全文获取类型
收费全文 | 288688篇 |
免费 | 6401篇 |
国内免费 | 1277篇 |
专业分类
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 |
出版年
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.
Faccio F. Anghinolfi F. Heijne E.H.M. Jarron P. Cristoloveanu S. 《Electron Devices, IEEE Transactions on》1998,45(5):1033-1038
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