全文获取类型
收费全文 | 26319篇 |
免费 | 2976篇 |
国内免费 | 1038篇 |
专业分类
电工技术 | 1507篇 |
技术理论 | 1篇 |
综合类 | 1691篇 |
化学工业 | 8016篇 |
金属工艺 | 4058篇 |
机械仪表 | 722篇 |
建筑科学 | 815篇 |
矿业工程 | 1854篇 |
能源动力 | 785篇 |
轻工业 | 1254篇 |
水利工程 | 138篇 |
石油天然气 | 448篇 |
武器工业 | 69篇 |
无线电 | 1053篇 |
一般工业技术 | 3392篇 |
冶金工业 | 4017篇 |
原子能技术 | 306篇 |
自动化技术 | 207篇 |
出版年
2024年 | 50篇 |
2023年 | 443篇 |
2022年 | 611篇 |
2021年 | 937篇 |
2020年 | 950篇 |
2019年 | 827篇 |
2018年 | 749篇 |
2017年 | 987篇 |
2016年 | 1186篇 |
2015年 | 1014篇 |
2014年 | 1476篇 |
2013年 | 1635篇 |
2012年 | 1817篇 |
2011年 | 1856篇 |
2010年 | 1368篇 |
2009年 | 1241篇 |
2008年 | 1040篇 |
2007年 | 1546篇 |
2006年 | 1464篇 |
2005年 | 1266篇 |
2004年 | 1153篇 |
2003年 | 990篇 |
2002年 | 946篇 |
2001年 | 781篇 |
2000年 | 693篇 |
1999年 | 569篇 |
1998年 | 426篇 |
1997年 | 368篇 |
1996年 | 326篇 |
1995年 | 320篇 |
1994年 | 260篇 |
1993年 | 185篇 |
1992年 | 192篇 |
1991年 | 132篇 |
1990年 | 118篇 |
1989年 | 91篇 |
1988年 | 73篇 |
1987年 | 44篇 |
1986年 | 40篇 |
1985年 | 35篇 |
1984年 | 28篇 |
1983年 | 18篇 |
1982年 | 32篇 |
1981年 | 17篇 |
1980年 | 8篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
针对江西宜丰地区氧化锂质量分数<2.0%以下中低品位锂瓷土矿,研究了硫酸铵法提取碳酸锂技术路线。首先,利用二步焙烧工艺,有利于脱氟、提高锂浸出率,并且能够有效防止结窑现象发生。在浸出液除杂过程中,采用成矾除铝的方法将大量溶出的铝离子转变为KAl(SO4)2·12H2O、NH4Al(SO4)2·12H2O等有价值复盐,规避了传统石膏法产生的大量固废,有70%的铝离子被转变为矾盐晶体,同时带出大量的结晶水,减轻后续浓缩压力,对比传统的石膏法产生大量固废而言,其优点是显而易见的。碳化反应产品的XRD以及氧化锂含量分析表明,碳酸锂的纯度达到99%以上,全程锂收率为50%~60%。作为提锂实验对比,采用宜春414矿锂质量分数为4.0%的锂云母,由于414矿样中铝的相对含量更低,导致相同的除杂难度下得到的414矿样中浸出液锂离子浓度更高,浓缩倍数更小,414矿样的锂回收率更高。实验结果表明,中低品位锂瓷土提锂的工艺规律,通过适当改变参数,能够应用于难度更低的高品位的锂云母提锂过程。 相似文献
103.
《Ceramics International》2020,46(12):19822-19826
Sodium Zirconium Phosphate (NaZr2(PO4)3, hereinafter NZP) and monazite are both potential materials for immobilization of nuclear waste. In this work, novel (1-x)Sr0.5Zr2(PO4)3-xNdPO4 composite ceramics (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) for simultaneously immobilizing the simulated fission product (FP) Sr and trivalent minor actinide (MA) Nd were prepared by one-step microwave sintering technique, in which Sr and Nd were immobilized into NZP and monazite type structures, respectively. The phase evolution and microstructure of the samples were investigated by X-ray diffraction (XRD), Raman, and backscattering scanning electron microscopy (BSE). The results showed that the expected composite ceramics were successfully obtained by one-step microwave sintering at 1050 °C for 2 h. The as-prepared samples consisted of Sr0.5Zr2(PO4)3 and NdPO4 phases, and the content of the two phases varied regularly as x changed, generally conforming to the designed nominal chemical composition. Importantly, the composite ceramics presented the homogenous and dense microstructure. The relative density of the composite ceramics was more than 95%, meanwhile, the Vickers-hardness of the samples was higher than 600 MPa. It was indicated that NZP-monazite type composite ceramics could be a potential matrix for the simultaneous immobilization of actinide and fission product. 相似文献
104.
