全文获取类型
收费全文 | 36542篇 |
免费 | 6724篇 |
国内免费 | 10057篇 |
专业分类
测绘学 | 2779篇 |
大气科学 | 7113篇 |
地球物理 | 9238篇 |
地质学 | 19835篇 |
海洋学 | 4280篇 |
天文学 | 1491篇 |
综合类 | 4168篇 |
自然地理 | 4419篇 |
出版年
2024年 | 113篇 |
2023年 | 431篇 |
2022年 | 1409篇 |
2021年 | 1616篇 |
2020年 | 1299篇 |
2019年 | 1576篇 |
2018年 | 1752篇 |
2017年 | 1615篇 |
2016年 | 1892篇 |
2015年 | 1673篇 |
2014年 | 1967篇 |
2013年 | 1951篇 |
2012年 | 1884篇 |
2011年 | 2362篇 |
2010年 | 2310篇 |
2009年 | 2336篇 |
2008年 | 1925篇 |
2007年 | 1977篇 |
2006年 | 1804篇 |
2005年 | 1798篇 |
2004年 | 2017篇 |
2003年 | 1611篇 |
2002年 | 1353篇 |
2001年 | 1306篇 |
2000年 | 1317篇 |
1999年 | 1700篇 |
1998年 | 1449篇 |
1997年 | 1357篇 |
1996年 | 1192篇 |
1995年 | 1027篇 |
1994年 | 882篇 |
1993年 | 987篇 |
1992年 | 815篇 |
1991年 | 564篇 |
1990年 | 362篇 |
1989年 | 366篇 |
1988年 | 286篇 |
1987年 | 201篇 |
1986年 | 166篇 |
1985年 | 90篇 |
1984年 | 101篇 |
1983年 | 75篇 |
1982年 | 69篇 |
1981年 | 56篇 |
1980年 | 34篇 |
1979年 | 36篇 |
1978年 | 18篇 |
1977年 | 25篇 |
1976年 | 16篇 |
1958年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
181.
On the basis of the wave energy balance equation, the response model of mean directions of locally wind-generated waves in slowly turning wind fields has been derived. The results show that in a homogeneous field, the time scale of the response is not only related to the rate of wave growth, but also to the directional energy distribution and the angle between the wind direction and the mean wave direction. Furthermore, the law of change in the mean wave direction has been derived. The numerical computations show that the response of wave directions to slowly turning wind directions can be treated as the superposition of the responses of wave directions to a series of sudden small-angle changes of wind directions and the turning rate of the mean wave direction depends on the turning rate and the total turning angles of the wind direction. The response of wave directions is in agreement with the response for a sudden change of wind directions if the change in wind directions is very fast. Based on the no 相似文献
182.
Gu Jialong Shen Xianrong
Professor Hohai University Nanjing
Engineer The Investigation Design Institute Bureau of Communications of Zhejiang Province Hangzhou 《中国海洋工程》1991,(2)
In accordance with the similarity between breaking waves and hydraulic jumps, the expressions for estimating wave decay and wave energy dissipation in the surf zone are derived based on the fundamental equations of fluid mechanics. Using the numerical solution of cnoidal wave theory, the various kinematic properties of waves in the surf zone, including the relative wave crest height, wave energy, and radiation stress are discussed. The values calculated with the method proposed in this paper are in good agreement with the experimental data gained by other researchers. The present expressions can be used in the studies of sediment transport on gently sloping beaches, especially on muddy beaches. 相似文献
183.
南黄海灾害性地质研究 总被引:2,自引:0,他引:2
本文研完了南黄海10种灾害地质因素的性质、危害性及分布,对其进行了分类,在此基础上对本区之灾害地质进行了区划和评价。 相似文献
184.
185.
By using occanographic data (luring 1955-1978, we have analysed aspects of volume transport variation of the Kuroshio tor PN-linc in the East China Sea, and relationships between volume transport variation of the Kuroshio and the subtropical high pressure (SHP) of the Pacific. We have found that volume transport of the Kuroshio is closely related to the long-period oscillations of the subtropical high pressure for 8-9 years and 2-3 years, respectively. The subtropical high pressure has a phase lag behind compared with volume transport of the Kuroshio. In addition, the seasonal volume transport of the Kuroshio is closely related to the subtropical high pressure, too. The results show that volume transport variation of the Kuroshio has certain influence on future variation of the subtropical high pressure. Therefore, the volume transport of the Kuroshio may be an important parameter lor long-period forecasting of the subtropical high pressure. 相似文献
186.
The numerical mode of nonlinear wave transformation based on both the Laplace equation for water field and the Bemoulli equation for water surface is a kind of time-domain boundary problem with initial conditions. And the basis for establishing the numerical mode of nonlinear wave in time domain is to trace the position of wave free surface and to calculale the instantaneous surface height and surface potential function. This paper firstly utilizes the ‘0-1‘ combined BEM to separate the boundary by means of discretization of Green‘ s integral equation based on the Laplace equation, then separates the free surface of wave with FEM and derives the FEM equation of wave surface that satisfies the nonlinear boundary conditions. By jointly solving the above BEM and FEM equations, the wave potential and surface height could be obtained with iteration in time domain. Thus a new kind of nonlinear numerical mode is established for calculating wave transformation. The wave test in the numerical wave tank shows that the numerical simulation with this mode is of high accuracy. 相似文献
187.
188.
Characteristics of Scour and Deposition in Front of Breakwaters Under Irregular Broken Clapotis 总被引:1,自引:0,他引:1
First the scour and deposition patterns of the sandy seabed in front of a vertical breakwater under the action of irregular broken clapotis are investigated experimentally and classified into five types: scour type Ⅰ , scour type Ⅱ, scour type Ⅲ, deposition type Ⅰ, and deposition type Ⅱ . Secondly, the processes of formation of scour and deposition patterns are probed in comparison with those induced by regular broken clapotis and standing waves. Thirdly, the criteria for distinguishing scour and deposition patterns under irregular broken clapotis are presented. 相似文献
189.
26S蛋白酶体是真核生物中一种具有ATP依赖性的蛋白酶复合体,主要通过泛肽途径选择性降解细胞内与代谢调控、细胞周期有关的功能蛋白及异常蛋白,参与多种细胞活动的调控过程。26S蛋白酶体由具有催化活性的20S亚复合体和一个具有调节作用的19S亚复合体组成,其中19S亚复合体中的ATP酶亚基是调节26S蛋白酶体活性的重要组件。本通过简并引物PCR手段,从软体动物合浦珠母贝(Pinctada fucata)中扩增到参与构成19S亚复合体的S4和S7(MSS1)两个亚基的基因片段。这两个基因片段所编码的ATP酶组件包含有Gx4GKT,DEID,SAT和H/QRxGRxxR等26S蛋白酶体ATP酶亚基的共同功能基序。这是首次在软体动物中报道26S蛋白酶体的ATP酶亚基基因序列,为研究软体动物中26S蛋白酶体的结构与功能奠定了分子基础。 相似文献
190.
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