全文获取类型
收费全文 | 4200篇 |
免费 | 50篇 |
专业分类
电工技术 | 30篇 |
化学工业 | 235篇 |
金属工艺 | 24篇 |
机械仪表 | 24篇 |
建筑科学 | 31篇 |
能源动力 | 33篇 |
轻工业 | 95篇 |
水利工程 | 4篇 |
石油天然气 | 4篇 |
无线电 | 127篇 |
一般工业技术 | 239篇 |
冶金工业 | 3220篇 |
原子能技术 | 15篇 |
自动化技术 | 169篇 |
出版年
2021年 | 13篇 |
2020年 | 9篇 |
2019年 | 18篇 |
2018年 | 14篇 |
2017年 | 23篇 |
2016年 | 26篇 |
2015年 | 13篇 |
2014年 | 30篇 |
2013年 | 54篇 |
2012年 | 25篇 |
2011年 | 54篇 |
2010年 | 37篇 |
2009年 | 29篇 |
2008年 | 37篇 |
2007年 | 51篇 |
2006年 | 34篇 |
2005年 | 44篇 |
2004年 | 29篇 |
2003年 | 32篇 |
2002年 | 20篇 |
2001年 | 26篇 |
2000年 | 23篇 |
1999年 | 107篇 |
1998年 | 982篇 |
1997年 | 566篇 |
1996年 | 365篇 |
1995年 | 209篇 |
1994年 | 176篇 |
1993年 | 211篇 |
1992年 | 48篇 |
1991年 | 57篇 |
1990年 | 44篇 |
1989年 | 58篇 |
1988年 | 69篇 |
1987年 | 59篇 |
1986年 | 51篇 |
1985年 | 46篇 |
1984年 | 13篇 |
1983年 | 21篇 |
1982年 | 26篇 |
1981年 | 44篇 |
1980年 | 38篇 |
1979年 | 14篇 |
1978年 | 30篇 |
1977年 | 74篇 |
1976年 | 197篇 |
1975年 | 24篇 |
1974年 | 18篇 |
1970年 | 9篇 |
1969年 | 9篇 |
排序方式: 共有4250条查询结果,搜索用时 46 毫秒
41.
P Fiset HL Lemmens TD Egan SL Shafer DR Stanski TE Egan 《Canadian Metallurgical Quarterly》1995,58(5):567-582
The purpose of this study was to model pharmacodynamically the reversal of midazolam sedation with flumazenil. Ten human volunteers underwent four different sessions. In session 1, individual midazolam pharmacokinetics and electroencephalographic pharmacodynamics were determined. In sessions 2 and 3, a computer-controlled infusion of midazolam with individual volunteer pharmacokinetic data was administered, targeting a plasma concentration corresponding to a light or deep level of sedation (20% or 80% of the maximal midazolam electroencephalographic effect) for a period of 210 minutes. After obtaining a stable electroencephalographic effect and constant midazolam plasma concentrations, a zero-order infusion of flumazenil was started until complete reversal of midazolam electroencephalographic effect was obtained. The flumazenil infusion was then stopped and the volunteer was allowed to resedate because of the constant midazolam drug effect. The electroencephalographic response was measured during a 180-minute period and analyzed by aperiodic analysis and fast-Fourier transforms. In session 4, a midazolam plasma concentration corresponding to a deep level of sedation was targeted for 210 minutes to examine for the possible development of acute tolerance. No flumazenil was given in session 4. For a light sedation level, with a mean midazolam plasma concentration of 160 +/- 64 ng/ml, the mean half-life of the equilibration rate constant of flumazenil reversal is 5.0 +/- 2.5 minutes, and the mean effect site concentration causing 50% of Emax is 13.7 +/- 5.8 ng/ml. For a deep level of sedation, with a mean midazolam plasma concentration of 551 +/- 196 ng/ml, the mean half-life of the equilibration rate constant is 3.9 +/- 1.5 minutes, and the mean effect site concentration causing 50% of Emax is 20.6 +/- 6.8 ng/ml. This study provides an estimate of the magnitude of the blood/central nervous system equilibration delay for flumazenil antagonism of midazolam sedation and further defines the usefulness of the electroencephalogram as a measure of midazolam pharmacodynamic effect. 相似文献
42.
43.
Summary ESCA is used to characterize ion beam irradiated P(p-ClPhMA)-samples. The results show a chlorine abstraction. The experimental
findings are in accordance with a recently proposed model for a crosslinking mechanism of halogenated aromatic polymers. 相似文献
44.
45.
The extent of the dominant singular field is investigated for a finite crack under stress wave loading. Using a boundary integral equation method the complete solution as well as the near field solution is determined. A comparison of the two fields indicates that the singular field dominates within a small domain at the crack tip. The size of the dominance region in the dynamic case may be very different from that in the static case. 相似文献
46.
The type I adenylyl cyclase is directly stimulated by Ca2+ and calmodulin in vitro, and the enzyme is also stimulated by increases in intracellular Ca2+ in vivo. Ca2+ stimulation of the enzyme in vivo may be due to direct interactions of the enzyme with Ca2+ and calmodulin or to an indirect mechanism involving stimulation of the enzyme by Ca(2+)-activated protein kinases. In this study, we have made several point mutations within the calmodulin binding domain to determine if the Ca2+ sensitivity of the enzyme can be modified by mutagenesis. The catalytic activities of the mutant enzymes were comparable to wild type type I adenylyl cyclase. Substitution of Cys-507 with Ser-507 did not have significant effects on the calmodulin or Ca2+ sensitivity of the enzyme. However, replacement of Lys-504 with Asp caused a 4-fold decrease in sensitivity to Ca2+. Ca2+ and calmodulin stimulation were abolished by substitution of Phe-503 with Arg-503. Stimulation of type I adenylyl cyclase activity in vivo by intracellular Ca2+ was also greatly diminished with the Arg-503 mutant indicating that Ca2+ stimulation of the enzyme in vivo is due primarily to direct interactions with calmodulin and Ca2+. These data demonstrate that the Ca2+ sensitivity of this enzyme can be modulated by point mutagenesis within the putative calmodulin binding domain and indicate that the enzyme can be directly regulated by Ca2+ and calmodulin in vivo. 相似文献
47.
