全文获取类型
收费全文 | 7087篇 |
免费 | 33篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 22篇 |
综合类 | 3篇 |
化学工业 | 249篇 |
金属工艺 | 56篇 |
机械仪表 | 46篇 |
建筑科学 | 79篇 |
矿业工程 | 7篇 |
能源动力 | 26篇 |
轻工业 | 122篇 |
水利工程 | 22篇 |
石油天然气 | 9篇 |
无线电 | 126篇 |
一般工业技术 | 209篇 |
冶金工业 | 5895篇 |
原子能技术 | 28篇 |
自动化技术 | 226篇 |
出版年
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 20篇 |
2017年 | 17篇 |
2016年 | 29篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 69篇 |
2012年 | 39篇 |
2011年 | 41篇 |
2010年 | 36篇 |
2009年 | 48篇 |
2008年 | 54篇 |
2007年 | 48篇 |
2006年 | 47篇 |
2005年 | 45篇 |
2004年 | 33篇 |
2003年 | 36篇 |
2002年 | 24篇 |
2001年 | 39篇 |
2000年 | 42篇 |
1999年 | 210篇 |
1998年 | 1832篇 |
1997年 | 1022篇 |
1996年 | 665篇 |
1995年 | 389篇 |
1994年 | 343篇 |
1993年 | 360篇 |
1992年 | 51篇 |
1991年 | 85篇 |
1990年 | 94篇 |
1989年 | 82篇 |
1988年 | 87篇 |
1987年 | 89篇 |
1986年 | 81篇 |
1985年 | 89篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 50篇 |
1981年 | 43篇 |
1980年 | 75篇 |
1979年 | 17篇 |
1978年 | 22篇 |
1977年 | 173篇 |
1976年 | 371篇 |
1975年 | 16篇 |
1974年 | 10篇 |
1973年 | 11篇 |
1971年 | 9篇 |
排序方式: 共有7125条查询结果,搜索用时 15 毫秒
991.
992.
WA Boisvert R Santiago LK Curtiss RA Terkeltaub 《Canadian Metallurgical Quarterly》1998,101(2):353-363
Cancer complicating pregnancy is uncommon, with an incidence of approximately 1 in 1000 pregnancies. The obstetrician attending 250 deliveries per year would need to accumulate 40 years of clinical experience to encounter two to three cases of PABC. The increases in the size, weight, vascularity, and density of the breasts associated with pregnancy make the detection of mass lesions difficult both clinically and mammographically. Most of the benign lesions seen in pregnancy are the same ones seen in the nongravid state. Most cases of PABC present as painless masses, and as many as 90% of these masses are detected by breast self-examination. Women with PABC generally have more advanced disease with larger tumors, a higher percentage of inoperable lesions, and a higher percentage of nodal involvement. Because most PABC presents with a palpable mass, the role of imaging modalities in the evaluation of these patients remains limited. Fine-needle aspiration cytology is the initial procedure of choice for evaluating breast masses during pregnancy and lactation. Therapeutic abortion does not improve survival. The general principle is to treat the cancer and to allow the pregnancy to proceed. No studies have shown an adverse effect of a subsequent pregnancy even in patients with positive axillary nodes and patients in whom pregnancy occurs earlier than 2 years after treatment. 相似文献
993.
The membrane fusion reaction promoted by the paramyxovirus simian virus 5 (SV5) and human parainfluenza virus type 3 (HPIV-3) fusion (F) proteins and hemagglutinin-neuraminidase (HN) proteins was characterized when the surface densities of F and HN were varied. Using a quantitative content mixing assay, it was found that the extent of SV5 F-mediated fusion was dependent on the surface density of the SV5 F protein but independent of the density of SV5 HN protein, indicating that HN serves only a binding function in the reaction. However, the extent of HPIV-3 F protein promoted fusion reaction was found to be dependent on surface density of HPIV-3 HN protein, suggesting that the HPIV-3 HN protein is a direct participant in the fusion reaction. Analysis of the kinetics of lipid mixing demonstrated that both initial rates and final extents of fusion increased with rising SV5 F protein surface densities, suggesting that multiple fusion pores can be active during SV5 F protein-promoted membrane fusion. Initial rates and extent of lipid mixing were also found to increase with increasing influenza virus hemagglutinin protein surface density, suggesting parallels between the mechanism of fusion promoted by these two viral fusion proteins. 相似文献
994.
995.
