全文获取类型
收费全文 | 45063篇 |
免费 | 4237篇 |
国内免费 | 2399篇 |
专业分类
电工技术 | 2931篇 |
综合类 | 3434篇 |
化学工业 | 9191篇 |
金属工艺 | 7003篇 |
机械仪表 | 2218篇 |
建筑科学 | 6597篇 |
矿业工程 | 1681篇 |
能源动力 | 1509篇 |
轻工业 | 2487篇 |
水利工程 | 1117篇 |
石油天然气 | 1440篇 |
武器工业 | 423篇 |
无线电 | 2369篇 |
一般工业技术 | 5927篇 |
冶金工业 | 1798篇 |
原子能技术 | 343篇 |
自动化技术 | 1231篇 |
出版年
2024年 | 167篇 |
2023年 | 835篇 |
2022年 | 1378篇 |
2021年 | 1902篇 |
2020年 | 1704篇 |
2019年 | 1401篇 |
2018年 | 1323篇 |
2017年 | 1810篇 |
2016年 | 1713篇 |
2015年 | 1740篇 |
2014年 | 2485篇 |
2013年 | 2535篇 |
2012年 | 3137篇 |
2011年 | 3524篇 |
2010年 | 2508篇 |
2009年 | 2793篇 |
2008年 | 2318篇 |
2007年 | 2695篇 |
2006年 | 2625篇 |
2005年 | 2188篇 |
2004年 | 1746篇 |
2003年 | 1518篇 |
2002年 | 1283篇 |
2001年 | 1095篇 |
2000年 | 909篇 |
1999年 | 815篇 |
1998年 | 687篇 |
1997年 | 565篇 |
1996年 | 437篇 |
1995年 | 424篇 |
1994年 | 354篇 |
1993年 | 231篇 |
1992年 | 188篇 |
1991年 | 151篇 |
1990年 | 112篇 |
1989年 | 90篇 |
1988年 | 65篇 |
1987年 | 51篇 |
1986年 | 32篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 24篇 |
1981年 | 10篇 |
1980年 | 21篇 |
1979年 | 8篇 |
1976年 | 3篇 |
1960年 | 3篇 |
1959年 | 8篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
131.
Results of metal testing in impact tension–compression and indentation are analyzed. As the analysis of these data demonstrates, the strength of metals increases greatly with strain rates and at moderate indentation rates. At high indentation rates, a decrease in the specific energy (per unit volume of a displaced material) necessary for the formation of a conical cavity was observed. The account of the effects of viscosity, temperature increase upon plastic deformation and its localization can be used to explain the above phenomena. 相似文献
132.
S. Vaidyanathan K. M. Kavadia L. P. Borkar S. P. Mahajan 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(2):121-128
With a view to evaluate the effects of hydraulic retention time and volatile solids loading rate on methane production using water hyacinth, experiments were conducted in a 160 dm3 capacity, well-mixed continuous digestion unit at ambient temperature. The optimal design of biogas plant using water hyacinth was elucidated, to provide a unit giving a maximum methane yield of 0.16 nm3 kg?1 volatile solids added, which was 60% greater than the conventional plant using cowdung. The calculations of optimal design factors were based on reactor size, hydraulic retention time and volatile solids loading rate; considerations were made of capital cost, running costs and operational revenue. 相似文献
133.
