全文获取类型
收费全文 | 26692篇 |
免费 | 3293篇 |
国内免费 | 1638篇 |
专业分类
电工技术 | 2248篇 |
技术理论 | 2篇 |
综合类 | 2205篇 |
化学工业 | 4041篇 |
金属工艺 | 1505篇 |
机械仪表 | 1919篇 |
建筑科学 | 2252篇 |
矿业工程 | 999篇 |
能源动力 | 956篇 |
轻工业 | 2124篇 |
水利工程 | 668篇 |
石油天然气 | 1104篇 |
武器工业 | 268篇 |
无线电 | 3275篇 |
一般工业技术 | 2954篇 |
冶金工业 | 902篇 |
原子能技术 | 279篇 |
自动化技术 | 3922篇 |
出版年
2024年 | 138篇 |
2023年 | 506篇 |
2022年 | 1089篇 |
2021年 | 1412篇 |
2020年 | 1037篇 |
2019年 | 867篇 |
2018年 | 957篇 |
2017年 | 1039篇 |
2016年 | 876篇 |
2015年 | 1287篇 |
2014年 | 1494篇 |
2013年 | 1801篇 |
2012年 | 2054篇 |
2011年 | 1991篇 |
2010年 | 1816篇 |
2009年 | 1650篇 |
2008年 | 1655篇 |
2007年 | 1513篇 |
2006年 | 1375篇 |
2005年 | 1123篇 |
2004年 | 884篇 |
2003年 | 910篇 |
2002年 | 1064篇 |
2001年 | 988篇 |
2000年 | 576篇 |
1999年 | 409篇 |
1998年 | 203篇 |
1997年 | 186篇 |
1996年 | 171篇 |
1995年 | 106篇 |
1994年 | 84篇 |
1993年 | 94篇 |
1992年 | 64篇 |
1991年 | 44篇 |
1990年 | 30篇 |
1989年 | 26篇 |
1988年 | 24篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1959年 | 4篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
制备了两种新型的分别含有以三苯胺为电子给体的偶氮类发色团作为特征活性官能团和3-呋喃甲酸及受保护的马来酰亚胺的可交联型聚合物体系.通过研究表明利用该制备方法,发色团在聚合物中的含量得到了极大的提高,分别达到32.1%(NLO1_P1)和44.4%(NLO1_P2).该聚合物体系以“DielsAlder”[4+2]环加成反应作为其交联特征,具有高温非交联、低温交联的特点,其过程与以往的热交联型聚合物相反,可解决传统电光交联聚合物中存在的热交联对极化效率影响的问题并用热失重分析法(TGA)和差示扫描量热法(DSC)分析了这一过程.此外DA交联型聚合物,不需要引入额外的助交联剂,克服了传统热交联聚合物分离难的问题,最大程度的保证了材料的纯度. 相似文献
143.
Copolymer gels were prepared from 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS), N,N-dimethylacrylamide (DMAA, comonomer) and N,N′-methylenebis(acrylamide) (BIS). The mole fraction of AMPS were 0.2674 and 0.4318, respectively, with the same BIS mole fraction of 0.013. These gels with counterions H+, Na+, and K+ were swollen at 25°C in mixtures of dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF). A volume phase transition was observed at the THF volume fraction of about 0.58, indicating that the volume phase transition in a polyelectrolyte gel occurs when the medium polarity decreases sufficiently for ion-pair formation. On changing the counterion, the fraction of DMSO in the solvent mixture which is required to initiate swelling decreases in the order Na+, H+, and K+, the same as for counterion condensation in identical gels. 相似文献
144.
145.
A novel sol–gel method based on V2O5·nH2O hydro-gel was developed to synthesize nanocrystalline Li3V2(PO4)3/carbon composite material. In this route, V2O5·nH2O hydro-gel, NH4H2PO4, Li2CO3 and high-surface-area carbon were used as starting materials to prepare precursor, and the Li3V2(PO4)3/carbon was obtained by sintering precursor at 750 °C for 4 h in flowing argon. The sol–gel synthesis ensures homogeneity of the precursors and improved reactivity. The sample was characterized by XRD, SEM and TEM. X-ray diffraction results show Li3V2(PO4)3 sample is monoclinic structure with the space group of P21/n. The TEM image indicates that the Li3V2(PO4)3 particles modified by conductive carbon are about 70 nm in diameter. The Li3V2(PO4)3/carbon system showed that the discharge capacities in the first and 50th cycle are about 155.3 and 143.6 mAh/g, respectively, in the range of 3.0–4.8 V. The sol–gel method is fit for the preparation of Li3V2(PO4)3/carbon composite material which may offer some favorable properties for commercial application. 相似文献
146.
Water‐insoluble polyaspartyl polymers were synthesized by using water as medium instead of organic medium. Taking Ca2+ as a reference, the binding of several heavy‐metal ions, including Pb2+, Cd2+, Hg2+, Cr3+, Cu2+, and Mn2+, by polyaspartyl polymers was studied. The experimental results revealed that polyaspartate is an excellent binding agent for the investigated heavy‐metal ions. These cation ions were bound to polyaspartate polymer by the same mechanism as Pb2+, which can be explained by ion exchange model. Since polyaspartate has a protein‐resembling structure that is sensitive to trace heavy metal, it was used to remove some trace heavy‐metal elements in Chinese herbal medicines. It was found that polyaspartate material was an effective agent for the removal of Pb2+, Cd2+, and Hg2+ ions from glycyrrhizin, angelica, and gynostemma pentaphyllum. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
147.
148.
149.
150.
高稳定性化学镀镍磷合金工艺 总被引:14,自引:1,他引:14
采用正交试验法筛选络合剂,确定了以柠檬酸,琥珀酸和苹果酸复配作为络合剂的化学镀镍磷工艺,该工艺具有高稳定性,高装载量等优点,易在工业生产中应用。 相似文献