全文获取类型
收费全文 | 555509篇 |
免费 | 30242篇 |
国内免费 | 16301篇 |
专业分类
电工技术 | 24463篇 |
技术理论 | 45篇 |
综合类 | 25601篇 |
化学工业 | 88471篇 |
金属工艺 | 28653篇 |
机械仪表 | 28487篇 |
建筑科学 | 32508篇 |
矿业工程 | 13005篇 |
能源动力 | 14781篇 |
轻工业 | 41098篇 |
水利工程 | 9068篇 |
石油天然气 | 27514篇 |
武器工业 | 2816篇 |
无线电 | 61533篇 |
一般工业技术 | 78588篇 |
冶金工业 | 55521篇 |
原子能技术 | 8715篇 |
自动化技术 | 61185篇 |
出版年
2023年 | 5962篇 |
2022年 | 10831篇 |
2021年 | 15495篇 |
2020年 | 11622篇 |
2019年 | 10111篇 |
2018年 | 12395篇 |
2017年 | 13714篇 |
2016年 | 12877篇 |
2015年 | 15675篇 |
2014年 | 20521篇 |
2013年 | 29731篇 |
2012年 | 27694篇 |
2011年 | 32085篇 |
2010年 | 27766篇 |
2009年 | 27321篇 |
2008年 | 27013篇 |
2007年 | 26113篇 |
2006年 | 25568篇 |
2005年 | 22813篇 |
2004年 | 16896篇 |
2003年 | 15510篇 |
2002年 | 14370篇 |
2001年 | 13429篇 |
2000年 | 13297篇 |
1999年 | 14055篇 |
1998年 | 18457篇 |
1997年 | 14185篇 |
1996年 | 12162篇 |
1995年 | 9409篇 |
1994年 | 8122篇 |
1993年 | 6673篇 |
1992年 | 5280篇 |
1991年 | 4626篇 |
1990年 | 4083篇 |
1989年 | 3931篇 |
1988年 | 3650篇 |
1987年 | 2922篇 |
1986年 | 2718篇 |
1985年 | 2969篇 |
1984年 | 2710篇 |
1983年 | 2508篇 |
1982年 | 2218篇 |
1981年 | 2278篇 |
1980年 | 2126篇 |
1979年 | 2167篇 |
1978年 | 2137篇 |
1977年 | 2388篇 |
1976年 | 3214篇 |
1975年 | 1839篇 |
1973年 | 1781篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Methylated-β-cyclodextrin (Me-β-CD) was used to complex the photoinitiator, 2,2-dimethoxy-2-phenyl acetophenone (DMPA), yielding a water-soluble host/guest complex. The comparative studies demonstrated that the Me-β-CD complexed DMPA exhibited a high photoreactivity identical to the uncomplexed DMPA, while the CD complex obviously influenced the products of primary photolysis of DMPA and the photopolymerization kinetics due to the steric effect of CD on the subsequent initiation reactions. The photopolymerization rate of acrylamide can be described by the equation: Rp=K[2a]0.62[M]1.37[I]0.5[Me-β-CD]0. The mechanism of polymerization was also discussed. 相似文献
82.
J Byrne S Kienzle D Johnson G Duke V Gannon B Selinger J Thomas 《Water science and technology》2006,53(10):327-334
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies. 相似文献
83.
Physically based simulation of human hair is a well studied and well known problem. But the “pure” physically based representation of hair (and other animation elements) is not the only concern of the animators, who want to “control” the creation and animation phases of the content. This paper describes a sketch-based tool, with which a user can both create hair models with different styling parameters and produce animations of these created hair models using physically and key frame-based techniques. The model creation and animation production tasks are all performed with direct manipulation techniques in real-time. 相似文献
84.
Filled fibrous sorbents modified with transition metal ferro- and ferricyanides capable to recover americium(III) and rare-earth metals(III) from nitric acid solutions were prepared. The most complete and rapid recovery is attained on complex-forming and cation-exchange sorbents (as filled fibrous materials) saturated with nickel ions. The sorbents are characterized by good kinetic properties and can be used for recovery of the above metals. 相似文献
85.
