全文获取类型
收费全文 | 51970篇 |
免费 | 2833篇 |
国内免费 | 58篇 |
专业分类
电工技术 | 418篇 |
综合类 | 36篇 |
化学工业 | 10488篇 |
金属工艺 | 943篇 |
机械仪表 | 986篇 |
建筑科学 | 1696篇 |
矿业工程 | 84篇 |
能源动力 | 1265篇 |
轻工业 | 7192篇 |
水利工程 | 454篇 |
石油天然气 | 211篇 |
武器工业 | 4篇 |
无线电 | 2881篇 |
一般工业技术 | 8881篇 |
冶金工业 | 11331篇 |
原子能技术 | 277篇 |
自动化技术 | 7714篇 |
出版年
2023年 | 444篇 |
2022年 | 824篇 |
2021年 | 1394篇 |
2020年 | 997篇 |
2019年 | 1022篇 |
2018年 | 1892篇 |
2017年 | 1854篇 |
2016年 | 1982篇 |
2015年 | 1400篇 |
2014年 | 1862篇 |
2013年 | 3467篇 |
2012年 | 3035篇 |
2011年 | 3078篇 |
2010年 | 2380篇 |
2009年 | 2172篇 |
2008年 | 2346篇 |
2007年 | 2059篇 |
2006年 | 1599篇 |
2005年 | 1330篇 |
2004年 | 1198篇 |
2003年 | 1068篇 |
2002年 | 969篇 |
2001年 | 633篇 |
2000年 | 628篇 |
1999年 | 762篇 |
1998年 | 3708篇 |
1997年 | 2234篇 |
1996年 | 1485篇 |
1995年 | 882篇 |
1994年 | 744篇 |
1993年 | 737篇 |
1992年 | 251篇 |
1991年 | 271篇 |
1990年 | 271篇 |
1989年 | 247篇 |
1988年 | 219篇 |
1987年 | 196篇 |
1986年 | 215篇 |
1985年 | 245篇 |
1984年 | 212篇 |
1983年 | 165篇 |
1982年 | 193篇 |
1981年 | 208篇 |
1980年 | 179篇 |
1979年 | 140篇 |
1978年 | 133篇 |
1977年 | 233篇 |
1976年 | 463篇 |
1975年 | 95篇 |
1973年 | 102篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
MJ Mulet Pons MT Sarrión Ferre A Barea Montoro N Marín Rueda JJ Blanquer Grégori MA Melchor Penella 《Canadian Metallurgical Quarterly》1995,16(7):423-427
OBJECTIVE: To find the reasons which determine failures to comply with anti-flu vaccinations, so that these can be corrected and the coverage of this preventive action be increased. DESIGN: Observational crossover study, done by means of a telephone survey of people over 65. A questionnaire with closed questions, composed after a pilot study and validated by Cronbach's alpha. SETTING: Primary Care Centre (PCC). PATIENTS: We calculated a population sample for qualitative variables (_ = 0.05; p = 0.60; e = 0.05) of 294 people over 65, chosen from the PCC records, by means of random sampling (K = 4) stratified for age and discounting the telephone selection bias. MEASUREMENTS AND RESULTS: The proportion of vaccinated patients (60.9%) obtained in our study did not significantly differ from that in the general population. The percentage of patients included in the programme for the first time was 14%. Level of satisfaction among those vaccinated was 89.4%, with 8.9% of problems detected being light. Main causes of non-vaccination were: thinking that they didn't need it (63.5%), ignorance of the campaign (35.7%), fear of the reaction (24.3%), forgetting (10.4%). The main form of access to the campaign information was from the PCC, both through individuals and posters. Lack of information was statistically significant (p < 0.00001) as a determinant of non-vaccination, without other factors (age, sex, associated pathologies...) explaining these differences. CONCLUSIONS: Individualised and on-going health education by the PCC is fundamental. This would enable the identification of the group not vaccinated due to their express refusal and the recovery of non-vaccinated patients. 相似文献
183.
184.
