全文获取类型
收费全文 | 130744篇 |
免费 | 16870篇 |
国内免费 | 6678篇 |
专业分类
电工技术 | 51000篇 |
技术理论 | 3篇 |
综合类 | 9934篇 |
化学工业 | 13543篇 |
金属工艺 | 5489篇 |
机械仪表 | 5547篇 |
建筑科学 | 6667篇 |
矿业工程 | 2511篇 |
能源动力 | 11205篇 |
轻工业 | 2945篇 |
水利工程 | 2920篇 |
石油天然气 | 2349篇 |
武器工业 | 1293篇 |
无线电 | 15568篇 |
一般工业技术 | 9230篇 |
冶金工业 | 3128篇 |
原子能技术 | 2803篇 |
自动化技术 | 8157篇 |
出版年
2024年 | 300篇 |
2023年 | 1939篇 |
2022年 | 3347篇 |
2021年 | 4140篇 |
2020年 | 4679篇 |
2019年 | 3981篇 |
2018年 | 3599篇 |
2017年 | 4929篇 |
2016年 | 5142篇 |
2015年 | 5660篇 |
2014年 | 9049篇 |
2013年 | 8152篇 |
2012年 | 10292篇 |
2011年 | 10974篇 |
2010年 | 8051篇 |
2009年 | 8234篇 |
2008年 | 7843篇 |
2007年 | 9385篇 |
2006年 | 8466篇 |
2005年 | 6757篇 |
2004年 | 5625篇 |
2003年 | 4522篇 |
2002年 | 3671篇 |
2001年 | 3158篇 |
2000年 | 2529篇 |
1999年 | 1870篇 |
1998年 | 1354篇 |
1997年 | 1133篇 |
1996年 | 1076篇 |
1995年 | 853篇 |
1994年 | 718篇 |
1993年 | 508篇 |
1992年 | 469篇 |
1991年 | 356篇 |
1990年 | 293篇 |
1989年 | 248篇 |
1988年 | 183篇 |
1987年 | 120篇 |
1986年 | 96篇 |
1985年 | 99篇 |
1984年 | 116篇 |
1983年 | 92篇 |
1982年 | 96篇 |
1981年 | 46篇 |
1980年 | 29篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1959年 | 20篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
Sarabjeet Singh Sidhu Malkeet Singh Preetkanwal Singh Bains 《Particulate Science and Technology》2018,36(3):324-331
The present study investigates the thermal conductivity of bimodal SiC particulate distribution in aluminum matrix composites fabricated via powder metallurgy route. The effects of the SiCp reinforcement size distribution and processing parameters such as sintering time and temperature on the thermal conductivity have been examined. The Box–Behnken experimental array was employed to identify the effects of selected variables on the thermal conductivity of the composite. A reasonable augmentation in the thermal conductivity was observed with an increase in sintering time and %volume fraction of fine SiC particulates. It has been demonstrated that the matrix doped with fine SiC particulates (37?µm) occupied interstitial positions and formed continuous SiC–matrix network resulting in minimizing the micropores that contributed for good thermal conductivity, that is, 235?W/mK. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were conducted to evaluate the microstructure architecture and interfacial phase formation. 相似文献
65.
Hun Soo Jang Seonggwang Yoo Seong Hyeon Kang Jongjun Park Gi‐Gwan Kim Heung Cho Ko 《Advanced functional materials》2020,30(5)
This work demonstrates a means of automatic transformation from planar electronic devices to desirable 3D forms. The method uses a spatially designed thermoplastic framework created via extrusion shear printing of acrylonitrile–butadiene–styrene (ABS) on a stress‐free ABS film, which can be laminated to a membrane‐type electronic device layer. Thermal annealing above the glass transition temperature allows stress relaxation in the printed polymer chains, resulting in an overall shape transformation of the framework. In addition, the significant reduction in the Young's modulus and the ability of the polymer chains to reflow in the rubbery state release the stress concentration in the electronic device layer, which can be positioned outside the neutral mechanical plane. Electrical analyses and mechanical simulations of a membrane‐type Au electrode and indium gallium zinc oxide transistor arrays before and after transformation confirm the versatility of this method for developing 3D electronic devices based on planar forms. 相似文献
66.
采用等离子堆焊技术在H13钢基体表面上制备了Ni60A/Cr3C2堆焊覆层,研究了覆层的磨损行为和热疲劳性能。在600 ℃下销盘试验的结果表明,镍基碳化铬复合覆层的耐磨性是Ni60A堆焊覆层的2.8倍和基材H13钢的11.6倍。镍基覆层可以显著降低H13钢的摩擦因数,加入碳化铬则会削弱覆层的摩擦性能。随着磨损的进行,主要磨损机理从氧化磨损演变为磨粒磨损和粘着磨损。在800 ℃到室温下的热疲劳测试结果表明,镍基碳化铬复合覆层在48个热循环后疲劳裂纹达到200 μm,早于镍基覆层的62次。这说明高温氧化促进热疲劳裂纹的产生。碳化铬增强相从镍基上剥离,导致镍基复合覆层热疲劳性能下降。 相似文献
67.
