全文获取类型
收费全文 | 12075篇 |
免费 | 503篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 203篇 |
综合类 | 21篇 |
化学工业 | 2342篇 |
金属工艺 | 297篇 |
机械仪表 | 477篇 |
建筑科学 | 354篇 |
矿业工程 | 28篇 |
能源动力 | 382篇 |
轻工业 | 997篇 |
水利工程 | 67篇 |
石油天然气 | 39篇 |
无线电 | 1712篇 |
一般工业技术 | 2007篇 |
冶金工业 | 1809篇 |
原子能技术 | 142篇 |
自动化技术 | 1720篇 |
出版年
2023年 | 68篇 |
2022年 | 100篇 |
2021年 | 167篇 |
2020年 | 141篇 |
2019年 | 165篇 |
2018年 | 203篇 |
2017年 | 186篇 |
2016年 | 270篇 |
2015年 | 238篇 |
2014年 | 386篇 |
2013年 | 784篇 |
2012年 | 583篇 |
2011年 | 650篇 |
2010年 | 498篇 |
2009年 | 593篇 |
2008年 | 559篇 |
2007年 | 526篇 |
2006年 | 512篇 |
2005年 | 420篇 |
2004年 | 398篇 |
2003年 | 359篇 |
2002年 | 398篇 |
2001年 | 298篇 |
2000年 | 271篇 |
1999年 | 253篇 |
1998年 | 439篇 |
1997年 | 294篇 |
1996年 | 234篇 |
1995年 | 212篇 |
1994年 | 188篇 |
1993年 | 190篇 |
1992年 | 150篇 |
1991年 | 104篇 |
1990年 | 126篇 |
1989年 | 114篇 |
1988年 | 99篇 |
1987年 | 111篇 |
1986年 | 105篇 |
1985年 | 120篇 |
1984年 | 114篇 |
1983年 | 101篇 |
1982年 | 97篇 |
1981年 | 97篇 |
1980年 | 60篇 |
1979年 | 70篇 |
1978年 | 75篇 |
1977年 | 68篇 |
1976年 | 73篇 |
1975年 | 70篇 |
1973年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Our fundamental premise is that energy consumption at the household level is a key indicator of standard of living. We employ state-of-the-art panel cointegration techniques to evaluate the nature of the relationship between income measures and energy consumption measures for seven East Indian Ocean countries. The general finding is that income and household electricity consumption are not cointegrated. Given this finding, we conclude that standard of living measures that rely on income measures and do not include household-level energy consumption information will necessarily miss important indications of both levels and changes of standard of living. 相似文献
42.
Factors affecting the activity of anammox bacteria during start up in the continuous culture reactor. 总被引:5,自引:0,他引:5
Factors affecting cultivation of extremely slow-growing bacteria (anaerobic ammonium oxidiser, doubling time 11 days) were investigated by using upflow anaerobic sludge blanket (UASB) reactors which can maintain high solid retention time. The effects of concentrations of DO, free ammonia (FA), and nitrite on activation of anammox activity were tested during the start-up period. The reactor was inoculated with granular sludge collected from a full-scale UASB reactor used for treating brewery wastewater, and sludge from a piggery wastewater treatment plant and rotating biological contactor treating sewage. Results of continuous operation showed that concentrations of DO, free ammonia (FA) and nitrite in the reactors played a key role in stimulating the anammox activity during start-up period. It is crucial to keep DO below 0.2 ppm, FA below 2 mg/L and nitrite nitrogen below 35 mg/L to cultivate anammox cells in the continuous bioreactor. When the levels of DO, FA and nitrite in the influent were controlled at less than the inhibition levels, the anammox activity increased gradually in the anaerobic condition. Addition of hydrogen sulphide into the reactor enhanced anammox activity in the continuous culture. Through the SEM, TEM and FISH analysis, anammox bacteria were detected in the granular sludge after 3 months of continuous operation. 相似文献
43.
