全文获取类型
收费全文 | 25598篇 |
免费 | 1320篇 |
国内免费 | 58篇 |
专业分类
电工技术 | 311篇 |
综合类 | 25篇 |
化学工业 | 4903篇 |
金属工艺 | 879篇 |
机械仪表 | 1298篇 |
建筑科学 | 427篇 |
矿业工程 | 6篇 |
能源动力 | 864篇 |
轻工业 | 1852篇 |
水利工程 | 91篇 |
石油天然气 | 20篇 |
无线电 | 3655篇 |
一般工业技术 | 4636篇 |
冶金工业 | 5358篇 |
原子能技术 | 291篇 |
自动化技术 | 2360篇 |
出版年
2024年 | 22篇 |
2023年 | 275篇 |
2022年 | 399篇 |
2021年 | 683篇 |
2020年 | 470篇 |
2019年 | 497篇 |
2018年 | 699篇 |
2017年 | 662篇 |
2016年 | 769篇 |
2015年 | 602篇 |
2014年 | 938篇 |
2013年 | 1389篇 |
2012年 | 1457篇 |
2011年 | 1789篇 |
2010年 | 1298篇 |
2009年 | 1332篇 |
2008年 | 1211篇 |
2007年 | 938篇 |
2006年 | 815篇 |
2005年 | 709篇 |
2004年 | 639篇 |
2003年 | 591篇 |
2002年 | 593篇 |
2001年 | 517篇 |
2000年 | 437篇 |
1999年 | 524篇 |
1998年 | 1851篇 |
1997年 | 1051篇 |
1996年 | 845篇 |
1995年 | 473篇 |
1994年 | 371篇 |
1993年 | 371篇 |
1992年 | 137篇 |
1991年 | 166篇 |
1990年 | 137篇 |
1989年 | 145篇 |
1988年 | 126篇 |
1987年 | 118篇 |
1986年 | 92篇 |
1985年 | 87篇 |
1984年 | 36篇 |
1983年 | 38篇 |
1982年 | 50篇 |
1981年 | 48篇 |
1980年 | 60篇 |
1979年 | 15篇 |
1977年 | 123篇 |
1976年 | 291篇 |
1975年 | 22篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Microllular plastics are cellular polymers characterized by cell densities greater than 109 cells/cm3 and cells smaller than 10 μm. One of the critical steps in the continuous production of microcellular plastics is the promotion of high cell nucleation rates in a flowing polymer matrix. These high nucleation rates can be achieved by first forming a polymer/gas solution followed by rapidly decreasing the solubility of gas in the polymer. Since, in the processing range of interest, the gas solubility in the polymer decreases as the pressure decreases, a rapid pressure drop element, consisting of a nozzle, has been employed as a continuous microcellular nucleation device. In this paper, the effects of the pressure drop rate on the nucleation of cells and the cell density are discussed. The experimental results indicate that both the magnitude and the cell density are discussed. The experimental results indicate that both the magnitude and the rate of pressure drop play a strong role in microcellular processing. The pressure phenomenon affects the thermodynamic instability induced in the polymer/gas solution and the competition between cell nucleation and growth. 相似文献
82.
AL Lindstrom SL Erlandsen JH Kersey CA Pennell 《Canadian Metallurgical Quarterly》1997,90(6):2323-2334
Vascular leak syndrome (VLS) is the dose-limiting toxicity observed in clinical trials of immunotoxins containing ricin toxin A chain (RTA). RTA itself is thought to cause VLS by damaging vascular endothelial cells, but the exact mechanism remains unclear. This is partially due to the paucity of appropriate models. To study VLS, we developed an in vitro model in which human umbilical vein-derived endothelial cells were first grown to confluence on microporous supports and then cultured under low pressure in the presence or absence of RTA. Endothelial cell barrier function was assessed by measuring the volume of fluid that passed through each monolayer per unit time. We found that RTA significantly increased monolayer permeability at times and concentrations consistent with the onset of VLS in patients treated with RTA-based immunotoxins. Scanning electron microscopy showed that intercellular gaps formed in endothelial monolayers exposed to RTA. Intercellular gap formation followed endothelial cell death caused by the enzymatic activity of RTA. We conclude that RTA is directly toxic to endothelial cells in vitro and speculate that this contributes to VLS in vivo. 相似文献
83.
