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   4999篇
  免费   5篇
电工技术   3篇
化学工业   45篇
金属工艺   1篇
机械仪表   8篇
建筑科学   15篇
矿业工程   1篇
能源动力   6篇
轻工业   16篇
无线电   14篇
一般工业技术   58篇
冶金工业   4827篇
原子能技术   2篇
自动化技术   8篇
  2020年   5篇
  2019年   4篇
  2018年   2篇
  2017年   7篇
  2016年   2篇
  2014年   4篇
  2013年   7篇
  2012年   9篇
  2011年   13篇
  2010年   2篇
  2009年   7篇
  2008年   9篇
  2007年   6篇
  2006年   8篇
  2005年   4篇
  2004年   6篇
  2003年   15篇
  2002年   4篇
  2001年   6篇
  2000年   3篇
  1999年   152篇
  1998年   1470篇
  1997年   876篇
  1996年   549篇
  1995年   302篇
  1994年   264篇
  1993年   293篇
  1992年   30篇
  1991年   54篇
  1990年   56篇
  1989年   61篇
  1988年   58篇
  1987年   56篇
  1986年   67篇
  1985年   51篇
  1983年   10篇
  1982年   22篇
  1981年   27篇
  1980年   27篇
  1979年   2篇
  1978年   15篇
  1977年   125篇
  1976年   284篇
  1975年   8篇
  1973年   2篇
  1971年   2篇
  1960年   1篇
  1957年   1篇
  1956年   4篇
  1955年   5篇
排序方式: 共有5004条查询结果,搜索用时 31 毫秒
991.
Syringolides are water-soluble, low-molecular-weight elicitors that trigger defense responses in soybean cultivars carrying the Rpg4 disease-resistance gene but not in rpg4 cultivars. 125I-syringolide 1 previously was shown to bind to a soluble protein(s) in extracts from soybean leaves. A 34-kDa protein that accounted for 125I-syringolide 1 binding activity was isolated with a syringolide affinity-gel column. Partial sequences of internal peptides of the 34-kDa protein were identical to P34, a previously described soybean seed allergen. In soybean seeds, P34 is processed from a 46-kDa precursor protein and was shown to have homology with thiol proteases. P34 is a moderately abundant protein in soybean seeds and cotyledons but its level in leaves is low. cDNAs encoding 46-, 34-, and 32-kDa forms of the soybean protein were cloned into the baculovirus vector, pVL1392, and expressed in insect cells. The resulting 32- and 34-kDa proteins, but not the 46-kDa protein, exhibited ligand-specific 125I-syringolide binding activity. These results suggest that P34 may be the receptor that mediates syringolide signaling.  相似文献   
992.
VM Reddy  DB McElhinney  CK Phoon  MM Brook  FL Hanley 《Canadian Metallurgical Quarterly》1998,115(6):1255-62; discussion 1262-3
BACKGROUND: There is often substantial mismatch between the diameters of the pulmonary and aortic anuli in young patients with systemic outflow tract disease. To implant the autologous pulmonary valve in the aortic position under such circumstances, it is necessary to adapt the geometry of the systemic outflow tract. The effects of such adaptations on autograft function in children are not well known. METHODS: To determine factors predictive of autograft regurgitation, we analyzed 41 cases of children who have undergone the Ross procedure. The diameter of the pulmonary valve was greater (by at least 3 mm) than that of the aortic valve in 20 cases, equal (within 2 mm) in 12 cases, and less (by at least 3 mm) in nine cases, with differences ranging from +10 to -12 mm. In 12 patients with a larger pulmonary anulus, aortoventriculoplasty was used to correct the mismatch. In patients with a larger aortic anulus, the mismatch was corrected by gradual adjustment along the circumference of the autograft, rather than by tailoring of the native aortic anulus. RESULTS: At follow-up (median 31 months), two patients had undergone reoperation on the neoaortic valve for moderate regurgitation. In the remaining 38 cases, autograft regurgitation was as follows: none or trivial in 30, mild in seven, and moderate in one. There was no correlation between regurgitation and age, geometric mismatch, or previous or concurrent procedures. CONCLUSIONS: Subtle technical factors that may result in distortion of the valve complex are probably more important determinants of autograft regurgitation than are indication for repair, geometric mismatch, or previous or concomitant outflow tract procedures. Significant mismatch of the semilunar anuli is not a contraindication to the Ross procedure in children.  相似文献   
993.
