全文获取类型
收费全文 | 82501篇 |
免费 | 27195篇 |
国内免费 | 54410篇 |
专业分类
测绘学 | 12143篇 |
大气科学 | 25621篇 |
地球物理 | 20747篇 |
地质学 | 63715篇 |
海洋学 | 23037篇 |
天文学 | 1419篇 |
综合类 | 7864篇 |
自然地理 | 9560篇 |
出版年
2024年 | 784篇 |
2023年 | 1909篇 |
2022年 | 3753篇 |
2021年 | 4689篇 |
2020年 | 4715篇 |
2019年 | 7878篇 |
2018年 | 7409篇 |
2017年 | 7037篇 |
2016年 | 7198篇 |
2015年 | 7361篇 |
2014年 | 6784篇 |
2013年 | 7874篇 |
2012年 | 8484篇 |
2011年 | 8629篇 |
2010年 | 8563篇 |
2009年 | 7814篇 |
2008年 | 6849篇 |
2007年 | 6619篇 |
2006年 | 6249篇 |
2005年 | 5399篇 |
2004年 | 5131篇 |
2003年 | 4070篇 |
2002年 | 3866篇 |
2001年 | 3504篇 |
2000年 | 2833篇 |
1999年 | 2128篇 |
1998年 | 1929篇 |
1997年 | 1958篇 |
1996年 | 1497篇 |
1995年 | 1421篇 |
1994年 | 1293篇 |
1993年 | 1431篇 |
1992年 | 1266篇 |
1991年 | 839篇 |
1990年 | 754篇 |
1989年 | 639篇 |
1988年 | 532篇 |
1987年 | 447篇 |
1986年 | 372篇 |
1985年 | 267篇 |
1984年 | 311篇 |
1983年 | 188篇 |
1982年 | 235篇 |
1981年 | 154篇 |
1980年 | 116篇 |
1979年 | 149篇 |
1978年 | 68篇 |
1977年 | 61篇 |
1976年 | 54篇 |
1971年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
901.
为了探讨西太平洋暧地区热带波动的天气效应,利用1980年2-9月140°E日本静止卫星纬度时间剖面卫星云图,分析了5d和14d左右周期热带波动云的演变特征,井综合分析了14d周期的云系演变型式与流场的关系,为预报热带中期天气变化规律提供了依据;热带波动中30-60d大气低频振荡的云量变化最显著,北半球夏半年热带波动的天气压主要在10°N-0°,各半年在10°N-10°S,超过这个区域热带云量的港分布型式就有明显的变化。 相似文献
902.
Liang Zheng Associate Professor Southwest petroleum Institute Nanchong Sichuan Province 《中国海洋工程》1994,(2)
-Considering both the seabed foundation and wave, an analytic model of "J" type is proposed for offshore pipeline-laying. The governing differential equation is also obtained for the pipeline on the seabed and for the suspension sections. By utilizing weighted- residual method and dual iteration technique, an approximate solution is obtained, too. In the end, calculation examples are given for analyzing the changeable relationship among the major parameters. 相似文献
903.
StudyonthecharacteristicsofthemarineboundarylayerintheEquatorialPacific¥ZhangZiyuandZhouMingyu(ReceivedAugust21,1993;accepted... 相似文献
904.
The present note deals with the effects of seawater with different copper concentrations and pH values on the larvae of the barnacle Balanus reticulatus Utinomi. The results show that the higher the copper concentration and the lower the pH value in the seawater, and the more acute the toxicity. In the natural seawater of pH 8.1 the effective concentration EC_(50), i.e. the copper concentration causing 50%. larvae fail to attach, is approx- 相似文献
905.
