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   493篇
  免费   0篇
综合类   2篇
化学工业   2篇
轻工业   3篇
水利工程   1篇
石油天然气   2篇
无线电   1篇
一般工业技术   2篇
冶金工业   477篇
自动化技术   3篇
  2020年   1篇
  2013年   1篇
  2011年   2篇
  2008年   3篇
  2007年   1篇
  2004年   1篇
  2002年   1篇
  1999年   18篇
  1998年   141篇
  1997年   76篇
  1996年   61篇
  1995年   32篇
  1994年   27篇
  1993年   26篇
  1992年   5篇
  1991年   5篇
  1990年   3篇
  1989年   1篇
  1988年   6篇
  1987年   6篇
  1985年   4篇
  1982年   2篇
  1981年   5篇
  1980年   5篇
  1978年   2篇
  1977年   15篇
  1976年   39篇
  1975年   4篇
排序方式: 共有493条查询结果,搜索用时 781 毫秒
391.
The epithelial glycoprotein called secretory component (SC) is quantitatively the most important receptor of the immune system because it is responsible for external transport of locally produced polymeric IgA (pIgA) to generate remarkably large amounts of secretory IgA. Antibodies of this type constitute the major mediators of specific humoral immunity. Transmembrane SC belongs to the Ig supergene family and functions as a common pIg receptor, also translocating pentameric IgM externally to form secretory IgM. The B cells responsible for mucosal pIg production are initially stimulated in organized mucosa-associated lymphoepithelial structures, particularly the Peyer's patches in the distal small intestine; from these inductive site they migrate as memory cells to exocrine tissues all over the body. Mucous membranes are thus furnished with secretory antibodies in an integrated way, ensuring a variety of specificities at every secretory effector site. There is currently great interest in exploiting this integrated or "common" mucosal immune system for oral vaccination against pathogenic infectious agents and also to induce tolerance in T cell-mediated autoimmune diseases. However, much remains to be learned about mechanisms for antigen uptake and processing necessary to elicit stimulatory or suppressive mucosal immune responses. Moreover, evidence is emerging for the existence of considerable regionalization with regard to functional links between inductive sites and effecter sites of mucosal immunity.  相似文献   
392.
We reported previously that consumption of one cup of milk (240 mL) per day produced negligible symptoms in lactase-nonpersistent (LNP) individuals self-described as being severely lactose intolerant. We hypothesized that such LNP individuals could also tolerate two cups of milk per day if taken in two widely divided doses with food, and that psychologic factors play a role in perceptions of lactose intolerance. The Minnesota Multiphasic Personality Inventory 2 (MMPI-2) was administered to 19 LNP subjects self-described as markedly lactose intolerant (S-LNP), 13 LNP subjects who denied lactose intolerance (A-LNP), and 10 lactase-persistent individuals who believed they were lactose intolerant (S-LP). Symptoms were recorded when LNP subjects ingested 240 mL regular or lactose-hydrolyzed milk twice daily for 7 d in a double-blind crossover study. The results showed that neither LNP group had a significant increase in symptoms (P < 0.05) during the regular compared with the lactose-hydrolyzed milk periods. However, S-LNP subjects reported significantly greater gaseous symptoms than did the A-LNP subjects during both treatment periods. The MMPI-2 showed a high score on the "lie" validity scale for S-LNP subjects. We conclude that LNP subjects tolerate two cups of milk per day without appreciable symptoms. S-LNP subjects have underlying flatulence that is misattributed to lactose intolerance. MMPI-2 results were of questionable validity because of the high rate of dissimulation by LNP subjects.  相似文献   
393.
This study was designed to determine the frequency of postoperative complications following elective surgeries (castration, ovariohysterectomy, onychectomy) of dogs and cats from private practices and to evaluate the use of electronic medical records for this type of research. All elective surgeries performed during the study period at 5 private practices were included. The surgical techniques and materials used for each procedure were similar across practices, but the interpretation of "complication," the amount of detail recorded on the primary medical record, and the intensity of follow-up varied. The frequencies and types of complications varied by species and procedure. The postoperative complication frequencies ranged from 1% to 24% for all complications and 1% to 4% for severe complications. The results of this study describe populations of elective-surgery patients at private practices, provide data for educating clients about the risks associated with these procedures, and demonstrate how computerized records can be used to collect practice-specific medical information.  相似文献   
394.
