全文获取类型
收费全文 | 42597篇 |
免费 | 5438篇 |
国内免费 | 2937篇 |
专业分类
电工技术 | 19111篇 |
技术理论 | 2篇 |
综合类 | 3163篇 |
化学工业 | 1766篇 |
金属工艺 | 1251篇 |
机械仪表 | 1827篇 |
建筑科学 | 2108篇 |
矿业工程 | 1136篇 |
能源动力 | 1527篇 |
轻工业 | 729篇 |
水利工程 | 1813篇 |
石油天然气 | 731篇 |
武器工业 | 315篇 |
无线电 | 6166篇 |
一般工业技术 | 2130篇 |
冶金工业 | 1501篇 |
原子能技术 | 667篇 |
自动化技术 | 5029篇 |
出版年
2024年 | 88篇 |
2023年 | 501篇 |
2022年 | 919篇 |
2021年 | 1192篇 |
2020年 | 1376篇 |
2019年 | 1090篇 |
2018年 | 1055篇 |
2017年 | 1553篇 |
2016年 | 1749篇 |
2015年 | 1986篇 |
2014年 | 3018篇 |
2013年 | 2692篇 |
2012年 | 3637篇 |
2011年 | 3858篇 |
2010年 | 2836篇 |
2009年 | 2978篇 |
2008年 | 2880篇 |
2007年 | 3179篇 |
2006年 | 2865篇 |
2005年 | 2170篇 |
2004年 | 1656篇 |
2003年 | 1517篇 |
2002年 | 1230篇 |
2001年 | 1071篇 |
2000年 | 837篇 |
1999年 | 644篇 |
1998年 | 401篇 |
1997年 | 345篇 |
1996年 | 298篇 |
1995年 | 254篇 |
1994年 | 236篇 |
1993年 | 180篇 |
1992年 | 146篇 |
1991年 | 101篇 |
1990年 | 67篇 |
1989年 | 61篇 |
1988年 | 52篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 21篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1966年 | 9篇 |
1964年 | 21篇 |
1962年 | 7篇 |
1958年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
1.
为研究低压静电场辅助冷冻对竹笋冻结特性的影响,以冻结曲线、硬度、水分损失率、水分迁移、冰晶形态和组织微观结构为指标,探究低压静电场辅助冷冻(-35 ℃)和普通冷冻(-35 ℃)条件下竹笋品质的变化规律。结果表明:低压静电场辅助冷冻提高了冻结效率,改变了冰晶形态及分布,减轻了组织微观结构破损程度,改善了解冻汁液流失情况。与静电板间距10、20、30、40 cm处的冷冻竹笋解冻后水分损失率分别为14.16%、12.58%、9.73%、10.44%,显著低于对照组(21.01%)(P<0.05),硬度分别为461.19、507.48、496.65 g和455.31 g,显著高于对照组(350.70 g)(P<0.05)。低场核磁共振分析结果表明,在低压静电场辅助冷冻下竹笋解冻后汁液流失减少,扫描电子显微镜观察结果显示,竹笋纤维排列整齐,组织微观结构保持较好。低压静电场辅助冷冻可有效改善竹笋品质,可为利用低压静电场进行果蔬的冷冻贮藏和冷链运输提供参考。 相似文献
2.
《Advanced Powder Technology》2022,33(6):103628
The charge sources, as well as the charging mechanism of the contact electrification (CE) of polymers, are still debatable. Since CE is accompanied by destruction, it is considered that “hard contacting” via ball milling can induce covalent bond scission and produce naked-activated-charge sources. Regarding “soft contacting” via nano-scale sliding, which does not induce covalent bond scission, a frontier-electron, “f-electron,” of the naked-activated-charge source is crucial to electron transfer among the naked-activated-charge sources. Here, we configure naked-activated-charge-source models, naked-activated-mechano-anion, and naked-activated-mechano-cation, which are produced by mechanical energy induced heterogeneous covalent bond scission, as well as naked-activated-mechano-radicals that are produced by homogeneous covalent bond scission. Regarding “soft contacting” among naked-activated-charge sources in a vacuum, f-electron can be transferred from a donor to an acceptor if the energy level of the donor is higher than that of the acceptor. The net amount of the normalized transferred-f-electrons is obtained by adopting settings in which the average energy level of the naked-activated-charge sources (as the donors) is higher than that of the sources employed as acceptors. Thus, the surfaces comprising the donors and acceptors will exhibit positive and negative net surface charges, respectively. We conclude that net surface charges depend on the average energy level of naked-activated-charge sources. Further, we observe that the alignment of polyethylene (PE)-polyvinyl chloride (PVC)-polytetrafluoroethylene (PTFE) to the average energy level is identical to that of the triboelectric series. 相似文献
3.
