全文获取类型
收费全文 | 6610篇 |
免费 | 1378篇 |
国内免费 | 1967篇 |
专业分类
测绘学 | 589篇 |
大气科学 | 1470篇 |
地球物理 | 1574篇 |
地质学 | 3738篇 |
海洋学 | 728篇 |
天文学 | 300篇 |
综合类 | 779篇 |
自然地理 | 777篇 |
出版年
2024年 | 32篇 |
2023年 | 133篇 |
2022年 | 330篇 |
2021年 | 384篇 |
2020年 | 305篇 |
2019年 | 325篇 |
2018年 | 420篇 |
2017年 | 359篇 |
2016年 | 403篇 |
2015年 | 380篇 |
2014年 | 385篇 |
2013年 | 428篇 |
2012年 | 373篇 |
2011年 | 393篇 |
2010年 | 459篇 |
2009年 | 416篇 |
2008年 | 380篇 |
2007年 | 411篇 |
2006年 | 313篇 |
2005年 | 294篇 |
2004年 | 235篇 |
2003年 | 208篇 |
2002年 | 186篇 |
2001年 | 216篇 |
2000年 | 205篇 |
1999年 | 262篇 |
1998年 | 250篇 |
1997年 | 241篇 |
1996年 | 212篇 |
1995年 | 159篇 |
1994年 | 152篇 |
1993年 | 144篇 |
1992年 | 116篇 |
1991年 | 86篇 |
1990年 | 62篇 |
1989年 | 65篇 |
1988年 | 59篇 |
1987年 | 31篇 |
1986年 | 36篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 16篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1975年 | 5篇 |
1965年 | 2篇 |
1960年 | 2篇 |
1958年 | 8篇 |
排序方式: 共有9955条查询结果,搜索用时 15 毫秒
991.
992.
A Study on the Meat and Bone Meal or Poultry By-product Meal as Protein Substitutes of Fishmeal in Concentrated Diets for Paralichthys olivaceus 总被引:2,自引:0,他引:2
A study was conducted to evaluate the effects of meat and bone meal (MBM) and poultry by-product meal (PBM) as the replacement of fishmeal in the diets on the growth performance, survival and apparent digestibility coefficient (ADC) of Japanese flounder (Paralichthys olivaceus). The experimental diets included 0%, 20%, 40%, 60% and 80% MBM or PBM replacement of total fishmeal respectively. All diets were iso-nitrogenous and isocaloric. The results showed that there are no significant differences (P 〉0.05) in growth performance among the treatments fed with 0% -60% MBM replacement of fishmeal, while the percent weight gain (WG, % ), body length gain (BLG, % ) and ADC significantly decrease when fishmeal is replaced by 80% MBM. The result showed also that there are no significant differences (P 〉0.05) in growth performance and ADC among all treatments fed with the diets with 0% -80% replacements of fishmeal with PBM. 相似文献
993.
国土资源部门作为政府职能部门,担负着管理辖区土地资源、矿产资源的调查、规划、管理、保护和合理利用的工作,因此,利用信息化手段提升国土资源的管理水平,已经成为加强国土资源管理的迫切需要。淄川区国土资源局充分利用国土资源部实施“金土工程”的契机,将信息化建设作为实 相似文献
994.
CVN硬盘系统和软件相关处理在e-VLBI试验中的应用 总被引:1,自引:0,他引:1
介绍了中国VLBI网(CVN)的e-VLBI技术研究进展.CVN包括上海佘山、乌鲁木齐南山2个固定观测站和云南昆明的流动站,以及上海天文台的2台站硬件相关处理机。2003年上海天文台自行研制了基于PC技术的VLBI数据记录、回放系统,命名为CVN硬盘系统,并成功将其安置于CVN观测站和处理机系统。硬件处理机经过改造后,已能处理来自硬盘和原有磁带系统的数据.从2003年至今,中国VLBI网采用该硬盘系统进行了多次VLBI观测和e-VLBI试验。在CVN硬盘系统基础上,软件相关处理技术的研究也得以开展。软件相关处理原型程序已经被用于台站条纹检测、卫星条纹搜索和数据处理中。该软件获得的计算结果被成功用于国内第一个3台站卫星VLBI的延迟和延迟率闭合试验,以及国内首次利用VLBI数据进行的卫星定轨试验。除此之外,该软件还用作硬件处理机的条纹引导器。为适应未来“嫦娥”月球探测工程,CVN将扩展成含有4个观测站和2个相关处理机(硬件、软件)的实时VLBI网。今后,e-VLBI将被应用于月球卫星导航以及测地和天体物理的VLBI观测。 相似文献
995.
