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   1717篇
  免费   23篇
  国内免费   9篇
电工技术   9篇
综合类   9篇
化学工业   59篇
金属工艺   9篇
机械仪表   8篇
建筑科学   5篇
矿业工程   2篇
能源动力   6篇
轻工业   69篇
水利工程   1篇
石油天然气   4篇
武器工业   1篇
无线电   23篇
一般工业技术   23篇
冶金工业   1459篇
自动化技术   62篇
  2022年   5篇
  2021年   10篇
  2020年   3篇
  2019年   4篇
  2018年   4篇
  2017年   11篇
  2016年   6篇
  2015年   13篇
  2014年   18篇
  2013年   31篇
  2012年   20篇
  2011年   19篇
  2010年   13篇
  2009年   14篇
  2008年   8篇
  2007年   12篇
  2006年   9篇
  2005年   43篇
  2004年   6篇
  2003年   9篇
  2002年   8篇
  2001年   6篇
  1999年   41篇
  1998年   416篇
  1997年   258篇
  1996年   162篇
  1995年   87篇
  1994年   81篇
  1993年   82篇
  1992年   11篇
  1991年   19篇
  1990年   13篇
  1989年   22篇
  1988年   26篇
  1987年   23篇
  1986年   17篇
  1985年   26篇
  1983年   1篇
  1982年   7篇
  1981年   10篇
  1980年   18篇
  1979年   2篇
  1978年   4篇
  1977年   37篇
  1976年   99篇
  1975年   7篇
  1974年   1篇
  1966年   2篇
  1965年   1篇
  1961年   1篇
排序方式: 共有1749条查询结果,搜索用时 15 毫秒
181.
RSR is now several years posttransplant. He has a serum creatinine of 2.1 mg/dl and his hypertension remains borderline with additional medication. He is seen regularly by his local nephrologist and once a year at the transplant center. In RSR's case, collaboration with physicians, nurses, and home health helped this patient achieve the goal of self-care. Illiteracy was no barrier to achieving this goal when assessing the patient's skills, developing a plan that uses those skills, and working together as a team to implement the plan.  相似文献   
182.
WA Hammond  RM Kay  DL Skaggs 《Canadian Metallurgical Quarterly》1998,68(2):186-99; quiz 203, 205-6, 208-10
Supracondylar fractures of the humerus are the most common fractures in children that require surgery. A significant advancement in the field of pediatric orthopedics has been closed reduction and percutaneous pinning of these fractures. This technique, using high quality fluoroscopic imaging, allows for a near anatomical reduction of fractures without the need for an open surgical procedure or prolonged traction. Supracondylar fractures in children are often associated with neurologic and vascular damage that must be recognized before fracture reduction. Nursing staff members' skill with pediatric patients can greatly aid the surgeon in the timely and safe treatment of these fractures.  相似文献   
183.
Translational recruitment of maternal mRNAs is an essential process in early metazoan development. To identify genes required for this regulatory pathway, we have examined a collection of Drosophila female-sterile mutants for defects in translation of maternal mRNAs. This strategy has revealed that maternal-effect mutations in the cortex and grauzone genes impair translational activation and cytoplasmic polyadenylation of bicoid and Toll mRNAs. Cortex embryos contain a bicoid mRNA indistinguishable in amount, localization, and structure from that in wild-type embryos. However, the bicoid mRNA in cortex embryos contains a shorter than normal polyadenosine (poly(A)) tail. Injection of polyadenylated bicoid mRNA into cortex embryos allows translation demonstrating that insufficient polyadenylation prevents endogenous bicoid mRNA translation. In contrast nanos mRNA, which is activated by a poly(A)-independent mechanism, is translated in cortex embryos, indicating that the block in maternal mRNA activation is specific to a class of mRNAs. Cortex embryos are fertilized, but arrest at the onset of embryogenesis. Characterization of grauzone mutations indicates that the phenotype of these embryos is similar to cortex. These results identify a fundamental pathway that serves a vital role in the initiation of development.  相似文献   
184.
