全文获取类型
收费全文 | 2378篇 |
免费 | 3篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 27篇 |
金属工艺 | 7篇 |
机械仪表 | 9篇 |
建筑科学 | 12篇 |
能源动力 | 2篇 |
轻工业 | 13篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 14篇 |
一般工业技术 | 46篇 |
冶金工业 | 2205篇 |
原子能技术 | 1篇 |
自动化技术 | 36篇 |
出版年
2022年 | 3篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2014年 | 4篇 |
2013年 | 11篇 |
2012年 | 10篇 |
2011年 | 10篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 8篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 7篇 |
2002年 | 2篇 |
2001年 | 9篇 |
2000年 | 2篇 |
1999年 | 73篇 |
1998年 | 710篇 |
1997年 | 382篇 |
1996年 | 257篇 |
1995年 | 154篇 |
1994年 | 126篇 |
1993年 | 139篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 29篇 |
1989年 | 27篇 |
1988年 | 36篇 |
1987年 | 28篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 13篇 |
1980年 | 19篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 43篇 |
1976年 | 105篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1962年 | 2篇 |
1955年 | 2篇 |
1923年 | 1篇 |
排序方式: 共有2381条查询结果,搜索用时 31 毫秒
21.
SR Babyar 《Canadian Metallurgical Quarterly》1996,76(3):226-38; discussion 239-47
BACKGROUND AND PURPOSE: Scapular excursion and the wrist speed were studied before and after instruction and practice designed to achieve symmetrical scapular movement. SUBJECTS: Subjects were 10 female and 6 male patients, aged 44 to 78 years (chi=60.3, SD=11.2), with diagnosed shoulder pathologies. METHODS: Subjects were videotaped performing a reaching task. Pain status was monitored. The subjects were instructed to make the scapular movement symmetrical. They then repeated the task, while being videotaped, to monitor the effect of instruction. RESULTS: Individuals with asymmetric upper-extremity starting positions had excessive vertical motion of the involved scapula, which they controlled after instruction. Peak wrist speed of the involved upper extremity was lower only after instruction. CONCLUSION AND DISCUSSION: Even in the absence of biomechanical factors or pain, excessive scapular vertical motion appears to occur in the involved upper extremities of individuals recovering from unilateral shoulder problems. Improved scapular control can follow simple verbal instruction and practice, with a slight decrement in wrist speed. 相似文献
22.
A polysaccharide containing D-galactose, 2-deoxy-2-N-acetylamino-D-galactose and 3,6-dideoxy-3-N-(D-3-hydroxybutyryl)amino-D-galactose, probably corresponding to the lipopolysaccharide side chain, was obtained from an aqueous phenol extract of isolated cell walls from Acinetobacter baumannii strain O2. By means of NMR studies and chemical degradations, the repeating unit of the polymer was identified as a branched hexasaccharide of the structure shown, where Fuc3N represents 3-amino-3,6-dideoxygalactose and R represents D-3-hydroxybutyryl. Serological tests indicated that the polymer corresponded to the O2 antigen. 相似文献
23.
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
24.
A Lander R Redkar G Nicholls A Lawson SR Choudhury JJ Corkery P Gornall RG Buick IW Booth 《Canadian Metallurgical Quarterly》1997,77(2):F119-F122
AIM: To assess the efficacy of cisapride in reducing ileus persisting to the tenth postoperative day after neonatal abdominal surgery. METHODS: A prospective, randomised, double blind trial comparing rectal cisapride (1.4-2.3 mg/kg/day) with placebo over seven days was undertaken in 33 neonates. RESULTS: Seven of 12 (58%) patients receiving placebo and eight of 11 (73%) receiving cisapride achieved a first sustained feed during treatment. Of those receiving cisapride, the first sustained feed occurred at 2.3 days (SEM 0.6) compared with 4.7 days (SEM 0.8) with placebo. By the seventh day the mean daily net enteral balance was 69 (SEM 18) ml/kg in the cisapride subgroup and 17 (SEM 8) ml/kg for those receiving placebo. Stool was passed on 6.3 (SEM 0.4) treatment days in the cisapride subgroup compared with 4.1 (SEM 1.0) treatment days in the placebo subgroup. CONCLUSION: Cisapride is effective in neonates with a prolonged ileus after abdominal surgery. 相似文献
25.
