全文获取类型
收费全文 | 2865篇 |
免费 | 5篇 |
专业分类
电工技术 | 5篇 |
综合类 | 16篇 |
化学工业 | 38篇 |
金属工艺 | 3篇 |
机械仪表 | 13篇 |
建筑科学 | 16篇 |
矿业工程 | 9篇 |
能源动力 | 6篇 |
轻工业 | 9篇 |
水利工程 | 5篇 |
石油天然气 | 2篇 |
武器工业 | 2篇 |
无线电 | 3篇 |
一般工业技术 | 70篇 |
冶金工业 | 2656篇 |
原子能技术 | 2篇 |
自动化技术 | 15篇 |
出版年
2024年 | 1篇 |
2015年 | 1篇 |
2014年 | 5篇 |
2013年 | 10篇 |
2012年 | 9篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 14篇 |
2008年 | 20篇 |
2007年 | 49篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 3篇 |
2003年 | 15篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 5篇 |
1999年 | 75篇 |
1998年 | 773篇 |
1997年 | 449篇 |
1996年 | 255篇 |
1995年 | 165篇 |
1994年 | 151篇 |
1993年 | 170篇 |
1992年 | 14篇 |
1991年 | 45篇 |
1990年 | 36篇 |
1989年 | 33篇 |
1988年 | 36篇 |
1987年 | 29篇 |
1986年 | 38篇 |
1985年 | 23篇 |
1984年 | 1篇 |
1983年 | 10篇 |
1982年 | 18篇 |
1981年 | 31篇 |
1980年 | 26篇 |
1979年 | 4篇 |
1978年 | 16篇 |
1977年 | 97篇 |
1976年 | 171篇 |
1975年 | 7篇 |
1974年 | 1篇 |
1959年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有2870条查询结果,搜索用时 15 毫秒
961.
GA Bocharov 《Canadian Metallurgical Quarterly》1998,192(3):283-308
Lymphocytic choriomeningitis virus (LCMV) infection in mice provides an example of an extraordinarily dynamic process with an extreme sensitivity of phenotype of infection to parameters of virus/host interaction. A mathematical model is developed to examine the dynamics of virus-specific cytotoxic T lymphocyte (CTL) response for LCMV infection in mice. The model, formulated by a system of nonlinear delay-differential equations, considers the interacting populations of viruses, precursor CTLs, terminally differentiated effector CTLs and total virus antigen load. Clonal elimination of virus-specific cytotoxic T cells in high-dose LCMV-Docile infection represents an example of the classical phenomenon--high zone tolerance. To describe both conventional and exhaustive CTL responses in the acute phase of LCMV-D infection two mechanisms are invoked: the high virus antigen load inhibition of T-cells proliferation via energy induction and the activation-induced cell death by apoptosis. Parameters of the model, characterizing the rates of virus and CTL production and elimination in spleen, are estimated by assimilating with the model data on the LCMV-D infection in C57BL/6 mice for low-, moderate- and high-dose infections. It is suggested that not only the clonal expansions have to be described in mathematical models as being virus regulated but also the later phases of primary immune response. Down-regulation of the primary CTL response is controlled by a network of mechanisms inducing anergy and apoptosis in activated T cells. The model is used to investigate the effect of variations in virus and CTL response parameters on LCMV infection outcome and suggest predictions for experimental studies, in particular the phenotype of LCMV-WE infection in C57BL/6 as a function of initial virus doses. 相似文献
962.
963.
964.
CG Maloney WA Kutchera KH Albertine TM McIntyre SM Prescott GA Zimmerman 《Canadian Metallurgical Quarterly》1998,160(3):1402-1410
The synthesis of prostanoids is regulated by cyclooxygenases (prostaglandin H synthases), which catalyze the conversion of arachidonic acid to PGH2. Cyclooxygenases are the target of aspirin and other nonsteroidal anti-inflammatory agents. In this study, we found that human polymorphonuclear leukocytes (PMNs) express the inducible isoform of cyclooxygenase, COX-2, when stimulated by LPS whereas the protein was not detectable in freshly isolated human PMNs. We also found by immunohistochemical analysis that COX-2 is expressed in PMNs in inflamed human tissues. COX-2 was induced in a time- and concentration-dependent fashion when isolated human PMNs were exposed to LPS; COX-2 was also induced, or its expression was increased, by TNF-alpha, IL-1, and IL-8. Expression of COX-2 in stimulated PMNs was paralleled by secretion of PGE2. The release of PGE2 was blocked by a selective nonsteroidal inhibitor of COX-2, indicating that the enzyme is responsible for the prostanoids produced, and was inhibited by dexamethasone. The time course of LPS-induced COX-2 expression and other features were different in freshly isolated PMNs, monocytes, and macrophages, indicating that COX-2 expression is differentially regulated in myeloid cells of different lineages and degrees of maturation. Consistent with this, IL-4 and IL-10, which suppressed LPS-induced COX-2 expression in monocytes, had little effect on this response by PMNs. These experiments demonstrate that PMNs express COX-2 when appropriately stimulated. Thus, they may actively influence the eicosanoid composition of the acute inflammatory milieu. 相似文献
965.