为提高注水泥过程中水泥浆顶替效率,国内外愈来愈多地使用旋流扶正器。但是,目前旋流扶正器结构参数主要靠经验设计,缺乏理论基础也没有相关行业标准。针对依据文丘里效应设计的柳叶形旋流扶正器,基于修正幂律流体模型,构建了旋流扶正器旋流长度计算模型。通过数值模拟对旋流扶正器井下旋流规律进行研究,推导出了旋流扶正器在修正幂律流体条件下,周向平均速度和完全顶替的临界速度公式。基于旋流扶正器井下旋流规律,分析了井眼环空结构、流体性能、井下井壁附着力对水泥浆顶替效率的影响,优化了柳叶形旋流扶正器旋流角、扶正棱长度、扶正棱有效体积和扶正器高度等设计参数。对比分析了柳叶形与常规旋流扶正器在不同工况下的旋流长度,柳叶形扶正器的旋流长度比常规扇形平均提升了32%,比常规梯形扶正器平均提升了47%。柳叶形扶正器在新疆顺北油田顺北3井等20多井次超深井应用,应用井固井质量明显优于常规扇形的旋流扶正器。 相似文献
68.
This paper proposes a novel hybrid technique called enhanced grey wolf optimization-sine cosine algorithm-cuckoo search (EGWO-SCA-CS) algorithm to improve the electrical power system stability. The proposed method comprises of a popular grey wolf optimization (GWO) in an enhanced and hybrid form. It embraces the well-balanced exploration and exploitation using the cuckoo search (CS) algorithm and enhanced search capability through the sine cosine algorithm (SCA) to elude the stuck to the local optima. The proposed technique is validated with the 23 benchmark functions and compared with state-of-the-art methods. The benchmark functions consist of unimodal, multimodal function from which the best suitability of the proposed technique can be identified. The robustness analysis also presented with the proposed method through boxplot, and a detailed statistical analysis is performed for a set of 30 individual runs. From the inferences gathered from the benchmark functions, the proposed technique is applied to the stability problem of a power system, which is heavily stressed with the nonlinear variation of the load and thereby operating conditions. The dynamics of power system components have been considered for the mathematical model of a multimachine system, and multiobjective function has been framed in tuning the optimal controller parameters. The effectiveness of the proposed algorithm has been assessed by considering two case studies, namely, (i) the optimal controller parameter tuning, and (ii) the coordination of oscillation damping devices in the power system stability enhancement. In the first case study, the power system stabilizer (PSS) is considered as a controller, and a self-clearing three-phase fault is considered as the system uncertainty. In contrast, static synchronous compensator (STATCOM) and PSS are considered as controllers to be coordinated, and perturbation in the system states as uncertainty in the second case study. 相似文献
69.
本工作以丙烯腈/衣康酸(IA)二元共聚原丝以及丙烯腈/IA/丙烯酸甲酯(MA)三元共聚原丝为研究对象,利用热重分析仪(TG)和热解-同步辐射真空紫外光电离质谱(Py-SVUV-PIMS)对其热稳定化过程进行研究。TG结果表明,氮气气氛下,二元共聚原丝(PAN/IA)和三元共聚原丝(PAN/IA/MA)分别呈现三阶段和两阶段的热分解过程,其中PAN/IA的第一和第二阶段均对应PAN线型分子链的断裂,但前者是由自由基环化反应放热引发的,后者则是由正常温度下的热分解所致,而单体MA的加入显著抑制了自由基环化反应,使得PAN原丝的热稳定化能够以单体IA诱导的离子型环化反应为主较平缓地进行,相应的热失重过程也由两阶段转变为了单阶段。Py-SVUV-MS的实验结果表明,两种共聚PAN原丝在程序升温过程中会生成包括含氮小分子、丙烯腈单体及低聚物、成环化合物在内的三类主要热解产物,对比各类产物的生成趋势和产量,推断单体MA通过降低PAN结构的规整度,使其无定形化,从而增加环化反应的引发点,促进PAN原丝向稳定的预氧丝转变,同时由典型热解产物——甲基丙烯腈的生成路径可知,MA本身并不参与PAN大分子的环化反应,属于中性共聚单体。空气气氛下,CO2的产量差异也间接证明了MA单体能够有效提升PAN纤维的固碳能力,采用三元共聚方法制得的PAN纤维热稳定性能更佳。 相似文献
70.
Massimo Cimmino 《Journal of Building Performance Simulation》2018,11(4):414-432
A model for the simulation of geothermal systems with parallel- and series-connected boreholes is presented. Mass and heat balance problems are formulated for each component in the system and are assembled into system-level problems. A third problem is formulated to account for heat transfer in the bore field, using the finite line source solution. This third problem is coupled to the system-level heat balance problem by an analytical solution of the heat transfer inside boreholes with multiple U-tubes. The simulation model allows for any number of independent fluid loops within the bore field or within individual boreholes and allows for combinations of specified inlet fluid temperatures and heat extraction rates in independent fluid loops. The model accounts for the axial variation of the fluid and borehole wall temperatures and heat extraction rates. The capabilities of the model are demonstrated through three example simulations. 相似文献