全文获取类型
收费全文 | 1220篇 |
免费 | 440篇 |
国内免费 | 316篇 |
专业分类
测绘学 | 176篇 |
大气科学 | 122篇 |
地球物理 | 450篇 |
地质学 | 653篇 |
海洋学 | 378篇 |
天文学 | 11篇 |
综合类 | 103篇 |
自然地理 | 83篇 |
出版年
2024年 | 7篇 |
2023年 | 24篇 |
2022年 | 77篇 |
2021年 | 83篇 |
2020年 | 88篇 |
2019年 | 98篇 |
2018年 | 94篇 |
2017年 | 84篇 |
2016年 | 87篇 |
2015年 | 101篇 |
2014年 | 93篇 |
2013年 | 98篇 |
2012年 | 96篇 |
2011年 | 91篇 |
2010年 | 96篇 |
2009年 | 95篇 |
2008年 | 91篇 |
2007年 | 75篇 |
2006年 | 71篇 |
2005年 | 57篇 |
2004年 | 54篇 |
2003年 | 21篇 |
2002年 | 28篇 |
2001年 | 33篇 |
2000年 | 40篇 |
1999年 | 26篇 |
1998年 | 17篇 |
1997年 | 20篇 |
1996年 | 30篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1965年 | 2篇 |
1958年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有1976条查询结果,搜索用时 617 毫秒
411.
A linearization method is proposed for the vectorial Morrison equation which enables the force spectrum on an inclined cylinder to be calculated in a relatively simple manner from the wave spectrum in the presence of a current. To test the method some random wave tests were carried out in a laboratory flume with forces measured on a cylinder over a range of inclinations, currents and angle of inclination to the current direction. Comparisons show the measured force spectra to be sufficiently close to the calculated ones for the method to be applicable to engineering practice. 相似文献
412.
413.
By using the shallow water wave data continuously recorded in the Bohai Sea, Huanghai Sea, East China sea and South China Sea. a model of wave spectrum in shallow water is developed with three parameters—average wave height, average period and relative depth—on the basis of the principle of the spectrum pattern simularity and the method of parameterization. The magnitude of frequency index in the high frequency 相似文献
414.
415.
In this paper, an exact analytical method is developed for the problem of wave radiation by a uniform cylinder in front of a vertical wall. Based on the image principle, the hydrodynamic problem of a cylinder in front of a vertical wall is transformed into the equivalent problem of double cylinders in unbounded fluid domain. Consequently, an analytical method of eigenfunction expansion is adopted to calculate the radiation of the cylinder due to the motion in surge, sway, roll and pitch, respectively. Moreover, numerical analysis has been carried out in detail in order to discuss the influences of the distance between the cylinder and the vertical wall and water depth on the added mass and radiation damping of the cylinder. It is shown that added mass and damping of the cylinder in front of a vertical wall are evidently different from those in case of the cylinder in unbounded fluid domain from the numerical results. It is also found that the added mass and radiation damping oscillate with wave number, and the oscillating frequency increases with the increasing of the distance between the cylinder and the wall. 相似文献
416.
江汉平原水质性缺水问题日益突出,识别江汉平原地下水流系统分布模式,对地下水资源的合理利用与保护具有重要意义.选取江汉平原典型区域,综合水文地质条件、水动力场及水化学同位素指标深入分析地下水补给过程、水岩作用及滞留时间.得出由于碳酸盐岩的溶解,研究区的地下水化学类型属于HCO3-Ca (Mg)型.地下水中典型离子随深度增加逐渐降低,同位素随深度增加逐渐偏负,表现出地下水流系统呈局部与区域水流系统的特点,系统深度界限在10~20m.独立而复杂的局部水流系统在平枯水期地下水向河渠地表水排泄.根据3H的含量,局部水流为现代水,水循环交替迅速.受地形控制,中深层地下水总体由西和西北向东和东南径流,汇入汉江和长江,为区域水流系统.由于补给源的高程效应,区域水流的18O值存在明显分区,指示不同的补给来源与水流路径.山前丘陵区基本为现代水,向平原腹地纵深至汉江和长江排泄区,地下水年龄在几百年至6000a不等,水循环交替缓慢.研究发现江汉平原低洼排泄区存在区域水流的顶托补给,可为原生劣质水的分布与聚集研究提供依据. 相似文献
417.
