全文获取类型
收费全文 | 19953篇 |
免费 | 2885篇 |
国内免费 | 969篇 |
专业分类
电工技术 | 343篇 |
技术理论 | 2篇 |
综合类 | 1094篇 |
化学工业 | 7499篇 |
金属工艺 | 377篇 |
机械仪表 | 288篇 |
建筑科学 | 1401篇 |
矿业工程 | 308篇 |
能源动力 | 576篇 |
轻工业 | 2144篇 |
水利工程 | 203篇 |
石油天然气 | 1375篇 |
武器工业 | 313篇 |
无线电 | 3069篇 |
一般工业技术 | 4065篇 |
冶金工业 | 368篇 |
原子能技术 | 105篇 |
自动化技术 | 277篇 |
出版年
2024年 | 128篇 |
2023年 | 613篇 |
2022年 | 540篇 |
2021年 | 810篇 |
2020年 | 929篇 |
2019年 | 873篇 |
2018年 | 754篇 |
2017年 | 866篇 |
2016年 | 869篇 |
2015年 | 860篇 |
2014年 | 1398篇 |
2013年 | 1309篇 |
2012年 | 1484篇 |
2011年 | 1516篇 |
2010年 | 1079篇 |
2009年 | 1109篇 |
2008年 | 846篇 |
2007年 | 1188篇 |
2006年 | 1146篇 |
2005年 | 978篇 |
2004年 | 774篇 |
2003年 | 735篇 |
2002年 | 533篇 |
2001年 | 477篇 |
2000年 | 427篇 |
1999年 | 299篇 |
1998年 | 227篇 |
1997年 | 207篇 |
1996年 | 153篇 |
1995年 | 126篇 |
1994年 | 119篇 |
1993年 | 72篇 |
1992年 | 68篇 |
1991年 | 58篇 |
1990年 | 39篇 |
1989年 | 30篇 |
1988年 | 14篇 |
1987年 | 25篇 |
1986年 | 13篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1964年 | 2篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Alkylated ureas: mineralization and evaluation as N sources 总被引:2,自引:0,他引:2
An incubation experiment was conducted for 11 weeks to study the mineralization of ten alkylated ureas and urea in soil. Six of the alkylated ureas viz. methylurea(MU), 1,3-dimethylurea(1,3DMU), 1,1-dimethylurea(1,1DMU), ethylurea(EU), 1,3-diethylurea(1,3DEU) and butylurea(BU) and urea mineralized during the experiment. Urea mineralized immediately, while alkylated ureas mineralized after an incubation period ranging from less than a week to four weeks (delay period of mineralization). The delay period increased in the following sequence MU < 1,3DMU < EU < BU < 1,1DMU < 1,3DEU, but after the delay period was over the compounds mineralized almost as rapidly as urea. The delay period varied according to the number of carbon atoms in the alkyl group and their position with respect to each other on the molecule. It appeared to be specific for each compound and was apparently not influenced by the presence of urea or other alkylated ureas. This character can be used to develop mixture of various alkylated ureas to obtain N mineralization at the desired time. Rapid evolution of CO2 and N2O was observed during the mineralization of urea as well as alkylated ureas. Increase in soil pH was also observed during this period. The simultaneous ocurrence of these events suggested the formation of urea as an intermediate during the mieralization of alkylated ureas. None of the alkylated ureas showed adverse affect on emergence of wheat seedlings and except DEU and BU at high concentration no other alkylated urea showed any adverse effect on initial growth of wheat seedlings. 相似文献
72.
73.
本文介绍了一种新近研制的光折聚合物。实验表明,除去吸收和反射,入射光束经聚合物后的第一布拉格衍射效率高达86%,材料也显示出双光束耦合的净增益高于240cm^-1。这些结果表明,这种新型研制的光折聚合物材料是替代无机光折晶体的实用材料。 相似文献
74.
75.
76.
Zhiwen Lei Qi Qiu Jinlai Shen Xiaohu Ao Bingqi Zhang Yuanfa Guo Jun Wang Yonghong Deng Chaoyang Wang 《大分子材料与工程》2021,306(10):2100336
Solid polymer electrolyte with good thermal stability and flexibility is an excellent candidate for solid-state lithium metal batteries, while its low ionic conductivity caused by high crystallinity limits its application at ambient temperature. Here a metal organic framework (zeolitic imidazolate framework-8, ZIF-8) composited comb-like methoxy poly(ethylene glycol) acrylate polymer electrolyte (MCPE) with high ionic conductivity (9.96 × 10−5 S cm−1 at 30 °C) is prepared by an in situ UV polymerization method. The as-prepared MCPE exhibits improved mechanical property due to the introduction of porous ZIF-8 nanofillers, which is beneficial to suppress the growth of lithium dendrites. Consequently, the LiFePO4||MCPE||Li cells show a high capacity of 116 mAh g−1 at 30 °C and 0.5 C, and maintain 89.4% of initial capacity after 150 cycles with the average Coulombic efficiency of 99.9%. These results demonstrate that the MCPE shows great potential in solid-state lithium metal batteries near room temperature. 相似文献
77.
采用高能球磨法研磨出PZT-5纳米粉料,添加外购的纳米有机添加剂,按照传统的固相工艺法制备出了压电陶瓷材料,研究分析纳米粉料和纳米有机添加剂对压电陶瓷性能的影响。通过测试分析可以看出,纳米压电粉料与纳米有机添加剂的综合作用,降低了材料的烧结温度、相对介电常数εr,Qm值和以d31,提高了压电应变常数d333,从而压电电压常数g33、gh、dh成倍提高,这些对制作宽带、高灵敏度的换能器是很有好处的。 相似文献
78.
79.
Polynitroalcohols (PNA) were obtained by AN‐reaction of nitro oligomers from ground waste rubbers (NO‐GWR) with C1‐C2‐aldehydes in presence of organic bases triethanolamine, triethylamine and cyclopropylamine. The AN‐reaction was studied at temperatures from 30 to 50°C, time 4 h, and NO‐GWR : aldehyde = 1 : 0.5/2.0 mass ratios in the solution. PNA were characterized by elemental analyses, such as 1H NMR spectra, IR spectroscopy—baseline method with internal standard and thermal analyses. The quantitative functional composition of PNA (%NO2, %C?O, and %OH groups) was proved to be similar to the composition of PNA obtained from model butadiene–styrene nitro oligomer (BSNO). It was concluded that NO‐GWR could replace NO based on elastomers in nitro aldol reaction with formaldehyde and acetaldehyde. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3241–3250, 2006 相似文献
80.