Rinji Akada Yoshirou Shimizu Yuji Matsushita Miho Kawahata Hisashi Hoshida Yoshinori Nishizawa 《Yeast (Chichester, England)》2002,19(1):17-28
Drug-resistance markers for yeast transformation are useful because they can be applied to strains without auxotrophic mutations. However, they are susceptible to technical difficulties, namely lower transformation efficiency and the appearance of drug-resistant mutants without the marker. To avoid these problems, we have constructed a phosphoglycerate kinase (PGK) promoter-driven YAP1 expression cassette, called PGKp-YAP1. Yeast cells containing PGKp-YAP1 were resistant to cycloheximide, a protein synthesis inhibitor, and also to cerulenin, a fatty acid synthesis inhibitor, but not to other drugs tested. The transformation efficiency of PGKp-YAP1 using cerulenin selection was comparable to that using a URA3 auxotrophic marker when low concentrations of cerulenin were used. Non-transformed drug-resistant colonies did appear on the low-concentration cerulenin plates. However, these non-transformed colonies could easily be identified, based on their cycloheximide sensitivity and/or their resistance to aureobasidin A to which the transformants were sensitive. Therefore, the dual drug resistance of PGKp-YAP1 could be used as an effective selection for PGKp-YAP1 recipient cells. The PGKp-YAP1 marker was used to disrupt the LYS2 gene and to transform an industrial yeast strain, indicating that this marker can be used for efficient and reliable gene manipulations in any Saccharomyces cerevisiae strain. 相似文献
134.
135.
Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full‐scale test and different small scale‐tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one‐sided fire exposed slab with the dimensions 1800 × 1200 mm2 giving an exposed area of 1500 × 1200 mm2. A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small‐scale furnace where the fire exposed surface was 450 × 360 mm2. The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre‐stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
136.
关于差阻式仪器的几个技术问题 总被引:1,自引:0,他引:1
本文对差阻式仪器的几个重要问题,如差阻式仪器的国家标准、监测数据的质量控制、长期埋设仪器的现场鉴定、仪器测值异常的分析处理等进行了讨论,并提出了自己的意见,供有关科研人员进一步研究和参考. 相似文献
137.
Samuel L. Manzello Richard G. Gann Scott R. Kukuck Kuldeep Prasad Walter W. Jones 《火与材料》2007,31(5):297-310
A gypsum wall assembly was exposed to an intense real‐scale compartment fire. For the wall assembly, temperatures were measured at the exposed face, within the stud cavity, and at the unexposed face during the fire exposure. Total heat flux gauges were used to measure the temporal variation of the energy incident on the walls, and cameras, both visual and infrared, were used to image the unexposed face of the wall assembly during the fire exposure. The behaviour of the wall assembly under the fire load is discussed as are current model results for a simulation of the fire test. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
138.
This study was to compare theoretical calculation and practical measurement structure response of asphalt pavement. Analysis of the pavement layer moduli was determined from a Back-calculation of Falling Weight Deflectometer (FWD) data and the measured stiffness moduli of asphalt layer cores. The pavement response was calculated using a theoretical model and the measured strain response at the bottom different layers. Layered elastic theory was used to back-calculate the layer moduli and three different theory models were used to forward calculate the strain and deflection. The models were: Layered Elastic Theory (LET), the Method of Equivalent Thicknesses (MET) with linear elastic and the Finite Element Method (FEM) where asphalt layer may be viscoelastic. The results showed that the calculation structure response from FEM was consistent with measured results. 相似文献
139.
140.
G. Biallas Dr.‐Ing. C. Sick J. Schneider K.‐H. Trautmann 《Materialwissenschaft und Werkstofftechnik》2007,38(9):705-711
Biaxial fatigue of friction stir welded stiffened panels Within the framework of the European WelAir project, cruciform specimens made from stiffening FSW overlap joints were fatigued in the DLR biaxial test rig. To resemble the loading situation of pressurized fuselage structures, proportional loading without any phase shift, but with different load ratios λ between the loading components in both directions was applied.Natural crack initiation and subsequent crack growth were governed by the stiffness gradient caused by introducing the stringer. Cracks initiated and propagated at run‐in and run‐out locations in a direction perpendicular to the weld seam. The shortest fatigue life was observed for uniaxial loading in welding direction (λ = 0). An additional stress component perpendicular to the joint line (λ > 0) resulted in a higher number of cycles to failure. Similar to single stringer panels, increasing the load ratio also increased the number of cycles to failure for FSW clip‐stringer structural members, but additionally gives a different location of the fatal crack. 相似文献