Petrology,phase equilibria modelling and zircon U–Pb geochronology of Paleoproterozoic mafic granulites from the Fuping Complex,North China Craton
下载免费PDF全文
![点击此处可从《Journal of Metamorphic Geology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
L. Tang M. Santosh T. Tsunogae T. Koizumi X.‐K. Hu X.‐M. Teng 《Journal of Metamorphic Geology》2017,35(5):517-540
The Fuping Complex is one of the important basement terranes within the central segment of the Trans‐North China Orogen (TNCO) where mafic granulites are exposed as boudins within tonalite–trondhjemite–granodiorite (TTG) gneisses. Garnet in these granulites shows compositional zoning with homogeneous cores formed in the peak metamorphic stage, surrounded by thin rims with an increase in almandine and decrease in grossular contents suggesting retrograde decompression and cooling. Petrological and phase equilibria studies including pseudosection calculation using thermocalc define a clockwise P–T path. The peak mineral assemblages comprise garnet+clinopyroxene+amphibole+quartz+plagioclase+K‐feldspar+ilmenite±orthopyroxene±magnetite, with metamorphic P–T conditions estimated at 8.2–9.2 kbar, 870–882 °C (15FP‐02), 9.6–11.3 kbar, 855–870 °C (15FP‐03) and 9.7–10.5 kbar, 880–900 °C (15FP‐06) respectively. The pseudosections for the subsequent retrograde stages based on relatively higher H2O contents from P/T–M(H2O) diagrams define the retrograde P–T conditions of <6.1 kbar, <795 °C (15FP‐02), 5.6–5.8 kbar, <795 °C (15FP‐03), and <9 kbar, <865 °C (15FP‐06) respectively. Data from LA‐ICP‐MS zircon U–Pb dating show that the mafic dyke protoliths of the granulite were emplaced at c. 2327 Ma. The metamorphic zircon shows two groups of ages at 1.96–1.90 Ga (peak at 1.93–1.92 Ga) and 1.89–1.80 Ga (peak at 1.86–1.83 Ga), consistent with the two metamorphic events widely reported from different segments of the TNCO. The 1.93–1.92 Ga ages are considered to date the peak granulite facies metamorphism, whereas the 1.86–1.83 Ga ages are correlated with the retrograde event. Thus, the collisional assembly of the major crustal blocks in the North China Craton (NCC) might have occurred during 1.93–1.90 Ga, marking the final cratonization of the NCC. 相似文献
418.
419.
Chen Guangbo Teng Pengcheng Duan Huiqiang Zhang Guohua Li Tan 《Geotechnical and Geological Engineering》2022,40(3):1121-1133
Geotechnical and Geological Engineering - After the coal mine disaster, the collapsed accumulation body blocked the roadway and interrupted the rescue route, which seriously affected the... 相似文献
420.
蚯蚓肠道内小分子有机酸与摄入的土壤矿物相互作用,加速矿物溶解。摄入的土壤在蚯蚓肠道内平均停留时间约为12 h,不足以使土壤矿物产生显著的溶解特征,因此这一过程难以在蚯蚓体内进行评估。本研究通过体外实验控制pH值和有机酸浓度,模拟蚯蚓肠道中有机酸对土壤中常见矿物的溶解反应,探讨了方解石和钾长石在蚯蚓肠道环境中的初始溶解动力学。研究发现,矿物在混合有机酸中的溶解速率比在纯水中高一个数量级,说明有机配体和质子促进了矿物溶解。溶解速率及粒度分析表明,方解石(CaCO3)溶解速率不受溶解过程中粒度变化的影响,而钾长石(KAlSi3O8)粒度在溶解期间未出现显著变化。在此基础上,采用初始速率法模拟了钾长石的初始溶解动力学,计算得出的溶解速率表明钾长石在溶解初期主要为表面K~+的释放。使用缩核模型(shrink core model)和Hixson-Crowell模型对方解石溶解过程进行动力学解析,发现方解石的溶解主要受溶液中反应物内扩散的速率影响。这定量描述了两种矿物在有机酸溶液和纯水中的溶解差异。现有研究表明,有机配体和质子协同促... 相似文献