全文获取类型
收费全文 | 8736篇 |
免费 | 1057篇 |
国内免费 | 3550篇 |
专业分类
测绘学 | 436篇 |
大气科学 | 1688篇 |
地球物理 | 2852篇 |
地质学 | 5376篇 |
海洋学 | 891篇 |
天文学 | 344篇 |
综合类 | 689篇 |
自然地理 | 1067篇 |
出版年
2024年 | 72篇 |
2023年 | 179篇 |
2022年 | 118篇 |
2021年 | 206篇 |
2020年 | 123篇 |
2019年 | 135篇 |
2018年 | 179篇 |
2017年 | 69篇 |
2016年 | 151篇 |
2015年 | 146篇 |
2014年 | 250篇 |
2013年 | 242篇 |
2012年 | 259篇 |
2011年 | 290篇 |
2010年 | 199篇 |
2009年 | 285篇 |
2008年 | 248篇 |
2007年 | 381篇 |
2006年 | 430篇 |
2005年 | 485篇 |
2004年 | 496篇 |
2003年 | 332篇 |
2002年 | 417篇 |
2001年 | 456篇 |
2000年 | 472篇 |
1999年 | 230篇 |
1998年 | 164篇 |
1997年 | 175篇 |
1996年 | 146篇 |
1995年 | 195篇 |
1994年 | 161篇 |
1993年 | 371篇 |
1992年 | 312篇 |
1991年 | 404篇 |
1990年 | 365篇 |
1989年 | 395篇 |
1988年 | 440篇 |
1987年 | 364篇 |
1986年 | 265篇 |
1985年 | 358篇 |
1984年 | 293篇 |
1983年 | 214篇 |
1982年 | 167篇 |
1981年 | 127篇 |
1980年 | 177篇 |
1964年 | 89篇 |
1960年 | 55篇 |
1959年 | 120篇 |
1958年 | 125篇 |
1957年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Barik Tapan K. Swain Surya N. Sahu Bijayalaxmi Tripathy Bibarani Acharya Usha R. 《海洋学报(英文版)》2020,39(6):26-35
Marine ecosystems provide a wide variety of diverse habitats that frequently promote migration and ecological adaptation. The extent to which the geographic distribution of marine organism has reshaped by human activities remains underappreciated. The limitations intrinsic to morphology-based identification systems have engendered an urgent need for reliable genetic methods that enable the unequivocal recognition of fish species,particularly those that are prone to overexploitation and/or market substitution. In the present study, however, an attempt has been taken to identify two locally adapted fish species, Siganus sutor(Valenciennes, 1835) and Seriolina nigrofasciata(Rüppell, 1829) of order Perciformes, which happens to be the first record in Odisha coast,Bay of Bengal. The diagnostic characteristics of Siganus sutor are: dorsal fin XIII-10, anal fin VII-9, pectoral fin 15,pelvic fin II-3, while that of Seriolina nigrofasciata dorsal fin VI-I-35, anal fin I-17, pectoral fin 16, pelvic fin 5. All COI barcodes generated in this study were matched with reference sequences of expected species, according to morphological identification. Bayesian and likelihood phylogenetic trees were drawn based on DNA barcodes and all the specimens clustered in agreement with their taxonomic classification at the species level. The phylogeographic studies based on haplotype network and migration rates suggest that both the species were not panmitic and the high-frequency population distribution indicates successful migration. The result of this study provides an important validation of the use of DNA barcode sequences for monitoring species diversity and changes within a complex marine ecosystem. 相似文献
902.
Yugui ZHU Shiyao ZHENG Bin KANG Gabriel REYGONDEAU Yan SUN Qianshuo ZHAO Yunfeng WANG William W.L.CHEUNG Jiansong CHU 《海洋湖沼学报(英文)》2023,(4):1504-1518
The research on the biological ecology of the Prydz Bay-Amery Ice Shelf in East Antarctica is inadequate under the increasing threat from climate change, especially for Antarctic fish and krill. The Dynamic Bioclimatic Envelope Model(DBEM) has been widely used in predicting the variation of species distribution and abundance in ocean and land under climate change; it can quantify the spatiotemporal changes of multi population under different climate emission scenarios by identifying the environm... 相似文献
903.
本文简述了在对地球过程的认识和联合国《海洋法》框架发展前提下的海洋非燃料矿产。在板块构造理论出现以前,洋盆被看成是被动的容体,接纳陆地风化物质形成重金属、宝石砂矿和一些化学沉淀矿床(磷矿)。板块构造认识到大洋板块边界是块状硫化物的物质来源,与陆缘物质一起形成锰结核、富钴铁锰结壳及相应的化能合成生态系统。就海洋矿产总体而言,海水淡化产生的淡水是最重要的资源,因为它是生命必须的物质,在陆地其消耗超过了补充。 相似文献
904.
905.
Obtaining depth of closure (DoC) in an accurate manner is a fundamental issue for coastal engineering, since good results for coastal structures and beach nourishment depend mainly on DoC. Currently, there are two methods for obtaining the DoC, mathematical formulations and profile surveys. However, these methods can incur important errors if one does not take into account the characteristics and morphology of the area, or if one does not have a sufficiently long time series. In this work the DoC is obtained from the break in the trend of the sediment with the depth, that is, in general with the increase of the depth a decrease in the size of the sediment takes place. However, at one point this tendency changes and the size increases, and then decreases again. When comparing the point where the minimum sediment size occurs before the increase, it is observed that the error incurred is small compared to other methods. If the Standard Deviation of Depth Change (SDDC) method is considered as the most accurate method, the error incurred by the proposed method is less than 7%. In addition, it can be seen that the dispersion of the sediment method always occurs outside the zone of bar movement. Whereas in the methods of profiles survey (using 2 cm precision profiles), sometimes the DoC is obtained within the active zone of bar movement. In addition, where the relative minimum of the median sediment size is found, and the sizes of 0.063 and 0.125 mm predominate in the composition of the sample. Therefore, this new method allows the precise location of the DoC to be obtained in a fast and simple way. Furthermore, this method has the advantage that it is not affected by the modifications that may be experienced by both the study area and the cross-shore beach profile. 相似文献
906.
