全文获取类型
收费全文 | 50157篇 |
免费 | 8555篇 |
国内免费 | 13852篇 |
专业分类
测绘学 | 4357篇 |
大气科学 | 5336篇 |
地球物理 | 9901篇 |
地质学 | 33953篇 |
海洋学 | 5467篇 |
天文学 | 2643篇 |
综合类 | 3386篇 |
自然地理 | 7521篇 |
出版年
2024年 | 287篇 |
2023年 | 801篇 |
2022年 | 1564篇 |
2021年 | 1787篇 |
2020年 | 1891篇 |
2019年 | 2162篇 |
2018年 | 1780篇 |
2017年 | 2021篇 |
2016年 | 2260篇 |
2015年 | 2436篇 |
2014年 | 2894篇 |
2013年 | 2777篇 |
2012年 | 3170篇 |
2011年 | 3280篇 |
2010年 | 2798篇 |
2009年 | 3277篇 |
2008年 | 3210篇 |
2007年 | 3556篇 |
2006年 | 3421篇 |
2005年 | 3027篇 |
2004年 | 2816篇 |
2003年 | 2698篇 |
2002年 | 2388篇 |
2001年 | 2089篇 |
2000年 | 1929篇 |
1999年 | 1787篇 |
1998年 | 1548篇 |
1997年 | 1399篇 |
1996年 | 1278篇 |
1995年 | 1080篇 |
1994年 | 1124篇 |
1993年 | 936篇 |
1992年 | 748篇 |
1991年 | 531篇 |
1990年 | 477篇 |
1989年 | 379篇 |
1988年 | 292篇 |
1987年 | 188篇 |
1986年 | 121篇 |
1985年 | 85篇 |
1984年 | 37篇 |
1983年 | 30篇 |
1982年 | 33篇 |
1981年 | 22篇 |
1980年 | 27篇 |
1979年 | 29篇 |
1978年 | 37篇 |
1977年 | 24篇 |
1975年 | 4篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
232.
南黄海表层沉积物天然湿容重和含水量的分布及其与粒度之间的关系 总被引:2,自引:0,他引:2
本文论述了南黄海表层沉积物天然湿容重和含水量的分布,并利用回归分析的方法讨论了容重和含水量与粒度之间的关系。结果表明,容重和含水量与粘土粒级相关性最好,容重与粘土粒级含量(相似文献
233.
本文根据有机地球化学资料,首次研究和探讨了珠江三角洲晚第四纪沉积物中有机质丰度和可溶有机质的组成特征。现代沉积物有机质丰度,有机碳为0.58%,氯仿沥青“A”为210ppm,烃含量为33.8ppm;钻孔中有机碳为0.77%,氯仿沥青“A”为253ppm,烃含量为16.4ppm。从有机质组成、红外吸收光谱特征、δ~(13)C、干酪根H/C原子比,均表现为陆生植物为主,水生生物为铺,为腐殖型或腐泥—腐殖型的母质类型。 相似文献
234.
本文提出了一种地震折射液的虚拟射线理论,根据该理论,只要已知地表层的速度,即可直接由折射波信息提取地震参数,从而可实现折射界面的反演。 文中通过实际介质模型的计算机实验结果,验证了该理论的正确性。 相似文献
235.
In this study, we investigate two internal wave generation methods in numerical modeling of time-dependent equations for water wave propagation, i.e., delta source function method and source term addition method, the latter of which has been called the line source method in literatures. We derive delta source functions for the Boussinesq-type equations and extended mild-slope equations. By applying the fractional step splitting method, we show that the delta source function method is equivalent to the source term addition method employing the energy velocity. This suggests that the energy velocity should be used rather than the phase velocity for the transport of incident wave energy in the source term addition method. Finally, the performance of the delta source function method is verified by accurately generating nonlinear cnoidal waves as well as linear waves for horizontally one-dimensional cases. 相似文献
236.
A.F. Velegrakis M.I. VousdoukasA.M. Vagenas Th. KarambasK. Dimou Th. Zarkadas 《Coastal Engineering》2007
This short contribution reports the results of a field study on the nearshore characteristics of waves generated by both conventional and high speed passenger ferries. The field observations took place in the late summer of 2005, at a beach close to the port of Mytilene (Island of Lesbos, Greece), and involved the visual observation of ship waves, using digital video recordings and image processing techniques. The results showed that passage of the fast ferry was associated with a longer, more complex and energetic nearshore event; this event not only did include higher nearshore waves (up to 0.74 m) and was organised in different wave packets, but it was also an order of magnitude longer (∼ 680 s) than the conventional ferry event. Regarding the effects on beach sediment dynamics, the fast ferry waves were estimated to be very efficient in mobilising the nearshore sediments in contrast to those of the conventional ferry. The fast ferry service appears to generate daily prolonged nearshore events, which contain waves with higher energy than those expected from the normal summer wind wave regime of the area; these events also include some high and very steep waves, which can be particularly erosive. Therefore, fast ferry wakes may have considerable impacts on the seasonal beach sediment dynamics/morphodynamics and the nearshore benthic ecology, as well as they may pose significant risks to bathers, affecting the recreational use of the beaches exposed to fast ferry traffic. Finally, the study has shown that satisfactory field observations of the nearshore characteristics of ship-generated (and wind) waves can be obtained using inshore deployments of calibrated poles, digital video cameras and appropriate image processing algorithms. 相似文献
237.
238.
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
239.
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
240.