全文获取类型
收费全文 | 36629篇 |
免费 | 5926篇 |
国内免费 | 7614篇 |
专业分类
测绘学 | 3384篇 |
大气科学 | 4413篇 |
地球物理 | 6277篇 |
地质学 | 19296篇 |
海洋学 | 4934篇 |
天文学 | 3386篇 |
综合类 | 2421篇 |
自然地理 | 6058篇 |
出版年
2024年 | 178篇 |
2023年 | 453篇 |
2022年 | 1197篇 |
2021年 | 1374篇 |
2020年 | 1296篇 |
2019年 | 1682篇 |
2018年 | 1211篇 |
2017年 | 1411篇 |
2016年 | 1465篇 |
2015年 | 1566篇 |
2014年 | 2017篇 |
2013年 | 2295篇 |
2012年 | 2130篇 |
2011年 | 2290篇 |
2010年 | 1991篇 |
2009年 | 2489篇 |
2008年 | 2449篇 |
2007年 | 2514篇 |
2006年 | 2441篇 |
2005年 | 2341篇 |
2004年 | 2028篇 |
2003年 | 1915篇 |
2002年 | 1658篇 |
2001年 | 1460篇 |
2000年 | 1497篇 |
1999年 | 1299篇 |
1998年 | 1107篇 |
1997年 | 789篇 |
1996年 | 670篇 |
1995年 | 571篇 |
1994年 | 549篇 |
1993年 | 448篇 |
1992年 | 329篇 |
1991年 | 289篇 |
1990年 | 188篇 |
1989年 | 147篇 |
1988年 | 124篇 |
1987年 | 73篇 |
1986年 | 44篇 |
1985年 | 45篇 |
1984年 | 28篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 16篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
231.
Monthon?Ganmanee Teruyoshi?Narita Hideo?SekiguchiEmail author 《Journal of Oceanography》2004,60(6):1071-1083
Based on our long-term data from megabenthos sampling from 1993 to 2002 in Ise Bay, central Japan, we examined spatio-temporal variations in taxon composition, species richness and its distribution of megabenthos in the bay in relation to the occurrence of the oxygen-poor water (i.e. oxygen content less than 3 ppm) in bottom waters of the bay. A total of 261 species were identified including 6 cnidarians, 1 tentaculate, 5 annelids, 71 molluscs, 72 crustaceans, 16 echinoderms, 12 urochordates and 78 pisces. Of the most abundant 10 megabenthos species, the following 4 species of echinoderms made up more than the half of megabenthos biomass: Luidia quinaria, Echinocardium cordatum, Asterias amurensis and Astropecten scoparius. Species richness of megabenthos varied significantly between seasons and among stations. The severity and period of occurrence of the oxygen-poor water developing every summer play an important role in determining spatial distributions of species richness in the bay. 相似文献
232.
233.
In most design applications such as alignment of the berthing structure and breakwater alignment, it becomes necessary to determine the direction of design wave. There are two different approaches to determine wave direction. One involves the use of first order Fourier coefficients (mean wave direction) while the other uses second order Fourier coefficients (principal wave direction). Both the average wave direction over the entire frequency range (0.03–0.58 Hz) and the direction corresponding to the peak frequency are used in practice. In the present study, comparison is made on wave directions estimated based on first and second order Fourier coefficients using data collected at four locations in the west and east coasts of India. Study shows that at all locations, the mean and principal wave directions for frequencies ranging from 0.07 to 0.25 Hz (±0.5 times peak frequency) co-vary with a correlation coefficient of 0.99 but at lower and higher frequencies, difference between the parameters is large. Average difference between the mean wave direction at peak frequency and the average over the frequency related to spectral energy more than 20% of maximum value is less, around 13°. Study shows that average difference in the sea and swell directions is around 39°. 相似文献
234.
Several significant international incidents in Asian exclusive economic zones (EEZs) have underscored the ambiguity and lack of agreement regarding the regime governing foreign military activities in coastal States’ EEZs. A group of senior officials and analysts participated in their personal capacities in a dialogue from 2002–2005 that discussed the issues with a view to improving mutual understanding of the regime and finding areas of agreement. The Tokyo meeting in September 2005 reached consensus on some voluntary, non-binding guidelines that are presented here. The guidelines are based selectively on the 1982 UNCLOS, State practice and emerging ‘soft’ law, and attempt to balance the interests of coastal States and user States. It is hoped that they may serve as the basis for discussion and eventual agreements between governments. 相似文献
235.
236.
报道1989~1990年山东省30多个大中型代表水库浮游动物的种类组成,种类频级、优势类群。主要种和生物量;统计分析掠食性与植食性浮游动物生物量,浮游动物与浮游植物生物量及浮游动物与代表水库营养状态指标的总磷,透明度和深度的关系。提出浮游动物个体越小,其生物量与水库营养水平关系越密切。 相似文献
237.
史重光 《中国海洋大学学报(自然科学版)》1994,(Z2)
提出用于十二相可控整流器的8098单片机控制系统的电路原理和软件策略。包括自适应控制算法和触发相序计算在内的多种操作全部用软件实现.与通常的方法相比,此系统的成本更低,动态性能和静态性能更好。 相似文献
238.
海底管道开沟机械的技术经济性能评定与选型 总被引:1,自引:0,他引:1
本文在对水下管道开沟机械的需求市场、实际应用和研制开发动向作深入调研的基础上,选择水下管道开沟机械特有的技术先进性、适用性、安全可靠性以及经济性评价指标,构造评价模型,对水下管道施工作业中广为应用的水力冲射开沟机械、海底管道犁、机械开沟机和土壤液化法埋管设备及其机型的技术经济性能作了较为详尽地分析对比及综合评价。在此基础上,笔者提出了水下管道开沟机械的一般选型原则和对我国海底管道开沟机械研究开发工 相似文献
239.
Five sequences are defined in the Oligocene succession of the Danish North Sea sector. Two of the sequences, 4.1a and 4.3, have been identified onshore Denmark.Two types of prograding lowstand deposits are recognized. Sand-dominated deposits occur proximally, comprising sharp-based forced regressive deposits covered with prograding low-stand deposits. Clay-dominated prograding lowstand deposits occur distally in the sequences. The highstand deposits are proximally represented by thick prograding sandy deposits and distally by thin and condensed intervals.The main sediment input direction was from the north and the northeast. A succession oif lithofacies, from shallow marine facies dominated by sand to outer shelf facies dominated by clay, is mapped in each of the sequences. An overall southward progradation of the shoreline took place during the Oligocene, interrupted only by minor shoreline retreats. 相似文献
240.
Paraconchoeciadiacanthusn.sp.,anewspeciesofplanktonicOstracoda¥ChenRuixiangandLinJinghong(ReceivedApril16,19931acceptedJuly20... 相似文献