全文获取类型
收费全文 | 287676篇 |
免费 | 3065篇 |
国内免费 | 817篇 |
专业分类
电工技术 | 5030篇 |
综合类 | 162篇 |
化学工业 | 45432篇 |
金属工艺 | 11895篇 |
机械仪表 | 8606篇 |
建筑科学 | 6851篇 |
矿业工程 | 1835篇 |
能源动力 | 6734篇 |
轻工业 | 25908篇 |
水利工程 | 3190篇 |
石油天然气 | 7087篇 |
武器工业 | 16篇 |
无线电 | 31459篇 |
一般工业技术 | 56938篇 |
冶金工业 | 51392篇 |
原子能技术 | 7533篇 |
自动化技术 | 21490篇 |
出版年
2021年 | 2098篇 |
2018年 | 3672篇 |
2017年 | 3622篇 |
2016年 | 3903篇 |
2015年 | 2466篇 |
2014年 | 4236篇 |
2013年 | 12021篇 |
2012年 | 6830篇 |
2011年 | 9214篇 |
2010年 | 7570篇 |
2009年 | 8647篇 |
2008年 | 8931篇 |
2007年 | 8813篇 |
2006年 | 7829篇 |
2005年 | 7316篇 |
2004年 | 6803篇 |
2003年 | 6559篇 |
2002年 | 6628篇 |
2001年 | 6500篇 |
2000年 | 6177篇 |
1999年 | 6231篇 |
1998年 | 14762篇 |
1997年 | 11035篇 |
1996年 | 8568篇 |
1995年 | 6528篇 |
1994年 | 5916篇 |
1993年 | 5788篇 |
1992年 | 4479篇 |
1991年 | 4440篇 |
1990年 | 4285篇 |
1989年 | 4301篇 |
1988年 | 4255篇 |
1987年 | 3598篇 |
1986年 | 3597篇 |
1985年 | 4162篇 |
1984年 | 3966篇 |
1983年 | 3622篇 |
1982年 | 3423篇 |
1981年 | 3559篇 |
1980年 | 3423篇 |
1979年 | 3365篇 |
1978年 | 3446篇 |
1977年 | 3925篇 |
1976年 | 5037篇 |
1975年 | 3159篇 |
1974年 | 3007篇 |
1973年 | 3024篇 |
1972年 | 2651篇 |
1971年 | 2473篇 |
1970年 | 2105篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
G Bioque D Vargas O Bulbena J Roselló-Catafau Gelpi E 《Canadian Metallurgical Quarterly》1993,38(1-2):38-43
N-phenyllinoleamide (NPLA) has been detected as extraneous compound in adulterated cooking oils associated with a unique epidemic disease known as the Toxic Oil Syndrome (TOS). In this communication we report on the action of NPLA on the endogenous cyclooxygenase and lipoxygenase arachidonate metabolism. Results show that mouse peritoneal macrophages (MPM) exposed to 1 mM NPLA for 2 h undergo significant increases of 6-keto prostaglandin F1a, prostaglandin E2, leukotriene B4, 12- and 15-hydroxyeicosatetraenoic acids. MPM prelabelled with 3H-AA showed an enhanced release when exposed to NPLA. Thus, it is concluded that NPLA potentiates AA release from cell membrane phospholipids and the subsequent cyclooxygenase and lipoxygenase oxidative metabolism of this precursor to various eicosanoids. This is in agreement with the implication of peroxidative process mediated by fatty acids anilides in TOS. 相似文献
982.
983.
G Appel A Briese K von Holleben G von Mickwitz M von Wenzlawowicz 《Canadian Metallurgical Quarterly》1995,102(6):233-234
It is reported on the fatal accident of a horse due to a cross-beam too low above the door of the stable, in which the animal suffered several skull fractures and a tear of the musculus longus capitis from the base of the skull. The aim of this article is, to supply a contribution to the establishment of minimal requirements for the housing of horses, in this case for the request of the minimum height of stable doors and ceilings as well as for constructions on horse transporters. On the grounds of this example, the natural behaviour of horses is discussed at the hand of the literature and the efforts are shown to improve the existing inadequacies in the housing and transport of horses with regard to the judicial situation. In the light of section 2 of the animal protection law, as to the construction of horse stables the importance is especially emphasized to consider the panic behaviour in connection with abrupt flight reactions as physiologic in the prevention of accidents. 相似文献
984.
