全文获取类型
收费全文 | 24723篇 |
免费 | 6731篇 |
国内免费 | 4447篇 |
专业分类
测绘学 | 1292篇 |
大气科学 | 4820篇 |
地球物理 | 6517篇 |
地质学 | 13221篇 |
海洋学 | 3106篇 |
天文学 | 1204篇 |
综合类 | 2786篇 |
自然地理 | 2955篇 |
出版年
2025年 | 14篇 |
2024年 | 506篇 |
2023年 | 682篇 |
2022年 | 1201篇 |
2021年 | 1370篇 |
2020年 | 1329篇 |
2019年 | 1260篇 |
2018年 | 1390篇 |
2017年 | 1314篇 |
2016年 | 1532篇 |
2015年 | 1135篇 |
2014年 | 1493篇 |
2013年 | 1417篇 |
2012年 | 1327篇 |
2011年 | 1398篇 |
2010年 | 1326篇 |
2009年 | 1302篇 |
2008年 | 1160篇 |
2007年 | 1123篇 |
2006年 | 896篇 |
2005年 | 921篇 |
2004年 | 680篇 |
2003年 | 729篇 |
2002年 | 721篇 |
2001年 | 696篇 |
2000年 | 794篇 |
1999年 | 1124篇 |
1998年 | 917篇 |
1997年 | 993篇 |
1996年 | 914篇 |
1995年 | 780篇 |
1994年 | 652篇 |
1993年 | 578篇 |
1992年 | 463篇 |
1991年 | 331篇 |
1990年 | 269篇 |
1989年 | 217篇 |
1988年 | 202篇 |
1987年 | 147篇 |
1986年 | 120篇 |
1985年 | 91篇 |
1984年 | 71篇 |
1983年 | 65篇 |
1982年 | 41篇 |
1981年 | 34篇 |
1980年 | 43篇 |
1979年 | 30篇 |
1978年 | 15篇 |
1975年 | 16篇 |
1958年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
51.
Jian Chen Guijian Liu Mengmeng JiangChen-Lin Chou Hui LiBin Wu Liugen ZhengDongdong Jiang 《International Journal of Coal Geology》2011,88(1):41-54
To study the geochemical characteristics of 11 environmentally sensitive trace elements in the coals of the Permian Period from the Huainan coalfield, Anhui province, China, borehole samples of 336 coals, two partings, and four roof and floor mudstones were collected from mineable coal seams. Major elements and selected trace elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), and hydride generation atomic absorption spectrometry (HAAS). The depositional environment, abundances, distribution, and modes of occurrence of trace elements were investigated. Results show that clay and carbonate minerals are the principal inorganic constituents in the coals. A lower deltaic plain, where fluvial channel systems developed successively, was the likely depositional environment of the Permian coals in the Huainan coalfield. All major elements have wider variation ranges than those of Chinese coals except for Mg and Fe. The contents of Cr, Co, Ni, and Se are higher than their averages for Chinese coals and world coals. Vertical variations of trace elements in different formations are not significant except for B and Ba. Certain roof and partings are distinctly higher in trace elements than underlying coal bench samples. The modes of occurrence of trace elements vary in different coal seams as a result of different coal-forming environments. Vanadium, Cr, and Th are associated with aluminosilicate minerals, Ba with carbonate minerals, and Cu, Zn, As, Se, and Pb mainly with sulfide minerals. 相似文献
52.
Progress in China’s sustainable development research: Contribution of Chinese geographers 总被引:2,自引:0,他引:2
Sustainable development has always been a hotspot in Chinese geographical research. Herein, we conduct a systematic statistical analysis of the contribution of Chinese geographers to sustainable development research using bibliometric methods. Based on the review of a vast amount of literature, we identify the main research teams, research funding sources, journals, and key research fields. The findings are as follows: (1) the resources and environmental institutes of the Chinese Academy of Sciences have a significant influence on sustainable development research; (2) China’s central government foundations (the National Natural Science Foundation of China and National Social Sciences Fund) are the main research funding sources; (3) most of the highly cited articles are published in journals sponsored by the Geographical Society of China; and (4) sustainable development theory and its research areas are being constantly enriched and perfected. Based on the statistics of keywords, the theory, research methods, research regional scales, and key research areas are summarized and expounded. 相似文献
53.
