全文获取类型
收费全文 | 16047篇 |
免费 | 958篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 153篇 |
综合类 | 11篇 |
化学工业 | 3913篇 |
金属工艺 | 299篇 |
机械仪表 | 316篇 |
建筑科学 | 565篇 |
矿业工程 | 27篇 |
能源动力 | 540篇 |
轻工业 | 2779篇 |
水利工程 | 148篇 |
石油天然气 | 55篇 |
无线电 | 751篇 |
一般工业技术 | 2567篇 |
冶金工业 | 2106篇 |
原子能技术 | 95篇 |
自动化技术 | 2699篇 |
出版年
2024年 | 30篇 |
2023年 | 126篇 |
2022年 | 386篇 |
2021年 | 619篇 |
2020年 | 397篇 |
2019年 | 443篇 |
2018年 | 676篇 |
2017年 | 640篇 |
2016年 | 693篇 |
2015年 | 470篇 |
2014年 | 660篇 |
2013年 | 1102篇 |
2012年 | 1000篇 |
2011年 | 1124篇 |
2010年 | 809篇 |
2009年 | 807篇 |
2008年 | 716篇 |
2007年 | 667篇 |
2006年 | 506篇 |
2005年 | 454篇 |
2004年 | 354篇 |
2003年 | 324篇 |
2002年 | 300篇 |
2001年 | 213篇 |
2000年 | 208篇 |
1999年 | 196篇 |
1998年 | 795篇 |
1997年 | 486篇 |
1996年 | 353篇 |
1995年 | 208篇 |
1994年 | 172篇 |
1993年 | 170篇 |
1992年 | 66篇 |
1991年 | 71篇 |
1990年 | 59篇 |
1989年 | 56篇 |
1988年 | 51篇 |
1987年 | 46篇 |
1986年 | 47篇 |
1985年 | 49篇 |
1984年 | 39篇 |
1983年 | 37篇 |
1982年 | 41篇 |
1981年 | 51篇 |
1980年 | 42篇 |
1979年 | 17篇 |
1978年 | 21篇 |
1977年 | 46篇 |
1976年 | 74篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
101.
102.
András Nagy 《Polymer Bulletin》1985,14(3-4):259-264
Summary The Kennedy-Smith plot routinely used for the characterization of end-reactive (telechelic) polyisobutylenes has been recast to increase its accuracy and thus to increase its diagnostic value for the compositional analysis of telechelic polymers containing chromophores. A detailed error estimation is given. The plotting method and error limits are shown for representative mono-, di-, and tri-ended telechelic polyisobutylenes. 相似文献
103.
Cruselles Ernesto J. Soriano Miguel Melús José Luis 《Wireless Personal Communications》1998,7(1):69-88
The prime characteristic of spread spectrum modulated signals is that their bandwidth is greater than the information rate. In this way a redundancy is introduced that allows the severe levels of inteference inherent in the transmission of digital information over radio and satellite links to be overcome. Current spread spectrum applications are primarily in military communications; nevertheless, there is growing interest in this technique for third generation mobile radio networks (UMTS, FPLTS, etc.) with open discussion regarding the practicality of using a multiple access system based on spread spectrum techniques (CDMA). However, in order to support as many users in the same bandwidth as other multiple access techniques such as TDMA or FDMA, it is important how to generate large families of sequences that present low cross-correlation. The aim of this paper is to describe a spreading codes generator that can produce a large number of PN sequences with good properties of auto- and cross-correlation. Moreover, the codes generated shows high unpredictability and good statistical behaviour. This also allows the implementation of some features that are common on military networks such as message privacy (increasingly important in commercial networks) without additional cost. The structure presented shows itself to be advantageous for high speed generation of codes at a low cost, low power consumption (allowing longer life for batteries), small size and simplicity of implementation, essential ingredients for commercial equipment. Another attractive feature is its structural parallelism, useful in VLSI implementations. All of these features render it potentially suitable for the implementation of channel bandwidth sharing systems in future wireless personal communications networks. 相似文献
104.