We have examined the formation of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) in reactions of peroxynitrite with 2'-deoxyguanosine (dG) and calf-thymus DNA. Peroxynitrite reacts with dG at neutral pH, but this reaction does not result in the buildup of 8-oxodG. We also do not find any evidence for the formation of 8-oxodG in calf-thymus DNA upon exposure to peroxynitrite. When 8-oxodG is mixed with 1000-fold excess dG and then allowed to react with peroxynitrite, about 50% of the 8-oxodG is destroyed. The preferential reaction of 8-oxodG is also evident when dG in calf-thymus DNA is partially oxidized in an Udenfriend system and then allowed to react with peroxynitrite. We suggest that 8-oxodG is not produced in peroxynitrite-mediated oxidations of dG and DNA or that it is produced but then is rapidly consumed in further reactions with peroxynitrite. Oxidized DNA bases frequently can be more oxidation sensitive than their corresponding progenitors and, therefore, may be present at] low steady-state concentrations and not represent stable markers of oxidative stress status. The importance of the 8-oxodG/peroxynitrite reaction is discussed in relation to the formation of more stable, secondary oxidation products that might be more useful markers of DNA damage.  相似文献   
185.
PURPOSE: We studied the effects of electrical stimulation on idiopathic detrusor instability. MATERIALS AND METHODS: Between January 1993 and December 1994, 30 men and 41 women (mean age plus or minus standard deviation 48 +/- 16 years) underwent transcutaneous electrical nerve stimulation (TENS) of the S2-S3 dermatomes, and 13 men and 22 women (mean age 48 +/- 12 years) underwent S3 neuromodulation. Subjective assessment was performed using a diary and symptom score of 0 to 14. Objective outcome was analyzed with urodynamic studies. RESULTS: Mean duration of TENS was 3 +/- 1 weeks (range 2 to 4). Although there were no major complications 31% of the patients reported local skin irritation. The overall urinary symptom scores improved from 10 +/- 2 (range 5 to 14) before the study to 7 +/- 3 (range 1 to 14) during stimulation. Urodynamic analysis revealed significant (p < 0.05) improvements in total bladder capacity and voided volume, and decreases in the number and frequency of unstable contractions. Mean duration of S3 neuromodulation was 6 +/- 1 days (range 4 to 8 days). Four procedures failed due to electrode displacement in 3 cases and procedure intolerance in 1. Hemorrhage from the puncture site occurred in 1 patient. Overall urinary symptom scores were 10 +/- 3 (range 5 to 14) before the study and 5 +/- 2 (range 2 to 10) during stimulation. Although symptomatic relief was more pronounced with S3 neuromodulation, no statistically significant differences were found regarding urinary symptoms compared to TENS. CONCLUSIONS: In patients with severe detrusor instability refractory to conservative treatments the use of TENS and S3 neuromodulation produced significant changes in urodynamic parameters and presenting symptoms. Our results appear to justify evaluation with neuromodulatory techniques before definitive surgical intervention in these patients.  相似文献   
186.
Killing of human cells by the parasite Entamoeba histolytica requires adherence via an amebic cell surface lectin. Lectin activity in the parasite is regulated by inside-out signaling. The lectin cytoplasmic domain has sequence identity with a region of the beta2 integrin cytoplasmic tail implicated in regulation of integrin-mediated adhesion. Intracellular expression of a fusion protein containing the cytoplasmic domain of the lectin has a dominant negative effect on extracellular lectin-mediated cell adherence. Mutation of the integrin-like sequence abrogates the dominant negative effect. Amebae expressing the dominant negative mutant are less virulent in an animal model of amebiasis. These results suggest that inside-out signaling via the lectin cytoplasmic domain may control the extracellular adhesive activity of the amebic lectin and provide in vivo demonstration of the lectin's role in virulence.  相似文献   
187.
In summary, the National Database Committee's Audit and Validation Subcommittee is working to maximize the data completeness and quality of the STS National Database. Toward this end, we welcome your suggestions for improvement.  相似文献   
188.
