全文获取类型
收费全文 | 3304篇 |
免费 | 638篇 |
国内免费 | 960篇 |
专业分类
测绘学 | 331篇 |
大气科学 | 74篇 |
地球物理 | 323篇 |
地质学 | 2934篇 |
海洋学 | 626篇 |
天文学 | 166篇 |
综合类 | 265篇 |
自然地理 | 183篇 |
出版年
2024年 | 37篇 |
2023年 | 140篇 |
2022年 | 168篇 |
2021年 | 162篇 |
2020年 | 161篇 |
2019年 | 171篇 |
2018年 | 145篇 |
2017年 | 165篇 |
2016年 | 147篇 |
2015年 | 186篇 |
2014年 | 299篇 |
2013年 | 220篇 |
2012年 | 240篇 |
2011年 | 270篇 |
2010年 | 216篇 |
2009年 | 217篇 |
2008年 | 199篇 |
2007年 | 153篇 |
2006年 | 164篇 |
2005年 | 133篇 |
2004年 | 100篇 |
2003年 | 114篇 |
2002年 | 90篇 |
2001年 | 112篇 |
2000年 | 111篇 |
1999年 | 101篇 |
1998年 | 131篇 |
1997年 | 67篇 |
1996年 | 79篇 |
1995年 | 78篇 |
1994年 | 47篇 |
1993年 | 56篇 |
1992年 | 58篇 |
1991年 | 35篇 |
1990年 | 49篇 |
1989年 | 34篇 |
1988年 | 8篇 |
1987年 | 13篇 |
1986年 | 4篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1954年 | 1篇 |
1948年 | 1篇 |
1942年 | 1篇 |
1933年 | 2篇 |
1924年 | 1篇 |
1922年 | 2篇 |
排序方式: 共有4902条查询结果,搜索用时 15 毫秒
31.
长牡蛎四倍体诱导的研究 总被引:5,自引:0,他引:5
本文采用长牡蛎三倍体卵子与二倍体精子授精,用0.5mg/dm3CB处理受精卵抑制第一极体排放诱导出四倍体.处理组在担轮幼虫期检测染色体,4个处理组的四倍体分别为13.95%、12.19%、0%和40.00%.处理组3染色体数在24、25条.其中处理组1、3、4获得稚贝(1~3mm),存活率分别为0.49×10-5、212×10-5和23×10-5.处理组1获得稚贝108粒,处理组3获得附着稚贝7万粒,处理组4获得附着稚贝7000粒.文中还就三倍体雌贝怀卵量及四倍体诱导机制进行了讨论. 相似文献
32.
1 .Introduction Submarine pipelines are one of the safest and the least environmentally disruptive means for ma-rine gas or oil transport . With the development of exploitation of submarine oil or gas ,the safety ofsubmarine pipelines has becomethe major … 相似文献
33.
Experimental Study on Vortex-Induced Vibrations of Submarine Pipeline near Seabed Boundary in Ocean Currents 总被引:2,自引:3,他引:2
1 .IntroductionThe submarine pipeline is a commonfacility widely usedfor offshore oil and gastransport . Whena pipeline is installed on a seabed and not buried,unsupportedspans may exist insomelocations ,es-peciallyinthe uneven zones of the seabed.The spa… 相似文献
34.
基于AHP法和灰色模式识别理论的海底管道系统路由定量风险评估 总被引:3,自引:1,他引:3
根据海底管道路由潜在风险的特点及风险类型,提出了一种将层次分析法(AHP法)和灰色模式识别理论相结合的海底管道系统路由定量风险评估方法,该方法利用AHP确定风险评价指标体系,运用灰色模式识别理论,建立识别结果标准,并结合实际工程进行计算,计算结果表明该方法是可行的. 相似文献
37.
Owing to the complexity of the pipe-in-pipe (PIP) riser system in structure, load and restraint, many problems arise in the structural analysis of the system. This paper presents a new method for nonlinear static finite element stress analysis of the PIP riser system. The finite element (FE) model of the PIP riser system is built via software AutoPIPE 6.1. According to the specialties of a variety of components in the PIP riser system, different elements are used so as to model the system accurately. Allowing for the complication in modeling the effects of seabed restraint, a technique based on the bilinear spring concept is developed to calculate the soil properties. Then, based on a pipeline project, the entire procedure of stress analysis is discussed in detail, including creation of an FE model, processing of input data and analysis of results. A wide range of loading schemes is investigated to ascertain that the stresses remain within the acceptable range of the pipe material strength. Finally, the effects of the location of flanges, the thermal expansion of submarine pipelines and the seabed restraint on stress distribution in the riser and expansion loop are studied, which are valuable for pipeline designers. 相似文献
38.
LIANGDong-fang CHENGLiang KervinYEOW 《中国海洋工程》2005,19(2):269-286
A numerical model for the self-burial of a pipeline trench is developed. Morphological evolutions of a pipeline trench under steady-current or oscillatory-flow conditions are simulated with/without a pipeline inside the trench. The oscillatory flow in this study represents the action of waves. The two-dimensional Reynolds-averaged continuity and Navier-Stokes equations with the standard k-e turbulence closure, as well as the sediment transport equations, are solved with the finite difference method in a eurvilirrear coordinate system. Both bed and suspended loads of sediment transport are included in the morphological model. Because of the lack of experimental data on the backfilling of pipeline trenches, the numericalmodel is firstly verified against three closely-relevant experiments available in literature. A detailed measurement of the channel migration phenomenon under steady currents is employed for the assessment of the integral performance of themodel. The two experimental results from U-tube tests are used to validate the model‘s ability in predicting oscillatory flows. Different time-marching schemes are employed for the morphological computation under unidirectional and oscillatory conditions. It is found that vortex motions within the trench play an important role in the trench development. 相似文献
39.
40.