全文获取类型
收费全文 | 85639篇 |
免费 | 6195篇 |
国内免费 | 2900篇 |
专业分类
电工技术 | 4314篇 |
技术理论 | 9篇 |
综合类 | 4627篇 |
化学工业 | 15194篇 |
金属工艺 | 4426篇 |
机械仪表 | 5227篇 |
建筑科学 | 6964篇 |
矿业工程 | 1960篇 |
能源动力 | 2480篇 |
轻工业 | 4884篇 |
水利工程 | 1436篇 |
石油天然气 | 4459篇 |
武器工业 | 488篇 |
无线电 | 10378篇 |
一般工业技术 | 11208篇 |
冶金工业 | 4606篇 |
原子能技术 | 822篇 |
自动化技术 | 11252篇 |
出版年
2024年 | 238篇 |
2023年 | 1248篇 |
2022年 | 1959篇 |
2021年 | 3012篇 |
2020年 | 2291篇 |
2019年 | 1990篇 |
2018年 | 2218篇 |
2017年 | 2469篇 |
2016年 | 2318篇 |
2015年 | 2919篇 |
2014年 | 3993篇 |
2013年 | 5051篇 |
2012年 | 5243篇 |
2011年 | 5519篇 |
2010年 | 4899篇 |
2009年 | 4714篇 |
2008年 | 4466篇 |
2007年 | 4404篇 |
2006年 | 4648篇 |
2005年 | 4132篇 |
2004年 | 2783篇 |
2003年 | 2497篇 |
2002年 | 2192篇 |
2001年 | 2018篇 |
2000年 | 2282篇 |
1999年 | 2556篇 |
1998年 | 2381篇 |
1997年 | 1875篇 |
1996年 | 1735篇 |
1995年 | 1438篇 |
1994年 | 1207篇 |
1993年 | 876篇 |
1992年 | 651篇 |
1991年 | 538篇 |
1990年 | 403篇 |
1989年 | 365篇 |
1988年 | 312篇 |
1987年 | 168篇 |
1986年 | 154篇 |
1985年 | 104篇 |
1984年 | 91篇 |
1983年 | 60篇 |
1982年 | 57篇 |
1981年 | 51篇 |
1980年 | 37篇 |
1979年 | 32篇 |
1978年 | 13篇 |
1977年 | 33篇 |
1976年 | 16篇 |
1975年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
微波辅助萃取鱼香草挥发油工艺的研究 总被引:1,自引:0,他引:1
利用正交实验研究微波辅助萃取鱼香草挥发油的工艺条件。考察了微波辐射时间、微波功率、溶剂用量、洗涤滤饼的溶剂量对提取率的影响。实验结果表明,微波萃取的最佳工艺条件:辐射时间60s,微波功率288w,溶剂用量120ml,洗涤滤饼溶剂量20ml。 相似文献
992.
993.
对空调负荷进行准确预测不仅对空调优化控制的意义重大,而且也是实现空调经济运行与节能的关键所在。为了提高建筑空调负荷的预测精度,在分析灰色模型和支持向量机建模特点基础上提出了一种空调负荷组合预测算法。该方法综合了灰色建模计算过程简单以及支持向量机自学习和泛化能力强的优点,能够更加有效地利用样本数据的有效信息,提高模型预测精度。首先,通过灰色建模过程弱化了样本数据的随机因素。然后,对灰色模型输出进行归一化处理及数据重构,以作为支持向量机的输入。最后,通过支持向量机模型的预测得到最终预测结果。将本文所提出的方法应用于福州一栋办公建筑的逐时空调负荷预测中,并与灰色模型及支持向量机模型作比较,证明了组合模型的预测值与实际运行值拟合度最高,平均绝对误差比灰色模型和支持向量机模型分别降低了47.84%和17.39%。该组合预测模型具有较高的预测精度和更好的泛化能力,具有较强的可行性和实用性。 相似文献
994.
分析用水水质对日用陶瓷铅溶出量测定具有重要影响,CL-、SO42-、CO2等严重抑制铅的溶出,使测定结果偏低。 相似文献
995.
