全文获取类型
收费全文 | 85729篇 |
免费 | 6224篇 |
国内免费 | 2898篇 |
专业分类
电工技术 | 4325篇 |
技术理论 | 9篇 |
综合类 | 4628篇 |
化学工业 | 15292篇 |
金属工艺 | 4426篇 |
机械仪表 | 5226篇 |
建筑科学 | 6961篇 |
矿业工程 | 1961篇 |
能源动力 | 2477篇 |
轻工业 | 4885篇 |
水利工程 | 1436篇 |
石油天然气 | 4460篇 |
武器工业 | 488篇 |
无线电 | 10378篇 |
一般工业技术 | 11214篇 |
冶金工业 | 4606篇 |
原子能技术 | 831篇 |
自动化技术 | 11248篇 |
出版年
2024年 | 247篇 |
2023年 | 1248篇 |
2022年 | 2056篇 |
2021年 | 3038篇 |
2020年 | 2290篇 |
2019年 | 1988篇 |
2018年 | 2216篇 |
2017年 | 2469篇 |
2016年 | 2316篇 |
2015年 | 2918篇 |
2014年 | 3993篇 |
2013年 | 5050篇 |
2012年 | 5243篇 |
2011年 | 5517篇 |
2010年 | 4898篇 |
2009年 | 4713篇 |
2008年 | 4465篇 |
2007年 | 4403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 625 毫秒
961.
A regenerated cellulose film (RC) was coated with a graft‐IPNs coating, which was composed of castor oil‐based polyurethane and 2.8 wt % nitrolignin (NL), to obtain water‐resistant films. The effects of NCO/OH molar ratio and different polyols, such as 1,4‐butanediol (BDO) and trimethanol propane (TMP), on the structure and properties of the coated RC films were investigated. With an increase of the NCO/OH molar ratio, the tensile strength of the coated films increased, but the water resistivity and size contraction hardly changed. The coated films with TMP exhibited the higher breaking elongation at 1.5 of the NCO/OH molar ratio, while those with BDO have more excellent tensile strength, water resistivity, and dimensional stability. The coated films with the graft‐IPNs coating exhibited superior water resistivity and dimensional stability. The light transmittance of the coated films was more excellent than that of the RC film. Moreover, the results from the IR and electron probe microanalysis (EPMA) showed that the chemical bonding occurred between cellulose and coating, and the introduction of NL plays an important role in the enhancement of the interface adhesion of the coated films. Atomic force microscopy (AFM) depicted the flat and dense surface of the coated films, which restricted the water vapor penetration and the size contraction, resulting in the enhancement of water resistivity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1799–1806, 2002 相似文献
962.
低密度冷模塑聚氨酯软质泡沫塑料 总被引:4,自引:0,他引:4
介绍了低密度冷模塑聚氨酯软质泡沫塑料的配方体系,工艺特点及泡沫性能。指出该泡沫应用范围较广,发展前景甚好。 相似文献
963.
Zehn-Kun Huang Tseng-Ying Tien Tung-Sheng Yen 《Journal of the American Ceramic Society》1986,69(10):241-C
The subsolidus phase relationships in Si3 N4 –AlN–rare-earth oxide (Me2 O3 where Me=Nd, Sm, Gd, Dy, Er, and Yb) systems were studied. Solid-solution regions with the α-Si3 N4 structure were delineated along the Si3 N4 –"Me2 O3 :9AIN" joins for all of the rare-earth oxide systems studied. The solubility limits of these solid solutions increased with decreasing size of the rare-earth ions. 相似文献
964.
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
965.
966.
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
967.
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
968.
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
969.
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
970.
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