全文获取类型
收费全文 | 122360篇 |
免费 | 7575篇 |
国内免费 | 3270篇 |
专业分类
电工技术 | 4720篇 |
技术理论 | 4篇 |
综合类 | 4946篇 |
化学工业 | 18662篇 |
金属工艺 | 4775篇 |
机械仪表 | 6004篇 |
建筑科学 | 5721篇 |
矿业工程 | 1655篇 |
能源动力 | 2936篇 |
轻工业 | 8051篇 |
水利工程 | 1868篇 |
石油天然气 | 2657篇 |
武器工业 | 487篇 |
无线电 | 12910篇 |
一般工业技术 | 15442篇 |
冶金工业 | 25240篇 |
原子能技术 | 1243篇 |
自动化技术 | 15884篇 |
出版年
2024年 | 238篇 |
2023年 | 1268篇 |
2022年 | 1966篇 |
2021年 | 3063篇 |
2020年 | 2128篇 |
2019年 | 2010篇 |
2018年 | 2654篇 |
2017年 | 3055篇 |
2016年 | 3538篇 |
2015年 | 3743篇 |
2014年 | 4256篇 |
2013年 | 5332篇 |
2012年 | 7377篇 |
2011年 | 8410篇 |
2010年 | 5769篇 |
2009年 | 5579篇 |
2008年 | 5342篇 |
2007年 | 4841篇 |
2006年 | 4641篇 |
2005年 | 6799篇 |
2004年 | 5205篇 |
2003年 | 4537篇 |
2002年 | 3670篇 |
2001年 | 3097篇 |
2000年 | 2205篇 |
1999年 | 2343篇 |
1998年 | 7903篇 |
1997年 | 5102篇 |
1996年 | 3687篇 |
1995年 | 2398篇 |
1994年 | 1819篇 |
1993年 | 1693篇 |
1992年 | 672篇 |
1991年 | 666篇 |
1990年 | 569篇 |
1989年 | 517篇 |
1988年 | 492篇 |
1987年 | 355篇 |
1986年 | 305篇 |
1985年 | 250篇 |
1984年 | 134篇 |
1983年 | 125篇 |
1982年 | 181篇 |
1981年 | 221篇 |
1980年 | 236篇 |
1979年 | 79篇 |
1978年 | 101篇 |
1977年 | 630篇 |
1976年 | 1360篇 |
1975年 | 122篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
331.
OBJECTIVE: To investigate the efficacy of the rectus abdominis muscle flap (RAMF) technique for the closure and augmentation of small, non-compliant bladder exstrophies. PATIENTS AND METHODS: The RAMF technique was used in two girls and two boys (mean age at operation, 31.7 months, range 3-72) with bladder exstrophy. The clinical outcome and urodynamics were assessed during a follow-up of 29 months to 6 years (mean 49.2 months) and included imaging, cystoscopy, biochemical and microbiological studies. RESULTS: There were no urinary tract infections, metabolic problems or electrolyte disturbances and kidney function remained normal in all patients. Radiography confirmed intact function and anatomy of the urinary tract and cystoscopy showed complete coverage of the inner peritoneal layer of RAMF with uroepithelium. No stone formation or mucus production were detected. Currently, three patients void using clean intermittent catheterization through the native urethra and the fourth through an appendiceal Mitrofanoff valve. However, the bladder volume was insufficient at the late follow-up and three patients required bladder augmentation. CONCLUSIONS: The RAMF technique is a good alternative for closing bladder exstrophies and achieves an increase in bladder capacity; however, although there is a mild improvement in bladder capacity and compliance. RAMF should not be used as a bladder augmentation procedure. The technique is indicated in the closure of large bladder defects, bladder exstrophies with small, inelastic, non-compliant bladder remnants and failed primary closures. 相似文献
332.
Fast DCT algorithm with fewer multiplication stages 总被引:1,自引:0,他引:1
Yeonsik Jeong Imgeun Lee Hak Soo Kim Kyu Tae Park 《Electronics letters》1998,34(8):723-724
A novel fast DCT scheme with reduced multiplication stages and fewer additions and multiplications is proposed. The proposed algorithm is structured so that most multiplications tend to be performed at the final stage, which reduces the propagation error that could occur in the fixed-point computation. Minimisation of the multiplication stages can further decrease the error 相似文献
333.
