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   288688篇
  免费   6401篇
  国内免费   1277篇
电工技术   5184篇
综合类   281篇
化学工业   44351篇
金属工艺   11621篇
机械仪表   8101篇
建筑科学   7616篇
矿业工程   605篇
能源动力   7105篇
轻工业   32165篇
水利工程   2331篇
石油天然气   1533篇
武器工业   9篇
无线电   32870篇
一般工业技术   52649篇
冶金工业   60482篇
原子能技术   4014篇
自动化技术   25449篇
  2021年   2632篇
  2020年   2030篇
  2019年   2484篇
  2018年   4293篇
  2017年   4130篇
  2016年   4481篇
  2015年   3403篇
  2014年   4936篇
  2013年   14585篇
  2012年   8231篇
  2011年   10274篇
  2010年   8368篇
  2009年   8787篇
  2008年   9446篇
  2007年   9392篇
  2006年   8201篇
  2005年   7493篇
  2004年   7137篇
  2003年   7091篇
  2002年   7000篇
  2001年   6940篇
  2000年   6348篇
  1999年   7002篇
  1998年   19819篇
  1997年   13744篇
  1996年   10306篇
  1995年   7475篇
  1994年   6519篇
  1993年   6407篇
  1992年   4292篇
  1991年   4225篇
  1990年   3761篇
  1989年   3687篇
  1988年   3633篇
  1987年   3070篇
  1986年   2989篇
  1985年   3585篇
  1984年   3206篇
  1983年   2849篇
  1982年   2687篇
  1981年   2732篇
  1980年   2612篇
  1979年   2360篇
  1978年   2328篇
  1977年   3121篇
  1976年   4829篇
  1975年   1967篇
  1974年   1855篇
  1973年   1864篇
  1972年   1481篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
We studied sequential changes in electrophysiological profiles of the ipsilateral substantia nigra neurons in an in vitro slice preparation obtained from the middle cerebral artery-occluded rats. Histological examination revealed marked atrophy and neurodegeneration in the ipsilateral substantia nigra pars reticulata at 14 days after middle cerebral artery occlusion. Compared with the control group, there was no significant change in electrical membrane properties and synaptic responses of substantia nigra pars reticulata neurons examined at one to two weeks after middle cerebral artery occlusion. On the other hand, there was a significant increase in the input resistance and spontaneous firing rate of substantia nigra pars compacta neurons at 13-16 days after middle cerebral artery occlusion. Furthermore, inhibitory postsynaptic potentials evoked by stimulation of the subthalamus in substantia nigra pars compacta neurons was suppressed at five to eight days after middle cerebral artery occlusion. At the same time excitatory postsynaptic potentials evoked by the subthalamic stimulation was increased. Bath application of bicuculline methiodide (50 microM), a GABA(A) receptor antagonist, significantly increased the firing rate of substantia nigra pars compacta neurons from intact rats. These results strongly suggest that changes in electrophysiological responses observed in substantia nigra pars compacta neurons is caused by degeneration of GABAergic afferents from the substantia nigra pars reticulata following middle cerebral artery occlusion. While previous studies indirectly suggested that hyperexcitation due to deafferentation from the neostriatum may be a major underlying mechanism in delayed degeneration of substantia nigra pars reticulata neurons after middle cerebral artery occlusion, the present electrophysiological experiments provide evidence of hyperexcitation in substantia nigra pars compacta neurons but not in pars reticulata neurons at the chronic phase of striatal infarction.  相似文献   
993.
An additional noise component is observed in the noise spectrum of transistors in a partially-depleted (PD) medium-thickness SOI-CMOS technology. We identify the origin of this additional noise in the noisy resistance of the body film. This resistance, coupled to the gate capacitance, forms an RC filter and generates the hump-shape of the additional noise component. Several experimental observations that support this model are presented  相似文献   
994.
