全文获取类型
收费全文 | 15609篇 |
免费 | 2182篇 |
国内免费 | 2931篇 |
专业分类
测绘学 | 3378篇 |
大气科学 | 2583篇 |
地球物理 | 2313篇 |
地质学 | 6517篇 |
海洋学 | 1827篇 |
天文学 | 413篇 |
综合类 | 1354篇 |
自然地理 | 2337篇 |
出版年
2024年 | 63篇 |
2023年 | 199篇 |
2022年 | 396篇 |
2021年 | 508篇 |
2020年 | 526篇 |
2019年 | 620篇 |
2018年 | 433篇 |
2017年 | 598篇 |
2016年 | 556篇 |
2015年 | 672篇 |
2014年 | 816篇 |
2013年 | 825篇 |
2012年 | 941篇 |
2011年 | 1052篇 |
2010年 | 853篇 |
2009年 | 899篇 |
2008年 | 922篇 |
2007年 | 1109篇 |
2006年 | 1046篇 |
2005年 | 999篇 |
2004年 | 911篇 |
2003年 | 781篇 |
2002年 | 797篇 |
2001年 | 606篇 |
2000年 | 579篇 |
1999年 | 470篇 |
1998年 | 464篇 |
1997年 | 389篇 |
1996年 | 335篇 |
1995年 | 292篇 |
1994年 | 276篇 |
1993年 | 196篇 |
1992年 | 152篇 |
1991年 | 118篇 |
1990年 | 95篇 |
1989年 | 84篇 |
1988年 | 52篇 |
1987年 | 44篇 |
1986年 | 21篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
The floating oil storage system has been proposed as a new facility for Strategic Petroleum Reserve (SPR) in China. Mooring is one of the key technologies to ensure the safety, reliability, and performance of the oil storage system. This paper describes the concept, analysis, design and reliability of the mooring system. For mooring system design of these oil vessels, analysis is essential of the behavior of the vessel in connection with mooring facilities of nonlinear resilience. A nonlinear mathematical model for analyzing a moored vessel is established and solved. Some results of numerical simulations are presented. Assessment of the safety regarding the mooring system in terms of failure probability is carried out. Another simulation model for calculating the failure probability of the mooring system is proposed. The design parameters that have an influence on the characteristics of the failure probability have been identified. The simulation results show that the mooring system has an annual reliab 相似文献
32.
INTRODUCTIONTheDenglouCape ,inthesouthwestoftheLeizhouPeninsula ,isatthenorthmarginoftropicalzone .SeveralresearchesandcartographiesoftheregionalgeomorphologyandQuater narygeology ,whichwerecarriedoutinthepast,allincludethisarea (MGL ,SCSIO ,CAS ,1 978;GPCSGRCZT… 相似文献
33.
Abstract. The synaptid holothuroid Leptosynapta inhaerens has the ability to expel unwanted particles that enter its body cavity. Intracoelomic particles ( viz. experimentally injected carmine particles) are trapped either by a coelom-produced mucoid net or by specialized organs (the vibratile urnae) that occur in bands in some interradial areas. Whatever the trapping method, particles are incorporated into dense mucoid masses that move towards the posterior part of the body cavity, in the vicinity of the rectum. These aggregates then cross the rectal wall through rectal pores, mix with the faeces, and are eventually incorporated into the wall of the synaptid burrow. Clearance of foreign particles requires 2 to 3 days. The coelom-cleaning system of synaptids appears to be the most effective within the class Holothuroidea , being well designed for endofaunal organisms whose walls are delicate and easily rupture. 相似文献
34.
基于非等间距模型的建筑物沉降预测方法研究 总被引:6,自引:0,他引:6
该文基于实测资料进行建筑物沉降预测。在灰色模型和泊松曲线模型理论的基础上,引入对非等间距数列进行变换处理的方法,从而建立了非等间距预测模型。结合建筑物沉降监测资料进行分析比较,结果表明,两种预测方法均能较好地反映建筑物的沉降趋势。 相似文献
35.
36.
37.
38.
Formation Dynamics and Quantitative Prediction of Hydrocarbons of the Superpressure System in the Dongying Sag 总被引:1,自引:0,他引:1
Based on the theory of formation dynamics of oil/gas pools, the Dongying sag can be divided into three dynamic systems regarding the accumulation of oil and gas: the superpressure closed system, the semi-closed system and the normal pressure open system. Based on the analysis of genesis of superpressure in the superpressure closed system and the rule of hydrocarbon expulsion, it is found that hydrocarbon generation is related to superpressure, which is the main driving factor of hydrocarbon migration. Micro fractures formed by superpressure are the main channels for hydrocarbon migration. There are three dynamic patterns for hydrocarbon expulsion: free water drainage, hydrocarbon accumulation and drainage through micro fissures. In the superpressure closed system, the oil-driving-water process and oil/gas accumulation were completed in lithologic traps by way of such two dynamic patterns as episodic evolution of superpressure systems and episodic pressure release of faults. The oil-bearing capacity of lithologic traps is intimately related to reservoir-forming dynamic force. Quantitative evaluation of dynamic conditions for pool formation can effectively predict the oil-bearing capability of traps. 相似文献
39.
40.
This paper describes the spatial and functional evolution of a central place system as market conditions change with population growth. Utilizing a partial equilibrium optimization model, we examine the spatial response of two economic sectors to increases in market populations resulting from natural increase and migration. Response in both sectors is conditioned by threshold demand, with factor prices also affecting one of the sectors. As the central place system evolves it exhibits spatial and functional characteristics that are initially consistent with a Löschian landscape, then a Christallerian landscape at higher populations, while at even larger populations Krugman’s landscape emerges. 相似文献