966.
967.
A Luchner JC Burnett M Jougasaki HW Hense GA Riegger H Schunkert 《Canadian Metallurgical Quarterly》1998,32(7):1839-1844
OBJECTIVES: The present retrospective analysis of data derived from a population-based study examined the relationship between intake of beta-receptor antagonists and plasma concentrations of the cardiac natriuretic peptides and their second messenger. BACKGROUND: Beta-receptor antagonists are widely used for treatment of cardiovascular disease. In addition to direct effects on heart rate and cardiac contractility, recent evidence suggests that beta-receptor antagonists may also modulate the cross talk between the sympathetic nervous system and the cardiac natriuretic peptide system. METHODS: Plasma concentrations of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and their second messenger cyclic guanosine monophosphate (cGMP) were assessed in addition to anthropometric, hemodynamic and echocardiographic parameters in a population-based sample (n = 672), of which 80 subjects used beta-receptor antagonists. RESULTS: Compared to subjects without medication, subjects receiving beta-receptor antagonists were characterized by substantially elevated ANP, BNP and cGMP plasma concentrations (plus 32%, 89% and 18%, respectively, p < 0.01 each). Analysis of subgroups revealed that this effect was highly consistent and present even in the absence of hypertension, left atrial enlargement, left ventricular hypertrophy or left ventricular dysfunction. The most prominent increase was observed in a subgroup with increased left ventricular mass index. By multivariate analysis, a statistically significant and independent association between beta-receptor antagonism and ANP, BNP and cGMP concentrations was confirmed. Such an association could not be demonstrated for other antihypertensive agents such as angiotensin-converting enzyme inhibitors or diuretics. CONCLUSIONS: Beta-receptor antagonists appear to augment plasma ANP, BNP and cGMP concentrations. The current observation suggests an important contribution of the cardiac natriuretic peptide system to the therapeutic mechanism of beta-receptor antagonists. 相似文献
968.
Agonist-induced phosphorylation of an epitope-tagged prostacyclin receptor (HAhIP) is mediated primarily by PKC (Smyth, E. M., Nestor, P. V., and FitzGerald G. A. (1996) J. Biol. Chem. 271, 33698-33704). Based on the two consensus sites for protein kinase C (PKC) phosphorylation in the C-terminal region mutant HAhIPs were generated: S328A and S374A, in which an alanine replaced Ser-328 or Ser-374, respectively, S328A/S374A and C-DEL, in which the C-terminal portion was truncated at amino acid 313. Mutant receptors, stably expressed in HEK293 cells, coupled normally to cAMP production. Substantially less coupling to inositol phosphate was apparent with S328A, S328A/S374A, and C-DEL compared with HAhIP or S374A. Point mutants resolved by SDS-polyacrylamide gel electrophoresis as a broad band with a molecular mass of 44-62, indicating that the receptors are glycosylated, and immunofluoresence staining demonstrated their membrane localization. C-DEL demonstrated a substantial reduction in glycosylation; bands with molecular masses of 38-54 (glycosylated), 30, and 27 kDa (unglycosylated) were apparent. Although membrane localization was evident, cellular localization was more diffuse. HAhIP and S374A underwent iloprost- and PMA-induced phosphorylation (1 and 5 microM, respectively, for 10 min). S328A and S328A/S374A showed a markedly less iloprost- and no PMA-induced phosphorylation. Phosphorylation of C-DEL was completely absent with either agonist. Electrospray mass spectrometry indicated that a peptide, including Ser-328, was phosphorylated in vitro by PKC, whereas one including Ser-374 was not. Iloprost (1 microM, 10 min) desensitized HAhIP- and S374A-mediated adenylyl cyclase activation. A less impressive desensitization was evident with S328A and S328A/S374A, and no desensitization of C-DEL coupling was apparent. Exposure of transfected cells to iloprost (1 microM) for increasing times induced a rapid desensitization of subsequent iloprost-induced (1 microM) HAhIP and S374A adenylyl cyclase coupling. In contrast, no significant time-dependent desensitization of S328A, S328A/S374A, or C-DEL coupling was evident. These results indicate that PKC-dependent phosphorylation is of critical importance to homologous regulation of hIP. Ser-328 is a primary site for PKC phosphorylation of hIP. 相似文献
969.
970.
Identification and localization of insulin-like growth factor-binding protein (IGFBP) messenger RNAs in human hair follicle dermal papilla 总被引:1,自引:0,他引:1
1. The cardiac functional response to extracellular Ca2+ in isolated working hearts was evaluated in streptozotocin-induced diabetic rats treated or not treated with gliclazide. 2. Gliclazide treatment of diabetic rats allowed a partial recovery of the body weight decrease, but not of the hyperglycemia nor insulinopenia. 3. The cardiac mechanical response of diabetic rats was altered, especially at high Ca2+ concentration, and 6-week gliclazide treatment restored the dysfunction close to the control values. 4. The results suggest that gliclazide treatment restores the cardiac function of chronic diabetic rats partly through modulating the Ca2+ metabolism. 相似文献