The floating oil storage system has been proposed as a new facility for Strategic Petroleum Reserve (SPR) in China. Mooring is one of the key technologies to ensure the safety, reliability, and performance of the oil storage system. This paper describes the concept, analysis, design and reliability of the mooring system. For mooring system design of these oil vessels, analysis is essential of the behavior of the vessel in connection with mooring facilities of nonlinear resilience. A nonlinear mathematical model for analyzing a moored vessel is established and solved. Some results of numerical simulations are presented. Assessment of the safety regarding the mooring system in terms of failure probability is carried out. Another simulation model for calculating the failure probability of the mooring system is proposed. The design parameters that have an influence on the characteristics of the failure probability have been identified. The simulation results show that the mooring system has an annual reliab 相似文献
906.
C. K. Paull W. Ussler H. G. Greene R. Keaten P. Mitts J. Barry 《Geo-Marine Letters》2003,22(4):227-232
A sediment gravity flow descended through the axis of Monterey Canyon on 20 December 2001 at 13:35 Pacific standard time.
The timing of this event is documented by a current-meter package which recorded an 11.9-dbar pressure increase in less than
10 min and was found 550 m down-canyon from its deployment site, buried completely within a >70-cm-thick gravity flow deposit.
This event is believed to have started in less than 290 m of water because an instrument at this location was also lost at
the same time. A 178-cm core collected after the event from the axis of the canyon at 1,297-m water depth contained fresh,
greenish, chlorophyll-rich organic material at 32-cm sub-bottom depth, suggesting the event extended to this water depth.
The only trigger identified for this mass movement event appears to be moderate sea and surf conditions. Thus, gravity flow
events of this magnitude do not require an exceptional triggering event. 相似文献
907.
Using benthic macrofauna to assess environmental quality of four intertidal mudflats in Hong Kong and Shenzhen Coast 总被引:4,自引:0,他引:4
Cai Lizhe Nora F. Y. Tam Teresa W. Y. Wong Ma Li Gao Yang Yuk-Shan Wong 《海洋学报(英文版)》2003,22(2):309-319
Abstract-Intertidal zone is a significant wetland between land and ocean. It plays an important rolein maintaining local ecological balance. Both Mai Po and Futian intertidal mudflats are located in Shen-zhen Bay and are important "refueling" point along the East Asian/Australian flyway of migratory birds.The environmental quality of Mai Po and Futian mudflats have aroused great concern due to rapid eco-nomic developments in Hong Kong and Shenzhen in recent decades. Microinfauna of Mai Po and Futianmudflats was investigated in December 2000 and the faunal data were used to assess their environmentalquality. Two other mudflats, namely Ma Wan Typhoon Shelter (a more disturbed area) and Luk Kengintertidal mudflat (a place with relatively less human disturbance), were also sampled for macroinfaunaand used as reference mudflats. Shannon-Weaver species diversity index (I_(sd)), biotic coefficient (C_b)and macrofaunal pollution index (I_(mp)) of the macrofauna community on four intertidal mudflats wereused to 相似文献
908.
909.
A time-domain method is applied to simulate nonlinear wave diffraction around a surface piercing 3-D arbitrary body. The method involves the application of Taylor series expansions and the use of perturbation procedure to establish the corresponding boundary value problems with respect to a time-independent fluid domain. A boundary element method based on B-spline expansion is used to calculate the wave field at each time step, and the free surface boundary condition is satisfied to the second order of wave steepness by a numerical integration in time. An artificial damping layer is adopted on the free surface for the removal of wave reflection from the outer boundary. As an illustration, the method is used to compute the second-order wave forces and run-up on a surface-piercing circular cylinder. The present method is found to be accurate, computationally efficient, and numerically stable. 相似文献
910.
Experimental Investigation of Instantaneous Properties of Wave Slamming on the Plate 总被引:1,自引:0,他引:1
The purpose of this paper is to investigate the instantaneous properties of wave slamming on the plate structure of an open structure.The advanced instantaneous measuring technique-Particle Image Velocimetry(PIV) is applied to acquire the instantaneous velocity field of wave slamming.From the cross-correlation analysis results of the images captured by the CCD camera,the flow fields of wave impacting on the structure are displayed visually,and the instantaneous whole-field fluid velocity vectors are obtained.The relation between the instantaneous peak impacting pressures and the instantaneous velocities of water particles is studied by probability analysis. 相似文献