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   2422篇
  免费   5篇
  国内免费   1篇
电工技术   1篇
化学工业   38篇
金属工艺   1篇
机械仪表   10篇
建筑科学   7篇
矿业工程   1篇
轻工业   6篇
石油天然气   1篇
无线电   19篇
一般工业技术   29篇
冶金工业   2292篇
原子能技术   2篇
自动化技术   21篇
  2023年   2篇
  2022年   3篇
  2021年   2篇
  2019年   1篇
  2018年   6篇
  2017年   2篇
  2016年   2篇
  2014年   2篇
  2013年   8篇
  2012年   9篇
  2011年   4篇
  2010年   5篇
  2008年   5篇
  2007年   5篇
  2006年   4篇
  2005年   3篇
  2004年   9篇
  2003年   6篇
  2002年   4篇
  2001年   3篇
  2000年   7篇
  1999年   75篇
  1998年   753篇
  1997年   380篇
  1996年   276篇
  1995年   133篇
  1994年   115篇
  1993年   123篇
  1992年   23篇
  1991年   30篇
  1990年   19篇
  1989年   22篇
  1988年   22篇
  1987年   22篇
  1986年   15篇
  1985年   19篇
  1984年   3篇
  1983年   5篇
  1982年   13篇
  1981年   13篇
  1980年   20篇
  1979年   4篇
  1978年   5篇
  1977年   72篇
  1976年   162篇
  1975年   4篇
  1974年   2篇
  1973年   2篇
  1964年   1篇
  1955年   2篇
排序方式: 共有2428条查询结果,搜索用时 62 毫秒
91.
Arthritis may be the presenting manifestation of iron overload. The metacarpophalangeal joints are often involved, producing a condition that resembles osteoarthritis but at a site typically affected by rheumatoid arthritis. Treatment of the arthritis is often disappointing, but identification of the underlying disease permits institution of life-saving phlebotomy therapy.  相似文献   
92.
93.
94.
The effective clinical use of the anticancer drug 5-fluorouracil (5-FU) requires the non-invasive assessment of its transport and metabolism, particularly in the tumor and the liver, where the drug is catabolized to alpha-fluoro-beta-alanine (FBAL). In this study, the potentials and limitations of dynamic 18F PET and metabolic 19F MRI examinations for noninvasive 5-FU monitoring were investigated in ACI and Buffalo rats with transplanted MH3924A and TC5123 Morris hepatomas, respectively. Selective 5-[19F]FU and [19F]FBAL MR images were acquired 5 and 70 min after 5-FU injection using a CHESS MRI sequence. After administration of 5-[18F]FU, the kinetics of the regional 5-[18F]FU uptake were measured by dynamic PET scanning over 120 min. To allow a comparison between PET and MRI data, standardized uptake values (SUV) were computed at the same points in time. The TC5123 hepatoma showed a significantly (p < 0.002) higher mean SUV at 5 and 70 min post-5-FU injection than the MH3924A cell lines, whereas there were no significant differences between the mean SUV measured in the liver of both animal populations. In contrast to the PET data, no significant differences in the mean 5-[19F]FU and [19F]FBAL MR signal values in the tumor of both models were observed. The MR images, however, yielded the additional information that 5-FU is converted to FBAL only in the liver and not in the hepatomas.  相似文献   
95.
BACKGROUND: Topical application of inhibitors of HMGCoA reductase, the rate-limiting enzyme of cholesterol synthesis, has been shown to induce impairment of barrier function. OBJECTIVE: Assessing whether oral administration of statins used for reducing blood levels of cholesterol induces functional changes in stratum corneum barrier. MATERIALS AND METHODS: 69 subjects of both sexes under-going treatment for hypercholesterolemia (mean age 48 +/- 11 years) entered the study; 43 had been treated with simvastatin and 11 with pravastatin for 6 months; 15 only on dietary regimen served as controls. Efficiency of stratum corneum water barrier was evaluated by transepidermal water loss (TEWL) measurement using an evaporimeter; water-holding capacity of the stratum corneum was assessed by the sorption-desorption test measured by capacitance. Statistical analysis was performed using ANOVA. RESULTS: No differences were found between the groups (simvastatin, pravastatin, diet) concerning both basal TEWL and the dynamic of water binding in the stratum corneum. CONCLUSIONS: Prolonged treatment with cholesterol-lowering drugs based on inhibition of HMGCoA reductase does not alter the permeability barrier of the skin.  相似文献   
96.