N Benito A Nú?ez M de Górgolas J Esteban T Calabuig MC Rivas ML Fernández Guerrero 《Canadian Metallurgical Quarterly》1997,157(14):1577-1580
BACKGROUND: Fever is commonly observed in patients with human immunodeficiency virus (HIV) disease and frequently eludes diagnosis. The role of bone marrow biopsy in the diagnosis of fever of unknown origin in patients infected with HIV remains controversial. PATIENTS AND METHODS: One hundred twenty-three consecutive patients with 137 episodes of fever lasting 10 or more days without diagnosis after 1 week of hospitalization were evaluated by bone marrow biopsy. RESULTS: Overall, a specific diagnosis was achieved in 52 episodes by means of culture and histopathological examination (diagnostic yield, 37.9%). Three types of disease were found: mycobacterial infections (n = 36, 69% of documented episodes), including 18 patients with disseminated tuberculosis and 14 with Mycobacterium avium-intracellulare complex infections; non-Hodgkin lymphomas (n = 12, 23%); and visceral leishmaniasis (n = 4, 8%). Although bone marrow cultures were more sensitive than microscopic examination with special stains for the diagnosis of mycobacterial infections, the pathological examination of bone marrow led to a more rapid diagnosis of disease. In addition, the histopathological examination of bone marrow alone led to the diagnosis of a specific condition in 43 episodes (31.3% of all episodes). CONCLUSIONS: Bone marrow biopsy is a useful procedure for the diagnosis of fever in patients with advanced HIV disease, particularly in areas where tuberculosis and leishmaniasis are prevalent. Involvement of the marrow may be the first indication of the existence of extranodal non-Hodgkin lymphoma. For Mycobacterium avium-intracellulare complex infection, blood cultures were more sensitive than bone marrow biopsy. 相似文献
105.
JF Tomás E Rodriguez-I?igo J Bartolomé A Madejón M Fogeda H Oliva A Moreno JM Fernández-Ra?ada V Carre?o 《Canadian Metallurgical Quarterly》1997,19(10):1053-1057
Long-term effects after blood or bone marrow transplantation (BMT) are emerging as an important issue, as more patients are included in BMT programmes and as this procedure becomes more successful. Long-term liver dysfunction, mainly due to chronic graft-versus-host disease or hepatitis C virus infection, is a well-known complication. Nevertheless, the diagnosis of liver disease in this patient group is sometimes difficult and, despite adequate studies, it may remain undetected. A novel hepatitis-associated virus, hepatitis G virus (HGV), has recently been identified. The virus belongs to the Flaviviridae family and is known to be parenterally transmitted, although there is no clear evidence to implicate this agent in causing acute or chronic hepatitis. We report a patient who developed mild, but persistent, abnormalities in transaminases for 2 years after an autologous BMT. HGV RNA was detected in both serum and liver. HGV RNA persisted in serum for at least 8 months. No other known hepatitis virus was found. This report provides the first direct evidence of a patient with long-term liver abnormalities after a BMT in whom the only known hepatitis virus isolated was the HGV. 相似文献
106.
RG Jaeger PT de Oliveira MM Jaeger VC de Araújo 《Canadian Metallurgical Quarterly》1997,84(6):663-667
BACKGROUND: Endoscopic sclerotherapy (ST), widely used as treatment of bleeding esophageal varices, might cause motility disturbances of the esophagus as well as mucosal damage. We performed this study to evaluate the long-term effects of repeated sclerotherapy on esophageal motility and mucosa. METHODS: Ten patients with liver cirrhosis and bleeding esophageal varices treated with repeated ST were evaluated after the last ST, median 52 months, by esophageal manometry and gastroscopy where forceps biopsies were taken. RESULTS: We found a significant difference in the distal esophageal sphincter intraabdominal length. The distal esophageal sphincter pressure was somewhat lower in the ST group although the difference did not reach statistical significance. There was infiltration of neutrophil leukocytes in biopsies from four patients and normal findings in the rest. CONCLUSIONS: Long-term follow-up evaluation showed statistically longer distal esophageal intraabdominal length in the ST group. No mucosal alterations were found at the histopathological investigation. 相似文献
107.
108.
Development of an octocalcium phosphate cement 总被引:2,自引:0,他引:2
O. Bermúdez M. G. Boltong F. C. M. Driessens J. A. Planell 《Journal of materials science. Materials in medicine》1994,5(3):144-146
From previous studies it is known that alpha-tertiary calcium phosphate and dicalcium phosphate form a cement upon mixing with water. In this study this cement was optimized in terms of the milling of the constituents, their molar ratio, the amount of hydroxyapatite added and the water/powder ratio. The optimum Ca/P molar ratio of the cement mixture was 1.36±0.03. X-ray diffraction showed the reaction product to be octocalcium phosphate. Addition of precipitated hydroxypatite of over 3% diminished the final strength of the cement significantly. However, admixtures of only 2% of precipitated hydroxyapatite (a) kept the final compressive strength at 30±5 MPa after soaking in Ringers solution at 37°C, (b) diminished the initial setting time from 27.5 to 10 min and the final setting time from 65 to 40 min, (c) diminished the time in which the final strength was reached from 36 to less than 14 h. The tensile strength of this cement is 19±1% of its compressive strength. The optimum water/powder ratio as found in this study was 0.30 g/g. 相似文献
109.
Vicente Rodríguez Montequín Francisco Ortega Fernández Nicolás Abajo de Martínez Juan Antonio González Rodríguez 《JOM Journal of the Minerals, Metals and Materials Society》2002,54(7):46-50
This research summary discusses the application of neural networks, evolutionary strategies, and other artificial intelligence
techniques in the modeling and optimization of the models used for temperature, rolling force, and torque calculation in heavy
plate milling. 相似文献
110.