全文获取类型
收费全文 | 21630篇 |
免费 | 3517篇 |
国内免费 | 5604篇 |
专业分类
测绘学 | 3761篇 |
大气科学 | 3366篇 |
地球物理 | 4406篇 |
地质学 | 11123篇 |
海洋学 | 2916篇 |
天文学 | 451篇 |
综合类 | 1735篇 |
自然地理 | 2993篇 |
出版年
2024年 | 55篇 |
2023年 | 243篇 |
2022年 | 612篇 |
2021年 | 730篇 |
2020年 | 849篇 |
2019年 | 1051篇 |
2018年 | 793篇 |
2017年 | 885篇 |
2016年 | 962篇 |
2015年 | 1081篇 |
2014年 | 1339篇 |
2013年 | 1394篇 |
2012年 | 1472篇 |
2011年 | 1634篇 |
2010年 | 1283篇 |
2009年 | 1408篇 |
2008年 | 1409篇 |
2007年 | 1578篇 |
2006年 | 1556篇 |
2005年 | 1412篇 |
2004年 | 1273篇 |
2003年 | 1055篇 |
2002年 | 1009篇 |
2001年 | 824篇 |
2000年 | 766篇 |
1999年 | 654篇 |
1998年 | 614篇 |
1997年 | 534篇 |
1996年 | 456篇 |
1995年 | 399篇 |
1994年 | 370篇 |
1993年 | 271篇 |
1992年 | 213篇 |
1991年 | 144篇 |
1990年 | 116篇 |
1989年 | 103篇 |
1988年 | 64篇 |
1987年 | 46篇 |
1986年 | 30篇 |
1985年 | 19篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1972年 | 3篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
1997年夏季西北太平洋环流模拟 总被引:5,自引:1,他引:5
采用1997年7月中日副热带环流合作调查资料,即“向阳红14”号、“东方红”两调查船CTD观测资料、日本TK和IK断面资料以及GTSPP同步资料,应用开边界情形的MOM2模式计算了西北太平洋21.875°~35.125°N,120.875°~137.125°E范围的环流,主要结果如下:在此期间,(1)黑潮在台湾以东并不存在东分支流向琉球群岛以东海域;(2)东海黑潮的流量约为30×106m3/s,日本以南黑潮流量最大约为70×106m3/s;(3)在21.875°~25°N之间大约有15×106m3/s的流量向西流去.速度分布与流函数分布均表明这一支向西的海流大约在冲绳岛西南分为3支,主要分支转向东北沿冲绳岛以东海域向东北流去;(4)琉球海流主要来自上述西向海流. 相似文献
92.
宋微波 《中国海洋大学学报(自然科学版)》1991,(1)
九脊游仆虫(Euplotes novemcarinata Wang、1930)是土壤及淡水中生活的原生动物。本文对其重要的分类特征诸如银线系及纤毛下器做了形态学研究,确认了其分类地位,并比较了国外迄今的研究工作,在此基础上,将同物异名苔藓游仆虫(E.muscicolaKahl、1932)作了归并。 相似文献
93.
This study is devoted to oceanographic features of the semi-enclosed Gulf of Aqaba, Red Sea. The data were recorded in winter—spring
1999 on the R/V Meteor cruise leg 44/2. Temperature and salinity profiles were measured at six positions (I—VI). The shipboard
NarrowBand Acoustic Doppler Current Profiler (NB ADCP) 150 kHz continuously recorded current profiles down to 350 m en route.
The research revealed that the current near the Strait of Tiran front (position VI) represents a semidiurnal signal of an
internal tide wave (∼12 h period; 0.2 ms−1 amplitude) that might be generated by the barotropic tide at the sill of the Strait. A sequence of cyclonic and anticyclonic
eddy pairs is found along the axis of the Gulf of Aqaba during winter-spring seasons. These sub-mesoscale signals are dominant
above the main thermocline and might be caused by wind forcing and the narrowness of the Gulf; it might remain in other seasons
with different dimensions in relation to the depth of thermocline. The total diameter of each pair was twice the baroclinic
Rossby radius (R ≈ 10 km). A single anti-cyclonic eddy was observed in the upper 300 m in the northern tip of the Gulf with a diameter of
about 5–8 km. 相似文献
94.
Toru?Iwata Keiko?Yoshikawa Katsutoshi?Nishimura Yoshihisa?Higuchi Takao?Yamashita Shigeru?Kato Eiji?OhtakiEmail author 《Journal of Oceanography》2004,60(6):995-1000
The measurements of the vertical transport of CO2 were carried out over the Sea of Japan using the specially designed pier of Kyoto University on September 20 to 22, 2000. CO2 fluxes were measured by the eddy correlation and aerodynamic techniques. Both techniques showed comparable CO2 fluxes during sea breeze conditions: −0.001 to −0.08 mg m−2s−1 with the mean of −0.05 mg m−2s−1. This means that the measuring site satisfies the fetch requirement for meteorological observations under sea breeze conditions. Moreover, the eddy diffusivity coefficient used in the aerodynamic technique is found to be consistent with the coefficient used in the eddy correlation technique. The present result leads us to conclude that the aerodynamic technique may be applicable to underway CO2 flux measurements over the ocean and may be used in place of the bulk technique. The important point is the need to maintain a measuring accuracy of CO2 concentration difference of the order of 0.1 ppmv on the research vessels or the buoys. 相似文献
95.
96.
97.
An offshore vessel with a dynamic positioning system (DP system) needs fast response to produce thrust to counteract the environmental forces acting on it for the purpose of maintaining its position and heading as close as possible to the working position. Therefore, quick and effective modulation of the thrust is the problem to determine the thrust and the rotation angle of the thruster devices of the ship. This paper presents an effective optimum control for a thruster system, using the sequential quadratic method to achieve economical and effective modulation of the thrust and the direction of the thruster. An optimum control study of a 2280 tons DP coring vessel with five rotary azimuth thruster marine positioning is studied in detail, which can quickly and exactly estimate the thrusts and angles of direction of all the thrusters. The results can provide a valuable thruster system for a dynamically positioned vessel. 相似文献
98.
根据冲量相似的要求进行船舶在冲击作用下的模型试验,并将模型试验结果与理论计算及实际试验进行了对比和分析。 相似文献
99.
1 .IntroductionAshiptravelingatseaundergoesundesirablewave inducedmotions ,namely ,surge ,sway ,heav ing ,rolling ,pitchingandyaw .Thesemotionsoftencauseproblemstothecrew ,theonboardequip mentand ,intheworstcase ,thesafetyofthevessel.Tominimizethewave inducedshipmotions ,controlsystemsmaybeapplied .Theaccuratemodelingofshipmotionsisthereforeveryimportantforshipdesignanddesignofmotioncontrolsystems .Manyresearchershavedevelopedshipmotionpredictionmethodsbasedonthepotentialflowtheo ries (Dong ,… 相似文献
100.