全文获取类型
收费全文 | 4726篇 |
免费 | 1003篇 |
国内免费 | 2446篇 |
专业分类
测绘学 | 295篇 |
大气科学 | 709篇 |
地球物理 | 1825篇 |
地质学 | 3883篇 |
海洋学 | 711篇 |
天文学 | 25篇 |
综合类 | 251篇 |
自然地理 | 476篇 |
出版年
2024年 | 16篇 |
2023年 | 99篇 |
2022年 | 204篇 |
2021年 | 184篇 |
2020年 | 291篇 |
2019年 | 371篇 |
2018年 | 334篇 |
2017年 | 240篇 |
2016年 | 352篇 |
2015年 | 354篇 |
2014年 | 450篇 |
2013年 | 483篇 |
2012年 | 440篇 |
2011年 | 464篇 |
2010年 | 373篇 |
2009年 | 445篇 |
2008年 | 383篇 |
2007年 | 356篇 |
2006年 | 401篇 |
2005年 | 319篇 |
2004年 | 266篇 |
2003年 | 217篇 |
2002年 | 170篇 |
2001年 | 137篇 |
2000年 | 111篇 |
1999年 | 112篇 |
1998年 | 115篇 |
1997年 | 98篇 |
1996年 | 85篇 |
1995年 | 67篇 |
1994年 | 61篇 |
1993年 | 54篇 |
1992年 | 38篇 |
1991年 | 25篇 |
1990年 | 22篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有8175条查询结果,搜索用时 406 毫秒
991.
厦门城市空间拓展的生态敏感性评价 总被引:1,自引:0,他引:1
在综合分析海湾型城市自然生态与社会生态属性的基础上,选取了高程、坡度、河流水库、植被覆盖、土地覆盖和生态保护区等6个因子,作为生态敏感性评价的指标。另外,借助GIS空间分析单因子评价与多因子加权综合评价方法,研究了生态敏感性程度及其空间分布特征,将厦门的生态敏感性划分为4级:不敏感、较敏感、中敏感和高敏感。综合评价结果表明,厦门市生态敏感性在空间分布上差异显著:高度敏感区占研究区总面积的28.1%,低敏感区和不敏感区分别占研究区总面积的27.9%和33.6%。中度敏感区占的比例较小,仅为10.4%。 相似文献
992.
Three main topics including the floor motion action mechanism, the test frame design, and the target spectrum simulation presented in the paper are discussed specifically. Floor motion action mechanism is critical in understanding the seismic performance of architectural nonstructural components. Seismic sensitiveness and earthquake response properties of the nonstructural components should be considered in the design of the test frame for the shaking table test. Target spectrum simulation is also a challenging job in the shaking table test, in which dynamic characteristics of the specimen, performance of the shaking table facilities, and the control techniques should be all considered. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
993.
Horizontal bidirectional loading tests are conducted for real-sized high-damping rubber (HDR) bearings with diameters of 700 mm (HDR700) and 1300 mm (HDR1300). The hysteresis loops of these bearings under bidirectional horizontal loadings are compared with those under unidirectional loadings. The results show that the bearing force measurement in the primary direction of loading increases when there is displacement in the orthogonal direction. Unusually, the maximum restoring force in the orthogonal direction to the primary loading direction occurs near zero displacement. On the basis of the observations of the restoring forces, a rate-independent model is proposed. This model simulates well the test results under both bidirectional loading and unidirectional loading. It can reproduce the irregular restoring forces characteristics around zero displacement as described above. Bidirectional loading induced twist deformation in the HDR bearings that increased local shear strains. This phenomenon results in an early failure as observed in HDR700. The additional shear strain is estimated based on the twist deformation measured by video image analysis. The comparison of the nominal total shear stress demonstrates that the increase of shear stress because of bidirectional loading occurs when the average shear strain is larger than about 200%. The larger the shear strain, the greater the bidirectional effect. It is shown that the nominal total shear stress of average strain of 350% under bidirectional circular loading pattern is approximately the same as the average shear strain of 400% under unidirectional loading. This means that the average shear strain of 350% under a bidirectional circular loading corresponds to a local shear strain of 400%. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
994.
