全文获取类型
收费全文 | 18391篇 |
免费 | 1043篇 |
国内免费 | 388篇 |
专业分类
电工技术 | 658篇 |
综合类 | 478篇 |
化学工业 | 1942篇 |
金属工艺 | 483篇 |
机械仪表 | 548篇 |
建筑科学 | 661篇 |
矿业工程 | 138篇 |
能源动力 | 374篇 |
轻工业 | 1123篇 |
水利工程 | 202篇 |
石油天然气 | 265篇 |
武器工业 | 75篇 |
无线电 | 1714篇 |
一般工业技术 | 1602篇 |
冶金工业 | 7670篇 |
原子能技术 | 154篇 |
自动化技术 | 1735篇 |
出版年
2024年 | 48篇 |
2023年 | 195篇 |
2022年 | 378篇 |
2021年 | 613篇 |
2020年 | 440篇 |
2019年 | 382篇 |
2018年 | 431篇 |
2017年 | 392篇 |
2016年 | 416篇 |
2015年 | 465篇 |
2014年 | 601篇 |
2013年 | 725篇 |
2012年 | 767篇 |
2011年 | 854篇 |
2010年 | 635篇 |
2009年 | 580篇 |
2008年 | 588篇 |
2007年 | 518篇 |
2006年 | 424篇 |
2005年 | 340篇 |
2004年 | 294篇 |
2003年 | 268篇 |
2002年 | 279篇 |
2001年 | 223篇 |
2000年 | 184篇 |
1999年 | 400篇 |
1998年 | 2471篇 |
1997年 | 1393篇 |
1996年 | 1022篇 |
1995年 | 536篇 |
1994年 | 475篇 |
1993年 | 491篇 |
1992年 | 117篇 |
1991年 | 166篇 |
1990年 | 114篇 |
1989年 | 142篇 |
1988年 | 107篇 |
1987年 | 105篇 |
1986年 | 109篇 |
1985年 | 93篇 |
1984年 | 38篇 |
1983年 | 44篇 |
1982年 | 62篇 |
1981年 | 68篇 |
1980年 | 90篇 |
1979年 | 29篇 |
1978年 | 32篇 |
1977年 | 176篇 |
1976年 | 374篇 |
1975年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
101.
JL Stringer 《Canadian Metallurgical Quarterly》1995,68(2):407-413
In a particular brain region specific changes in inhibition or excitation may be the basis of seizure initiation. Alternatively, changes in the balance of excitation and inhibition in the circuit, which may be detectable as polysynaptic responses may be more important indicators of epileptogenesis. That the appearance of polysynaptic responses precedes the initiation and, therefore, may be necessary for the onset of epileptiform activity in the hippocampal-parahippocampal circuit was tested using the chemical convulsant pentylenetetrazol. Excitation and paired-pulse inhibition were measured in CA1 and the dentate gyrus of the urethane-anaesthetized rat before and after administration of pentylenetetrazol. In addition, three polysynaptic responses were monitored. In both CA1 and the dentate gyrus, pentylenetetrazol, 100 mg/kg, caused a trend towards increased excitability and caused a relatively mild loss of inhibition. Two polysynaptic responses appeared in the dentate gyrus after the administration of pentylenetratrazol, both apparently mediated through the entorhinal cortex. A polysynaptic response of the CA1 pyramidal neurons to contralateral angular bundle stimulation was not observed. These experiments demonstrate that pentylenetetrazol will facilitate only the appearance of polysynaptic responses mediated through the entorhinal cortex. These results support the hypothesis that pentylenetetrazol has a specific action within the entorhinal cortex that may facilitate the synchronization and spread of epileptiform activity. These results are also consistent with the hypothesis that the appearance of polysynaptic responses may be necessary for the onset of epileptogenesis in the hippocampal-parahippocampal circuit. 相似文献
102.
103.