L Struillou M Fiks-Sigaud JH Barrier E Blat G Magadur-Joly 《Canadian Metallurgical Quarterly》1993,60(7-8):524-526
The authors report an exceedingly rare complication of rheumatoid arthritis, i.e. acquired hemophilia due to anti-factor VIII autoantibody production. Treatment with intravenous immune globulin ensured control of hemorrhagic manifestations by inducing a transient rise in factor VIII level. 相似文献
84.
85.
86.
87.
The incidence of stress fractures is increasing among competitive and recreational athletes as well as among children and the elderly. By understanding the continuum of bone's response to stress and maintaining an appropriate index of suspicion, the health care provider can diagnose these injuries appropriately. An accurate history and examination is essential and will differentiate stress fractures from other stress reactions. The more common stress fractures are discussed. 相似文献
88.
The purpose of this study was to identify family physicians' firearm safety counseling beliefs and behaviors. A survey was mailed to a random sample of 600 members of the American Academy of Family Physicians. A three wave mailing technique was used to maximize the response rate and yielded 271 usable surveys (55% response rate). Outcome measures included training experience in firearm safety counseling, the prevalence of firearm safety counseling by family physicians, and their perceptions regarding such counseling. The majority (78%) of family physicians lacked formal training on how to counsel patients about firearm safety and 49% believed more time should be spent in residency programs on firearm safety counseling. The majority (84%) of respondents never or rarely counseled patients on firearm safety and 50% believed firearm safety counseling should be a low priority in their delivery of primary care. The majority of respondents did not regularly counsel patients about firearm safety, did not believe firearm safety counseling should be a priority, and did not believe firearm safety counseling would be effective in reducing firearm-related trauma. 相似文献
89.
This concerns a patient with compression myelopathy following passive hyperextension of the cervical spine during a dental procedure. Although he had been asymptomatic prior to the procedure, subsequent cervical spinal imaging revealed advanced spondylosis and spinal stenosis. Spinal stenosis is often asymptomatic for a long time. However, when radiculomyelopathy occurs after minor trauma to the head or neck, the patient is often found to have spinal stenosis. Specifically, hyperextension of a cervical spine with spondylotic changes can lead to compression myelopathy. Acquired spinal stenosis correlates positively with aging. As the size of the elderly population continues to increase the prevalence of cervical spondylotic radiculo-myelopathy will likely increase as well. Since appropriate precautions against potential neurologic damage can be undertaken, we suggest radiographic screening for pre-existing spinal stenosis prior to a procedure requiring hyperextension of the neck. Preventive measures for individuals with asymptomatic spondylotic changes and education of all health-care professionals to avoid abrupt or prolonged hyperextension of the cervical spine is emphasized. 相似文献
90.
Cheol-Min Park Byung-Hyuk Min Jae-Hong Jun Juhn-Suk Yoo Min-Koo Han 《Electron Device Letters, IEEE》1997,18(1):16-18
We have fabricated a self-aligned offset-gated poly-Si thin film transistor (TFT) by employing a novel photoresist reflow process. The gate structure of the new device is consisted of two unique patterns: A main-gate and a sub-gate. The new fabrication method extends the gate-oxide over the offset region. With the assistance of the sub-gate and reflowed photoresist a self-aligned offset region is successfully obtained due to the offset oxide acting as an implantation mask. The poly-Si TFT with symmetrical offsets is easily fabricated and the new method does not require any additional offset mask step. Compared with the misaligned offset gated poly-Si TFTs, excellent symmetric electrical characteristics are obtained 相似文献