全文获取类型
收费全文 | 35837篇 |
免费 | 6255篇 |
国内免费 | 10020篇 |
专业分类
测绘学 | 5396篇 |
大气科学 | 5424篇 |
地球物理 | 8955篇 |
地质学 | 18717篇 |
海洋学 | 4441篇 |
天文学 | 265篇 |
综合类 | 2663篇 |
自然地理 | 6251篇 |
出版年
2024年 | 236篇 |
2023年 | 622篇 |
2022年 | 1331篇 |
2021年 | 1587篇 |
2020年 | 1863篇 |
2019年 | 1959篇 |
2018年 | 1723篇 |
2017年 | 1779篇 |
2016年 | 2054篇 |
2015年 | 2205篇 |
2014年 | 2419篇 |
2013年 | 2643篇 |
2012年 | 2463篇 |
2011年 | 2566篇 |
2010年 | 2144篇 |
2009年 | 2361篇 |
2008年 | 2340篇 |
2007年 | 2398篇 |
2006年 | 2429篇 |
2005年 | 2038篇 |
2004年 | 1876篇 |
2003年 | 1576篇 |
2002年 | 1450篇 |
2001年 | 1200篇 |
2000年 | 1070篇 |
1999年 | 937篇 |
1998年 | 865篇 |
1997年 | 746篇 |
1996年 | 655篇 |
1995年 | 557篇 |
1994年 | 480篇 |
1993年 | 409篇 |
1992年 | 271篇 |
1991年 | 226篇 |
1990年 | 149篇 |
1989年 | 120篇 |
1988年 | 108篇 |
1987年 | 74篇 |
1986年 | 38篇 |
1985年 | 38篇 |
1984年 | 24篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
261.
1 .IntroductionThepenetratingbucketandboxfoundationisanewtypeofstructure ,whichhasbeenappliedinmanyengineeringfields .Inviewofthehighconstructioncostandtheformidableconstructibilityofoff shoreplatformswithpiledfoundations ,Baerheimetal.(1 990 )proposedtheconc… 相似文献
262.
针对常垂直湍流系数和变垂直湍流系数两种情况,给出了开阔静止海面对风应力的非定常响应的解析表达式,并讨论了水深,风应力强弱对响应过程的影响,尽管没有考虑风场的非定常性,但本文的结果对理解海洋对风应力的非定常响应过程具有一定的帮助,对分析海面停风后的消衰过程也具有实际意义。通过与实测资料比较,认为垂直湍流系数模式要比常垂直湍流系数模式更为合理。 相似文献
263.
264.
The method has been established to calculate the environmental capacity (ECo),surplus environment capacity (SECo) of water with respect to marine petroleum hydrocarbons associated with oil (PHAOs) and the self-purification capacity (SPCo) of main self-purification process to PHAOs in the Jiaozhou Bay, China, according to the dynamic model for distribution of marine PHAOs among multiphase environments. The variation of concentration of PHAOs in the Jiaozhou Bay is well simulated by the dynamic model. Based on the model.the ECo, SECo of water with respect to PHAOs in the Jiaozhou Bay were calculated during the last 10 years under the first-class and second-class quality standard requirement, according to SPCoof main self-purification process to PHAOs. The results show that about 200 tons of PHAOs could be discharged into the Jiaozhou Bay for maintaining the first class seawater quality standard, and about 600 tons of PHAOs for the second class seawater quality standard later. 相似文献
265.
266.
267.
动力定位系统发展状况及研究方法 总被引:21,自引:2,他引:21
动力定位系统(Dynamic Positioning System)是一种闭环的控制系统,其采用推力器来提供抵抗风、浪、流等作用在船上的环境力,从而使船尽可能地保持在海平面上要求的位置上,其定位成本不会随着水深增加而增加,并且操作也比较方便。本文对动力定位系统发展及各组成部分进行了介绍,以期对动力定位系统有个比较完整的认识。 相似文献
268.
- The dynamic response behaviors of upright breakwaters under broken wave impact are analysed based on the mass-damper-spring dynamic system model. The effects of the mass, damping, stiffness, natural period, and impulse duration (or oscillation period) on the translation, rotation, sliding force, overturning moment, and corresponding dynamic amplifying factors are studied. It is concluded that the ampli-ying factors only depend on the ratio of the system natural period to impulse duration (or oscillation period) under a certain damping ratio. Moreover, the equivalent static approach to breakwater design is also discussed. 相似文献
269.
1 .IntroductionEvery year ,Taiwanis subjectedtotwo or three typhoonintrusions in average which always causedisasters . Most of the disasters which occur around the coastal zone are due to seabed instability andcoastal structure destruction caused bytyphoo… 相似文献
270.
Estimation of Land Subsidence Based on Groundwater Flow Model 总被引:8,自引:0,他引:8
This article presents an approach for estimating land subsidence due to withdrawal of groundwater. The proposed method calculates the groundwater seepage in 3-D-condition and calculates the land subsidence one-dimensionally. The governing equation on groundwater seepage is based on the three-dimensional mass conservation law and the principle of effective stress. The land subsidence calculation method is derived based on the following assumptions: (1) displacements occur only in the vertical direction, and (2) in vertical direction the total stresses do not change. The governing equation is solved by numerical method, i.e., finite element method (FEM) in spatial discretization and finite difference method (FDM) in time series discretization. In FEM Galerkin method is adopted and in FDM, lumped matrix method is employed. The proposed method is calibrated via analyzing 1-D consolidation problem and the results are compared with those from Terzaghi's one-dimensional consolidation theory and oedometer test. The proposed method is employed to analyze the consolidation of a soft layer due to withdrawal of groundwater from an aquifer under it. Moreover, this method is also applied to a field case of land subsidence due to groundwater pumping in a gas production field in Japan. The analytical results are compared with the field observed data. The results show that this approach simulates the field case well. 相似文献