E Pittenauer ER Schmid G Allmaier B Pfanzagl W L?ffelhardt CQ Fernández MA de Pedro W Stanek 《Canadian Metallurgical Quarterly》1993,22(9):524-536
A strategy for the structural characterization of the four major NaBH4-reduced peptidoglycan monomers derived from muramidase-digested peptidoglycan from the cyanelles of the flagellate Cyanophora paradoxa Korschikoff is described. Initial molecular weight determination of these glycopeptides was performed by positive and negative ion plasma desorption mass spectrometry. Due to the presence of two pairs of disaccharide tripeptide and disaccharide tetrapeptide monomers differing in mass by 112 units, respectively, an as yet unknown peptidoglycan modification either at the carbohydrate or at the peptide moiety was assumed. beta-Elimination of the disaccharide unit from the unreduced peptidoglycan monomers yielded the corresponding (modified) N1-lactyltripeptides and -tetrapeptides, respectively. These peptides, N-terminally blocked with lactic acid, unambiguously showed the modification to be located on the peptide moiety. By positive ion fast atom bombardment/hybrid tandem mass spectrometry of the reduced peptidoglycan monomers as well as of the corresponding deglycosylated monomers (= N1-lactylpeptides) the modification was determined to be linked to the glutamic acid moiety. Based on combined data from plasma desorption mass spectrometry, tandem mass spectrometry, accurate mass measurement and amino acid analysis of the acid hydrolysate after derivatization with o-phthaldialdehyde by high-performance liquid chromatography we could establish the structure of the modification as N-acetylputrescine. Finally, the confirmation of the linkage of the glutamic acid to diaminopimelic acid via the gamma-COOH was based on the presence of a-type peptide backbone fragment ions in the positive ion plasma desorption mass spectra of the modified N1-lactylpeptides. 相似文献
185.
The initiator methionine transfer RNA (tRNA(fMet)) gene was identified on a 347 bp Eco RI-Hind III DNA fragment of the potato mitochondrial (mt) genome. The sequence of this gene shows 1 to 7 nucleotide differences with the other plant mt tRNAs(fMet) or tRNA(fMet) genes studied so far. Whereas the tRNA(fMet) gene is present as a single copy in the potato mt genome, a tRNA 'pseudogene' corresponding to 60% of a complete tRNA (from the 5' end to the variable region) and located at 105 nucleotides upstream of the tRNA(fMet) gene on the opposite strand was shown to be repeated at least three times. Furthermore, the physical environment of the tRNA(fMet) gene in the mt genome is very different among plants, which suggests that the tRNA(fMet) gene region has often been implicated in recombination events of plant mt genomes leading to important rearrangements in gene order. 相似文献
186.
187.
BACKGROUND: Recently, investigators have reported the use of endoscopic myotomy in the treatment of esophageal achalasia. As with the open operation, considerable disagreement exists regarding the appropriate length of the myotomy and the need for a concomitant antireflux procedure. METHODS: Patients presenting with symptomatic achalasia between 1993 and 1997 were included in this prospective study. Preoperative studies included barium upper gastrointestinal study, endoscopy, and esophageal manometry. Laparoscopic myotomy was completed in all 20 patients; 18 had concomitant Toupet fundoplication. RESULTS: Operative times ranged from 95 to 345 minutes (mean 216). Blood loss ranged from 50 to 300 cc (mean 100 cc). There were 7 minor complications (5 mucosal injuries repaired laparoscopically, 1 bile leak and 1 splenic capsular tear). Nine patients began a liquid diet on the first day postoperatively; 19 were tolerating liquids by postoperative day 3. Hospital stay ranged from 2 to 20 days (mean 5). Eighteen patients had complete relief of dysphagia, with less than one reflux episode per month. One individual continues to have mild persistent solid food dysphagia. Another patient initially did well but subsequently developed mild recurrent dysphagia and reflux. One patient required laparoscopic take-down of the wrap because of recurrent dysphagia and now has no problems swallowing, but does complain of mild reflux. Two other patients also have mild reflux, 1 of whom did not undergo fundoplication. CONCLUSIONS: Laparoscopic Heller myotomy can be performed safely with excellent results in patients with achalasia. Adding a partial fundoplication appears to help control postoperative symptoms of reflux. This procedure should be considered the procedure of choice in patients with symptomatic esophageal achalasia. 相似文献
188.
189.
190.