全文获取类型
收费全文 | 2861篇 |
免费 | 265篇 |
国内免费 | 631篇 |
专业分类
测绘学 | 174篇 |
大气科学 | 307篇 |
地球物理 | 1047篇 |
地质学 | 1395篇 |
海洋学 | 307篇 |
天文学 | 119篇 |
综合类 | 150篇 |
自然地理 | 258篇 |
出版年
2023年 | 29篇 |
2022年 | 31篇 |
2021年 | 31篇 |
2020年 | 39篇 |
2019年 | 36篇 |
2018年 | 38篇 |
2016年 | 42篇 |
2015年 | 30篇 |
2014年 | 62篇 |
2013年 | 48篇 |
2012年 | 117篇 |
2011年 | 136篇 |
2010年 | 62篇 |
2009年 | 94篇 |
2008年 | 121篇 |
2007年 | 147篇 |
2006年 | 142篇 |
2005年 | 144篇 |
2004年 | 120篇 |
2003年 | 98篇 |
2002年 | 120篇 |
2001年 | 98篇 |
2000年 | 172篇 |
1999年 | 55篇 |
1998年 | 61篇 |
1997年 | 66篇 |
1996年 | 63篇 |
1995年 | 95篇 |
1994年 | 81篇 |
1993年 | 114篇 |
1992年 | 79篇 |
1991年 | 116篇 |
1990年 | 113篇 |
1989年 | 91篇 |
1988年 | 89篇 |
1987年 | 86篇 |
1986年 | 54篇 |
1985年 | 79篇 |
1984年 | 72篇 |
1983年 | 59篇 |
1982年 | 42篇 |
1981年 | 28篇 |
1980年 | 40篇 |
1965年 | 13篇 |
1964年 | 24篇 |
1960年 | 14篇 |
1959年 | 28篇 |
1958年 | 35篇 |
1957年 | 32篇 |
1954年 | 13篇 |
排序方式: 共有3757条查询结果,搜索用时 21 毫秒
121.
cDNA clones for glutathione S-transferases A (GST-A) and A1 (GST-A1) from plaice (Pleuronectes platessa) were expressed as N-terminally 6XHis tagged proteins in Escherichia coli and purified to homogeneity from Ni-NTA silica. GST-A was an efficient catalyst for conjugation of unsaturated alkenals derived from peroxidation of polyunsaturated fatty acids with the highest activity observed with trans-non-2-enal (8 micromol min(-1) mg(-1)). GST-A1 was a very efficient Se-independent glutathione peroxidase with an activity towards cumene hydroperoxide of 25 micromol min(-1) mg(-1). Although the enzymes exhibited moderately high activities towards the model substrate 1-chloro-2,4-dinitrobenzene (CDNB) they exhibited little or no activity towards other common prototypical xenobiotic substrates. Together with data for ontogeny, tissue distribution and inducibility of these enzymes, we contend that a primary function of these enzymes is protection from the harmful effects of lipid peroxidation products generated naturally or exacerbated by xenobiotic exposure. 相似文献
122.
由于多次的电子——光学投影,在电子显微镜中构成了影像。如果在投影时能保持正象立体条件的话,那么从几何观点将用投影方法获得电子——显微镜影像。 相似文献
123.
Experimental hydraulic heads and electrical (self-potential) signals associated with a pumping test were used in an inverse model to estimate the transmissivity distribution of a real aquifer. Several works reported in the literature show that there is a relatively good linear relationship between the hydraulic heads in the aquifer and electrical signals measured at the ground surface. In this experimental test field, first, the current coupling coefficient was determined by the best fit between experimental and modeled self-potential signals at the end of the pumping phase. Soon afterward, with the hydraulic heads obtained from the self-potential signals, the transmissivity distribution of the aquifer was conditioned by means an inverse model based on the successive linear estimator (SLE). To further substantiate the estimated T field from the SLE analysis, we analyzed the drawdown rate, the derivative of the drawdown with respect to the ln(t), because the drawdown rate is highly sensitive to the variability in the transmissivity field. In our opinion, these results show that self-potential signals allow the monitoring of subsurface flow in the course of pumping experiments, and that electrical potentials serve as a good complement to piezometric observations to condition and characterize the transmissivity distribution of an aquifer. 相似文献
124.
海岸带泥砂运动的形态学与岩石学的研究方法 总被引:2,自引:0,他引:2
在苏联,近十年来,海岸地貌学的研究有了很大的发展,而对于海岸地带,即海与陆相互作用地带的泥砂运动及其迁移规律性的研究则是其中最重要的一个方向。实际上,正像所指出的,对岩石圈物质迁移过程的研究是从“岩石颗粒及原生岩塊的破碎开始直到它们在地质作用中重新结合为止”而且是作为研究地壳表面地形的形成及共发展的地貌学中的一个重要任务。正是在这个作用的过程中及其后果,就建立着并发展着各种地形的形态。通常,这些形态可划分为二种基本类型:剥蚀的和堆积的。 相似文献
125.
126.
大地震发生后立即在断层带上进行钻探可以帮助我们获取更多的地震信息,尤其是可获得决定断层动态破裂的摩擦水平和强度,观测断层的愈合过程及可能触发余震的应力变化,并可获取控制破裂过程的重要的物理和化学属性。在2008年11月由国际大陆科学钻探项目(ICDP)和南加州地震中心(SCEC)联合在日本东京举办的为期3天的“震后快速钻探:历史、现状与未来”研讨会上, 相似文献
127.
128.
This paper presents a new concept for enhancing the seismic ductility and damping capacity of diagrid structural frames by using shear-link fuse devices and its seismic performance is assessed through nonlinear static and dynamic analysis.The architectural elegancy of the diagrid structure attributed to its triangular leaning member configuration and high structural redundancy make this system a desirable choice for tall building design.However,forming a stable energy dissipation mechanism in diagrid framing remains to be investigated to expand its use in regions with high seismicity.To address this issue,a diagrid framing design is proposed here which provides a competitive design option in highly seismic regions through its increased ductility and improved energy dissipation capacity provided by replaceable shear links interconnecting the diagonal members at their ends.The structural characteristics and seismic behavior(capacity,stiffness,energy dissipation,ductility) of the diagrid structural frame are demonstrated with a 21-story building diagrid frame subjected to nonlinear static and dynamic analysis.The findings from the nonlinear time history analysis verify that satisfactory seismic performance can be achieved by the proposed diagrid frame subjected to design basis earthquakes in California.In particular,one appealing feature of the proposed diagrid building is its reduced residual displacement after strong earthquakes. 相似文献
129.
土地是民生之本,发展之基。土地问题是现代工业进程中一个带有全局性、战略性的重大问题。目前,广西工业化、城镇化水平比全国平均水平低很多,"八山一水一分田"的广西要加快推进工业化、城 相似文献
130.
该《细则》自2010年4月启动编制以来,课题组全体技术人员在认真学习部、省有关土地整理开发规范、规程、标准的基础上,结合本地资源的分布与特点,开展调查研究,总结近年来我市垦造耕地工作的经验和教训。历时一年半时间,完成了《细则》课题研究成果。 相似文献