全文获取类型
收费全文 | 1352篇 |
免费 | 2篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 15篇 |
机械仪表 | 9篇 |
建筑科学 | 22篇 |
能源动力 | 9篇 |
轻工业 | 14篇 |
水利工程 | 9篇 |
石油天然气 | 1篇 |
无线电 | 38篇 |
一般工业技术 | 35篇 |
冶金工业 | 1008篇 |
原子能技术 | 5篇 |
自动化技术 | 188篇 |
出版年
2021年 | 4篇 |
2020年 | 2篇 |
2016年 | 6篇 |
2014年 | 26篇 |
2013年 | 5篇 |
2012年 | 3篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 4篇 |
2008年 | 5篇 |
2007年 | 7篇 |
2006年 | 15篇 |
2005年 | 7篇 |
2004年 | 10篇 |
2003年 | 6篇 |
2002年 | 18篇 |
2001年 | 6篇 |
2000年 | 11篇 |
1999年 | 36篇 |
1998年 | 310篇 |
1997年 | 167篇 |
1996年 | 95篇 |
1995年 | 67篇 |
1994年 | 41篇 |
1993年 | 55篇 |
1992年 | 15篇 |
1991年 | 23篇 |
1990年 | 17篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 22篇 |
1982年 | 28篇 |
1981年 | 26篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1977年 | 43篇 |
1976年 | 105篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1966年 | 1篇 |
1964年 | 2篇 |
1962年 | 1篇 |
1955年 | 2篇 |
1954年 | 1篇 |
1925年 | 2篇 |
排序方式: 共有1354条查询结果,搜索用时 281 毫秒
131.
132.
Low concentrations of ADP are shown to increase the rate of phosphoenzyme formation of E. coli succinyl-coenzyme A (CoA) synthetase (SCS) without altering the fraction of phosphorylated enzyme. This is true when either ATP or succinyl-CoA and Pi are used to phosphorylate the enzyme. The stimulatory effect of ADP is not altered by sample dilution, is retained upon partial purification of the enzyme, and reflects the binding of ADP to a site other than the catalytic site. GDP also alters the phosphorylation of the E. coli SCS but does so primarily by enhancing the level of the phosphoenzyme and only when ATP is used as the phosphate donor. GDP appears to function by neutralizing the action of a specific inhibitory protein. This inhibitor of SCS allows for interconversion of succinate and succinyl-CoA in a manner dissociated from changes in ATP-ADP metabolism. These previously unidentified and varied mechanisms by which SCS is regulated focus attention on this enzyme as an important control point in determining the cell's potential to meet its metabolic demands. 相似文献
133.
134.
JE Stern AL Givan JL Gonzalez DM Harper HD White CR Wira 《Canadian Metallurgical Quarterly》1998,91(6):987-992
OBJECTIVE: To quantify the numbers of leukocytes in the normal cervix and relate these numbers to the diagnosis of cervicitis. METHODS: Isolated cell suspensions were prepared from cervical tissue recovered at hysterectomy from 37 women who had no obvious cervical disease. The percentages of CD45+ cells (leukocytes) in these preparations were determined using immunofluorescence-based flow cytometric analysis. These percentages were compared with the pathologist's assessment of cervicitis. RESULTS: Leukocytes were present in all cervical samples tested. For endocervical samples, the mean (+/- standard error of the mean [SEM]) percentage of CD45+ cells was 12.4 +/- 1.9% of cells in patients with a diagnosis of cervicitis (n = 16) and 9.1 +/- 1.1% in patients without cervicitis (n = 17). For ectocervical samples, the mean (+/- SEM) percentage was 14.8 +/- 3.0% in those with cervicitis (n = 16) and 9.5 +/- 1.6% in those without cervicitis (n = 19). The differences between samples from patients with cervicitis and those without cervicitis were not statistically significant at the .05 level. Intra- and interassay variabilities were 5.7 +/- 1.2% and 7.3 +/- 1.6%, respectively. CONCLUSION: Our study demonstrates there is a resident population of leukocytes in the cervix. Leukocyte number did not relate clearly and consistently to the diagnosis of cervicitis made by the pathologist. We suggest that the resident population of leukocytes, in the absence of other indicators of infection, may confuse determinations of cervicitis. 相似文献
135.