This paper proposes a method for the coordinated control of power factor by means of a multiagent approach. The proposed multiagent system consists of two types of agent: single feeder agent (F_AG) and bus agent (B_AG). In the proposed system, an F_AG plays as an important role, which decides the power factors of all distributed generators by executing the load flow calculations repeatedly. The voltage control strategies are implemented as the class definition of Java into the system. In order to verify the performance of the proposed method, it has been applied to a typical distribution model system. The simulation results show that the system is able to control very violent fluctuation of the demands and the photovoltaic (PV) generations. 相似文献
4.
5.
6.
在45钢表面电刷镀得到三价铬镀层,镀液组成和工艺条件为:Cr2(SO4)36H2O 0.4 mol/L,甲酸铵0.5 mol/L,氨基乙酸0.5 mol/L,H3BO30.6 mol/L,NaH2PO2 H2O 0.3 mol/L,pH=1.5,温度50°C,镀笔移动速率15 cm/s。研究了电压对镀铬层显微结构、表面粗糙度、厚度、显微硬度和耐磨性的影响。随电压增大,镀层厚度增大,显微硬度和耐磨性均先提高后降低。电压为14 V时,镀层的表面平整,粗糙度为2.387μm,显微硬度为602 HV,耐磨性最好。 相似文献
7.
孙振 《水电自动化与大坝监测》2015,(2):75-79
本文首先分析国内典型的AVC的一般配置、控制策略和控制原理,针对巨型水电站孤岛试验期间的AVC控制的复杂工况进行阐述,对出现的AVC电压波动的情况进行分析,并对采用的解决方案进行介绍,为今后类似电站的孤岛运行期间的AVC电压控制提供一些参考建议。 相似文献
8.
The mammalian cell cycle is important in controlling normal cell proliferation and the development of various diseases. Cell cycle checkpoints are well regulated by both activators and inhibitors to avoid cell growth disorder and cancerogenesis. Cyclin dependent kinase 20 (CDK20) and p21Cip1/Waf1 are widely recognized as key regulators of cell cycle checkpoints controlling cell proliferation/growth and involving in developing multiple cancers. Emerging evidence demonstrates that these two cell cycle regulators also play an essential role in promoting cell survival independent of the cell cycle, particularly in those cells with a limited capability of proliferation, such as cardiomyocytes. These findings bring new insights into understanding cytoprotection in these tissues. Here, we summarize the new progress of the studies on these two molecules in regulating cell cycle/growth, and their new roles in cell survival by inhibiting various cell death mechanisms. We also outline their potential implications in cancerogenesis and protection in heart diseases. This information renews the knowledge in molecular natures and cellular functions of these regulators, leading to a better understanding of the pathogenesis of the associated diseases and the discovery of new therapeutic strategies. 相似文献
9.
介绍了尿素装置中3起液位仪表失真案例,分析了故障现象和设备工况,确定失真原因,采取了相应的处理措施,解决了仪表故障。 相似文献
10.
仪器仪表产品的脉冲耐压试验是产品型式试验、例行试验中的基本内容。通过对GB4793.1标准的整理,归纳了仪器仪表产品的脉冲耐压试验要求。通过对试验方法和设备特性的梳理,总结了特性参数,并介绍了应对脉冲耐压试验可采取的保护器件的类别及选用方法。 相似文献