全文获取类型
收费全文 | 7850篇 |
免费 | 1600篇 |
国内免费 | 1849篇 |
专业分类
测绘学 | 616篇 |
大气科学 | 1433篇 |
地球物理 | 2074篇 |
地质学 | 4108篇 |
海洋学 | 1021篇 |
天文学 | 423篇 |
综合类 | 749篇 |
自然地理 | 875篇 |
出版年
2024年 | 33篇 |
2023年 | 101篇 |
2022年 | 285篇 |
2021年 | 388篇 |
2020年 | 279篇 |
2019年 | 370篇 |
2018年 | 399篇 |
2017年 | 371篇 |
2016年 | 396篇 |
2015年 | 350篇 |
2014年 | 428篇 |
2013年 | 438篇 |
2012年 | 471篇 |
2011年 | 519篇 |
2010年 | 504篇 |
2009年 | 482篇 |
2008年 | 458篇 |
2007年 | 406篇 |
2006年 | 372篇 |
2005年 | 337篇 |
2004年 | 273篇 |
2003年 | 285篇 |
2002年 | 311篇 |
2001年 | 295篇 |
2000年 | 290篇 |
1999年 | 320篇 |
1998年 | 297篇 |
1997年 | 286篇 |
1996年 | 244篇 |
1995年 | 185篇 |
1994年 | 211篇 |
1993年 | 190篇 |
1992年 | 138篇 |
1991年 | 104篇 |
1990年 | 97篇 |
1989年 | 74篇 |
1988年 | 75篇 |
1987年 | 46篇 |
1986年 | 43篇 |
1985年 | 33篇 |
1984年 | 27篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
热带气旋活动对中国夏季雨带类型与ENSO的响应关系 总被引:2,自引:0,他引:2
本文分析研究了热带气旋1)活动与中国夏季2)3组(包括8种)主要多雨带类型的响应关系。同时对热带气旋活动与夏季大陆气温和ENSO事件的始终时间的响应关系,也进行了探讨。分析表明,夏季中国的雨带分布特征对热带气旋活动有着十分重要的指示意义。热带气旋活动与中国大陆气温有着正相关关系,与ENSO事件的发生有着反相关关系 相似文献
62.
63.
分析了上海石化总厂化工物料码头周围水下地形工程前后的变化。指出在淤泥质岸段,由于沿岸工程的影响,造成工程附近水域动力环境的改变,水下地形随之作出相应的调整。特别在淤泥质岸段附近流急、含沙量高的水域中构筑沿岸工程,工程的水流下方一侧,水流减缓,水流挟沙能力大大减弱,出现明显的局部淤浅地形,为提高工程效益,对各工程之间的相互影响,应予以重视。 相似文献
64.
65.
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
66.
Frequency-selective attenuation of sound propagaion and reverberation in shallow waterTXFrequency-selectiveattenuationofsoundp... 相似文献
67.
On the radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas 总被引:1,自引:0,他引:1
The radiation and diffraction of linear water waves by an infinitely long rectangular structure submerged in oblique seas of finite depth is investigated. The analytical expressions for the radiated and diffracted potentials are derived as infinite series by use of the method of separation of variables. The unknown coefficients in the series are determined by the eigenfunction expansion matching method. The expressions for wave forces, hydrodynamic coefficients and reflection and transmission coefficients are given and verified by the boundary element method. Using the present analytical solution, the hydrodynamic influences of the angle of incidence, the submergence, the width and the thickness of the structure on the wave forces, hydrodynamic coefficients, and reflection and transmission coefficients are discussed in detail. 相似文献
68.
Shen Yang Xue Shen Hanlong Liu Huayang Ge Xiaoxi Rui 《Marine Georesources & Geotechnology》2020,38(6):706-715
AbstractConstruction of the reefs in the South China Sea is a significant foundation to the secure stability and economic development of China. The construction of an airport runway is necessary for this realization. The calcareous sand is the main primary material in the runway construction. A certain type of calcareous sand near a certain reef of the South China Sea was studied in this paper. To investigate this specific calcareous sand, quartz sand was used as a reference for comparison. Microscopic 3-D imaging, compression and triaxial tests were conducted to test the micro, squeezing and shear properties. The effect mechanism of gradation on the calcareous sand’s compressibility and shear characteristics are discussed from a mesoscopic viewpoint using 3-D morphology. Calcareous sand particles are multiangular and flatter in comparison with quartz sand. The larger the particle sizes are, the more different the two sands’ morphologies are. The compressibility of calcareous sand is greater, and the effect of the coarse fraction (5–1?mm) content in the gradation plays the most significant role in this feature. When the coarse particles’ content is less than 25% and the mass ratio of the middle and fine particles (M) is constant, there is the worst coarse fraction content causing the calcareous sand to be most likely compressed. The worst coarse fraction content decreases with the increase in M, and an empirical formula is proposed. When the gradation, relative density and confining pressure are the same, the peak shear stress and strain of calcareous sand are all at a high level. The effect of confining pressure is manifested in calcareous sand. The shear strength and dilation of calcareous sand are also most affected by the medium coarse fraction (5–0.25?mm) content. 相似文献
69.
Young-Ok Kim Eun Jin Yang Jung-Hoon Kang Kyoungsoon Shin Man Chang Cheol Soo Myung 《Ocean Science Journal》2007,42(1):9-17
The summer distributions of planktonic microbial communities (heterotrophic and phtosynthetic bacteria, phtosynthetic and
heterotrophic nanoflagellates, ciliate plankton, and microphytoplankton) were compared between inner and outer areas of Lake
Sihwa, divided by an artificial breakwater, located on the western coast of Korea, in September 2003. The semienclosed, inner
area was characterized by hyposaline surface water (<17 psu), and by low concentrations of dissolved oxygen (avg. 0.4 mg L1) and high concentrations of inorganic nutrients (nitrogenous nutrients >36 μM, phosphate <4 μM) in the bottom layer. Higher
densities of heterotrophic bacteria and nanoflagellates also occurred in the inner area than did in the outer area, while
microphytoplankton (mainly diatoms) occurred abundantly in the outer area. A tiny tintinnid ciliate, Tintinnopsis nana, bloomed
into more than 106 cells L1 at the surface layer of the inner area, while its abundance was much lower (103-104 cells L1) in the outer area of the breakwater. Ciliate abundance was highly correlated with heterotrophic bacteria (r = 0.886, p <
0.001) and heterotrophic flagellates (r = 0.962, p < 0.001), indicating that rich food availability may have led to theT. nana bloom. These results suggest that the breakwater causes the eutrophic environment in artificial lakes with limited flushing
of enriched water and develops into abundant bacteria, nanoflagellates, and ciliates. 相似文献
70.
The longitudinal strength of turret mooring productive/storage tanker is studied.A numeri-cal example has been implemented according to the method presented in this paper to give practical il-lustration.From the results of the numerical example,it is concluded that the turret hole located near theforward of the amidships has small effect on the longitudinal strength of the ship hull.As for design ex-treme value of wave bending moment of storage tanker,statistic method is a more reasonablemethodology,especially with the consideration of the servere environmental conditions.The primary esti-mation of design section modulus of turret storage tanker can be determined by this design bending mo-ment. 相似文献