全文获取类型
收费全文 | 81182篇 |
免费 | 26837篇 |
国内免费 | 53868篇 |
专业分类
测绘学 | 12142篇 |
大气科学 | 25463篇 |
地球物理 | 20225篇 |
地质学 | 62260篇 |
海洋学 | 23111篇 |
天文学 | 1313篇 |
综合类 | 7699篇 |
自然地理 | 9674篇 |
出版年
2024年 | 797篇 |
2023年 | 1972篇 |
2022年 | 3853篇 |
2021年 | 4808篇 |
2020年 | 4796篇 |
2019年 | 7942篇 |
2018年 | 7465篇 |
2017年 | 7069篇 |
2016年 | 7227篇 |
2015年 | 7411篇 |
2014年 | 6897篇 |
2013年 | 7957篇 |
2012年 | 8588篇 |
2011年 | 8389篇 |
2010年 | 8521篇 |
2009年 | 7573篇 |
2008年 | 6860篇 |
2007年 | 6678篇 |
2006年 | 6143篇 |
2005年 | 5236篇 |
2004年 | 4775篇 |
2003年 | 3829篇 |
2002年 | 3698篇 |
2001年 | 3403篇 |
2000年 | 2761篇 |
1999年 | 2041篇 |
1998年 | 1792篇 |
1997年 | 1820篇 |
1996年 | 1417篇 |
1995年 | 1356篇 |
1994年 | 1214篇 |
1993年 | 1192篇 |
1992年 | 1037篇 |
1991年 | 757篇 |
1990年 | 727篇 |
1989年 | 594篇 |
1988年 | 519篇 |
1987年 | 407篇 |
1986年 | 353篇 |
1985年 | 266篇 |
1984年 | 308篇 |
1983年 | 188篇 |
1982年 | 231篇 |
1981年 | 153篇 |
1980年 | 109篇 |
1979年 | 139篇 |
1978年 | 53篇 |
1977年 | 46篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
881.
Using benthic macrofauna to assess environmental quality of four intertidal mudflats in Hong Kong and Shenzhen Coast 总被引:4,自引:0,他引:4
Cai Lizhe Nora F. Y. Tam Teresa W. Y. Wong Ma Li Gao Yang Yuk-Shan Wong 《海洋学报(英文版)》2003,22(2):309-319
Abstract-Intertidal zone is a significant wetland between land and ocean. It plays an important rolein maintaining local ecological balance. Both Mai Po and Futian intertidal mudflats are located in Shen-zhen Bay and are important "refueling" point along the East Asian/Australian flyway of migratory birds.The environmental quality of Mai Po and Futian mudflats have aroused great concern due to rapid eco-nomic developments in Hong Kong and Shenzhen in recent decades. Microinfauna of Mai Po and Futianmudflats was investigated in December 2000 and the faunal data were used to assess their environmentalquality. Two other mudflats, namely Ma Wan Typhoon Shelter (a more disturbed area) and Luk Kengintertidal mudflat (a place with relatively less human disturbance), were also sampled for macroinfaunaand used as reference mudflats. Shannon-Weaver species diversity index (I_(sd)), biotic coefficient (C_b)and macrofaunal pollution index (I_(mp)) of the macrofauna community on four intertidal mudflats wereused to 相似文献
882.
883.
A time-domain method is applied to simulate nonlinear wave diffraction around a surface piercing 3-D arbitrary body. The method involves the application of Taylor series expansions and the use of perturbation procedure to establish the corresponding boundary value problems with respect to a time-independent fluid domain. A boundary element method based on B-spline expansion is used to calculate the wave field at each time step, and the free surface boundary condition is satisfied to the second order of wave steepness by a numerical integration in time. An artificial damping layer is adopted on the free surface for the removal of wave reflection from the outer boundary. As an illustration, the method is used to compute the second-order wave forces and run-up on a surface-piercing circular cylinder. The present method is found to be accurate, computationally efficient, and numerically stable. 相似文献
884.
