全文获取类型
收费全文 | 701921篇 |
免费 | 27957篇 |
国内免费 | 13535篇 |
专业分类
电工技术 | 24929篇 |
技术理论 | 56篇 |
综合类 | 19944篇 |
化学工业 | 108183篇 |
金属工艺 | 32638篇 |
机械仪表 | 31836篇 |
建筑科学 | 34022篇 |
矿业工程 | 12887篇 |
能源动力 | 18777篇 |
轻工业 | 47777篇 |
水利工程 | 8959篇 |
石油天然气 | 29298篇 |
武器工业 | 2613篇 |
无线电 | 82696篇 |
一般工业技术 | 110535篇 |
冶金工业 | 96760篇 |
原子能技术 | 11158篇 |
自动化技术 | 70345篇 |
出版年
2023年 | 5825篇 |
2022年 | 10391篇 |
2021年 | 15117篇 |
2020年 | 11718篇 |
2019年 | 10576篇 |
2018年 | 13440篇 |
2017年 | 14691篇 |
2016年 | 13766篇 |
2015年 | 15166篇 |
2014年 | 21024篇 |
2013年 | 34741篇 |
2012年 | 28701篇 |
2011年 | 34339篇 |
2010年 | 28806篇 |
2009年 | 29376篇 |
2008年 | 29387篇 |
2007年 | 28990篇 |
2006年 | 28484篇 |
2005年 | 25729篇 |
2004年 | 19704篇 |
2003年 | 18309篇 |
2002年 | 16859篇 |
2001年 | 16686篇 |
2000年 | 16692篇 |
1999年 | 19050篇 |
1998年 | 33490篇 |
1997年 | 24108篇 |
1996年 | 19818篇 |
1995年 | 15140篇 |
1994年 | 13077篇 |
1993年 | 11615篇 |
1992年 | 8637篇 |
1991年 | 7835篇 |
1990年 | 7184篇 |
1989年 | 6815篇 |
1988年 | 6257篇 |
1987年 | 5041篇 |
1986年 | 4866篇 |
1985年 | 5350篇 |
1984年 | 4806篇 |
1983年 | 4393篇 |
1982年 | 3997篇 |
1981年 | 4171篇 |
1980年 | 3764篇 |
1979年 | 3664篇 |
1978年 | 3622篇 |
1977年 | 4213篇 |
1976年 | 5712篇 |
1975年 | 3113篇 |
1974年 | 2987篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Simulation is useful for evaluating protocol performance and operation. However, the lack of rigor with which it's applied threatens the credibility of the published research within the manet research community. Mobile ad hoc networks (manets) allow rapid deployment because they don't depend on a fixed infrastructure. Manet nodes can participate as the source, the destination, or an intermediate router. This flexibility is attractive for military applications, disaster-response situations, and academic environments where fixed net working infrastructures might not be available. 相似文献
12.
Observer-based estimators (OBE) were used for estimation of state variables and kinetic parameters in an anaerobic digestion (AD) process. A simplified first-order model with time-varying kinetic parameters was used to design an OBE for kinetic parameter estimation. This approach was validated on a laboratory-scale anaerobic reactor equipped with a multiwavelength fluorometer for on-line measurements of COD and VFA concentrations in the reactor effluent. The proposed estimators provide continuous adjustment of kinetic parameters and can be used for predictions of state variables between samples acquisition and during sensor failure. 相似文献
13.
In this study, feasibility of membrane separation for the removal of indigenous noroviruses (NVs) is evaluated. The indigenous NV gene was never detected from ultrafiltration (UF) permeates of sewage sludge and treated wastewater. Indigenous NV gene was also not detected from permeates of sewage sludge and treated wastewater by microfiltration (MF) with a pore size of 0.1 microm (MF0.1). Even though the pore size of MF (0.1 microm) was much larger than the diameter of virus particle (approximately 30-40nm), more than 4-log10 reduction value (LRV) at maximum was achieved by membrane separation with MF0.1. NV genes were often detected from permeates of sewage sludge and treated wastewater by MF with a pore size of 0.45 microm (MF0.45), although the maximum log10 reduction values were more than 3.59 for sewage sludge and more than 2.90 for treated wastewater. It is important to verify factors determining the removal efficiency of viruses with MF membranes. 相似文献
14.
15.
S H Lee J H Ko J R Kim Y J Kim J J Lee C W Kim T H Lee 《Water science and technology》2006,53(4-5):115-123
The adverse effect of nitrate on the phosphate release rate in the anaerobic phase was observed and was hardly explainable with conventional EBPR process models. Four possible mechanisms were proposed including substrate competition, reduced fermentation, parallel reaction and sequential reaction. Batch experiments were designed and conducted to identify the dominant mechanism. Results showed that the sequential reaction was the only possible mechanism where only denitrification occurred if any nitrate existed in the anaerobic phase. Then the phosphate release following after the nitrate was completely removed. Nitrate inhibition effect was added into the PHA storage rate to incorporate the sequential reaction in the conventional ASM3 plus EAWAG bio-P module (ASM3 + P). Nitrate inhibition coefficient, K(I,NO,PAO) was found to be as low as 0.05 mg/L. This correlated well with experimental observation where no also meant that the anaerobic compartment of a continuous flow reactor could be seriously affected by the residual nitrate contained in the sludge recycle flow. This phenomenon caused overestimation of the phosphate uptake rate and consequently underestimation of PO4(3-) -P concentration. This problem was resolved by incorporation of a nitrate inhibition term in the ASM3 + P for more accurate simulation of the EBPR process. 相似文献
16.
17.
18.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content
of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen
content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient,
the duration of the degassing operation, and the vacuum used in the treatment.
__________
Translated from Metallurg, No. 7, pp. 68–69, July, 2006. 相似文献
19.
The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%. 相似文献
20.
Supported metal catalysts, particularly noble metals supported on SiO2, have attracted considerable attention due to the importance of the silica–metal interface in heterogeneous catalysis and in electronic device fabrication. Several important issues, e.g., the stability of the metal–oxide interface at working temperatures and pressures, are not well-understood. In this review, the present status of our understanding of the metal–silica interface is reviewed. Recent results of model studies in our laboratories on Pd/SiO2/Mo(1 1 2) using LEED, AES and STM are reported. In this work, epitaxial, ultrathin, well-ordered SiO2 films were grown on a Mo(1 1 2) substrate to circumvent complications that frequently arise from the silica–silicon interface present in silica thin films grown on silicon. 相似文献