本文研究了库仑应力变化与自1484年以来中国河北省内发生的强震的关系。华北板块在过去的一个世纪里有许多历史地震和一些破坏性的地震发生,其中包括1976年的唐山大地震(M = 7.8)。我们的研究包含了河北省及其邻近区域的最活跃的地震断裂带和频繁遭受过强烈地震的区域。华北板块,包括鄂尔多斯高原和华北平原,是中国太古宙克拉通的一部分,而且是世界上地震最活跃的地区之一。这些地震活动主要发生在东西向的走滑断裂带上。研究区域内的断裂活动导致了复杂的应力场。通过计算库仑破裂函数(ACFF)的变化来得出这个地区的地震灾害评估,这库仑破裂函数的变化是由强震(MS≥6.5)产生的同震滑动和主要区域性大断裂的连续构造载荷产生的应力引起的。在应力演化模型计算的每一步都对下一次可能触发的强震进行了估计,模型最终提出了易于发生即将到来的强烈活动断层段的理由。从而提供了未来地震危险性评价研究依据。在本文中,以张家口断裂,夏垫断裂,廊坊断裂的结果为例,说明通过计算得出的ACFF结果,对未来地震危险性提供依据是可行的。 相似文献
907.
This paper presents a new concept for enhancing the seismic ductility and damping capacity of diagrid structural frames by using shear-link fuse devices and its seismic performance is assessed through nonlinear static and dynamic analysis.The architectural elegancy of the diagrid structure attributed to its triangular leaning member configuration and high structural redundancy make this system a desirable choice for tall building design.However,forming a stable energy dissipation mechanism in diagrid framing remains to be investigated to expand its use in regions with high seismicity.To address this issue,a diagrid framing design is proposed here which provides a competitive design option in highly seismic regions through its increased ductility and improved energy dissipation capacity provided by replaceable shear links interconnecting the diagonal members at their ends.The structural characteristics and seismic behavior(capacity,stiffness,energy dissipation,ductility) of the diagrid structural frame are demonstrated with a 21-story building diagrid frame subjected to nonlinear static and dynamic analysis.The findings from the nonlinear time history analysis verify that satisfactory seismic performance can be achieved by the proposed diagrid frame subjected to design basis earthquakes in California.In particular,one appealing feature of the proposed diagrid building is its reduced residual displacement after strong earthquakes. 相似文献
908.
Vertical profiles of fluid velocity and suspended sediment concentration in nearshore 总被引:2,自引:0,他引:2
Based on the power function of velocity and the friction velocity,a velocity profile is obtained.By solving the Schmidt’s diffusion equation,an equilibrium suspended sediment concentration profile is further deduced.The profiles of velocity and suspended sediment concentration agree well with the field data,and the profile of suspended sediment concentration avoids the unreasonableness of the classical Rouse profile such as a zero value at the water surface.According to these profiles,an expression which is easy to use for calculating the suspended sediment transport rate is derived. 相似文献
909.
P. Alfaro J. Delgado F. J. Garcia-Tortosa L. Lenti J. A. Lopez C. Lopez-Casado S. Martino 许冲译 吕春来校 《世界地震译丛》2013,(3):66-80
2011年5月11日,一个中等震级地震(Mw5.1)袭击了西班牙东南部洛尔卡城和邻近地区,造成了显著的破坏和人员伤亡。通过地震影响区的野外考察对250多处主要是碎裂型(岩/土崩塌、碎裂的土质滑坡和岩崩)诱发滑坡进行了定点和特征描述。与以前该区域相似震级(Mw4.7~5.0)的地震事件,以及以前预测地震期间斜坡表现的模型结果相比,本次地震诱发滑坡的数量相当大。提出了几个原因来解释这种差异:(1)地震序列中相对高震级(Mw4.5)的前震可能弱化了区域内的斜坡强度;(2)这些事件产生了高的地震动峰值;(3)发生了地形场地效应。本研究的结果指出了在改进区域斜坡特征研究模型时考虑这些影响的重要性。 相似文献
910.
Cantarero S Camino-Sánchez FJ Zafra-Gómez A Ballesteros O Navalón A Vílchez JL Verge C Reis MS Saraiva PM 《Marine pollution bulletin》2012,64(3):587-594
The contamination of aquatic environments has become the focus of increasing regulation and public concern due to their potential and unknown negative effects on the ecosystems. The present work develops a monitoring and statistical study, based on the analysis of variance test (ANOVA) and the multivariable analysis, both for insoluble soap and LAS in order to compare the behavior of different anionic surfactants in this environmental compartment. First, a novel and successfully validated methodology to analyze insoluble soap in these samples is developed. The matrix effect and the comparison of different extraction techniques were also performed. The optimized analytical methodologies were applied to 48 representative samples collected from the Almeria Coast (Spain) and then a statistical analysis to correlate anionic surfactant concentration and several variables associated with marine sediment samples was also developed. The results obtained showed relevant conclusions related to the environmental behavior of anionic surfactants in marine sediments. 相似文献