26.
SR Khan 《Canadian Metallurgical Quarterly》1997,157(1):376-383
PURPOSE: Most stones contain more than one type of crystals, and some combinations, such as calcium phosphate/calcium oxalate, are more common than others. Epitaxy between the crystals has been suggested to play a role in growth of such stones. The specific aim of this study is to investigate the involvement of calcium phosphate in crystallization of calcium oxalate. MATERIALS AND METHODS: Twenty calcium oxalate stones or stone fragments were examined using various microscopic techniques, including scanning, transmission and back-scattered electron microscopy. Similarly, calcium oxalate stones induced on a plastic foreign body implanted inside urinary bladders of laboratory rats were also investigated. Examination of the interface between calcium phosphate and calcium oxalate crystals was emphasized. RESULTS: Close association between crystals of calcium phosphate and calcium oxalate were found in both the human and rat stones. All crystals examined were associated with an organic matrix on the surface and contained copious amounts of organic material within the crystalline entities. Interface between the crystals also appeared to be occupied by organic matrix. CONCLUSIONS: Results of this and other studies from our laboratory indicate that epitaxy between various crystals, even though theoretically possible, appears unlikely in vivo. The appearance of specific crystalline combinations in stones is probably a result of the urinary environment being conducive for crystallization of those components. Heterogeneous nucleation of calcium oxalate is most probably induced by biological elements, including membranous cellular degradation products. 相似文献
27.
28.
Shock increases mortality from brain injuries, but the mechanism is poorly understood. We hypothesized that brain injury followed by shock and resuscitation leads to a secondary reperfusion injury mediated in part by polymorphonuclear leukocytes (PMNs). To validate this hypothesis, we studied cerebral perfusion pressure (CPP), intracranial pressure (ICP), cerebral blood flow (CBF), cortical water content (CWC), and hemodynamic variables in a porcine model of focal cryogenic brain injury and hemorrhagic shock. Cerebral PMN accumulation (CPMN) in the injured and uninjured hemispheres was determined histologically from the total PMNs in five high-power fields (400x). Twenty-nine mature swine were randomized to four groups. Group 1, the control group, was instrumented only. Group 2 animals had a brain injury alone and were studied for 24 hours. Group 3 animals had a brain injury and hemorrhagic shock. Group 4 animals had hemorrhagic shock alone. Brain injury followed by shock caused a significantly greater ICP and a significantly lower CBF than brain injury or shock alone. There was no significant difference in CPP between groups after resuscitation. The CWC of the lesioned area was similar in both brain-injured groups but was significantly increased when compared with the controls and the shock-only group. The CWC of the nonlesioned hemisphere was higher in group 3 than in group 2. The CPMN in both hemispheres in group 3 was significantly greater than in either group 2 or group 4. There was a significant positive correlation between CPMN and both ICP and CWC, and a significant negative correlation between CPMN and CBF. These data suggest an association between CPMN accumulation and secondary brain injury. 相似文献
29.
30.
D. B. Longmore D. M. Firmin J. Keegan G. Z. Yang P. Gatehouse S. R. Underwood 《Magma (New York, N.Y.)》1994,2(3):211-217
Conclusions Functional evaluation of the cardiovascular system using rapid imaging (spiral echo planar), chemical shift, and velocity mapping is capable of making the diagnosis in congenital and acquired cardiovascular disease which, between them, cause the largest number of deaths of any disease in the western world and massive morbidity and suffering. Furthermore, for the first time in the history of medicine, there is the opportunity to apply preventive measures to eardicate the epidemic of preventable arterial disease. There needs to be a change of emphasis and a switching of resources to apply to the most common diseases rather than to those which are most easily studied. There also needs to be proper training in cardiovascular MR, not so much for imagers as for cardiologists and experts in vascular disease. 相似文献