全文获取类型
收费全文 | 3218篇 |
免费 | 542篇 |
国内免费 | 432篇 |
专业分类
测绘学 | 242篇 |
大气科学 | 506篇 |
地球物理 | 795篇 |
地质学 | 1190篇 |
海洋学 | 343篇 |
天文学 | 572篇 |
综合类 | 132篇 |
自然地理 | 412篇 |
出版年
2024年 | 8篇 |
2023年 | 22篇 |
2022年 | 62篇 |
2021年 | 71篇 |
2020年 | 95篇 |
2019年 | 109篇 |
2018年 | 88篇 |
2017年 | 143篇 |
2016年 | 102篇 |
2015年 | 115篇 |
2014年 | 169篇 |
2013年 | 217篇 |
2012年 | 190篇 |
2011年 | 162篇 |
2010年 | 139篇 |
2009年 | 219篇 |
2008年 | 191篇 |
2007年 | 271篇 |
2006年 | 248篇 |
2005年 | 164篇 |
2004年 | 185篇 |
2003年 | 157篇 |
2002年 | 130篇 |
2001年 | 127篇 |
2000年 | 99篇 |
1999年 | 94篇 |
1998年 | 99篇 |
1997年 | 85篇 |
1996年 | 79篇 |
1995年 | 57篇 |
1994年 | 61篇 |
1993年 | 51篇 |
1992年 | 28篇 |
1991年 | 21篇 |
1990年 | 24篇 |
1989年 | 24篇 |
1988年 | 13篇 |
1987年 | 22篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1978年 | 1篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有4192条查询结果,搜索用时 15 毫秒
991.
NCAR分析资料在大气边界层内误差的初步分析 总被引:2,自引:1,他引:1
通过比较1998年南海季风试验(SCSMEX)期间(1998年5月5日~5月25日,6月4日~6月20日)7个站点的探空加密观测资料与NCAR分析资料,分析了在大气边界层内分析资料存在的误差.结果表明:在大气边界层内,NCAR分析资料存在较大的误差.位温和比湿误差随着高度的增加呈现下高上低的特征.比湿的误差要大于位温的误差,7个站点的位温均方差最小值基本都小于1 K,最大均方差也不大于2 K,而比湿均方差最小值基本都大于1.0 g·kg~(-1),部分站点的误差最大值超过2.0 g·kg~(-1).初步说明,下垫面对NCAR分析资料误差的产生有较大影响,内陆地区和海岛地区的分析资料位温的误差比沿海地区大,而比湿数据则相反;在垂直方向上,分析资料的位温误差在0.98~1.33 K之间,比湿误差介于1.39~1.60 g·kg~(-1)之间. 相似文献
992.
L波段气象探测网监控系统用来监视包括L波段探空设备与探空数据在内的全国高空气象探测网总体运行情况。基于L波段探空系统提供的监控信息与探空资料,结合业务运行经验与用户需求建立L波段高空气象探测网监控系统。运行结果表明:利用L波段高空监视系统,结合探空资料质量检查,能够及时发现探空系统存在的问题;高空监视系统有助于全面掌握全国探测网系统设备的运行状况,保障高空探测网稳定运行,提高气象探空数据质量,业务效果显著。但是在探空质量评估中也发现位势高度、温度以及风向与风速变化阈值存在控制过严的现象,需要加以改进,以避免虚警次数过多。 相似文献
993.
