全文获取类型
收费全文 | 209820篇 |
免费 | 24544篇 |
国内免费 | 10530篇 |
专业分类
电工技术 | 23961篇 |
技术理论 | 25篇 |
综合类 | 14375篇 |
化学工业 | 28105篇 |
金属工艺 | 7763篇 |
机械仪表 | 10263篇 |
建筑科学 | 30351篇 |
矿业工程 | 6911篇 |
能源动力 | 20277篇 |
轻工业 | 16317篇 |
水利工程 | 8755篇 |
石油天然气 | 7728篇 |
武器工业 | 1759篇 |
无线电 | 15320篇 |
一般工业技术 | 18882篇 |
冶金工业 | 9128篇 |
原子能技术 | 2445篇 |
自动化技术 | 22529篇 |
出版年
2024年 | 1109篇 |
2023年 | 4218篇 |
2022年 | 8604篇 |
2021年 | 10195篇 |
2020年 | 8541篇 |
2019年 | 7382篇 |
2018年 | 6726篇 |
2017年 | 8228篇 |
2016年 | 9823篇 |
2015年 | 10519篇 |
2014年 | 15683篇 |
2013年 | 14625篇 |
2012年 | 14772篇 |
2011年 | 15203篇 |
2010年 | 11678篇 |
2009年 | 11640篇 |
2008年 | 10459篇 |
2007年 | 12742篇 |
2006年 | 11338篇 |
2005年 | 9295篇 |
2004年 | 7356篇 |
2003年 | 6380篇 |
2002年 | 5222篇 |
2001年 | 4207篇 |
2000年 | 3647篇 |
1999年 | 2782篇 |
1998年 | 2050篇 |
1997年 | 1620篇 |
1996年 | 1480篇 |
1995年 | 1216篇 |
1994年 | 1083篇 |
1993年 | 825篇 |
1992年 | 627篇 |
1991年 | 541篇 |
1990年 | 471篇 |
1989年 | 380篇 |
1988年 | 284篇 |
1987年 | 236篇 |
1986年 | 182篇 |
1985年 | 243篇 |
1984年 | 209篇 |
1983年 | 138篇 |
1982年 | 147篇 |
1981年 | 83篇 |
1980年 | 111篇 |
1979年 | 56篇 |
1966年 | 32篇 |
1964年 | 50篇 |
1962年 | 71篇 |
1959年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Weiguo Cao Wenjuan Li Liang Zhang Jianfa Chen Shuo Yu Zhuanghong Zhou Yun Zhang Xiaobo Shen Yingxin Tan 《International Journal of Hydrogen Energy》2021,46(52):26693-26707
The explosion venting duct can effectively reduce the hazard degree of a gas explosion and conduct the venting energy to the safe area. To investigate the flame quantitative propagation law of explosion venting with a duct, the effects of hydrogen fraction and explosion venting duct length on jet flame propagation characteristics of premixed H2-air mixtures were analyzed through experiment and simulation. The experiment results under initial conditions of room temperature and 1 atm show that when hydrogen fraction was high enough, part of the unburned hydrogen was mixed with air again to reach an ignitable concentration, resulting in the secondary combustion was easier produced and the duration of the secondary flame increased. With the increase of venting duct length, the flame front distance and propagation velocity increased. Meanwhile, the spatial distribution of pressure field and temperature field, and the propagation process and mechanism of the flame venting with a duct were analyzed using FLUENT software. The variation of the pressure wave and the pressure reflection oscillation law in the explosion venting duct was captured. Therefore, in the industrial explosion venting design with a duct, the hazard caused by the coupling of venting pressure and venting flame under different fractions should be considered comprehensively. 相似文献
112.
本实验采用4D-非标记蛋白质组学技术研究秦川牛肉贮藏过程中(0~8 d)肌红蛋白含量及其衍生物的转化情况,阐释冷却秦川牛肉中肌红蛋白含量及其衍生物转化的分子机制。结果表明:贮藏过程中,肌红蛋白表达量在宰后0~4 d上升、4~8 d下降,利用非标记蛋白质组学技术鉴定出与肌红蛋白及其衍生物相关的差异蛋白14 种,具体包括代谢酶、氧化还原酶、过氧化物酶、伴侣蛋白4 类,这4 类蛋白的表达共同调控贮藏过程中肌红蛋白含量的变化及其3 种衍生物之间的转化,具体表现为贮藏过程中肌红蛋白表达量整体呈下降趋势,氧合肌红蛋白相对含量持续下降,脱氧肌红蛋白、高铁肌红蛋白相对含量逐渐增加,导致肉色发生褐变。本研究结果有利于理解秦川牛肉贮藏过程肉类变色的复杂生化变化机制。 相似文献
113.
