全文获取类型
收费全文 | 731篇 |
免费 | 0篇 |
专业分类
化学工业 | 2篇 |
无线电 | 2篇 |
冶金工业 | 726篇 |
自动化技术 | 1篇 |
出版年
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2000年 | 1篇 |
1999年 | 16篇 |
1998年 | 228篇 |
1997年 | 104篇 |
1996年 | 75篇 |
1995年 | 45篇 |
1994年 | 43篇 |
1993年 | 40篇 |
1992年 | 2篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 16篇 |
1976年 | 62篇 |
1975年 | 1篇 |
1965年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有731条查询结果,搜索用时 15 毫秒
81.
Body mass index and mortality in a general population sample of men and women. The Buffalo Health Study 总被引:1,自引:0,他引:1
JM Dorn EF Schisterman W Winkelstein M Trevisan 《Canadian Metallurgical Quarterly》1997,146(11):919-931
The objective of this research was to investigate the long-term relation between body mass index (BMI) and mortality from all causes and from specific causes in the general population. A 29-year follow-up study was conducted in a random sample of white men (n = 611) and women (n = 697) aged 20-96 years who were residents of Buffalo, New York, in 1960. At baseline, height and weight were determined by self-report. BMI was calculated as weight (kg)/height (m2). During the follow-up period, 295 (48.3 percent) men and 281 (40.3 percent) women died. With the Cox proportional hazards model and adjustment for age, education, and cigarette smoking, a significant linear association was found between BMI and all-cause mortality in men less than age 65 years at baseline (relative risk (RR) = 1.06, 95 percent confidence interval 1.02-1.09), but not in women (RR = 1.02, 95 percent confidence interval 0.99-1.05). In men age 65 years and older, the relation was quadratic in form (p = 0.02), with the lowest risks appearing in the BMI range of 23-27. BMI was most strongly related to cardiovascular disease (CVD) and coronary heart disease mortality in women and younger men. No such associations were observed in older men. BMI was not related to an increased risk of death from non-CVD or cancer in either sex. These findings illustrate the importance of BMI as a risk factor for CVD and coronary heart disease mortality in certain gender-age groups and indicate that the majority of the impact of BMI on overall mortality is due to the strong relation between relative weight and these specific causes of death. 相似文献
82.
OBJECTIVE: To determine the incidence and clinical presentation of prostatic urethral paragangliomas and to compare these findings with paragangliomas occurring in the other sites of the lower urinary tract. PATIENTS AND METHODS: The clinical records of three patients with prostatic urethral paragangliomas were reviewed, as was the histology of each specimen. The tumours were stained immunocytochemically with neuron-specific enolase, chromogranin, S100 protein, protein gene product 9.5, prostate-specific acid phosphatase and prostate-specific antigen. RESULTS: The three tumours occurred in elderly men, two of whom presented with haematuria, one of whom also had a vesical transitional cell carcinoma, and the third patient had obstructive symptoms due to co-existent prostatic hyperplasia. The histological appearances and immunocytochemical findings were consistent with paraganglioma. Treatment consisted of local excision and there were no recurrences or metastases at 5 and 6 years in two patients for whom follow-up was available. CONCLUSION: Urethral paragangliomas are rare tumours arising in elderly men and are hormonally inactive. Although haematuria may be the presenting symptom, it is important to exclude additional more common and possibly more sinister lesions such as transitional cell carcinoma. Local excision appears to be curative. 相似文献
83.
The effects of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) on renal medullary thick ascending limb (mTAL) have not been fully understood. The aim of this study is to examine the second-messenger responses of rat mTAL to ANF, BNP, and CNP. Characterizations of the ANF, BNP, and CNP receptors in mTAL were also performed by radioligand studies. Results showed that ANF and BNP were both capable of eliciting cyclic guanosine monophosphate (cGMP) responses in mTAL. Conversely, no cGMP response was observed upon stimulation by CNP in mTAL. The presence of ANF receptors was demonstrated by radioligand studies. One receptor site was found, and the Kd and maximum binding capacity were 4.0 +/- 0.45 nmol/L and 277.8 +/- 47.7 fmol/mg protein, respectively. BNP receptors were also found in mTAL, and ANF and BNP were sharing the same receptor. On the contrary, no CNP receptor could be shown by radioligand studies. These results suggest that guanylyl cyclase-coupled receptors (atrial natriuretic peptide receptor-A [ANPR-A]) specific for ANF and BNP are present in rat mTAL, while those for CNP (ANPR-B) are absent. ANF and BNP but not CNP act on mTAL to control water excretion. 相似文献
84.
