全文获取类型
收费全文 | 3230篇 |
免费 | 19篇 |
专业分类
电工技术 | 24篇 |
综合类 | 1篇 |
化学工业 | 235篇 |
金属工艺 | 18篇 |
机械仪表 | 18篇 |
建筑科学 | 45篇 |
矿业工程 | 1篇 |
能源动力 | 19篇 |
轻工业 | 111篇 |
水利工程 | 9篇 |
石油天然气 | 8篇 |
无线电 | 140篇 |
一般工业技术 | 160篇 |
冶金工业 | 2327篇 |
原子能技术 | 11篇 |
自动化技术 | 122篇 |
出版年
2021年 | 14篇 |
2020年 | 14篇 |
2019年 | 8篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 13篇 |
2013年 | 59篇 |
2012年 | 23篇 |
2011年 | 32篇 |
2010年 | 36篇 |
2009年 | 35篇 |
2008年 | 48篇 |
2007年 | 47篇 |
2006年 | 37篇 |
2005年 | 28篇 |
2004年 | 35篇 |
2003年 | 43篇 |
2002年 | 35篇 |
2001年 | 31篇 |
2000年 | 22篇 |
1999年 | 90篇 |
1998年 | 777篇 |
1997年 | 380篇 |
1996年 | 275篇 |
1995年 | 147篇 |
1994年 | 148篇 |
1993年 | 144篇 |
1992年 | 31篇 |
1991年 | 39篇 |
1990年 | 49篇 |
1989年 | 37篇 |
1988年 | 33篇 |
1987年 | 33篇 |
1986年 | 25篇 |
1985年 | 25篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 39篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 59篇 |
1976年 | 119篇 |
1975年 | 20篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1970年 | 6篇 |
排序方式: 共有3249条查询结果,搜索用时 15 毫秒
31.
32.
33.
The number of patients requiring revision total hip arthroplasty continues to increase each year. Accurate preoperative planning is a key factor in obtaining a good result. Radiographs provide little information concerning the actual extent of the acetabular defects. Computed tomography-generated models of the acetabulum can provide the surgeon with accurate information concerning the size and location of the defects. Evaluation of radiographs and models in 24 cases showed that radiographs alone failed to detect all 13 anterior wall defects (P < .001), 8 of 18 posterior wall defects (44.4%, P < .001), and 8 of 19 segmental central defects (42%, P < .001), all of which were easily identified with the models. This study showed that preoperative planning based on the foam models accurately predicted the actual implant used in 22 of 24 cases (92%). 相似文献
34.
There is little information on the possible value of screening children who are liable to haemoglobinopathies as part of pre-operative assessment for dental treatment under general anaesthesia. The present retrospective investigation examined, first, the number of patients having low haemoglobin levels among 1000 patients who had undergone haematological investigation prior to general anaesthesia in a dental outpatient unit, and, secondly, the subsequent clinical management of these patients. Haemoglobin levels of 10.0 g/dl or less were found in 31 children: 13 Asian, 7 Afro-Caribbean, 5 Mediterranean, 3 Arabic, 1 white Caucasian and 2 Oriental children. In addition, 17 patients had sickle-cell trait and 2 had beta-thalassaemia trait, but there was no relationship between the presence of haemoglobinopathy and low levels of haemoglobin. The planned general anaesthesia was undertaken for 22 of the 31 children who had low levels of haemoglobin and for the 19 children with haemoglobinopathy. Only 6 children ultimately did not undergo general anaesthesia, all failing to return. It is concluded that pre-anaesthetic haematological assessment of children needing minor dental surgery is rarely of any significant clinical value. 相似文献
35.
The design and evaluation of an optically triggered, fully integrated sample and hold circuit (OS/H) is described. Measured results are presented that demonstrate operation of this circuit at 250 Ms/s and with effective resolution approaching 8 bits. The integrated circuit, which measures 2.1 mm×1.4 mm, is realized in -1.0-V threshold, 20-GHz ft GaAs MESFET technology, consumes approximately 200 mW of power, and requires one optical address. The OS/H will find applications in high precision, hybrid, and integrated signal processing systems where high speed, high levels of parallelism, and low timing jitter are important. Measured results of a series photoconducting (Auston switch) OS/H realized in the same technology are presented for comparison purposes 相似文献
36.
Neoxanthin, a major carotenoid pigment of spinach, is found in the Chloroplast membrane and has an unknown function in plants. Neoxanthin inhibited the production of superoxide anions in an artificial xanthine and xanthine oxidase system and depressed DNA synthesis in methylcholanthrene (MCA)-initiated C3H10T1/2 fibroblasts. in two-stage carcinogenesis experiments, neoxanthin at 0.2 micrograms/0.2 ml inhibited the formation of tumors that were induced sequentially by 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA) in the buccal pouch of Syrian Golden hamsters. To assess the ongoing process of carcinogenesis, the activity of ornithine decarboxylase (ODC), required for cell proliferation, was analyzed. Neoxanthin inhibited the activity of ODC when animals were treated with neoxanthin one hour before the application of TPA in two-stage carcinogenesis. However, neoxanthin did not inhibit ODC activity when animals were treated with neoxanthin one hour before the application of DMBA in two-stage carcinogenesis, and there was no subsequent tumor formation. In a short-term anti-initiation experiment, neoxanthin inhibited the covalent binding of isotope-labeled DMBA to DNA by 53%. These results indicate that neoxanthin inhibits the initiation stage and the promotion stage in two-stage carcinogenesis. This suggests that neoxanthin may act as a potential chemopreventive agent. 相似文献
37.
38.
Hilar cholangiocarcinoma, a highly lethal tumor, is difficult to diagnose with conventional computed tomography (CT) because of its small size. Spiral CT allows more effective evaluation of these small lesions and better demonstrates the status of the hepatic arterial or portal venous circulation. Among 27 patients with hilar cholangiocarcinoma (infiltrative in 21, exophytic in two, polypoid in one, diffuse in three), thin-section spiral CT allowed identification of each tumor as an area of focal wall thickening that obliterated the lumen. Seventeen of the infiltrative tumors (81%) showed high attenuation. Identification of the level of biliary obstruction was possible in 63% of the patients (17 of 27). The level of obstruction was underestimated in six patients and overestimated in four. Spiral CT is a valuable method for diagnosis of hilar cholangiocarcinoma; however, spiral CT is less accurate in evaluation of intraductal tumor extent because of the limited z-axis resolution. 相似文献
39.
40.
Basicity values have been determined for series of monoazo dyes incorporating a pyrrolidino or a piperidino moiety. In general, the pKa value is found to decrease as the donor capacity of the terminal nitrogen atom decreases.The basicities of the 4'-substituted piperidinoazobenzenes decrease as the electron withdrawing strength of the 4'-substituent increases. However, the pKa values of the related pyrrolidino compounds appear to be insensitive to the substituent. 相似文献