全文获取类型
收费全文 | 2235篇 |
免费 | 18篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 92篇 |
金属工艺 | 5篇 |
机械仪表 | 9篇 |
建筑科学 | 1篇 |
能源动力 | 16篇 |
轻工业 | 34篇 |
水利工程 | 1篇 |
石油天然气 | 2篇 |
无线电 | 22篇 |
一般工业技术 | 34篇 |
冶金工业 | 1992篇 |
原子能技术 | 3篇 |
自动化技术 | 42篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 5篇 |
2013年 | 19篇 |
2012年 | 17篇 |
2011年 | 28篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 11篇 |
2007年 | 21篇 |
2006年 | 6篇 |
2005年 | 10篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 59篇 |
1998年 | 589篇 |
1997年 | 338篇 |
1996年 | 202篇 |
1995年 | 122篇 |
1994年 | 120篇 |
1993年 | 112篇 |
1992年 | 25篇 |
1991年 | 39篇 |
1990年 | 28篇 |
1989年 | 44篇 |
1988年 | 40篇 |
1987年 | 25篇 |
1986年 | 28篇 |
1985年 | 20篇 |
1984年 | 2篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 55篇 |
1976年 | 122篇 |
1975年 | 2篇 |
排序方式: 共有2255条查询结果,搜索用时 15 毫秒
991.
JC Coelho M Wajner MG Burin CR Vargas R Giugliani 《Canadian Metallurgical Quarterly》1997,156(8):650-654
The number of diagnosed inborn errors of metabolism (IEM) is growing constantly due to the improvement and widespread availability of analytical techniques. In 1982, a laboratory for the detection of IEM was set up in Porto Alegre, Brazil, and became a national reference centre for the diagnosis of these disorders. Ten thousand patients with signs and symptoms suggestive of IEM were investigated in our laboratory from 1982 to 1995 using specific protocols which included tests for the detection of glucosaminoglycans (GAGS), amino acids, sugars, oligosaccharides, sialyloligosaccharides, organic acids, as well as various metabolite. The biochemical investigation was completed in 9,901 patients and an IEM was detected in 647 cases (6.5%). Groups of IEM of higher incidence in our sample were lysosomal storage disorders (59.8%) and aminoacidopathies (21.2%). The disorders most frequently diagnosed were classical phenylketonuria, GM1 gangliosidosis, mucopolysaccharidosis type I, mucopolysaccharidosis type VI and metachromatic leukodystrophy. CONCLUSION: This study shows that the establishment of reference centres for the investigation of rare genetic diseases is a suitable approach to the study of IEM in developing countries such as Brazil. 相似文献
992.
MJ Hohol CR Guttmann J Orav GA Mackin R Kikinis SJ Khoury FA Jolesz HL Weiner 《Canadian Metallurgical Quarterly》1997,54(8):1018-1025
OBJECTIVE: To assess the correlation between cognitive dysfunction and disease burden in multiple sclerosis (MS) during a 1-year period. DESIGN: The Brief, Repeatable Battery of Neuropsychological Tests in Multiple Sclerosis was performed at entrance and 1 year. Patients underwent at least 20 proton density (range, 20-24) and T2-weighted axial magnetic resonance imaging (MRI) brain scans except for stable patients who were scanned monthly. Magnetic resonance imaging was evaluated using computer-automated, 3-dimensional volumetric analysis. SETTING: A research clinic of a university hospital. PATIENTS: Forty-four patients with MS of the following disease categories: relapsing-remitting (14), relapsing-remitting progressive (12), chronic progressive (13), and stable (5). MAIN OUTCOME MEASURES: The relationships between scores on the Brief, Repeatable Battery of Neuropsychological Tests in Multiple Sclerosis and 2 MRI measures (total lesion volume and brain to intracranial cavity volume ratio) were assessed using linear regression. These MRI measures were also compared with cognitive status at 1 year using analysis of variance. RESULTS: Overall, there was no decline in mean cognitive test performance during 1 year. Significant correlations were found between baseline neuropsychological test scores of nonverbal memory, information-processing speed, and attention and both MRI measures. Patients with chronic progressive MS demonstrated the strongest correlations. At 1 year, change in information-processing speed and attention correlated with change in total lesion volume. The mean increase in total lesion volume was 5.7 mL for 4 patients whose cognitive status worsened compared with 0.4 mL for 19 patients who improved and 0.5 mL for 21 patients who remained stable. CONCLUSIONS: During a 1-year period mean cognitive performance did not worsen. Automated volumetric MRI measures of total lesion volume and brain to intracranial cavity volume ratio correlated with neuropsychological performance, especially in patients with chronic progressive MS. Worsening MRI lesion burden correlated with cognitive decline. 相似文献
993.