Experimental Investigation of Instantaneous Properties of Wave Slamming on the Plate 总被引:1,自引:0,他引:1
The purpose of this paper is to investigate the instantaneous properties of wave slamming on the plate structure of an open structure.The advanced instantaneous measuring technique-Particle Image Velocimetry(PIV) is applied to acquire the instantaneous velocity field of wave slamming.From the cross-correlation analysis results of the images captured by the CCD camera,the flow fields of wave impacting on the structure are displayed visually,and the instantaneous whole-field fluid velocity vectors are obtained.The relation between the instantaneous peak impacting pressures and the instantaneous velocities of water particles is studied by probability analysis. 相似文献
885.
Under artificial LD cycles(6,12,18 L),the elvers of Japanese eel,Anguilla japonica,showed a 24 h cycle of locomotor activity rhythm being most active at light transitions:the eels' activity rose to a primary peak after lights-off,followed by a quiescent period during which they buried into the shelters or lying motionlessly on sand for most of the time,and then reached a secondary peak before lights-on.Elvers could resynchronize their activity rhythm with a new photo cycle within 4 d.Moreover,their activity level at dark phase significantly increased as the light period was prolonged:higher activity levels during shorter dark period.However,the elvers did not display clearly the existence of a circadian rhythm under constant light or dark conditions.The timing of daily activity rhythm evidenced in the Japanese eels may occur through the action of the LD cycles with a weak participation of an endogenous circadian system.In all the LD cycles,over 99% of the activity occurred in the dark phase,indicating that the eels were always nocturnally active no matter what time of day it might be.Under 12 L conditions,the eels' activity level and the time outside sand were significantly elevated both at light and dark phases as temperature increased from 10~15 to 20~25 ℃.The activity rhythm pattern(i.e.,two peaks occurring around light transitions) did not apparently change among temperatures.However,in contrast with the primary activity peaks immediately after lights-off at 20 and 25 ℃,the timing of the primary peaks at 10 and 15 ℃ showed a latency of a few hours following lights-off,indicating the inhibiting effect of low temperature on the eels' activity. 相似文献
886.
1 .IntroductionInthe whole service period of the platforms ,some damage is unavoidable due to the corrosion,impact ,fatigue and so on.The damage whould cause the structures’ultimate capacity and safety de-crease .Presently,it is generally acceptedthat the detection of damage involes considerable statisticaluncertainties,thus lot of efforts is made for the damage probalility model ,for example Song and Lu(1996) usedthefuzzy-settheoryto estimatethe humanerrorsthroughthe definitionof inspection… 相似文献
887.
不同水温对文昌鱼性腺发育的影响 总被引:10,自引:1,他引:10
研究表明,不同水温对文昌鱼性腺发育分化和成熟有十分显著的影响。14℃对文昌鱼性腺发育没有显著的作用,20和25℃十分有利于性腺发育和成熟,经40d培养,出现一些雌、雄文昌鱼产卵和释精以及加速性腺发育。本文还讨论了水温促进性腺发育可能的机制。 相似文献
888.
889.
Baseline of mercury in mangrove swamp The mercury content in sediments in the Jiulong Estuary was determined in 1984 and 1985(Table 1). The highest content of mercury in sediments (300×10~(-9)) was found in Ditou, contrast-ing strongly with the low content of 36×10~(-9) in Port Dongzhai in the Hainan Island. Tab1e 1 showsthat the average content of mercury in sediments in the Jiulong Estuary is 140×10~(-9) and the averageof four areas is 72×10~(-9). This value means that these areas have not been heavily contaminated by 相似文献
890.
为了能够精确地拟合天然水域不规则的水陆边界,并能保持有限差分数值计算在矩形网格中进行,本文利用Thompson的数值网格生成技术,在长江口南支七丫口至横沙河段设计了一个椭圆型边界拟合坐标系,并在这个坐标系下建立了平面二维潮流数学模型。通过数值求解此数学模型,实现了计算区域内现状潮流的一个数值模拟,模拟结果表明,模式的设计是成功的。 相似文献