全文获取类型
收费全文 | 1111篇 |
免费 | 1篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 28篇 |
金属工艺 | 3篇 |
机械仪表 | 2篇 |
建筑科学 | 2篇 |
能源动力 | 1篇 |
轻工业 | 2篇 |
水利工程 | 1篇 |
无线电 | 31篇 |
一般工业技术 | 13篇 |
冶金工业 | 1000篇 |
原子能技术 | 6篇 |
自动化技术 | 21篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2014年 | 6篇 |
2013年 | 5篇 |
2012年 | 4篇 |
2011年 | 4篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 10篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 2篇 |
2003年 | 7篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 32篇 |
1998年 | 280篇 |
1997年 | 163篇 |
1996年 | 113篇 |
1995年 | 58篇 |
1994年 | 70篇 |
1993年 | 56篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 6篇 |
1989年 | 20篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 33篇 |
1976年 | 74篇 |
1975年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有1112条查询结果,搜索用时 15 毫秒
81.
The purpose of this study was to compare the effect, both in vitro and in vivo, of cefepime with those of four other cephalosporins, namely ceftriaxone, cefotaxime, cefuroxime and cephalothin, against penicillin-resistant pneumococci. One hundred pneumococcal strains, 31 penicillin-susceptible, 30 penicillin-intermediate-resistant and 39 penicillin-resistant pneumococci, were used in MIC studies. Time-kill experiments were carried out for four strains. In the mouse peritonitis model, the dose that gave protection to 50% of mice challenged with a lethal dose of pneumococci (ED50) was determined for three pneumococci and five cephalosporins. The MICs of all five cephalosporins and penicillin correlated significantly with each other. In vitro, the most potent cephalosporins against pneumococci were cefotaxime, ceftriaxone and cefepime, followed by cefuroxime and cephalothin. In time-kill experiments, carried out for four pneumococci, no differences were found in the killing effect of these five cephalosporins in relation to MICs. In the mouse peritonitis model, there was no significant correlation between log(MIC) and log(ED50) for the five cephalosporins against three pneumococci (Spearman's rho = 0.39, P = 0.16). However, if the values for cefepime against the three pneumococci were excluded, there was a significant correlation for the remaining four cephalosporins (Spearman's rho = 0.62, P = 0.04). For all three pneumococci, the ED50s of cefepime were lower than expected from the MICs. It was not possible to explain this beneficial difference in the effect of cefepime in terms of in-vitro bactericidal activities, serum protein binding or pharmacodynamic parameters. 相似文献
82.
Biological monitoring of cadmium exposure and renal effects in a population group residing in a polluted area in China 总被引:1,自引:0,他引:1
GF Nordberg T Jin Q Kong T Ye S Cai Z Wang F Zhuang X Wu 《Canadian Metallurgical Quarterly》1997,199(1-2):111-114
In an area of China, not previously studied in detail concerning cadmium pollution and possible adverse effects on the kidney of exposed populations, concentrations of cadmium in urine as an indicator of renal accumulation of cadmium was studied and related to indicators of renal dysfunction in order to examine if a relationship could be documented. Cadmium concentrations in urine were analysed by graphite furnace atomic absorption spectrometry and urinary beta-2 microglobulin (UBM) and albumin (UALB) were measured as indicators of renal dysfunction, Rice samples and urine samples were obtained from three areas in Zhejiang province, China, representing a highly exposed area, a medium exposed area and a control area, respectively. Cadmium concentrations in rice were 3.70, 0.51 and 0.072 mg/kg for the heavily, medium polluted areas and the control area, respectively. Cadmium concentrations in urine (geometric means) were 10.7, 1.62 and 0.40 micrograms/l in the high, medium and control areas respectively. There was a clear increase in UBM and UALB in the heavily exposed group in comparison to the control group and a slight increase in the medium exposed group. There was a statistically significant dose-response relationship between cadmium in urine and beta 2-microglobulin excretion in urine, which is similar to what has previously been reported in other countries. The findings constitute the first report concerning a dose-response relationship in this population group in Zhejiang province in China. 相似文献
83.
84.
RD Randall SY Lee JH Meyer GF Wittenberg DL Gruol 《Canadian Metallurgical Quarterly》1995,701(1-2):238-248
Effects of ethanol (22 mM) on the modulation of synaptic transmission and long-term potentiation (LTP) by the neurosteroid dehydroepiandrosterone sulfate (DHEAS; 10 microM) was examined in the in vitro rat hippocampal slice preparation. The synaptic responses were elicited by Schaffer collateral stimulation and recorded extracellularly in the somatic and dendritic regions of CA1 pyramidal neurons. LTP induction produced an increase (approximately 55% to 75%) in the amplitude of synaptic responses in ethanol and ethanol plus DHEAS (ethanol/DHEAS) treated slices. These increases were significantly smaller than the approximately 130% increase observed previously in slices treated with DHEAS, but were not significantly different from the approximately 82% increase observed in control slices. These results indicate that an ethanol/DHEAS interaction prevents the enhancement of LTP normally observed with DHEAS treatment of hippocampal slices. An ethanol/DHEAS interaction also altered DHEAS's effects on individual synaptic components of the synaptic response to Schaffer collateral stimulation. Ethanol applied before but not after DHEAS prevented DHEAS's enhancement of the NMDA receptor-mediated synaptic component. DHEAS's depression of the GABAA receptor-mediated synaptic component was also blocked by ethanol. Ethanol or DHEAS individually had no effect on the AMPA receptor-mediated synaptic component, but application of ethanol after DHEAS resulted in a small enhancement of this synaptic component, an effect that was not observed if ethanol was applied before DHEAS. These results show that ethanol and DHEAS interact, altering DHEAS's effects on synaptic transmission and LTP in the hippocampus. Such an interaction may be involved in ethanol's actions on the CNS and raises the possibility that ethanol and DHEAS may act via a common site or pathway. 相似文献
85.
