全文获取类型
收费全文 | 37218篇 |
免费 | 5875篇 |
国内免费 | 8233篇 |
专业分类
测绘学 | 4936篇 |
大气科学 | 5597篇 |
地球物理 | 7669篇 |
地质学 | 15628篇 |
海洋学 | 4555篇 |
天文学 | 5333篇 |
综合类 | 2597篇 |
自然地理 | 5011篇 |
出版年
2024年 | 129篇 |
2023年 | 375篇 |
2022年 | 1089篇 |
2021年 | 1320篇 |
2020年 | 1541篇 |
2019年 | 1794篇 |
2018年 | 1457篇 |
2017年 | 1637篇 |
2016年 | 1744篇 |
2015年 | 1885篇 |
2014年 | 2273篇 |
2013年 | 2635篇 |
2012年 | 2392篇 |
2011年 | 2554篇 |
2010年 | 2229篇 |
2009年 | 2667篇 |
2008年 | 2644篇 |
2007年 | 2707篇 |
2006年 | 2543篇 |
2005年 | 2231篇 |
2004年 | 2000篇 |
2003年 | 1703篇 |
2002年 | 1472篇 |
2001年 | 1275篇 |
2000年 | 1148篇 |
1999年 | 1039篇 |
1998年 | 882篇 |
1997年 | 689篇 |
1996年 | 604篇 |
1995年 | 537篇 |
1994年 | 492篇 |
1993年 | 420篇 |
1992年 | 246篇 |
1991年 | 208篇 |
1990年 | 170篇 |
1989年 | 118篇 |
1988年 | 121篇 |
1987年 | 64篇 |
1986年 | 51篇 |
1985年 | 56篇 |
1984年 | 43篇 |
1983年 | 16篇 |
1982年 | 27篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 18篇 |
1976年 | 3篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
111.
112.
113.
114.
This paper considers the problem of estimatingm, the number of components in a finite mixture of distributions from a parametric family. A step-up procedure using the bootstrap method is proposed. Some properties of the procedure are illustrated with simulation studies. An example of the method, applied to orientation of beach clasts, is given. 相似文献
115.
116.
Yanjun ZHANG Fenglong ZHANG Full QI Fuquan NI 《东北亚地学研究》2006,9(2):199-203
In view of the situation of excavation of open coal mine for the underground water disaster,we should carry out simulation studies for the numerical value of the water lowering project and improve the accuracy and the level of the water lowering project.On the basis of the hydrological geological conditions of certain open mine digging,a more reasonable seepage numerical model was built according to MODFLOW.It was simulated in advance that the process of the confined water level descending with the time,and combining with the actual observations to test the correctness of the model.The calculation showed that the results coincided well with the results of actual measurement.Based on this,different water lowering numerical simulations were built for the open coal mine digging.It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit,and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process,which provide an important basis for the actual water lowering project and the possible project disposal. 相似文献
117.
笔者曾对广西芒场锡多金属矿田的稳定同位素进行研究。本文根据硫、铅、氢、氧、碳等稳定同位素组成和锶的初始值提供的信息.探讨了矿床成因。并结合矿田矿床地质特征、控矿条件及有关统计参数,参考前人对矿床认识的基础上,修正提出了该矿田混合热液成矿模式,可供类似矿床研究和找矿的参考。 相似文献
118.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1990,11(4):533-540
Photoelectric radial-velocity measurements show that HD 118670 is a double-lined spectroscopic binary in an orbit which is
not quite circular and whose period is about 48 days. Spectral types of K0 V and K7 V would satisfy the photometry and the
mass ratio; the mass function would then suggest the possibility of eclipses. However, actual spectral classification indicates
a luminosity somewhat above the main sequence 相似文献
119.
Simulation of double cold cores of the 35°N section in the Yellow Sea with a wave-tide-circulation coupled model 总被引:1,自引:0,他引:1
Based on the MASNUM wave-tide-circulation coupled numerical model, the temperature structure along 35°N in the Yellow Sea
was simulated and compared with the observations. One of the notable features of the temperature structure along 35°N section
is the double cold cores phenomena during spring and summer. The double cold cores refer to the two cold water centers located
near 122°E and 125°E from the depth of 30m to bottom. The formation, maintenance and disappearance of the double cold cores
are discussed. At least two reasons make the temperature in the center (near 123°E) of the section higher than that near the
west and east shores in winter. One reason is that the water there is deeper than the west and east sides so its heat content
is higher. The other is invasion of the warm water brought by the Yellow Sea Warm Current (YSWC) during winter. This temperature
pattern of the lower layer (from 30m to bottom) is maintained through spring and summer when the upper layer (0 to 30m) is
heated and strong thermocline is formed. Large zonal span of the 35°N section (about 600 km) makes the cold cores have more
opportunity to survive. The double cold cores phenomena disappears in early autumn when the west cold core vanishes first
with the dropping of the thermocline position.
Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No.
49736190). 相似文献
120.
Autotrophic biomass and productivity as well as nutrient distributions and phytoplankton cell populations in the James River estuary, Virginia, were quantified both spatially and temporally over a 17-month period. Emphasis was placed on the very low salinity region of the estuary in order to gain information on the fate of freshwater phytoplankters. Differing amounts of freshwater plant biomass are advected into the estuary as living material, DOC or POC and the demonstrated variability of this input must play an important role in marine biogeochemical cycling.Late summer and fall maxima in both chlorophyll a and the photosynthetic production of particulate organic carbon in very low salinity regions were inversely correlated with river discharge.During periods of low river discharge greater than 50% of the chlorophyll a biomass measured at 0‰ disappeared within a narrow range of salinity (0–2‰). Cell enumeration data suggest that species introduced from the freshwater end-member tend to comprise the bulk of the biomass removed. Confounding factors, which may contribute to the regulation of both the abundance and species of phytoplankters mid-river, include the flocculation of colloidal material with phytoplankton cells, the presence of the turbidity maximum and the growth of endemic phytoplankton populations.An inverse relationship exists between the phytoplankton abundance in very low salinity waters and the abundance of biomass measured in the lower portion of the river (estuary). Thus, autotrophic production in the fresh and very low salinity areas may indirectly regulate the onset on the spring bloom in the estuary by controlling the amount of nutrients available. 相似文献