首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5758篇
  免费   95篇
  国内免费   2篇
电工技术   51篇
化学工业   549篇
金属工艺   70篇
机械仪表   67篇
建筑科学   130篇
矿业工程   4篇
能源动力   93篇
轻工业   285篇
水利工程   21篇
石油天然气   20篇
无线电   359篇
一般工业技术   610篇
冶金工业   2925篇
原子能技术   47篇
自动化技术   624篇
  2022年   23篇
  2021年   26篇
  2019年   35篇
  2018年   45篇
  2017年   49篇
  2016年   34篇
  2015年   41篇
  2014年   82篇
  2013年   186篇
  2012年   80篇
  2011年   121篇
  2010年   110篇
  2009年   109篇
  2008年   111篇
  2007年   127篇
  2006年   92篇
  2005年   87篇
  2004年   84篇
  2003年   110篇
  2002年   92篇
  2001年   95篇
  2000年   88篇
  1999年   149篇
  1998年   849篇
  1997年   481篇
  1996年   382篇
  1995年   218篇
  1994年   197篇
  1993年   201篇
  1992年   67篇
  1991年   86篇
  1990年   83篇
  1989年   81篇
  1988年   92篇
  1987年   75篇
  1986年   57篇
  1985年   58篇
  1984年   61篇
  1983年   56篇
  1982年   54篇
  1981年   61篇
  1980年   63篇
  1979年   56篇
  1978年   45篇
  1977年   92篇
  1976年   164篇
  1975年   41篇
  1974年   33篇
  1972年   24篇
  1966年   23篇
排序方式: 共有5855条查询结果,搜索用时 0 毫秒
21.
The charts of all patients with acute cholecystitis undergoing either laparoscopic or minilap cholecystectomy at the Chinle Comprehensive Health Care Facility between October 1, 1991, and August 15, 1993, were retrospectively reviewed. During that period, 54 patients underwent laparoscopic cholecystectomy and 45 patients had minilap procedures. The two groups had similar mean age, sex distribution, temperature, leukocyte count, gallbladder wall thickness, and duration of preoperative symptoms. While laparoscopic cholecystectomy took an average of 16 min longer to perform than minilap cholecystectomy, patients who had laparoscopic cholecystectomy had less blood loss, reduced postoperative narcotic needs, and shorter hospital stays.  相似文献   
22.
Reconsideration of the effect of an electrical field applied across a phospholipid bilayer membrane shows that, in addition to a compressive stress normal to the membrane plane, transverse traction stresses are generated in the lateral plane of the membrane. In the fields usually employed for electroporation these transverse stresses are likely to be sufficient to reduce the membrane tension considerably, causing electroporation and rupture. This mode of field-induced change in the membrane provides a natural model for the various forms of electroporation.  相似文献   
23.
We conducted a study to determine if the risk of airway compromise following tonsillectomy with uvulopalatopharyngoplasty justifies the added cost and inconvenience of step-down monitoring in an intensive care unit. We performed a retrospective chart review of 130 patients with obstructive sleep apnea who had undergone isolated tonsillectomy with uvulopalatopharyngoplasty at our tertiary care center. The average length of stay in the step-down unit was 18 hours. We found that only eight of these patients (6.2%) had a postoperative desaturation level of less than 90%, including three of 12 patients (25%) who had comorbid conditions. No patient had an adverse respiratory event. We conclude that step-down monitoring in an intensive care unit is not necessary, although caution should be exercised in monitoring patients with comorbidities because they appear to be more prone to desaturation. A complete lack of adverse respiratory events has not been reported in previous studies.  相似文献   
24.
Ion-molecule reactions of free phenyl cations with six-membered nitrogen-containing heterocyclic compounds: α-, β-, and γ-picolines, were studied. Phenyl cations were generated by tritium β-decay in double-labeled benzene. The mechanism of competing reactions of electrophilic addition to the nitrogen heteroatom in the ring and electrophilic substitution of the C-H bond in the pyridine ring was examined. The effect of methyl substituent in the pyridine molecule on the reaction pathway was evaluated. A one-step procedure for nuclear-chemical synthesis of tritium-labeled N-phenylpicolinium salts and phenyl-substituted picolines was developed.  相似文献   
25.
26.
