全文获取类型
收费全文 | 8510篇 |
免费 | 229篇 |
国内免费 | 46篇 |
专业分类
电工技术 | 133篇 |
综合类 | 24篇 |
化学工业 | 843篇 |
金属工艺 | 111篇 |
机械仪表 | 201篇 |
建筑科学 | 348篇 |
矿业工程 | 3篇 |
能源动力 | 148篇 |
轻工业 | 319篇 |
水利工程 | 23篇 |
石油天然气 | 25篇 |
武器工业 | 3篇 |
无线电 | 1473篇 |
一般工业技术 | 1037篇 |
冶金工业 | 3022篇 |
原子能技术 | 34篇 |
自动化技术 | 1038篇 |
出版年
2023年 | 40篇 |
2022年 | 77篇 |
2021年 | 92篇 |
2020年 | 58篇 |
2019年 | 70篇 |
2018年 | 106篇 |
2017年 | 82篇 |
2016年 | 135篇 |
2015年 | 112篇 |
2014年 | 134篇 |
2013年 | 325篇 |
2012年 | 307篇 |
2011年 | 327篇 |
2010年 | 238篇 |
2009年 | 298篇 |
2008年 | 330篇 |
2007年 | 320篇 |
2006年 | 311篇 |
2005年 | 257篇 |
2004年 | 209篇 |
2003年 | 220篇 |
2002年 | 160篇 |
2001年 | 172篇 |
2000年 | 167篇 |
1999年 | 236篇 |
1998年 | 1050篇 |
1997年 | 578篇 |
1996年 | 453篇 |
1995年 | 320篇 |
1994年 | 212篇 |
1993年 | 231篇 |
1992年 | 96篇 |
1991年 | 101篇 |
1990年 | 86篇 |
1989年 | 67篇 |
1988年 | 74篇 |
1987年 | 72篇 |
1986年 | 66篇 |
1985年 | 94篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 43篇 |
1981年 | 41篇 |
1980年 | 39篇 |
1979年 | 24篇 |
1978年 | 21篇 |
1977年 | 49篇 |
1976年 | 148篇 |
1975年 | 23篇 |
1973年 | 19篇 |
排序方式: 共有8785条查询结果,搜索用时 0 毫秒
981.
982.
MT Dorak G Owen I Galbraith N Henderson D Webb KI Mills C Darke AK Burnett 《Canadian Metallurgical Quarterly》1995,9(5):875-878
A molecular analysis was carried out in 63 sequentially diagnosed childhood acute lymphoblastic leukemia (ALL) patients and 1011 controls to investigate the homozygosity rate for HLA-DR53. HLA-DR53 is associated with acute myeloblastic leukemia at the protein level, and our previous study has shown its association with early-onset chronic myeloid leukemia only in homozygous form at the DNA level. In the present study, the homozygosity rates for DR53 were 17.5 and 13.6% in patients and controls, respectively. Ten of the 11 homozygous patients were boys. In the common ALL group (n = 40), all seven DR53 homozygous patients were boys, and among 19 girls this genotype was not observed (P = 0.006). For males, homozygosity for DR53 revealed a relative risk (RR) of 3.29 (P = 0.008) for common ALL. Five of the 11 relapsed patients were homozygous for DR53. Heterozygous frequencies for HLA-DR53 were not different between patients and controls. Homozygosity for DR53 was associated with a very high relapse rate (45.5 vs 7.7%, P = 0.002, RR = 9.1). These results extended our findings in chronic myeloid leukemia and showed the recessive nature and the male predominance of the interactive HLA influence on the development of childhood leukemia. Molecular mimicry of an HLA-DR53 epitope by oncogenic (retro)viruses or putative susceptibility genes in linkage disequilibrium with HLA-DR53 may be responsible for this association. 相似文献
983.
Paravertebral catheters were placed bilaterally through a Tuohy needle under direct video control in a patient undergoing video-assisted thoracoscopic (VAT) surgery for recurrent, bilateral pneumothoraces. Postoperative analgesia was produced by infusing bupivacaine through the catheters. This provided good analgesia. VAT placement of paravertebral catheters is easily accomplished and may be a part of the surgical procedure. 相似文献
984.
