全文获取类型
收费全文 | 2549篇 |
免费 | 330篇 |
国内免费 | 446篇 |
专业分类
测绘学 | 801篇 |
大气科学 | 250篇 |
地球物理 | 572篇 |
地质学 | 897篇 |
海洋学 | 347篇 |
天文学 | 66篇 |
综合类 | 204篇 |
自然地理 | 188篇 |
出版年
2024年 | 11篇 |
2023年 | 38篇 |
2022年 | 69篇 |
2021年 | 87篇 |
2020年 | 108篇 |
2019年 | 123篇 |
2018年 | 66篇 |
2017年 | 123篇 |
2016年 | 119篇 |
2015年 | 134篇 |
2014年 | 186篇 |
2013年 | 175篇 |
2012年 | 203篇 |
2011年 | 183篇 |
2010年 | 127篇 |
2009年 | 124篇 |
2008年 | 120篇 |
2007年 | 160篇 |
2006年 | 136篇 |
2005年 | 141篇 |
2004年 | 107篇 |
2003年 | 102篇 |
2002年 | 83篇 |
2001年 | 82篇 |
2000年 | 68篇 |
1999年 | 59篇 |
1998年 | 52篇 |
1997年 | 58篇 |
1996年 | 50篇 |
1995年 | 44篇 |
1994年 | 47篇 |
1993年 | 32篇 |
1992年 | 25篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1979年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有3325条查询结果,搜索用时 15 毫秒
51.
青藏公路路基变形分析 总被引:29,自引:8,他引:29
为研究青藏公路多年冻土人为上限在退化过程中对路基变形产生的影响过程和程度, 在唐古拉山以南选择了3处具有代表性的路面进行了为期2 a的路面变形观测. 资料表明, 在多年冻土人为上限退化过程中随着公路路基结构、冻土类型的不同, 路基变形从冻胀和融沉过程、冻胀量和融沉量、发生的时间都有很大的不同. 在高含冰量多年冻土区采用半挖半填结构产生的路基变形最为剧烈, 在含冰量相对少且采用较高路堤结构的地段路基变形过程相对平缓. 同时结合探地雷达的勘察结果对路基下的融化区、多年冻土区的内部结构进行了分析. 结果显示,多年冻土人为上限的下移、地下冰的融化会在多年冻土人为上限以上的地质体中导致较强烈的层间错动和扰动. 相似文献
52.
53.
在中国区域定位系统(Chinese Area Positioning System,CAPS)中,带通滤波器是用户接收机的重要组成部分,对于宽频测距码来说,其群时延特性是测距的重要误差来源之一.分析了接收机码跟踪环路,给出相关函数估算测距偏差,对带通滤波器群时延开展仿真分析,并研究了改进接收机设计以优化群时延特性的方法.研究对GNSS接收机的射频和环路设计有一定借鉴意义. 相似文献
54.
55.
56.
利用直接电位法,采用标准加入的方式测定了不同浓度和温度条件下,LiPF6水溶液中的F-浓度,同时考察了碱处理对LiPF6水解的影响,并采用电导率测定结果进行了验证.实验表明,LiPF6能够在水中稳定存在,且几乎不受碱度和温度的影响. 相似文献
57.
The accuracy of temperature measurement by the expendable bathythermograph (XBT) is examined for five types of recorders by
comparison with co-located CTD measurements and statistical analysis of temperature profiles including an isothermal layer.
A positive temperature error increasing downward is occasionally detected for two types of Japanese recorder which have been
commonly used among Japanese oceanographic institutions and marine observatories. This error resembles to that reported by
Bailey et al. (1989) and Wright (1991) for a different type of recorders, although its cause is not clearly understood. The irregular
occurrence of the error suggests that the problem is not solely due to the recorders but rather by some inconsistency of the
whole measuring system including them, an XBT probe and sea water. The error is estimated to increase at a rate of O (0.1°C/100 m), and it could be close to 1°C at the deepest part of the profiles (760 m for Tsurumi T-7).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
58.
Kyung-Il Chang Nelson G. Hogg Moon-Sik Suk Sang-Kyung Byun Young-Gyu Kim Kuh Kim 《Deep Sea Research Part I: Oceanographic Research Papers》2002,49(12)
The Ulleung Basin is one of three deep basins that are contained within the East/Japan Sea. Current meter moorings have been maintained in this basin beginning in 1996. The data from these moorings are used to investigate the mean circulation pattern, variability of deep flows, and volume transports of major water masses in the Ulleung Basin with supporting hydrographic data and help from a high-resolution numerical model. The bottom water within the Ulleung Basin, which must enter through a constricted passage from the north, is found to circulate cyclonically—a pattern that seems prevalent throughout the East Sea. A strong current of about 6 cms−1 on average flows southward over the continental slope off the Korean coast underlying the northward East Korean Warm Current as part of the mean abyssal cyclonic circulation. Volume transports of the northward East Korean Warm Current, and southward flowing East Sea Intermediate Water and East Sea Proper Water are estimated to be 1.4 Sv (1 Sv=10−6 m3 s−1), 0.8 Sv, and 3.0–4.0 Sv, respectively. Deep flow variability involves a wide range of time scales with no apparent seasonal variations, whereas the deep currents in the northern East Sea are known to be strongly seasonal. 相似文献
59.
60.
There is a need to obtain the hydrologic data including ocean current,wave,temperature and so on in the South China Sea.A new profiling instrument which does not suffer from the damage due to nature forces or incidents caused by passing ships,is under development to acquire data from this area.This device is based on a taut single point mid-water mooring system.It incorporates a small,instrumented vertically profiling float attached via an electromechanical cable to a winch integral with the main subsurface flotation.On a pre-set schedule,the instrument float with sensors is winched up to the surface if there is no ship passing by,which is defined by an on-board miniature sonar.And it can be immediately winched down to a certain depth if the sonar sensor finds something is coming.Since,because of logistics,the area can only be visited once for a long time and a minimum of 10 times per day profiles are desired,energy demands are severe.To respond to these concerns,the system has been designed to conserve a substantial portion of the potential energy lost during the ascent phase of each profile and subsequently use this energy to pull the instrument down.Compared with the previous single-point layered measuring mode,it is advanced and economica1.At last the paper introduces the test in the South China Sea. 相似文献