全文获取类型
收费全文 | 732篇 |
免费 | 140篇 |
国内免费 | 190篇 |
专业分类
测绘学 | 126篇 |
大气科学 | 73篇 |
地球物理 | 95篇 |
地质学 | 441篇 |
海洋学 | 202篇 |
综合类 | 38篇 |
自然地理 | 87篇 |
出版年
2024年 | 6篇 |
2023年 | 11篇 |
2022年 | 35篇 |
2021年 | 47篇 |
2020年 | 26篇 |
2019年 | 34篇 |
2018年 | 34篇 |
2017年 | 19篇 |
2016年 | 31篇 |
2015年 | 29篇 |
2014年 | 42篇 |
2013年 | 62篇 |
2012年 | 74篇 |
2011年 | 65篇 |
2010年 | 69篇 |
2009年 | 69篇 |
2008年 | 70篇 |
2007年 | 74篇 |
2006年 | 58篇 |
2005年 | 49篇 |
2004年 | 42篇 |
2003年 | 25篇 |
2002年 | 22篇 |
2001年 | 28篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1958年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有1062条查询结果,搜索用时 15 毫秒
231.
根据厦门岛东南岸沙滩剖面1999年2月-2002年11月4年的观测资料,分析了该剖面上平均高潮位、平均海平面、平均低潮位的位置变化,绘制了冲淤变化曲线,研究剖面的形态特征及季节和长周期变化趋势。结果表明,风暴潮影响后沙滩剖面呈风暴型剖面,而常浪季节均表现为滩肩型复式剖面。受滨外地形、岸线走向、季节性风浪和潮汐活动等因素影响,沙滩剖面的季节变化比较复杂,长周期变化及风暴潮后剖面的恢复过程各岸段有所不同:泥沙流上游的岸段供沙不足,呈侵蚀状态,剖面恢复较慢;下游则呈基本稳定或淤长状态,剖面恢复相对较快。暴风浪和季节性常风浪交替作用控制着本区沙滩剖面的长周期循环变化过程,该过程一般包括风暴侵蚀期、快速恢复期、稳定恢复期和基本稳定期4个阶段。 相似文献
232.
壳聚糖季铵盐的合成及性质研究 总被引:16,自引:0,他引:16
为开发利用壳聚糖及其衍生物,采用异相法合成了壳聚糖季铵盐——羟丙基三甲基氯化铵(HACC),并分别用红外光谱、核磁共振对其结构进行了表征;通过扫描电镜图对比分析了CS和HACC的粒度和外貌形态变化。在此基础上,测定了HACC的取代度(DQ),并对其溶液性质进行研究。结果表明:通过在壳聚糖分子结构中N上引入季铵盐侧链合成的HACC,具有较好的水溶性和较高的稳定性,室温下水中溶解度达10%,1%醋酸水溶液粘度在12d内、水溶液粘度在pH=3~9范围内几乎没有降低。 相似文献
233.
海底地震仪是一种重要的海洋地震观测设备。针对中国近岸浅海洋流噪声大和人类活动频繁的特点,提出链式地震观测方式并对链式海底地震仪节点进行机械结构设计。首先根据内部构件尺寸与布局对地震仪节点整体结构进行设计;然后通过理论计算与有限元仿真方式确定地震仪节点仓体的壳体厚度、端盖厚度和密封尺寸;最后通过压力试验验证所设计的地震仪节点结构的耐压和水密性能符合要求,通过地震观测对比试验验证其接收天然地震的能力。此链式海底地震仪未来将应用于浙江近海的实际地震观测,提供实时连续的地震观测数据。 相似文献
234.