334.
O Ukkola MJ Savolainen PI Salmela K von Dickhoff T Kiema YA Kes?niemi 《Canadian Metallurgical Quarterly》1995,73(6):307-311
In the search for new risk factors for diabetic macroangiopathy the insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme gene was studied in 237 consecutive patients (125 men and 112 women) with non-insulin-dependent diabetes. The female population showed an excess of ischemic electrocardiographic changes or definite myocardial infarctions in the patients homozygous for the deletion [D/D; odds ratio (OR) 2.8; 95% confidence interval (CI) 1.4-5.3] and in the insertion/deletion heterozygotes (I/D; OR 1.8; CI 1.1-3.1) compared with the patients homozygous for the insertion (I/I). In the total series coronary heart disease, cerebrovascular disease, and claudication were more often observed in the patients with I/D (OR 1.5; CI 1.0-2.2) or the D/D genotype patients (OR 1.7; CI 1.1-2.6) than in those with the genotype I/I. The systolic blood pressure was lower in patients with genotype I/I (138 +/- 19 mmHg) than in those with the genotype I/D (149 +/- 22 mmHg) or D/D (150 +/- 21 mmHg; P < 0.02). The prevalence of hypertension and the median urinary albumin excretion rate also tended to be lowest in the I/I genotype patients. Multiple logistic analysis revealed that in women the angiotensin-converting enzyme D/D genotype is independently associated with coronary heart disease. Our findings suggest that variation at the angiotensin-converting enzyme gene locus is one of the factors involved in the predisposition of diabetic patients to the development of arterial disease and hypertension. 相似文献
335.
研究了步、机枪射击密集度试验中弹着点半经的顺序统计量,给出了作图法测定R_(50)的理论分析,得到了作图法是测定R_(50)的好方法的结论. 相似文献
336.
SV Varha OH Reznikov IS Turchyn VM Demchenko OP Potikha PV Sinitsyn LV Tarasenko LV Cha?kovs'ka 《Canadian Metallurgical Quarterly》1994,40(5-6):105-109
The effect exerted by transplantation of the 5 day culture of testicles from newly born piglets on the hypogonadal state of mature X-ray irradiated (3 Gy) rats was studied. It has been found that a month after transplantation (two months after irradiation) the hypogonadal state disappeared for a while, which is confirmed by normalization of the weight of seminal vesicles, content of testosterone and biologically active lutropine, restoration of the reproductive function of rats. No significant changes in steroidogenesis activity have been found, which proves a substituent character of transplantation. The effect disappears three months later but certain restoration of the content of nucleic acids in the testicles is observed. 相似文献
337.
E Aurelius B Andersson M Forsgren B Sk?ldenberg O Stranneg?rd 《Canadian Metallurgical Quarterly》1994,170(3):678-681
Sequential samples of serum and cerebrospinal fluid (CSF), from 9 patients with herpes simplex encephalitis (HSE), were analyzed for cytokines and soluble cytokine receptors. The response to herpes simplex virus was characterized by a vigorous compartmentalized immune response. The intrathecal response comprised three different phases: an acute stage (first week of illness), characterized by elevated CSF levels of interleukin (IL)-6 and interferon-gamma; an early convalescence stage (weeks 2-6 after onset of disease), associated with peaking levels of tumor necrosis factor-alpha and late markers of the specific T cell-mediated immune response, soluble IL-2 receptor, and soluble CD8 antigen (sCD8); and finally, a late convalescence stage, lasting months to years and associated with persistently increased levels of sCD8 in particular. These findings show the compartmentalization and kinetics of the inflammatory response in HSE and demonstrate persistence of the intrathecal inflammatory process, which may have implications for antiviral and antiinflammatory therapy. 相似文献
338.
339.
340.
智能工程与控制技术:历史,发展与未来 总被引:3,自引:0,他引:3
本文综述了智能工程和控制技术的发展历程和基本问题。文中着重论述了人工智能在过程控制系统中的必要性及开发实时智能控制系统的步骤;对符号推理系统、耦合推理系统、人工神经网络和集成分布式智能系统的特点和局限进行了比较。最后讨论了计算机集成过程系统(CIPS)的基本问题、基础技术和发展前景。 相似文献