Simultaneous cytotoxicity of Ukrain and protoporphyrin amino-acid derivatives was tested on four malignant cell lines and the cytotoxic effect after laser irradiation was compared with cytotoxicity of Ukrain and protoporphyrin amino-acid derivatives applied on similar cell lines separately. It was found that Ukrain and protoporphyrin amino-acid derivatives act synergistically as cytotoxic substances on the malignant cell lines.  相似文献   
97.
98.
99.
Neu (c-erbB2) is a proto-oncogene product that encodes an epidermal growth factor-like receptor tyrosine kinase. Amplification of wild-type c-Neu and mutational activation of Neu (Neu T) have been implicated in oncogenic transformation of cultured fibroblasts and mammary tumorigenesis in vivo. Here, we examine the relationship between Neu tyrosine kinase activity and caveolin-1 protein expression in vitro and in vivo. Recent studies have suggested that caveolins may function as negative regulators of signal transduction. Our current results show that mutational activation of c-Neu down-regulates caveolin-1 protein expression, but not caveolin-2, in cultured NIH 3T3 and Rat 1 cells. Conversely, recombinant overexpression of caveolin-1 blocks Neu-mediated signal transduction in vivo. These results suggest a reciprocal relationship between c-Neu tyrosine kinase activity and caveolin-1 protein expression. We next analyzed a variety of caveolin-1 deletion mutants to map this caveolin-1-dependent inhibitory activity to a given region of the caveolin-1 molecule. Results from this mutational analysis show that this functional in vivo inhibitory activity is contained within caveolin-1 residues 32-95. In accordance with these in vivo studies, a 20-amino acid peptide derived from this region (the caveolin-1 scaffolding domain) was sufficient to inhibit Neu autophosphorylation in an in vitro kinase assay. To further confirm or refute the relevance of our findings in vivo, we next examined the expression levels of caveolin-1 in mammary tumors derived from c-Neu transgenic mice. Our results indicate that dramatic reduction of caveolin-1 expression occurs in mammary tumors derived from c-Neu-expressing transgenic mice and other transgenic mice expressing downstream effectors of Neu-mediated signal transduction, such as Src and Ras. Taken together, our data suggest that a novel form of reciprocal negative regulation exists between c-Neu and caveolin-1.  相似文献   
100.
The effects of arginine on cell proliferation and subsequent T helper (Th) 1 and Th 2 cytokine synthesis by murine Peyer's patch (PP) Th cells in vitro and the influence of arginine on the induction of antigen-specific mucosal and systemic immune responses in vivo were examined. When the PP T cells were stimulated with the anti-alpha beta T cell receptor (TCR) antibody in the presence of different concentrations of arginine, a higher proliferative response was observed in the culture with an optimal concentration of arginine compared with that with a minimum amount of this amino acid. The concentration of cytokines in the supernatant, the number of cytokine-producing cells and the cytokine-specific mRNA expression of PP T cells were also increased in a dose-dependent fashion. Furthermore, when mice fed on an arginine-supplemented liquid diet were orally immunized with tetanus toxoid plus cholera toxin as a mucosal adjuvant, a higher level of antigen-specific fecal IgA was observed when compared with the response in mice fed on an arginine-free diet. Taken together, these results suggest that arginine enhanced antigen-specific mucosal immune response resulting from the supporting activation of cell proliferation and subsequent cytokine synthesis of PP Th cells.  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