全文获取类型
收费全文 | 10935篇 |
免费 | 2235篇 |
国内免费 | 3987篇 |
专业分类
测绘学 | 638篇 |
大气科学 | 1916篇 |
地球物理 | 2872篇 |
地质学 | 7603篇 |
海洋学 | 1366篇 |
天文学 | 504篇 |
综合类 | 1295篇 |
自然地理 | 963篇 |
出版年
2024年 | 28篇 |
2023年 | 109篇 |
2022年 | 292篇 |
2021年 | 344篇 |
2020年 | 271篇 |
2019年 | 287篇 |
2018年 | 369篇 |
2017年 | 308篇 |
2016年 | 370篇 |
2015年 | 356篇 |
2014年 | 385篇 |
2013年 | 405篇 |
2012年 | 360篇 |
2011年 | 830篇 |
2010年 | 656篇 |
2009年 | 788篇 |
2008年 | 475篇 |
2007年 | 597篇 |
2006年 | 742篇 |
2005年 | 749篇 |
2004年 | 1334篇 |
2003年 | 873篇 |
2002年 | 677篇 |
2001年 | 546篇 |
2000年 | 424篇 |
1999年 | 523篇 |
1998年 | 587篇 |
1997年 | 527篇 |
1996年 | 435篇 |
1995年 | 339篇 |
1994年 | 300篇 |
1993年 | 451篇 |
1992年 | 399篇 |
1991年 | 229篇 |
1990年 | 134篇 |
1989年 | 135篇 |
1988年 | 79篇 |
1987年 | 109篇 |
1986年 | 72篇 |
1985年 | 27篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1978年 | 10篇 |
1977年 | 16篇 |
1976年 | 13篇 |
1937年 | 16篇 |
1933年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
141.
Following Bagnold's approach, a relationship between sediment transport and energy dissipation is developed. The major assumption made in the study is that the near bed velocity plays a dominant role in the process of sediment transport. A general relationship between energy dissipation and sediment transport is first proposed. Then the equations for total sediment transport are derived by introducing the appropriate expression of energy dissipation rate under different conditions, such as open channel flows, combination of wave and current, as well as longshore sediment transport. Within the flows investigated, the derived relationships are fairly consistent with the available data over a wide range of conditions. 相似文献
142.
143.
1 .IntroductionRecentlygreatinteresthasbeenshowninthedevelopmentofverylargefloatingstructuressuchasMegaFloatofJapan (Isobe ,1 999)andMOBofUSA (Remmers ,1 999) .Owingtotheirextremelargesizeandgreatflexibility ,thecouplingbetweenthestructuraldeformationandfluidmotionissignifi cant.Thisisatypicalproblemofhydroelasticity .Efficientandaccurateestimationofthehydroelasticresponseofverylargefloatingstructuresinwavesisveryimportantfordesign .Manymethodshavebeenproposedinliteratureforthepredictiono… 相似文献
144.
黄河口及渤海中南部沉积物工程特性及其机理 总被引:3,自引:0,他引:3
采用Kasten取样器从黄河口及渤海湾中南部海底沉积物中取样,对样品通过土工性质、微结构研究以及粘土矿物分析,阐明本研究区三维空间展布的海底沉积物形成机理及其工程地质规律,论证水动力作用和斜坡不稳定性对工程特性和微结构的重要影响. 相似文献
145.
146.
本文介绍了国家标准《潜水员水下用电安全技术规范》的研究、编制过程,以及编者对该标准性质、适用范围、总体结构、电气安全数值取舍等的基本认识,并就该标准制定实施后的经济、社会效益进行了初步预测。 相似文献
147.
南极布兰斯菲尔德海峡表层沉积物的酸解烃 总被引:1,自引:0,他引:1
本文研究了南极布兰斯菲尔德海峡表层沉积物的酸解烃分布特征,并佐以热释汞和蚀变碳酸盐的分析。从酸解烃中甲烷含量的低值和C1/(C2+C3)比值,以及乙烯的存在等判断,布兰斯菲尔德海峡沉积物的烃类气体来自于生物成因。 相似文献
148.
The large cylinder is a new-type structure that has been applied to harbor and offshore engineering. An analytic method of the relationship between loads and the structure displacement is developed based on the failure mode of deep embedded large cylinder structures. It can be used to calculate directly the soil resistance and the ultirnate bearing capacity of the structure under usage. A new criterion of the large cylinder structure, which discriminates the deep embedded cylinder from the shallow embedded cylinder, is defined. Model tests prove that the proposed method is feasible for the analysis of deep embedded large cylinder structures. 相似文献
149.
Shipborne GPS attitude determination during MMST-93 总被引:1,自引:0,他引:1
Lachapelle G. Cannon M.E. Lu G. Loncarevic B. 《Oceanic Engineering, IEEE Journal of》1996,21(1):100-104
The attitude parameters of a ship underway were measured using a configuration of four 10-channel NovAtel Model 951 narrow-correlator-spacing receivers. These C/A code receivers have output rates of up to 10 Hz and maintain effective carrier phase lock under relatively harsh ship dynamics. The attitude parameters are calculated independently at each epoch using differential carrier phase measurements, carrier phase ambiguities are resolved on-the-fly by constraining the approximately known distances between the antennas that are rigidly mounted on the ship. Carrier phase thermal noise and multipath are minimized by mounting the antennas as far apart as possible. The four-antenna configuration provides redundancy and further improves accuracy. During the Matthew Motion Sensor Trials (MMST-93) conducted off the coast of Halifax, Nova Scotia, in June-July 1993, the GPS-derived attitude parameters were compared with those obtained with a Honeywell HG1050 ring laser gyro inertial navigation system (INS) which provides roll and pitch with an accuracy of 15 arcsecs and heading with an accuracy of 2 arcmins. To simulate rough weather conditions, sharp maneuvers were performed to induce roll angles in excess of 10°. No accuracy degradation nor any loss of GPS measurements occurred. The RMS agreement between GPS and INS derived attitude parameters is better than 2 arcmins in heading, 1 arcmin in pitch and 3 arcmins in roll. This level of accuracy demonstrates the capability of GPS for cost-effective shipborne attitude determination at an accuracy level of 0.05 相似文献
150.
A Preliminary Study of Shear Wave in Seafloor Surface Sediments 总被引:1,自引:0,他引:1
This article preliminarily reports and analyses the transmission characteristics and behaviors of shear wave in the offshore seafloor surface sediments in China, discusses the relationships between the physical and mechanical features of the shear wave and the compression wave, and compares the testing results with that of Hamilton and Chen et al. The result shows that the shear wave can be tested if the seafloor surface sediment has tangent modulus. The shear wave velocity ranges from 50-600 m/s and the measuring frequency from 50-200 kHz. The sound velocity rate of shear wave and compression wave can be used to appraise the stress-strain feature of seafloor surface sediments. This study provides a basis for further describing and appraising the seafloor sedimentary acoustic-mechanical feature and building a geological-acoustic model on China's offshore sea area. 相似文献