首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3344篇
  免费   53篇
  国内免费   14篇
电工技术   45篇
综合类   28篇
化学工业   96篇
金属工艺   6篇
机械仪表   107篇
建筑科学   17篇
矿业工程   6篇
能源动力   9篇
轻工业   390篇
水利工程   4篇
无线电   49篇
一般工业技术   123篇
冶金工业   2386篇
原子能技术   6篇
自动化技术   139篇
  2022年   27篇
  2021年   6篇
  2020年   28篇
  2019年   33篇
  2018年   15篇
  2017年   9篇
  2016年   6篇
  2015年   11篇
  2014年   10篇
  2013年   162篇
  2012年   34篇
  2011年   38篇
  2010年   37篇
  2009年   38篇
  2008年   41篇
  2007年   43篇
  2006年   29篇
  2005年   27篇
  2004年   30篇
  2003年   23篇
  2002年   19篇
  2001年   10篇
  2000年   14篇
  1999年   83篇
  1998年   787篇
  1997年   444篇
  1996年   300篇
  1995年   160篇
  1994年   131篇
  1993年   152篇
  1992年   28篇
  1991年   31篇
  1990年   42篇
  1989年   41篇
  1988年   41篇
  1987年   54篇
  1986年   38篇
  1985年   38篇
  1984年   10篇
  1983年   6篇
  1982年   13篇
  1981年   22篇
  1980年   19篇
  1979年   8篇
  1977年   63篇
  1976年   127篇
  1975年   6篇
  1969年   5篇
  1955年   18篇
  1954年   16篇
排序方式: 共有3411条查询结果,搜索用时 22 毫秒
991.
Melioidosis, an infection caused by the gram-negative bacterial pathogen Burkholderia pseudomallei, is endemic in south-east Asia and northern Australia. Acute septicaemic melioidosis is a major cause of morbidity and mortality, especially in north-east Thailand. B. pseudomallei is highly resistant to the bactericidal activity of normal human serum (NHS), and we have found that B. pseudomallei 1026b multiplies in 10-30% NHS. We developed a simple screen for the identification of serum-sensitive mutants based on this novel phenotype. Approximately 1200 Tn5-OT182 mutants were screened, and three serum-sensitive mutants were identified. The type II O-antigenic polysaccharide (O-PS) moiety of lipopolysaccharide was not present in the serum-sensitive mutants. A representative serum-sensitive mutant, SRM117, was killed by the alternative pathway of complement and was less virulent than 1026b in three animal models of melioidosis. The Tn5-OT182 integrations in the serum-sensitive mutants were physically linked on the B. pseudomallei chromosome, and further genetic analysis of this locus revealed a cluster of 15 genes required for type II O-PS production. The proteins encoded by these genes were similar to proteins involved in bacterial polysaccharide biosynthesis. The results presented here demonstrate that type II O-PS is essential for B. pseudomallei serum resistance and virulence.  相似文献   
992.
Previous reports by this laboratory demonstrated that acute alcohol exposure combined with a 15% body surface area dorsal scald injury results in significant reductions in delayed-type hypersensitivity (DTH) and splenocyte proliferative responses compared to either insult alone. Previous studies by this lab have also shown that these defects are mediated, in part, by increased production of interleukin-6 (IL-6). Because both alcohol exposure and thermal injury are known to modulate glucocorticoid (CORT) levels, and CORT regulates IL-6 gene expression, the relationship between circulating CORT and IL-6 production in burn + ethanol mice was examined. At 24 and 48 h post-burn, a positive correlation existed between circulating CORT levels and measurements of cellular immune function. Administration of exogenous CORT to burn + ethanol-treated mice resulted in significant restoration (to 60% of control) of DTH and splenocyte proliferative responses. This restoration was concomitant with a down-regulation of circulating and macrophage-derived IL-6. The specificity of CORT in modulating these responses was tested by assessing cellular immune function and IL-6 levels after glucocorticoid receptor blockade with RU486. Taken together, these data strongly suggest that under normal circumstances CORT protects burned mice from severe immune dysfunction, a protection that is not afforded to burn + ethanol-treated mice. Furthermore, the immune dysfunction observed in burn + ethanol mice may be due to a lack of glucocorticoid attenuation of IL-6.  相似文献   
993.
