全文获取类型
收费全文 | 63099篇 |
免费 | 2383篇 |
国内免费 | 4081篇 |
专业分类
测绘学 | 2676篇 |
大气科学 | 5716篇 |
地球物理 | 11989篇 |
地质学 | 28430篇 |
海洋学 | 5473篇 |
天文学 | 8579篇 |
综合类 | 3090篇 |
自然地理 | 3610篇 |
出版年
2023年 | 366篇 |
2022年 | 996篇 |
2021年 | 1354篇 |
2020年 | 1219篇 |
2019年 | 1307篇 |
2018年 | 6553篇 |
2017年 | 5694篇 |
2016年 | 4340篇 |
2015年 | 1395篇 |
2014年 | 1880篇 |
2013年 | 2377篇 |
2012年 | 2903篇 |
2011年 | 4811篇 |
2010年 | 3998篇 |
2009年 | 4423篇 |
2008年 | 3756篇 |
2007年 | 4379篇 |
2006年 | 1896篇 |
2005年 | 1211篇 |
2004年 | 1291篇 |
2003年 | 1342篇 |
2002年 | 1282篇 |
2001年 | 997篇 |
2000年 | 793篇 |
1999年 | 713篇 |
1998年 | 626篇 |
1997年 | 640篇 |
1996年 | 513篇 |
1995年 | 512篇 |
1994年 | 463篇 |
1993年 | 361篇 |
1992年 | 367篇 |
1991年 | 290篇 |
1990年 | 282篇 |
1989年 | 289篇 |
1988年 | 232篇 |
1987年 | 242篇 |
1986年 | 227篇 |
1985年 | 247篇 |
1984年 | 240篇 |
1983年 | 229篇 |
1982年 | 227篇 |
1981年 | 213篇 |
1980年 | 203篇 |
1979年 | 205篇 |
1978年 | 171篇 |
1977年 | 155篇 |
1976年 | 153篇 |
1975年 | 158篇 |
1973年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
François Farges 《Physics and Chemistry of Minerals》2009,36(8):463-481
Cr K-edge XANES spectra were obtained for a variety of Cr-bearing model compounds containing Cr(II), Cr(III), Cr(IV), Cr(V) and Cr(VI), in which the Cr-site symmetry is D4h, Oh and Td. The centroid position of the pre-edge feature is a better indicator of the Cr valence than the edge position. In Cr-rich oxides, higher-energy transitions must be excluded in order to refine a robust valence for Cr. The pre-edge for chromates is not unique and varies as a function of the CrO4 2? moiety distortion, which is often related to Cr-polymerization (monochromate vs. dichromate). Both the analogy with the Mn K-pre-edge information and ab initio FEFF calculations of the pre-edge feature for Cr(III) and Cr(VI) confirm the experimental trends. This methodology is applied to the Cr K-edge pre-edge feature collected in gems (emerald, spinel and ruby), the layered minerals fuchsite and kämmererite, two Cr-bearing aqueous solutions and a set of sodo-calcic silicate glasses used for bottling sparkling white wine. In emerald and fuchsite, the Cr-site is differently distorted than its ruby or spinel counterpart. In a Cr(III)-bearing aqueous solution and sodo-calcic glass, no evidence for Cr(III) with Td and C3v symmetry is detected. However, minor amounts of chromate moieties (most likely monomeric) are detected in a glass synthesized in air. Preliminary spectra for the wine bottle glass suggest that only trace amounts of chromates might possibly be present in these glasses. 相似文献
992.
An application of a new method in permafrost environment assessment of Muli mining area in Qinghai-Tibet Plateau,China 总被引:1,自引:2,他引:1
The permafrost environment in the Muli mining area, an opencast mining site in the Qinghai-Tibet Plateau, China, is now undergoing
significant degradation because of the ongoing mining activities. The permafrost environment in this mining site had already
been evaluated by previous study, in which analytic hierarchy process was applied. Although this method can roughly characterize
the permafrost environment of this mining site, it has limitations by being easily affected by man-made factors. In view of
this limitation, this study attempts to employ a new method, the catastrophe progression method, to estimate the current stage
of the permafrost environment in this mining area. The results show that, by catastrophe progression method, currently the
calculated indexes of the permafrost freezing–thawing disintegration, permafrost thermal stability, permafrost ecological
fragility, and the permafrost environment are 0.43 (general situation), 0.77 (general situation), 0.71 (bad situation) and
0.83 (general situation), respectively. These values imply that the permafrost environment has been damaged by anthropologic
activities to a certain degree and potentially may be further degenerated. However, at this degree, a new equilibrium stage
of permafrost environment could be achieved if the current state of environmental degradation is stabilized and treatments
are constructed against further damages. 相似文献
993.
