全文获取类型
收费全文 | 79250篇 |
免费 | 14160篇 |
国内免费 | 15744篇 |
专业分类
测绘学 | 9837篇 |
大气科学 | 8766篇 |
地球物理 | 21999篇 |
地质学 | 39194篇 |
海洋学 | 8423篇 |
天文学 | 2997篇 |
综合类 | 6187篇 |
自然地理 | 11751篇 |
出版年
2024年 | 283篇 |
2023年 | 782篇 |
2022年 | 2154篇 |
2021年 | 2663篇 |
2020年 | 2672篇 |
2019年 | 3292篇 |
2018年 | 2578篇 |
2017年 | 3166篇 |
2016年 | 3166篇 |
2015年 | 3564篇 |
2014年 | 4364篇 |
2013年 | 4547篇 |
2012年 | 4823篇 |
2011年 | 5070篇 |
2010年 | 4406篇 |
2009年 | 5183篇 |
2008年 | 5011篇 |
2007年 | 5496篇 |
2006年 | 5365篇 |
2005年 | 4724篇 |
2004年 | 4347篇 |
2003年 | 3994篇 |
2002年 | 3504篇 |
2001年 | 3199篇 |
2000年 | 2884篇 |
1999年 | 2644篇 |
1998年 | 2352篇 |
1997年 | 2150篇 |
1996年 | 1941篇 |
1995年 | 1650篇 |
1994年 | 1619篇 |
1993年 | 1335篇 |
1992年 | 1079篇 |
1991年 | 729篇 |
1990年 | 625篇 |
1989年 | 497篇 |
1988年 | 383篇 |
1987年 | 227篇 |
1986年 | 173篇 |
1985年 | 115篇 |
1984年 | 57篇 |
1983年 | 54篇 |
1982年 | 46篇 |
1981年 | 31篇 |
1980年 | 33篇 |
1979年 | 45篇 |
1978年 | 53篇 |
1977年 | 35篇 |
1975年 | 4篇 |
1954年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
311.
研究了2003年10月采于珠江口5个站位的沉积物剖面酸挥发性硫化物(AVS)和同时提取的重金属(SEM:Pb,Zn,Cu,Cd,Ni)。其中,站位1、2位于中滩,其沉积物的AVS含量变化范围较小,为0.25—4.06μmol.g-1;站位3、4位于西滩,其沉积物的AVS含量变化范围较大,为0—26.09μmol.g-1。中滩和西滩沉积物的AVS含量均随深度增加。西滩表层沉积物的AVS含量接近于零,这可能与该水域较强的底层流和沉积物的再悬浮作用有关。站位5位于珠江口外侧,其表层沉积物的AVS含量相对较高,且垂向变化较小,可能是还原性沉积物间歇性再悬浮后重新沉积的结果。站位1、2和5沉积物中同时提取的重金属含量大体在0.95±0.2μmol.g-1范围内,随深度增加略呈下降趋势;而西滩沉积物重金属含量相对较高,为1.43—2.42μmol.g-1,且在一定深度范围内随深度增加呈明显下降的趋势,表明珠江口西滩沉积物中的重金属污染有加重的趋势。对AVS/SEM摩尔比值和单个金属的毒性效应研究显示,珠江口内尤其是西滩的表层沉积物存在重金属污染,对其中生活的底栖生物具有潜在的毒性效应。 相似文献
312.
This study is devoted to oceanographic features of the semi-enclosed Gulf of Aqaba, Red Sea. The data were recorded in winter—spring
1999 on the R/V Meteor cruise leg 44/2. Temperature and salinity profiles were measured at six positions (I—VI). The shipboard
NarrowBand Acoustic Doppler Current Profiler (NB ADCP) 150 kHz continuously recorded current profiles down to 350 m en route.
