全文获取类型
收费全文 | 17302篇 |
免费 | 3466篇 |
国内免费 | 4656篇 |
专业分类
测绘学 | 1642篇 |
大气科学 | 3451篇 |
地球物理 | 4487篇 |
地质学 | 8525篇 |
海洋学 | 2923篇 |
天文学 | 593篇 |
综合类 | 1701篇 |
自然地理 | 2102篇 |
出版年
2024年 | 134篇 |
2023年 | 443篇 |
2022年 | 906篇 |
2021年 | 1145篇 |
2020年 | 899篇 |
2019年 | 957篇 |
2018年 | 1026篇 |
2017年 | 921篇 |
2016年 | 1063篇 |
2015年 | 946篇 |
2014年 | 1080篇 |
2013年 | 1170篇 |
2012年 | 1058篇 |
2011年 | 1132篇 |
2010年 | 1121篇 |
2009年 | 1046篇 |
2008年 | 931篇 |
2007年 | 911篇 |
2006年 | 781篇 |
2005年 | 718篇 |
2004年 | 534篇 |
2003年 | 451篇 |
2002年 | 491篇 |
2001年 | 528篇 |
2000年 | 479篇 |
1999年 | 629篇 |
1998年 | 526篇 |
1997年 | 505篇 |
1996年 | 478篇 |
1995年 | 374篇 |
1994年 | 356篇 |
1993年 | 336篇 |
1992年 | 275篇 |
1991年 | 225篇 |
1990年 | 182篇 |
1989年 | 155篇 |
1988年 | 130篇 |
1987年 | 62篇 |
1986年 | 75篇 |
1985年 | 46篇 |
1984年 | 38篇 |
1983年 | 21篇 |
1982年 | 39篇 |
1981年 | 13篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1962年 | 5篇 |
1958年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
作者运用三维T.Kohonen自组织人工神经网络对我国沉积碳酸盐型锰矿中菱锰矿进行分类、识别。所选研究实例中,识别成功率达100%.结果表明,该网络性能良好,可望成为矿物识别的有效手段。 相似文献
82.
Retrograde metamorphism played the dominant role in changing the low-field rock magnetic properties and density of 198 specimens of variably retrograded eclogites from the main borehole of the Chinese Continental Scientific Drilling Project (CCSD) and from surface outcrops in the Donghai area in the southern part of the Sulu UHP belt, China. Bulk magnetic susceptibility (κ) of unretrogressed UHP eclogite is controlled by whole-rock chemical composition and ranges from 397 to 2312 μSI with principal magnetic susceptibility carrying minerals paramagnetic garnet, omphacite, rutile and phengite. Partially retrograded eclogites show large variations in magnetic susceptibility between 804 and 24,277 μSI, with high mean magnetic susceptibility values of 4372 ± 4149 μSI caused by appreciable amounts of Fe-Ti oxide minerals such as magnetite, ilmenite and/or titanohematite produced by retrograde metamorphic reactions. Completely retrograded eclogites have lower susceptibilities of 1094 ± 600 μSI and amphibolite facies mineral assemblages lacking high magnetic susceptibility minerals. Jelínek's corrected anisotropy (Pj) of eclogites ranges from 1.001 to 1.540, and shows a positive correlation with low-field magnetic susceptibility (κ). Arithmetic mean bulk density (ρ) shows a steady decrease from 3.54 ± 0.11 g/cm3 (fresh eclogite) to 2.98 ± 0.06 g/cm3 (completely retrograded eclogite). Retrograde metamorphic changes in mineral composition during exhumation appear to be the major factor causing variations in low field magnetic susceptibility and anisotropy. Retrograde processes must be taken into account when interpreting magnetic surveys and geophysical well logs in UHP metamorphic terranes, and petrophysical properties such as density and low-field magnetic susceptibility could provide a means for semi-quantifying the degree of retrogression of eclogite during exhumation. 相似文献
83.
