全文获取类型
收费全文 | 41498篇 |
免费 | 4997篇 |
国内免费 | 2347篇 |
专业分类
电工技术 | 3735篇 |
综合类 | 2916篇 |
化学工业 | 10701篇 |
金属工艺 | 3736篇 |
机械仪表 | 1814篇 |
建筑科学 | 3932篇 |
矿业工程 | 600篇 |
能源动力 | 3788篇 |
轻工业 | 1951篇 |
水利工程 | 507篇 |
石油天然气 | 1566篇 |
武器工业 | 727篇 |
无线电 | 3426篇 |
一般工业技术 | 6333篇 |
冶金工业 | 1563篇 |
原子能技术 | 716篇 |
自动化技术 | 831篇 |
出版年
2024年 | 105篇 |
2023年 | 835篇 |
2022年 | 1210篇 |
2021年 | 1613篇 |
2020年 | 1744篇 |
2019年 | 1470篇 |
2018年 | 1340篇 |
2017年 | 1697篇 |
2016年 | 1611篇 |
2015年 | 1631篇 |
2014年 | 2388篇 |
2013年 | 2838篇 |
2012年 | 2932篇 |
2011年 | 3017篇 |
2010年 | 2246篇 |
2009年 | 2350篇 |
2008年 | 2026篇 |
2007年 | 2633篇 |
2006年 | 2551篇 |
2005年 | 1977篇 |
2004年 | 1718篇 |
2003年 | 1383篇 |
2002年 | 1262篇 |
2001年 | 1075篇 |
2000年 | 837篇 |
1999年 | 640篇 |
1998年 | 557篇 |
1997年 | 521篇 |
1996年 | 443篇 |
1995年 | 365篇 |
1994年 | 279篇 |
1993年 | 242篇 |
1992年 | 237篇 |
1991年 | 216篇 |
1990年 | 176篇 |
1989年 | 146篇 |
1988年 | 111篇 |
1987年 | 66篇 |
1986年 | 61篇 |
1985年 | 65篇 |
1984年 | 58篇 |
1983年 | 44篇 |
1982年 | 45篇 |
1981年 | 24篇 |
1980年 | 17篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1975年 | 4篇 |
1959年 | 7篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
1.
Xiao-Mei Sha Li-Jun Zhang Wen-Mei Chen Guang-Yao Wang Jin-Lin Li Zi-Zi Hu Zong-Cai Tu 《International Journal of Food Science & Technology》2022,57(3):1573-1586
Thermal action in extraction process had effects on characteristic tryptic peptides identification and gelling properties of porcine gelatin. SDS-PAGE, HPLC-LTQ/Orbitrap high-resolution mass spectrometry, texture analyser and rheometer were used to evaluate collagen depolymerisation degree, characteristic tryptic peptides and gelling properties of gelatins prepared in various thermal actions. Results showed that with increasing temperature and time, depolymerisation degree enlarged, while gel strength, gelling and melting temperature decreased. Mass spectra showed that 47 and 49 common characteristic tryptic peptides were identified in gelatins extracted at 50 °C and 100 °C with various times, respectively. Moreover, 34 common characteristic tryptic peptides were identified in all gelatin samples. Further comparison between this work and our previous investigations yielded 20 common characteristic tryptic peptides, which stably exist in various thermal actions. These common characteristic tryptic peptides may be very helpful for the accurate authentication of porcine gelatin. 相似文献
2.
In the present paper, therapeutic treatment of infected tumorous cells has been studied through mathematical modeling and simulation of heat transfer in tissues by using a nonlinear dual-phase lag bioheat transfer model with Dirichlet boundary condition. The components of volumetric heat source in this model such as blood perfusion and metabolism are assumed experimentally validated temperature-dependent function, which gives more accurate temperature distribution in tissues through this model. We have used the finite difference and RK (4, 5) techniques of numerical methods to solve the proposed problem and obtained the exact solution in a particular case. After comparison, we got a good agreement between them. We have used dimensionless quantities throughout this paper. The effect of relaxation and thermalization time with respect to dimensionless temperature distribution has been analyzed in the treatment process. 相似文献
3.
