全文获取类型
收费全文 | 2962篇 |
免费 | 526篇 |
国内免费 | 766篇 |
专业分类
测绘学 | 211篇 |
大气科学 | 517篇 |
地球物理 | 694篇 |
地质学 | 1681篇 |
海洋学 | 401篇 |
天文学 | 164篇 |
综合类 | 219篇 |
自然地理 | 367篇 |
出版年
2024年 | 20篇 |
2023年 | 63篇 |
2022年 | 171篇 |
2021年 | 163篇 |
2020年 | 149篇 |
2019年 | 208篇 |
2018年 | 178篇 |
2017年 | 159篇 |
2016年 | 165篇 |
2015年 | 157篇 |
2014年 | 175篇 |
2013年 | 239篇 |
2012年 | 194篇 |
2011年 | 174篇 |
2010年 | 166篇 |
2009年 | 172篇 |
2008年 | 137篇 |
2007年 | 142篇 |
2006年 | 124篇 |
2005年 | 89篇 |
2004年 | 66篇 |
2003年 | 71篇 |
2002年 | 84篇 |
2001年 | 87篇 |
2000年 | 90篇 |
1999年 | 103篇 |
1998年 | 103篇 |
1997年 | 82篇 |
1996年 | 83篇 |
1995年 | 69篇 |
1994年 | 54篇 |
1993年 | 56篇 |
1992年 | 56篇 |
1991年 | 36篇 |
1990年 | 37篇 |
1989年 | 27篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有4254条查询结果,搜索用时 9 毫秒
51.
珍珠陶石的夹层化合物法鉴定 总被引:1,自引:0,他引:1
应用联氨、使珍珠陶石形成其夹层物,然后再用水洗获是水合珍珠陶石,这种水合珍珠陶石具有十分特征的0.835nmX射线衍射峰,而高岭石族的其它矿物却保持不变,利用这一明显的特征,可以容易地区分出混合在高岭石中的少量珍珠陶石。 相似文献
52.
Ultrahigh-pressure metamorphism in the forbidden zone: the Xugou garnet peridotite, Sulu terrane, eastern China 总被引:21,自引:3,他引:21
The Xugou garnet peridotite body of the southern Sulu ultrahigh‐pressure (UHP) terrane is enclosed in felsic gneiss, bounded by faults, and consists of harzburgite and lenses of garnet clinopyroxenite and eclogite. The peridotite is composed of variable amounts of olivine (Fo91), enstatite (En92?93), garnet (Alm20?23Prp53?58Knr6?9Grs12?18), diopside and rare chromite. The ultramafic protolith has a depleted residual mantle composition, indicated by a high‐Mg number, very low CaO, Al2O3 and total REE contents compared to primary mantle and other Sulu peridotites. Most garnet (Prp44?58) clinopyroxenites are foliated. Except for rare kyanite‐bearing eclogitic bands, most eclogites contain a simple assemblage of garnet (Alm29?34Prp32?50Grs15?39) + omphacite (Jd24?36) + minor rutile. Clinopyroxenite and eclogite exhibit LREE‐depleted and LREE‐enriched patterns, respectively, but both have flat HREE patterns. Normalized La, Sm and Yb contents indicate that both eclogite and garnet clinopyroxenite formed by high‐pressure crystal accumulation (+ variable trapped melt) from melts resulting from two‐stage partial melting of a mantle source. Recrystallized textures and P–T estimates of 780–870 °C, 5–7 GPa and a metamorphic age of 231 ± 11 Ma indicate that both mafic and ultramafic protoliths experienced Triassic UHP metamorphism in the P–T forbidden zone with an extremely low thermal gradient (< 5 °C km?1), and multistage retrograde recrystallization during exhumation. Develop of prehnite veins in clinopyroxenite, eclogite, felsic blocks and country rock gneiss, and replacements of eclogitic minerals by prehnite, albite, white mica, and K‐feldspar indicate low‐temperature metasomatism. 相似文献
53.
山西义兴寨金矿床地球化学研究 总被引:12,自引:1,他引:12
晋东北地区以唐河大断裂为核心的一组早燕山期 NW向张剪性断裂与区域 NE向复向斜复合部位 ,控制着区内燕山期中酸性浅成侵入体及其与之有关的铁、金、铜矿化 ,义兴寨金矿是该地区具代表性的典型矿床。金矿床为热液型脉状金 -多金属矿床 ,矿体受岩体和断裂构造控制。金矿床分 4个成矿期 ,8个亚期。对金矿床的矿床地质特征、成矿流体成分、性质、成矿物理化学条件及成矿时代的研究表明 ,成矿溶液的 p H值为 6 .1 6~ 6 .5 3:Eh值为 -0 .2 81~-0 .2 80 ;lgf O2 =-3.6~ -2 9,lgf CO2 =4 .3~ 5 .2 ;成矿温度为 1 90~ 349℃ ;成矿压力为 2 0 .0~ 76 .0 MPa;矿床主成矿期石英的 40 Ar— 3 9Ar坪年龄为 ( 1 31 .4± 3.1 ) Ma。 相似文献
54.