空间治理的社区实践与正当性建构——以浙江省永嘉县芙蓉村传统村落保护为例 总被引:3,自引:1,他引:2
空间治理是一个复杂的政治过程。以浙江省永嘉县芙蓉村的传统村落保护为例,通过叙事研究展示了地方特性对空间治理实践的影响,探讨了空间治理正当性建构的困难及可能的解决思路。研究认为:① 空间治理的宏观意义与被治理社区地方性知识之间的冲突可能引发政策和行政的正当性危机。② 不同政策措施对于正当性的建构有不同作用,对抗性措施必然引发正当性危机,调和性措施往往难以有效建立正当性,共赢性措施是最佳之选,但其对于正当性的调节效果受限于外部条件,各种政策措施在地方特性的影响下均面临失效风险。③ 空间治理正当性的建立首先需要正确把握地方性政治互动方式,理解正当性在地方特性作用下得以建立或趋于消解的原因,在此基础上根据情境适当调用对抗性政策措施、调和性政策措施和共赢性政策措施,从而建立良好的意义沟通和平等协商机制,使正当性得以长久维系。 相似文献
235.
目的:探讨心痛泰对急性心肌缺血大鼠新生微血管密度及血管内皮活性物质的影响。方法:将SD大鼠随机分成假手术组,模型组,心痛泰低、中、高剂量组,麝香保心丸组。除假手术组外,其余组大鼠均予以结扎冠状动脉左前降支制备成急性心肌缺血损伤模型,成模后分别给予蒸馏水,心痛泰低、中、高剂量药液及麝香保心丸进行灌胃治疗2周。HE染色光镜观察心肌形态结构改变;ELISA试剂盒检测血清中一氧化氮(NO)、一氧化氮合酶(NOS)、内皮素1(ET-1)含量;免疫组化法测定新生微血管密度。结果:与假手术组相比,模型组血清中NO、NOS表达减少(P<0.01),ET-1表达增加(P<0.01),缺血心肌微血管密度表达增加(P<0.05);与模型组相比,各用药组均可升高血清中NO、NOS含量(P<0.01),降低ET-1含量(P<0.01),促进缺血区微血管密度的表达(P<0.05)。结论:心痛泰具有保护缺血心肌之效,这可能与其提高血清中NO、NOS含量、减少ET-1的含量、促进缺血区新生血管生成相关。 相似文献
236.
水利、铁道、冶金等工业部门,在基坑开挖、隧道掘进,矿山开采等作业中通常用圆柱状条形药包.此外,某些工程如洞库爆炸也可看成条形药包.显然,这类药包在岩体中爆炸时,应力波的传播和动应力的分布均不同于球形药包的爆炸而具有自己的特点.这些特点直接影响爆破破岩机理和对地下工程施加动荷载的特征,以及对它的动态稳定性的评价. 相似文献
237.
ZHANG Yan-hui LI Shi-wen WENG Ai-hua ZHANG Su-qin YANG Yue LI Jian-ping TANG Yu 《地震地质》2019,41(4):979-995
Geomagnetic depth sounding is an effective method for exploring deep structure of the earth. There are dense geomagnetic observatories in China, which lays a foundation to obtain the electrical structure of the transition zone and the upper part of the lower mantle beneath China. However, the corresponding C-responses estimation methods which are applied now cannot get the stable C-responses for many observatories. Thus, a large amount of geomagnetic data is wasted. Therefore, in order to make full use of the geomagnetic data, the estimation of C-responses needs to be systematically studied. Because of the heterogeneous characteristics of the data quality of China's geomagnetic observation data, such as the quality of the data, the length of the record, the types of data(absolute and relative observation)and data discontinuity condition, many geomagnetic data are abandoned, this limits the resolution of mantle electrical structure studies. In this paper, the following techniques are used to improve the stability of the data and increase the number of the available geomagnetic observatories, in the meantime, the stability of the C-responses curves can be effectively improved:1)obtaining the stable spectrums of the different components for each frequency by the BIRRP(Bounded Influence, Remote Reference Processing)software, and using the global smoothing technique to suppress data noise on geomagnetic data; 2)As for the geomagnetic data which only records the relative variation of the D, H and Z components and doesn't have the baseline value, the horizontal component is decomposed by the approximate estimation method to obtain the C-responses of the relative variation data, and then the relative variation data is used directly for the C-responses estimation; 3)the effects of discontinuous data and short-record data on C-responses estimation are discussed. Under normal conditions, the discontinuity of the data has little influence on C-responses, and when the data length is shorter than 5 years, we can hardly get the available C-responses whose periods are longer than 40 days. All these experiments can provide a basis for the data processing of these kinds of observation data; 4)for coastal observatories, the ratio method is used to eliminate the influence of ocean effect on the C-responses functions. After carefully processing the data of more than 100 geomagnetic observatories in China by the above techniques, the stable C-responses function of 42 observatories is finally obtained, among them, the number of the observatories with C-responses ranging from 1.3 to 113.7 days is 24, and the observatories with C-responses ranging from 1.3 to 42.6 days are 18. The techniques of this paper can process heterogeneous data well and obtain more stable C-responses, which provides more basic data for high-resolution geomagnetic depth sounding inversion researches in China. 相似文献
238.