GF Fries 《Canadian Metallurgical Quarterly》1995,73(6):1639-1650
The polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxins) are groups of compounds with similar chemical and toxicological properties. Carcinogenicity was considered the most serious toxic end point when setting previous regulatory policies, but recent concerns have focused on the possible endocrine-disrupting activities of the dioxins. Toxicity is related to the 2,3,7,8 pattern of chlorine substitution, a pattern that also leads to chemical and metabolic stability. Dioxins are practically insoluble in water and concentrate in lipids of biological systems, leading to low background concentrations in fat of the general human population. Major environmental sources of dioxins are emissions from industrial chlorination processes and combustion of materials containing chlorine. Inhalation and water have been ruled out as significant exposure pathways, which suggests that food is the primary source. Pathways of entry into food chains are atmospheric transport of emissions and their subsequent deposition on plants, soils, and water. The major food sources seem to be fat-containing animal products and some seafoods. This conclusion is based on evaluations of potential environmental pathways involving dioxins and related compounds. Generally, dioxins and other lipophilic compounds are not taken up and translocated by plants, so residues in foods and feeds derived from seeds should be negligible. Animals on high-roughage diets, or those that ingest contaminated soil, are the most likely to accumulate dioxin residues from the environment. The conclusion that animal products are a major source of human exposure requires verification by appropriate food sampling programs and animal metabolism studies. If it is desirable to reduce human exposure to dioxins via the food supply, reduction of sources would be a more effective strategy than changing agricultural practices and food consumption patterns. 相似文献
86.
DJ Quint GF Tuite JD Stern SE Doran SM Papadopoulos JE McGillicuddy CA Lundquist 《Canadian Metallurgical Quarterly》1997,4(11):742-752
RATIONALE AND OBJECTIVES: The authors evaluated a method for obtaining reproducible, reliable measurements from standard lumbar spine radiographs for determining the degree of spondylolisthesis, vertebral body height, intervertebral disk space height, disk space angle, and degree of vertebral body wedging. MATERIALS AND METHODS: Four to six easily defined points were identified on each vertebral body on anteroposterior and lateral plain radiographs of the lumbosacral spine of patients. From these points, the degree of spondylolisthesis, the vertebral body height, the intervertebral disk space height, the disk space angle, and the degree of vertebral body wedging were easily calculated by using well-known geometric relationships. This method requires the use of a personal computer and a standard spreadsheet program but does not require the use of any other specialized radiographic equipment, computer hardware, or custom software. RESULTS: Calculations of intra- and interobserver variability for the measurement of spondylolisthesis, disk space height, disk space angle, and vertebral body height measurement showed that the technique is extremely reproducible. CONCLUSION: This technique may prove useful in the prospective evaluation of potential candidates for lumbar spinal stenosis surgery. 相似文献
87.
88.
89.
A strategy to design potent antagonists of human coagulation factor VIIa (FVIIa) by linking two proteins that independently inhibit activity and bind at separate, nonoverlapping sites is presented. A bifunctional inhibitor (KDTF5), comprising a Kunitz-type domain engineered to inhibit the FVIIa active site and a soluble tissue factor (TF) variant that is defective as a cofactor for factor X (FX) activation, was developed from structure-based modeling of a ternary FVIIa-Kunitz domain-TF complex. KDTF5 inhibited FVIIa-dependent FX activation with a Ki* of 235 +/- 45 pM, a 193-fold and 398-fold increase in potency compared to the TF variant and Kunitz domain individually. Similarly, KDTF5 was a more potent anticoagulant in vitro compared to either inhibitory domain alone. The results demonstrate the harnessing of a macromolecular chelate effect by fusing two inhibitory ligands that bind a target at spatially distinct sites. 相似文献
90.
GF Hankard N Brousse JP Cézard D Emilie M Peuchmaur 《Canadian Metallurgical Quarterly》1997,24(5):568-572
BACKGROUND: Eosinophils contribute to the intestinal inflammatory infiltrate in Crohn's disease (CD). Eosinophilic infiltration occurs early in Crohn's recurrences, and a release of eosinophil cationic proteins has been observed in active CD. The proliferation, differentiation, and activation of eosinophils are highly dependent on the cytokine interleukin 5 (IL5). In the present study, we used in situ hybridization (ISH) to investigate the expression of the IL5 gene in intestinal specimens from patients with CD. METHODS: We studied 14 intestinal samples from eight children who had undergone ileocolectomy for advanced CD. The samples were examined for the intensity of the inflammatory infiltrate. Normal pediatric intestine specimens served as controls. In situ hybridization was performed on frozen tissue using radiolabeled IL5 mRNA probes. RESULTS: Positive signal with the IL5 antisense probe was observed within numerous cells infiltrating the specimens involved with CD. The number of IL5-expressing cells correlated with the histological grade of inflammation. Most of the labeled cells were eosinophils, characterized by their bilobed nuclei. Rare IL5-positive cells were detected in the control tissues. No positive signal was obtained with the IL5 sense probe. CONCLUSION: These results suggest that IL5 can be produced by eosinophils at the sites of inflammation in active CD and could be involved in the immune response by activating eosinophils, at least in part through an autocrine pathway, and perhaps by interacting with B and T cells. 相似文献