Melt inclusions and aqueous fluid inclusions in quartz phenocrysts from host felsic volcanics, as well as fluid inclusions in minerals of ores and wall rocks were studied at the Cu-Zn massive sulfide deposits in the Verkhneural’sk ore district, the South Urals. The high-temperature (850–1210°C) magmatic melts of volcanic rocks are normal in alkalinity and correspond to rhyolites of the tholeiitic series. The groups of predominant K-Na-type (K2O/Na2O = 0.3–1.0), less abundant Na-type (K2O/Na2O = 0.15–0.3), and K-type (K2O/Na2O = 1.9–9.3) rhyolites are distinguished. The average concentrations (wt %) of volatile components in the melts are as follows: 2.9 H2O (up to 6.5), 0.13 Cl (up to 0.28), and 0.09 F (up to 0.42). When quartz was crystallizing, the melt was heterogeneous, contained magnetite crystals and sulfide globules (pyrrhotite, pentlandite, chalcopyrite, bornite). High-density aqueous fluid inclusions, which were identified for the first time in quartz phenocrysts from felsic volcanics of the South Urals, provide evidence for real participation of magmatic water in hydrothermal ore formation. The fluids were homogenized at 124–245°C in the liquid phase; the salinity of the aqueous solution is 1.2–6.2 wt % NaCl equiv. The calculated fluid pressure is very high: 7.0–8.7 kbar at 850°C and 5.1–6.8 kbar at 700°C. The LA-ICP-MS analysis of melt and aqueous fluid inclusions in quartz phenocrysts shows a high saturation of primary magmatic fluid and melt with metals. This indicates ore potential of island-arc volcanic complexes spatially associated with massive sulfide deposits. The systematic study of fluid inclusions in minerals of ores and wall rocks at five massive sulfide deposits of the Verkhneural’sk district furnished evidence that ore-forming fluids had temperature of 375–115°C, pressure up to 1.0–0.5 kbar, chloride composition, and salinity of 0.8–11.2 (occasionally up to 22.8) wt % NaCl equiv. The H and O isotopic compositions of sericite from host metasomatic rocks suggest a substantial contribution of seawater to the composition of mineral-forming fluids. The role of magmatic water increases in the central zones of the feeding conduit and with depth. The dual nature of fluids with the prevalence of their magmatic source is supported by S, C, O, and Sr isotopic compositions. The TC parameters of the formation of massive sulfide deposits are consistent with the data on fluid inclusions from contemporary sulfide mounds on the oceanic bottom. 相似文献
994.
用固相反应法和sol-gel法合成了不同类型的磷灰石(AP),并采用TEM、XRD、IR、BET比表面积法及静、动态吸附等方法研究了不同AP的比表面积、结晶度、晶胞参数、结晶尺寸、晶格缺陷度、Ca/P摩尔比和煅烧温度等与吸氟能力的关系,结果表明:结晶度高、晶粒大的AP有较小的吸氟量,属表面单分子层化学络合吸附机理;酸活化的AP有较大的吸氟量,属溶解-沉淀与沉淀物表面纳米尺寸效应吸附的复合去氟机理;具纳米尺寸的HAP在常温、常压、无二次污染、小于11mg/L的低含氟浓度废水中且不酸化情况下有较大吸氟量,属纳米尺寸效应吸附机理。 相似文献
995.
996.
Re–Os and U–Pb Geochronology of Porphyry and Skarn Types Copper Deposits in Jilin Province,NE China 下载免费PDF全文
Yong Zhang Shu–Wen Xing Quan–Heng Song Yan Wang Zheng–Tao Yu Xiao–Hui Du Yu–Bo Ma Zeng–Jie Zhang 《Resource Geology》2015,65(4):394-404
Jilin Province in NE China lies on the eastern edge of the Xing–Meng Orogenic Belt. Mineral exploration in this area has resulted in the discovery of numerous large, medium, and small sized Cu, Mo, Au, and Co deposits. To better understand the formation and distribution of both the porphyry and skarn types Cu deposits of the region, we examined the geological characteristics of the deposits and applied zircon U–Pb and molybdenite Re–Os isotope dating to constrain the age of the mineralization. The Binghugou Cu deposit yields a zircon U–Pb age for quartz diorite of 128.1 ± 1.6 Ma; the Chang'anpu Cu deposit yields a zircon U–Pb age for granite porphyry of 117.0 ± 1.4 Ma; the Ermi Cu deposit yields a zircon U–Pb age for granite porphyry of 96.8 ± 1.1 Ma; the Tongshan Cu deposit yields molybdenite Re–Os model ages of 128.7 to 130.2 Ma, an isochron age of 129.0 ± 1.6 Ma, and a weighted mean model age of 129.2 ± 0.7 Ma; and the Tianhexing Cu deposit yields molybdenite Re–Os model ages of 113.9 to 115.2 Ma, an isochron age of 114.7 ± 1.2 Ma, and a weighted mean model age of 114.7 ± 0.7 Ma. The new ages, combined with existing geochronology data, show that intense porphyry and skarn types Cu mineralization was coeval with Cretaceous magmatism. The geotectonic processes responsible for the genesis of the Cu mineralization were probably related to lithospheric thinning. By analyzing the accumulated molybdenite Re–Os, zircon U–Pb, and Ar–Ar ages for NE China, it is concluded that the Cu deposits formed during multiple events coinciding with periods of magmatic activity. We have identified five phases of mineralization: early Paleozoic (~476 Ma), late Paleozoic (286.5–273.6 Ma), early Mesozoic (~228.7 Ma), Jurassic (194.8–137.1 Ma), and Cretaceous (131.2–96.8 Ma). Although Cu deposits formed during each phase, most of the Cu mineralization occurred during the Cretaceous. 相似文献
997.