J Valla A Leguerrier H Corbineau B Sevray T Langanay H Le Couls M Sellin C Rioux Y Logeais 《Canadian Metallurgical Quarterly》1995,49(9):816-823
From 1978 to 1992, 121 cases of postinfarction left ventricular aneurysm (99 males, 22 females, mean age 60 years) were operated on. The authors insist on a high rate of clinical arhythmogenicity (31.4%) and associated mechanical complications (21%). 76% of patients were in functional NYHA class III or IV. Resection was performed in 90% of patients, plication in 10%. 58% underwent coronary artery bypass grafting (1.7 graft/patient), 16% encircling ventriculotomy, 8% mitral valve replacement and 13% closure of ventricular septal defect. Operative mortality was 14.9% (10% when other mechanical complications where excluded). 5-year survival is 67.9%. Late cardiac deaths are as follow: left ventricular failure (1.8% A/P), Sudden death (1.4% A/P), Myocardial infarction (0.6% A/P). 82% of survivals are in functional NYHA class I or II. Only functional class NYHA III or IV is predictive of late death. We conclude that postinfarction left ventricular aneurysm remains a high risk complication especially when associated with other mechanical complications. When arhythmogenicity is present we suggest rhythmologic surgery and in all cases, complete revascularization. 相似文献
104.
105.
106.
107.
FM Scott AM Treston GL Shaw I Avis J Sorenson K Kelly EC Dempsey AB Cantor M Tockman JL Mulshine 《Canadian Metallurgical Quarterly》1996,14(2-3):239-251
Monitoring respiratory epithelial biology may reveal individuals with incipient lung cancer. The expression of neuroendocrine (NE) markers in pulmonary epithelium is thought to be central to lung development, repair of injury and may contribute to carcinogenesis. In this study, we evaluate several candidate NE markers to determine the feasibility of prospective analysis of clinical specimens. The potential NE markers include the enzyme L-DOPA decarboxylase (DDC), the neuropeptide gastrin releasing peptide (GRP), and peptidyl-glycine alpha-amidating monooxygenase (PAM), the bifunctional enzyme responsible for the final bioactivation step of many neuropeptides. A comparison of PAM activity and DDC levels in 30 lung cancer cell lines indicated that peptide amidating activity may be an indicator of NE status. Bronchoalveolar lavage (BAL) fluid from subjects at risk of developing second primary lung cancer and from volunteers was obtained. The activity of the first PAM enzyme, peptidylglycine alpha-hydroxylating monooxygenase (PHM), ranged from not detectable to 507 pmol/h/mg protein in 57 specimens. The second PAM enzyme, peptidylamidoglycolate lyase (PAL), ranged from not detectable to 414 pmol/h/mg protein in 56 specimens. Using cluster analysis by the average linkage method, a group of enzyme values with PHM greater than 230 pmol/h/mg protein was determined. Long-term follow-up of these patients for new second primary lung cancers may help to determine the potential predictive value of PAM detected in the BAL fluid. 相似文献
108.
E Darai F Filippini JL Benifla JN Guglielmina G Pennehouat B Deval P Madelenat 《Canadian Metallurgical Quarterly》1996,25(4):353-359
OBJECTIVE: Our objective was to determine the interest of laparoscopic assisted vaginal hysterectomy. STUDY DESIGN: Between January 1991 to december 1994, 80 patients had laparoscopically assisted vaginal hysterectomy. We reviewed with particular emphasis characteristic indications, complications. RESULTS: Eighty were performed as laparoscopically assisted vaginal hysterectomy. 14 patients (17.5%) had laparotomy conversion; because of size of uterus in 3 cases, suspected ovarian tumor in 3 cases. Pelvic adherences in 4 cases, urinary tract injuries in 1 case, hypercapnia in 1 case, hemorrhage in 2 cases. 9 patients experienced febrile morbidity and 1 urinary infection. 1 patient received 2 units of packed red blood cells. The hospital stay was 5 days for laparoscopically assisted vaginal hysterectomy versus 5.9 for laparotomic hysterectomy. CONCLUSION: Laparoscopically assisted vaginal hysterectomy offers a technique to convert certain abdominal hysterectomies into vaginal hysterectomies with a 17.5% laparoconversion rate. 相似文献
109.
D Mandrus JL Sarrao A Migliori JD Thompson Z Fisk 《Canadian Metallurgical Quarterly》1995,51(8):4763-4767
110.