The authors derive the systolic array implementation of the block LMS algorithm, consisting of N processing elements, where N is the filter order. The resulting array attains an order-independent sampling rate. Computer simulation results show that the block LMS algorithm is faster than the delayed LMS algorithm, which has previously been implemented on systolic arrays  相似文献   
995.
We present a local Dissemination of EPIC, a project which has been devised to support health and social primary care by an information system. One key point of the EPIC project was a standardization effort at European level, providing a standardized basis for the management system based on client needs for planning and manpower control. Whilst EPIC has been designed as a general community information system, the main EPIC applications focus is on the care of the elderly. Savona is a middle size Italian town with a high percentage of elderly people and has already had an experience of integration of health and social care within an Italian project. It has therefore been regarded as a suitable site for the dissemination of EPIC. The EPIC application solved some of the information problems which emerged during the validation of the previous Italian project, such as the definition of the requirements; the collection, processing and retrieval of the clinical/social data; the definition of responsibilities and relations of the operators.  相似文献   
996.
997.
OBJECTIVE: Experiences obtained with nonoperative treatment (NOT), i.e. total prohibition of per oral food intake for a minimum of 7 days, administration of combinations of broad-spectrum antibiotics, and parenteral hyperalimentation, are described in the management of esophageal perforations. SUMMARY BACKGROUND DATA: The place, value, and indication of NOT in the management of esophageal perforation has not yet been unequivocally defined. As a result, contradictory data have been published regarding the outcome of NOT. METHODS: During the past 15 years (1979 to 1994), 20 of 86 patients (23.3%) with esophageal perforation have been treated nonoperatively from the outset. In this group, perforations were located to the upper, middle, and lower third of the esophagus in 50%, 30%, and 20%, respectively. In the operative management group (OT)--in which conservative (drainage, endeprothesis), reconstructive (suture, reinforced suture), and radical (resection) surgical methods were applied--lesions were preponderantly located in the lower one third of the esophagus (56.1%--37/66). As to the interval between the perforation and the onset of treatment, 14 patients had been diagnosed within 24 hours, whereas in 6 cases treatment had been begun beyond 24 hours. RESULTS: NOT could be successfully carried out in 16 patients; the decision to use NOT had to be revised in 4 other cases (Table 1). Two patients were lost; the mortality rate was 10% (2 of 20). The rate of complications was lower in the NOT group (20%, or 4 of 20) than in the OT group (50%, or 33 of 66). CONCLUSIONS: NOT can be suggested for the treatment of intramural perforations. In the case of transmural perforation, this approach should be taken into consideration if the esophageal lesion is circumscribed, is not in neoplastic tissue, is not in the abdominal cavity, and is not accompanied by simultaneous obstructive esophageal disease; in addition, symptoms and signs of septicemia should be absent.  相似文献   
998.
999.
The rare case of neurilemmoma of the larynx was presented. The difficulties in histopathologic diagnosis of such tumors were emphasized. The tumor was removed by surgery from external approach.  相似文献   
1000.
Unrecognized and untreated depression occurs frequently in Alzheimer's disease (AD) patients, adding to the agony already experienced by patient and caregiver. The authors screened AD patients living with a family caregiver for depression. Twelve patients with confirmed depression were treated in an open-label study with antidepressant medication, with dosage adjustment by a psychiatrist at Weeks 2, 4, 8, and 16. Data collection occurred at baseline, Week 4, and Week 16. Depression decreased significantly (p < .01). Contrary to expectations, patient functional capacity declined (p = .045). Cognition remained unchanged (p > .05). Caregiver burden, caregiver depressive symptomatology, and quality of life of patient and caregiver remained unchanged (p > .05). The authors conclude that depression in AD can be detected if a collateral source, such as the caregiver, is available. The depression can and should be treated. More research is needed to determine the impact on patient functioning, caregiver burden, caregiver depressive symptomatology, and quality of life of patient and caregiver.  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