《Ceramics International》2022,48(20):29862-29872
Thermal shock parameters (R, R''', R'''' and Rst) of MgAlON–MgO composites obtained with additions of spent MgO–C brick were calculated using measured mechanical properties and thermal expansion coefficient, determining their resistance to fracture initiation and crack propagation. The cyclic thermal shock experiments of MgAlON–MgO composites performed from 1398 K to ambient temperature indicate that as number of thermal shock cycle increases, retained strength ratio of MgAlON and MgAlON–4.2 wt%MgO sharply decrease and then keep constant, while that of MgAlON–10.5 wt%MgO and MgAlON–15.7 wt%MgO slowly decrease. The reason for the difference is that MgAlON and MgAlON–4.2 wt%MgO show low value of R''' and R'''', and high value of R and Rst. Moreover, precipitation of impurity containing Fe may play a positive role in improvement of thermal shock resistance of MgAlON–MgO composites. MgAlON?4.2 wt%MgO has the maximum retained strength (55 MPa) even after 5 thermal shock cycles, which is expected to be used in the metallurgical industry. 相似文献
4.
《Advanced Powder Technology》2022,33(11):103817
The heat production and thermal storage characteristics of rapid-preparation amorphous powder activated coke (RAC) were investigated. RAC was prepared by using a drop-tube reactor system. The natural oxidation characteristics of RAC were studied through combined TG–FTIR analysis and temperature-programmed experiment. Experimental results showed that CO and CO2 were the main oxidation products of RAC in air, and that the oxidation reaction was in accordance with the Arrhenius equation and law of mass action. Thermal storage characteristics were studied through computational fluid dynamics simulation. The maximum excess temperature θmax increases linearly with the increase of the initial temperature. The concentration fields of the products show that CO2 is mainly concentrated in the upper part of the coke bin, and the CO generated by CO2 at high temperature is mainly concentrated in the central part of the coke bin. 相似文献
5.
Ya-Nan Yang Yin-Ning Zhou Bo Ouyang Yi-Yang Wu Xi-Bao Zhang Zheng-Hong Luo 《American Institute of Chemical Engineers》2022,68(5):e17645
The computational fluid dynamics (CFD) and kinetic-based moment methods coupled approach is adopted to simulate the bulk copolymerization of styrene–acrylonitrile (SAN) in a stirred tank reactor. Numerical simulations are carried out to investigate the impacts of impeller speed, monomer ratio, initiator ratio, and initial reaction temperature on the copolymerization process and product properties. Particularly, the Chaos theory is selected as a criterion for evaluating the occurrence of the thermal runaway. The Flory's and Stockmayer's distributions are employed to calculate chain length distribution and copolymer composition distribution of copolymer. The simulation results highlight that the appearance of thermal runaway can be postponed by properly increasing the rotation speed, decreasing the initiator loadings, initial acrylonitrile contents and initial reactor temperature. Furthermore, significant differences exist in the product properties that predicted by the ideal and non-ideal models, which demonstrates that the temperature heterogeneity plays a crucial role in SAN copolymerization. This study could offer references for the safe operation and design of polymerization processes. 相似文献
6.
Hongyu Lv Zhichao Liu Chao Wang Yiyu Cai Hao Zhang Ting Wang Xiuxia Yang Xue Yu Jianbei Qiu Xuhui Xu 《Journal of the American Ceramic Society》2022,105(2):966-976
The exploration of the high thermal stability near-infrared (NIR) phosphors is significantly crucial for the development of plant lighting. However, NIR phosphors suffer from the poor chemical and thermal stability, which severely limits their long-term operation. Here, the successful improvement of luminous intensity (149.5%) and thermal stability at 423 K of Zn3Ga2GeO8 (ZGGO): Cr3+ phosphors is achieved for the introduction of Al3+ ions into the host. The release of carriers in deep traps inhibits the emission loss for the thermal disturbance. Furthermore, an NIR light emitting diodes (LEDs) lamp is explored by combining the optimized Zn3Ga1.1675Al0.8GeO8: 0.0325Cr3+ phosphors with a commercial 460 nm blue chip, and the emission band can match well with the absorption bands of photosynthetic pigments and the phytochrome (PR and PFR) of plants. The explored LEDs lamp further determines the growth and the pheromone content of the involved plants for the participation of the NIR emission originated from Cr3+ ions. Our work provides a promising NIR lamp as plant light with improved thermal stability for long-term operation. 相似文献
7.