Multiple ventricular septal defects: how and when should they be repaired?   总被引:1,自引:0,他引:1  
BACKGROUND: Congenital heart lesions with multiple ventricular septal defects remain a surgical challenge. Traditional approaches often rely on either ventriculotomy for exposure or palliation with pulmonary artery banding. However, indications for repair versus palliation and for various approaches to surgical exposure are not clearly defined. METHODS: From July 1992 to January 1998, 45 patients with multiple (>/=2) ventricular septal defects (37 with associated lesions) underwent surgery. Median age was 86 days; all but 4 patients were infants. The mean number of defects was 3.7, and almost half of the patients had more than 3 defects. Apical muscular defects were present in 62% of patients. Thirty-one patients underwent primary complete repair through a right atriotomy or trans-semilunar valve approach (group 1), 8 had palliation (group 2), and 6 underwent complete repair after prior palliation elsewhere (group 3). No patient had a ventriculotomy. RESULTS: One early death occurred in a group 1 patient. Four patients who had had palliation (50%) underwent early reoperation for pulmonary artery band revision because of failure to thrive or band removal after spontaneous closure of the defects. At follow-up (median 22 months), there was 1 death in a group 2 patient (palliation) and 1 other group 2 patient required cardiac transplantation. The only late reoperation was for removal of the pulmonary artery band and closure of multiple apical defects in a group 2 (palliation) patient. No patients who underwent repair have hemodynamically significant residual defects. CONCLUSIONS: In our experience, palliation of multiple ventricular septal defects is associated with greater morbidity than primary repair. Multiple defects can almost always be repaired adequately in early infancy without ventriculotomy, although "Swiss-cheese" septum may be an indication for palliation.  相似文献   
395.
眼镜店的促销可谓五花八门,几乎天天有、月月有、年年有,每家都有。可以说促销已是众多眼镜店日常行销工作中的重要组成部分,寒假暑假搞促销,新店开业搞促销,国庆春节等假日促销,已经够让众多眼镜店从年头忙到年尾。虽然,促销活动几乎每家眼镜店都有搞,也时时都在搞,但是,每次促销活动后盘点成果,却往往是几家欢乐几家愁。促销活动成功的眼镜店,活动期间的营业额比平日要高出几倍甚至上十倍、数十倍,店主自然眉开眼笑;促销活动不成功的眼镜店,别说活动期间营业额有增长,有的甚至连促销费都收不回来,自是愁在心底,爽不起来。为什么同样的眼镜店,同样是搞促销,效果却是忧喜两重天,有人欢笑有人哭?问题显然出在促销活动的策划及实施操作的整个过程中。为了总结促销经验,丰富眼镜业的促销内涵,提升眼镜零售业的促销水平,分析眼镜业的促销现状、在此特别推出《眼镜店玩转促销之葵花宝典》,以供业界同仁参考借鉴。  相似文献   
396.
We report seven cases of particular cutaneous tumors selected from the register of the French Study Group on Cutaneous Lymphomas. The patients (three men, four women) were aged 37-86 years. They initially presented with cutaneous nodules or papules. Three cases presented with regional lymph nodes. Stagings were negative, except for one patient with bone marrow involvement. Histological features were relevant with pleomorphic medium T-cell lymphoma, but these cells exhibited a distinguishing phenotype. They were positive for CD4, CD56, and also CD45, CD43, and HLA-DR. All other T-cell and B-cell markers were negative. The myelomonocytic markers (CD13, CD14, CD15, CD33, CD117, myeloperoxidase, and lysozyme) were negative excepted CD68, which was clearly positive in four cases and weakly in two cases. Others natural killer cell markers (CD16, CD57, TiA1, granzyme B), TdT, and CD34 were negative. Polymerase chain reaction studies did not detect any B or T clonal rearrangement. The cytogenetic studies, performed in five cases, showed a del(5q) in two cases. All patients were treated successfully by polychemotherapy, but relapsed quickly in the skin, between 4 and 28 months. Five patients developed bone marrow involvement, with leukemia in three cases, and they died in 5-27 months. One patient died at 17 months with skin progression. The seventh patient is alive at 33 months, with cutaneous progression. The origin of these cells is unclear. Despite expression of CD4 or CD56, we failed to demonstrate a T-cell, natural killer cell origin. However, CD4 and CD56 are not specific for T or natural killer lineages. Although these two markers are also known to be expressed by monocytic cells, classic myeloid antigens were negative. These seven cases, together with other rare similar cases already reported, seem to represent a distinct entity likely developed from hematological precursor cells.  相似文献   
397.
