全文获取类型
收费全文 | 18580篇 |
免费 | 1650篇 |
国内免费 | 900篇 |
专业分类
电工技术 | 977篇 |
综合类 | 1213篇 |
化学工业 | 2973篇 |
金属工艺 | 975篇 |
机械仪表 | 956篇 |
建筑科学 | 1204篇 |
矿业工程 | 390篇 |
能源动力 | 616篇 |
轻工业 | 1217篇 |
水利工程 | 297篇 |
石油天然气 | 644篇 |
武器工业 | 197篇 |
无线电 | 2680篇 |
一般工业技术 | 2296篇 |
冶金工业 | 996篇 |
原子能技术 | 140篇 |
自动化技术 | 3359篇 |
出版年
2024年 | 60篇 |
2023年 | 261篇 |
2022年 | 507篇 |
2021年 | 752篇 |
2020年 | 559篇 |
2019年 | 532篇 |
2018年 | 594篇 |
2017年 | 592篇 |
2016年 | 674篇 |
2015年 | 710篇 |
2014年 | 850篇 |
2013年 | 1108篇 |
2012年 | 1086篇 |
2011年 | 1173篇 |
2010年 | 1123篇 |
2009年 | 1038篇 |
2008年 | 1074篇 |
2007年 | 1007篇 |
2006年 | 901篇 |
2005年 | 740篇 |
2004年 | 716篇 |
2003年 | 852篇 |
2002年 | 1096篇 |
2001年 | 877篇 |
2000年 | 431篇 |
1999年 | 299篇 |
1998年 | 306篇 |
1997年 | 209篇 |
1996年 | 166篇 |
1995年 | 137篇 |
1994年 | 96篇 |
1993年 | 112篇 |
1992年 | 61篇 |
1991年 | 61篇 |
1990年 | 43篇 |
1989年 | 39篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 29篇 |
1985年 | 24篇 |
1984年 | 28篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1975年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Deterministic chaos theory offers useful quantitative tools to characterize the non-linear dynamic behavior of a fluidized bed and the developed complexity theory presents a new approach to evaluate finite sequences. In this paper,the non-linear,hydrodynamic behavior of the pressure flutuation signals in a reactor was discussed by chaos parameters and complexity measures.Coherent results were achieved by our multi-scale analysis,which further exposed the behavior in a gas-solid two-phase system. 相似文献
83.
84.
H. Launay S. Loridant D.L. Nguyen A.M. Volodin J.L. Dubois J.M.M. Millet 《Catalysis Today》2007,128(3-4):176-182
New vanadium oxide supported on mesoporous silica catalysts for the oxidation of methane to formaldehyde were investigated by infrared and Raman spectroscopies to identify and characterize the molecular structure of the most active and selective catalytic sites. In situ and operando experiments have been conducted in order to understand the redox and hydroxylation/dehydroxylation processes of the vanadium species. (SiO)2VO(OH) species were identified in these catalysts in reaction conditions and shown to undergo a deprotonation at 580 °C under vacuum, leading to a site giving a photoluminescence band at 550 nm attributed to reverse radiative decay from the excited triplet state:
(V4+–O−)* (V5+O2−). An activation mechanism of vanadium monomeric species with electrophilic oxygen species is proposed. 相似文献
85.
Integrated Microfluidic CustomArray Device for Bacterial Genotyping and Identification 总被引:2,自引:0,他引:2
86.
R Kneen NG Pham T Solomon TM Tran TT Nguyen BL Tran J Wain NP Day TH Tran CM Parry NJ White 《Canadian Metallurgical Quarterly》1998,27(4):845-850
PURPOSE: To review the University of Florida experience in treating ependymomas, analyze prognostic factors, and provide treatment recommendations. METHODS AND MATERIALS: Forty-one patients with ependymoma and no metastases outside the central nervous system received postoperative radiotherapy with curative intent between 1966 and 1989. Ten patients had supratentorial lesions, 22 had infratentorial lesions, and 9 had spinal cord lesions. All patients had surgery (stereotactic biopsy, subtotal resection, or gross total resection). Most patients with high-grade lesions received radiotherapy to the craniospinal axis. Low-grade intracranial lesions received more limited treatment. Spinal cord lesions were treated using either partial spine or whole spine fields. RESULTS: Of 32 intracranial tumors, 21 recurred, all at the primary site; no spinal cord tumors recurred. Overall 10-year survival rates were 51% (absolute) and 46% (relapse-free); by tumor site: spinal cord, 100%; infratentorial, 45%; supratentorial, 20% (p = 0.002). On multivariate analysis, tumor site was the only factor that influenced absolute survival (p = 0.0004); other factors evaluated included grade, gender, age, duration of symptoms, resection extent, primary tumor dose, treatment field extent, surgery-to-radiotherapy interval, and days under radiotherapy treatment. CONCLUSIONS: Patients with supratentorial or infratentorial tumors receive irradiation, regardless of grade. Craniospinal-axis fields are used when spinal seeding is radiographically or pathologically evident. Spinal cord tumors are treated using localized fields to the primary site if not completely resected. Failure to control disease at the primary site remains the main impediment to cure. 相似文献
87.
本文通过对光存储系统出错特性的分析,研究了一些描述出错特性的主要参数,并且给出了描述出错特性的Gilbert模型及其改进型模型。 相似文献
88.
HK Nguyen E Bonfils P Auffray P Costaglioli P Schmitt U Asseline M Durand JC Maurizot D Dupret NT Thuong 《Canadian Metallurgical Quarterly》1998,26(18):4249-4258
Sequencing by the recently reported hybridization technique requires the formation of DNA duplexes with similar stabilities. In this paper we describe a new strategy to obtain DNA duplexes with a thermal stability independent of their AT/GC ratio content. Melting data were acquired on 35 natural and 27 modified duplexes of a given length and of varying base compositions. Duplexes built with AT and/or G4EtC base pairs exhibit a thermal stability restrained to a lower range of temperature than that of the corresponding natural compounds (16 instead of 51 degrees C). The 16 degrees C difference in thermal stability observed between the least stable and the most stable duplex built with AT and/or G4EtC base pairs is mainly due to the sequence effect and not to their AT/G4EtC ratio content. Thus N -4-ethyl-2'-deoxycytidine (d4EtC) hybridizes specifically with natural deoxyguanosine leading to a G4EtC base pair whose stability is very close to that of the natural AT base pair. Oligonucleotide probes involving d4EtC can be easily prepared by chemical synthesis with phosphoramidite chemistry. Modified DNA targets were successfully amplified by random priming or PCR techniques using d4EtCTP, dATP, dGTP and dTTP in the presence of DNA polymerase. This new system might be very useful for DNA sequencing by hybridization. 相似文献
89.
90.
The rapid development of compressive sensing(CS)shows that it is possible to recover a sparse signal from very limited measurements.Synthetic aperture radar(SAR)imaging based on CS can reconstruct the target scene with a reduced number of collected samples by solving an optimization problem.For multi-channel SAR imaging based on CS,each channel requires sufficient samples for separate imaging and the total number of samples could still be large.We propose an imaging algorithm based on distributed compressive sensing(DCS)that reconstructs scenes jointly under multiple channels.Multi-channel SAR imaging based on DCS not only exploits the sparsity of the target scene,but also exploits the correlation among channels.It requires significantly fewer samples than multi-channel SAR imaging based on CS.If multiple channels offer different sampling rates,DCS joint processing can reconstruct target scenes with a much more flexible allocation of the number of measurements offered by each channel than that used in separate CS processing. 相似文献