A Simulation Study of the Mesoscale Convective Systems Associated with a Meiyu Frontal Heavy Rain Event 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this study, evolution of the mesoscale convective systems (MCSs) within a Meiyu front during a particularly heavy rainfall event on 22 June 1999 in East China was simulated by using a nonhydrostatic numerical model ARPS (Advanced Regional Prediction System). Investigations were conducted with emphasis on the impact of the interaction among multi-scale weather systems (MWSs) on the development of MCSs in the Meiyu frontal environment. For this case, the development of MCSs experienced three different stages. (1) The convections associated with MCSs were firstly triggered by the eastward-moving Southwest Vortex (SWV) from the Sichuan Basin, accompanying the intensification of the upper-level jet (ULJ) and the low-level jet (LLJ) that were approaching the Meiyu front. (2) Next, a low-level shear line (LSL) formed, which strengthened and organized the MCSs after the SWV decayed. Meanwhile, the ULJ and LLJ enhanced and produced favorable conditions for the MCSs development. (3) Finally, as the MCSs got intensified, a mesoscale convective vortex (MCV), a mesoscale LLJ and a mesoscale ULJ were established. Then a coupled-development of MWSs was achieved through the vertical frontal circulations, which further enhanced the MCV and resulted in the heavy rainfall. This is a new physical mechanism for the formation of Meiyu heavy rainfall related to the SWV during the warm season in East China. In the three stages of the heavy rainfall, the vertical frontal circulations exhibited distinguished structures and played a dynamic role, and they enhanced the interaction among the MWSs. A further examination on the formation and evolution of the MCV showed that the MCV was mainly caused by the latent heat release of the MCSs, and the positive feedback between the MCSs and MCV was a key characteristic of the scale interaction in this case. 相似文献
994.
黑河流域中西部子水系水资源分布特征研究 总被引:13,自引:3,他引:10
根据研究区的气象、水文、地质和冰川等资料,结合野外调查,研究了黑河流域中西部子水系的降水资源、冰川资源、地表水资源、地下水资源、水资源总量及其时空分布特征.山区水资源主要由祁连山南部的降水、冰雪融水等形式补给,以冰川、地表水、地下基流形式存在,冰川融水补给量为0.5532×108m3,地表水资源量为11.64×108m3,出山口基流量为5.264×108m3.河流进入山前平原后,地表水与地下水多次重复转化,南盆地地下水资源量为8.74×108m3,北盆地地下水资源量为2.06×108m3.中游耗水量的增加,加剧了中游和下游地区用水矛盾.对河流水质现状进行了分析评价,中、下游受生活污水、工业废水、农业退水的影响,河流水质较差.随着张掖市节水型社会建设和黑河流域综合治理的逐步推进,黑河流域中西部子水系的水资源问题日趋突出,研究水资源的分布特征,可为区域水资源的管理调度、可持续利用提供科学的决策依据. 相似文献
995.
松辽盆地北部深层层序地层格架建立与模式研究——以古龙-常家围子断陷沙河子组为例 总被引:3,自引:0,他引:3
松辽盆地北部徐家围子等地区深层勘探相继取得了一系列重大突破,但由于古龙—常家围子断陷深层地质认识程度较低,该区还处于深层勘探初期阶段。古龙—常家围子断陷区沙河子组充填了一套扇三角洲和湖泊沉积,是该区重要的储层和生油层。综合利用测井、钻井、地震等资料,将层序地层学原理应用于陆相断陷湖盆沉积,识别出沙河子组三级层序顶底界面,将其划分为2个三级层序,并在层序内部识别出高水位体系域、水进体系域、低水位体系域,建立了该区高精度的等时层序地层格架。根据沙河子组地质结构和地层发育的构造背景,建立了沙河子组层序地层模式:双向多断阶层序模式、双箕状不对称层序模式。 相似文献
996.