《Journal of the European Ceramic Society》2020,40(6):2489-2496
Hydroxyapatite (HA) is considered as the most promising biomaterial candidate to replace and regenerate hard tissues. A small amount of β-tricalcium phosphate (β-TCP) phase is advantageous for rapid bonding of the artificial bones to natural ones due to its high solubility compared to hydroxyapatite. Synthesizing HA nanofibers from electrospinning of sol-gel is considered as a widely researched topic. Motivation of the current work was to investigate the influence of polymeric binder in the final phase evolution after heat treatment of electrospun nanofibers. Calcium phosphate nanofibers were fabricated by electrospinning sols using gelatine and polyvinylpyrrolidone as carrier polymers and subjected to heat treatment. It was realized that carrier polymers facilitate preferential calcium phosphate phase formation by forming hydroxyapatite as major phase while PVP was used and β-TCP with HA as secondary phase while gelatine was employed. XRD and thermal analyses were performed to ascertain the reason behind this interesting behaviour. 相似文献
105.
《Ceramics International》2020,46(2):1954-1961
Na-superionic conductor (NASICON) structured NaTi2(PO4)3 (NTP) as anode shows broad prospect in aqueous lithium ion battery. However, inherent low electrical conductivity of NaTi2(PO4)3 remains a pivotal issue to be resolved. Herein, we report N-doped carbon encapsulated NaTi2(PO4)3 microflower (NTP-CN) as anode for aqueous lithium ion battery, which is prepared via solvothermal way. NTP-CN with unique structural feature displays superb electrochemical performances. It delivers the discharge capacities of 131.2, 110.1, and 84.3 mAh g−1 at 0.2, 3.0, and 15 C, respectively, 38.8, 33.8, and 51.1 mAh g−1 higher than these of pristine NTP. NTP-CN also shows remarkable cycling stability at 6 C after 1000 cycles (capacity retention: 88.8%), superior to NTP (70.7%). The outstanding properties of NTP-CN may be due to that microflower structure can increase touching area between electrolyte and electrode, and carbon coating for electrode improves stability in aqueous electrolyte and ameliorates electrical conductivity. Moreover, nitrogen doping can further enhance hydrophilicity and conductivity of the sample, and also form lots of defects on electrode surface, which is beneficial for the intercalation/deintercalation of Li ions. This work reveals that the combination of microflower structure and N-doped carbon layer offers a promising method to improve electrochemical performances of NaTi2(PO4)3. 相似文献
106.
通过微波法直接在水溶液中制备了碳量子点(CDs),并研究了其荧光性质。重点讨论了铁(Ⅲ)对该量子点的荧光猝灭效应,并将其应用于铁(Ⅲ)的测定。实验表明,在pH值为6.40的磷酸氢二钠-柠檬酸缓冲溶液中,控制CDs浓度为6.24×10-5 mol/L(以碳计),在常温下反应10min时,于激发波长335nm,发射波长为450nm处进行测定,铁(Ⅲ)浓度与体系荧光猝灭程度(ΔF)呈良好的线性关系,线性回归方程为ΔF=69.816 c+4.813 6,相关系数为0.9987,线性范围为0.004~0.15mmol/L。方法检出限为2.4×10-4 mmol/L。将体系应用于水样中铁(Ⅲ)的测定,结果与原子吸收光谱法(AAS)基本一致,相对标准偏差(RSD,n=6)在1.5%~2.1%之间,加标回收率为92%~104%。 相似文献
107.
108.
Hiroaki Matsumori Toshihisa Shimizu Koushi Takano Hitoshi Ishii 《Electrical Engineering in Japan》2015,190(2):57-71
In recent years, remarkable advancement of new power semiconductor devices, such as SiC and GaN, enables the increase of switching frequency of power converters, and hence the volume of passive components, such as ac filters and transformers, can be reduced. However, temperature rise caused by the inductor loss is increasing, and hence iron loss evaluation of the inductor is one of the most important issues to realize high power density converters. Conventionally, an improved generalized Steinmetz equation (iGSE) has proposed in order to calculate the iron loss under a pulse voltage magnetizing condition. However, accurate iron loss calculation of the ac filter inductor used in a PWM inverter cannot be realized. The authors have proposed two methods of iron loss evaluation of ac filter inductors. The first one is a loss map method which can calculate the iron loss without using a real PWM inverter. Another one is an ILA (Inductor Loss Analyzer) which can measure the iron loss in every switching period in a real PWM inverter. In this paper, comparisons of the iron loss between the ILA and the loss map method on both the single‐phase and three‐phase inverters are studied. It is found that iron loss of the ac filter inductor in the three‐phase PWM inverter which is calculated by the loss map method cause a large error on a specific condition. In order to prevent the calculation error, the authors proposed a revised loss map method and proved the effectiveness of the method. 相似文献
109.
Current political, economic and ecological guidelines demand the increase of power densities of nearly all machinery parts. In order to further lower the wear rate towards the ultra-mild sliding wear regime, an integral approach is needed, which has to regard contact conditions, surface topography, surface chemistry, as well as sub-surface properties. Still, there are no simple parameters to classify the performance of a tribosystem. In this study the area affected by tribocontacts is calculated by means of a three dimensional elastic–ideal plastic contact model. The surfaces are prepared by means of conventional machining procedures and characterized by scanning white light interferometry. The further input data as to normal and friction forces are derived by reciprocating sliding wear tests under boundary lubrication conditions of carburized steel against carburized steel and 52100 steel against case-hardened spheroidal cast iron. This contribution will depict the distinct influence of the topography on friction and ultra-mild sliding wear of common Fe-base materials and point out the marked importance of highly localized effects, which govern the acting mechanisms. 相似文献
110.