全文获取类型
收费全文 | 208910篇 |
免费 | 15927篇 |
国内免费 | 8049篇 |
专业分类
电工技术 | 11544篇 |
技术理论 | 15篇 |
综合类 | 11396篇 |
化学工业 | 36211篇 |
金属工艺 | 10790篇 |
机械仪表 | 12241篇 |
建筑科学 | 16706篇 |
矿业工程 | 5037篇 |
能源动力 | 5931篇 |
轻工业 | 12905篇 |
水利工程 | 3288篇 |
石油天然气 | 11338篇 |
武器工业 | 1384篇 |
无线电 | 25860篇 |
一般工业技术 | 27063篇 |
冶金工业 | 11060篇 |
原子能技术 | 2180篇 |
自动化技术 | 27937篇 |
出版年
2024年 | 932篇 |
2023年 | 3403篇 |
2022年 | 6099篇 |
2021年 | 8268篇 |
2020年 | 6014篇 |
2019年 | 5187篇 |
2018年 | 5570篇 |
2017年 | 6383篇 |
2016年 | 5850篇 |
2015年 | 7544篇 |
2014年 | 9777篇 |
2013年 | 12494篇 |
2012年 | 12467篇 |
2011年 | 14089篇 |
2010年 | 11797篇 |
2009年 | 11594篇 |
2008年 | 10978篇 |
2007年 | 10561篇 |
2006年 | 10973篇 |
2005年 | 9708篇 |
2004年 | 6625篇 |
2003年 | 5829篇 |
2002年 | 5295篇 |
2001年 | 4746篇 |
2000年 | 4890篇 |
1999年 | 5673篇 |
1998年 | 5301篇 |
1997年 | 4380篇 |
1996年 | 3975篇 |
1995年 | 3324篇 |
1994年 | 2778篇 |
1993年 | 2196篇 |
1992年 | 1710篇 |
1991年 | 1282篇 |
1990年 | 1018篇 |
1989年 | 878篇 |
1988年 | 682篇 |
1987年 | 496篇 |
1986年 | 396篇 |
1985年 | 334篇 |
1984年 | 214篇 |
1983年 | 198篇 |
1982年 | 165篇 |
1981年 | 147篇 |
1980年 | 133篇 |
1979年 | 97篇 |
1978年 | 63篇 |
1977年 | 63篇 |
1976年 | 77篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
WC对Cu/WC_P复合材料性能及组织的影响 总被引:8,自引:0,他引:8
通过WC含量对WC/Cu复合材料性能的影响,确定了冷压-烧结法制备Cu/WC材料的适宜WC含量为10vol%左右。并就WC对该材料组织和再结晶行为的影响进行了有益的探讨。 相似文献
82.
利用挤压铸造制备氧化铝/锌合金复合材料,在扫描电镜(SEM)上观察复合材料的界面。结果表明,在复合材料中纤维与基体间存在致密界面层,合金元素通过适当的化学反应可改善纤维与基体间的结合;在凝固过程中,纤维/基体界面上的硅在共晶体的共生生长过程中起了领先相作用,导致复合材料的共晶转变是由铝硅共晶转变和锌铝共晶转变两者组成。 相似文献
83.
Analysis of Combined Systems of Two Endoreversible Engines 总被引:3,自引:0,他引:3
A single endoreversible engine can operate as a cooler, a true heat engine, a heat pump, or a refrigerator. We investigate how many different modes of operation a combined system of two endoreversible engines may display. Special attention is paid to the independent combined system which neither consumes nor supplies power. 相似文献
84.
The changes of nitric oxide synthase (NOS) activity and nitrite level in rat brain regions after spatial learning were investigated. NOS activity was assayed by conversion of [3H]L-arginine to [3H]L-citrulline, and a sensitive fluorometric assay for quantification of nitrite was used. Compared with sham-trained rats, NOS activity and nitrite level in hippocampus and cortex, and also the nitrite level in cerebellum, was elevated significantly one day after rats had learnt a water-rewarded spatial alteration task. These results suggest a spatial memory-related changes of endogenous NO in rat brain, and support the idea that NO participates in learning and memory processes. 相似文献
85.
DA Sacks W Chen JS Greenspoon G Wolde-Tsadik 《Canadian Metallurgical Quarterly》1997,177(5):1113-1119
OBJECTIVE: Our purpose was to determine whether the same maternal glycemic control is necessary to achieve similar perinatal outcomes for type 1 as for type 2 diabetics. STUDY DESIGN: The subjects were all women with pregestational diabetes mellitus delivered of live-born singletons. Glycemic control was achieved with diet and insulin. Self-monitoring of blood glucose was performed before meals and at bedtime. Target glucose values were 60 to 90 mg/dl fasting and 60 to 105 mg/dl at other times. RESULTS: Of 60,628 deliveries, 46 type 1 and 113 type 2 diabetic women met inclusion criteria. Respective differences were found between type 1 and type 2 diabetics in average daily glucose levels (112 mg/dl vs 97 mg/dl, p < 0.001), percent of values within target ranges (35% vs 57%, p < 0.001), and mean amplitude of glycemic excursion (48.1 mg/dl vs 24.9 mg/dl, p < 0.001). At least one daily glucose value was < 50 mg/dl during 19% of observation days for type 1 vs 2% of observation days for type 2 pregnancies (p < 0.001). There were no statistically significant differences between type 1 and type 2 diabetic pregnancies in neonatal macrosomia (30% vs 34%), proportion of cesarean deliveries during labor for arrest disorders (67% vs 69%), shoulder dystocia (2% vs 6%), and neonatal hypoglycemia (18% vs 26%). CONCLUSIONS: Less stringent maternal glycemic control may permit comparable maternal and neonatal outcomes for type 1 compared with type 2 diabetics. Higher target values for type 1 diabetics may decrease the frequency of maternal hypoglycemic episodes. 相似文献
86.
Rong-Jie Tu Chern-Lin Chen 《Industrial Electronics, IEEE Transactions on》1998,45(2):256-262
A unidirectional three-phase switch-mode rectifier that delivers sinusoidal input currents in phase with the corresponding input phase voltages is proposed and analyzed in this paper. In the proposed topology, three AC switches are placed before the bridge rectifier and, respectively, across two power lines. A simple control scheme combing space-vector modulation and hysteresis current control is presented. Sinusoidal input line currents are observed in experimental results 相似文献
87.
本文基于静态相关性分析和动态调整相结合的方法,提出了一种逻辑程序的执行模型,它不仅开发了“与“并行,同进也开发了一定的“或“并行,从而有效地加速了逻辑程序的执行。 相似文献
88.
阐述了小电炉采用投资少,见较快,简单易行的炉外处理措施,提高了钢质量和生产率,生产实践和应用结果表明,本措施可为同类型企业的炼钢工艺完善和技术进步提供参考。 相似文献
89.
Hsin-Li Chen Ching-Yuan Wu 《Electron Devices, IEEE Transactions on》1998,45(10):2245-2247
An analytical model for the grain-barrier height of the intrinsic poly-Si thin-film transistors (TFTs) is developed, in which the grain-barrier height for the applied gate voltage smaller than the threshold voltage is obtained by solving the charge neutrality equation and the grain-barrier height for the applied gate voltage larger than the threshold voltage is obtained by using the quasi-two-dimensional (2-D) method. Good agreements between experimental and simulation results are obtained for a wide gate voltage range 相似文献
90.