全文获取类型
收费全文 | 65019篇 |
免费 | 759篇 |
国内免费 | 1262篇 |
专业分类
测绘学 | 2610篇 |
大气科学 | 4940篇 |
地球物理 | 12849篇 |
地质学 | 24758篇 |
海洋学 | 4596篇 |
天文学 | 11713篇 |
综合类 | 2248篇 |
自然地理 | 3326篇 |
出版年
2021年 | 329篇 |
2020年 | 363篇 |
2019年 | 449篇 |
2018年 | 5537篇 |
2017年 | 4767篇 |
2016年 | 3662篇 |
2015年 | 883篇 |
2014年 | 1188篇 |
2013年 | 2032篇 |
2012年 | 2154篇 |
2011年 | 4174篇 |
2010年 | 3390篇 |
2009年 | 4217篇 |
2008年 | 3590篇 |
2007年 | 4026篇 |
2006年 | 1743篇 |
2005年 | 1458篇 |
2004年 | 1673篇 |
2003年 | 1577篇 |
2002年 | 1463篇 |
2001年 | 1131篇 |
2000年 | 1067篇 |
1999年 | 905篇 |
1998年 | 905篇 |
1997年 | 888篇 |
1996年 | 711篇 |
1995年 | 666篇 |
1994年 | 625篇 |
1993年 | 543篇 |
1992年 | 475篇 |
1991年 | 487篇 |
1990年 | 466篇 |
1989年 | 485篇 |
1988年 | 434篇 |
1987年 | 503篇 |
1986年 | 456篇 |
1985年 | 535篇 |
1984年 | 658篇 |
1983年 | 568篇 |
1982年 | 557篇 |
1981年 | 522篇 |
1980年 | 457篇 |
1979年 | 432篇 |
1978年 | 445篇 |
1977年 | 381篇 |
1976年 | 346篇 |
1975年 | 349篇 |
1974年 | 324篇 |
1973年 | 362篇 |
1972年 | 260篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
91.
92.
93.
94.
Expression of putative zinc-finger protein lcn61 gene in lymphocystis disease virus China (LCDV-cn) genome 总被引:1,自引:0,他引:1
An open reading frame (lcn61) of lymphocystis disease virus China (LCDV-cn), probably responsible for encoding putative zinc-finger proteins was amplified
and inserted into pET24a (+) vector. Then it expressed in E. coli BL21 (DE3), and His-tag fusion protein of high yield was obtained. It was found that the fusion protein existed in E. coli mainly as inclusion bodies. The bioinformatics analysis indicates that LCN61 is C2H2 type zinc-finger protein containing
four C2H2 zinc-finger motifs. This work provides a theory for functional research of lcn61 gene.
Supported by High Technology Research and Development Program of China (863 Program, No. 2006AA100309) 相似文献
95.
In contaminant hydrogeology, investigations at fractured rock sites are typically undertaken to improve understanding of the fracture networks and associated groundwater flow that govern past and/or future contaminant transport. Conventional hydrogeologic, geophysical, and hydrophysical techniques used to develop a conceptual model are often implemented in open boreholes under conditions of cross-connected flow. A new approach using high-resolution temperature (±0.001°C) profiles measured within static water columns of boreholes sealed using continuous, water-inflated, flexible liners (FLUTe™) identifies hydraulically active fractures under ambient (natural) groundwater flow conditions. The value of this approach is assessed by comparisons of temperature profiles from holes (100 to 200 m deep) with and without liners at four contaminated sites with distinctly different hydrogeologic conditions. The results from the lined holes consistently show many more hydraulically active fractures than the open-hole profiles, in which the influence of vertical flow through the borehole between a few fractures masks important intermediary flow zones. Temperature measurements in temporarily sealed boreholes not only improve the sensitivity and accuracy of identifying hydraulically active fractures under ambient conditions but also offer new insights regarding previously unresolvable flow distributions in fractured rock systems, while leaving the borehole available for other forms of testing and monitoring device installation. 相似文献
96.
Summary The change of rainfall totals with height has been the subject of much investigation in many parts of the world. The rates of increase or decrease vary with the climatic regime experienced. This study of Sri Lankan rainfall shows that the relationship between height and mean annual rainfall is complex. Examples of increases and decreases of rainfall with height are found. The climatic regime of the area is important in controlling the level of maximum rainfall.With 7 Figures 相似文献
97.