C Schleper EF DeLong CM Preston RA Feldman KY Wu RV Swanson 《Canadian Metallurgical Quarterly》1998,180(19):5003-5009
Molecular phylogenetic surveys have recently revealed an ecologically widespread crenarchaeal group that inhabits cold and temperate terrestrial and marine environments. To date these organisms have resisted isolation in pure culture, and so their phenotypic and genotypic characteristics remain largely unknown. To characterize these archaea, and to extend methodological approaches for characterizing uncultivated microorganisms, we initiated genomic analyses of the nonthermophilic crenarchaeote Cenarchaeum symbiosum found living in association with a marine sponge, Axinella mexicana. Complex DNA libraries derived from the host-symbiont population yielded several large clones containing the ribosomal operon from C. symbiosum. Unexpectedly, cloning and sequence analysis revealed the presence of two closely related variants that were consistently found in the majority of host individuals analyzed. Homologous regions from the two variants were sequenced and compared in detail. The variants exhibit >99.2% sequence identity in both small- and large-subunit rRNA genes and they contain homologous protein-encoding genes in identical order and orientation over a 28-kbp overlapping region. Our study not only indicates the potential for characterizing uncultivated prokaryotes by genome sequencing but also identifies the primary complication inherent in the approach: the widespread genomic microheterogeneity in naturally occurring prokaryotic populations. 相似文献
85.
86.
Staphylococcus aureus is a pathogen important in causing human infections and intoxication. A sensitive fiber-optic that produces evanescent waves was developed for the detection of protein A, a product secreted only by S. aureus. In the immunosensor, a 40-mV argon-ion laser that generated laser light at 488 nm was used together with plastic optical fiber and antibodies to protein A were physically adsorbed onto the fiber. The principle of the detection involved a sandwich immunoassay with fluorescein isothiocyanate conjugated with anti-(protein A) immunoglobulin G to produce signals of the antigen-antibody reaction. The detection limit was 1 ng of protein A per milliliter. The fiber-optic immunosensor could be used for rapid and specific detection of S. aureus in clinical specimens and foods. 相似文献
87.
Measurements of the width and depth of the palate were used to predict the race (American black or white) or sex or both of an individual. The sample consisted of 332 living subjects with permanent dentitions, and measurements were made between cusp tips, so palate size includes bony and dental components. Blacks, with a more square palate, were distinguished from whites primarily by greater interpremolar widths and P1-to-M2 depths. Simultaneous prediction of race and sex had a correct classification of 48%, which is about twice that expected from chance. Pooling the two sex increases correct classification of race to 83%. Formulas also are provided for each variable separately to accommodate fragmentary remains. Resilience of palatal structures to traumatic and natural forces makes this method practical in several forensic situations. 相似文献
88.
MI Matee EF Lyamuya EE Simon JH Mwinula EC Mbena LP Samaranayake FF Scheutz 《Canadian Metallurgical Quarterly》1995,72(11):694-698
Seroprevalence of HIV-1 infection was determined in children aged between eighteen months and five years, attending maternal and child health (MCH) clinics in Dar es Salaam, Tanzania. A total of 889 children were eligible for the study, however seven children could not be enrolled because their mothers/guardians absconded and blood could not be drawn from 21 children due to refusal of mothers/guardians and from another 12 children due to technical reasons. Therefore, the participation rate was 95.5%. Of the 849 children screened, 14 (1.65%) were found to have IgG anti HIV-1 antibodies in their sera. The main clinical features found in children with symptomatic HIV-1 disease were weight loss, generalized lymphadenopathy, recurrent fevers, and prolonged diarrhoea. The utility of clinical features suggestive of HIV-1 infection (according to CDC classification) in identifying HIV-1 infection in children was evaluated and found to have high sensitivity (100%), specificity (96.9%) and negative predictive value (100%), but a low positive predictive value (35%). Marked variations in progression to symptomatic phase were noted, whereby some relatively young children had progressed to symptomatic phase (CDC class P-2A), while some older children were still in the asymptomatic stage (CDC class P-1 C). None of the symptomatic HIV-1 infected children presented with neurological disease, severe opportunistic infections, or malignancies. Although reduced mid-upper arm circumference and weight-for-age were associated with HIV seropositivity, these clinical parameters had low positive predictive values compared to the CDC classification. 相似文献
89.
90.