全文获取类型
收费全文 | 24301篇 |
免费 | 3648篇 |
国内免费 | 1773篇 |
专业分类
电工技术 | 16005篇 |
综合类 | 1471篇 |
化学工业 | 640篇 |
金属工艺 | 445篇 |
机械仪表 | 826篇 |
建筑科学 | 381篇 |
矿业工程 | 424篇 |
能源动力 | 867篇 |
轻工业 | 169篇 |
水利工程 | 273篇 |
石油天然气 | 1297篇 |
武器工业 | 57篇 |
无线电 | 4106篇 |
一般工业技术 | 796篇 |
冶金工业 | 461篇 |
原子能技术 | 247篇 |
自动化技术 | 1257篇 |
出版年
2024年 | 47篇 |
2023年 | 337篇 |
2022年 | 604篇 |
2021年 | 755篇 |
2020年 | 868篇 |
2019年 | 716篇 |
2018年 | 674篇 |
2017年 | 1020篇 |
2016年 | 1071篇 |
2015年 | 1332篇 |
2014年 | 1797篇 |
2013年 | 1467篇 |
2012年 | 2126篇 |
2011年 | 2264篇 |
2010年 | 1586篇 |
2009年 | 1668篇 |
2008年 | 1646篇 |
2007年 | 1847篇 |
2006年 | 1679篇 |
2005年 | 1249篇 |
2004年 | 937篇 |
2003年 | 855篇 |
2002年 | 657篇 |
2001年 | 629篇 |
2000年 | 454篇 |
1999年 | 328篇 |
1998年 | 204篇 |
1997年 | 154篇 |
1996年 | 159篇 |
1995年 | 122篇 |
1994年 | 118篇 |
1993年 | 101篇 |
1992年 | 64篇 |
1991年 | 44篇 |
1990年 | 36篇 |
1989年 | 25篇 |
1988年 | 23篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
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
12.
西湖凹陷中部西斜坡地区超压成因机制 总被引:10,自引:5,他引:5
沉积盆地超压成因研究已取得了重要进展,关于超压主要成因的认识也发生了重要变化,以往一些被普遍认为属于典型不均衡压实成因的超压已被部分或完全否定,生烃作用作为超压成因的普遍性得到愈来愈多的证实。西湖凹陷多个构造带的不同层位均发育超压,目前认为超压的形成仍然离不开不均衡压实(欠压实作用)的贡献。根据异常压力形成的基本地质条件和异常压力产生的地质、地球物理效应两方面因素,利用测井曲线组合分析法、鲍尔斯法(加载-卸载曲线法)、声波速度-密度交会图法、孔隙度对比法、压力计算反推法以及综合分析法系统解剖分析了西湖凹陷中部西斜坡地区平湖组不同岩性异常压力成因。研究结果表明:西湖凹陷中部西斜坡泥岩中烃源岩超压主要为自源生烃增压,非烃源岩超压为邻源压力传导成因。储层中至少存在常压-超压型和常压-超压-常压型两种压力结构类型,异常压力自南向北顶界面逐渐变深,主要为油气在生烃增压驱动下向储层运移过程中的压力传导所致。 相似文献
13.
分级加载电压技术能够有效延长电渗处理的时间,改善地基的处理效果并能有效降低能耗。在利用分级加载电压技术开展电渗试验时,随着土体的排水固结,土体各点的电势会发生明显的变化,这与现有的电渗固结理论假设土体各点电势保持不变有所差异。利用自主设计的电渗试验仪器开展了分级加载电压下的电渗室内试验,分析了电渗过程中土体有效电势变化的规律。基于该规律并结合Esrig固结理论建立了在阳极处不排水、阴极处排水条件下考虑土体有效电势变化的电渗固结理论,得到了分级加载电压条件下考虑土体有效电势变化的超静孔隙水压力和平均固结度的解析表达式。研究表明,在电压分级加载过程中,土体有效电势变化规律表现为随时间先基本保持不变,后呈抛物线状先增后减。通过试验案例验证了考虑土体有效电势变化所求得解析解的合理性,且该数值计算结果相较于Esrig数值计算结果,前者更加接近实测值,该固结方程的建立为后续分级加载电压技术的推广应用提供了理论依据,也为实际工程提供了参考。 相似文献
14.
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
15.
Mohammad Maleki Shahraki Mohammad Golmohammad Iman Safaee Mehdi Delshad Chermahini 《Ceramics International》2018,44(3):3388-3393
In this research, the addition effects of three different quantities of micron-sized seeds (microseeds) to a SnO2 varistor prepared from nanomaterials on the microstructure and electrical properties were studied. Moreover, surge-withstanding capability of low-voltage SnO2 varistors was investigated. The X-ray diffraction pattern disclosed a single phase SnO2 for microseed grains. The morphological features of samples were characterized using scanning electron microscopy. The abnormal distribution of grain size with elongated grains of SnO2 in fine grains matrix was observed in sintered samples without microseeds. The low content of microseed addition (0.3 wt%) had not controlled abnormal grain growth, however, it increased mean grain size to 37 µm. Although the high content of microseeds (7.5 wt%) stopped abnormal grain growth, it had a negative effect on relative density and mean grain size. The normal grain size distribution with maximum mean grain size (45 µm) was obtained in samples containing 1.5 wt% microseeds. These samples showed the lowest breakdown field (240 V/cm) and the highest surge-withstanding capability (1.5 kA/cm2). Furthermore, the standard deviation of the electrical parameters of these samples was improved due to normal grain-size distribution. 相似文献
16.
