全文获取类型
收费全文 | 13171篇 |
免费 | 2281篇 |
国内免费 | 2143篇 |
专业分类
测绘学 | 1797篇 |
大气科学 | 1096篇 |
地球物理 | 5051篇 |
地质学 | 5372篇 |
海洋学 | 1919篇 |
天文学 | 265篇 |
综合类 | 705篇 |
自然地理 | 1390篇 |
出版年
2024年 | 32篇 |
2023年 | 134篇 |
2022年 | 369篇 |
2021年 | 456篇 |
2020年 | 511篇 |
2019年 | 597篇 |
2018年 | 445篇 |
2017年 | 552篇 |
2016年 | 500篇 |
2015年 | 625篇 |
2014年 | 824篇 |
2013年 | 777篇 |
2012年 | 832篇 |
2011年 | 886篇 |
2010年 | 810篇 |
2009年 | 810篇 |
2008年 | 819篇 |
2007年 | 998篇 |
2006年 | 860篇 |
2005年 | 754篇 |
2004年 | 717篇 |
2003年 | 640篇 |
2002年 | 528篇 |
2001年 | 446篇 |
2000年 | 466篇 |
1999年 | 386篇 |
1998年 | 351篇 |
1997年 | 294篇 |
1996年 | 238篇 |
1995年 | 167篇 |
1994年 | 172篇 |
1993年 | 140篇 |
1992年 | 118篇 |
1991年 | 76篇 |
1990年 | 62篇 |
1989年 | 46篇 |
1988年 | 41篇 |
1987年 | 29篇 |
1986年 | 15篇 |
1985年 | 14篇 |
1984年 | 19篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
据开发应用水产饲料膨化机实践,初步论述了膨化机生产能力与动力匹配,螺杆设计参数长径比,物料在腔内滞留时间,膨化腔设计及其温度调控,并提出改进设计的见解. 相似文献
112.
113.
114.
A numerical procedure is described for predicting the motion and structural responses of tension leg platforms (TLPs) in waves. The developed numerical approach, in a TLP is assumed to be flexible instead of rigid, is based on a combination of the three dimensional source distribution method and the finite-element method. The hydrodynamic interactions among TLP members, such as columns and pontoons, are included in the motion and structural response analysis. Numerical results are compared with the experimental and numerical ones. The results of comparison confirmed the validity of the proposed approach. 相似文献
115.
二色桌片参酶解液对转化细胞的效应 总被引:3,自引:2,他引:3
用二色桌片参(Mensamariaintercedens)酶解液处理转化的人胚肺成纤维细胞(NLF)后,细胞生长受到显著抑制,抑制率达64.84%,光镜下细胞透光性加强,铺展较好,细胞核形更为规则,核畸形现象减少;线粒体结构趋于正常;软琼脂集落实验表明,细胞集落形成率由23x10-5下降至12.5x10-5,裸小鼠致瘤实验显示抑瘤率为82.39%,差异显著(p<5%)。结果提示,二色桌片参酶解液可能逆转转化的HLF细胞的恶性表型,对其有一定的诱导分化作用。 相似文献
116.
117.
118.
Fisheries in boreal ecosystems 总被引:2,自引:1,他引:2
119.
Adaptive optimal control of an autonomous underwater vehicle in the dive plane using dorsal fins 总被引:1,自引:0,他引:1
In this paper, adaptive control of low speed bio-robotic autonomous underwater vehicles (BAUVs) in the dive plane using dorsal fins is considered. It is assumed that the model parameters are completely unknown and only the depth of the vehicle is measured for feedback. Two dorsal fins are mounted in the horizontal plane on either side of the BAUV. The normal force produced by the fins, when cambered, is used for the maneuvering. The BAUV model considered here is non-minimum phase. An indirect adaptive control system is designed for the depth control using the dorsal fins. The control system consists of a gradient based identifier for online parameter estimation, an observer for state estimation, and an optimal controller. Simulation results are presented which show that the adaptive control system accomplishes precise depth control of the BAUV using dorsal fins in spite of large uncertainties in the system parameters. 相似文献
120.
Anna Badosa Dani Boix Sandra Brucet Rocío Lpez-Flores Xavier D. Quintana 《Estuarine, Coastal and Shelf Science》2006,66(3-4):513-522
The role of the hydrological regime in the nutrients and zooplankton composition and dynamics has been analysed in five lagoons of La Pletera salt marshes (NE Iberian Peninsula) during a complete hydrological cycle (2002–2003). Two of the lagoons have their origin in the old river mouths while the other three were recently created in the framework of a Life Restoration project. This fact has also allowed us to study the effect of the lagoon age on nutrient and zooplankton composition and dynamics. The salt marsh hydrology is determined by a prolonged period of confinement without water inputs, irregularly interrupted by sudden water inputs due to flooding events (sea storms or intense rainfalls). While the dynamics of oxidized nitrogen compounds in the lagoons depends on the water inputs variability within each hydrological cycle, the internal load of phosphorus, total nitrogen and organic matter is related more to the cumulative mechanisms during the confinement periods. Accumulation processes may be easily related to lagoon age, since old lagoons have higher content of nutrients and organic matter, suggesting that these lagoons progressively accumulate nutrients during the successive confinement events. This is the usual case for most Mediterranean salt marshes without an artificially manipulated water regime. The zooplankton community in La Pletera integrates the effects of both the hydrological regime and the lagoon age since the former determines the temporal pattern of the main zooplankton species and the latter explains differences in composition and structure between old and new lagoons. 相似文献