996.
997.
Initial results of centralized autonomous orbit determination of the new-generation BDS satellites with inter-satellite link measurements 总被引:3,自引:0,他引:3
Chengpan Tang Xiaogong Hu Shanshi Zhou Li Liu Junyang Pan Liucheng Chen Rui Guo Lingfeng Zhu Guangming Hu Xiaojie Li Feng He Zhiqiao Chang 《Journal of Geodesy》2018,92(10):1155-1169
Autonomous orbit determination is the ability of navigation satellites to estimate the orbit parameters on-board using inter-satellite link (ISL) measurements. This study mainly focuses on data processing of the ISL measurements as a new measurement type and its application on the centralized autonomous orbit determination of the new-generation Beidou navigation satellite system satellites for the first time. The ISL measurements are dual one-way measurements that follow a time division multiple access (TDMA) structure. The ranging error of the ISL measurements is less than 0.25 ns. This paper proposes a derivation approach to the satellite clock offsets and the geometric distances from TDMA dual one-way measurements without a loss of accuracy. The derived clock offsets are used for time synchronization, and the derived geometry distances are used for autonomous orbit determination. The clock offsets from the ISL measurements are consistent with the L-band two-way satellite, and time–frequency transfer clock measurements and the detrended residuals vary within 0.5 ns. The centralized autonomous orbit determination is conducted in a batch mode on a ground-capable server for the feasibility study. Constant hardware delays are present in the geometric distances and become the largest source of error in the autonomous orbit determination. Therefore, the hardware delays are estimated simultaneously with the satellite orbits. To avoid uncertainties in the constellation orientation, a ground anchor station that “observes” the satellites with on-board ISL payloads is introduced into the orbit determination. The root-mean-square values of orbit determination residuals are within 10.0 cm, and the standard deviation of the estimated ISL hardware delays is within 0.2 ns. The accuracy of the autonomous orbits is evaluated by analysis of overlap comparison and the satellite laser ranging (SLR) residuals and is compared with the accuracy of the L-band orbits. The results indicate that the radial overlap differences between the autonomous orbits are less than 15.0 cm for the inclined geosynchronous orbit (IGSO) satellites and less than 10.0 cm for the MEO satellites. The SLR residuals are approximately 15.0 cm for the IGSO satellites and approximately 10.0 cm for the MEO satellites, representing an improvement over the L-band orbits. 相似文献
998.
Acta Geotechnica - Given copper and lead mine enrichment and the high yield of North-Western China, the metallurgical industry attains prosperity. Metallurgical industrial waste which contains... 相似文献
999.
Acta Geotechnica - Interlocking refers to a kind of resistance caused by the staggered arrangement of granular materials. In geotechnical engineering, it is considered as one of the important... 相似文献
1000.
采用岩石薄片鉴定、X射线衍射分析、扫描电镜以及元素地球化学等分析测试手段,对罗布泊盐湖罗北凹地杂卤石的沉积和分布特征进行了研究。结果显示,罗北凹地杂卤石主要发育于含盐系中上部,或以质地较纯的层状杂卤石岩产出,或与钙芒硝/石盐/白钠镁矾共同产出。杂卤石有交代和原生两种成因类型:前者是罗北凹地杂卤石产出的主要类型,是罗布泊硫酸盐型盐湖自身蒸发析出产物,在盐湖演化中后期交代钙芒硝或者石膏形成;后者可能为富钙卤水补给富钾镁盐湖形成。罗北凹地杂卤石的分布具有在南北方向上南厚北薄、在东西方向上中间厚两侧薄的特点,对应的KCl含量也同样具有南高北低、中间高两侧低的特点,它们的分布特征明显受控于区域构造活动,构造导致的沉降区有利于杂卤石聚集成矿。本区杂卤石矿埋藏浅、规模较大,可作为后备钾盐资源。 相似文献