994.
Mass spectrometry of fragments produced by limited proteolytic digestion of pro-enkephalin was used to locate the disulfide bridges in synenkephalin (pro-enkephalin 1-73), a domain which contains sorting information for targeting the pro-neuropeptide to the granules of the regulated secretory pathway in neuroendocrine cells. Mass spectrometric analysis was optimized by using chemicals that gave low interference with the ionization and desorption processes, and computer software which simplified the identification of all possible disulfide-linked peptide fragments. Three disulfide bridges between Cys2-Cys24, Cys6-Cys28, and Cys9-Cys41 were identified. Protein conformational prediction of synenkephalin1-42 shows beta-turns which facilitate the formation of these disulfide bonds. 相似文献
995.
JI García Alonso M Gutiérrez Camblor M Montes Bayón JM Marchante-Gayón A Sanz-Medel 《Canadian Metallurgical Quarterly》1997,32(5):556-564
For the analysis of biological and environmental materials by inductively coupled plasma mass spectrometry (ICP-MS), several quantification procedures can be used depending on the precision and accuracy required. Semi-quantitative methods based on the molar response curve were compared with conventional external calibration and standard additions for the analysis of waters and sewage sludges. For the analysis of biological materials, where higher quality data were required, isotope dilution analysis using enriched isotopes was applied. It was observed that the molar sensitivity for different elements in ICP-MS was a simple function of the mass of the isotopes measured after normalization for ionization efficiency which could be fitted to a third-order polynomial equation. Element ionization adjustments for the third-order polynomial, using the Saha equation, allowed the calculation of the plasma ionization temperature and electron density. For the determination of trace metals in waters and sewage sludges, the samples were spiked with different internal standards, ionization corrections were performed and the results obtained agreed with those obtained by external calibration and standard addition within a factor of 2 but, on average, the agreement was within 20%. The determination of molybdenum in biological reference materials was performed by isotope dilution analysis taking into account possible sources of error in the measurements by ICP-MS such as mass discrimination, detector dead time, isobaric interferences and random error propagation. 相似文献
996.
997.
F Courtin AL Craigmill SE Wetzlich CR Gustafson TS Arndt 《Canadian Metallurgical Quarterly》1997,20(5):368-373
Twelve (12) lactating dairy goats (46-71 kg body wt at study initiation) were divided into four treatment groups and dosed with ceftiofur sodium at 1.1 mg ceftiofur free acid equivalents (CFAE)/kg or 2.2 CFAE/kg using a complete two route (intravenous, i.v.; intramuscular, i.m.), two-period crossover design, with a 2-week washout between injections. After another 2-week washout period, the goats were dosed with ceftiofur sodium i.m. for 5 consecutive days at either 1.1 or 2.2 mg CFAE/kg. The goats from the 2.2 mg/kg multiple dose group were dried off and the i.v. kinetic study repeated. After all injections, blood samples were obtained serially for determination of combined serum concentrations of ceftiofur and metabolites. After intravenous doses of 1.1 and 2.2 mg/kg, the harmonic means of the terminal phase half-lives were 171.8 and 233 min, respectively, for lactating does. The harmonic mean of the terminal phase half-life after an i.v. dose of 2.2 mg/kg in non-lactating does was 254 min. The AUC0-infinity was significantly less and the clearance significantly greater during lactation. After i.m. doses of 1.1 and 2.2 mg/kg, the harmonic mean terminal phase half-lives were 163 and 156 min, respectively. The i.m. bioavailability of ceftiofur sodium in goats was 100%, and the AUC0-infinity was dose-proportional from 1.1-2.2 mg CFAE/kg body weight. After five daily i.m. doses of ceftiofur sodium at either 1.1 or 2.2 mg CFAE, there was minimal accumulation of drug in serum as assessed by Cmax, and serum concentrations were dose-proportional after the multiple dosing regimen. 相似文献
998.
