全文获取类型
收费全文 | 2425篇 |
免费 | 486篇 |
国内免费 | 582篇 |
专业分类
测绘学 | 185篇 |
大气科学 | 448篇 |
地球物理 | 667篇 |
地质学 | 1283篇 |
海洋学 | 319篇 |
天文学 | 84篇 |
综合类 | 240篇 |
自然地理 | 267篇 |
出版年
2024年 | 20篇 |
2023年 | 68篇 |
2022年 | 134篇 |
2021年 | 161篇 |
2020年 | 104篇 |
2019年 | 120篇 |
2018年 | 156篇 |
2017年 | 126篇 |
2016年 | 147篇 |
2015年 | 133篇 |
2014年 | 134篇 |
2013年 | 148篇 |
2012年 | 131篇 |
2011年 | 145篇 |
2010年 | 149篇 |
2009年 | 127篇 |
2008年 | 101篇 |
2007年 | 113篇 |
2006年 | 70篇 |
2005年 | 82篇 |
2004年 | 59篇 |
2003年 | 59篇 |
2002年 | 59篇 |
2001年 | 64篇 |
2000年 | 85篇 |
1999年 | 123篇 |
1998年 | 72篇 |
1997年 | 108篇 |
1996年 | 86篇 |
1995年 | 55篇 |
1994年 | 58篇 |
1993年 | 78篇 |
1992年 | 50篇 |
1991年 | 42篇 |
1990年 | 24篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1973年 | 2篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有3493条查询结果,搜索用时 31 毫秒
991.
湖北江陵凹陷深层高温富钾卤水特征及其成因探讨 总被引:4,自引:0,他引:4
江汉盆地江陵凹陷深处赋存高温富钾卤水,含卤地层主要是古新统沙市组。富钾卤水的分布受持续的继承性沉降中心(洼陷)、沙市组含盐系、石盐-硫酸盐沉积相的控制,聚集在砂岩、玄武岩、辉绿岩和白云岩等孔隙-裂隙内,裂隙的发育又与局部构造(背斜、盐构造等)枢纽部共轭裂隙带有关。古新世,盐湖已经蒸发浓缩到钙芒硝-石盐阶段,可能短暂达到硫酸镁盐和硫酸钾镁盐阶段。以后,原生的晶间卤水在成岩后期受到玄武岩侵入和高温流体影响,发生变质作用、去镁和去硫酸根作用,同时带入丰富的钾、铷、铯等元素,最后形成了高温富钾卤水。这种成矿过程可称为地下热事件激发成矿机制,值得进一步探讨。 相似文献
992.
993.
To understand the electrical structure of the Sulu(苏鲁) terrane,we analyzed the resis-tivity logs of the Chinese Continental Scientific Drilling main hole(CCSD-MH) and obtained the statis-tical characteristics of the resistivity log of ultrahigh-pressure(UHP) metamorphic rocks.To check the logs' quality,we compared the resistivity log data with the core test data.The two datasets show a good coherence.On the whole,the resistivity of the UHP metamorphic rocks from the CCSD-MH is very high(mostly higher than 1... 相似文献
994.
Many tropical cnidarians, including anemones and corals, contain symbiotic dinoflagellates known as zooxanthellae. Photosynthesis by symbiotic dinoflagellates benefits the animal host and the proficiency of host metabolism also plays an important role in the nutrient status of the photosynthetic dinoflagellates. We aimed to determine the responses of symbiotic dinoflagellates to host starvation. The ultrastructure and some physiological indicators of symbiotic dinoflagellates (Symbiodinium sp., zooxanthellae) were examined in starved sea anemones (Stichodactyla mertensii; 3‐, 45‐ and 280‐day starvation). The cell size of zooxanthellae was not affected by starving the host; however, the ultrastructure and other physiological indicators of the zooxanthellae were affected. The photochemical efficiency of symbiotic dinoflagellates from anemones after 280 days of starvation was significantly (P < 0.01) higher than that of symbiotic dinoflagellates from anemones after 3‐ and 45‐day starvation. The number of symbiotic dinoflagellates from anemones decreased with increasing starvation duration. Generally, the chlorophyll a and c content of symbiotic dinoflagellates decreased significantly with longer anemone starvation. The tentacles of 3‐day starved anemones contained the most zooxanthellae, some of which were dividing and still enclosed within one periplast, and some had split entirely within one host vacuole. Moreover, each cell from 3‐day starved anemone contained up to five or six more mitochondria than those from 45‐ to 280‐day starved anemones. More lipid granules appeared in the zooxanthellae from 45‐ to 280‐day starved anemones. Pyrenoids, lobed accumulation bodies and calcium oxalate crystals existed in the symbiotic dinoflagellates from anemones at different starvation stages, which suggested that their existence had no correlation with host starvation. These findings contribute to an improved mechanistic understanding of the symbiotic relationship between zooxanthellae and anemones. 相似文献
995.