The low-grade vanadium-containing stone coal used in this experiment was collected from Wuxi Coun- try, Chongqing City, China. The experiment focused on the vanadium recovery from roasted residue through opti- mizing the process conditions of an effective and environmentally-friendly technology, named calcified roast- ing-sulfuric acid leaching technology. By single-factor experiments and orthogonal experiments, the effects of roast- ing temperature, roasting time, sulfuric acid concentration and leaching time on the leaching ratio of vanadium were analyzed. The results showed that the leaching ratio of vanadium reached 85.5% under the proper technological con- ditions of roasting temperature=950℃, roasting time=4 h, 40% concentration of sulfuric acid and leaching time=6 h. 相似文献
84.
Despite a recent increase in the number of vulnerability analyses there has been relatively little discussion of vulnerability
assessment of social–environment system, especially when they face multiple hazards. In this study, we developed an applicable
and convenient method to assess vulnerability of social–environment system at a regional scale. Vulnerability is quantified
by measuring three critical elements (i.e. hazards, sensitivity, and resilience) through some key variables. The results showed
that vulnerability is high in Miaofeng Mountain in Mengtougou District, the hills of Pinggu County and the riparian zones
of the lower courses of the Beiyun and Yongding Rivers; but low in the city of Beijing and the southwestern part of the Fangshan
District. Areas of very high, high, medium, and low-vulnerability account for 6.19, 25.48, 33.06, and 35.27% of the total
area, respectively. The degree of vulnerability decreases in a northwest direction in mountainous areas and declines from
watercourses to riparian zones along a lateral direction in the plain. Some adaptive strategies are also proposed. 相似文献
85.
“云南麻栗坡地区矿产远景调查”及与之匹配的“越北古陆北缘地质构造演化及其成矿效应研究”中,经实测剖面和填图扫面,以“岩石地层单位填图”的要义比照,测区晚寒武世及相涉延及早奥陶世早期的岩石地层单位序列宜为:唐家坝组\“大老堡组”\博菜田组。其中,“大老堡组”为新拟建增设单位,也导致相关临叠地层单位现在定义和分割界面的更新。介绍唐家坝组\“大老堡组”界线层型及其层型界面所反映的沉积环境转换面属性,上、下邻叠岩层联合构成的标志层组合,是融地层学、沉积学为一体“’的优化挟择。 相似文献
86.
近45年雅鲁藏布江流域极端气候事件趋势分析 总被引:21,自引:2,他引:21
利用雅鲁藏布江流域10个气象台站1961-2005年逐日最高气温、最低气温和日降水量资料,分析了该流域气温和降水等气候极端事件的变化趋势.研究表明:近45年以来,雅鲁藏布江流域夜间和白天极端低温日数分别以1.94和0.97天/10年的趋势在显著减少,夜间极端低温日数减少在冬季最明显,白天极端低温日数在秋季减少最明显:夜间极端高温日数和白天极端高温日数分别以3.03和1.26天/10年的速度显著增加,夜间极端高温日数增加在夏季最明显,白天极端高温日数增加在冬季最明显;日较差以0.11℃/10a的速度在显著减少,主要发生在冬季:最大的1天降水总量和逐年连续无降水天数有减少趋势,最大的5天降水总量、中雨天数、逐年平均降水强度和逐年连续降水天数有增加趋势,90年代以来增加趋势明显,与该地区经向风与水汽通量增加有关. 相似文献
87.
基于CMIP5多模式集合资料的中国气温和降水预估及概率分析 总被引:3,自引:1,他引:3
选用国际耦合模式比较计划第五阶段(CMIP5)提供的30个全球大气-海洋耦合模式(AOGCMs)在典型浓度路径(RCPs)情景下气温和降水量的预估结果,采用扰动法,用站点观测资料作为气候背景场替代AOGCM模拟的气候平均,尝试校正气候预估结果的系统性偏差。通过集合方法,用概率的形式给出中国平均气温升高1 ℃,2 ℃和3 ℃以及降水量增加10%,20%和30%概率的空间分布,讨论了中国未来平均气温和降水量可能的变化。结果表明:经过扰动法处理后的气温和降水量预估集合保留了当前气候的局地信息。预估平均气温在中国均有上升,北方地区尤其是青藏高原地区变暖的程度大于南方地区,北方大部分地区平均气温升高的趋势为0.28 ℃/10a。在21世纪初,中国北方地区年平均气温升高1 ℃的可能性超过50%。到了21世纪末期,中国大部分地区平均气温升高2 ℃的可能性超过60%,新疆北部以及青藏高原南部地区气温升高3 ℃的可能性超过50%。预估中国降水量普遍增多,中国北方地区降水量增多的程度要明显大于江淮流域及其以南地区,尤其是西北地区降水量增多非常显著,降水量增多30%的可能性超过70%以上。 相似文献
88.