《Ceramics International》2022,48(8):10885-10894
Lead-free bismuth sodium titanate-strontium titanate (NBT-ST) dielectric ceramic materials have been extensively investigated energy storage materials because of their relaxor characteristics. In this study, four different lanthanide elements were introduced into the ferroelectric NBT-ST ceramic to improve their relaxor properties. The introduction of the lanthanide resulted in an increase in disorder at location A within the perovskite lattice and improved relaxor characteristics, leading to a stored energy density of more than 3.5 J/cm3. In particular, an ultrahigh recoverable stored energy density of 4.94 J/cm3 and efficiency of 88.45% were achieved at 440 kV/cm when the NBT-ST ceramic was modified with neodymium. The modified ceramic also exhibited good thermal stability in the range of 30–120 °C, as well as a fast discharge time of ~153 ns, indicating that Nd-incorporated NBT-ST is a promising candidate for electrical energy storage ceramic. 相似文献
114.
《International Journal of Hydrogen Energy》2021,46(66):33186-33196
Additive doping is one of the effective methods to overcome the shortcomings of MgH2 on the aspect of relatively high operating temperatures and slow desorption kinetics. In this paper, hollow g-C3N4 (TCN) tubes with a diameter of 2 μm are synthesized through the hydrothermal and high-temperature pyrolysis methods, and then nickel is chemically reduced onto TCN to form Ni/TCN composite at 278 K. Ni/TCN is then introduced into the MgH2/Mg system by means of hydriding combustion and ball milling. The MgH2–Ni/TCN composite starts to release hydrogen at 535 K, which is 116 K lower than the as-milled MgH2 (651 K). The MgH2–Ni/TCN composite absorbs 5.24 wt% H2 within 3500 s at 423 K, and takes up 3.56 wt% H2 within 3500 s, even at a temperature as low as 373 K. The apparent activation energy (Ea) of the MgH2 decreases from 161.1 to 82.6 kJ/mol by the addition of Ni/TCN. Moreover, the MgH2–Ni/TCN sample shows excellent cycle stability, with a dehydrogenation capacity retention rate of 98.0% after 10 cycles. The carbon material enhances sorption kinetics by dispersing and stabilizating MgH2. Otherwise, the phase transformation between Mg2NiH4 and Mg2NiH0.3 accelerates the re/dehydrogenation reaction of the composite. 相似文献
115.
A mathematical model for open pit mine production scheduling with Grade Engineering® and stockpiling
《矿业科学技术学报(英文版)》2021,31(4):717-728
This paper presents the development and implementation of an innovative mixed integer programming based mathematical model for an open pit mining operation with Grade Engineering framework. Grade Engineering comprises a range of coarse-separation based pre-processing techniques that separate the desirable (i.e. high-grade) and undesirable (i.e. low-grade or uneconomic) materials and ensure the delivery of only selected quantity of high quality (or high-grade) material to energy, water, and cost-intensive processing plant. The model maximizes the net present value under a range of operational and processing constraints. Given that the proposed model is computationally complex, the authors employ a data pre-processing procedure and then evaluate the performance of the model at several practical instances using computation time, optimality gap, and the net present value as valid measures. In addition, a comparison of the proposed and traditional (without Grade Engineering) models reflects that the proposed model outperforms the traditional formulation. 相似文献
116.
Xianjin Li Tianyu Li Pengcheng Xu Congxin Xie Yunhe Zhang Xianfeng Li 《Advanced functional materials》2021,31(22):2100133
Bromine-based flow batteries (Br-FBs) are considered one of the most promising energy storage systems due to their features of high energy density and low cost. However, they generally suffer from uncontrolled diffusion of corrosive bromine particularly at high temperatures. That is because the interaction between polybromide anions and the commonly used complexing agent (N–methyl–N–ethyl–pyrrolidinium bromide [MEP]) decreases with increasing temperatures, which causes serious self-discharge and capacity fade. Herein, a novel bromine complexing agent, 1–ethyl–2–methyl–pyridinium bromide (BCA), is introduced in Br-FBs to solve the above problems. It is proven that BCA can combine with polybromide anions very well even at a high temperature of 60 °C. Moreover, the BCA contributes to decreasing the electrochemical polarization of Br−/Br2 couple, which in turn improves their power density. As a result, a zinc–bromine flow battery with BCA as the complexing agent can achieve a high energy efficiency of 84% at 40 mA cm−2, even at high temperature of 60 °C and it can stably run for more than 400 cycles without obvious performance decay. This paper provides an effective complexing agent to enable a wide temperature range Br-FB. 相似文献
117.