G Arepally C Reynolds A Tomaski J Amiral A Jawad M Poncz DB Cines 《Canadian Metallurgical Quarterly》1995,104(6):648-654
The diagnosis of heparin-induced thrombocytopenia (HIT) may be affirmed by demonstrating heparin-dependent anti-platelet antibodies using the 14C-serotonin release assay (SRA). In this study, results of the SRA was compared with the recently described platelet factor 4 (PF4)/heparin enzyme-linked immunosorbent assay (ELISA). Compared with the SRA, the sensitivity and specificity of a PF4/heparin ELISA was 87% and 92%, respectively, using an assay developed in our laboratory; and 90% and 98%, respectively, using a commercially developed kit (Diagnostica Stago, Asnieres, France). However, antibodies to PF4/heparin were also detected in up to 8% of patients whose plasma was negative by SRA, and 23% of patients receiving heparin who were not thrombocytopenic. These data indicate that results obtained with the PF4/heparin ELISA and the SRA are generally in accord in patients with a clinical diagnosis of HIT. However, discrepant results occur in approximately 20% of cases because of the greater sensitivity of ELISA and the possible involvement of other heparin-binding proteins. The fact that each assay contributes independent information in some cases must be considered in the sequence of test performance and in providing consultation to the practicing hematologist. 相似文献
985.
986.
987.
G Bottino G Antognozzi R Degrandi C Augeri G Bogliolo P Zoccali 《Canadian Metallurgical Quarterly》1995,17(2-3):63-66
Blood concentration of endogenous beta-endorphines can change during the clinical evolution of chronic bronchopneumopathies. The authors assessed the beta-endorphine concentrations in the pulmonary arterial and systemic arterial blood in 8 asthmatic patients during a symptom-free period and after methacholine-induced bronchospasm. The beta-endorphine analysis was performed in duplicate dor each sample, by means of a RIA assay. There is not difference in the systemic arterial blood concentration of beta-endorphines between asthmatic patients and normal subjects. Furthermore, there is no change in the beta-endorphine blood concentration during the passage through the pulmonary tissue after methacoline-induced bronchospasm. 相似文献
988.
Neuronal somata in the rat kidney are very often part of ganglionated plexus and contain nitric oxide synthase (NOS). Examining serial 100 microns slices of whole kidneys, we identified three subpopulations of neuronal somata by: (a) staining for NADPH-diaphorase (NADPH-d) histochemistry followed by the demonstration of dopamine beta-hydroxylase (DBH) by immunoperoxidase, and (b) staining for DBH by immunofluorescence followed by the demonstration of NADPH-d histochemical activity. The largest subpopulation of neuronal somata displayed both DBH immunoreactivity and NADPH-d histochemical activity. The second largest group of somata showed NADPH-d activity only. A small group of neuronal somata showed only DBH immunoreactivity. The presence of catecholaminergic characteristics in NOS-containing neuronal somata is unusual and raises the question as to their origin. Their heterogeneity suggests different functions for the different subpopulations. 相似文献
989.
990.
S Rothemund M Beyermann E Krause G Krause M Bienert RS Hodges BD Sykes FD S?nnichsen 《Canadian Metallurgical Quarterly》1995,34(40):12954-12962
D-Amino acid replacements and the determination of resulting structural changes are a useful tool to recognize amphipathic helices in biologically active peptides such as neuropeptide Y and corticotropin-releasing factor. In this paper the secondary structures of one amphipathic alpha-helical peptide and its double D-amino acid analog have been determined by means of 1H NMR and CD spectroscopies under equivalent conditions. The chemical shifts (NH and C alpha H) and the analysis of nuclear Overhauser effects show a split of the continuous helix for the all-L peptide into two helices at the position of double D-amino acid replacement. Hydrogen exchange rates correlate with water accessibilities in the hydrophobic/hydrophilic face and confirm the amphipathic helical structure in the all-L peptide as well as in its double D-amino acid analog. A significantly accelerated hydrogen isotope exchange rate is observed for the D-Ala9 backbone proton, implying an increased flexibility at that position. These results show that the incorporation of an adjacent pair of D-amino acids only causes a local change in structure and flexibility, which makes the double D replacement interesting as a tool for specific helix-disturbing modifications to search for helical conformations in biologically active peptides. 相似文献