REE Geochemistry of the Lead—Zinc Ores from the Jinding Lead—Zinc Deposit,Lanping,Yunnan 总被引:3,自引:1,他引:3
Nineteen volcanic and magmatic rock samples were collectecd from the Jinding leadzinc deposit and its surrounding areas in Yunnan.The ICP and AES analyses,feferred to the previous results,show that the metal minerals and altered rocks in the Jinding lead-zinc deposit display a decreasing trend of ∑REE from the early to late stages of mineralization,and similarities in REE distribution patterns,indicating that the ore fluids are characterized by high LREE enrichment,markedly negative δCe anomaly and slight δEu anomaly.These REE distribution paterns exhibit striking similarities to those of the Pliocene trachyte in the study area,both of which are similar in ∑REE,LREE/HREE ratio,δEu and δCe.The ore fluids besides the basin fluids in the deposit are also closely related to those associated with Pliocene trachyte magmas. 相似文献
998.
We consider a hypothesis for the origin of PGE-bearing ultramafic rocks of the Inagli massif (Central Aldan) through fractional crystallization from ultrabasic high-potassium magma. We studied dunites and wehrlites of the Inagli massif and olivine lamproites of the Ryabinovy massif, which is also included into the Central Aldan high-potassium magmatic area. The research is focused on the chemistry of Cr-spinels and the phase composition of Cr-spinel-hosted crystallized melt inclusions and their daughter phases. Mainly two methods were used: SEM-EDS (Tescan Mira-3), to establish different phases and their relationships, and EPMA, to obtain precise chemical data on small (2-100 μm) phases. The obtained results show similarity in chromite composition and its evolutionary trends for the Inagli massif ultramafites and Ryabinovy massif lamproites. The same has been established for phlogopite and diopside from crystallized melt inclusions from the rocks of both objects. Based on the results of the study, the conclusion is drawn that the ultramafic core of the Inagli massif resulted from fractional crystallization of high-potassium melt with corresponding in composition to low-titanium lamproite. This conclusion is consistent with the previous hypotheses suggesting an ultrabasic high-potassium composition of primary melt for the Inagli ultramafites. 相似文献
999.
N. P. Romanovskii Yu. F. Malyshev M. V. Goroshko 《Russian Journal of Pacific Geology》2008,2(2):137-149
Evidence on the Paleozoic granitoids of the eastern part of the Central Asian Fold Belt (CAFB) was analyzed. A tectonic chart of orogenic belts was compiled. Sketch maps were constructed for the geodynamic settings of the formation of Paleozoic granitoids and the extensiveness of their occurrence. Two types of deep controlling structures were distinguished: zones of lithospheric faults and plumes, including the newly recognized Jiamusi-Bureya plume. It was sown that the distribution of large and superlarge Paleozoic ore deposits is related to these structures, primarily to plumes. Sites promising for large and superlarge deposits related to the Paleozoic granitoid magmatism were determined in the Russian Far East. 相似文献
1000.
滇黔桂地区晚古生代浅水碳酸盐岩台地与深水硅泥质盆地共存的古地理格局,是在加里东期褶皱基底上发生裂陷及差异沉降而发展起来的。广西宜州—柳州一带既是晚古生代上扬子碳酸盐岩地台南缘1条重要的沉积相分界线,也是晚古生代桂中和桂北地层分区、古生代—中生代雪峰山南段构造体系和桂中坳陷构造体系的分界线。文中通过对宜山—柳州一带晚古生代地层的区域对比和成因分析,恢复了桂中宜山—柳州地区晚古生代沉积盆地的演化历史。狭长型宜州裂陷槽盆地西起丹池断裂,向东经龙头、北牙、宜州延伸至柳州。自中泥盆世开始,首先在东西两端开始裂陷下沉,至早石炭世发展成型。受北侧来自江南隆起带陆源碎屑物质充填影响,其表现为南北不对称并在早石炭世晚期被填平。在宜州裂陷槽内发育多处早石炭世沉积型碳酸锰矿,含矿地层分布、地层序列及其沉积背景明显与裂陷槽演化有关。它们既是盆地演化历史的见证,也体现了桂中地区裂陷海槽的特色,值得在后续锰矿成因研究中予以重视。 相似文献