《Ceramics International》2021,47(20):28338-28347
Transition metal oxides have been explored in supercapacitor applications owing to their safety, low cost, high specific capacitance and high electrochemical activity. Among all transition metal oxides, zinc oxide based materials show remarkable response for designing the supercapacitors with high electrochemical activity. Here in, Mn doped ZnO (Zn1-xMnxO3 with x = 0, 0.25, 0.50, 0.75 and 1) was synthesized by a facile hydrothermal method. Doping of Mn into the ZnO increased the surface area and decease the charge transfer resistance for the Zn0.5Mn0.5O3. All the synthesized materials were characterized by x-ray diffraction (XRD), scanning electron microscopy SEM), BET, electrochemical tests and other various analytical techniques to confirm the structural, morphological, textural and suprcapacitive properties. The synthesized material Zn0.5Mn0.5O3 having the porous nanoribons structure with BET surface area (2490 cm2/g). The electrochemical studies showed significantly enhanced response toward pseudocapacitive nature. The synthesized material exhibited the excellent specific capacitance (515F/g), specific energy (28.61 Wh/kg) and specific power (1000 W/kg) at current density of 2 mA/g. Such impressive and superior properties make the MnZnO3 material as promising candidate for new generation supercapacitor applications. 相似文献
118.
《International Journal of Hydrogen Energy》2021,46(59):30267-30287
This work aims to improve the existing monitoring systems MS for two grid-connected PV stations GCPVS of URERMS ADRAR, to eliminate its limitations. This improvement consists of developing an MS which is used for two PV stations with different configurations. This MS contains new LabVIEW-based monitoring software for visualizing real-time measured data and evaluating GCPVS performance. In addition, it illustrates the 2D and 3D real-time relationships of PV system parameters, which allow us to understand the dynamic behavior of PV system components. This developed monitoring software synchronizes also the various data acquisition units DAU of GCPVS, allowing simultaneous data access.To perform a reliable performance analysis and a comparative study of different GCPVS based on accurate measurements, the sensor's calibration is performed with its DAU. The MS autonomy is ensured by integrating developed PV-UPS. A graphical user interface is provided for the evaluation of PV-UPS performance. 相似文献
119.
对赤红球菌的组氨酸激酶基因进行密码子优化,将优化后的组氨酸激酶基因(rhks)构建重组表达质粒pGEX-4T-2-rhks。将此质粒导入到大肠杆菌BL21(DE3)中进行异源表达。在25 ℃和1 mmol/L异丙基-β-D-硫代吡喃半乳糖苷诱导条件下,组氨酸激酶融合蛋白(GST-RHK)获得成功表达,并具有催化活性。经谷胱甘肽琼脂糖亲和层析纯化,获得电泳纯的GST-RHK,其中纯化倍数为3.1,得率为19.5%。该蛋白大小约为72.75 kDa,Km、Vmax和Kcat值分别为20.92 μmol/L、0.17 μmol/(L·min)和1.4 min-1。野生型赤红球菌、组氨酸激酶基因增强株sdrhkE和组氨酸激酶基因敲减株sdrhkD在分别含有苯酚、甲苯、氯苯、异辛烷4 种有机溶剂的培养基中培养,菌株sdrhkD的生长情况都优于野生型赤红球菌,菌株sdrhkE的生长情况都低于野生型赤红球菌。本研究为进一步揭示赤红球菌SD3中组氨酸激酶涉及的信号转导途径与赤红球菌有机溶剂耐受性的关联机制提供一定参考依据。 相似文献
120.
Lorenzo Zallocco Laura Giusti Maurizio Ronci Andrea Mussini Marco Trerotola Maria Rosa Mazzoni Antonio Lucacchini Laura Sebastiani 《International journal of molecular sciences》2021,22(9)
The autonomic nervous system (ANS) plays a crucial role both in acute and chronic psychological stress eliciting changes in many local and systemic physiological and biochemical processes. Salivary secretion is also regulated by ANS. In this study, we explored salivary proteome changes produced in thirty-eight University students by a test stress, which simulated an oral exam. Students underwent a relaxation phase followed by the stress test during which an electrocardiogram was recorded. To evaluate the effect of an olfactory stimulus, half of the students were exposed to a pleasant odor diffused in the room throughout the whole session. Saliva samples were collected after the relaxation phase (T0) and the stress test (T1). State anxiety was also evaluated at T0 and T1. Salivary proteins were separated by two-dimensional electrophoresis, and patterns at different times were compared. Spots differentially expressed were trypsin digested and identified by mass spectrometry. Western blot analysis was used to validate proteomic results. Anxiety scores and heart rate changes indicated that the fake exam induced anxiety. Significant changes of α-amylase, polymeric immunoglobulin receptor (PIGR), and immunoglobulin α chain (IGHA) secretion were observed after the stress test was performed in the two conditions. Moreover, the presence of pleasant odor reduced the acute social stress affecting salivary proteome changes. Therefore, saliva proteomic analysis was a useful approach to evaluate the rapid responses associated to an acute stress test also highlighting known biomarkers. 相似文献