全文获取类型
收费全文 | 2294篇 |
免费 | 12篇 |
专业分类
综合类 | 1篇 |
化学工业 | 20篇 |
金属工艺 | 1篇 |
机械仪表 | 3篇 |
建筑科学 | 2篇 |
能源动力 | 1篇 |
轻工业 | 14篇 |
水利工程 | 10篇 |
石油天然气 | 1篇 |
无线电 | 8篇 |
一般工业技术 | 18篇 |
冶金工业 | 2216篇 |
自动化技术 | 11篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 3篇 |
2012年 | 4篇 |
2011年 | 4篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 1篇 |
2004年 | 4篇 |
2003年 | 9篇 |
1999年 | 79篇 |
1998年 | 660篇 |
1997年 | 403篇 |
1996年 | 229篇 |
1995年 | 141篇 |
1994年 | 119篇 |
1993年 | 125篇 |
1992年 | 34篇 |
1991年 | 45篇 |
1990年 | 29篇 |
1989年 | 41篇 |
1988年 | 29篇 |
1987年 | 32篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 2篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 1篇 |
1978年 | 9篇 |
1977年 | 60篇 |
1976年 | 111篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1965年 | 1篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2306条查询结果,搜索用时 15 毫秒
31.
32.
Membrane fusion mediated by interaction of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein with the human CD4 molecule generally requires that the CD4 be expressed on a human cell. The failure of murine or simian cells expressing human CD4 to form syncytia upon mixing with cells expressing envelope glycoprotein could not be corrected by expression of both molecules at extremely high surface levels using vaccinia virus expression vectors. Video fluorescence microscopic analysis of fluorescent dye transfer between fusing cells indicated that the block occurred at the level of membrane fusion between individual pairs of cells. To gain insight into the basis for this fusion block, we tested the ability of fluorescent probe cells expressing envelope glycoprotein to fuse with transient animal x human hybrid giant cells expressing human CD4. The hybrid giant cells were generated either by low-pH-induced fusion of vaccinia-infected cells or by CD4/HIV-1 envelope glycoprotein-mediated cell fusion. We observed that envelope glycoprotein-expressing probe cells efficiently fused with CD4-expressing animal x human hybrid giant cells, independent of whether the CD4 was originally expressed on the animal or on the human cell. Fusion did not occur with CD4-expressing giant cells derived from animal cells alone. These results indicate that the fusion block is not due to dominant inhibitory components in the animal cell. Rather, they suggest that human cells contain an additional component(s) which, when transferred to the CD4-bearing animal cell, confers the ability to undergo membrane fusion mediated by the HIV-1 envelope glycoprotein. 相似文献
33.
JM Chen ML Barr A Chadburn G Frizzera FA Schenkel RR Sciacca DS Reison LJ Addonizio EA Rose DM Knowles 《Canadian Metallurgical Quarterly》1993,56(3):527-538
We conducted a retrospective study of 516 cardiac recipients who underwent transplantation between April 1983 and April 1992, 19 of whom had development of post-transplantation lymphoproliferative disorders (PTLDs). These 19 patients presented with involvement of lung (5), gastrointestinal tract (5), disseminated disease (6), and adenoids and lymph nodes (3). B-cell proliferations ranging from an atypical hyperplasia to malignant lymphoma developed in 18 patients, and mixed cellularity Hodgkin's disease developed in 1 patient. The 19 patients with PTLD displayed a predominance of both women and cardiomyopathy as the indication for transplantation when compared with two separate control populations. No correlation was found between demographic criteria analyzed and (1) early versus late diagnosis of PTLD after transplantation, (2) the site of PTLD involvement, or (3) the histopathologic category of the PTLD lesion. Patients with gastrointestinal tract and lung PTLD involvement enjoyed an improved survival after both transplantation and PTLD diagnosis when compared with patients with PTLD involvement of all other extranodal sites. We report a high incidence of PTLD involving the lung and gastrointestinal tract in our cohort study. These sites of involvement responded better to a reduction in immunosuppression than did the other extranodal sites of involvement. 相似文献
34.
OBJECTIVE: To investigate the effect of amniotic fluid on prostaglandin synthesis and metabolism in the fetal membranes. DESIGN: A cell culture study of amnion and chorion obtained at elective cesarean section incubated with amniotic fluid collected following either spontaneous labor and delivery, or elective cesarean section. SUBJECTS: Forty-eight pregnant women at 3742 weeks gestation: 24 in spontaneous labor and 24 delivered by elective cesarean section. RESULTS: Significantly more PGE2 and PGF2alpha were produced by amnion and chorion treated with amniotic fluid from spontaneous labor compared with elective cesarean section. Spontaneous labor amniotic fluid favors PGE2 and PGFM production by amnion and chorion respectively; while elective section fluid stimulates PGE2 synthesis by both tissues (reflected as PGEM in chorion). Amniotic fluid, from either spontaneous labor or elective section, had no effect on the metabolism of exogenous PGE2 or PGF2alpha by chorion cells. CONCLUSION: Spontaneous labor is associated with the presence of a substance in amniotic fluid which facilitates prostaglandin synthesis in the fetal membranes, but which is without effect on prostaglandin metabolism. 相似文献
35.