The research revealed that the current near the Strait of Tiran front (position VI) represents a semidiurnal signal of an
internal tide wave (∼12 h period; 0.2 ms−1 amplitude) that might be generated by the barotropic tide at the sill of the Strait. A sequence of cyclonic and anticyclonic
eddy pairs is found along the axis of the Gulf of Aqaba during winter-spring seasons. These sub-mesoscale signals are dominant
above the main thermocline and might be caused by wind forcing and the narrowness of the Gulf; it might remain in other seasons
with different dimensions in relation to the depth of thermocline. The total diameter of each pair was twice the baroclinic
Rossby radius (R ≈ 10 km). A single anti-cyclonic eddy was observed in the upper 300 m in the northern tip of the Gulf with a diameter of
about 5–8 km. 相似文献
313.
We develop techniques of numerical wave generation in the time-dependent extended mild-slope equations of Suh et al. [1997. Time-dependent equations for wave propagation on rapidly varying topography. Coastal Engineering 32, 91–117] and Lee et al. [2003. Extended mild-slope equation for random waves. Coastal Engineering 48, 277–287] for random waves using a source function method. Numerical results for both regular and irregular waves in one and two horizontal dimensions show that the wave heights and the frequency spectra are properly reproduced. The waves that pass through the wave generation region do not cause any numerical disturbances, showing usefulness of the source function method in avoiding re-reflection problems at the offshore boundary. 相似文献
314.
315.
316.
考虑到平台所在海区台风出现的频次及其诱发之风、浪、潮、流极端海况联合出现的概率特性,本文推导出Poisson—Logistic二元复合极值模式,并以平台甲板标高进行实例计算。新模式增加了概率模型的物理内涵,解决了Logistic模型阈值选取的任意性。对海洋工程极端海况荷载组合预测具有广泛的应用前景。 相似文献
317.
我国的渤海和黄海北部在每年冬季都出现不同程度的冰情,它直接影响结冰海区的石油平台、船舶以及港口等设施的正常作业,对海冰的观测与预报随着上述海区的开发利用越发显得重要,利用航海雷达连续准确地跟踪海冰漂移运动轨迹,是当今观测、调查、研究冰漂流移动规律的有效方法之一,我国的科研人员利用雷达成像技术对渤海的冰情进行了长期的雷达海冰观测、研究,在由雷达海冰图像对海冰的物理特征的识别、分类以及冰漂流场测量方面取得了一些进展[1-4]。 相似文献
318.
A three-dimensional fixed offshore platform in deep water modeled by the finite element method is studied in this paper. Analysis of the dynamic response of the MDOF structure is realized taking the non-linearity of the wave drag force and the wave-structure interaction into account. The structural response statistics, which have Gaussian distributions, are used to evaluate the vibration effect of the structure without TMD and with TMD. And an optimal method to design TMD controlling the first mode of the multi-mode structure is proposed. Moreover, the probabilities of occurrence of sea states at the platform site are considered for prediction of the long-term effect of a TMD. Simulation results demonstrate that the long-term effect of a well-designed TMD is good and the practical use is possible due to the good stability of its optimal parameters under different sea states. 相似文献
319.
320.
P Thoya S Pérez-Jorge GM Okemwa H Mwamlavya A Tuda N Wambiji 《African Journal of Marine Science》2020,42(1):23-33
Ringnet fishing began in the early 20th century and is practised worldwide, mainly to target nearshore pelagic species. The method was introduced to Kenya’s coastal waters by migrant fishers from Tanzania. However, the impacts of this fishing gear remain poorly assessed. We assessed the spatial distribution of ringnet fishing effort and its possible effects on ecosystem components, such as coral reefs, marine megafauna and marine protected areas, on the south coast of Kenya. We tracked 89 ringnet fishing trips made from December 2015 to January 2016 and used spatial multicriteria analysis to determine hotspots of possible environmental risks. The results showed that habitat type and bathymetric profile influenced the spatial distribution of ringnet fishing effort. Mixed seagrass and coral habitats had the highest concentration of the effort. Most of the habitats in the study area were moderately exposed to the impacts of the ringnet fishery. The study identifies high-risk areas that require spatial measures to minimise possible environmental risks of the gear both to habitats and to endangered sea turtles. 相似文献