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   2002篇
  免费   5篇
电工技术   2篇
综合类   1篇
化学工业   21篇
金属工艺   12篇
机械仪表   6篇
建筑科学   1篇
轻工业   5篇
无线电   1篇
一般工业技术   20篇
冶金工业   1936篇
自动化技术   2篇
  2021年   3篇
  2020年   4篇
  2019年   1篇
  2018年   6篇
  2017年   9篇
  2016年   1篇
  2015年   2篇
  2014年   3篇
  2013年   7篇
  2012年   4篇
  2011年   2篇
  2010年   3篇
  2009年   2篇
  2008年   1篇
  2007年   7篇
  2006年   6篇
  2005年   2篇
  2003年   5篇
  2001年   1篇
  2000年   2篇
  1999年   53篇
  1998年   562篇
  1997年   318篇
  1996年   222篇
  1995年   139篇
  1994年   116篇
  1993年   100篇
  1992年   9篇
  1991年   23篇
  1990年   31篇
  1989年   24篇
  1988年   30篇
  1987年   22篇
  1986年   23篇
  1985年   23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   131篇
  1975年   4篇
  1964年   1篇
排序方式: 共有2007条查询结果,搜索用时 15 毫秒
971.
BACKGROUND: This study describes 12 cases of restrictive dermopathy seen during a period of 8 years by the Dutch Task Force on Genodermatology. We present these unique consecutive cases to provide more insight into the clinical picture and pathogenesis of the disease. OBSERVATIONS: Clinical features in more than 85% of these children were prematurity, fixed facial expression, micrognathia, mouth in O position, rigid and tense skin with erosions and denudations, and multiple joint contractures. Ten patients underwent histopathologic skin biopsy. The biopsy results showed flattening of rete ridges in all 10 patients, a thin dermis with collagen aligned parallel to the epidermis in 9 patients, and poorly developed dermal appendages in 9 patients. Additional findings in individual patients included blepharophimosis, inguinal skin tear, skin tear in the frontal neck area that developed during delivery, absent eyelashes, a wide ascendent aorta, and dextrocardia. Fibroblast cultures taken from 5 patients did not show abnormal alpha 2 beta 1 and alpha 1 beta 1 integrin expressions. CONCLUSIONS: The alleged rarity of restrictive dermopathy may be partially caused by medical unfamiliarity with this entity, despite its characteristic clinical and histopathologic picture. The pathogenesis of the disease still needs to be elucidated.  相似文献   
972.
This article describes a high-performance liquid chromatographic (HPLC) method for the measurement of azithromycin (AZI) and two of its metabolites, 9a-N-desmethylazithromycin (ADES) and N-desmethylazithromycin (NDES), in human tears and plasma. The drug, metabolites, and internal standard (n-propylazithromycin [IS]) were detected electrochemically after injection of the extracted sample into the HPLC system. The peak height ratio (AZI, ADES, or NDES to IS) varied linearly, with concentrations in the ranges of 0.1 mg/L to 2.0 mg/L (tears) and 0.01 mg/L to 2.0 mg/L (plasma) of AZI, ADES, and NDES; the correlation coefficient (r) was more than 0.994 mg/L for all of the compounds (n=6). The analysis of tear samples collected at different intervals within 12 hours to 144 hours after a dose of 20 mg/kg of AZI from a trachoma patient yielded concentrations ranging from 1.52 mg/L to 0.34 mg/L for AZI, 0.79 mg/L to 0.27 mg/L for ADES, and 1.99 mg/L to less than 0.20 mg/L for NDES. The concentration of AZI in plasma ranged from 0.15 mg/L to 0.01 mg/L, whereas ADES and NDES were undetectable.  相似文献   
973.
Cyclooxygenase-2 has been reported to play an important role in colorectal carcinogenesis. The effects of meloxicam (a COX-2 inhibitor) on the growth of two colon cancer cell lines that express COX-2 (HCA-7 and Moser-S) and a COX-2 negative cell line (HCT-116) were evaluated. The growth rate of these cells was measured following treatment with meloxicam. HCA-7 and Moser-S colony size were significantly reduced following treatment with meloxicam; however, there was no significant change in HCT-116 colony size with treatment. In vivo studies were performed to evaluate the effect of meloxicam on the growth of HCA-7 cells when xenografted into nude mice. We observed a 51% reduction in tumor size after 4 weeks of treatment. Analysis of COX-1 and COX-2 protein levels in HCA-7 tumor lysates revealed a slight decrease in COX-2 expression levels in tumors taken from mice treated with meloxicam and no detectable COX-1 expression. Here we report that meloxicam significantly inhibited HCA-7 colony and tumor growth but had no effect on the growth of the COX-2 negative HCT-116 cells.  相似文献   
974.