ABSTRACTThe RF output power dissipated per unit area is calculated using Runge-Kutta method for the high-moderate-moderate-high (n+-n-p-p+) doping profile of double drift region (DDR)-based impact avalanche transit time (IMPATT) diode by taking different substrate at Ka band. Those substrates are silicon, gallium arsenide, germanium, wurtzite gallium nitride, indium phosphide and 4H-silicon carbide. A comparative study regarding power dissipation ability by the IMPATT using different material is being presented thereby modelling the DDR IMPATT diode in a one-dimensional structure. The IMPATT based on 4H-SiC element has highest power density in the order of 1010 Wm?2 and the Si-based counterpart has lowest power density of order 106 Wm?2 throughout the Ka band. So, 4H-SiC-based IMPATT should be preferable over others for the power density preference based application. This result will be helpful to estimate the power density of the IMPATT for any doping profile and to select the proper element for the optimum design of the IMPATT as far as power density is concerned in the Ka band. Also, we have focused on variation of power density with different junction temperatures and modelled the heat sink with analysis of thermal resistances. 相似文献
17.
以三塘湖盆地中、低煤阶煤层含气量和主要气体成分为基础,结合盆地构造、沉积及水文地质特征,对汉水泉凹陷和条湖凹陷煤层甲烷风化带进行了划分,并对库木苏凹陷、马朗凹陷、淖毛湖凹陷和苏鲁克凹陷煤层甲烷风化带进行了预测。结果表明,三塘湖盆地甲烷风化带深度为400~1000 m.由于受东北冲断隆起带的影响,三塘湖盆地北部甲烷风化带浅于南部。沉积方面,盆地东部淖毛湖凹陷、马朗凹陷和条湖凹陷深湖—半深湖和辫状河三角洲成煤环境优于盆地西部汉水泉凹陷和库木苏凹陷扇三角洲成煤环境,盆地东部甲烷风化带普遍浅于西部;水文地质方面,条湖凹陷和马朗凹陷中开启性局部滞留水文地质单元形成的甲烷风化带浅于其他凹陷封闭性弱径流水文地质单元的甲烷风化带。初步预测马朗凹陷北部为下一步煤层气勘探开发的优势区块,条湖凹陷北部为下一步煤系气勘探开发的优势区块。 相似文献
18.
Dr. Dimitra T. Pournara Anna Durner Dr. Eftichia Kritsi Alexios Papakostas Dr. Panagiotis Zoumpoulakis Prof. Dr. Annette Nicke Dr. Maria Koufaki 《ChemMedChem》2020,15(24):2530-2543
The P2X7 receptor is a promising target for the treatment of various diseases due to its significant role in inflammation and immune cell signaling. This work describes the design, synthesis, and in vitro evaluation of a series of novel derivatives bearing diverse scaffolds as potent P2X7 antagonists. Our approach was based on structural modifications of reported (adamantan-1-yl)methylbenzamides able to inhibit the receptor activation. The adamantane moieties and the amide bond were replaced, and the replacements were evaluated by a ligand-based pharmacophore model. The antagonistic potency of the synthesized analogues was assessed by two-electrode voltage clamp experiments, using Xenopus laevis oocytes that express the human P2X7 receptor. SAR studies suggested that the replacement of the adamantane ring by an aryl-cyclohexyl moiety afforded the most potent antagonists against the activation of the P2X7 cation channel, with analogue 2-chloro-N-[1-(3-(nitrooxymethyl)phenyl)cyclohexyl)methyl]benzamide ( 56 ) exhibiting the best potency with an IC50 value of 0.39 μM. 相似文献
19.
Mostafa Dellahi Hattab Maker Guillermo Botella Enrique Alameda-Hernandez Azeddine Mouhsen 《International Journal of Circuit Theory and Applications》2020,48(6):887-905
The three-phase four-wire shunt active power filter (SAPF) was developed to suppress the harmonic currents generated by nonlinear loads, and for the compensation of unbalanced nonlinear load currents, reactive power, and the harmonic neutral current. In this work, we consider instantaneous reactive power theory (PQ theory) for reference current identification based on the following two algorithms: the classic low-pass filter (LPF) and the second-order generalized integrator (SOGI) filter. Furthermore, since an important process in SAPF control is the regulation of the DC bus voltage at the capacitor, a new controller based on the Lyapunov function is also proposed. A complete simulation of the resultant active filtering system confirms its validity, which uses the SOGI filter to extract the reference currents from the distorted line currents, compared with the traditional PQ theory based on LPF. In addition, the simulation performed also demonstrates the superiority of the proposed approach, for DC bus voltage control based on the Lyapunov function, compared with the traditional proportional-integral (PI) controller. Both novel approaches contribute towards an improvement in the overall performance of the system, which consists of a small rise and settling time, a very low or nonexistent overshoot, and the minimization of the total harmonic distortion (THD). 相似文献
20.