全文获取类型
收费全文 | 2436篇 |
免费 | 34篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 28篇 |
综合类 | 9篇 |
化学工业 | 170篇 |
金属工艺 | 15篇 |
机械仪表 | 24篇 |
建筑科学 | 43篇 |
矿业工程 | 4篇 |
能源动力 | 13篇 |
轻工业 | 81篇 |
水利工程 | 14篇 |
石油天然气 | 7篇 |
武器工业 | 1篇 |
无线电 | 120篇 |
一般工业技术 | 148篇 |
冶金工业 | 1685篇 |
原子能技术 | 2篇 |
自动化技术 | 120篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 51篇 |
2012年 | 21篇 |
2011年 | 36篇 |
2010年 | 32篇 |
2009年 | 26篇 |
2008年 | 36篇 |
2007年 | 46篇 |
2006年 | 34篇 |
2005年 | 60篇 |
2004年 | 22篇 |
2003年 | 27篇 |
2002年 | 29篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 69篇 |
1998年 | 487篇 |
1997年 | 308篇 |
1996年 | 199篇 |
1995年 | 125篇 |
1994年 | 113篇 |
1993年 | 105篇 |
1992年 | 19篇 |
1991年 | 32篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 39篇 |
1987年 | 33篇 |
1986年 | 31篇 |
1985年 | 39篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 31篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 45篇 |
1976年 | 112篇 |
1975年 | 12篇 |
1973年 | 4篇 |
排序方式: 共有2484条查询结果,搜索用时 15 毫秒
91.
92.
93.
The role of the blood-brain barrier transporter PTS-1 in regulating concentrations of methionine enkephalin in blood and brain 总被引:1,自引:0,他引:1
The entrainment of the circadian rhythm of locomotor activity was studied in the field mouse Mus booduga in order to examine the relationship between the free-running period (tau) and minimum tolerable light pulse interval of the skeleton photoperiods. The animals were entrained under three different light/dark (LD) schedules, each out of phase with the other. They were then subjected to various skeleton photoperiods created by two repeated light pulses (LPs) interrupting darkness. Animals that selected the shorter interval between the LPs as their "subjective night" had significantly shorter tau (23.13 +/- 0.38 h) as compared to those that selected the longer dark interval as subjective night (tau = 23.87 +/- 0.18 h). When the longer dark interval was 12 h, animals selecting that interval as their subjective night included both long-tau and short-tau individuals. When both intervals of darkness were of equal duration, no difference in the selection of subjective night was seen between short and long-tau animals. When the "dusk" LP for the animals that selected the longer dark interval as subjective night was advanced by 2 h to create a new skeleton photoperiod, the number of transient cycles appearing before steady-state entrainment was found to depend on the duration of the photoperiods. When the night defined by the two LPs was reduced below 6h, a dramatic "phase jump" in the activity rhythm was observed, and the initial phase relationship was restored after a relaxation in the night duration. We observed considerable interindividual variation in the "minimum tolerable light pulse interval of skeleton photoperiods," which we suggest may be due to the observed variation in tau among individuals. 相似文献
94.
假定股票价格过程服从分数跳-扩散过程,利率满足分数Vasicek利率模型,利用分数跳-扩散过程理论以及保险精算方法,讨论了创新重置期权的定价问题,获得了创新重置看涨期权定价公式,推广了关于创新重置期权定价的相关结果. 相似文献
95.
首先通过体外模拟唾液-胃液-肠液应激实验研究乳杆菌的耐消化应激能力,然后研究其对肠道黏蛋白和Caco-2细胞的黏附及抑制肠道病原菌黏附的能力,最后探讨消化应激对乳杆菌黏附能力的影响。结果表明,副干酪乳杆菌W125、m111和发酵乳杆菌146在依次经过模拟唾液-胃液-肠液应激后存活率分别为2.70%、3.53%及11.15%,活菌数分别为7.46、7.24(lg(CFU/mL))及8.35(lg(CFU/mL)),且对黏蛋白和Caco-2细胞的黏附率显著高于其他菌株(P<0.05),分别为15.67%、8.75%、8.38%和11.47%、21.34%、10.44%;3株菌株均可通过排除、竞争和替代的方式抑制大肠杆菌CICC10899和沙门菌WX29对肠道的黏附,黏附抑制率均大于13.51%;消化应激显著降低了副干酪乳杆菌W125和发酵乳杆菌146对肠道的黏附能力(P<0.05),但显著增加了副干酪乳杆菌m111的黏附能力(P<0.05),黏附率由17.60%增加到30.45%,且主要黏附素由消化应激前的表层蛋白变为应激后的蛋白和多糖;消化应激前后副干酪乳杆菌m111均... 相似文献
96.
