全文获取类型
收费全文 | 1259篇 |
免费 | 42篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 8篇 |
化学工业 | 227篇 |
金属工艺 | 2篇 |
机械仪表 | 9篇 |
建筑科学 | 35篇 |
能源动力 | 21篇 |
轻工业 | 141篇 |
水利工程 | 12篇 |
石油天然气 | 2篇 |
无线电 | 72篇 |
一般工业技术 | 193篇 |
冶金工业 | 456篇 |
原子能技术 | 1篇 |
自动化技术 | 124篇 |
出版年
2022年 | 19篇 |
2021年 | 20篇 |
2020年 | 32篇 |
2019年 | 23篇 |
2018年 | 20篇 |
2017年 | 23篇 |
2016年 | 30篇 |
2015年 | 24篇 |
2014年 | 25篇 |
2013年 | 49篇 |
2012年 | 54篇 |
2011年 | 57篇 |
2010年 | 58篇 |
2009年 | 50篇 |
2008年 | 68篇 |
2007年 | 53篇 |
2006年 | 57篇 |
2005年 | 62篇 |
2004年 | 42篇 |
2003年 | 37篇 |
2002年 | 39篇 |
2001年 | 29篇 |
2000年 | 19篇 |
1999年 | 32篇 |
1998年 | 22篇 |
1997年 | 21篇 |
1996年 | 24篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 16篇 |
1992年 | 20篇 |
1991年 | 7篇 |
1990年 | 19篇 |
1989年 | 26篇 |
1988年 | 20篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 4篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有1303条查询结果,搜索用时 15 毫秒
101.
Holmbeck Grayson N.; Johnson Sharon Z.; Wills Karen E.; McKernon Wendy; Rose Brigid; Erklin Shannon; Kemper Therese 《Canadian Metallurgical Quarterly》2002,70(1):96
The purpose of this study was to test a mediational model of associations between parental overprotectiveness (OP), behavioral autonomy, and psychosocial adjustment in 68 families with 8- and 9-year-old preadolescents with spina bifida and a demographically matched sample of 68 families with able-bodied children. Measures included questionnaire and observational assessments of parental OP; parent and child reports of behavioral autonomy; and parent, child, and teacher reports of preadolescent adjustment. On the basis of both questionnaire and observational measures of OP, mothers and fathers of children with spina bifida were significantly more overprotective than their counterparts in the able-bodied sample, although this group difference was partially mediated by children's cognitive ability. Both questionnaire and observational measures of parental OP were associated with lower levels of preadolescent decision-making autonomy as well as with parents being less willing to grant autonomy to their offspring in the future. For the questionnaire measure of OP, and only for the spina bifida sample, the mediational model was supported such that parental OP was associated with less behavioral autonomy, which was, in turn, associated with more externalizing problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
Hall Sharon M.; Tunstall Chrystal; Rugg Deborah; Jones Reese T.; Benowitz Neal 《Canadian Metallurgical Quarterly》1985,53(2):256
120 Ss (who smoked a mean of 30.5 cigarettes/day) were assigned either to intensive behavioral treatment, to nicotine gum in a low-contact treatment, or to the intensive behavioral plus nicotine gum treatment. At each assessment, Ss reported the number of cigarettes smoked in the previous 24 hrs and provided blood samples; assessments were conducted at 0, 3, 12, 26, and 52 wks. Results show that the combined treatment produced higher abstinence rates than the other 2 conditions at all assessments. These differences were significant at 3, 12, and 26 wks, but not at 52 wks. Nicotine dependence was assessed by blood cotinine levels, scores on a dependence scale, and by number of cigarettes smoked at pretreatment. It was found that Ss with high blood cotinines were more likely to be helped by nicotine gum treatment than were less dependent Ss. (4 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
104.
Processes based upon solid sorbents are currently under consideration for post-combustion CO2 capture. Twenty-four different sorbent materials were examined on a laboratory scale in a cyclic temperature swing adsorption/regeneration CO2 capture process in simulated coal combustion flue gas. Ten of these materials exhibited significantly lower theoretical regeneration energies compared to the benchmark aqueous monoethanolamine, supporting the hypothesis that CO2 capture processes based upon solids may provide cost benefits over solvent-based processes. The best performing materials were tested on actual coal-fired flue gas. The supported amines exhibited the highest working CO2 capacities, although they can become poisoned by the presence of SO2. The carbon-based materials showed excellent stability but were generally categorized as having low CO2 capacities. The zeolites worked well under dry conditions, but were quickly poisoned by the presence of moisture. Although no one type of material is without concerns, several of the materials tested have theoretical regeneration energies significantly lower than that of the industry benchmark, warranting further development research. 相似文献
105.
