全文获取类型
收费全文 | 105653篇 |
免费 | 11806篇 |
国内免费 | 7727篇 |
专业分类
电工技术 | 11061篇 |
技术理论 | 3篇 |
综合类 | 9251篇 |
化学工业 | 12498篇 |
金属工艺 | 3619篇 |
机械仪表 | 11154篇 |
建筑科学 | 4856篇 |
矿业工程 | 2736篇 |
能源动力 | 6063篇 |
轻工业 | 2238篇 |
水利工程 | 5886篇 |
石油天然气 | 4665篇 |
武器工业 | 1367篇 |
无线电 | 19046篇 |
一般工业技术 | 11754篇 |
冶金工业 | 4445篇 |
原子能技术 | 2358篇 |
自动化技术 | 12186篇 |
出版年
2024年 | 469篇 |
2023年 | 1447篇 |
2022年 | 2489篇 |
2021年 | 3001篇 |
2020年 | 3315篇 |
2019年 | 2700篇 |
2018年 | 2666篇 |
2017年 | 3664篇 |
2016年 | 3971篇 |
2015年 | 4405篇 |
2014年 | 6173篇 |
2013年 | 6665篇 |
2012年 | 7417篇 |
2011年 | 7943篇 |
2010年 | 5663篇 |
2009年 | 5998篇 |
2008年 | 5967篇 |
2007年 | 7119篇 |
2006年 | 6642篇 |
2005年 | 5801篇 |
2004年 | 4892篇 |
2003年 | 4482篇 |
2002年 | 3521篇 |
2001年 | 3216篇 |
2000年 | 2695篇 |
1999年 | 2184篇 |
1998年 | 1735篇 |
1997年 | 1650篇 |
1996年 | 1385篇 |
1995年 | 1121篇 |
1994年 | 1024篇 |
1993年 | 829篇 |
1992年 | 660篇 |
1991年 | 483篇 |
1990年 | 446篇 |
1989年 | 318篇 |
1988年 | 221篇 |
1987年 | 151篇 |
1986年 | 107篇 |
1985年 | 85篇 |
1984年 | 98篇 |
1983年 | 65篇 |
1982年 | 50篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 26篇 |
1977年 | 14篇 |
1974年 | 13篇 |
1959年 | 31篇 |
1951年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
介绍了35t/h锅炉扩容改造为55t/h非标锅炉的技术成功经验。从增加锅炉的容积、受热面面积、燃烧器喷嘴改造三个方面介绍了对锅炉本体的改造,改造后实现了锅炉的水位、汽温及燃烧自动调节,提高了锅炉的热效率为以后的锅炉扩容改造提供了实践经验。 相似文献
102.
103.
对企业账面利润与现金流量关系的认识 总被引:3,自引:0,他引:3
本文阐述了企业账面利润与现金流量的关系 ,指出了企业账面利润与现金流量的四个不同点 ,并且提出了一个现代企业应如何在四个方面做好工作 ,正确处理好这两者的关系。 相似文献
104.
本文通过对中州分公司正在考虑建设的信息网建设实际情况,结合山东分公司、广西分公司取得的经验,对计量管理信息网的应用进行了探讨。 相似文献
105.
ListofSymbol B———Buoyancy ,m·s- 2 ; c———Concentrationofsoluteelement ; Cμ———Turbulentconstant; D———Diffusivityofsoluteelement ,m2 ·s- 1 ; fl,fs———Liquidandsolidfraction ; fμ———Turbulentcoefficient ; h———Enthalpy ,J·kg- 1 ; k———Turbulentkineticenergy ,m2 ·s- 2 ; kp———Equilibriumpartitioncoefficient; Kp———Permeabilityofmushyzone ,m2 ; K0 ———Permeabilitycoefficient; p———Pressure ,Pa ; Pr———Prandtlnumber ;… 相似文献
106.
David M. Scott Debendra K. Das Vijayagandeeban Subbaihaannadurai 《Petroleum Science and Technology》2006,24(8):895-909
A finite element scheme is presented to model the dissociation of gas hydrates in porous media by hot water injection. We show a complete derivation of the finite element formulation, including the associated mass and energy conservation equations capable of performing transient analysis of both conductive and convective heat transfer for gas and liquid flow in porous media. The scheme also includes the latent heat effect to accommodate the change of phase due to melting of hydrate. In the companion paper, Part II, this method is successfully applied to hydrate reservoirs. 相似文献
107.
Ronald Smith 《Canadian Metallurgical Quarterly》2004,130(2):165-169
For longitudinally uniform stretches of waterways there is a mixing center for the across-channel location of a steady point source in steady flow, such that complete mixing is achieved as soon as possible and there is no concentration overshoot at either of the two shorelines. A mathematical definition of the mixing center is the zero of the first oscillatory cross-channel diffusion mode. With the shorelines plus four interior data points across the channel, the starting estimate for the mixing center suffices to keep peak shoreline concentrations to within 6% of optimal. For comparison, a source at mid flow gives 18% shoreline concentration overshoot in the test case. Should very high precision be required, the Appendix gives an iterative construction that converges to the first oscillatory diffusion mode. 相似文献
108.
Predictions of the discharge and the associated sediment concentration are very useful ingredients in any water resources reservoir design, planning, maintenance, and operation. Although there are many empirical relationships between the discharge and sediment concentration amounts, they need estimation of model parameters. Generally, parameter estimations are achieved through the regression method (RM), which has several restrictive assumptions. Such models are locally valid and their structures and parameter values are questionable from region to others. This paper proposes a new approach for sediment concentration prediction provided that there are measurements of discharge and sediment concentration. The basis of the methodology is a dynamic transitional model between successive time instances based on two variables, namely, discharge and sediment concentration measurements. The transition matrix elements are estimated from the measurements through a special form of the artificial neural networks as perceptrons. The sediment concentration predictions from discharge measurements are achieved through a perceptron Kalman filtering (PKF) technique. In the meantime, this technique also provides temporal predictions. A certain portion of the measurement sequence is employed for the model parameter estimations through training and the remaining part is used for the model verification. Detailed comparisons between RM and PKF approaches are presented and, finally, it is shown that the latter model works dynamically by simulating the observation scatter diagram in the best possible manner with smaller prediction errors. The application of the methodology is performed for the discharge and sediment concentration measurements obtained from the Mississippi River basin at St. Louis, Missouri. It is found that the PKF methodology has smaller average relative, root-mean-square, and absolute errors than RM. Furthermore, graphical representation, such as the scatter and frequency diagrams, indicated that the PKF approach has superiority over the RM. 相似文献
109.
A weighting algorithm to determine the coordinates of the center of a Gaussian laser beam projected onto a matrix photodetector is considered. The influence of the internal noise of the photodetector, the maximum brightness of the signal at the beam maximum, and the beam radius on the precision of the algorithm is investigated. Recommendations on image processing are presented. 相似文献
110.