丙烯腈悬浮床催化水合制备丙烯酰胺的催化剂研究 总被引:1,自引:0,他引:1
考察了丙烯腈悬浮床水合制备丙烯酰胺的各种催化剂性能,研究了雷尼铜(Raney Cu)催化剂的三种影响因素:铜铝成分的比例、冷却成型方式和添加组分的影响及催化剂的再生性能。结果表明:喷雾法制备的雷尼铜[Al∶Cu=52∶48(质量比)]催化剂比普通雷尼铜催化剂活性高10%,强度高24%,并具有良好的再生性能,适于作为悬浮床催化剂 相似文献
996.
An ionic liquid, 1-butyl-3-methylimidazolium bromide, is used as reaction medium for the synthesis and crystallization of a coordination polymer, (BMIM)2[Cd3(BDC)3Br 2] (1) (BMIM = 1-butyl-3-methylimidazolium, BDC = 1,4-benzenedicarboxylate), which forms an anionic two-dimensional framework with the imidazolium cations located between the layers. This compound is thermally stable up to ca. 340 °C and exhibits blue emission in solid state at room temperature. Other characterizations by IR and UV–visible spectra are also described. 相似文献
997.
Nanocrystalline hydroxyapatite (HAp) was prepared by a precipitation method with aid of ultrasonic irradiation using Ca(NO3)2 and NH4H2PO4 as source material and carbamide (NH2CONH2) as precipitator. The crystallization and morphology of the prepared nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The mechanism and kinetics of the nano-hydroxyapatite were considered in particular, and the influence of the temperature and time on the HAp formation rate was also investigated. The results show that the needle-like HAp crystalline was prepared by the ultrasonic precipitation process. The HAp content increases with the preparation temperature and time. The adding of carbamide is helpful for formation of HAp nanoparticles. An Arrhenius relationship was found between the HAp formation rate and the temperature, and an apparent activation energy of 59.9 kJ/mol was obtained by calculation. 相似文献
998.
Using TiO2 as carrier, CuO/TiO2 catalysts with different CuO loading were prepared by the impregnation method. The catalytic activities in NO+CO reaction
were examined with a micro-reactor gas chromatography reaction system and the methods of TPR, XPS and NO-TPD. It was found
that the catalytic activities were affected by pretreatment atmosphere, i.e. H2 atmosphere > reduction–reoxidation > 10%CO/He > reaction gas (fresh sample). NO decomposition was better by low-valence Cu
species than by high-valence Cu species, i.e. Cu0>Cu+>Cu2+. The XPS results indicated that Cu species on CuO/TiO2 were Cu0, Cu+, normal Cu2+(Cu2+(I)) and chain-structured Cu2+(Cu2+(II)) as –Cu–O–Ti–O–. The activities of Cu2+(II) were much higher than that of Cu2+(I), but both species were very unstable in the reaction atmosphere and easily reduced by CO, which accounted for the variable
activities of fresh catalysts with increasing reaction temperature. In NO+CO reaction, the redox process was a cycle of Cu+–Cu2+(I) at low reaction temperature but was a cycle of Cu0–Cu+ at high reaction temperature. As shown by NO-TPD, high catalytic activities could be attributed to the following factors,
e.g. oxygen caves on the catalyst’s surface after pretreatment with H2 and reduction–reoxidation, formation of Cu0 after pretreatment with H2, and increment of Cu species dispersion and formation of Cu2+(II) after pretreatment with reduction–reoxidation. 相似文献
999.
Polymeric composites with conductivities ranging from 10–4 to 1 S cm–1 were prepared by electrochemically polymerizing pyrrole in a matrix of polyurethane. The polypyrrole/polyurethane alloy films obtained were characterized by element analysis, electron microscopy and electrical conductivity measurements. The morphology of the films depended on the solvent, the electrolyte and the current density. The mechanism of the electrochemical polymerization showed that PPy grew in a treelike structure, with molecular chains extending from the electrode surface into the solution. The transition temperature of the PPy/PU increased with the PPy content. 相似文献
1000.
对ISOMap、LDA、LLE、PCA这4种典型降维算法的主要思想和算法步骤进行了详细分析,并将它们用于有监督分类。从实验结果分析得到结论 ,其可为有监督分类提供有益的借鉴。 相似文献