Sharon N. Greenwood Dr. Rashmi S. Kulkarni Dr. Michel Mikhail Dr. Brian P. Weiser 《Chembiochem : a European journal of chemical biology》2023,24(10):e202200765
DNA repair proteins participate in extensive protein−protein interactions that promote the formation of DNA repair complexes. To understand how complex formation affects protein function during base excision repair, we used SpyCatcher/SpyTag ligation to produce a covalent complex between human uracil DNA glycosylase (UNG2) and replication protein A (RPA). Our covalent “RPA−Spy−UNG2” complex could identify and excise uracil bases in duplex areas next to ssDNA−dsDNA junctions slightly faster than the wild-type proteins, but this was highly dependent on DNA structure, as the turnover of the RPA−Spy−UNG2 complex slowed at DNA junctions where RPA tightly engaged long ssDNA sections. Conversely, the enzymes preferred uracil sites in ssDNA where RPA strongly enhanced uracil excision by UNG2 regardless of ssDNA length. Finally, RPA was found to promote UNG2 excision of two uracil sites positioned across a ssDNA−dsDNA junction, and dissociation of UNG2 from RPA enhanced this process. Our approach of ligating together RPA and UNG2 to reveal how complex formation affects enzyme function could be applied to examine other assemblies of DNA repair proteins. 相似文献
106.
Cervically inseminated cryopreserved ram spermatozoa have reduced fertility due to poor mucus-penetrating ability. This effect is ameliorated by the addition of 20% (v/v) seminal plasma (SP) to the phosphate-buffered saline (PBS) thawing medium. The aims of this study were to determine whether the impaired mucus penetration was due to alterations in the sperm motility and, if so, whether these alterations were due to the SP or its viscosity, or to the medium components. To this end, artificial SP medium (ASP), a medium which supports motility but not capacitation, was compared with PBS and SP. Thawed, pooled semen from seven mature rams was layered under 1 ml each of PBS, SP and ASP and motile spermatozoa allowed to swim up (37 degrees C, 30 min). Upper regions of the overlays were harvested, and the capacitation status of the spermatozoa in each suspension determined by chlortetracycline (CTC) analysis. Sperm movement was videotaped in 300 microm chambers for both computer-aided sperm analysis assessment and manual flagellar curvature analysis. There was no effect of the culture medium on the concentration of spermatozoa recovered by swim up, nor on the proportion of motile spermatozoa. However, the spermatozoa resuspended in PBS did show changes associated with capacitation in both the CTC-binding patterns and in their movement patterns. These changes were significantly greater than those observed in spermatozoa resuspended in SP or ASP. These results indicated that the differences in sperm movement and function observed in SP medium were not due to changes in viscosity, but rather to components of the medium. 相似文献
107.
Sharon L Woodward Alexandre V Chaves Garry C Waghorn Ian M Brookes Jennifer L Burke 《Journal of the science of food and agriculture》2006,86(8):1263-1270
A trial was conducted to compare benefits obtained from feeding four types of silage. There were two silages that contained condensed tannins (CT)—lotus (Lotus corniculatus) and sulla (Hedysarum coronarium)—maize silage or traditional ryegrass pasture silage, all fed at 5 kg dry matter (DM) cow?1 day?1 with restricted pasture (RP). Cows on the RP (control) treatment and those fed the silage treatments were offered an allowance of 25 kg pasture DM cow?1 day?1, while the full pasture (FP) cows were offered 50 kg pasture DM cow?1 day?1. Silage supplementation increased both DM intake and milk yield compared with cows given RP only. Cows on the lotus silage supplement and the FP treatment had significantly higher milk production than the other silage supplemented cows (P < 0.001). For cows given lotus silage, the high milk yield was probably due to a combination of the higher nutritive value of the silage and possibly to the protein‐sparing effects of the lotus condensed tannins because the total DM intake of cows fed the lotus silage was the same as that of cows given the pasture and maize silages (P > 0.25). The high milk yield of the FP treatment was mainly a result of the cows having a higher intake of pasture than cows on all the other treatments. This study demonstrated the potential benefit of silage supplementation, particularly with lotus silage, for increased milksolids yield in summer when low pasture growth rates and quality may otherwise limit production. Copyright © 2006 Society of Chemical Industry 相似文献
108.
109.
M. Penchal Reddy W. Madhuri N. Ramamanohar Reddy K.V. Siva Kumar V.R.K. Murthy R. Ramakrishna Reddy 《Materials science & engineering. C, Materials for biological applications》2010,30(8):1094-1099
Polycrystalline MgCuZn ferrites with chemical formula Mg0.50-xCuxZn0.50Fe2O4 (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) were prepared by microwave sintering method. These powders were calcined, compacted and sintered at 950 °C for 30 min. Structural, microstructural and elemental analyses were carried out using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDS), respectively. The lattice parameter is found to increase with increasing copper content. A remarkable densification is observed with the addition of Cu ions in the ferrites. The sintered ferrite was characterized for initial permeability, dielectric constant and dielectric loss tangent and ac conductivity measurements. The temperature variation of the initial permeability of these samples was carried out from 30 °C to 200 °C. The dielectric constant, dielectric loss tangent and ac conductivity have been measured in the frequency range of 100 Hz to 1 MHz. Initial permeability and dielectric constant were found to increase and dielectric loss decreased with Cu substitution for Mg, up to x = 0.20. The ferrite powder prepared is suitable for the application in multilayer chip inductor due to its low-temperature sinterability, good magnetic properties and low loss at high frequency. 相似文献
110.