全文获取类型
收费全文 | 1650篇 |
免费 | 2篇 |
专业分类
电工技术 | 5篇 |
综合类 | 2篇 |
化学工业 | 7篇 |
金属工艺 | 2篇 |
建筑科学 | 3篇 |
矿业工程 | 1篇 |
轻工业 | 8篇 |
水利工程 | 1篇 |
无线电 | 1篇 |
一般工业技术 | 3篇 |
冶金工业 | 1615篇 |
自动化技术 | 4篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 2篇 |
2006年 | 5篇 |
2005年 | 1篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2000年 | 1篇 |
1999年 | 53篇 |
1998年 | 502篇 |
1997年 | 300篇 |
1996年 | 193篇 |
1995年 | 105篇 |
1994年 | 70篇 |
1993年 | 95篇 |
1992年 | 11篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 18篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1978年 | 4篇 |
1977年 | 50篇 |
1976年 | 80篇 |
1975年 | 2篇 |
排序方式: 共有1652条查询结果,搜索用时 0 毫秒
51.
BM Gburek TA Kollmorgen J Qian SM D''Souza-Gburek MM Lieber RB Jenkins 《Canadian Metallurgical Quarterly》1997,157(1):223-227
We previously reported a HPLC assay method using fluorimetric detection for the simultaneous determination of urinary N2-(3-aminopropyl)biopterin (oncopterin, a natural pteridine newly found in urine from cancer patients), biopterin and neopterin. We now have observed that an unknown substance, which may be derived from methotrexate, in urine from a patient with stomach cancer interfered with the assay of oncopterin and demonstrated that oncopterin could be completely separated from the unidentified substance by HPLC using a Nucleosil 100-5SA strong cation-exchange column. Furthermore, oncopterin was not detectable by this HPLC-fluorimetric method in urine samples from patients with stomach cancer who were not treated with methotrexate. The content of urinary oncopterin from cancer patients is supposed to be very low, with less than 1 mumol/mol creatinine. The present results indicate that the peak found with elution from the C18 column was a methotrexate-derived compound and co-eluted with the analyte oncopterin. 相似文献
52.
53.
M Chaour P Théroux BM Gilfix L Campeau J Lespérance M Ghitescu F Gélinas BC Solymoss 《Canadian Metallurgical Quarterly》1997,8(11-12):683-688
BACKGROUND: Increased fasting serum insulin level not associated with hypoglycemia is considered to be a practical indicator of the insulin resistance syndrome, a frequent risk factor for atherosclerosis in industrialized countries. However, in most studies, insulin was measured by using antibodies which cross-react with proinsulin and 31/32, 32/33 split products of insulin. We re-examined the correlations between the insulin resistance syndrome and 'true' fasting serum insulin level. METHODS: We studied 242 post-menopausal women (age 63 +/- 8 years), a population in whom insulin resistance syndrome is particularly frequent. Serum insulin was measured by a recent specific microparticle immunoassay. RESULTS: There was a significant correlation between elevated 'true' fasting serum insulin level and various constituents of the insulin resistance syndrome, such as obesity, dyslipidemia (hypertriglyceridemia, increased apolipoprotein B and decreased high-density lipoprotein cholesterol and apolipoprotein A1 concentrations), increased serum glucose, uric acid levels, and plasminogen activator inhibitor type I concentration, as well as increased frequency of diabetes. There was also a correlation between insulin level and various manifestations of coronary artery disease: patients in the highest quartile of 'true' insulin level had significantly more entirely occluded coronary arteries than in the lowest one. Similarly, in the highest insulin quartile more patients had occluded arteries with lumen diameter stenoses greater than 50% (P < 0.05) and more of them had history of previous myocardial infarction approaching the level of significance (P = 0.0587) than in the lowest one. Most of these correlations were also noted in nondiabetic people. CONCLUSIONS: An increase of 'true' fasting serum insulin level is a useful practical index to identify patients with the insulin resistance syndrome exposed to increased risk of coronary artery disease. 相似文献
54.
55.
The first examples of the use of racemic vinylaziridines in a Pd-catalyzed dynamic kinetic asymmetric transformation have been examined. Optimization studies of the Pd-catalyzed addition of vinylaziridines to isocyanates revealed that the chiral ligand between trans-1,2-diaminocyclohexane and 2-diphenylphosphino-1-naphthoic acid is superior to that involving 2-diphenylphosphino benzoic acid. Surprisingly, high ee's required the use of an acid whose pKa was about 4.7 +/- 0.1 as a cocatalyst. Both acetic acid and hydroxybenzotriazole meet this requirement. Less electrophilic isocyanates (e.g., benzyl, p-methoxyphenyl) gave higher ee's than more electrophilic ones (phenyl or benzoyl). Both N-benzyl and N-arylaziridines react well to give good yields and ee's, whereas N-tosylaziridines gave lower ee's. A 1,1-disubstituted aziridine led to the formation of a tertiary C-N bond with ee's comparable to the formation of the secondary C-N bond. The products were easily reduced almost quantitatively to the sensitive imidazolidines which can be readily hydrolyzed to the vicinal diamines. The reactivity pattern is consistent with a Curtin-Hammett situation wherein the enantiodiscriminating event is the cyclization of a rapidly equilibrating dynamic pi-allyl palladium intermediate. 相似文献
56.
57.
58.
59.
BM Ruden 《Canadian Metallurgical Quarterly》1996,13(4):219-225
Human herpesvirus-6 (HHV6) is a lymphotropic virus genetically related to human cytomegalovirus (CMV) and for which two variants, A and B, have been distinguished. Human CMV is usually cultivated with human fibroblasts (HF). The lack of cell lines useful for HHV6 isolation and propagation led us to investigate whether HHV6 variants A and B could infect HFs as CMV does. Isolates of HHV6 variants A and B were used to infect MRC-5 HFs. HHV6 infection was detected by means of immunoperoxidase assay using three specific monoclonal antibodies. HHV6-specific antigens were detected in 88 and 38% of cases after infection with variants A and B, respectively. The highest number of HHV6-antigen-positive cells was obtained at 4-5 days p.i. The titre of HHV6 stocks was determined in parallel by immunoperoxidase assay on HFs and by observation of cytopathic effect using serial dilutions on peripheral blood mononuclear cells (PBMC). The number of infectious particles inducing the appearance of antigen-positive HF cells was consistently lower than the titre of virus stocks, expressed as TCID50. The amount of HF-associated HHV6 DNA was measured using limiting dilution PCR assay; it was significantly increased during 4-day infection in the case of variant A but not variant B. The yield of virus from infected HFs was demonstrated only for variant A by the serial propagation of virus from HFs to PBMCs and by the increase in cell-free HHV6 DNA in HF culture supernatant. Our results show that HHV6 can reproducibly infect HFs, albeit at a low level, and that HFs are more permissive to variant A than to variant B, as reported previously for PBMCs and human T-cell lines. 相似文献
60.
BM Gadzella 《Canadian Metallurgical Quarterly》1995,81(1):153-154
The subjects were 55 undergraduates enrolled in psychology classes and classified by their scores on the Human Information Processing Survey as having preferences of left hemisphericity (n = 17), right (n = 19), and integrated hemisphericity found between left- and right-hemisphericity groups with the left-hemisphericity group obtaining higher course grades. 相似文献