Summary The thermal cure of a monofunctional maleimide N-(4-phenoxy)-phenylmaleimid (1) was examined using differential scanning calorimetry (DSC). The analogous bis-maleimide bis-(4-maleimidophenyl)ether (2) was also analyzed in the same manner for comparison. Polymerization kinetics derived from scanning DSC measurements showed an order of reaction varying between n=1 and 2 for (1), compared to an order of reaction between n=2 and 3 (by multiple linear regression analysis) for (2). The overall enthalpy of polymerization (Ho) for N-(4-phenoxy)-phenylmaleimide (94kJ/mole) agrees well with that obtained for maleimide itself (89kJ/mole) using conventional calorimetric techniques indicating that polymerization appears complete within the timescale of the experiment. In contrast the analogous BMI displays a markedly lower overall polymerization enthalpy (ca. 66kJ/mole) indicating an apparent conversion of only 37%. 相似文献
97.
Steam‐air blown bubbling fluidized bed biomass gasification (BFBBG): Multi‐scale models and experimental validation 下载免费PDF全文
Richard B. Bates Ahmed F. Ghoniem Whitney S. Jablonski Daniel L. Carpenter Christos Altantzis Aaron Garg John L. Barton Ran Chen Randall P. Field 《American Institute of Chemical Engineers》2017,63(5):1543-1565
During fluidized bed biomass gasification, complex gas‐solid mixing patterns and numerous chemical and physical phenomena make identification of optimal operating conditions challenging. In this work, a parametric experimental campaign was carried out alongside the development of a coupled reactor network model which successfully integrates the individually validated sub‐models to predict steady‐state reactor performance metrics and outputs. The experiments utilized an integrated gasification system consisting of an externally‐heated, bench‐scale, 4‐in., 5 kWth, fluidized bed steam/air blown gasifier fed with woody biomass equipped with a molecular beam mass spectrometer to directly measure tar species. The operating temperature (750–850°C) and air/fuel equivalence ratio (ER = 0–0.157) were independently varied to isolate their effects. Elevating temperature is shown to improve the char gasification rate and reduce tar concentrations. Air strongly impacts the composition of tar, accelerating the conversion of lighter polycyclic‐aromatic hydrocarbons into soot precursors, while also improving the overall carbon conversion. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1543–1565, 2017 相似文献
98.
Todd J. Toops D. Barton Smith William P. Partridge 《Applied catalysis. B, Environmental》2005,58(3-4):245-254
A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NOx adsorber catalyst, Pt/K/Al2O3, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al2O3 phase with associated hydroxyl groups at the surface, and an alkalized-Al2O3 phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7 nm-sized Pt, 34% for pure Al2O3 and 65% for the alkalized-Al2O3. NO2 and CO2 chemisorption at 250 °C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250 °C. Pt/Al2O3 adsorbs 0.087 μmol CO2/m2and 2.0 μmol NO2/m2, and Pt/K/Al2O3 adsorbs 2.0 μmol CO2/m2and 6.4 μmol NO2/m2. This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al2O3 during both lean and rich periods of the NOx adsorber catalyst cycle. 相似文献
99.
100.
Pedestrian injuries are a significant health risk to children, particularly those 5–9 years of age. Surprisingly, few studies have explored parent-related factors that may moderate this risk. The present study used naturalistic observations of parent–child pairs crossing at uncontrolled intersections and a short interview to examine parental supervision of children during crossings, modeling of safe-crossing behaviors, beliefs about how children come to cross streets safely, and whether child attributes (age, sex) relate to parental practices and beliefs. Results revealed that parents more closely supervised younger than older children, they modeled safer crossing practices for sons more than daughters, particularly younger sons, and although over half the sample believed children need to be explicitly taught how to cross safely, few actually provided any instruction when crossing with their children. Providing parents both with guidelines for how to accurately appraise their child's readiness for crossing independently and with information about best practices for teaching children how to cross safely may facilitate parents’ implementing these practices, particularly if this is coupled with public advocacy highlighting the important role they could play to reduce the risk of child pedestrian injury. 相似文献