P. P. Malovichko 《Kinematics and Physics of Celestial Bodies》2007,23(5):185-190
Current instability of Alfvén waves in coronal loops is considered. Such a mechanism of Alfvén wave generation is shown to be very efficient, and it can give rise to low-frequency perturbations even in the case of very weak currents, thus fostering the reconnection of magnetic fields and development of a flare. The low-frequency turbulence which arises in the process can be favorable to the heating and acceleration of particles. 相似文献
98.
A. Carraro P. Fabbri A. Giaretta L. Peruzzo F. Tateo F. Tellini 《Environmental Earth Sciences》2013,70(7):3067-3084
A pilot area within the Venetian Plain was selected to assess the arsenic (As) contamination of groundwater. The area represents a typical residential, industrial and agricultural organization representative of most western countries, and is also devoid of lithologies with high or anomalous As content. Hydrogeological and chemical data have been collected, the latter spatialized by a geostatistical approach. The unconfined aquifer reservoir varies from a predominantly gravel composition in the north to a sandy and silt–clay composition further south, including peat layers. The hydrochemical features of the waters are rather homogeneous, featuring low mineral content and a Ca-bicarbonate signature. In contrast, the redox state is highly variable; oxidizing conditions are predominant in the northern and coarse parts of the aquifer, whereas reducing potentials prevail in the southern and silt–clay parts. Several well waters contain arsenic in excess of drinkable limits (=10 ppb), and most of these wells are located in the southern area. A large portion of the studied area has a high probability of containing non-potable water (up to 150 ppb As). Remarkably, As “hot spots” (As > 300 ppb, up to 431 ppb) were identified at the transition from gravel to silt–clay sediments. No industrial or agricultural source of As has been found. 相似文献
99.
Graça Cabeçadas M. José Brogueira M. Gelena Cavaco Célia Gonçalves 《Journal of Oceanography》2010,66(2):201-210
Although the circulation of intermediate water masses in the eastern North Atlantic remains poorly defined, the presence of
fresher intermediate waters, the Sub-Artic (SAIW) and the Antarctic Intermediate Water (AAIW), as well the saline intermediate
Mediterranean Water (MW), has been tracked using biogeochemical properties. Here we assess the hydrographic and chemical structures
of intermediate waters along the western Portuguese margin by examining the vertical distributions and property-property plots
of chemical tracers (oxygen and nutrients). AAIW was traced by low oxygen and high nutrients, while SAIW was recognized by
low nutrients. The Mediterranean Water (MW) undercurrent is shown to spread towards the eastern flank of Gorringe bank. Concurrently,
the fresher waters gained salt by direct incorporation of MW, while this water was enriched in nutrients on its way northward
and westward owing, to a great extent, to the entrainment of an AAIW branch. The distributions of nutrients and apparent oxygen
utilization are discussed in terms of regional ocean circulation. Our analysis suggests a circulation pattern of the various
intermediate waters along the western Portuguese margin: MW extends all over the area, but its presence is more pronounced
around cape St. Vincent; SAIW apparently moves southward, reaching the Gorringe bank region, and AAIW flows northward along
the coast and around the bank. 相似文献
100.
Kieran P. Donaghy 《Journal of Geographical Systems》2011,13(1):17-30
In the literatures of regional science, urban economics, and urban development planning, a working assumption is that individuals
respond to incentives and regulations, given their preferences. Models for planning and policy analyses are used to consider
what might occur if the incentives or regulations were different. In these models, however, preferences are usually assumed
to be given and stable, and agents are usually assumed to be homogeneous. This paper focuses on the implications of making
preferences in models of policy implementation endogenously determined and time varying heterogeneous agents. We consider
first the recent literature on intertemporal choice and preference change, which cuts across many disciplines, and more briefly
the literature on norm-regarding behavior. We then elaborate a simple model of transportation demand—from a static to a dynamic
orientation, from fixed and exogenously given preferences of strictly self-regarding agents to endogenously determined and
policy-induced preferences of heterogeneous agents—and illustrate its characteristics with simple numerical examples. 相似文献