全文获取类型
收费全文 | 32559篇 |
免费 | 6524篇 |
国内免费 | 9408篇 |
专业分类
测绘学 | 3684篇 |
大气科学 | 4834篇 |
地球物理 | 8769篇 |
地质学 | 17600篇 |
海洋学 | 5288篇 |
天文学 | 1671篇 |
综合类 | 2656篇 |
自然地理 | 3989篇 |
出版年
2024年 | 96篇 |
2023年 | 448篇 |
2022年 | 1126篇 |
2021年 | 1328篇 |
2020年 | 1477篇 |
2019年 | 1645篇 |
2018年 | 1444篇 |
2017年 | 1586篇 |
2016年 | 1632篇 |
2015年 | 1928篇 |
2014年 | 2104篇 |
2013年 | 2162篇 |
2012年 | 2231篇 |
2011年 | 2282篇 |
2010年 | 2002篇 |
2009年 | 2169篇 |
2008年 | 2206篇 |
2007年 | 2499篇 |
2006年 | 2454篇 |
2005年 | 2122篇 |
2004年 | 1893篇 |
2003年 | 1577篇 |
2002年 | 1381篇 |
2001年 | 1114篇 |
2000年 | 1232篇 |
1999年 | 1180篇 |
1998年 | 971篇 |
1997年 | 788篇 |
1996年 | 627篇 |
1995年 | 523篇 |
1994年 | 494篇 |
1993年 | 417篇 |
1992年 | 376篇 |
1991年 | 221篇 |
1990年 | 161篇 |
1989年 | 208篇 |
1988年 | 113篇 |
1987年 | 82篇 |
1986年 | 62篇 |
1985年 | 39篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1954年 | 19篇 |
1877年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
新型城镇化是中国经济社会健康、稳定、可持续发展的根本途径,也是消除中国城乡社会经 济“二元结构”的根本出路。根据新型城镇化的内涵,从人口、经济发展、生活质量、基础设施、资源 环境、城乡统筹 6 个方面,构建了包含 24 项指标的新型城镇化水平综合测度指标体系,运用熵值
法,对西部 11 个省会城市 2005—2015 年的城镇化发展水平进行综合测度。研究表明:西部省会城
市的新型城镇化发展水平存在显著差异,总体上可分为“高等水平”、“中等水平”、“低等水平”3 个 级别,基础设施建设是造成差异的主要驱动力。各城市不同年间的城镇化单项水平影响因素呈现 多元化,在今后的发展中应有所侧重,同时兼顾城镇化质量,推动城乡协调发展。 相似文献
22.
An increasing number of experiments are being conducted to study the design and performance of wave energy converters. Often in these tests, a real-time realization of prospective control algorithms is applied in order to assess and optimize energy absorption as well as other factors. This paper details the design and execution of an experiment for evaluating the capability of a model-scale WEC to execute basic control algorithms. Model-scale hardware, system, and experimental design are considered, with a focus on providing an experimental setup capable of meeting the dynamic requirements of a control system. To more efficiently execute such tests, a dry bench testing method is proposed and utilized to allow for controller tuning and to give an initial assessment of controller performance; this is followed by wave tank testing. The trends from the dry bench test and wave tank test results show good agreement with theory and confirm the ability of a relatively simple feedback controller to substantially improve energy absorption. Additionally, the dry bench testing approach is shown to be an effective and efficient means of designing and testing both controllers and actuator systems for wave energy converters. 相似文献
23.
利用内蒙古西部12个台站的地脉动噪声数据,采用噪声谱比法研究台站的场地响应情况。分析表明,台站场地响应按曲线形态可分为3类,且可能受地形地貌、局部构造和台基状况等条件影响。对比分析噪声谱比法与Moya方法的场地响应结果发现,场地响应曲线形态基本一致,只有极少数台站存在明显差异。结果表明,内蒙古西部区域大部分台站的台基状况总体较好,场地响应曲线较为平坦,无明显频率放大点。 相似文献
24.
Microbial degradation technologies have been developed to restore ground water quality in aquifers polluted by organic contaminants effectively in recent years. However, in course of the degradation, the formation of biofilms in ground water remediation technology can be detrimental to the effectiveness of a ground water remediation project. Several alternatives are available to a remedial design engineer, such as Permeable Reactive Barriers (PRBs) and in -situ bioremediation, Hydrogen Releasing Compounds (HRCs) barrier, Oxygen Releasing Compounds (ORCs) barrier etc. which are efficient and cost- effective technologies. Excessive biomass formation renders a barrier ineffective in degrading the contaminants, Efforts are made to develop kinetics models which accurately determine bio - fouling and bio - filn formation and to control excessive biomass formation. 相似文献
25.
孙艳玲 《成都信息工程学院学报》2003,18(4):433-440
利用用友软件对如何合并会计报表进行了初步研究,并以案例的形式阐明了采用用友软件实现合并会计报表的步骤,提出了合并会计报表的编制方法。 相似文献
26.
A CASE STUDY ON CONCENTRATION AND DECENTRALIZATION:BEHAVIOR AND DYNAMIC MECHANISM OF SPATIAL EVOLUTION IN METROPOLITAN AREA,NANJING,CHINA 总被引:1,自引:1,他引:0
In rapid socio-economic development,the process of concentration and dispersal of various elements tends to be more dramatic,tremendously influencing the shaping and transformation of the space in metropolitan area.Survey of spatial concentration and decentralization has thus become a basic method in examining metropolitan spatial evolution.In this research,three elements were selected as the essential indicators of the process:demographic density distribu-tion,employment density distribution and business office location.Performance of these elements in Nanjing City was exam-ined historically.As Nanjing City could be regarded as a representative of metropolitan areas in China,its situation large-ly suggestes the general characteristics in similar areas of China.Hence based on the investigation of Nanjing City,four general implications were highlighted.First ,metropolitan areas in China are in a violent process and shift of spatial concentra-tion and decentralization.Second,from now to at least the near future,concentration will continue to be the central fea-ture.Third,the landscape of metropolitan areas basically exhibits a dual structure character.The gap in environmental and ecological qualities among different districts will continue for a long time.Fourth,Central Business District (CBD) is playing an important role in helping to convert the traditionally single-centered city structure into a polycentric one. 相似文献
27.
唐森铭 《中国海洋湖沼学报》2002,(1)
INTRODUCTIONThemainpurposeofthisstudywastodeterminethemagnitudeandfrequencyofharmfuldiatomanddinoflagellateoutbreaksinHongKong’swesternandeasternwaters (e .g.LammaStraitsandPortShelterrespectively)fortheperiodJanuary 1 997toDecember1 999.Thiswasdoneinordertod… 相似文献
28.
本文依据稳恒磁场中的高斯定理和安培环路定理,用迭代法推导出对称轴上的磁感应强度与空间任意一点磁感应强度的关系式,从而可得出轴对称稳恒磁场的无电流分布空间的解式。 相似文献
29.
A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems, one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of δScuti stars. 相似文献
30.