Sonic hedgehog signaling is essential for hair development   总被引:4,自引:0,他引:4  
BACKGROUND: The skin is responsible for forming a variety of epidermal structures that differ amongst vertebrates. In each case the specific structure (for example scale, feather or hair) arises from an epidermal placode as a result of epithelial-mesenchymal interactions with the underlying dermal mesenchyme. Expression of members of the Wnt, Hedgehog and bone morphogenetic protein families (Wnt10b, Sonic hedgehog (Shh) and Bmp2/Bmp4, respectively) in the epidermis correlates with the initiation of hair follicle formation. Further, their expression continues into either the epidermally derived hair matrix which forms the hair itself, or the dermal papilla which is responsible for induction of the hair matrix. To address the role of Shh in the hair follicle, we have examined Shh null mutant mice. RESULTS: We found that follicle development in the Shh mutant embryo arrested after the initial epidermal-dermal interactions that lead to the formation of a dermal papilla anlage and ingrowth of the epidermis. Wnt10b, Bmp2 and Bmp4 continued to be expressed at this time, however. When grafted to nude mice (which lack T cells), Shh mutant skin gave rise to large abnormal follicles containing a small dermal papilla. Although these follicles showed high rates of proliferation and some differentiation of hair matrix cells into hair-shaft-like material, no hair was formed. CONCLUSIONS: Shh signaling is not required for initiating hair follicle development. Shh signaling is essential, however, for controlling ingrowth and morphogenesis of the hair follicle.  相似文献   
975.
976.
Patterning of the vertebrate limb along the anterior-posterior axis is controlled by the zone of polarizing activity (ZPA) located at the posterior limb margin. One of the vertebrate Hh family members, Shh, has been shown to be able to mediate the function of the ZPA. Several naturally occurring mouse mutations with the phenotype of preaxial polydactyly exhibit ectopic Shh expression at the anterior limb margin. In this study, we report the molecular characterization of a spontaneous mouse mutation, Doublefoot (Dbf). Dbf is a dominant mutation which maps to chromosome 1. Heterozygous and homozygous embryos display a severe polydactyly with 6 to 8 digits on each limb. We show here that Shh is expressed normally in Dbf mutants. In contrast, a second Hh family member, Indian hedgehog (Ihh) which maps close to Dbf, is ectopically expressed in the distal limb bud. Ectopic Ihh expression in the distal and anterior limb bud results in the ectopic activation of several genes associated with anterior-posterior and proximal-distal patterning (Fgf4, Hoxd13, Bmp2). In addition, specific components in the Hedgehog pathway are either ectopically activated (Ptc, Ptc-2, Gli1) or repressed (Gli2). We propose that misexpression of Ihh, and not a novel Smoothened ligand as recently suggested (Hayes et al., 1998), is responsible for the Dbf phenotype. We consider that Ihh has a similar activity to Shh when expressed in the early Shh-responsive limb bud. To determine whether Dbf maps to the Ihh locus, which is also on chromosome 1, we performed an interspecific backcross. These results demonstrate that Dbf and Ihh are genetically separated by approximately 1.3 centimorgans, suggesting that Dbf mutation may cause an exceptionally long-range disruption of Ihh regulation. Although this leads to ectopic activation of Ihh, normal expression of Ihh in the cartilaginous elements is retained.  相似文献   
977.
The article reviews the history of development of free-flap skin transplantation and basic role of acad. B.A. Petrov who was the first to show the role of dermatom skin transplantation in vast granulating wounds as the only method saving the life of patients with severe burns. He also suggested to solve an actual problem--deficiency of resources of donor skin--by repeated excision of skin flaps from previously used donor sites and use of cadaver skin. Very important is ales the role of B.A. Petrov in development of such particular questions as the role of patient's condition, wound bed am microbial flora of the wound in survival of skin transplants. In aspect of historical relationships the perspective of new approach to treatment of deep burns by transplantation of ceratinocytes, cultivated outside the patient's organism is shown.  相似文献   
978.
We report six cases of intrauterine vascular deficiency of the upper limb, presenting over a 12-year period, with established areas of necrosis at the time of birth. Three of the six mothers were diabetic. An urgent examination of the neonate should be done to exclude occult systemic thomboses, as early anticoagulation or thrombolytic therapy may be indicated. The majority of cases were managed conservatively with dressings and splintage of the limb; exceptionally surgical intervention was required. Long-term sequelae included flexion contractures and shortening of the forearm bones.  相似文献   
979.
980.
STUDY OBJECTIVE: To compare withholding warfarin therapy with low-dose (2.5 mg) oral vitamin K therapy in excessively anticoagulated patients without bleeding complications. DESIGN: Prospective and retrospective studies. SETTING: Anticoagulation clinic at a Veterans Affairs institution. PATIENTS: Twenty-eight men were matched according to initial international normalized ratio (INR) and INR goal ranges. INTERVENTIONS: The retrospective arm of the study consisted of chart reviews of overanticoagulated patients whose warfarin doses were held until therapeutic INR values were reached. The prospective arm included overanticoagulated patients who were administered a single 2.5-mg dose of oral vitamin K. MEASUREMENTS AND MAIN RESULTS: Mean days to therapeutic INR values were 2.3+/-0.6 and 1.4+/-0.6 (p=0.001), and mean reduction in INR 1 day after treatment intervention was 1.32+/-0.79 and 3.46+/-1.31 (p<001) U for the withholding and vitamin K groups, respectively. CONCLUSION: Compared with withholding the warfarin dose, administration of 2.5 mg of oral vitamin K to excessively anticoagulated patients receiving warfarin significantly reduced the time required to reach a therapeutic INR as well as final INR.  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