Drug-using women with or at risk for HIV infection have many competing unmet needs, especially for social services, drug treatment, and medical care. High-risk drug-using women were recruited through street outreach, at needle exchange sites, a prison, and local community based organizations in New Haven, Connecticut for a study of the service needs of out-of-treatment drug users and the ability of an interactive case management intervention (ICM) to address those needs. These women were administered baseline and follow-up interviews to identify their health and social service needs and the degree to which these needs were resolved. The women who chose to enroll in the interactive case management intervention (n = 38) did not differ demographically nor in their HIV risk behaviors from those not receiving case management (n = 73). Provision of ICM was most successful in meeting needs for supportive mental health counseling, basic services, and long term housing. The impact of interactive case management was less evident for the acquisition of medical and dental services, which were accessed comparably by women not receiving the intervention. Overall, the women who enrolled in the ICM intervention showed a significant decrease in the number of unmet service needs as compared to those who did not enroll. Multiple contacts were required by the case manager to establish trust and to resolve the unmet service needs of these high-risk women. Women with or at risk for HIV infection can be effectively engaged in an ICM intervention in order to meet their multiple unmet service needs, although such interventions are time-and-labor intensive.  相似文献   
398.
Protein geranylgeranyltransferase type-I (GGTase-I) transfers a geranylgeranyl group to the cysteine residue of candidate proteins containing a carboxyl-terminal CAAX (C, cysteine; A, aliphatic amino acid; X, any amino acid) motif in which the "X" residue is leucine. The enzyme is composed of a 48-kilodalton alpha subunit and a 43-kilodalton beta subunit. Peptides isolated from the alpha subunit of GGTase-I were shown to be identical with the alpha subunit of a related enzyme, protein farnesyltransferase. Overlapping cDNA clones containing the complete coding sequence for the beta subunit of GGTase-I were obtained from rat and human cDNA libraries. The cDNA clones from both species each predicted a protein of 377 amino acids with molecular masses of 42.4 kilodaltons (human) and 42.5 kilodaltons (rat). Amino acid sequence comparison suggests that the protein encoded by the Saccharomyces cerevisiae gene CDC43 is the yeast counterpart of the mammalian GGTase-I beta subunit. Co-expression of the GGTase-I beta subunit cDNA together with the alpha subunit of protein farnesyltransferase in Escherichia coli produced recombinant GGTase-I with electrophoretic and enzymatic properties indistinguishable from native GGTase-I.  相似文献   
399.
400.
Hepatitis C is a major cause of liver disease leading to cirrhosis. Although interferon (IFN) is the only approved therapy, treatment is characterized by low response rates and dose-limiting side effects. We evaluated the addition of thymosin alpha1 (TA1), an immunomodulatory peptide, to the standard treatment regimen for hepatitis C to determine if combination therapy shows biological activity using outcome measures including normalization of alanine aminotransferase levels, histological activity, and viral load during treatment. We performed a randomized, double-blind, placebo-controlled trial to compare the biological activity of a combination TA1 and IFN with that seen for IFN alone in patients with chronic hepatitis C infection. One hundred nine patients were randomized for intention to treat and received 1.6 mg of TA1 subcutaneously twice weekly and 3 MU of IFN three times weekly; 3 MU of IFN three times weekly and placebo TA1; or placebo for both agents. All patients had chronic HCV infection with confirmation of chronic hepatitis on liver biopsy. Biochemical responders were followed up until alanine aminotransferase (ALT) levels became abnormal or for 26 weeks, and relapsers were retreated for 26 weeks in the same treatment arm. One hundred three patients completed treatment for 26 weeks, and six patients dropped out. The groups were similar with regard to sex, gender distribution, baseline histological activity index (HAI) score, risk factors, and viral titers. End-of-treatment biochemical response was seen in 37.1% of patients treated with combination therapy, 16.2% of patients treated with IFN alone, and 2.7% of untreated controls by intent-to-treat analysis (IFN/TA1 vs. IFN, chi2 = 4.05, P = .04). HCV RNA clearance was seen in 37.1% of IFN/TA1-treated patients and 18.9% of IFN-treated subjects. Mean HCV RNA titers were significantly lower than baseline at weeks 8, 16, and 24 after drug initiation among patients treated with IFN/TA1 but not in the other treatment arms. Histological improvement, as evidenced by a decrease in HAI of more than two points, occurred in the combination therapy arm more frequently than in comparison groups. Cumulative sustained biochemical responses were 14.2% and 8.1% in the IFN/TA1 and IFN arms, respectively, based on an intention-to-treat model. The combination of TA1 and standard IFN treatment for chronic hepatitis C showed evidence of biological activity at the completion of treatment by biochemical, histological, and virological outcome measures. Further research involving longer duration and varied dosing is needed.  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