全文获取类型
收费全文 | 3680篇 |
免费 | 723篇 |
国内免费 | 345篇 |
专业分类
测绘学 | 877篇 |
大气科学 | 197篇 |
地球物理 | 1373篇 |
地质学 | 1363篇 |
海洋学 | 473篇 |
天文学 | 32篇 |
综合类 | 206篇 |
自然地理 | 227篇 |
出版年
2025年 | 2篇 |
2024年 | 46篇 |
2023年 | 44篇 |
2022年 | 86篇 |
2021年 | 106篇 |
2020年 | 129篇 |
2019年 | 160篇 |
2018年 | 120篇 |
2017年 | 183篇 |
2016年 | 156篇 |
2015年 | 145篇 |
2014年 | 191篇 |
2013年 | 272篇 |
2012年 | 238篇 |
2011年 | 258篇 |
2010年 | 182篇 |
2009年 | 237篇 |
2008年 | 257篇 |
2007年 | 257篇 |
2006年 | 249篇 |
2005年 | 197篇 |
2004年 | 182篇 |
2003年 | 165篇 |
2002年 | 117篇 |
2001年 | 109篇 |
2000年 | 109篇 |
1999年 | 93篇 |
1998年 | 65篇 |
1997年 | 77篇 |
1996年 | 66篇 |
1995年 | 47篇 |
1994年 | 47篇 |
1993年 | 31篇 |
1992年 | 24篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有4748条查询结果,搜索用时 15 毫秒
951.
952.
An Erratum has been published for this article in Earthquake Engineering and Structural Dynamics 2000; 29(7):1076. Two interrelated issues related to the design of non-linear viscous dampers are considered in this paper: structural velocities and equivalent viscous damping. As the effectiveness of non-linear viscous dampers is highly dependent on operating velocities, it is important to have reliable estimates of the true velocity in the device. This should be based on the actual relative structural velocity and not the commonly misused spectral pseudo-velocity. This is because if spectral pseudo-velocities (PSV) are used, they are based on design displacements (Sv=ω0Sd) and are thus fundamentally different from the actual relative structural velocity. This paper examines the difference between these two velocities, and based on an extensive study of historical earthquake motions proposes empirical relations that permit the designer to transform the well-known spectral pseudo-velocity to an actual relative structural velocity for use in design. Non-linear static analysis procedures recommended in current guidelines for the design of structural systems with supplement damping devices are based on converting rate-dependent device properties into equivalent viscous damping properties based on an equivalent energy consumption approach. Owing to the non-linear velocity dependence of supplemental devices, an alternative approach for converting energy dissipation into equivalent viscous damping is advanced in this paper that is based upon power consumption considerations. The concept of a normalized damper capacity (ϵ) is then introduced and a simple design procedure which incorporates power equivalent linear damping based on actual structural velocities is presented. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
953.
954.
JD Klein AE Bester-van der Merwe ML Dicken A Emami-Khoyi KL Mmonwa 《African Journal of Marine Science》2019,41(1):115-118
Genomic data can be a useful tool in the management and conservation of biodiversity. Here, we report the development of genomic resources for the spotted ragged-tooth shark Carcharias taurus using genome-wide DNA data from Illumina next-generation sequencing. We explored two commonly used genetic marker types: microsatellites and mitochondrial DNA. A total of 4 394 putative microsatellites were identified, of which 10 were tested on 24 individuals and found to have ideal properties for population genetic analyses. Additionally, we reconstructed the first complete mitochondrial genome of a South African spotted ragged-tooth shark, and highlight the most informative gene regions to facilitate future primer design. The data reported here may serve as a resource for future studies and can ultimately be applied in the sustainable conservation and fisheries management of this apex predator. 相似文献
955.
In recent years, offshore reservoirs have been developed in deeper and deeper water environments. Steel catenary risers (SCRs) are being considered in deepwater development such as Northern North Sea. SCRs used in conjunction with a semi-submersible or floating production, storage and offloading (FPSO) in deepwater harsh environments present significant design challenges. The large vertical motions at the semi or FPSO induce severe riser response, which results in difficulty meeting strength and fatigue criteria at the hang off and touch down point locations. To improve the understanding of SCR behaviour and increase the confidence in the design of such systems in deepwater harsh environments, a parametric study on a SCR connected to a semi-submersible was carried out in this paper to deal with the factors that mainly influence the loading condition and fatigue life of the riser. Weight-optimized configurations were applied during the course of riser design. Riflex combined with DeepC was the primary analysis tool used for the long-term response of the nonlinear SCR structure simulations, which requires a large amount of computer time. Hence, the parameters affecting the efficiency and accuracy of the simulations have also been studied during the analysis process. 相似文献
956.
光照、温度和营养盐对三株盐生杜氏藻生长和色素积累的影响 总被引:5,自引:0,他引:5
通过正交试验研究了光照、温度和营养盐对3株盐生杜氏藻株系(BJ,OUC38和OUC8)生长和色素积累的影响,旨在探明适于盐生杜氏藻生长和β-胡萝卜素积累的光照、温度和营养盐条件,并对实验中3株株系生长和β-胡萝卜素积累速率进行了初步的比较。结果表明,盐生杜氏藻生长的最适光照和温度分别是145.3μmol.m-2.s-1和23℃;适于β-胡萝卜素积累的光照和温度分别是218.2μmol.m-2.s-1和23℃;适于生长的营养盐条件是NaNO30.4 mmo/L、尿素0.6 mmol/L和NaHCO318 mmol/L,而当NaNO3、尿素和NaHCO3浓度分别为0,0.2和18 mmol/L时有利于β-胡萝卜素的积累。高光照、低温有利于杜氏藻细胞β-胡萝卜素的积累,在218.2μmol.m-2.s-1光强和15℃条件下藻细胞β-胡萝卜素积累平均值可分别达10.39和12.46 pg/cell。3个株系中OUC38积累β-胡萝卜素的能力高于另外2株,但差异不显著。 相似文献
957.
房产面积的测算,在很多情况下采用设计图纸上的尺寸进行相应的计算。但由于施工控制网误差、放样误差、施工误差等的综合影响,导致了实际房子的尺寸与设计的理论数据有差异,从而使得算得的房产面积与实际的不符。这种差异或者说误差能达到什么样的数量级?对面积计算的影响有多大?本文分析了这些差异即误差的一般规律,对依据设计数据所计算的房产面积精度进行了探讨。 相似文献
958.
GPS技术在柴阿润水电站工程中的应用 总被引:1,自引:0,他引:1
介绍了GPS技术在柬埔寨王国柴阿润水电站工程中的应用,设计了首级GPS D级控制网,实现了GPS技术在国外水电工程中的高效运用,解决了柬方的工程实践问题. 相似文献
959.
文章通过介绍美国应急系统("911"系统)、城市服务系统("311"系统)和电子政务建设与使用情况,提出推进我国公共管理现代化和电子政务建设的建议与措施,特别提出电子政务的规划与建设应"以人为本,服务于民"。 相似文献
960.
在海南省农村土地确权登记发证工作技术细则的基础上,对海口市农村土地地籍测量项目进行了详细的技术设计,可用于指导和规范项目的实际工作。 相似文献