Relationships between Interannual and Intraseasonal Variations of the Asian-Western Pacific Summer Monsoon Hindcasted by BCC_CSM1.1(m) 总被引:4,自引:0,他引:4
LIU Xiangwen ;WU Tongwen ;YANG Song ;LI Qiaoping ;CHENG Yanjie ;LIANG Xiaoyun ;FANG Yongjie ;JIE Weihua ;NIE Suping 《大气科学进展》2014,31(5):1051-1064
Using hindcasts of the Beijing Climate Center Climate System Model, the relationships between interannual variability (IAV) and intraseasonal variability (ISV) of the Asian-western Pacific summer monsoon are diagnosed. Predictions show reasonable skill with respect to some basic characteristics of the ISV and IAV of the western North Pacific summer monsoon (WNPSM) and the Indian summer monsoon (ISM). However, the links between the seasonally averaged ISV (SAISV) and seasonal mean of ISM are overestimated by the model. This deficiency may be partially attributable to the overestimated frequency of long breaks and underestimated frequency of long active spells of ISV in normal ISM years, although the model is capable of capturing the impact of ISV on the seasonal mean by its shift in the probability of phases. Furthermore, the interannual relationships of seasonal mean, SAISV, and seasonally averaged long-wave variability (SALWV; i.e., the part with periods longer than the intraseasonal scale) of the WNPSM and ISM with SST and low-level circulation are examined. The observed seasonal mean, SAISV, and SALWV show similar correlation patterns with SST and atmospheric circulation, but with different details. However, the model presents these correlation distributions with unrealistically small differences among different scales, and it somewhat overestimates the teleconnection between monsoon and tropical central-eastern Pacific SST for the ISM, but underestimates it for the WNPSM, the latter of which is partially related to the too-rapid decrease in the impact of E1 Nifio-Southern Oscillation with forecast time in the model. 相似文献
89.
Vanadium-bearing stone coal is a new vanadium resource;recovery ofV_2O_5 from the coal has been investigated.It has been found that a satisfactoryextraction of V_2O_5 depends on both the oxidation of V and its reaction with so-dium salt.V in the coal ash of Yushan mainly exists in two oxidation states:98%V(Ⅲ)and2%V(Ⅳ).The distribution of valency of V shows that organicmatter determines V valency at low temperatures,at about470℃,V(Ⅲ)iscompletely oxidized to V(Ⅳ);above500℃,the temperature is the most impor-tant factor for the oxidation of V .At higher temperatures no more V is oxidizedto V(Ⅴ);an equilibrium is established after92%of V is oxidized to V(Ⅴ).The roles of NaCl in the recovery of V_2O_5 from the coal ash were discussed.The best conditions for roasting are temperature750-800℃for1 h.underthe oxidation-chlorination atmosphere.When the ore:NaCl=100:10 by weight,η_roast reaches85.5%.According to the results,a flowsheet for V_2O_5 extrac-tion from coal ash has been proposed. 相似文献
90.
且干布拉克蛭石的矿物学研究 总被引:4,自引:2,他引:4
本文对产于新疆且干布拉克的我国最大蛭石矿的组成、结构和谱学特征做了系统的阐述。研究表明:且干布拉克蛭石是由金云母风化而成。由于风化的不完全,该蛭石保留了许多金云母的特征。该蛭石不是个严格矿物学意义上的蛭石,它是由金云母、严格矿物学意义上的蛭石、以及两者组成的多种混层矿物的混合物。金云母风化过程中可能有杂质铁相生成。蛭石的颜色和多色性,可能起因于其中的O~(2-)→Fe~(2+23+)和Fe~(2+)→Fe~(3+) 相似文献