全文获取类型
收费全文 | 12112篇 |
免费 | 1454篇 |
国内免费 | 1988篇 |
专业分类
测绘学 | 949篇 |
大气科学 | 1382篇 |
地球物理 | 2544篇 |
地质学 | 5963篇 |
海洋学 | 1405篇 |
天文学 | 1557篇 |
综合类 | 660篇 |
自然地理 | 1094篇 |
出版年
2024年 | 73篇 |
2023年 | 250篇 |
2022年 | 512篇 |
2021年 | 554篇 |
2020年 | 472篇 |
2019年 | 498篇 |
2018年 | 657篇 |
2017年 | 592篇 |
2016年 | 765篇 |
2015年 | 562篇 |
2014年 | 713篇 |
2013年 | 802篇 |
2012年 | 697篇 |
2011年 | 719篇 |
2010年 | 709篇 |
2009年 | 719篇 |
2008年 | 601篇 |
2007年 | 553篇 |
2006年 | 589篇 |
2005年 | 409篇 |
2004年 | 358篇 |
2003年 | 335篇 |
2002年 | 266篇 |
2001年 | 271篇 |
2000年 | 250篇 |
1999年 | 286篇 |
1998年 | 238篇 |
1997年 | 239篇 |
1996年 | 212篇 |
1995年 | 164篇 |
1994年 | 150篇 |
1993年 | 153篇 |
1992年 | 116篇 |
1991年 | 92篇 |
1990年 | 71篇 |
1989年 | 78篇 |
1988年 | 63篇 |
1987年 | 67篇 |
1986年 | 85篇 |
1985年 | 66篇 |
1984年 | 60篇 |
1983年 | 54篇 |
1982年 | 60篇 |
1981年 | 37篇 |
1980年 | 41篇 |
1979年 | 43篇 |
1978年 | 22篇 |
1976年 | 23篇 |
1975年 | 24篇 |
1973年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Z Dhurmeea H Pethybridge EV Romanov C Appadoo N Bodin 《African Journal of Marine Science》2020,42(2):131-140
The diet of albacore Thunnus alalunga from their spawning ground in the waters of Mauritius was investigated. The stomach contents of 249 albacore individuals, caught by industrial longliners and artisanal fishers, was analysed, and the dominant prey taxa were selected for lipid and fatty acid (FA) analysis. The FA profiles of prey were compared with those of liver tissue of spawning-capable and post-spawning female albacore, using multivariate analysis. Whereas stomach content analysis identified cephalopods and crustaceans as the dominant prey items in number, FA-profile analysis identified crustaceans and fishes as the most-frequently consumed prey of post-spawning female albacore. In contrast, the FA profiles of spawning-capable albacore and those of prey showed very low similarity. Analysis of the prey suggests that although cephalopods, crustaceans and fishes could all provide albacore with the required lipids and FAs, cephalopod prey seem to be less desirable owing to their lower energy content (i.e. low in total lipid, triacylglycerol, 16:0, 18:0 and 18:1ω9). Instead, the most beneficial food appeared to be locally available fishes, which are more energy-rich and have a higher docosahexaenoic acid/ eicosapentaenoic acid ratio. These results provide new information on the trophic ecology of albacore, promote our understanding of the importance of prey type for successful reproduction of albacore, and highlight the advantages of FA profiling to study diet. 相似文献
92.
93.
报道一种新的有效催化剂-碘-钒盐和在一定条件下合成四溴邻苯二甲酸酐的方法。探讨催化剂的组成配比、用量、温度及废酸循环使用等因素对合成方法的影响。该催化剂的催化效果和常用的碘、碘-铁催化剂相同,适用于四溴邻苯二甲酸酐的合成。 相似文献
94.
L. D. Wright Z. -S. Yang B. D. Bornhold G. H. Keller D. B. Prior W. J. Wiseman Jr. Y. B. Fan Z. Su 《Geo-Marine Letters》1986,6(2):115-120
Internal waves with periods of about 5 minutes and trough to crest heights of up to 6.2 m were observed acoustically over the actively accreting delta front of the Huanghe (Yellow River) in the western portion of the Gulf of Bohai, Peoples Republic of China. The radian frequency of the internal waves was close to the locally-observed Brunt-Vaisala frequency. Through the relatively short (one hour) duration of an internal wave train, the amplitude was observed to decrease progressively with time. These internal waves may cause resuspension of delta-front sediments. 相似文献
95.
The sway, heave and roll added masses of three uniform cylinders with semi-circular, rectangular and triangular cross-sectional shapes in shallow and narrow water are numerically analysed. The method is based on simulation of the potential flow induced by the cylinder's mode of motion. The effects of shallow and narrow water on added mass are analysed and presented. It is concluded that the shallow and narrow water effects on added mass depend on the different cross-section shapes of the cylinders. In particular, the water depth effect on sway added mass is stronger than that on heave added mass while the narrow water effect on sway is weaker than that on heave. The shallow water effect on added mass tends to weaken the narrow water effect. Lastly the effect of shallow and narrow water on added mass on a rectangular cylinder is the strongest while that on a triangular cylinder is the weakest. 相似文献
96.
Sloshing in a two-dimensional rectangular tank in horizontal motion is analysed based on the velocity potential theory. It is found that even when the first-order excitation is away from all the natural frequencies of the tank, second-order resonance can still occur when the sum-frequency or the difference-frequency is equal to one of the natural frequencies corresponding to the even mode. However, such resonance is not excited when the sum or difference frequency is equal to the natural frequency of an odd mode. 相似文献
97.
This paper proposes a nonlinear robust adaptive control strategy to force a six degrees of freedom underactuated underwater vehicle with only four actuators to follow a predefined path at a desired speed despite of the presence of environmental disturbances and vehicle’s unknown physical parameters. The proposed controller is designed using Lyapunov’s direct method, the popular backstepping and parameter projection techniques. The closed loop path following errors can be made arbitrarily small. Interestingly, it is shown that our developed control strategy is easily extendible to situations of practical importance such as parking and point-to-point navigation. Numerical simulations are provided to illustrate the effectiveness of the proposed methodology. 相似文献
98.
99.
100.
The anoxic rates of heat dissipation by mussels (Mytilus edulis) were enhanced after exposure to pentachlorophenol (PCP) and tributyltin (TBT), both known uncouplers of oxidative phosphorylation. The degree of metabolic activation under anoxia was dependent upon the amount of toxicant accumulated in the tissues, but the concentration-response relationship was different to that under aerobic conditions. Biochemical measurements indicated that the anaerobic metabolic pathways were significantly disturbed by PCP and TBT. There was a decline in succinate, an increase in the fumarate: succinate ratio, and an increase in the accumulation of lactate, indicating a shift from succinate to lactate anaerobic pathways. A consequence of organic toxicant exposure was a reduction in anoxic survival time of mussels. 相似文献