TM Munger DL Packer SC Hammill BJ Feldman KR Bailey DJ Ballard DR Holmes BJ Gersh 《Canadian Metallurgical Quarterly》1993,87(3):866-873
BACKGROUND: Virtually all natural history studies of Wolff-Parkinson-White (WPW) syndrome have been case series and, as such, have been constrained by referral biases, skewed age and sex distributions, or brief follow-up periods. The purpose of our study was to examine the natural history, the development of arrhythmias, and the incidence of sudden death in an entire cohort of pediatric and adult WPW patients from a community-based local population. METHODS AND RESULTS: We identified 113 residents of Olmsted County, Minnesota, during the period 1953-1989 using the centralized records-linkage system provided by the Mayo Clinic and the Rochester Epidemiology Program Project. Medical records and ECGs were reviewed to confirm the diagnosis and to establish pathway location by ECG criteria. Follow-up, via record review and telephone interview, was complete in 95% of subjects through 1990. The incidence of newly diagnosed cases was approximately four per 100,000 per year. Preexcitation was not present on the initial ECG of 22% of the cohort. Approximately 50% of the population was asymptomatic at diagnosis, with 30% subsequently having symptoms related to arrhythmia at follow-up. Two sudden cardiac deaths (SCD) occurred over 1,338 patient-years of follow-up, yielding an overall SCD rate of 0.0015 (95% confidence interval, 0.0002-0.0054) per patient-year. No SCD occurred in patients asymptomatic at diagnosis. CONCLUSIONS: The incidence of sudden death in a local community-based population is low and suggests that electrophysiological testing should not be performed routinely in asymptomatic patients with WPW syndrome. Nevertheless, young, asymptomatic patients, particularly those < 40 years old, should return for medical follow-up should symptoms develop. 相似文献
48.
AIMS: This study was designed to assess the efficacy of low dose methotrexate, 15 mg weekly, as a steroid-sparing agent in asthmatic patients requiring long-term oral prednisone treatment. METHODS: The study was a randomised, double blind, placebo controlled, cross over study of 48 weeks duration. Eleven patients with severe steroid-dependent asthma were included. A successful outcome was defined as a reduction in mean prednisone requirements of 7 mg daily compared to baseline requirements, during active treatment. RESULTS: Two patients were required to be withdrawn owing to methotrexate-related adverse effects. The mean prednisone dose for patients who completed the study was 14.4 mg per day (95% CI; 13.6, 15.1) during active treatment, and 12.9 mg per day (95% CI: 12.2, 13.6) during placebo treatment (NS). Only one patient reduced his individual dose requirements by more than 7 mg per day, whereas in three patients prednisone requirements actually increased during active treatment. There were no significant differences in symptom scores, pulmonary function data, and exacerbations between active and placebo treatments. CONCLUSION: No significant steroid-sparing effect was obtained using low dose methotrexate in this study. This negative outcome may be attributable to the small population of patients studied, low baseline FEV1, and the omission of a steroid minimisation run-in period. Our results highlight the importance of careful patient selection and a painstaking approach in the management of patients with steroid-dependent asthma. 相似文献
49.
S Sidney B Sternfeld SS Gidding DR Jacobs DE Bild A Oberman WL Haskell RS Crow JM Gardin 《Canadian Metallurgical Quarterly》1993,25(8):911-916
Symptom-limited, graded exercise treadmill testing was performed by 4,968 white and black adults, ages 18-30 yr, during the baseline examination for the Coronary Artery Risk Development in Young Adults (CARDIA) study. Compared with nonsmokers, the mean exercise test duration of smokers was 29-64 s shorter depending on race/gender group (all P < 0.001), but mean duration to heart rate 130 (beats.min-1) ranged from 20-50 s longer (P < 0.05). In each race/gender group, test duration to heart rates up to 150 was 15-35 s longer (P < 0.05) in smokers than in nonsmokers after adjustment for age, sum of skinfolds, hemoglobin, and physical activity score. The mean maximum heart rate was lower in smokers than in nonsmokers (difference ranging from 6.7 beats.min-1 in white men to 11.2 beats.min-1 lower in black women, P < 0.001), although maximum rating of perceived exertion was nearly identical in smokers and nonsmokers. Chronic smoking appears to blunt the heart rate response to exercise, so that exercise duration to submaximal heart rates is increased even though maximal performance is impaired. This may result from downloading of beta-receptors caused by smoking. Smoking status should be considered in the evaluation of physical fitness data utilizing submaximal test protocols, or else the fitness of smokers relative to nonsmokers is likely to be overestimated. 相似文献
50.
Warren J. Batchelor Trevor R. Finlayson Anita K. Gross 《Journal of the American Ceramic Society》1993,76(7):1895-1897
The measured plastic deformation of Mg-PSZ under stress contains contributions from both transformation and microcracking. A method is described to separate the contributions from transformation and microcracking for samples deformed in uniaxial tension. Such a separation enables the ratio of the longitudinal to transverse strains arising from the transformation to be estimated. The results are compared to the predictions of the shear–dilatation model of Chen and Reyes-Morel. Serious discrepancies are found between the experimental results and the predictions of the model and the possible reason for this is discussed. 相似文献