首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6395篇
  免费   1218篇
  国内免费   1382篇
测绘学   267篇
大气科学   1432篇
地球物理   1799篇
地质学   3056篇
海洋学   660篇
天文学   346篇
综合类   624篇
自然地理   811篇
  2024年   29篇
  2023年   110篇
  2022年   304篇
  2021年   361篇
  2020年   299篇
  2019年   320篇
  2018年   368篇
  2017年   364篇
  2016年   387篇
  2015年   322篇
  2014年   382篇
  2013年   380篇
  2012年   381篇
  2011年   396篇
  2010年   353篇
  2009年   387篇
  2008年   335篇
  2007年   320篇
  2006年   233篇
  2005年   229篇
  2004年   179篇
  2003年   157篇
  2002年   162篇
  2001年   160篇
  2000年   188篇
  1999年   297篇
  1998年   222篇
  1997年   234篇
  1996年   190篇
  1995年   177篇
  1994年   130篇
  1993年   143篇
  1992年   109篇
  1991年   78篇
  1990年   40篇
  1989年   66篇
  1988年   49篇
  1987年   27篇
  1986年   22篇
  1985年   14篇
  1984年   17篇
  1983年   10篇
  1982年   15篇
  1981年   9篇
  1980年   9篇
  1979年   6篇
  1978年   5篇
  1975年   2篇
  1974年   2篇
  1958年   10篇
排序方式: 共有8995条查询结果,搜索用时 31 毫秒
951.
江苏非物质文化遗产的时空分布及其影响因素   总被引:2,自引:0,他引:2  
韩顺法  徐鹏飞  马培龙 《地理科学》2021,41(9):1598-1605
以江苏为例,运用地理学相关方法将非遗的时空分布可视化,并探讨其分布的影响因素。研究表明:江苏非遗在时间上呈“迂回向南”发展轨迹,其数量和类型在不同阶段具有明显差异;在空间上呈聚集性分布,分别在苏州、扬州、南京、常州、镇江和南通形成6个高密度核心;通过地理探测器分析,得知河流水系、政策导向、历史文化和经济等因素对非遗的时空分布有较大影响。由此得出重视江苏大运河文化带建设、将非遗纳入文化生态系统内整体性保护、正视非遗与经济合理互动等启示。  相似文献   
952.
A well‐constrained plate deformation model may lead to an improved understanding of sedimentary basin formation and the connection between subduction history and over‐riding plate deformation. Building quantitative models of basin kinematics and deformation remains challenging often due to the lack of comprehensive constraints. The Bohai Bay Basin (BBB) is an important manifestation of the destruction of the North China Craton, and records the plate kinematic history of East Asia during the Cenozoic. Although a number of interpretations of the formation of the BBB have been proposed, few quantitative basin reconstruction models have been built to test and refine previous ideas. Here, we developed a quantitative deformation reconstruction of the BBB constrained with balanced cross‐sections and structural, stratigraphic and depositional age data. Our reconstruction suggests that the basin formation process was composed of three main stages: Paleocene‐early Eocene (65–42 Ma) extension initiation, middle Eocene‐early Oligocene (42–32.8 Ma) extension climax and post‐Oligocene (32.8–0 Ma) post‐extensional subsidence. The deformation of the BBB is spatially heterogeneous, and its velocity directions rotated clockwise during the basin formation process. The reconstruction supports the interpretation that the BBB formed via strike‐slip faulting and orthogonal extension and that the basin is classified as a composite extensional‐transtensional basin. We argue that the clockwise rotation of the basin velocity field was driven by the counter‐clockwise rotation in the direction of Pacific Plate subduction. The kinematics of the BBB imply that the Pacific Plate may have been sufficiently coupled to the over‐riding East Asian Plate during the critical period of Pacific Plate reorganization. The new reconstruction provides a quantitative basis for studies of deformation processes not only in the vicinity of the BBB, but also more broadly throughout East Asia.  相似文献   
953.
Zhao  Kang  Zhou  Yun  Yu  Xiang  Yan  Yajing  Song  Yufeng  Wang  Junqiang  Suo  Tianyuan  Guo  Xiao 《Natural Resources Research》2021,30(5):3839-3852
Natural Resources Research - Depletion of shallow mineral resources caused by deep mining has become an inevitable trend, and deep mining can increase safety accidents and geological hazards....  相似文献   
954.
Wang  Kai  Ren  Haoyang  Wang  Zhaofeng  Ma  Shujun  Wei  Junjie  Ke  Wei  Guo  Yangyang 《Natural Resources Research》2021,30(6):4597-4620
Natural Resources Research - The accurate determination of coalbed methane (CBM) content is of great significance for its development and utilization as well as for the prevention and control of...  相似文献   
955.
Ma  Jun  Song  Jinming  Li  Xuegang  Yuan  Huamao  Li  Ning  Duan  Liqin  Wang  Qidong 《中国海洋湖沼学报》2020,38(4):1215-1224
An investigation was carried out in the Y3 seamount area of the Western Pacific Ocean in December 2014,and the distribution of dissolved inorganic carbon(DIC) and its relationship with environmental factors in this area were explored.The results show that DIC concentration was higher in the adjacent waters of the Y3 seamount area,and the uplift of DIC isolines at the stations was close to the seamount.Meanwhile,interaction between the North Equatorial Current(NEC) and the Y3 seamount affected the DIC distribution i.e.,the upwelling in the same direction of the NEC was obvious,resulting in a decreasing trend of average concentration of DIC in the 200 m water column from the top to the two side s in this direction but in the cross direction.The DIC concentration increased with the water depth increase,and its distribution was affected by various environmental factors.In the surface water,high temperature was a decisive factor for the decrease of the DIC concentration,but the photosynthesis of phytoplankton showing only a weak influence.In the North Pacific Tropic Water(NPTW),DIC production rate from organic matter decomposition was higher than that of DIC consumption by phytoplankton photosynthesis,leading to a continual increase of DIC.In the North Pacific Intermediate Water(NPIW),organic matter decomposition played a leading role in the increase of DIC.In the deep water,decomposition of organic matter weakened,and the dissolution of CaCO_3 controlled the carbonate system,and DIC had the smallest variation range.  相似文献   
956.