JL Cohen J Cheirif DS Segar LD Gillam JS Gottdiener E Hausnerova DE Bruns 《Canadian Metallurgical Quarterly》1998,32(3):746-752
We investigated whether changes in iron metabolism and the transferrin receptor (TRF-R) expression were involved in the antileukaemic effects of arabinoside cytosine (ara-C). Treatment with 100 nM ara-C for 48h reduced thymidine uptake and increased the surface expression of the TRF-R on leukaemic blasts derived from 13/16 (81%) patients and on the HL-60 and U-937 cell lines. Whereas intracellular non-haem iron was strongly depleted 24 h after ara-C addition, TRF-R up-regulation and recovery of intracellular non-haem iron concentration occurred together after a longer exposure of the cultured cells to the drug. Since iron is an essential regulator of cell proliferation we have evaluated the effects of the combination between ara-C and the iron chelator desferioxamine (DSF) on the growth of HL-60 and U-937 cells. We found that desferioxamine strongly potentiated the effects of ara-C on leukaemic cell growth inhibition and apoptosis. This is the first report of a positive interaction between ara-C and an iron chelator in terms of antileukaemic effects. 相似文献
36.
37.
A systematic investigation was undertaken to study the effects of varying concentrations of additives in the acetonitrile/water high performance liquid chromatography mobile phase, especially formic acid and ammonium formate, on the negative ion electrospray response of a carboxylic acid compound. The study showed that the response progressively decreased with increase in the formic acid concentration. While such a decrease in the response could be qualitatively explained by the decrease in the concentration of the ionized form of the carboxylic acid compound due to the lower pH of the mobile phase, the change in response was not as large as expected from the change of the concentration of the ionized form. The response also progressively decreased with increase in the ammonium formate concentration but the decrease cannot be explained by the change in the pH of the mobile phase. Although the best negative ion electrospray response was obtained with a water/acetonitrile mobile phase that contained no additives at all, the retention time of the analyte was not found to be adequately reproducible on repeated injections. Thus, this mobile phase was deemed unacceptable for practical, routine use. Comparing formic acid against ammonium formate, the former was preferable since it caused a smaller attenuation of the negative ion response. Equally important was the fact that addition of formic acid had the desirable effect of maintaining a reasonably high capacity factor (k') for the analyte even at a relatively high acetonitrile concentration. A concentration of 1 mM formic acid in the mobile phase was large enough to achieve the reproducible elongated retention time for the analyte, with a loss in the analyte response of about 60% only. It should be noted that the sensitivity achieved with the 1 mM formic acid mobile phase, in which the carboxylic acid is expected to be about 10% in the ionized form, is about 9 times better than the sensitivity achieved in the 1 mM ammonium formate mobile phase, in which the carboxylic acid is expected to be about 99% in the ionized form. 相似文献
38.
A novel amperometric HPLC detection method for the cyanobacterial (blue-green algal) peptide toxins microcystin-LR, -YR and -RR was developed. Purified microcystins and cyanobacterial extracts were chromatographed using an internal surface reversed-phase column with acetate- and phosphate-based mobile phase systems. Electrochemical oxidation reactions at 1.20 V vs. Ag/AgCl (glassy carbon working electrode) were show to originate in arginine and tyrosine residues of microcystins. 相似文献
39.
40.
WR Bishai NM Graham S Harrington DS Pope N Hooper J Astemborski L Sheely D Vlahov GE Glass RE Chaisson 《Canadian Metallurgical Quarterly》1998,280(19):1679-1684
Stevioside is a sweet-tasting glycoside, composed of stevia, a diterpenic carboxylic alcohol with three glucose molecules, mainly used as a substitute for non-alcoholic sweetener. It has previously been shown to reduce blood pressure in studies in animals and human. The effect of intravenous stevioside on the blood pressure was studied in spontaneously hypertensive rats (SHR). The hypotensive effect on both systolic and diastolic blood pressure was dose-dependent for intravenous doses of 50, 100 and 200 mg/kg in conscious SHR. The maximum reductions in systolic and diastolic blood pressure were 31.4 +/- 4.2% and 40.8 +/- 5.6% (mean +/- SEM) respectively and the hypotensive effect lasted for more than 60 min with a dose of 200 mg/kg. Serum dopamine, norepinephrine and epinephrine levels were not changed significantly 60 min after intravenous injection of stevioside 100 mg/kg in anesthetized SHR. The present data show that stevioside given intravenously to conscious SHR was effective in blood pressure reduction and there was no change in serum catecholamines in anaesthetized animals with this natural compound. 相似文献