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   5933篇
  免费   25篇
电工技术   11篇
化学工业   51篇
金属工艺   1篇
机械仪表   8篇
建筑科学   15篇
矿业工程   2篇
能源动力   1篇
轻工业   75篇
水利工程   1篇
石油天然气   4篇
无线电   25篇
一般工业技术   74篇
冶金工业   5647篇
原子能技术   5篇
自动化技术   38篇
  2021年   9篇
  2018年   2篇
  2017年   3篇
  2016年   4篇
  2015年   7篇
  2014年   2篇
  2013年   18篇
  2012年   6篇
  2011年   13篇
  2010年   9篇
  2009年   11篇
  2008年   24篇
  2007年   26篇
  2006年   26篇
  2005年   11篇
  2004年   11篇
  2003年   24篇
  2002年   20篇
  2001年   5篇
  2000年   9篇
  1999年   172篇
  1998年   1697篇
  1997年   932篇
  1996年   662篇
  1995年   350篇
  1994年   330篇
  1993年   351篇
  1992年   42篇
  1991年   61篇
  1990年   84篇
  1989年   73篇
  1988年   66篇
  1987年   84篇
  1986年   67篇
  1985年   64篇
  1984年   6篇
  1983年   17篇
  1982年   32篇
  1981年   40篇
  1980年   42篇
  1979年   6篇
  1978年   12篇
  1977年   147篇
  1976年   343篇
  1975年   10篇
  1971年   2篇
  1966年   2篇
  1965年   2篇
  1963年   2篇
  1955年   5篇
排序方式: 共有5958条查询结果,搜索用时 218 毫秒
751.
The balance between the inductive signals and endogenous anti-apoptotic mechanisms determines whether or not programmed cell death occurs. The widely expressed inhibitor of apoptosis gene family includes three closely related mammalian proteins: c-IAP1, c-IAP2, and hILP. The anti-apoptotic properties of these proteins have been linked to caspase inhibition. Here we show that one member of this group, hILP, inhibits interleukin-1beta-converting enzyme-induced apoptosis via a mechanism dependent on the selective activation of c-Jun N-terminal kinase 1. These data demonstrate that apoptosis can be inhibited by an endogenous cellular protein by a mechanism that requires the activation of a single member of the mitogen-activating protein kinase family.  相似文献   
752.
To clarify whether asthma may be caused by fume from welding mild steel and to evaluate the possible strength of such an effect, we quantified airway responsiveness among young shipyard workers with different levels of fume exposure. Clinical investigation comprised a cross-sectional survey of 19- to 27-yr-old workers who were completing 3 to 9 yr of employment in various trades, and a control group of 15- to 17-yr-old school leavers who were applying for apprenticeships within the same trades. Both groups were subdivided into negligible-, ambient-, or high-exposure subgroups according to expected levels of fume exposure. Actual exposures were assessed in a parallel environmental survey. Participants were investigated by questionnaire, skin prick tests, spirometry, and methacholine tests. Complete data sets were obtained from 1,024 of the 1,070 eligible subjects (96%). Among the workers but not the school leaver controls, there was an increasing prevalence of positive methacholine tests across the exposure subgroups-negligible 37%, ambient 44%, high 49% (p < 0.05). Regression analyses showed that in males after allowing for the effects of atopy, current smoking, and age, the estimated geometric mean level of airway responsiveness of regular welders was twice that of workers with negligible exposure after 5 yr of work. This implies that fume exposure may have been critical in causing asthma in about 1% of the welders. A lesser effect (though not significantly so) was noted among the workers with ambient exposure.  相似文献   
753.
Fimbriae are considered important in the adherence and colonization of Porphyromonas gingivalis in the oral cavity. It has been demonstrated that purified fimbriae bind to whole human saliva adsorbed to hydroxyapatite (HAP) beads, and the binding appears to be mediated by specific protein-protein interactions. Recently, we expressed the recombinant fimbrillin protein (r-Fim) of P. gingivalis corresponding to amino acid residues 10 to 337 of the native fimbrillin (A. Sharma, H.T. Sojar, J.-Y. Lee, and R.J. Genco, Infect. Immun. 61:3570-3573, 1993). We examined the ability of individual salivary components to promote the direct attachment of r-Fim to HAP beads. Purified r-Fim was radiolabeled with 125I and incubated with HAP beads which were coated with saliva or purified individual salivary components. Whole, parotid, and submandibular-sublingual salivas increased the binding of 125I-r-Fim to HAP beads. Submandibular-sublingual saliva was most effective in increasing the binding of 125I-r-Fim to HAP beads (1.8 times greater than that to uncoated HAP beads). The binding of 125I-r-Fim to HAP beads coated with acidic proline-rich protein 1 (PRP1) or statherin was four and two times greater, respectively, than that to uncoated HAP beads. PRP1 and statherin molecules were also found to bind 125I-r-Fim in an overlay assay. The binding of intact P. gingivalis cells to HAP beads coated with PRP1 or statherin was also enhanced, by 5.4 and 4.3 times, respectively, over that to uncoated HAP beads. The interactions of PRP1 and statherin with 125I-r-Fim were not inhibited by the addition of carbohydrates or amino acids. PRP1 and statherin in solution did not show inhibitory activity on 125I-r-Fim binding to HAP beads coated with PRP1 or statherin. These results suggest that P. gingivalis fimbriae bind strongly through protein-protein interactions to acidic proline-rich protein and statherin molecules which coat surfaces.  相似文献   
754.
755.
