全文获取类型
收费全文 | 116327篇 |
免费 | 11306篇 |
国内免费 | 6842篇 |
专业分类
电工技术 | 8489篇 |
综合类 | 9902篇 |
化学工业 | 15215篇 |
金属工艺 | 6507篇 |
机械仪表 | 6536篇 |
建筑科学 | 6961篇 |
矿业工程 | 4010篇 |
能源动力 | 3124篇 |
轻工业 | 13256篇 |
水利工程 | 3276篇 |
石油天然气 | 3229篇 |
武器工业 | 1593篇 |
无线电 | 10642篇 |
一般工业技术 | 10070篇 |
冶金工业 | 15247篇 |
原子能技术 | 1616篇 |
自动化技术 | 14802篇 |
出版年
2024年 | 653篇 |
2023年 | 1698篇 |
2022年 | 4028篇 |
2021年 | 5146篇 |
2020年 | 3610篇 |
2019年 | 2632篇 |
2018年 | 2885篇 |
2017年 | 3185篇 |
2016年 | 2997篇 |
2015年 | 4419篇 |
2014年 | 5506篇 |
2013年 | 6988篇 |
2012年 | 8175篇 |
2011年 | 8625篇 |
2010年 | 8075篇 |
2009年 | 7532篇 |
2008年 | 7614篇 |
2007年 | 7457篇 |
2006年 | 6373篇 |
2005年 | 4991篇 |
2004年 | 3954篇 |
2003年 | 3149篇 |
2002年 | 3174篇 |
2001年 | 2816篇 |
2000年 | 2073篇 |
1999年 | 1313篇 |
1998年 | 4208篇 |
1997年 | 2535篇 |
1996年 | 1741篇 |
1995年 | 1073篇 |
1994年 | 856篇 |
1993年 | 944篇 |
1992年 | 328篇 |
1991年 | 290篇 |
1990年 | 285篇 |
1989年 | 260篇 |
1988年 | 233篇 |
1987年 | 205篇 |
1986年 | 197篇 |
1985年 | 217篇 |
1984年 | 99篇 |
1983年 | 118篇 |
1982年 | 128篇 |
1981年 | 151篇 |
1980年 | 185篇 |
1979年 | 97篇 |
1978年 | 73篇 |
1977年 | 271篇 |
1976年 | 494篇 |
1975年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
The catalysts of CeO2 and the mixture of CeO2 and CuO were prepared, and the activities of these catalysts for completely oxidizing benzene were studied.The results show that the optimal proportion of CeO2/CuO is 6: 4.The highest temperature at which benzene was completely oxidized on these catalysts at different airspeed was measured.Compared these catalysts with the noble metal used, our catalysts had superiority in the resources and the industrial cost besides good activities. 相似文献
52.
Simonetta Balsamo Vittoria De Nitto Person Paola Inverardi 《Performance Evaluation》2003,51(2-4):269-288
A review is carried out on how queueing network models with blocking have been applied so far into the performance evaluation and prediction of Software Architectures (SA). Queueing network models with finite capacity queues and blocking have recently been introduced and applied as more realistic models of systems with finite capacity resources and population constraints. Queueing network models have been often adopted as models for the evaluation of software performance. Starting from our own experience, we observe the need of a more accurate definition of the performance models of SA to capture some features of the communication systems. We consider queueing networks with finite capacity and blocking after service (BAS) to represent some synchronization constraints that cannot be easily modeled with queueing network models with infinite capacity queues. We investigate the use of queueing networks with blocking as performance models of SA with concurrent components and synchronous communication. Queueing theoretic analysis is used to solve the queueing network model and study the synchronous communication and performance of concurrent software components. Our experience is supported by other approaches that also propose the use of queueing networks with blocking. Directions for future research work in the field are included. 相似文献
53.
马勇 《金属材料与冶金工程》2003,31(1):21-24
通过煤种,入窑球冷态强度和还原过程强度,以及钛精矿与煤灰混合物的软化温度等分析探讨了钛精矿预热球团回转窑直接还原产生结圈的可能性,获得了可以避免结圈的结论。 相似文献
54.
55.
