘学 | 255篇 |
大气科学 | 101篇 |
地球物理 | 341篇 |
地质学 | 457篇 |
海洋学 | 105篇 |
天文学 | 5篇 |
综合类 | 84篇 |
自然地理 | 137篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 24篇 |
2020年 | 27篇 |
2019年 | 33篇 |
2018年 | 41篇 |
2017年 | 35篇 |
2016年 | 46篇 |
2015年 | 41篇 |
2014年 | 72篇 |
2013年 | 71篇 |
2012年 | 70篇 |
2011年 | 67篇 |
2010年 | 54篇 |
2009年 | 56篇 |
2008年 | 63篇 |
2007年 | 82篇 |
2006年 | 106篇 |
2005年 | 74篇 |
2004年 | 65篇 |
2003年 | 60篇 |
2002年 | 57篇 |
2001年 | 56篇 |
2000年 | 50篇 |
1999年 | 43篇 |
1998年 | 28篇 |
1997年 | 29篇 |
1996年 | 20篇 |
1995年 | 17篇 |
1994年 | 13篇 |
1993年 | 16篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有1485条查询结果,搜索用时 902 毫秒
891.
2008年奥运会帆船帆板比赛期间正值青岛的主汛期,天气复杂多变,气象保障任务繁重。利用青岛市区3个气象站和奥帆赛场附近的自动站资料,统计分析了可能对奥帆赛产生影响的天气出现概率,指出影响奥帆赛的天气主要是强降雨、雷暴和热带气旋,做好这3种天气的准确预报对保障好比赛至关重要。此外,重点分析了对风帆运动有显著影响的风的基本特征,指出由于不同的地理环境和地势,以及一日中不同的时段风的差异都比较明显,得出午后至傍晚期间风速较大,且风向稳定,比赛选在此时更有利的结论。 相似文献
892.
刘智超 《测绘与空间地理信息》2013,36(7):192-193,195
以单基站CORS在工程测量中的应用为研究对象,结合南方单基站的系统组成、系统设置及测量实践对其应用环节进行了详细地剖析。 相似文献
893.
P. Calosi S.P.S. Rastrick M. Graziano S.C. Thomas C. Baggini H.A. Carter J.M. Hall-Spencer M. Milazzo J.I. Spicer 《Marine pollution bulletin》2013
To reduce the negative effect of climate change on Biodiversity, the use of geological CO2 sequestration has been proposed; however leakage from underwater storages may represent a risk to marine life. As extracellular homeostasis is important in determining species’ ability to cope with elevated CO2, we investigated the acid–base and ion regulatory responses, as well as the density, of sea urchins living around CO2 vents at Vulcano, Italy. We conducted in situ transplantation and field-based laboratory exposures to different pCO2/pH regimes. Our results confirm that sea urchins have some ability to regulate their extracellular fluid under elevated pCO2. Furthermore, we show that even in closely-related taxa divergent physiological capabilities underlie differences in taxa distribution around the CO2 vent. It is concluded that species distribution under the sort of elevated CO2 conditions occurring with leakages from geological storages and future ocean acidification scenarios, may partly be determined by quite subtle physiological differentiation. 相似文献
894.
Relative contributions of stream concentration,stream discharge and shoreline load to base cation trends in Red Chalk and Harp lakes,south‐central Ontario,Canada 下载免费PDF全文
Huaxia Yao April James Christopher McConnell Brian Turnbull Timothy Field Keith M. Somers 《水文研究》2016,30(6):858-872
We evaluated the importance and contributions of changes in stream base cation concentration, stream discharge and lake shoreline load to changes in base cation concentrations in two small inland lakes in south‐central Ontario. The shoreline load from ungauged drainage areas was calculated with a mass balance equation. An evaluation method based on the partial Mann–Kendall test quantified the relative contributions of these three explanatory drivers to the observed trends in lake concentration of Ca, K, Mg and Na. Over a 29‐year period (1978–2006) at Red Chalk and Harp lakes, declines in stream concentration and discharge were correlated with the declines in lake concentrations of all base cations (except for Na in Harp Lake), with contributions of 21–81% from stream concentration and 12–58% from discharge, whereas the shoreline load had little contribution to observed trends. The observed unusual increase in Na concentration at Harp Lake was correlated with the increase in stream Na concentration and additional load from road salts, with the shoreline load contributing a substantial 37%. These results may be applicable to numerous inland lakes with similar site conditions, including lakes found on the Canadian Shield. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
895.
The paper deals with the applicability of the extended N2 method to base‐isolated plan‐asymmetric building structures. The results obtained by the usual pushover analysis of a 3D structural model are further combined with the aid of linear dynamic (spectral) analysis to account for the dynamic effects caused by structural asymmetry. In the paper, the method has been applied to the seismic analysis of a mass‐eccentric four‐storeyed RC frame building isolated with lead rubber bearings. Three different positions of the center of isolation system (CI) with respect to the center of mass (CM) and the center of stiffness of the superstructure (CS) were considered. The response was analyzed for three different eccentricities, three different torsional to lateral frequency ratios of the superstructure, and two ground motion intensities. The stiffness of the isolators was selected for three different protection levels, which resulted in elastic as well as moderately to excessively damaged superstructure performance levels. The results are presented in terms of the top, base and relative displacements, as well as the stiff/flexible side amplification factors. A more detailed insight into the nonlinear behavior of the superstructure is given in a form of ductility factors for the flexible and stiff side frames. The results of the extended N2 method for selected lateral load distributions are compared with the average results of nonlinear dynamic analyses. It was concluded that the extended N2 method could, with certain limitations, provide a reasonable prediction of the torsional influences in minor to moderately asymmetric base‐isolated structures. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
896.
A series of shallowly embedded steel column bases consisting of an exposed column base and a floor slab is tested under horizontal cyclic loading to very large deformation. The effects of floor slabs on strength and ductility are examined using concrete and Steel fiber‐reinforced cementitous composites (SFRCC) for the floor slab. The elastic stiffness, maximum strength, and dissipated energy of the column bases when they include SFRCC increase by 40, 70, and 70% over those of corresponding column bases with concrete floor slab. Better bonding behavior is notable for SFRCC, and the maximum strength and dissipated energy further increase by 15–30% and 70–90%, respectively, owing to the careful arrangement of reinforcing bars. Numerical models are developed to enhance the understanding the behavior of shallowly embedded column bases. Procedures for estimating the elastic stiffness and maximum strength of shallowly embedded column bases with conventional concrete are calibrated for their applicability to those with SFRCC slab. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
897.
898.
选用胡聿贤平稳地震地面运动模型作为基础隔震结构的随机地震动输入,采用Bouc-Wen模型描述隔震结构的层间滞变位移,将滞变体系动力特性矩阵随机等效线性化,并建立等价线性状态方程。引入左右特征向量系,对振动微分方程进行解耦,推导了基础隔震结构随机地震响应的统计矩解析解。采用变形失效准则,定义了上部结构和隔震层的功能状态极限函数。在此基础上,采用首次超越破坏模型,基于Possion分布假设和串联系统可靠度模型,建立了从整体上评价基础隔震体系抗震可靠度的简化分析方法。最后,通过一个基础隔震框架结构计算实例,说明了这种方法的运用。 相似文献
899.
900.