全文获取类型
收费全文 | 1958篇 |
免费 | 5篇 |
专业分类
电工技术 | 2篇 |
综合类 | 1篇 |
化学工业 | 16篇 |
金属工艺 | 1篇 |
机械仪表 | 3篇 |
建筑科学 | 2篇 |
轻工业 | 5篇 |
无线电 | 1篇 |
冶金工业 | 1930篇 |
自动化技术 | 2篇 |
出版年
2020年 | 2篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 2篇 |
2011年 | 1篇 |
2010年 | 2篇 |
2007年 | 1篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2003年 | 5篇 |
2000年 | 2篇 |
1999年 | 54篇 |
1998年 | 566篇 |
1997年 | 315篇 |
1996年 | 221篇 |
1995年 | 137篇 |
1994年 | 117篇 |
1993年 | 100篇 |
1992年 | 9篇 |
1991年 | 23篇 |
1990年 | 30篇 |
1989年 | 25篇 |
1988年 | 31篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 24篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 14篇 |
1979年 | 1篇 |
1978年 | 9篇 |
1977年 | 66篇 |
1976年 | 130篇 |
1975年 | 4篇 |
1964年 | 1篇 |
排序方式: 共有1963条查询结果,搜索用时 15 毫秒
991.
SE Theocharis AP Margeli C Spiliopoulou SD Skaltsas A Koutselinis 《Canadian Metallurgical Quarterly》1998,43(8):1732-1736
The liver is of central importance in the metabolism of essential and toxic metals such as cadmium. Cadmium pretreatment suppressed the liver regenerative response to partial hepatectomy, due to the inhibition of the enzymatic activity of thymidine kinase. Exogenous putrescine administration has been reported to stimulate liver regeneration in animal models of acute liver failure. The purpose of this study was to document whether the administration of this polyamine enhances the impaired regenerative capacity of hepatocytes in cadmium-pretreated partially hepatectomized rats. The intraperitoneal administration of putrescine (1 or 10 mg/kg body weight), at the time of surgery and at 4 and 8 hr postoperatively partly restored the suppressed hepatocyte deoxyribonucleic acid (DNA) biosynthesis and thymidine kinase activity in cadmium-pretreated partially hepatectomized rats. Mitotic activity and the percentage of hepatocytes positive for proliferating cell nuclear antigen nuclei were in accordance with the liver proliferative status. Our results showed that exogenous putrescine administration is able to improve diminished liver regeneration after partial hepatectomy in this animal model of acute hepatic injury. 相似文献
992.
The frequency of schistosomiasis mansoni, of its clinicopathological forms, and of the distribution of Schistosoma mansoni eggs in ectopic locations in each clinicopathological form were studied in 1863 complete consecutive autopsies performed in Belo Horizonte, Brazil, in the period from 1971 to 1990. Three hundred and thirteen cases of S. mansoni infection (16.8%) were found. The intestinal form was the most frequent (67.4%), followed by the hepatosplenic form without pulmonary hypertension (24.9%). The intestinal form showed a smaller number of ectopic sites and a lower percentage of involvement of these sites compared to the more severe forms, particularly the hepatosplenic form with pulmonary hypertension. The distribution of the frequency of schistosomiasis mansoni cases, of the clinicopathological forms of the disease, and of the ectopic sites of S. mansoni eggs over the decades considered showed a marked reduction in all of these parameters, particularly in the more severe forms. These findings can be explained only by earlier diagnosis of the disease and the greater efficacy of the specific chemotherapy used today, preventing progression to the more severe forms of the parasitosis. 相似文献
993.
994.
995.
pulE, one of 14 genes specifically required for pullulanase secretion in Klebsiella oxytoca, codes for a putative nucleotide-binding protein. Subcellular fractionation indicated that the majority of PulE in Escherichia coli cells expressing all 14 secretion genes is mainly associated with the cytoplasmic membrane through both hydrophobic and non-hydrophobic interactions. Mutational analysis revealed that one of the two regions of PulE that are conserved in many nucleotide-binding proteins (Walker box A) is essential for pullulanase secretion. Likewise, mutations that removed aspartate residues from each of two regions immediately downstream from the Walker box A also reduced secretion. These aspartate-rich regions are highly conserved in all 16 known PulE homologues but not in any other nucleotide-binding proteins. Altogether, these results indicate that PulE might belong to a new family of nucleotide-binding proteins. The protein could not be cross-linked to the photoactivatable ATP analogue azido-ATP, however. Most pulE point or deletion mutations which prevented pullulanase secretion exhibited transdominance when expressed at high levels in cells producing wild-type PulE protein. Evidence presented suggests that PulE might be a homodimer. 相似文献
996.
Twelve cases of optic nerve glioma seen over a 28 year period are analysed herein in this autopsy study. 相似文献
997.
NR Murray GP Baumgardner DJ Burns AP Fields 《Canadian Metallurgical Quarterly》1993,268(21):15847-15853
The human erythroleukemia (K562) cell line undergoes megakaryocytic differentiation and cessation of proliferation when treated with phorbol myristate acetate (PMA). To investigate the role of individual protein kinase C (PKC) isotypes in these events, we have assessed PKC isotype expression during leukemic proliferation and PMA-induced differentiation. Immunoblot analysis using isotype-specific antibodies demonstrates that proliferating K562 cells express the alpha, beta II, and zeta PKC isotypes. PMA-induced differentiation and cytostasis lead to a decrease in beta II PKC and increases in alpha and zeta PKC levels. The role of the alpha and beta II PKC isotypes was further assessed in cells overexpressing these isotypes. K562 cells overexpressing human alpha PKC grew more slowly and were more sensitive to the cytostatic effects of PMA than control cells, whereas cells overexpressing beta II PKC were less sensitive to PMA. PMA-induced cytostasis is reversed upon removal of PMA. Resumption of proliferation is accompanied by reexpression of beta II PKC to near control levels, whereas alpha and zeta PKC levels remain elevated for several days after removal of PMA. Proliferation of PMA-withdrawn cells can be partially inhibited by antisense beta II PKC oligodeoxyribonucleotide. Growth inhibition is dose-dependent, specific for beta II PKC-directed antisense oligonucleotide, and associated with significant inhibition of beta II PKC levels indicating that beta II PKC is essential for K562 cell proliferation. Sodium butyrate, which unlike PMA induces megakaryocytic differentiation without cytostasis, causes increases in both alpha and beta II PKC levels. These data demonstrate that beta II PKC is required for K562 cell proliferation, whereas alpha PKC is involved in megakaryocytic differentiation. 相似文献
998.
999.
The effect of surface charge reversal of a fused-silica capillary was investigated for the conditions used in the determination of inorganic anions with potentiometric detection. A 25-micron-i.d. capillary was coated with permanently bonded polyacrylamide incorporating a quaternary amine, and a sodium sulfate solution was employed as electrolyte. As expected, it was found that the analysis time is reduced in comparison with an uncoated column of the same length. However, the effect is much less pronounced than that for the common chromate buffer. Since the reduction in analysis time also causes a loss of resolution, the effect is very close to that obtained simply by using a shorter capillary; therefore, coating was not found to be of benefit here. This is in contrast to results reported for the conditions usually employed for the indirect photometric detection of anions. 相似文献
1000.