全文获取类型
收费全文 | 37011篇 |
免费 | 4621篇 |
国内免费 | 2975篇 |
专业分类
电工技术 | 2347篇 |
综合类 | 2935篇 |
化学工业 | 4712篇 |
金属工艺 | 1413篇 |
机械仪表 | 3472篇 |
建筑科学 | 1558篇 |
矿业工程 | 730篇 |
能源动力 | 1506篇 |
轻工业 | 878篇 |
水利工程 | 580篇 |
石油天然气 | 1540篇 |
武器工业 | 369篇 |
无线电 | 3542篇 |
一般工业技术 | 3083篇 |
冶金工业 | 3862篇 |
原子能技术 | 138篇 |
自动化技术 | 11942篇 |
出版年
2024年 | 413篇 |
2023年 | 1082篇 |
2022年 | 1735篇 |
2021年 | 1695篇 |
2020年 | 1383篇 |
2019年 | 1128篇 |
2018年 | 1043篇 |
2017年 | 1227篇 |
2016年 | 1459篇 |
2015年 | 1578篇 |
2014年 | 2236篇 |
2013年 | 2246篇 |
2012年 | 2339篇 |
2011年 | 3201篇 |
2010年 | 2308篇 |
2009年 | 2444篇 |
2008年 | 2322篇 |
2007年 | 2569篇 |
2006年 | 2127篇 |
2005年 | 1916篇 |
2004年 | 1580篇 |
2003年 | 1428篇 |
2002年 | 1123篇 |
2001年 | 901篇 |
2000年 | 641篇 |
1999年 | 452篇 |
1998年 | 345篇 |
1997年 | 267篇 |
1996年 | 206篇 |
1995年 | 185篇 |
1994年 | 151篇 |
1993年 | 137篇 |
1992年 | 110篇 |
1991年 | 87篇 |
1990年 | 77篇 |
1989年 | 73篇 |
1988年 | 38篇 |
1987年 | 30篇 |
1986年 | 42篇 |
1985年 | 29篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1966年 | 12篇 |
1964年 | 23篇 |
1963年 | 17篇 |
1961年 | 15篇 |
1960年 | 16篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
水电站引水发电系统无压隧洞中的水力过渡过程是近年来电站设计中出现的一个新课题,特别是流域梯级电站开发中经常遇到。结合工程实例应用扩散法,给出了无压隧洞水力过渡过程数值模拟的基本方程以及上下游及弃水堰等边界附加方程,模拟了弃水堰布置在不同位置下,无压隧洞内的水位变化过程。研究成果和讨论对实际工程应用具有参考意义。 相似文献
53.
54.
This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 demonstrated that the relative allocation of attention shifts rapidly, favoring one item and then another. In Experiment 2, a paradigm was used that made it possible to track the absolute allocation of attention to individual items. This experiment showed that attention was allocated to one object for 100-150 ms before attention began to be allocated to the next object. These findings support models of attention that posit serial processing in demanding visual search tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
55.
Qing Li 《Computer Standards & Interfaces》1991,13(1-3):99-103
The term ‘object-oriented database’ has been used to refer to different characteristics and mechanisms supported by semantic databases and (behaviorally) object-oriented ones. While this indicates the current confusion due to the lack of a common model, it also suggests the potential desirability of combining these two kinds of modeling facilities into the same nutshell. This paper summarizes from these two paradigms the features common to both, the features influenced/adopted by each other, and the features which are presented in one paradigm but missing from the other. After a brief analysis and discussion of these features, we conclude this paper by proposing our major theme: a complete object data model should take the union of the facilities offered by these two kinds of models. 相似文献
56.
This experiment was designed to use the graded dose-related amnesia produced by the benzodiazepine lorazepam (1.0, 2.0 mg/70 kg, oral) and the anticholinergic scopolamine (0.3, 0.6 mg/70 kg, subcutaneous) as a tool to explore the cognitive and neurochemical mechanisms underlying metamemory in the judgment of learning paradigm, with a placebo-controlled independent groups design in healthy volunteers (n=12/group). Results provide evidence for a pharmacological dissociation between effects on memory versus metamemory (relative accuracy of item-by-item monitoring) across a range of levels of memory performance and suggest that the drugs selectively impair those aspects of metamnemonic monitoring that require participants' awareness of their overall current state of functioning (absolute accuracy of prospective item-by-item monitoring, prospective global monitoring) but not those that rely solely on assessment of individual item characteristics (relative accuracy of item-by-item monitoring). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
57.
Melt index is considered an important quality variable determining product specifications. Reliable prediction of melt index (MI) is crucial in quality control of practical propylene polymerization processes. In this paper a least squares support vector machines (LS‐SVM) soft‐sensor model of propylene polymerization process is developed to infer the MI of polypropylene from other process variables. Considering the use of a SSE cost function without regularization might lead to less robust estimates; the weighted least squares support vector machines (weighted LS‐SVM) approach of propylene polymerization process is further proposed to obtain a robust estimation of melt index. The performance of standard SVM model is taken as a basis of comparison. A detailed comparison research among the standard SVM, LS‐SVM, and weighted LS‐SVM models is carried out. The research results confirm the effectiveness of the presented methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 285–289, 2006 相似文献
58.
Hydrocarbon exploration risk evaluation through uncertainty and sensitivity analyses techniques 总被引:1,自引:0,他引:1
Paolo Ruffo Livia Bazzana Alberto Consonni Anna Corradi Andrea Saltelli Stefano Tarantola 《Reliability Engineering & System Safety》2006,91(10-11):1155-1162
The evaluation of the exploration risk in the oil industry is a fundamental component of the decision process related to the exploratory phase. In this paper the two basic components of the exploratory risk: trap geometry and trapped hydrocarbon quantities (fluid), are compounded in a single coherent uncertainty and sensitivity approach. The results clarify that the model geometry influences each Petroleum System Modeling step and that the geometric uncertainty is correlated with the fluid uncertainty. The geometric uncertainty evaluation makes use of geostatistical techniques that produce a number of possible realizations of the trap geometry, all compatible with available data. The evaluation of the fluid uncertainty, through a Monte Carlo methodology, allows us to compute the possible quantities of oil and gas, generated in a basin and migrated from the hydrocarbon source location to each single trap. The final result is the probability distribution of oil and gas for each trap in the basin, together with other useful indicators like: the hydrocarbon filling probability map, the closure probability map, the drainage area probability map, the spilling paths probabilities, the trap-filling scenarios. 相似文献
59.
60.