136.
137.
HD Schr?der 《Canadian Metallurgical Quarterly》1998,111(5):173-174
Antibodies to Coxiella burnetii were recorded from approximately 13% of 469 ungulates which had been examined by means of micro-CFT (complement fixation test). Particular reference is made to a Q-fever situation in a musk ox herd. The results obtained from these investigations are likely to support the conclusion that latent Q-fever infection may be expected to occur in ungulates and to grow manifest in stress situations. 相似文献
138.
Human calcitonin (hCT) has been reported to have a less hypocalcemizing effect on rats and to have a lower binding affinity for the receptor of mouse osteoclasts than salmon CT(sCT). In this study we comparatively examined the effect of hCT and sCT on osteoclastic bone-resorbing activity of unfractionated cells obtained from human giant cell tumor of bone and from rabbit and mouse long bones. We found that hCT had the same inhibitory effect as sCT on the bone-resorbing activity of human and rabbit osteoclastic cells, but a different one on that of mouse cells. These results indicate that the activity of drugs should be assayed using human cells if possible. 相似文献
139.
The purpose of this study was to determine the effect of intracerebroventricular (i.c.v.) injections of a synthetic, opioid-related hexapeptide, growth-hormone-releasing peptide-6 (GHRP-6), on stimulation of eating by rats and to correlate this aspect of feeding behavior with the peripheral plasma growth hormone (GH) response to the administered peptide. GHRP-6 dissolved in 5 microL of saline was injected into the lateral ventricles of sated, adult, male, Sprague-Dawley rats in doses from 0 pmol (saline only) to 1000 pmol. For 1 hour after injection, the occurrence of eating was noted, and specimens of arterial blood were collected at 0, 15, 30, and 60 minutes. The plasma was assayed for GH. A nearly linear, statistically significant (p < 0.01) dose-response relationship between the dose of GHRP-6 and the incidence of eating was noted. The mean change from baseline of plasma GH during the 60 minutes after injection was not dose-related (p > 0.2, p > 0.1, and p > 0.1 at 15, 30, and 60 minutes, respectively). We conclude that GHRP-6 given intracerebroventricularly to sated, adult, male, Sprague-Dawley rats stimulates eating and suggest that it does so by some mechanism that is independent of its GH-releasing property. 相似文献
140.
P Verdier-Pinard JY Lai HD Yoo J Yu B Marquez DG Nagle M Nambu JD White JR Falck WH Gerwick BW Day E Hamel 《Canadian Metallurgical Quarterly》1998,53(1):62-76
Originally purified as a major lipid component of a strain of the cyanobacterium Lyngbya majuscula isolated in Cura?ao, curacin A is a potent inhibitor of cell growth and mitosis, binding rapidly and tightly at the colchicine site of tubulin. Because its molecular structure differs so greatly from that of colchicine and other colchicine site inhibitors, we prepared a series of curacin A analogs to determine the important structural features of the molecule. These modifications include reduction and E-to-Z transitions of the olefinic bonds in the 14-carbon side chain of the molecule; disruption of and configurational changes in the cyclopropyl moiety; disruption, oxidation, and configurational reversal in the thiazoline moiety; configurational reversal and substituent modifications at C13; and demethylation at C10. Inhibitory effects on tubulin assembly, the binding of colchicine to tubulin, and the growth of MCF-7 human breast carcinoma cells were examined. The most important portions of curacin A required for its interaction with tubulin seem to be the thiazoline ring and the side chain at least through C4, the portion of the side chain including the C9-C10 olefinic bond, and the C10 methyl group. Only two modifications totally eliminated the tubulin-drug interaction. The inactive compounds were a segment containing most of the side chain, including its two substituents, and analogs in which the methyl group at the C13 oxygen atom was replaced by a benzoate residue. Antiproliferative activity comparable with that observed with curacin A was only reproduced in compounds that were potent inhibitors of the binding of colchicine to tubulin. Molecular modeling and quantitative structure-activity relationship studies demonstrated that most active analogs overlapped extensively with curacin A but failed to provide an explanation for the apparent structural analogy between curacin A and colchicine. 相似文献