239.
FINE ELECTRICAL STRUCTURE BENEATH THE EPICENTER OF 1668 TANCHENG MS8.5 EARTHQUAKE REVEALED BY MT SOUNDING
下载免费PDF全文
![点击此处可从《地震地质》网站下载免费的PDF全文](/ch/ext_images/free.gif)
WENG Ai-hua LI Jian-ping FAN Xiao-ping LI Si-rui HAN Jiang-tao LI Da-jun LI Ya-bin ZHAO Xiang-yang TANG Yu 《地震地质》2018,40(2):396-409
In order to understand the mechanism of the 1668 MS8.5 earthquake occurred in Tancheng, it is important to probe the fine deep geological structure beneath the epicenter. A MT profile 20km south of the epicenter has been deployed. There are 17 sites along the profile, with a 3km average separation. Signals in Ex, Ey, Hx and Hy were measured in a cross manner, with x-axis orientated to the north. Record length for each site was at least 20h. The impedance and phase at sites in high cultural noisy environment were estimated by remote reference technique. As the Tanlu Fault Zone(TLFZ)is in NNE, nearly northerly, thus YX mode was considered as TM mode. Gauss-Newton inversion was done in 2-D mode with only the TM impedance and phase as input data. The electrical sections of 10km and 40km depth were respectively obtained after 8 iterations. The both initial models were created by Bostic approximation. The sections reveal the following features.
The TLFZ consists of five faults, from east to west numbered as F0 to F4. F1 is the primary fault, steeply dipping west down to mantle, which has turned into a buried one overthrust by the east dipping Fault F0. F2 and F3 dip east at 45 degrees, parallel to F4, truncated by F1 at depth. F4 dips east in the shallow subsurface and gradually dips to west toward depth through the entire crust merging with F1 to form a bigger one. These four faults constitute a flower-shaped structure, showing the nature of strike-slip of the TLFZ, associated with normal faulting in the late Yanshanian to early Himalayan. F1 dips west, overthrust by east-dipping F0, implying the compression from the westward subduction of the Pacific plate, thus present-day compression is superposed on the early tensile and strike-slip feature.
Based on MT data, it is inferred that the 1668 Tancheng M8.5 earthquake occurred at the junction of F1 and F3 about 15km deep. Thus it was likely resulted from westward compression of the Pacific plate, leading to thrust of the Sulu uplift along F0, inducing activity of F1 at depth, reactivated F3, and adjusting the stress distribution in the region. 相似文献
240.
大型浅水湖泊藻类模型参数敏感性分析 总被引:2,自引:1,他引:1
选取太湖作为典型湖泊在之前研究基础上建立藻类模型,对模型中与藻类有关的40个参数进行拉丁超立方抽样,并使用区域敏感性分析方法和普适似然不确定性分析方法进行敏感性分析.结果表明:在所选的40个参数中,有7个参数是敏感的参数,对模拟的结果影响较大.在藻类生长、基础代谢、牧食和沉降4个藻类变化过程中藻类生长的敏感参数最多,影响最大;在藻类生长项中,叶绿素的消光系数是藻类生长光照限制中的最敏感参数,而最低适宜生长温度及其对藻类生长的影响系数则是温度限制中的敏感参数;并且不同湖区的不确定性在不同时间差异明显,对于藻类低浓度湖区和藻类暴发期的模拟需要加以关注. 相似文献