We describe a case of positional dyspnea due to compression of the tracheobronchial tree by an extensive thoracic aneurysm. In a 77-year-old woman with long-standing systemic hypertension, intermittent anterior chest pain gradually developed over several years. She had no history of asthma or thoracic trauma. She was admitted to our hospital because of sudden, severe shortness of breath. The breathlessness was markedly worse when she lay on her back or on her right side. On physical examination, she was in acute respiratory distress with cyanosis, severe hypertension (180/110 mmHg), tachycardia, and inspiratory stridor. A chest X-ray film showed loss of volume and nearly complete radiopacity of the left hemithorax. Arterial blood gas analysis revealed an arterial oxygen partial pressure of 54.8 mmHg, a carbon dioxide partial pressure of 39.8 mmHg, and an oxygen saturation of 84.5 percent on room air. Computed tomographic examination of the thorax showed dilation of the aortic arch and descending aorta, and marked compression of the trachea and the left main bronchus. Examination with a fiberoptic bronchoscope revealed extrinsic compression of the trachea just proximal to the carina. The patient's symptoms stabilized. However, she did not undergo surgery because of her age and because of the size of the aneurysm. She died due to rupture of the aneurysm.  相似文献   
27.
Urinary protein and calcium excretion were assessed in 77 patients with the hepatic glycogen storage diseases (GSD): 30 with GSD-I (median age 12.4 years, range 3.2-32.9 years), 25 with GSD-III (median age 10.5 years, range 4.2-31.3 years) and 22 with GSD-IX (median age 11.8 years, range 1.2-35.4 years). Inulin (Cinulin) and para-aminohippuric acid (CPAH) clearances were also measured in 33 of these patients. Those with GSD-I had significantly greater albumin (F = 15.07, P < 0.001), retinol-binding protein (RBP) (F = 14.66, P < 0.001), N-acetyl-beta-D-glucosaminidase (NAG) (F = 9.41, P < 0.001) and calcium (F = 7.41, P = 0.001) excretion than those with GSD-III and GSD-IX. GSD-I patients (n = 18) also had significantly higher Cinulin (F = 5.57, P = 0.009), but CPAH did not differ (F = 0.77, NS). Renal function was normal in GSD-III and GSD-IX patients. In GSD-I, Cinulin (r = -0.51, P = 0.03) and NAG excretion (r = -0.40, P = 0.03) were inversely correlated with age, whereas albumin excretion was positively correlated with age (r = +0.41, P = 0.03). RBP and calcium excretion were generally high throughout all age groups. Hyperfiltration in GSD-I is associated with renal tubular proteinuria that occurs before the onset of significant albuminuria. Deficiency of glucose-6-phosphatase within the proximal renal tubule may primarily cause tubular dysfunction, glomerular hyperfiltration being a secondary phenomenon.  相似文献   
28.
Osteotomy has been used in treatment of unstable intertrochanteric hip fractures in an attempt to increase the stability of the fracture fragments. We have assessed this stability in a randomised prospective study on 138 patients, all having been fixed by dynamic hip screen, comparing anatomical reduction with medialisation osteotomy. The groups were similar in terms of age, gender and fracture configuration. There was no difference in final results in both groups except that operation time was longer in osteotomy group and the blood loss was more. We found no clear benefit from osteotomy and therefore recommend anatomical reduction and fixation by a sliding hip screw in most cases. Rarely, a fracture configuration which does not allow anatomical reduction may benefit from an osteotomy.  相似文献   
29.
The management of pain in patients with burn wounds is complex and problematic. Burn-wound pain is severe, inconsistent and underestimated. Patients experience severe pain, especially during procedures, until wound healing has occurred. A multi-modality approach is needed for effective management of pain, which requires an understanding of the mechanisms of pain. Altered pharmacokinetics and pharmacodynamics in burn-wound patients makes drug actions unpredictable. Opioids alone are seldom sufficient for pain control. The multi-modality approach includes the use of opioids and non-steroidal anti-inflammatory, anxiolytic and alternative drugs. Ketamine has been found to be a useful agent for analgesia in burn-wound patients; a dose of 10 mg/kg qid per os was found to be an effective adjunct to pain therapy.  相似文献   
30.
Lewis  L. Dreo  G. 《IEEE network》1993,7(6):44-51
Network management in large heterogeneous communication environments requires the incorporation of more advanced tools than are currently available, especially in the area of fault management. By providing an informational infrastructure for documenting network behavior and maintenance activities, TTSs (trouble ticket systems) have provided some relief for the fault management problem. Researchers have recognized TTSs as a means for realizing more advanced functions in network management platforms to effect automatic trouble ticket generation, fault diagnostics, and the correlation of multiple views network problems and behavior. The authors describe current research trends towards understanding and implementing these advanced functions in a TTS framework  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号