全文获取类型
收费全文 | 1582篇 |
免费 | 323篇 |
国内免费 | 476篇 |
专业分类
测绘学 | 62篇 |
大气科学 | 372篇 |
地球物理 | 382篇 |
地质学 | 910篇 |
海洋学 | 230篇 |
天文学 | 64篇 |
综合类 | 209篇 |
自然地理 | 152篇 |
出版年
2024年 | 10篇 |
2023年 | 33篇 |
2022年 | 73篇 |
2021年 | 86篇 |
2020年 | 60篇 |
2019年 | 99篇 |
2018年 | 89篇 |
2017年 | 82篇 |
2016年 | 96篇 |
2015年 | 82篇 |
2014年 | 81篇 |
2013年 | 82篇 |
2012年 | 82篇 |
2011年 | 109篇 |
2010年 | 99篇 |
2009年 | 104篇 |
2008年 | 82篇 |
2007年 | 86篇 |
2006年 | 76篇 |
2005年 | 57篇 |
2004年 | 52篇 |
2003年 | 35篇 |
2002年 | 49篇 |
2001年 | 49篇 |
2000年 | 59篇 |
1999年 | 93篇 |
1998年 | 66篇 |
1997年 | 65篇 |
1996年 | 57篇 |
1995年 | 65篇 |
1994年 | 48篇 |
1993年 | 49篇 |
1992年 | 19篇 |
1991年 | 23篇 |
1990年 | 24篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1965年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有2381条查询结果,搜索用时 390 毫秒
341.
Protease is wildly used in various fields, such as food, medicine, washing, leather, cosmetics and other industrial fields. In this study, an alkaline protease secreted by Micrococcus NH54PC02 isolated from the South China Sea was purified and characterized. The growth curve and enzyme activity curve indicated that the cell reached a maximum concentration at the 30th hour and the enzyme activity reached the maximum value at the 36th hour. The protease was purified with 3 steps involving ammonium sulfate precipitation, ion-exchange chromatography and hydrophobic chromatography with 8.22-fold increase in specific activity and 23.68% increase in the recovery. The molecular mass of the protease was estimated to be 25 kDa by SDS-PAGE analysis. The optimum temperature and pH for the protease activity were 50°C and pH 10.0, respectively. The protease showed a strong stability in a wide range of pH values ranging from 6.0–11.0, and maintained 90% enzyme activity in strong alkaline environment with pH 11.0. Inhibitor trials indicated that the protease might be serine protease. But it also possessed the characteristic of metalloprotease as it could be strongly inhibited by EDTA and strongly stimulated by Mn2+. Evaluation of matrix-assisted laser desorption ionization/time-of-flight MS (MALDI-TOF-TOF/MS) showed that the protease might belong to the peptidase S8 family. 相似文献
342.
343.
Samples of suspended particulate matters(SPMs),surface sediment and road dust were collected from the Yangtze estuarine and nearby coastal areas,coastal rivers,and central Shanghai.The samples were analyzed for the presence of 16 polycyclic aromatic hydrocarbons(PAHs)in the USEPA priority-controlled list by GC-MS.The compound-specific stable carbon isotopes of the individual PAHs were also analyzed by GC-C-IRMS.The sources of PAHs in the SPMs and surface sediments in the Yangtze estuarine and nearby coastal... 相似文献
344.
Perciformes, the largest order of vertebrates with 20 suborders, is the most diverse fish order that dominates vertebrate
ocean life. The complete mitochondrial control region (CR) of Trichiurus japonicus (Trichiuridae, Scombroidei) and Pampus sp. (Stromateidae, Stromateoidei) were amplified and sequenced. Together with data from GenBank, the tandem repeats in the
mitochondrial CR from 48 species, which covered nine suborders of Perciformes, are reported in this study. The tandem repeats
tend to be long in the suborder Percoidei and Stromateoidei. The identical repeats in 21 species of Cichlidae suggest a common
origin and have existed before species divergence. Larimichthys crocea shows tandem repeats instead of the typical structure of the central conserved sequence blocks, which was first reported
in Perciformes and vertebrates. This might have resulted from interruption of the polymerase activity during the H-strand
synthesis. The four broader patterns presented here for the tandem repeats, including those in both the 5′ and 3′ ends, only
in the either 5′ or 3′ end, and in the central conserved domain of the control region, will be useful for understanding the
evolution of species. 相似文献
345.
Shipboard X-band radar images acquired on 24 June 2009 are used to study nonlinear internal wave characteristics in the northeastern
South China Sea. The studied images show three nonlinear internal waves in a packet. A method based on the Radon Transform
technique is introduced to calculate internal wave parameters such as the direction of propagation and internal wave velocity
from backscatter images. Assuming that the ocean is a two-layer finite depth system, we can derive the mixed-layer depth by
applying the internal wave velocity to the mixed-layer depth formula. Results show reasonably good agreement with in-situ
thermistor chain and conductivity-temperature-depth data sets. 相似文献
346.
第32届国际沉积学会议(32nd IAS Meeting of Sedimentology)于2016年5月23—25日在摩洛哥马拉喀什召开, 来自43个国家和地区的360余名学者参加了本次会议。综述研究表明, 会议研究热点为陆相沉积环境、浅水沉积与滨岸潮汐、深水沉积与事件沉积、碳酸盐与化学岩沉积、沉积过程与盆地分析、成岩作用与油气储集层等研究领域。会议主要研究进展表现为: 波浪再悬浮作用(wave resuspension)与异重流(hyperpycnal flows)是陆架边缘斜坡快速进积的主要因素;海啸发生周期为14~35, ka, 后积层理(backset-bedding)为海啸沉积识别标志;海底滑坡多由海底地震、天然气水合物泄露等触发, 其块状搬运沉积物(MTD)包括滑塌头部、滑动底面、滑塌主体以及滑塌后期浊流沉积;玄武岩等基岩的风化作用提供硅与富镁碱性水, 有利于菱沸石与白云石的形成;受构造作用影响, 隆起剥蚀区与沉积区可互为转化;物源性质、供给量及搬运或分散过程控制了沉积面貌(源汇系统);构造活动直接控制可容纳空间变化、地貌变化、源区剥蚀速率、沉积物供应速率等。最后, 本文对比了中外沉积学发展差异, 讨论了中国沉积学发展方向。 相似文献
347.
在野外专题考察、大比例尺活断层地质填图、高精度地质剖面及阶地剖面实测的基础上,较系统地讨论了武威- 天祝- 庄浪河NNW 向断裂的活动时代、变形方式及分段特征。结果表明: 该断裂带是一条典型的全新世活动断裂,整个断裂可分为不同几何结构、不同构造类型、不同变形特征的南、中、北三个断层段。其中北段和中段为隐伏断层,发育有第四纪活动褶皱和1927 年古浪8 级地震破裂带;南段断裂呈弧形几何形态展布,显示了逆断层构造面的基本特征 相似文献
348.
349.
350.
On the study of the basic characteristics of geological objects and the special requirement for computing 3D geological model, this paper gives an object-oriented 3D topologic data model. In this model, the geological objects are divided into four object classes: point, line, area and volume. The volume class is further divided into four subclasses: the composite volume, the complex volume, the simple volume and the component. Twelve kinds of topological relations and the related data structures are designed for the geological objects. 相似文献