A rare presentation of vertebral artery ectasia is reported with magnetic resonance imaging and angiographic correlation. The unusually low level of the abnormality had previously resulted in an incorrect diagnosis of primary pyramidal degeneration. One similar case has been reported in the world literature.  相似文献   
756.
757.
BACKGROUND: After a 12-year absence, epidemic typhus has re-emerged among the displaced population of Burundi. Following the outbreak of civil war in 1993, over 760000 people now inhabit refugee camps, under appalling conditions. A typhus outbreak occurred among prisoners in a jail in N'Gozi in 1995. At the time, the disease was not recognised, and was referred to as sutama. Reports of sutama among the civilian population date back to late 1995 and, in association with body-louse infestation, the disease has subsequently swept across the higher and colder regions of the country. METHODS: During a field study in February, 1997, 102 refugees with sutama underwent clinical examination and interview. Serum samples were collected and infesting body lice removed. Microbiological analysis included antibody estimations and specific PCRs aimed at diagnosis of Rickettsia prowezekii, Bartonella quintana, and Borrelia recurrentis. Between January and September, 1997, nationwide epidemiological data on the prevalence and distribution of sutama was obtained through liaison with local health services. A second field study in March, 1997, entailed the collection of further serum samples from suspected cases of sutama in different regions of Burundi. FINDINGS: Most of the 102 patients with sutama during initial assessment presented with manifestations similar to those previously described for typhus in Africa, though skin eruptions occurred in only 25 (25%) cases. Microbiological testing revealed evidence of R prowazeki infection in 76 (75%) patients, confirming that most cases of clinically-diagnosed sutama were epidemic typhus, and supporting the reliability of clinical diagnosis as a basis for the nationwide surveillance of the disease. Up to September, 1997, 45558 typhus cases were clinically diagnosed, most of which occurred in regions at an altitude of over 1500 m. Serological testing of 232 individuals from different regions of Burundi provided microbiological evidence to support clinical diagnoses in seven provinces, confirming the widespread nature of the outbreak. Serum from 13 of the original 102 patients and 19 (8%) of the 232 suspected cases had raised antibody titres against B quintana. A fatality rate of 15% among jail inmates fell to 0.5% after administration of a single dose of 200 mg doxycycline to suspected cases. INTERPRETATION: A gigantic outbreak of R prowazekii-induced typhus and B quintana-induced trench fever is continuing in Burundi. Transmission of both diseases to such a large number of people has followed a widespread epidemic of body-louse infestation. Diagnosis of typhus could be reliably made by means of clinical criteria, and the disease could be efficiently and easily treated by antibiotics. This epidemic highlights the appalling conditions in central-African refugee camps and the failure of public-health programmes to serve their inhabitants. Louse-associated disease remains a major health threat in this and other war-torn regions of the world.  相似文献   
758.
The purpose of this study was to determine the effect of augmenting NMDA receptor activation on cognitive deficits produced by traumatic brain injury (TBI). Specifically, D-cycloserine (DCS), a partial agonist of the NMDA-associated glycine site, was tested as a potential cognitive enhancer. Rats were injured using lateral fluid percussion TBI (2.8 +/- .10 atm). On days 1-15 post-injury, animals were injected (i.p.) with vehicle (n = 8), 10 mg/kg (n = 9), or 30 mg/kg (n = 8) of DCS. Sham-injured animals treated with either vehicle (n = 8) or 30 mg/kg of DCS (n = 8) were used for comparison. On days 11-15 post-injury, cognitive function was assessed using the Morris water maze (MWM). Results indicate that the 30 mg/kg dose of DCS significantly attenuated memory deficits as compared to injured vehicle-treated animals (P < 0.01). Analysis also revealed that performance of the injured-DCS (30 mg/kg) group was not significantly different from sham-injured animals treated with vehicle (P > 0.10). In contrast, the 10 mg/kg dose of DCS was ineffective in reducing injury-induced memory deficits. DCS (30 mg/kg) also significantly improved the spatial memory of sham-injured animals when compared with sham-injured animals treated with vehicle (P < 0.05). In conclusion, chronic, post-injury enhancement of the NMDA receptor is an effective strategy for ameliorating TBI-associated cognitive deficits.  相似文献   
759.
760.
There is little agreement on which outcome measures to use to express the efficacy of treatments for cervical dystonia. We analyzed change scores on various scales of 64 new patients with cervical dystonia before and after repeated injections with botulinum toxin. METHOD: The association between change in impairment (Tsui), and change in pain (TWSTRS-Pain) and functional health (TWSTRS-D, MOS-20) was expressed in percentages of variance explained. Effect sizes of the outcome measures from patients who continued botulinum treatment and dropouts were compared. Performance of outcome measures to distinguish patients who continued treatment and dropouts was analyzed with ROC curves and areas under the curve (AUC). Results: Impairments explained < or =7% of the score variance in functional health. There were no differences between the effect sizes of impairment and pain of patients who continued treatment and dropouts (p > 0.60). This suggests a poor reflection of the treatment efficacy by these outcome measures. Conversely, there were significant differences between the effect sizes of the functional status scales of the patients who continued treatment and the dropouts (p < or = 0.01). ROC curve analysis showed that the disability, handicap, and global disease burden scale accurately distinguished between the two groups (AUCs > 0.80). Impairments showed no discriminative accuracy (AUC = 0.46). CONCLUSION: Neurologic impairments have a small impact on the functional health of cervical dystonia patients. Disability, handicap, and a global measure of disease burden were the most suitable outcome parameters to express the clinical efficacy of botulinum therapy.  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