Advances in the understanding of lung cancer biology have led to observations that specific genetic changes occur in premalignant dysplasia. These observations have occurred predominantly in molecular studies of resected lung tumors and consequently, they may not be fully representative of those biological abnormalities characterizing premalignant lesions in individuals without overt lung cancer. Studies of premalignant epithelial cell biology and chemoprevention are needed in this patient subgroup. Such an initiative is now underway through the lung cancer Specialized Program of Research Excellence (SPORE) grant awarded to the University of Colorado Cancer Center (and affiliated institutions) by the National Cancer Institute. To identify participants for the early detection and chemoprevention trials of the Colorado SPORE, we initiated a sputum cytology screening program targeting persons with chronic obstructive pulmonary disease and smoking histories of 40 or more pack-years. During the first 26 months after activation of the screening program, sputum samples from 632 participants were evaluated. Of these, 533 (84%) of the subjects submitted specimens deemed adequate for cytopathological interpretation; 99 (16%) provided sputum samples unsuitable for cytodiagnosis. Of those participants who submitted adequate samples, 48% had cytodiagnoses of mild dysplasia, 26 % had moderate to severe dysplasia, and 2% presented with carcinoma in situ or invasive carcinoma. Logistic regression modeling was pursued to determine whether selected demographic and/or clinical status variables could be identified as statistically significant predictors of the specific cytological outcome to be expected (mild dysplasia, moderate dysplasia, and so forth). The only apparent associations found from both univariate and multivariate analyses were that the total number of pack-years of smoking history decreased with severity of cytodiagnosis and that those individuals with mild or moderate dysplasia were more likely to be ex-smokers than those with grades of regular metaplasia or lower. Based on the initial results of the Colorado SPORE sputum cytology screening program, we conclude that persons with chronic obstructive pulmonary disease and 40 or more pack-years of smoking history have a high prevalence of premalignant dysplasia detectable through sputum cytology and should be targeted for research programs focusing on lung cancer prevention, early detection, and exploratory biomarker studies.  相似文献   
189.
IFN-gamma is a potent pro-inflammatory cytokine involved in the immunologic rejection of transplanted organs. Having previously demonstrated differential suppressive effects of methylprednisolone (MP), prednisolone (P) and cyclosporine (CsA) on dialysis patients' lymphocyte proliferative responses to phytohaemagglutinin (PHA), we studied the effects of these drugs on dialysis patients' lymphocyte IFN-gamma production during mitogenic and allogeneic (MLR) stimulation. The mean +/- SEM 50% inhibitory concentration (ng/ml) on cell proliferation was significantly lower for MP than P in PHA-stimulated haemodialysis (HD) patients' (35 +/- 7 vs 152 +/- 25, P < 0.001) and peritoneal dialysis (PD) patients' (35 +/- 11 vs 134 +/- 33, P = 0.001) cultures and in HD patients' MLR cultures (15 +/- 3 vs 48 +/- 9, P < 0.001). The mean +/- SEM fractional responses (PHA or MLR + drug/PHA or MLR) in culture supernatant IFN-gamma concentrations were significantly lower with 10(-7) M concentrations of MP than P in HD (0.19 +/- 0.05 vs 0.31 +/- 0.06, P = 0.01) and PD (0.30 +/- 0.11 vs 0.46 +/- 0.11, P < 0.05) PHA cultures and in HD MLR cultures (0.15 +/- 0.04 vs 0.28 +/- 0.07, P = 0.01). CsA (400 ng/ml) alone not only caused less than 50% inhibition of IFN-gamma production in 15/27 HD PHA, 6/14 PD PHA and 4/13 HD MLR cultures, but actually stimulated it in 9 HD and 5 PD PHA cultures. The results suggest that: (1) MP has greater immunosuppressive potential than P for renal transplant recipients; (2) the stimulation of IFN-gamma by CsA in some patients could be harmful in patients with initial allograft dysfunction; and (3) pre-transplant in-vitro assessment of recipients' PBMC responsiveness to glucocorticoids and CsA may help individualize the post-transplant immunosuppressive regimen.  相似文献   
190.
The modulatory effects of 1DMe (d-Tyr-Leu-(NMe)Phe-Gln-Pro-Gln-Arg-Phe-NH2), an agonist of Neuropeptide FF (NPFF) receptors, on opioid antinociceptive activity have been compared in naive and tolerant mice in the tail-flick and the hot-plate tests. In naive mice, 1DMe alone had no effect on pain threshold but decreased dose-dependently (3-22 nmol) the analgesic activity of morphine in both tests. In tolerant mice, injections of 60-fold lower doses of 1DMe (0.05-0.5 nmol) reverse morphine-induced analgesia in the tail-flick test but this anti-opioid effect was no longer observed with the highest doses of 1DMe tested (3-22 nmol). In the hot-plate test, the anti-opioid action of 1DMe was not detected, whatever doses tested. Neither the NPFF-like immunoreactivity content of spinal cord and of olfactory bulbs, nor the density of NPFF receptors in olfactory bulbs, were altered. These results indicate that a chronic morphine treatment modifies the pharmacological properties of NPFF but the type of pain test is crucial in determining NPFF effects.  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