OBJECTIVES: To determining whether inhibition of platelet aggregation prevents development of carbohydrate overload-induced alimentary laminitis. ANIMALS: 22 healthy adult ponies. PROCEDURES: Acute laminitis was induced by oral administration of corn starch/wood flour to 16 ponies, 8 of which were treated with a synthetic analogue of the platelet fibrinogen receptor antagonist peptide (RPR) RGDS (arginine-glycine-aspartic acid-serine) 110885; 6 ponies served as negative controls. Blood was collected before and at 4, 8, 12, 24, 28, and 32 hours after administration of carbohydrate overload, and PCV, total plasma protein concentration, platelet count, activated clotting time, whole blood recalcification time, spontaneous platelet aggregation, ex vivo platelet aggregation responses, in vivo platelet activation, and platelet-neutrophil aggregates were evaluated. RESULTS: Of 16 ponies given carbohydrate, 6 of 8 untreated ponies developed laminitis and 0 of 8 ponies treated with RPR 110885 developed laminitis. The RPR 110885 treatment attenuated the increase in platelet-neutrophil aggregates observed in untreated ponies. CONCLUSIONS: Platelets are involved in the pathogenesis of equine alimentary laminitis. CLINICAL RELEVANCE: Platelet aggregation inhibitors may be useful for prevention or treatment of laminitis, or both.  相似文献   
994.
In the treatment of chronic myelocytic leukaemia (CML) allogeneic bone marrow transplantation (BMT) from a sibling donor is the treatment of choice in patients younger than 50 years; the overall 5-year survival is about 60%. Donor lymphocyte infusion without chemotherapy may serve as an efficacious therapy for recurrence of CML after allogeneic BMT. Application of allogeneic BMT from a matched unrelated donor is increasing, but the outcome is still inferior to that of sibling BMT, largely due to more severe and more frequent complications. Treatment with interferon-alpha has been shown to prolong the overall median survival, but especially in a subgroup of patients (about 15%) who achieve a major cytogenic response. Combination of interferon-alpha and low-dose cytarabine leads to increased survival and a better cytogenic response than interferon-alpha alone. Current investigations are aimed at further improving survival and cytogenic response by using more intensive chemotherapy, such as high-dose cytarabine, followed by interferon-alpha maintenance therapy.  相似文献   
995.
How well antibodies can protect against disease due to HIV-1 infection remains a pivotal but unresolved issue with important implications for vaccine design and the use of prophylactic antibody to prevent infection after accidental exposure to the virus and to interrupt transmission of virus from mother to child. Strong doubts about the possible utility of antibodies in vivo have been raised because of the relative resistance of primary viruses to antibody neutralization in vitro. Primary viruses are likely to be close to the viruses transmitted during natural infection in humans. Vaccine studies have been of little value in assessing antibody efficacy in vivo because none of the strategies described to date have elicited significant neutralizing antibody responses to primary viruses. Passive immunization studies are similarly hindered by the paucity of reagents able to neutralize primary viruses effectively and a single study has suggested some benefit. Here we describe experiments to explore the ability of passive antibody to protect against primary virus challenge in hu-PBL-SCID mice. In this model, severe combined immunodeficient (SCID) mice are populated with human peripheral blood mononuclear cells (PBMCs) and infected with HIV-1. We find that the potent neutralizing human monoclonal antibody IgG1b12 at high dose is able to completely protect even when given several hours after viral challenge. The results are encouraging for antibody-based postexposure prophylaxis and support the notion that antibody induction could contribute to an effective vaccine.  相似文献   
996.
The disposition of amiodarone, an antiarrhythmic agent was evaluated after a single intravenous infusion (5 mg/kg over 15 minutes) in patients of various ages and with various degrees of renal function and left ventricular function. The plasma concentration-time data were obtained from three clinical studies with similar protocols. The data were analyzed by nonlinear mixed-effects modeling (NONMEM) to estimate the population pharmacokinetic parameters of amiodarone and to determine the significant demographic covariates affecting these parameters. The pharmacokinetic parameters of amiodarone (weight-corrected) also were calculated using two-stage analysis and were compared with the results obtained from the mixed-effects analysis. The population plasma concentration-time profile of amiodarone was best described by a four-compartment model. Demographic covariates (i.e., creatinine clearance and ejection fraction) did not improve the final pharmacostatistical model significantly. The results from the two-stage analysis showed no significant relationship between amiodarone pharmacokinetic parameters and age, gender, renal function, or ejection fraction. The results from one study, however, demonstrated that advanced age (> or = 65 years) resulted in reduced amiodarone clearance coupled with a prolonged elimination half-life. No such correlation was detected with NONMEM analysis, which may be partly attributable to the small number of elderly patients. Overall, the results from NONMEM analysis validated the results obtained from the two-stage analysis.  相似文献   
997.