Zhihui Zhang Bing Q. Han Kyung H. Chung Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2006,37(7):2265-2273
The current study aims to provide fundamental insight into the behavior of microstructures containing grain sizes that span
multiple length scales. A commercial 5083 Al alloy was selected as the material of interest to facilitate comparison with
recently published data. The materials studied here were prepared via the thermal consolidation of powders that were cryomilled
for different times (i.e., 0, 2, 4, and 8 hours). Following consolidation, the resultant microstructure was characterized by an equiaxed grain morphology
with a size distribution centered around 200∼300 nm. Dispersed among the 200- to 300-nm grains were coarse-grained regions
or ligaments with a grain size ranging from 600 nm to 2 μm. The occurrence of coarse-grained regions is rationalized on the
basis of recrystallization or subgrain coarsening, whereas the occurrence of equiaxed fine regions is proposed to be a result
of continuous grain growth. Two types of microstructures were selected for study, containing coarse-grained volumes of approximately
28 pct and 43 pct that corresponded to an ultimate tensile strength (UTS) of 566 MPa and 535 MPa, and a fracture strain of
3.2 pct and 3.5 pct, respectively. The observed ductility and the relevant toughening mechanisms were discussed in light of
the presence of multiple length scales. 相似文献
44.
Small-scale models of reinforced concrete beam-column joint were subjected to large cyclic displacements at two rates: 2.5×10−3 and 1.0 Hz. To assess damage, free-vibration tests were conducted. The reliability of the modelling techniques was established
by comparison of the results for the slower rate with those obtained from the full-scale tests on prototype. The higher rate
of loading caused a greater damage than that at the lower rate. This was evidenced by the measurements of the energy absorbed
in the hysteresis loops, equivalent damping, and the stiffness and damping obtained from the free-vibration test. The relatively
greater extent of damage appears to result from the different bond behaviour at different rates of loading. 相似文献
45.
Boesch Ronald D. Magin Richard L. Franke Stevenb J. 《IEEE transactions on bio-medical engineering》1987,(11):904-907
This paper describes a design for an analog phase shifter operating at 915 MHz and suitable for use in a phased array microwave hyperthermia system. Here, the major operating constraint was minimization of amplitude variation over a 1800 phase shift, whereas previous phase shifters were designed to obtain a linear relationship between phase and control voltage. The result is a simple, inexpensive hybrid coupler phase shifter that operates over a narrow bandwidth and provides 180°of continuous phase shift with input powers up to 1 W. 相似文献
46.
Who Kee Chung 《Microelectronics Reliability》1987,27(4)
The paper presents a reliability model of a k-out-of-N:G redundant system with M mutually exclusive failure modes and common cause failures. Failed system repair times are arbitrarily distributed. The system is in a failed state when (N−k+1) units failed or a common cause failure occurred. Laplace transforms of the state probabilities and the availability of the system are derived. Finally, the system steady-state availability is also reported. 相似文献
47.
Maisto Stephen A.; Chung Tammy A.; Cornelius Jack R.; Martin Christopher S. 《Canadian Metallurgical Quarterly》2003,17(2):98
This study investigated the Stages of Change Readiness and Treatment Eagerness Scale (SOCRATES: W. R. Miller & J. S. Tonigan, 1996) in adolescents presenting for treatment of alcohol use disorder (AUD). The participants were 80 males and 43 females (mean age=16.8 years) who presented for AUD treatment (95.1% outpatient, 4.9% inpatient). Participants completed assessments at baseline and 1 year and provided information on alcohol use and related variables monthly between these 2 assessments. Principal-components and confirmatory factor analyses of the baseline SOCRATES identified 2 factors, Taking Steps and Recognition, which showed good internal consistency and concurrent and predictive evidence of validity. The results were interpreted as supporting the use of the SOCRATES with clinical samples of adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
48.
49.
50.
Ronald Smith 《Canadian Metallurgical Quarterly》2004,130(2):165-169
For longitudinally uniform stretches of waterways there is a mixing center for the across-channel location of a steady point source in steady flow, such that complete mixing is achieved as soon as possible and there is no concentration overshoot at either of the two shorelines. A mathematical definition of the mixing center is the zero of the first oscillatory cross-channel diffusion mode. With the shorelines plus four interior data points across the channel, the starting estimate for the mixing center suffices to keep peak shoreline concentrations to within 6% of optimal. For comparison, a source at mid flow gives 18% shoreline concentration overshoot in the test case. Should very high precision be required, the Appendix gives an iterative construction that converges to the first oscillatory diffusion mode. 相似文献