55.
56.
铀矿山废石堆表面氡析出率的变化规律 总被引:1,自引:0,他引:1
铀矿的退役处理是放射性固体废物处理的一个重要领域,研究退役铀矿的放射性水平及其影响因素具有重要的意义。对某矿山的11个废石堆进行表面氡析出率的实地测量,探讨废石堆表面氡析出率的影响变化规律,提出平地堆放型较依山堆放型的析出率高且更不稳定,建立了废石的粒度大小、在堆表面所处的位置和废石中u,Ra的活度与表面氡析出率的相关性,并建立了表面氡析出率与气温、地温、气压、相对湿度、降雨等气象因素的相关规律,为铀矿山退役治理提供理论依据。 相似文献
57.
Impacts of Drought, Flow Regime, and Fishing on the Fish Assemblage in Southern Australia’s Largest Temperate Estuary 总被引:1,自引:0,他引:1
Greg J. Ferguson Tim M. Ward Qifeng Ye Michael C. Geddes Bronwyn M. Gillanders 《Estuaries and Coasts》2013,36(4):737-753
We analysed a 25-year time series of fishery catch and effort data, and age/size information for four large-bodied, native fish species to investigate the hypotheses that under conditions of reduced freshwater inflows and high fishing pressure: (1) the structure of fish assemblages in the lower Murray River system have changed, (2) species diversity of fishes has declined and (3) population age structures of large-bodied, late-maturing, native fish (Macquaria ambigua, Argyrosomus japonicus, Rhombosolea tapirina and Acanthopagrus butcheri) have been reduced. Annual catches and effort in the lower Murray River system were stable for 25 years, but proportional contribution to the total catch from each of freshwater, estuarine and adjacent marine habitats, and the species within them varied. Fish assemblages generally differed between subsequent 5-year periods, with the exception of 1989–1993 when floods occurred in 4 out of 5 years, and the following 5-year period (1994–1998). Species richness declined steeply over 25 years in freshwater and estuarine habitat and species diversity (Hill’s H 2) also declined after 2001 in estuarine habitat. Species with rapid growth and early maturation (opportunistic strategists), increasingly dominated catches, whilst species with slow growth and late maturation (periodic strategists) declined. Truncated population age structures suggested longevity overfishing of three periodic strategist species: golden perch (M. ambigua), black bream (A. butcheri), mulloway (A. japonicus) and a fourth species with an intermediate strategy, greenback flounder (R. tapirina). This has implications for management because loss of older/larger individuals suggests reduced capacity to withstand or recover from deteriorated environmental conditions associated with a historically extreme drought in the lower Murray River system. Management of these species should seek to preserve the remnant population age structures and then to rebuild age structures by allowing recruits to become established in the adult population. We recommend that assessment of multi-species fisheries in changeable environments, such as occur in estuaries and other end-river environments, requires a suite of indicators that address changes in fish assemblages and populations. 相似文献
58.
中亚巴尔喀什成矿带晚古生代岩浆活动与斑岩铜矿成矿时代 总被引:3,自引:0,他引:3
巴尔喀什成矿带是中亚成矿域重要的晚古生代斑岩铜钼成矿带。通过该成矿带科翁腊德、博尔雷和阿克斗卡地区与斑岩铜成矿作用密切相关的花岗斑岩类岩体锆石SHRIMP U-Pb定年,主量、稀土和微量元素地球化学,Sr、Nd同位素示踪分析,进一步厘定了斑岩铜成矿作用的时代,并推测了板块构造环境。斑岩铜成矿时代分为两期:早期约为327 Ma,形成科翁腊德和阿克斗卡超大型斑岩铜矿床;晚期约为316 Ma,形成博尔雷大型斑岩铜矿床。与成矿有关的斑岩类主要为高钾钙碱性系列花岗岩,可能为火山岛弧环境,部分具有埃达克岩特征和经典岛弧花岗岩类特征。斑岩类εSr(t)和εNd(t)的变化范围分别为-6.35~34.03和-0.46~5.53。其中,科翁腊德-博尔雷地区斑岩类来源于亏损地幔与大陆地壳表层物质(老地壳物质)的显著混染作用,而阿克斗卡地区斑岩类直接来自于亏损地幔。将巴尔喀什成矿带与我国西准噶尔成矿带进行了对比,认为可能属于同一个晚古生代斑岩铜钼成矿带。 相似文献
59.
60.