Wu Jing Wu Li Sun Miao Lu Ya-ni Han Yan-hua 《Geotechnical and Geological Engineering》2022,40(3):1363-1372
Geotechnical and Geological Engineering - The Empirical Mode Decomposition (EMD) of blasting seismic wave monitoring signal with noise can get IMFs with serious modal confusion and endpoint... 相似文献
54.
55.
嵌岩桩理论研究和设计中的几个问题 总被引:27,自引:0,他引:27
明确嵌岩桩的定义和分类,对嵌岩桩的承载机理、临界嵌入深度、设计理论和数值模拟方法等问题进行讨论,并对未来的工作进行论述。 相似文献
56.
珠江三角洲软土微结构的定量研究 总被引:4,自引:0,他引:4
对用不同长度的PVC管在珠海和广州两地采得的淤泥样柱施于一定荷载,然后在扫描电镜下研究软土受压后在样柱垂深方向上的微结构变化,并将样品的微结构照片扫描,在计算机内进行量化处理。结果表明,样品的孔隙分布分维差随着离施压点距离的增加而逐渐减小,从而得到两者的关系方程。据此,可了解在一定荷载下应力在软土层中向下的衰减趋势。文章还对软土的天然含水量和围压对压缩变形的影响作了初步的讨论。 相似文献
57.
Chinese overseas industrial parks in Southeast Asia: An examination of policy mobility from the perspective of embeddedness 总被引:2,自引:2,他引:2
The development of overseas industrial parks is a key component of the Belt and Road Initiative and an expected experimental way of promoting inclusive globalization by inventing new forms of cooperation between China and local host countries. Policy mobility, a classic theory within international political geography addressing the connection between local and global policies, has implications for overseas industrial parks development. In this paper, we argue that policies are not easily moved directly from one place to another; instead, policies are embedded due to the role of local actors in policy mobility. This article first provides an overview of seven China-Southeast Asia economic and trade cooperation zones identified by the Ministry of Commerce, and analyzes their key participants. It then discusses policy mobility by looking into the roles of revenue, land, and talent in developing these industrial parks. The paper finds that these parks face challenges, such as the complicated geographical environments of host countries, huge pressure from enterprise investment capital, the lack of overseas service platforms, and underdeveloped agglomeration economies. In the light of the current situation, policy suggestions for the future sustainable development of overseas industrial parks are put forward. 相似文献
58.
滇、川、黔成矿区的铅锌矿源层(岩) 总被引:23,自引:3,他引:23
滇、川、黔铅锌成矿区的矿源层(岩)及其成矿作用,具多矿源层(岩)、多容矿层和多遮挡层共存的特点。矿源层(岩)改造成矿分海西晚期改造生成贫铅锌矿床和燕山期改造生成铅锌富矿床两个旋回,改造成矿的3个主因是:多条继承、发展了基底构造的深一道断层系统,峨眉山玄武岩浆上涌产生的高热能、喷气、矿质和广泛、多中心循环的热卤水,铅锌矿床为沉积─改造─后成成矿。 相似文献
59.
青鹏煤矿位于重庆市沙坪坝区青木关镇及壁山县壁城镇,已开采50余年.随着开采水平的延深,矿井地下水流场发生了相应的变化,改变了地下水原有的补、径、排条件.2012年2月,青鹏煤矿-200m水平-22103运输巷施工过程中,碛头煤层(M2)顶板裂隙突水造成局部淹井事故.通过地面及井下水文地质调查以及采取地表水、泉水、矿井水样进行水质分析,指出矿井突水水源由须家河组裂隙水、采空区积水和嘉陵江组灰岩岩溶裂隙水的越流补给3部分组成.为矿井防治水提供了水文地质依据. 相似文献
60.