《Ceramics International》2022,48(20):29959-29966
High-purity SiC ceramic devices are applied in semiconductor industry owing to their outstanding properties. Nevertheless, it is difficult to densify SiC ceramics without any sintering additive even by HP sintering. In this work, high-purity and dense SiC ceramics were fabricated by HP sintering with very low amounts of sintering aids. Residual B content was only 556 ppm and relative density was more than 99.5%. Furthermore, thermal conductivity of as-prepared SiC ceramics was improved from 155 W m?1 K?1 to 167 W m?1 K?1 by increasing holding time and their plasma corrosion resistance was promoted in the meantime. The as-prepared high-purity SiC ceramics have broad application prospects in the field of semiconductor industry. 相似文献
8.
以氧化铍、二氧化钛为原料,通过还原气氛烧结制备出BeO-TiO2衰减瓷,采用扫描电镜、矢量网络分析仪及闪射法导热仪等检测仪器,研究了BeO-TiO2衰减瓷的微观形貌及在W波段(75~110GHz)的微波衰减性能和导热性能。 相似文献
9.
Roberto Orrostieta Chavez Timothy P. Lodge Juan Huitron Mircea Chipara Mataz Alcoutlabi 《应用聚合物科学杂志》2021,138(18):50396
Aqueous solutions of poly(vinylpyrrolidone) (PVP) of various concentrations (20, 25, and 28 wt%) were successfully spun into fibers by centrifugal spinning. The pristine PVP fibers were annealed and carbonized to produce flexible carbon fibers for use as binder-free anodes in lithium-ion batteries. These flexible carbon fibers were prepared by developing a novel three-step heat treatment to reduce the residual stresses in the pristine PVP precursor fibers, and to prevent fiber degradation during carbonization. The thermogravimetric analysis data showed that the annealed fibers yielded a residual mass percentage of 36.0% while the pristine PVP fibers suffered a higher mass loss and only retained 26.5% of original mass above 450 °C (under nitrogen). The electrochemical performance of the carbon-fiber anodes was evaluated by conducting galvanostatic charge/discharge, rate performance, and cycle voltammetry experiments. The 20, 25, and 28 wt% derived binder-free anodes delivered specific charge capacities of 205, 189, and 275 mAh g−1, respectively, after the first cycle at a current density of 100 mA g−1. The results obtained in this work indicate that a feasible pathway towards a large-scale production of carbon-fiber anodes from a 100% aqueous solution can be achieved via centrifugal spinning and subsequent heat treatment. 相似文献
10.
Lindsey Yue Alicia Bayon Wojciech Lipiński 《American Institute of Chemical Engineers》2021,67(8):e17267
The effects of particle size and carbon dioxide concentration on chemical conversion in engineered spherical particles undergoing calcium oxide looping are investigated. Particles are thermochemically cycled in a furnace under different carbon dioxide concentrations. Changes in composition due to chemical reactions are measured using thermogravimetric analysis. Gas composition at the furnace exit is evaluated with mass spectroscopy. A numerical model of thermal transport phenomena developed previously is adapted to match the physical system investigated in the present study. The model is used to elucidate effects of reacting medium characteristics on particle temperature and reaction extent. Experimental and numerical results show that (1) an increase in particle size results in a decrease in carbonation extent, and (2) the carbonation step consists of fast and slow reaction regimes. The reaction rates in the fast and slow carbonation regimes increase with increasing carbon dioxide concentration. The effect of carbon dioxide concentration and the distinction between the fast and slow regimes become more pronounced with increasing particle size. 相似文献