OBJECTIVE: To compare the effect of staffing with general surgeons vs trauma specialists on patient outcome at a trauma center. DESIGN: The care of injured patients at a level I urban trauma center serving a population of 2.5 million was the responsibility of 12 surgeons (10 general surgeons and 2 trauma specialists) between January 1 and June 30, 1996 (group 1). Between July 1 and December 31, 1996 (group 2), trauma was the responsibility solely of 4 trauma specialists. An additional comparison was made with those patients in group 1 who were admitted to the general surgeons (group 1A). The outcomes and quality of care for these periods, as determined by the quality assurance screens, were retrospectively analyzed and compared. SETTING: Urban, tertiary care, level I trauma center. PARTICIPANTS: Each trauma and burn patient admitted during the study periods is included in this study. Upon the patient's discharge from the hospital, specially trained nurses completed a review of the patient's stay and entered it into the TraumaOne database (Lancet Technology Inc, Cambridge, Mass). There were 693 trauma patients in group 1 (472 in group 1A) and 734 patients in group 2. MAIN OUTCOME MEASURES: Mortality, length of stay, and 16 quality assurance screens were quantified and compared using chi(2) analyses and t tests. RESULTS: The age and sex of the 2 groups were similar. The mortality rate was 6.2% (43/693) in group 1, 6.1% (29/472) in group 1A, and 6.5% (48/734) in group 2 (P = .80 and P = .78, respectively). When stratified by injury severity score (ISS), lengths of stay were statistically similar, except for patients with an ISS of 0 to 7. Patients with an ISS of 0 to 7 in groups 1 and 1A stayed a mean of 2.6 days, compared with 3.2 days for group 2 (P = .01 and P = .02, respectively). The results of quality assurance screens (missed injury, wound infection, readmission, and 13 others) were similar in the 2 groups. CONCLUSIONS: Transitions in staffing afforded the opportunity to examine patient outcomes by surgeon specialization and frequency of call. In our sample, 12 well-trained surgeons taking call less frequently managed a trauma service as efficiently as a group of 4 trauma specialists, without any differences in morbidity and mortality. 相似文献
996.
A Krippner A Matsuno-Yagi RA Gottlieb BM Babior 《Canadian Metallurgical Quarterly》1996,271(35):21629-21636
Mitochondrial function was examined in Jurkat cells undergoing Fas-mediated apoptosis. With succinate or ascorbate/tetramethylphenylenediamine as substrate, oxygen uptake by digitonin-permeabilized apoptotic mitochondria was greatly decreased as compared with control. Assessment of the function of the cytochrome c-cytochrome oxidase segment of the electron transport chain of apoptotic mitochondria showed that the activity of cytochrome oxidase appeared to be normal, but that of cytochrome c was greatly diminished. A death protease was found to participate in the events leading to the loss of cytochrome c activity, but the cytochrome did not seem to be extensively degraded during the course of apoptosis. Our results suggest that a rapid loss in mitochondrial function due at least in part to the inhibition or inactivation of cytochrome c is a potentially fatal component of the apoptosis program of Jurkat cells. 相似文献
997.
Ventilatory acclimatization to sustained hypoxia (VASH) is the time-dependent increase in ventilation that occurs during prolonged exposure to hypoxia. We tested the hypothesis that carotid body (CB) dopaminergic mechanisms are down-regulated during VASH, which would allow CB afferent discharge and ventilation to increase beyond the initial response to hypoxia. Domperidone (DOM; 1.0 mg.kg-1) was administered intravenously to block CB dopamine (DA) receptors after VASH was complete in awake goats. DOM caused a significant augmentation of the ventilatory response to hypoxia in acclimatized goats, failing to support the hypothesis. We conclude that inhibitory CB dopaminergic function is not significantly reduced following prolonged hypoxia, and that down-regulation of CB dopaminergic mechanisms may not be involved in VASH in the goat. 相似文献
998.
A brief overview of the theory of corrosion and the formation of galvanic couples is presented, followed by a discussion of the metals and alloys used in the fabrication of orthodontic appliances and devices. Attention is paid to the factors that contribute to establishment of corrosion cells in the mouth. Although oral corrosion generally does not cause significant destruction of metal, it can elicit in patients adverse physiological responses such as local irritation and metal hypersensitivity. There are indications that orthodontic treatment may lower the incidence of nickel hypersensitivity. Destructive attack on orthodontic appliances does occur, however, when certain types of denture cleanser are used to clean appliances that contain soldered joints. 相似文献
999.
This paper studies the problems of inference and prediction in a class of models known as hierarchical mixtures-of-experts (HME). The statistical model underlying an HME is a mixture model in which both the mixture coefficients and the mixture components are generalized linear models. Bayesian inference regarding an HME's parameters is presented in the contexts of regression and classification using Markov chain Monte Carlo methods. A benefit of this Bayesian approach is the ability to obtain a sample from the posterior distribution of any functional of the parameters of the given model. In this way, more information is obtained than provided by a point estimate. The methods are illustrated on a nonlinear regression problem and on a breast cancer classification problem. The results indicate that the HME showed good prediction performance, and also gave the additional benefit of providing for the opportunity to assess the degree of certainty of the model in its predictions. 相似文献
1000.
RA Nicholas ER Lazarowski WC Watt Q Li J Boyer TK Harden 《Canadian Metallurgical Quarterly》1996,16(6):319-323
An autopsy case of a 67-year-old man with typical clinical features of progressive supranuclear palsy (PSP) characterized by impairment of vertical ocular pursuit movement, pseudobulbar palsy, nuchal stiffness, parkinsonism, and dementia is described. In addition to typical pathological changes of PSP, the present case showed fronto-temporal cortical atrophy, accompanied with various Gallyas/tau-positive neuronal and glial structures such as neurofibrillary tangles, pretangle neurons, glial coiled bodies, astrocytic plaques and argyrophilic threads in the cerebral cortex and subcortical nuclei, and many senile plaques throughout the whole cerebral cortex. The present report suggests that PSP and corticobasal degeneration share a common background in neuronal and glial pathologies, that pathological changes of PSP and Alzheimer's disease are mixed in the entorhinal cortex, amygdala. Meynert nucleus, and hypothalamus, and that dementia with frontal lobe-like syndrome in PSP is related to the frontal and temporal cortical pathologies, and is cortical dementia as well as subcortical dementia. 相似文献