B Singh P Merchant CR Walker M Kryworuchko F Diaz-Mitoma 《Canadian Metallurgical Quarterly》1996,39(6):976-979
BACKGROUND: The occurrence of hepatocellular neoplasms is frequently reported in young females. The role of oral contraceptives in the development of these tumors is considered. METHODS: A 14-cm tumor was diagnosed in a 24-year-old female who had been taking the contraceptive pill for the last 3 years. Numerous blocks of this lesion were histologically and immunohistochemically analyzed. Some fragments of the lesion were snap-frozen in order to search for sex hormonal receptors and hepatitis B and C virus. RESULTS: On histological examination, the tumor was found to be a hepatocellular, multilobular adenoma with small foci of hepatocellular carcinoma. Neither hepatitis B virus nor hepatitis C virus was found in serum or in the tumor. Nuclear estrogen receptors and progesterone receptors were detected by immunohistochemical analysis in both the adenoma and the carcinoma, but only progesterone receptors were detected by a radio-ligand binding assay in the tumor. CONCLUSION: This finding suggests that the contraceptive pill may stimulate the growth of hepatocellular, multilobular adenomas through the binding of hormonal compounds to their specific receptors within tumoral cells. 相似文献
999.
MA Jenike HC Breiter L Baer DN Kennedy CR Savage MJ Olivares RL O'Sullivan DM Shera SL Rauch N Keuthen BR Rosen VS Caviness PA Filipek 《Canadian Metallurgical Quarterly》1996,53(7):625-632
BACKGROUND: A previous pilot study of only posterior brain regions found lower white-matter volume in patients with obsessive-compulsive disorder than in normal control subjects. We used new cohorts of patients and matched normal control subjects to study whole-brain volume differences between these groups with magnetic resonance imaging-based morphometry. METHODS: Ten female patients with obsessive-compulsive disorder and 10 female control subjects, matched for handedness, age, weight, education, and verbal IQ, underwent magnetic resonance imaging with a 3-dimensional volumetric protocol. Scans were blindly normalized and segmented by means of well-characterized semiautomated intensity contour mapping and differential intensity contour algorithms. Brain structures investigated included the cerebral hemispheres, cerebral cortex, diencephalon, caudate, putamen, globus pallidus, hippocampus amygdala, third and fourth ventricles, corpus callosum, operculum, cerebellum, and brain stem. Anterior to posterior neocortical regions, including precallosum, anterior pericallosum, posterior pericallosum, and retrocallosum, with adjacent white matter were also measured. Volumes found different between groups were correlated with Yale-Brown Obsessive Compulsive Scale score and Rey-Osterieth Complex Figure Test measures. RESULTS: Confirming results of our earlier pilot study and expanding the findings to the whole brain, patients with obsessive-compulsive disorder had significantly less total white matter but, in addition, significantly greater total cortex and opercular volumes. Severity of obsessive-compulsive disorder and nonverbal immediate memory correlated with opercular volume. CONCLUSIONS: Replication of volumetric white-matter differences suggests a widely distributed structural brain abnormality in obsessive-compulsive disorder. Whereas determining the etiogenesis may require research at a microscopic level, understanding its functional significance can be further explored via functional neuroimaging and neuropsychological studies. 相似文献
1000.