Rejane De Césaro Oliveski Arno Krenzinger 《International Journal of Heat and Mass Transfer》2003,46(11):2015-2026
A numerical and an experimental analysis of velocity and temperature fields inside a storage tank submitted to natural convection is presented. The analysis was performed in two stages. In the first stage, the temperature profile along the vertical axis of the storage tank was obtained experimentally and numerically, for cooling time ranging from 45 to 60 h. The numerical analysis was carried out using a transient bi-dimensional model in cylindrical co-ordinates. In the second stage, after the numerical code validation, 40 cases of cooling with four aspect ratios, five insulation thicknesses, and two different volumes were simulated. In all simulations, thermal losses for the environment in all tank walls (side, top and bottom) were considered. Two correlations for the Nusselt number, encompassing all the forty cases, were obtained with these results. 相似文献
56.
L. M. Du Plessis J. B. M. De Villiers W. H. Van Der Walt 《Journal of the American Oil Chemists' Society》1985,62(4):748-752
Fatty acid esters, high in linoleic acid, were prepared and stored for long-term engine tests. Storage tests with these esters were undertaken to obtain more information on optimal storage requirements and general stability characteristics. Samples were kept at three temperature levels (20 C, 30 C and fluctuating around 50 C) for a 90-day period and were removed at regular intervals for chemical and physical analysis. The influence of air, temperature, light, TBHQ and contact with mild steel was evaluated by comparing the free fatty acid, peroxide, anisidine, ultraviolet absorption, viscosity and induction periods. A statistical model was used to evaluate the data and to reduce the large number of data points to comparable curves. Storage of esters in contact with air, especially at a temperature above 30 C, resulted in significant increases in peroxide, ultraviolet absorption, free fatty acid, viscosity and anisidine values. Exclusion of air retarded oxidation at all temperature levels. A direct relationship between viscosity increases and oxidation parameters was evident. Exposure to light caused a small increase in the oxidation parameters of esters stored at the highest temperature level. Addition of TBHQ prevented oxidation of samples stored under moderate conditions. Under unfavorable storage conditions the anti-oxidant was no longer effective. Mild steel had very little effect on the oxidation parameters. Only the anisidine values of samples stored at the highest temperature level were slightly increased. Methyl esters performed slightly better than ethyl esters during the storage test. The following practical guidelines for storage of fatty acid ester fuels are: (i) airtight containers should be used; (ii) the storage temperature should be <30 C; (iii) mild steel (rust free) containers may be used, and (iv) TBHQ has a beneficial effect on oxidation stability. 相似文献
57.
58.
RF Speck K Wehrly EJ Platt RE Atchison IF Charo D Kabat B Chesebro MA Goldsmith 《Canadian Metallurgical Quarterly》1997,71(9):7136-7139
The chemokine receptor CCR5 acts as an essential cofactor for cell entry by macrophage-tropic human immunodeficiency virus type 1 (HIV-1) strains, whereas CXCR4 acts as an essential cofactor for T-cell-line-adapted strains. We demonstrated that the specific amino acids in the V3 loop of the HIV-1 envelope protein that determine cellular tropism also regulate chemokine coreceptor preference for cell entry by the virus. Further, a strong correlation was found between HIV-1 strains classified as syncytium inducing in standard assays and those using CXCR4 as a coreceptor. These data support the hypothesis that progressive adaptation to additional coreceptors is a key molecular basis for HIV-1 phenotypic evolution in vivo. 相似文献
59.
Comparison of two methods of surfactant administration and the effect on dosing-associated hypoxemia
M Nelson JJ Nicks MA Becker LA Vrlenich V Bhatt-Mehta RE Schumacher 《Canadian Metallurgical Quarterly》1997,17(6):450-454
OBJECTIVE: The purpose of our study was to test the hypothesis that surfactant dosing through a proximal sideport adapter on an endotracheal tube leads to more dosing-associated hypoxemia compared with a method of dosing that uses a double-lumen endotracheal tube. STUDY DESIGN: Using adequate sample size to compare significant changes in O2 saturation (power > 0.8, alpha < 0.05) we enrolled 36 infants with respiratory distress syndrome in this randomized trial. A 10% change in O2 saturation was considered clinically significant. Nineteen infants received 38 doses of surfactant through the sideport adapter. Seventeen infants received 31 doses of surfactant through the nonventilation lumen of a double-lumen endotracheal tube. Two main outcome measures were assessed: time-averaged O2 saturation values 30 minutes after dosing and the largest absolute fall in O2 saturation for each patient. RESULTS AND CONCLUSIONS: Time-averaged O2 saturation measures were higher in the proximal sideport group (p = 0.02), but the magnitude of difference was probably not clinically significant. No significant difference was detected between groups when we compared largest absolute drop in O2 saturation. Secondary analyses found no effect of birth weight or dose number (second vs third dose) on either outcome measure. 相似文献
60.