Yunlei Li Dick de Ridder Robert P.W. Duin Marcel J.T. Reinders 《Pattern recognition》2008,41(1):320-330
Samples can be measured with different precisions and reliabilities in different experiments, or even within the same experiment. These varying levels of measurement noise may deteriorate the performance of a pattern recognition system, if not treated with care. Here we seek to investigate the benefit of incorporating prior knowledge about measurement noise into system construction. We propose a kernel density classifier which integrates such prior knowledge. Instead of using an identical kernel for each sample, we transform the prior knowledge into a distinct kernel for each sample. The integration procedure is straightforward and easy to interpret. In addition, we show how to estimate the diverse measurement noise levels in a real world dataset. Compared to the basic methods, the new kernel density classifier can give a significantly better classification performance. As expected, this improvement is more obvious for small sample size datasets and large number of features. 相似文献
86.
The discrimination problem for two normal populations with the same covariance matrix when additional information on the population is available is considered. A study of the robustness properties against training sample contamination of classification rules that incorporate this additional information is performed. These rules have received recently attention where their total misclassification probability (TMP) is proved to be lower than Fisher's linear discriminant rule. The results of a simulation study on the TMP which compares the behaviour of the new rules against Fisher's rule and some of its robustified versions under different types of contamination are presented. These results show that the rules that incorporate the additional information not only have lower TMP, but they also prevent against some types of contamination. In order to achieve prevention from all types of contamination a robustifed version of these rules is recommended. 相似文献
87.
During experiments on the MSL-1 (first microgravity science laboratory) mission of the space shuttle (STS-83 and STS-94, April
and July 1997), a droplet of palladium-silicon alloy was electromagnetically levitated for viscosity measurements. For the
nondeforming droplet, the resultant magnetohydrodynamic (MHD) flow inside the drop can be inferred from motion of impurity
particulates on the surface. In the experiments, subsequent to melting, Joule heating produces a continuous reduction of viscosity
of the fluid resulting in an acceleration of the flow with time. These observations indicate formation of a pair of co-rotating
toroidal flow structures inside the spheroidal drop that undergo flow instabilities. As the fluid temperature rises, the amplitude
of the secondary flow increases, and beyond a point, the tracers exhibit noncoherent chaotic motion signifying emergence of
turbulence inside the drop. Assuming that the observed laminar-turbulent transition is shear-layer type, the internal structure
of the toroidal loops is used to develop a semiempirical correlation for the onset of turbulence. Our calculations indicate
that the suggested correlation is in modest agreement with the experimental data, with the transition occurring at a Reynolds
number of 600. 相似文献
88.
结合兰州市的水泥标准稠度用水量方法测定 (代用法 )的实例 ,分析代用法测定标准稠度用水量的缺点 ,并对此方法提出了一些改进措施 相似文献
89.
Bestehen ausreichende Anhaltspunkte für die Hochwassergef?hrdung, ist die Gemeinde verpflichtet, sich durch Nachforschungen
Gewissheit über das Vorliegen oder Nichtvorliegen eines Hochwasserabflussgebietes gem § 38 Abs 3 WRG zu verschaffen. Liegt
ein solches vor, hat sie gem § 12 Abs 1 Z 2 krnt GplG dieses im Fl?chenwidmungsplan ersichtlich zu machen. Erteilt die Gemeinde
eine Baubewilligung ohne diese von der Erteilung einer wasserrechtlichen Bewilligung abh?ngig zu machen, haftet sie für die
Kosten der Bauführung, die bei gesetzes-konformer Vorgangsweise unterlassen worden w?re. 相似文献
90.
风管摩擦阻力的直接计算方法 总被引:2,自引:1,他引:1
提出用高精度的反映密度、黏度和温度关系的经验公式和Colebrook公式计算风管摩擦阻力系数的方法。分析和算例表明,用该方法计算,计算结果比采用常用工程设计方法更为准确,为应用计算机进行风道设计提供了直接、简便的方法。 相似文献