A gene(NANOC-D6D) encoding a desaturase that removes two hydrogen atoms from fatty acids at delta 6 position was isolated from a cDNA library of Nannochloropsis oculata(Droop) D.J.Hibberd(Eustigmatophyceae).The unicellular marine microalga N.oculata synthesizes rich long chain polyunsaturated fatty acids(LCPUFAs),including eicosapentaenoic acid(20:5n-3,EPA).The deduced protein contains 474 amino acids that fold into 4 trans-membrane domains.The neighbor-joining phylogenetic tree indicates that NANOC-D6D is ... 相似文献
996.
充电开关组件是发射机回扫充电电路关键组件,通过充电变压器完成对人工线的充电,它直接决定了人工线高压的稳定性和准确性,是影响发射机输出功率大小和稳定的关键因素之一。根据改进后开关组件线路图,总结出充电开关组件主通道、充电控制信号、故障监控信号流程和与此相关的故障树图。在此基础上,依据实际测试的发射机充电开关组件关键点波形或电平,研究出规范化的充电开关组件芯片级故障诊断流程,列举了依据充电开关组件芯片级故障诊断流程,解决了充电开关组件主通道充电赋能驱动电路芯片损坏导致无充电脉冲信号,引起无人工线高压和发射机输出功率故障,以及修复充电控制电路的充电电流传感器故障导致人工线电压过高,发射机束流报警。充电开关组件故障维修效果表明:充电开关组件芯片级故障诊断流程可以快速定位充电开关组件故障点到芯片,方法简洁,操作规范,雷达技术保障人员容易掌握,能满足国家级、省级雷达测试维修平台和雷达站器件(芯片)级维修需求,为发射机人工智能故障诊断提供借鉴,可有效缩短雷达故障维修时间,提高雷达业务运行可用性指标。 相似文献
997.
998.
999.
红色文化产业集群化发展是全球文化产业发展到一定阶段的客观趋势,是当前经济文化一体化浪潮的必然结果。本文在对河北省红色文化产业发展的条件和存在问题进行分析之后,提出了河北省红色文化产业集群建设的总体思路和发展模式,以期推动河北省红色文化产业的发展。 相似文献
1000.
The research of coupling WRF (Weather Research and Forecasting Model) with a land surface model is enhanced to explore the
interaction of the atmosphere and land surface; however, regional applicability of WRF model is questioned. In order to do the
validation of WRF model on simulating forcing data for the Heihe River Basin, daily meteorological observation data from 15 stations
of CMA (China Meteorological Administration) and hourly meteorological observation data from seven sites of WATER
(Watershed Airborne Telemetry Experimental Research) are used to compare with WRF simulations, with a time range of a whole
year for 2008. Results show that the average MBE (Mean Bias Error) of daily 2-m surface temperature, surface pressure, 2-m relative
humidity and 10-m wind speed were ?0.19 °C, ?4.49 hPa, 4.08% and 0.92 m/s, the average RMSE (Root Mean Square Error)
of them were 2.11 °C, 5.37 hPa, 9.55% and 1.73 m/s, and the average R (correlation coefficient) of them were 0.99, 0.98, 0.80 and
0.55, respectively. The average MBE of hourly 2-m surface temperature, surface pressure, 2-m relative humidity, 10-m wind speed,
downward shortwave radiation and downward longwave were ?0.16 °C, ?6.62 hPa, ?5.14%, 0.26 m/s, 33.0 W/m2 and ?6.44
W/m2, the average RMSE of them were 2.62 °C, 17.10 hPa, 20.71%, 2.46 m/s, 152.9 W/m2 and 53.5 W/m2, and the average R of
them were 0.96, 0.97, 0.70, 0.26, 0.91 and 0.60, respectively. Thus, the following conclusions were obtained: (1) regardless of
daily or hourly validation, WRF model simulations of 2-m surface temperature, surface pressure and relative humidity are more
reliable, especially for 2-m surface air temperature and surface pressure, the values of MBE were small and R were more than 0.96;
(2) the WRF simulating downward shortwave radiation was relatively good, the average R between WRF simulation and hourly
observation data was above 0.9, and the average R of downward longwave radiation was 0.6; (3) both wind speed and rainfall
simulated from WRF model did not agree well with observation data. 相似文献