This article compares the social and health characteristics of patients of five kinds of practitioners: family physicians (used as a baseline group); chiropractors; acupuncturist/traditional Chinese medicine doctors; naturopaths; and Reiki practitioners. The data were gathered in a large Canadian city during the period 1994 to 1995. Face-to-face interviews were conducted with 300 patients (60 from each type of treatment group). While the most striking social and health differences occur between patients of family physicians and the patients of alternative practitioners, significant differences are also evident between the different groups of alternative patients. Reiki patients, for example, have a higher level of education and are more likely to be in managerial or professional positions than other alternative patients. The profiles presented here indicate that users of alternative care should not be regarded as a homogeneous population. The findings also show that almost all alternative patients also consult family physicians. The pattern revealed is one of multiple use: patients choose the kind of practitioner they believe can best help their particular problem.  相似文献   
998.
The purpose of this study was to investigate the in vitro effect of two irrigation solutions used in endodontics (5.25% sodium hypochlorite and 1% glutaraldehyde) on substrate adherence capacity of macrophages to determine if these substances can alter macrophage function. Inflammatory macrophages were obtained from Wistar rats and resuspended in RPMI-1640 medium. Substrate adherence capacity assays were carried out in Eppendorf tubes for 15 min of incubation at 37 degrees C in a humidified atmosphere of 5% CO2. The adherence index was calculated. Results showed that both sodium hypochlorite and glutaraldehyde significantly decreased the substrate adherence capacity of inflammatory macrophages. To take into account that adhesion is the first step in the phagocytic process of macrophages and in antigen presentation, sodium hypochlorite and glutaraldehyde could inhibit macrophage function and reduce inflammatory reactions in periapical tissues when they are used in root-canal therapy.  相似文献   
999.
BACKGROUND: We have recently reported that interleukin (IL)-12 prevents acute graft-versus-host disease (GVHD)-induced mortality in a full major histocompatibility complex- plus multiple minor antigen-mismatched A/J-->B10 bone marrow transplantation (BMT) model. Because most patients have access to a haploidentical, one haplotype-mismatched donor, we have now investigated the protective effect of IL-12 against GVHD and GVHD-associated immune dysfunction in a haploidentical CBD2F1 (H2kxd) --> B6D2F1 (H2bxd) strain combination. METHODS: GVHD was induced by injecting CBD2F1 marrow and spleen cells into lethally irradiated B6D2F1 mice. RESULTS: In untreated control mice, GVHD resulted in 87% mortality by day 8 after BMT, with no survivors beyond day 17. Treatment with a single injection of IL-12 on the day of BMT led to 87% long-term survival, with no significant weight loss, diarrhea or GVHD skin changes. The majority of T cells recovering in these mice showed the CD62L+, CD44low, CD45RBhigh naive phenotype. These T cells showed specific tolerance to both host and donor histocompatibility antigens, but normal anti-third party (H2s) alloresponses in vitro. B-cell proliferative responses to lipopolysaccharide were also normal in IL-12-protected mice. Moreover, normal negative selection of thymocytes bearing T cell receptors with Vbeta that recognize endogenous superantigens was observed among CD4+CD8- thymocytes, indicating a lack of GVHD-associated thymic selection abnormalities in IL-12-protected allogeneic BMT recipients. CONCLUSIONS: IL-12 provides permanent protection against an otherwise severe, rapidly lethal GVHD, with no clinical manifestations of chronic GVHD, immunosuppression or autoimmune features, in a full major histocompatibilty complex haplotype-mismatched murine BMT model.  相似文献   
1000.
PURPOSE: We evaluate the long-term outcome of the Gittes procedure for urinary stress incontinence. MATERIALS AND METHODS: A total of 87 women with proved genuine stress incontinence were treated with the Gittes procedure. The same urologist performed 95 consecutive operations during an 8-year period. Patients were evaluated by a postal questionnaire. RESULTS: Of the patients 52 (60%) (55 operations) responded to the questionnaire. Mean and median followup were 53 and 46 months, respectively (range 24 to 103). Twelve patients (23.1%) reported complete absence of postoperative urinary incontinence and were considered cured, 14 (26.9%) were significantly improved and a total of 30 (57.7%) benefited from the operation. The short-term results were initially encouraging but by 2 years only 20 patients were completely continent (38.5% cured). Of the 40 patients who were not cured 32 (80.0%) experienced incontinence within 2 years postoperatively. There were 26 who had complained of frequency and/or urgency preoperatively. There was a statistically significant subjective failure rate in this group (p = 0.007). CONCLUSIONS: The Gittes procedure is simple and has minimal complications. Although it provides continence in the early weeks and months following surgery, the long-term cure rate is disappointing, with most failures occurring within 2 years of surgery. Preoperative irritative symptoms, even when multichannel cystometry did not reveal instability, were associated with a poor subjective outcome. Our results suggest that the Gittes procedure is not satisfactory for the management of genuine stress incontinence in women.  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