全文获取类型
收费全文 | 2491篇 |
免费 | 22篇 |
专业分类
电工技术 | 13篇 |
综合类 | 3篇 |
化学工业 | 111篇 |
金属工艺 | 18篇 |
机械仪表 | 10篇 |
建筑科学 | 34篇 |
矿业工程 | 2篇 |
能源动力 | 15篇 |
轻工业 | 108篇 |
水利工程 | 2篇 |
石油天然气 | 37篇 |
无线电 | 50篇 |
一般工业技术 | 75篇 |
冶金工业 | 1948篇 |
原子能技术 | 6篇 |
自动化技术 | 81篇 |
出版年
2021年 | 13篇 |
2020年 | 6篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 46篇 |
2012年 | 24篇 |
2011年 | 25篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 21篇 |
2007年 | 30篇 |
2006年 | 20篇 |
2005年 | 23篇 |
2004年 | 26篇 |
2003年 | 20篇 |
2002年 | 11篇 |
2001年 | 18篇 |
2000年 | 6篇 |
1999年 | 79篇 |
1998年 | 626篇 |
1997年 | 320篇 |
1996年 | 218篇 |
1995年 | 134篇 |
1994年 | 119篇 |
1993年 | 118篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1990年 | 37篇 |
1989年 | 19篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 46篇 |
1976年 | 95篇 |
1975年 | 15篇 |
1973年 | 9篇 |
1972年 | 7篇 |
1971年 | 8篇 |
1967年 | 5篇 |
排序方式: 共有2513条查询结果,搜索用时 15 毫秒
71.
Several studies have documented the occurrence of high ventilation rates during cardiopulmonary resuscitation, but to date, there have been no scientific investigation of the causes of hyperventilation. The objective of the current study was to test the effects of socio-emotional stressors on lay rescuers' ventilation rate in a simulated resuscitation setting using a manikin model. A within-subjects experiment with randomized order of conditions tested lay rescuers' ventilation rate on an intubated manikin during exposure to socio-emotional stressors and during a control condition where no external stressors were present. Ventilation rates and subjective workload were significantly higher during exposure to socio-emotional stressors than during the control condition. All but one of the nine participants ventilated at a higher ventilation rate in the experimental condition. All nine participants rated the subjective workload to be higher during exposure to socio-emotional stressors. Hence, exposure to socio-emotional stressors is associated with increased ventilation rates performed by lay rescuers during simulated cardiac arrest using a manikin model. These findings might have implications for the understanding of the type of situations which hyperventilation may occur. Awareness of these situations may have implications for training of lay rescues. 相似文献
72.
Bypass surgery for vascular disease of the carotid system 总被引:2,自引:0,他引:2
TM Sundt RG Siekert DG Piepgras FW Sharbrough OW Houser 《Canadian Metallurgical Quarterly》1976,51(11):677-692
A series of 58 operations on 56 patients, in whom a branch of the superficial temporal artery was anastomosed to a branch of the middle cerebral artery (STA-MCA bypass or Yasargil procedure), is reviewed. These operations were performed chiefly for occlussions or for inaccessible stenotic lesions of the internal carotid or middle cerebral arteries. Patency in eight patients operated on from April 1971 through November 1973 was low (25%). Patency in patients operated on since July 1974 has been high (95%). There have been no deaths and no major ischemic strokes attributable to the surgery. The rationale for this procedure is considered in relationship to the anatomy and physiology of the cerebral circulation and the pathogenesis of syndromes of cerebral ischemia. The operation appears to have a low morbidity in good-risk patients. The role of this operation in managing common manifestations of cerebral vascular disease such as focal transient cerebral ischemic attacks (TIAs) and amaurosis fugax, although not fully established, appears encouraging. The procedure seems useful for orthostatic cerebral ischemia caused by multiple occlusions of major extracranial (and intracranial) vessels and, occasionally, for progressing strokes related to internal carotid artery occlusion, both of which are relatively uncommon manifestations of cerebral vascular occlusive disease. It may have application in the rare "slow stroke." The procedure is probably of limited value, if any, in the management of large completed infarcts but may be indicated in selected patients with small infarctions who have preserved most of their cerebral function and who have had evidence of subsequent focal ischemic events. The procedure is useful for bypassing giant aneurysms or basofrontal tumors invading major vessels. It may have a role in the management of fibromuscular disease of the internal carotid artery. 相似文献
73.
