全文获取类型
收费全文 | 24207篇 |
免费 | 2338篇 |
国内免费 | 1170篇 |
专业分类
电工技术 | 2322篇 |
技术理论 | 2篇 |
综合类 | 2241篇 |
化学工业 | 4604篇 |
金属工艺 | 1364篇 |
机械仪表 | 1666篇 |
建筑科学 | 1870篇 |
矿业工程 | 1437篇 |
能源动力 | 4787篇 |
轻工业 | 626篇 |
水利工程 | 347篇 |
石油天然气 | 955篇 |
武器工业 | 617篇 |
无线电 | 506篇 |
一般工业技术 | 1626篇 |
冶金工业 | 1686篇 |
原子能技术 | 189篇 |
自动化技术 | 870篇 |
出版年
2024年 | 99篇 |
2023年 | 328篇 |
2022年 | 657篇 |
2021年 | 758篇 |
2020年 | 838篇 |
2019年 | 591篇 |
2018年 | 619篇 |
2017年 | 683篇 |
2016年 | 715篇 |
2015年 | 782篇 |
2014年 | 1349篇 |
2013年 | 1216篇 |
2012年 | 1589篇 |
2011年 | 1871篇 |
2010年 | 1314篇 |
2009年 | 1464篇 |
2008年 | 1223篇 |
2007年 | 1637篇 |
2006年 | 1465篇 |
2005年 | 1338篇 |
2004年 | 1193篇 |
2003年 | 1059篇 |
2002年 | 888篇 |
2001年 | 733篇 |
2000年 | 637篇 |
1999年 | 495篇 |
1998年 | 382篇 |
1997年 | 345篇 |
1996年 | 280篇 |
1995年 | 245篇 |
1994年 | 177篇 |
1993年 | 139篇 |
1992年 | 138篇 |
1991年 | 91篇 |
1990年 | 76篇 |
1989年 | 69篇 |
1988年 | 50篇 |
1987年 | 33篇 |
1986年 | 22篇 |
1985年 | 30篇 |
1984年 | 25篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
介绍了电子商务,以及目前电子商务的发展趋势及对社会的影响,特别阐述了蓬勃发展的电子商务对企业集团的经营环境与手段的影响。 相似文献
92.
分析了汽油机缸内气体爆震燃烧压力的频率特性并推导了爆震压力共振频率计算公式。研究表明:在爆震工况下,缸内压力在高频域中有几个共振峰,峰的大小表明了汽油机爆震强度。汽油机的表面振动在这些共振频率峰处也出现相应振动峰。表面振动峰与缸力压内峰值近似成正比。汽油机表面振动峰值可作为爆震强度的评价指标,该结论在CA1102汽油机上得到了证实。 相似文献
93.
本文介绍了对63CY14-IB型轴向柱塞泵配流副油膜的实验研究结果。该研究结果为改进该泵配流副的性能提供了依据。 相似文献
94.
95.
The global robust output regulation problem for nonlinear plants subject to nonlinear exosystems has been a challenging problem and has not been well addressed. The main difficulty lies in finding a suitable internal model. The existing internal model for handling the nonlinear exosystem is not zero input globally asymptotically stable, and can only guarantee a local solution for the output regulation problem. In this paper, we first propose a new class of internal models, which is guaranteed to exist under the generalized immersion condition. An advantage of this internal model is that it is zero input globally asymptotically stable. This fact will greatly facilitate the global stabilization of the augmented system associated with the given plant and the internal model. Then we will further utilize this class of internal models to solve the global robust output regulation problem for output feedback systems with a nonlinear exosystem. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
96.
Ag-3a/oMg was oxidized in air over the range of 400–900°C. Internal-oxide bands of MgO formed approximately parallel to the surface, the first band appearing at some finite, but irregular depth below the surface. The region between the surface and the first band appeared to be free of precipitates, but TEM showed that very small clusters, about 50 Å in diameter, formed in the PFZ, causing significant hardness (greater than 300 VHN). The clusters contain more oxygen than that corresponding to stoichiometric MgO. The hardness between oxide bands was also high, but not as high as in the PFZ. The kinetics of thickening of the internal-band region followed the parabolic rate law between 400 and 700° C, with departures from the parabolic law occurring at higher temperatures. The activation energy for the parabolic rate constants was 19.4 Kcal/mol, a value less than the total for oxygen diffusion and oxygen dissolution. The reaction front was planar and parallel to the surface prior to band formation at temperatures of 400–600° C. Nucleation of the first band resulted in nonplanar and nonparallel oxide. Little or no correlation existed between grain boundaries and oxide formation. Nodules of virtually pure silver formed on the surface initially at grain boundaries and subsequently within grains. Nodule formation is attributed to stress-enhanced (resulting from strains associated with precipitation) diffusion of silver to the surface via dislocation pipes. Internal-band formation is discussed in terms of prior data in the literature and various models. It is thought that stress effects (induced by precipitation), nucleation, and clustering of oxygen with Mg play significant roles in causing internal-band formation. 相似文献
97.