Concentrated whey (about 50% solids) was stabilized against microbial deterioration by a combination of a slight reduction of water activity (aw) (0.94 or 0.92), lowered pH (5.2 or 5.4) and addition of 0.2% potassium sorbate. Color changes and available lysine loss in the above shelf stable whey, stored at different temperatures, were studied. A zero order reaction kinetics was observed for color changes during browning of the concentrated whey; activation energy was found to be 26 Kcal/mole. The loss of available lysine amounted to 20–30% of the initial value after three months of storage at 30°C.  相似文献   
994.
995.
This article describes in short sections the use and interpretation of indirect blood pressure measurements, central venous pressure, body temperature, pulse oximetry, end tidal CO2 measurements, pulse and heart rate, urine production and emergency laboratory values. Most of these parameters are directly or indirectly linked to the perfusion of the patient. Optimizing these values are one of the most important goals in emergency and critical care medicine.  相似文献   
996.
1. Antagonists at 5-HT3 receptors have shown activity in animal models of mental illness, however, few radiolabeled 5-HT3 ligands are available for preclinical studies. MIZAC, an analogue of the selective 5-HT3 antagonist, zacopride, binds with high affinity (1.3-1.5 nM) to CNS 5-HT3 sites. The authors report here the selectivity of MIZAC for these sites in rat brain homogenates. 2. Ninety-seven percent of total specific binding of [125I]MIZAC (0.1 nM) of was displaced by bemesetron (3 microM), a selective 5-HT3 antagonist. Competition studies using ligands with known affinities for 5-HT3 sites give a high correlation with reported pKi values (r2 0.98). Bemesetron displaceable binding has a regional distribution consistent with that of the 5-HT3 receptor, i.e. highest in cortex and hippocampus, and lowest in striatum and cerebellum. 3. Potent antagonists present at concentrations sufficient to occupy 95% of other 5-HT receptor populations (1A, 1B, 1D, 2A, 2B, 2C, 5A, 5B, 6, and 7) showed minimal ability to displace [125I]MIZAC binding (3 nM). Specificity studies using radioligand binding assays selective for 5-HT4, 5-HT6, and 5-HT7 receptors, and for binding sites of other neurotransmitters indicate a high degree of selectivity of [125I]MIZAC for the 5-HT3 receptor. 4. [125I]MIZAC binds to an apparent low affinity (benzac) site having a unique pharmacology. Low affinity binding was displaceable by benztropine, but not by other muscarinic agents nor inhibitors of dopamine uptake. The regional distribution of the low affinity site differed markedly from that of the high affinity site. The apparent affinity of [125I]MIZAC for the benzac site is two orders of magnitude lower than for the 5-HT3 receptor. Given its high selectivity for 5-HT3 binding sites, [125I]MIZAC appears to be a promising ligand for labeling 5-HT3 receptors in vitro and in vivo.  相似文献   
997.
998.
999.
1000.
Monoclonal antibody 1-12-3 reactive against scup (Stenotomus chrysops) cytochrome P450 E (a teleost CYP IA1) has been used to immunohistochemically localize CYP IA1 within hepatocytes and presumably sinusoidal endothelial and biliary epithelial cells of scup and trout. The goal of the present study was to extend immunohistochemical studies to the ultrastructural level determining intracellular locations of CYP IA1 in fish liver. Juvenile trout (5-10 g) were given i.p. injections once (50 micrograms/g b beta-naphthoflavone in cod liver oil; 0.5-ml injectate volume). After 5 days, livers were fixed (0.25% glutaraldehyde) via vascular in situ perfusion, removed, cut in 100-microns slices, infiltrated, and embedded in LR White monomer. Ultrathin sections of exposed livers were incubated in monoclonal antibody 1-12-3, rabbit anti-mouse IgG, and protein G colloidal gold. Membranes of granular endoplasmic reticulum in perinuclear regions of hepatocytes were consistently labeled. In addition, hepatocyte plasma membrane, particularly microvilli at bile canaliculi, was labeled. Biliary epithelial cells were labeled on luminal plasma membrane surrounding biliary passageway. Plasma membrane facing sinusoid and immediately subjacent cytoplasm was labeled in endothelial cells. Presence of CYP IA1 in sinusoidal endothelium could contribute to detoxication and/or bioactivation of blood borne chemicals. Granular endoplasmic reticulum was not uniformly labeled in hepatocytes. Rather, distribution seemed sequestered within highly specific regions and not dispersed along all membrane surfaces. Localization within biliary epithelial cells could signify potential of this cell type to bioactivate polycyclic aromatic hydrocarbons and may explain the common finding of biliary as well as hepatocytic tumors of trout liver.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号