Hu  Shijian  Liu  Lingling  Guan  Cong  Zhang  Linlin  Wang  Jianing  Wang  Qingye  Ma  Jie  Wang  Fujun  Jia  Fan  Feng  Junqiao  Lu  Xi  Wang  Fan  Hu  Dunxin 《中国海洋湖沼学报》2020,38(4):1092-1107
Near-inertial oscillation is an important physical process transferring surface wind energy into deep ocean.We investigated the near-inertial kinetic energy(NIKE) variability using acoustic Doppler current profiler measurements from a mooring array deployed in the tropical western Pacific Ocean along130°E at 8.5°N,11°N,12.6°N,15°N,and 17.5°N from September 2015 to January 2018.Spatial features,decay timescales,and significant seasonal variability of the observed NIKE were described.At the mooring sites of 17.5°N,15°N,and 12.6°N,the NIKE peaks occurred in boreal autumn and the NIKE troughs were observed in boreal spring.By contrast,the NIKE at 11°N and 8.5°N showed peaks in winter and troughs in summer.Tropical cyclones and strong wind events played an important role in the emergence of high-NIKE events and explained the seasonality and latitudinal characteristics of the observed NIKE.  相似文献   
957.
Liu  Changshui  Zang  Kun  Li  Shihao  Li  Fuhua  Ma  Qingjun 《中国海洋湖沼学报》2020,38(6):1891-1899
Journal of Oceanology and Limnology - Thymidylate synthase (TS) is a key enzyme in the de novo biosynthesis of thymidine monophosphate, serving as a well-known drug target in chemotherapy against...  相似文献   
958.
This study investigated the difference of nutrient composition in Caulerpa lentillifera collected from different regions.The nutrient compositions of C.lentillifera from China's Hainan and Shandong provinces were determined and compared with those from Semporna(Malaysia),Sabah(Malaysia),Petchburi(Thailand),and two other species of seaweeds(Malaysia).The results showed that the polysaccharide and protein contents of C.lentillifera from Hainan(44.82%±0.98%and 12.5%±0.70%),Shandong(43.22%±1.42%and 14.7%±0.72%),Petchburi(59.27%±2.31%and 12.49%±0.30%),and Sabah(44.02%±2.01%and 19.38%±1.48%)were higher than those of Eucheuma cottonii(26.49%±3.01%and 9.76%±1.33%)and Sargassum polycystum(33.49%±1.70%and 5.40%±0.07%),respectively.The polyunsaturated fatty acid contents in C.lentillifera from Hainan(29.98%)and Shandong(22.11%)were higher than that in Semporna(16.76%±0.27%),Sabah(9.49%),and S.polycystum(20.34%±0.43%),but lower than that in E.cottonii(51.55%±0.57%).In Caulerpa lentillifera of Hainan and Shandong provinces,the essential amino acid(EAA)/total amino acid(TAA)ratios were 35.22%and 38.78%,respectively;and the EAA/ETAA ratios were 54.36%and 63.35%,respectively.The EAA composition of C.lentillifera was close to the ideal model of Food and Agriculture Organization/World Health Organization.C.lentillifera was rich in mineral elements,including calcium((3315.85±127.55)mg(100 g)^-1 and(3728.35±92.38)mg(100 g)^-1),magnesium((6715.74±82.58)mg(100 g)^-1 and(8128.59±242.72)mg(100 g)^-1),and trace elements,including iron((510.65±5.47)mg(100 g)^-1 and(1972.97±183.35)mg(100 g)^-1),selenium((1.04±0.08)mg(100 g)^-1 and(0.83±0.15)mg(100 g)^-1),and zinc((33.90±0.13)mg(100 g)^-1 and(11.75±2.05)mg(100 g)^-1).These results showed that C.lentillifera was more nutritious than S.polycystum or E.cottonii in terms of polysaccharide,protein,and fatty acid contents.Furthermore,both C.lentillifera species collected from Hainan and Shandong provinces show more basic nutrients.Therefore,C.lentillifera has important development and application prospects.  相似文献   
959.
This paper has established a high-precision hierarchical estimated pose parameters of image. Firstly, we select corresponding three image points of 3D points which constitute the largest area in image as a base, in order to estimate the depth and translate information; then based on the above method, we obtain the scale parameter of camera exterior information. And finally, the topic is transformed to a problem of estimating rotation relationship by vector, using Procrustes theory to obtain the best estimate of the angle elements of exterior parameters. The method can effectively solve problems which depth and coupling pose parameters cannot deal with. Experimental results show that this method of determining position and orientation parameter estimation model is of briefness, easy convergence and it can also achieve higher parameter estimation accuracy than the direct projection matrix factorization.  相似文献   
960.
Zhao  Qile  Wang  Chen  Guo  Jing  Yang  Guanglin  Liao  Mi  Ma  Hongyang  Liu  Jingnan 《GPS Solutions》2017,21(3):1179-1190
GPS Solutions - A key limitation for precise orbit determination of BeiDou satellites, particularly for satellites in geostationary orbit (GEO), is the relative weak geometry of ground stations....  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号