Sensitivity of hydrological variables to climate change in the Haihe River basin,China 总被引:1,自引:0,他引:1
Zhenxin Bao Jianyun Zhang Jiufu Liu Guoqing Wang Xiaolin Yan Xiaojun Wang Liru Zhang 《水文研究》2012,26(15):2294-2306
Using the defined sensitivity index, the sensitivity of streamflow, evapotranspiration and soil moisture to climate change was investigated in four catchments in the Haihe River basin. Climate change contained three parts: annual precipitation and temperature change and the change of the percentage of precipitation in the flood season (Pf). With satisfying monthly streamflow simulation using the variable infiltration capacity model, the sensitivity was estimated by the change of simulated hydrological variables with hypothetical climatic scenarios and observed climatic data. The results indicated that (i) the sensitivity of streamflow would increase as precipitation or Pf increased but would decrease as temperature increased; (ii) the sensitivity of evapotranspiration and soil moisture would decrease as precipitation or temperature increased, but it to Pf varied in different catchments; and (iii) hydrological variables were more sensitive to precipitation, followed by Pf, and then temperature. The nonlinear response of streamflow, evapotranspiration and soil moisture to climate change could provide a reference for water resources planning and management under future climate change scenarios in the Haihe River basin. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
995.
996.
以内蒙古中部的呼和浩特-包头地区(40°~42°N,108°~114°E)作为研究区域,收集整理2001年1月1日至2010年4月30日ML≥1.0地震作为研究对象,按地震样本数目滑动扫描并计算最小完整性震级Mc,绘制Mc的时序变化曲线.分析认为Mc在时间上的变化主要反映台网监测能力和地震活动规律,但台站布局、地震信噪比和人为因素也会引起Mc的短期或不连续性的变化.同时在Rydelek等提出的2个假设条件下,对呼包地区的地震目录完整性进行了RS检验,其结果与上述扫描计算结果一致,也与根据台网监测能力所得到的震级范围吻合,证明本文的计算结果能够比较真实的反映2001年以来呼包地区地震目录在各时段内的完整性. 相似文献
997.
提出了带竖向构造钢筋再生混凝土砖砌体结构,进行了2个两层再生混凝土砖砌体房屋结构1/2缩尺模型的模拟地震振动台试验研究,2个结构模型的墙体厚度均为120 mm,一层设有门洞和窗洞,二层设有窗洞。2个模型中,1个为带竖向构造钢筋再生混凝土砖砌体房屋,1个为普通无竖向构造钢筋再生混凝土砖砌体房屋。试验中输入El Centro地震动,测试分析了台面加速度反应、一层和二层顶板加速度反应、结构层间位移反应以及各阶段结构损伤与破坏特征等。研究表明:带竖向构造钢筋再生混凝土砖砌体房屋比普通再生混凝土砖砌体房屋的破坏程度轻,墙体裂缝位置相对错动小,抗震性能显著提高;带竖向构造钢筋再生混凝土砖砌体房屋可用于地震区村镇建筑。 相似文献
998.
999.
使用1900年以来的太阳黑子数据,统计分析了其与新疆地区MS≥6.6强震的关系。结果显示:新疆地区69%的MS≥6.6和86%的MS≥7的地震,发生在黑子数月均值≤35的时段内。以黑子数月均值≤20和≤35的时段作为MS≥6.6强震的预测指标,报准率分别为71%和64%;以黑子数月均值≤35的时段作为MS≥6.6强震的预测指标,报准率为69%。R值评分检验表明,上述预测指标是有效的。最后使用这些统计关系和指标对新疆未来几年发生强震的可能性作了估计。 相似文献
1000.