The influence of surgical stress on resistance to i.v. challenge with Walker 256 tumour cells was investigated in rats, with respect to the functional state of the reticuloendothelial system (RES). Phagocytic activity of the RES was evaluated by colloid (gelatinized [131I] "RE test lipid emulsion") clearance, and opsonin levels were determined by bioassay. Reticuloendothelial clearance capacity was significantly (P less than 0-05) depressed 60 min following surgery (coeliotomy plus jejunal enterotomy) as quantified by both humoral and cellular parameters of RE function. Phagocytic depression was primarily due to impaired hepatic Kupffer cell function and related to a deficiency in the phagocytic supporting capacity of plasma, also referred to as opsonic or recognition factor (RF) capacity. During the postoperative period of RES colloid clearance depression, pulmonary localization of the blood-borne test particulate matter increased. Rats challenged with 51Cr-labelled viable tumour cells at a dose of 1-0 X 106 i.v., either prior to or during the postoperative period of RE depression, manifested a significant (P less than 0-05) increment in pulmonary localization of the viable tumour cells, and a decrease (P less than 0-05) in hepatic clearance. Evaluation of survival patterns demonstrated a significant (P less than 0-01) decrease in host resistance to i.v. tumour cell challenge (2 X 103 cells) during the postoperative period of RE depression and hypo-opsonaemia. Sham-anaesthetized control animals survived 17-9 +/- 0-8 days, while animals challenged during the period of RE depression survived 7-9 +/- 0-4 days. An increased incidence of respiratory distress and nasal discharge was observed in the animals with impaired survival. Thus, surgical manipulation may transiently compromise RES systemic host defence and may be reflected in an increment in the pulmonary localization of blood-borne tumour cells. The relationship of this altered pattern of tumour cell distribution to the impaired survival remains to be determined, and warrants investigations. 相似文献
74.
Although the construction pollution index has been put forward and proved to be an efficient approach to reducing or mitigating pollution level during the construction planning stage, the problem of how to select the best construction plan based on distinguishing the degree of its potential adverse environmental impacts is still a research task. This paper first reviews environmental issues and their characteristics in construction, which are critical factors in evaluating potential adverse impacts of a construction plan. These environmental characteristics are then used to structure two decision models for environmental-conscious construction planning by using an analytic network process (ANP), including a complicated model and a simplified model. The two ANP models are combined and called the EnvironalPlanning system, which is applied to evaluate potential adverse environmental impacts of alternative construction plans. 相似文献
75.
An integrated model for supplier selection process 总被引:1,自引:1,他引:1
0 INTRODUCTIONIntoday’shighlycompetitivemanufacturingen vironment,manufacturingcompaniesmustconstantlyaskthemselvesthesetoughquestions :Dowehavethebestsuppliersatthelowestpossibleprices?Arewegettingandsendingmaterialsasquicklyaspossible ?Additionally ,the… 相似文献
76.
In this letter we propose a piece-wise linear (PL) classifier for use as the decision stage in a two-modal verification system, comprised of a face and a speech expert. The classifier utilizes a fixed decision boundary that has been specifically designed to account for the effects of noisy audio conditions. Experimental results on the VidTIMIT database show that in clean conditions, the proposed classifier is outperformed by a traditional weighted summation decision stage (using both fixed and adaptive weights). Using white Gaussian noise to corrupt the audio data resulted in the PL classifier obtaining better performance than the fixed approach and similar performance to the adaptive approach. Using a more realistic noise type, namely “operations room” noise from the NOISEX-92 corpus, resulted in the PL classifier obtaining better performance than both the fixed and adaptive approaches. The better results in this case stem from the PL classifier not making a direct assumption about the type of noise that causes the mismatch between training and testing conditions (unlike the adaptive approach). Moreover, the PL classifier has the advantage of having a fixed (non-adaptive, thus simpler) structure. 相似文献
77.
Longin Jan Latecki Christopher Conrad Ari Gross 《Journal of Mathematical Imaging and Vision》1998,8(2):131-159
The main task of digital image processing is to recognize properties of real objects based on their digital images. These images are obtained by some sampling device, like a CCD camera, and represented as finite sets of points that are assigned some value in a gray-level or color scale. Based on technical properties of sampling devices, these points are usually assumed to form a square grid and are modeled as finite subsets of Z2. Therefore, a fundamental question in digital image processing is which features in the digital image correspond, under certain conditions, to properties of the underlying objects. In practical applications this question is mostly answered by visually judging the obtained digital images. In this paper we present a comprehensive answer to this question with respect to topological properties. In particular, we derive conditions relating properties of real objects to the grid size of the sampling device which guarantee that a real object and its digital image are topologically equivalent. These conditions also imply that two digital images of a given object are topologically equivalent. This means, for example, that shifting or rotating an object or the camera cannot lead to topologically different images, i.e., topological properties of obtained digital images are invariant under shifting and rotation. 相似文献
78.
79.
80.