CO2 laser conization for cervical intraepithelial neoplasia grade II-III: complications and efficacy
B Hagen FE Skjeldestad H Bratt S Tingulstad AK Lie 《Canadian Metallurgical Quarterly》1998,77(5):558-563
PURPOSE: Functional outcome after anterior resection for rectal cancer is improved by colonic J-pouch reconstruction compared with straight anastomosis. The indications for colonic J-pouch reconstruction have yet to be determined. Therefore, we attempted to determine the level at which J-pouch reconstruction provides an advantage over straight anastomosis. METHODS: A total of 48 patients who underwent 5-cm colonic J-pouch reconstruction (J-pouch group) and 80 patients who underwent straight anastomosis (straight group) underwent functional assessment one year postoperatively. RESULTS: The functional outcome in the J-pouch group was significantly better than that in the straight group when the distance of the anastomosis from the anal verge was less than 8 cm. The difference was particularly obvious when the level of the anastomosis was below 4 cm. However, functional outcome in the straight group when the anastomosis was between 9 and 12 cm from the anal verge was also satisfactory and did not differ from that in the J-pouch group when the anastomosis was between 5 and 8 cm from the anal verge. CONCLUSIONS: Colonic J-pouch reconstruction is indicated when the distance of anastomosis from the anal verge is less than 8 cm, and it is essential when the distance is less than 4 cm. 相似文献
985.
Studies were conducted at Radford Army Ammunition Plant (RAAP) to compare selected wastewater treatment methods, to define the treatment parameters and to prepare the design criteria for facilities to treat wastewater containing dissolved nitroguanidine (NGu), nitroglycerin (NG) and other nitrate esters and colloidal nitrocellulose (NC).The design criteria for two pretreatment facilities were prepared based on the results of the pilot plant evaluation and transmitted to the Army Corps of Engineers who constructed the facilities at RAAP. 相似文献
986.
Gan Zheng Kai-Kit Wong Paulraj A. Ottersten B. 《Signal Processing, IEEE Transactions on》2009,57(8):3130-3143
Relay communications is a promising technique to extend the range of wireless communications by forwarding the message from the sender to the intended destination. While fixed or variable-power relays have been previously investigated, this paper addresses the collaborative use of variable-phase variable-power amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of the CSI error vector from the relays to the destination. Our main contribution is that we prove, under a condition on the quality of the estimated CSI, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-procedure and rank relaxation techniques. In addition, a distributed algorithm is developed by examining the structure of the optimal CRBF solution. Results demonstrate a significant gain of CRBF over non-robust approaches. 相似文献
987.
This paper presents the design, implementation and performance evaluation of a coarse-grain dynamically reconfigurable FPGA platform for multi-service edge and access network devices. The platform consists of two MicroBlaze RISC processors and a number of hardware co-processors used for the processing of packet payloads (Data Encryption Standard (DES) and Lempel-Ziv Compression). The co-processors can be connected either directly to the processors or using a shared bus. The functionality of the co-processors is dynamically reconfigured to meet the requirements of the network workload. The system has been implemented on the Xilinx Virtex II Pro platform and the network traces from real passive measurements have been used for performance evaluation. The use of dynamically reconfigurable co-processors for network applications shows that the performance speedup versus a static version varies from 12% to 35% in the best case and from 10% to 15% on average, depending on the network traffic fluctuation. 相似文献
988.
For a thin-film transistor (TFT) built on excimer-laser crystallized polycrystalline silicon, the dependence of the effective ldquograin-boundary mobilityrdquo on the gate-to-source voltage can be divided into two subregimes exhibiting different power-law characteristics. An expression for the effective mobility is developed using a procedure previously proposed for a TFT built on polycrystalline silicon exhibiting only single power-law dependence. The additional power-law component is reflected in the model by a pair of measurable and physically meaningful parameters. The procedure for determining these parameters is described and demonstrated. Both the measured and calculated transfer characteristics are reported and compared. The double power-law dependence implies a grain-boundary trap-state energy dispersion characterized by two exponential functions. This is presently verified. 相似文献
989.
Chi-Yen Lin You-Ming Chen Hsiao-Fan Chen Fu-Chuan Fang Yu-Cheng Lin Wen-Yi Hung Ken-Tsung Wong Raymond C. Kwong Sean C. Xia 《Organic Electronics》2009,10(1):181-188
This paper describes the synthesis of three triaryldiamine derivatives presenting two thermally polymerizable trifluorovinyl ether groups that can be polymerized through thermal curing to form perfluorocyclobutyl (PFCB) polymers. These PFCB polymers, studied using time-of-flight techniques for the first time, exhibited remarkable non-dispersive hole-transport properties, with values of μh of ca. 10?4 cm2 V?1 s?1. When we employed these thermally polymerized polymers as hole-transport layers (HTLs) in electroluminescence devices containing tris(8-hydroxyquinolate) aluminum (Alq3) as the emission layer, we obtained high current densities (ca. 3400 mA cm?2), impressive brightnesses (5 × 104 cd m?2), and high external quantum efficiencies (EQEs = 1.43%). These devices exhibited the same turn-on voltage, but higher EQEs, relative to those incorporating the vacuum-processed model compound N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (α-NPD) (EQE = 1.37%) as the HTL under the same device structure. 相似文献
990.