凝胶燃烧法合成LiCoO2超细粉体的研究 总被引:7,自引:0,他引:7
以LiNO3和Co(NO3)2@6H2O为原料,柠檬酸为燃料.采用凝胶低温燃烧技术合成了LiCoO2超细粉体.并利用各种分析技术对柠檬酸和硝酸盐形成的凝胶及凝胶燃烧合成的粉体进行了研究柠檬酸硝酸盐凝胶在350-400℃之间发生燃烧反应,得到黑色疏松粉体X射线衍射分析表明.适当提高柠檬酸在凝胶中的含量.燃烧后得到的粉体晶粒尺寸显著减小未经燃烧的粉体中除含有LiCoO2外.还有CoO,Li2CO3等杂质相.但在450℃下经短时间煅烧后.杂质相消失,其晶相为层状岩盐结构的高温LiCoO2相扫描电镜和透射电镜观察发现.随着煅烧温度的提高.LiCoO2粉体的粒径有所增大.但远小于在相同煅烧条件下用固相反应法制备的LiCoO2粉体.这表明采用燃烧法更适于合成具有单一相结构的,可在低温条件下烧结的超细LiCoO2粉体. 相似文献
98.
燃烧合成三元碳化合物Ti2AlC1-x 总被引:1,自引:0,他引:1
采用Ti,Al和C元素粉末为反应物原料,通过燃烧合成法首次成功地制备出了单相三元碳化合物Ti2AlC1-x。实验结果表明:若以“理想”晶体结构化学式Ti2AlC化学计量比为起始反应原料配比,燃烧产物主晶相为Ti2AlC2;以缺碳的非化学计量比(Ti2AlC1-x)为反应原料配比,即Ti:Al:C=3:1.5:1=2:1:0.7(摩尔比),得到单相的燃烧产物Ti2AlC1-x。从热力学原理的角度探讨了不同原料摩尔配比对燃烧产物相组成的影响机理。 相似文献
99.
为研究包覆方式对片状发射药燃烧性能的影响,建立了不同包覆方式下多层片状发射药的物理模型,并推导了形状函数和燃气生成猛度表达式,利用Matlab软件对不同的宽厚比、长厚比及多层结构的片状发射药进行了数值计算;制备了不同长厚比的片状变燃速发射药,并进行了密闭爆发器实验。结果表明,四面包覆和全包覆可以很好地消除临界宽厚比对片状发射药燃烧性能的影响;与两面包覆的片状发射药相比,四面包覆和全包覆的片状发射药能够延缓内层药减面燃烧的时间,其燃气生成猛度的阶跃程度分别提高了1.17%和1.23%,呈现出良好的燃烧渐增性。 相似文献
100.
Patrizia Marchese Maria Lombardi Maria Elena Mantione Domenico Baccellieri David Ferrara Roberto Chiesa Ottavio Alfieri Chiara Foglieni 《International journal of molecular sciences》2021,22(8)
Atherothrombosis exposes vascular components to blood. Currently, new antithrombotic therapies are emerging. Herein we investigated thrombogenesis of human arteries with/without atherosclerosis, and the interaction of coagulation and vascular components, we and explored the anti-thrombogenic efficacy of blockade of the P2X purinoceptor 7 (P2X7). A confocal blood flow videomicroscopy system was performed on cryosections of internal mammary artery (IMA) or carotid plaque (CPL) determining/localizing platelets and fibrin. Blood from healthy donors elicited thrombi over arterial layers. Confocal microscopy associated thrombus with tissue presence of collagen type I, laminin, fibrin(ogen) and tissue factor (TF). The addition of antibodies blocking TF (aTF) or factor XI (aFXI) to blood significantly reduced fibrin deposition, variable platelet aggregation and aTF + aFXI almost abolished thrombus formation, showing synergy between coagulation pathways. A scarce effect of aTF over sub-endothelial regions, more abundant in tissue TF and bundles of laminin and collagen type I than deep intima, may suggest tissue thrombogenicity as molecular structure-related. Consistently with TF-related vascular function and expression of P2X7, the sections from CPL but not IMA tissue cultures pre-treated with the P2X7 antagonist A740003 demonstrated poor thrombogenesis in flow experiments. These data hint to local targeting studies on P2X7 modulation for atherothrombosis prevention/therapy. 相似文献