长江中下游成矿带九瑞矿集区叠合断裂系统和叠加成矿作用 总被引:30,自引:21,他引:9
通过矿坑和地表勘察并结合区域构造分析,初步阐述九瑞矿集区叠合断裂系统和叠加成矿作用及其相互匹配关系。与矿有关的断裂梳理成海西期陆缘同生断裂,印支期褶皱断裂和燕山晚期负反转断裂三个系统,并以武山铜矿的F1断层对其在三期断裂系统中的交接复合和成矿作用进行了个例描述,综合三个时期的地质勘探和野外及室内观测资料提出一个三阶段的成因模式。即:第一阶段为海西期,此时陆缘伸展、掀斜和裂陷活动引发张性同生断裂,顺层-切层(阶梯状)生长断裂发育。此阶段晚期通过与深构造位的隐伏断裂交接复合可形成海底火山和热液通道,喷流沉积形成层(块)状含铜黄铁矿。第二阶段为印支期,此阶段发育背驼式或叠瓦式构造类型,且逆掩-逆冲构造很可能将第一阶段形成的层状矿体逆向移位上推。第三阶段为燕山晚期,此时发生高角度冲断和区域应力场变更,有利于断裂由压性转为张性,形成负反转构造,断裂扩张,与燕山期岩浆热液有关的成矿溶液上升,再次叠加成矿。 相似文献
997.
E.E. Mamajek 《Astronomische Nachrichten》2010,331(7):704-708
Greaves (2006) proposed that three red, high proper motion stars within 10° of 51 Peg (NLTT 54007, 54064, and 55547) are co‐moving companions to this famous exoplanet host star. While the stars clearly have proper motions similar to 51 Peg, the inferred kinematic parallaxes for these stars produce extremely inconsistent color‐magnitude positions 2 to 4 magnitudes below the main sequence. All three stars are likely to be background stars unrelated to 51 Peg (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
998.
Roberto Furfaro Jeffrey S. Kargel Wolfgang Fink Michael P. Bishop 《Planetary and Space Science》2010,58(5):761-779
Future planetary exploration of Titan will require higher degrees of on-board automation, including autonomous determination of sites where the probability of significant scientific findings is the highest. In this paper, a novel Artificial Intelligence (AI) method for the identification and interpretation of sites that yield the highest potential of cryovolcanic activity is presented. We introduce the theory of fuzzy cognitive maps (FCM) as a tool for the analysis of remotely collected data in planetary exploration. A cognitive model embedded in a fuzzy logic framework is constructed via the synergistic interaction of planetary scientists and AI experts. As an application example, we show how FCM can be employed to solve the challenging problem of recognizing cryovolcanism from Synthetic Aperture Radar (SAR) Cassini data. The fuzzy cognitive map is constructed using what is currently known about cryovolcanism on Titan and relies on geological mapping performed by planetary scientists to interpret different locales as cryovolcanic in nature. The system is not conceived to replace the human scientific interpretation, but to enhance the scientists’ ability to deal with large amounts of data, and it is a first step in designing AI systems that will be able, in the future, to autonomously make decisions in situations where human analysis and interpretation is not readily available or could not be sufficiently timely. The proposed FCM is tested on Cassini radar data to show the effectiveness of the system in reaching conclusions put forward by human experts and published in the literature. Four tests are performed using the Ta SAR image (October 2004 fly-by). Two regions (i.e. Ganesa Macula and the lobate high backscattering region East of Ganesa) are interpreted by the designed FCM as exhibiting cryovolcanism in agreement with the initial interpretation of the regions by Stofan et al. (2006). Importantly, the proposed FCM is shown to be flexible and adaptive as new data and knowledge are acquired during the course of exploration. Subsequently, the FCM has been modified to include topographic information derived from SAR stereo data. With this additional information, the map concludes that Ganesa Macula is not a cryovolcanic region. In conclusion, the FCM methodology is shown to be a critical and powerful component of future autonomous robotic spacecraft (e.g., orbiter(s), balloon(s), surface/lake lander(s), rover(s)) that will be deployed for the exploration of Titan. 相似文献
999.
地下水地球物理勘查技术模式 总被引:2,自引:0,他引:2
通过对音频大地电磁测深法(EH-4电导率成像系统)和激发极化法的使用条件以及勘查特点的分析研究,结合在保定市顺平县的找水实例,提出了两种方法在组合形式、工作原理以及资料解释等方面勘查地下水的技术模式,并在实际工作中进行验证,取得了令人满意的效果。 相似文献
1000.