全文获取类型
收费全文 | 376007篇 |
免费 | 7485篇 |
国内免费 | 3380篇 |
专业分类
电工技术 | 8766篇 |
技术理论 | 7篇 |
综合类 | 2988篇 |
化学工业 | 57405篇 |
金属工艺 | 20390篇 |
机械仪表 | 15654篇 |
建筑科学 | 10509篇 |
矿业工程 | 3385篇 |
能源动力 | 7646篇 |
轻工业 | 29318篇 |
水利工程 | 4560篇 |
石油天然气 | 9533篇 |
武器工业 | 460篇 |
无线电 | 39542篇 |
一般工业技术 | 75259篇 |
冶金工业 | 57230篇 |
原子能技术 | 7164篇 |
自动化技术 | 37056篇 |
出版年
2022年 | 2443篇 |
2021年 | 3811篇 |
2020年 | 2790篇 |
2019年 | 3055篇 |
2018年 | 12587篇 |
2017年 | 13124篇 |
2016年 | 9345篇 |
2015年 | 4673篇 |
2014年 | 6455篇 |
2013年 | 14241篇 |
2012年 | 12594篇 |
2011年 | 20767篇 |
2010年 | 18029篇 |
2009年 | 17556篇 |
2008年 | 18010篇 |
2007年 | 19982篇 |
2006年 | 10895篇 |
2005年 | 12863篇 |
2004年 | 9974篇 |
2003年 | 9161篇 |
2002年 | 8111篇 |
2001年 | 7515篇 |
2000年 | 7219篇 |
1999年 | 7259篇 |
1998年 | 14735篇 |
1997年 | 11003篇 |
1996年 | 8601篇 |
1995年 | 6441篇 |
1994年 | 5841篇 |
1993年 | 5539篇 |
1992年 | 4352篇 |
1991年 | 4132篇 |
1990年 | 4077篇 |
1989年 | 4010篇 |
1988年 | 3716篇 |
1987年 | 3145篇 |
1986年 | 3146篇 |
1985年 | 3478篇 |
1984年 | 3375篇 |
1983年 | 3111篇 |
1982年 | 2731篇 |
1981年 | 2938篇 |
1980年 | 2664篇 |
1979年 | 2846篇 |
1978年 | 2743篇 |
1977年 | 2849篇 |
1976年 | 3712篇 |
1975年 | 2464篇 |
1974年 | 2295篇 |
1973年 | 2328篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
三元复合驱油体系中驱油剂的协同效应,会使油水间的界面张力大幅度下降,原油采收率大幅度提高;但三元复合驱油体系的色谱分离现象也会破坏其协同效应和完整性,揭示色谱分离现象及其影响因素对于改善三元复合驱油效果具有十分重要意义。以油藏工程和分析化学理论为指导,以化学分析和物理模拟为技术途径,并以大庆喇嘛甸油田典型区块地质特征和流体性质为研究对象,开展强碱三元复合驱色谱分离现象及其影响因素研究。结果表明,采用前置高浓度聚合物段塞后,可以有效扩大波及体积,但表面活性剂与碱和聚合物之间无因次等浓距增加,色谱分离现象加剧。大庆油区喇嘛甸油田不同区块油水性质差异对色谱分离现象存在影响,原因在于部分重烷基苯石油磺酸进入油相,影响水相中浓度检测值。强碱三元复合驱油体系中表面活性剂与碱和聚合物之间色谱分离程度比较严重,碱与聚合物之间较弱。 相似文献
92.
Thin Film Thermoelectric Metal–Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity 下载免费PDF全文
93.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention. 相似文献
94.
V. A. Eremenko V. N. Karpov V. V. Timonin N. G. Barnov I. O. Shakhtorin 《Journal of Mining Science》2015,51(6):1113-1125
The authors have determined the causes of drop in performance of induced block caving using fans of blastholes 105 mm in diameter and single blastholes 250 mm in diameter, as well as the sources of increased drilling cost and expansion of start-up time of production blocks in Abakan underground mine. Alternatives of improvement in drilling efficiency under current conditions are discussed. 相似文献
95.
In this study, 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3-x wt% Er2O3 ceramics (SBNCTEx; x?=?0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3 ceramics, the Er2O3 dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x?≥?1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1?kV/mm to 34.4?kV/mm, which is good for energy storage. The energy storage density of 0.28?J/cm3 and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors. 相似文献
96.
Catalysis Letters - In this work we studied the reactivity of the Trifluoroacetic acid hydroxylamine system in the one step salt free synthesis of amides from ketones. A particular regards was paid... 相似文献
97.
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,... 相似文献
98.
99.
Russian Journal of Nondestructive Testing - The possibility of approaching the problems of testing the regularities of elastoplastic deformation of 20GL steel by the method of analyzing the... 相似文献
100.
Do T. Hue Rebel Skirving Tong Chen John L. Williams Cynthia D.K. Bottema Kiro Petrovski 《Journal of dairy science》2021,104(7):8164-8176
Colostrum is essential for good neonate health; however, it is not known whether different calves absorb the nutrients from colostrum equally well. In this study, the absorption of protein, IgG, and γ-glutamyl transferase was compared in newborn dairy bull calves for 1 wk after feeding colostrum from different sources. Thirty-five Holstein-Friesian bull calves were randomly allocated into 3 groups and fed colostrum within 4 h after birth. Group A calves (n = 12) were bottle fed colostrum from their own dam for 3 d. Colostrum from these group A cows was also used as foster cow colostrum for the group B calves (n = 12), such that each group A and B calf pair received identical colostrum from each milking of the respective group A dam (10% of birth weight per day). The group C calves (n = 11) were fed 1 bottle (2 L) of pooled colostrum and transition milk (referred to as pooled colostrum), as was the standard practice on the dairy farm. The pooled colostrum was collected from the other dairy cows on the farm 0 to 4 d postpartum and stored at 4°C for less than 12 h. Blood was sampled from calves before the first feeding and at 1, 2, 3, and 7 d after birth. Levels of total solids, total protein, and IgG were higher in the dam colostrum than in the pooled colostrum. At birth, there were no differences between the calf groups for any measurements, and all calves had very low IgG levels. After receiving colostrum, the glucose, plasma γ-glutamyl transferase, serum total protein, and IgG concentrations increased significantly in all calves. There were no differences in any blood measurements at any time point between the pairs of group A and group B calves that received colostrum from the same cow except for the IgG concentration 2 d after birth. However, the group A calves had a higher total serum protein level and IgG concentration than the group C calves for all the time points after the first feeding. The group B calves had a higher IgG concentration than the group C calves on d 1, 2, and 7 after birth. Compared with groups A and B, there was no difference in the proportion of calves in group C that failed to have passive immunity transferred adequately based on the IgG threshold (<10 g/L). Thus, the calves receiving identical colostrum from the same cow had the same levels of IgG, and even the pooled colostrum provided sufficient transfer of IgG as the calves were fed within 4 h after birth. 相似文献