全文获取类型
收费全文 | 72445篇 |
免费 | 6254篇 |
国内免费 | 3781篇 |
专业分类
电工技术 | 5316篇 |
技术理论 | 1篇 |
综合类 | 5534篇 |
化学工业 | 11873篇 |
金属工艺 | 7723篇 |
机械仪表 | 4339篇 |
建筑科学 | 6357篇 |
矿业工程 | 1843篇 |
能源动力 | 4419篇 |
轻工业 | 4632篇 |
水利工程 | 1684篇 |
石油天然气 | 3638篇 |
武器工业 | 639篇 |
无线电 | 5991篇 |
一般工业技术 | 8214篇 |
冶金工业 | 5111篇 |
原子能技术 | 1437篇 |
自动化技术 | 3729篇 |
出版年
2024年 | 305篇 |
2023年 | 1001篇 |
2022年 | 1910篇 |
2021年 | 2284篇 |
2020年 | 2435篇 |
2019年 | 1976篇 |
2018年 | 1862篇 |
2017年 | 2489篇 |
2016年 | 2625篇 |
2015年 | 2735篇 |
2014年 | 4228篇 |
2013年 | 4456篇 |
2012年 | 5224篇 |
2011年 | 5679篇 |
2010年 | 3953篇 |
2009年 | 4128篇 |
2008年 | 3683篇 |
2007年 | 4713篇 |
2006年 | 4324篇 |
2005年 | 3547篇 |
2004年 | 3113篇 |
2003年 | 2671篇 |
2002年 | 2205篇 |
2001年 | 1946篇 |
2000年 | 1607篇 |
1999年 | 1298篇 |
1998年 | 1039篇 |
1997年 | 905篇 |
1996年 | 816篇 |
1995年 | 628篇 |
1994年 | 556篇 |
1993年 | 402篇 |
1992年 | 376篇 |
1991年 | 326篇 |
1990年 | 250篇 |
1989年 | 163篇 |
1988年 | 134篇 |
1987年 | 77篇 |
1986年 | 86篇 |
1985年 | 68篇 |
1984年 | 63篇 |
1983年 | 48篇 |
1982年 | 32篇 |
1981年 | 18篇 |
1980年 | 25篇 |
1979年 | 18篇 |
1977年 | 11篇 |
1975年 | 5篇 |
1959年 | 13篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 2 毫秒
81.
82.
Baudilio Coto Carmen Martos Jos L. Pea Juan J. Espada María D. Robustillo 《Fuel》2008,87(10-11):2090-2094
Wax precipitation is one of the most important flow assurance problems. Unfortunately, experimental data are very scarce to confirm existing models for prediction of such precipitation problem. This work reports a new experimental method. Multistage fractional wax precipitation was carried out by decreasing the temperature of crude oil. No solvent dilution was used, so the effect of solvent on temperature wax precipitation was avoided. The reproducibility of the method was tested with comparable results. The precipitation curve and the wax appearance temperature were obtained for two crude oils with different chemical nature using the reported method. 相似文献
83.
Degumming of hemp fiber by high temperature alkali cooking was investigated, and the effect of temperature and dosage of alkali on the constituents, structure, and thermal degradation of hemp fiber was also discussed in this work. The morphology, structure, and thermal degradation of hemp fiber after high temperature cooking were investigated through SEM, FTIR, WAXD, and TG analysis. The results indicated that the high temperature cooking process was effective for removing hemicelluloses and lignin and could also improve the thermal stability of cellulose. Crystallinity index of the treated hemp fiber was increased, which was related to the cooking temperature and NaOH dosage. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
84.
The radical copolymerization of acyclic terpene namely geraniol [GER] with acrylonitrile [AN] in DMF at (70 ± 0.1)°C for 1 h, using benzoylperoxide (BPO) as an initiator has been carried out under inert atmosphere of nitrogen. The kinetic expression for reaction is Rp ∝ [BPO]0.5 [AN]1.0 [GER]1.0. The IR spectrum of the copolymer shows bands at 3432 and at 2244 cm?1 due to ? OH group of GER and ? CN group of AN, respectively. The 13C‐NMR spectrum shows peaks at 73–75 δ ppm and 116–120 δ ppm due to ? OH group of GER and ? CN group of AN, respectively. The thermogravimetric analysis and differential scanning calorimetry study shows that copolymer is thermally stable up to 407°C and has glass transition temperatures (Tg) 56°C. The reactivity ratios r1 (AN) and r2 (GER) have been calculated as 0.05 and 0.005, respectively. The Alfrey‐Price Q‐e parameter for GER has been calculated as 0.094 and ?2.0, respectively. The molecular weights of the copolymers have been evaluated by gel‐permeation chromatography. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
85.
86.
87.
通过高温氧化和高温磨损实验,研究了C、Cr、Ni 3个主要元素对高铬铸铁在高温条件下抗氧化和抗磨损性能的影响。结果表明:Cr含量越高,抗氧化性能和抗磨损性能越好;提高碳含量,明显提高高铬铸铁的高温抗磨性能;当w(Cr)=16%时,加入Ni能提高高铬铸铁的高温抗氧化性能;w(Cr)=30%时,Ni对高铬铸铁的抗氧化性能和抗磨损性能影响不明显.在1100℃以下,选用w(C)=2.8%,w(Cr)=30%、不加Ni的高铬铸铁铸造高温抗磨热电偶保护管,既有较好的使用寿命,又可降低成本. 相似文献
88.
系统分析了新钢公司一钢厂转炉入炉铁水温度低的原因及铁水温度对炼钢的影响,提出了提高铁水温度的措施及转炉应对低温铁水的办法。 相似文献
89.
Patterns in the solidification of a pure material are dealt with in this article. Results, deduced from a simple model based on heat conduction in the two phases and the effect of surface tension on the equilibrium temperature at the moving front, present a guide for experimental work. By introducing far-field conditions imitating what can be achieved in an experiment, we explain how the depths of the phases and the width of the container influence the patterns that can be seen if one advances the control variable to the critical point and then just beyond. Our new result is the existence of a third critical point. It occurs at small wave numbers and it is independent of surface tension. It appears because we take the depths of the phases into account. These depths are input values that offer the possibility of controlling crest-to-trough conduction, stabilizing in the solid, destabilizing in the liquid. The new critical point, and the patterns attending its appearance, can be found in cells of easily attainable widths. 相似文献
90.
Cu-Cr合金高温氧化行为分析 总被引:3,自引:0,他引:3
该文用热分析天平,结合金相、X射线衍射(XRD)、扫描电镜(SEM)和能谱(EXD)研究了Cu—Cr合金在不同温度下的氧化行为。结果表明,Cu—Cr合金在700℃-900℃氧化符合抛物线规律,其最外层氧化膜为CuO,内层为Cu2O和Cr2O3,铬有助于提高合金的抗氧化能力。 相似文献