全文获取类型
收费全文 | 3810篇 |
免费 | 262篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 36篇 |
综合类 | 8篇 |
化学工业 | 889篇 |
金属工艺 | 144篇 |
机械仪表 | 66篇 |
建筑科学 | 81篇 |
矿业工程 | 5篇 |
能源动力 | 232篇 |
轻工业 | 442篇 |
水利工程 | 45篇 |
石油天然气 | 15篇 |
无线电 | 382篇 |
一般工业技术 | 751篇 |
冶金工业 | 444篇 |
原子能技术 | 27篇 |
自动化技术 | 517篇 |
出版年
2024年 | 9篇 |
2023年 | 47篇 |
2022年 | 79篇 |
2021年 | 133篇 |
2020年 | 87篇 |
2019年 | 99篇 |
2018年 | 171篇 |
2017年 | 181篇 |
2016年 | 157篇 |
2015年 | 112篇 |
2014年 | 163篇 |
2013年 | 327篇 |
2012年 | 212篇 |
2011年 | 270篇 |
2010年 | 183篇 |
2009年 | 174篇 |
2008年 | 154篇 |
2007年 | 135篇 |
2006年 | 132篇 |
2005年 | 91篇 |
2004年 | 98篇 |
2003年 | 74篇 |
2002年 | 44篇 |
2001年 | 33篇 |
2000年 | 43篇 |
1999年 | 58篇 |
1998年 | 120篇 |
1997年 | 86篇 |
1996年 | 76篇 |
1995年 | 57篇 |
1994年 | 50篇 |
1993年 | 38篇 |
1992年 | 33篇 |
1991年 | 36篇 |
1990年 | 30篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 24篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 15篇 |
1978年 | 11篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1973年 | 12篇 |
1970年 | 8篇 |
排序方式: 共有4084条查询结果,搜索用时 46 毫秒
1.
2.
3.
4.
Tek Bahadur Gurung Ram Prasad Dhakal Jay Dev Bista 《Lakes & Reservoirs: Research and Management》2006,11(3):141-148
The seasonal patterns of phytoplankton primary production, chlorophyll‐a concentration, cell number and several other limnological variables in Lake Phewa, located in the active monsoon zone in Central Himalaya, Nepal, were studied for a year beginning in April 2001. During the study period, the gross primary production and chlorophyll‐a concentrations were relatively low during the monsoon season. The phytoplankton cell number, represented by 24 genera, also fluctuated seasonally, but tended to increase in the pre‐ and post‐monsoon period. These results suggest that the monsoon plays a crucial role in the primary production and phytoplankton dynamics for Lake Phewa. Among the phytoplankton species, Microcystis aeruginosa, a representative species for eutrophic lakes, was the dominant phytoplankton. At the same time, however, it is clear that the lake is not yet heavily eutrophic. The present study suggests that the exchange of lake water during the monsoon season contributes to maintaining the health of the lake against further degradation. Nevertheless, the silt carried in the monsoon rain run‐off from the lake's catchment area suggests increasingly serious degradation problems for this small mountainous lake. 相似文献
5.
K.P. Pipe R.J. Ram 《Photonics Technology Letters, IEEE》2003,15(4):504-506
By measuring the total energy flow from an optical device, we can develop new design strategies for thermal stabilization. Here we present a comprehensive model for heat exchange between a semiconductor laser diode and its environment that includes the mechanisms of conduction, convection, and radiation. We perform quantitative measurements of these processes for several devices, deriving parameters such as a laser's heat transfer coefficient, and then demonstrate the feasibility of thermal probing for the nondestructive wafer-scale characterization of optical devices. 相似文献
6.
A comprehensive study of hazelnut oil composition with comparisons to other vegetable oils,particularly olive oil. 总被引:4,自引:0,他引:4
Benitez-Sánchez Pedro Luis León-Camacho Manuel Aparicio Ramón 《European Food Research and Technology》2003,218(1):13-19
Crude and refined hazelnut oils from different countries were characterised by major and minor compounds. Fatty acids, triacylglycerides, waxes, sterols, methyl-sterols, terpenic and aliphatic alcohols, tocopherols, tocotrienols and hydrocarbons were identified and quantified by gas chromatography and high-performance liquid chromatography. The levels of these chemical compounds in hazelnut oils together with the equivalent carbon numbers and triacylglyceride carbon numbers, were compared with the results of analyses of samples of other vegetable oils. The statistical procedure of cluster analysis was used to characterise hazelnut oils versus other edible oils. 相似文献
7.
Ramanujam J. Jinpyo Hong Kandemir M. Narayan A. Agarwal A. 《Signal Processing, IEEE Transactions on》2006,54(1):286-294
Most embedded systems have limited amount of memory. In contrast, the memory requirements of the digital signal processing (DSP) and video processing codes (in nested loops, in particular) running on embedded systems is significant. This paper addresses the problem of estimating and reducing the amount of memory needed for transfers of data in embedded systems. First, the problem of estimating the region associated with a statement or the set of elements referenced by a statement during the execution of nested loops is analyzed. For a fixed execution ordering, a quantitative analysis of the number of elements referenced is presented; exact expressions for uniformly generated references and a close upper and lower bound for nonuniformly generated references are derived. Second, in addition to presenting an algorithm that computes the total memory required, this paper also discusses the effect of transformations (that change the execution ordering) on the lifetimes of array variables, i.e., the time between the first and last accesses to a given array location. The term maximum window size is introduced, and quantitative expressions are derived to compute the maximum window size. A detailed analysis of the effect of unimodular transformations on data locality, including the calculation of the maximum window size, is presented. 相似文献
8.
9.
The thermal decomposition products of pyridinium sulfate differ from those of pyridinium sulfate supported on zirconia which in turn differs from that of pyridine adsorbed on a sulfated zirconia. Unsupported pyridinium sulfate decomposes to produce pyridine and sulfuric acid, and these subsequently react to produce oxides of carbon and sulfur. Zirconia that is sulfated and then exposed to pyridine does not release detectable amount of pyridine during heating in an inert gas; rather the pyridine undergoes oxidation reduction reactions simultaneously to release CO2 and sulfur compounds. Pyridinium sulfate supported on zirconia decomposes upon heating to release pyridine and sulfuric acid, which reacts with the zirconia. The desorption of pyridine in one case and only CO2/SOx in the other case suggests that sulfated zirconia does not contain Brønsted acidity that can form pyridinium sulfate. 相似文献
10.