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   1540篇
  免费   5篇
电工技术   15篇
综合类   2篇
化学工业   49篇
金属工艺   26篇
机械仪表   17篇
建筑科学   12篇
矿业工程   2篇
能源动力   4篇
轻工业   24篇
水利工程   3篇
石油天然气   6篇
无线电   79篇
一般工业技术   82篇
冶金工业   1065篇
原子能技术   12篇
自动化技术   147篇
  2021年   6篇
  2018年   9篇
  2016年   3篇
  2015年   3篇
  2014年   7篇
  2013年   28篇
  2012年   8篇
  2011年   17篇
  2010年   23篇
  2009年   23篇
  2008年   15篇
  2007年   24篇
  2006年   8篇
  2005年   14篇
  2004年   21篇
  2003年   10篇
  2002年   9篇
  2001年   9篇
  2000年   11篇
  1999年   39篇
  1998年   299篇
  1997年   161篇
  1996年   136篇
  1995年   73篇
  1994年   59篇
  1993年   70篇
  1992年   16篇
  1991年   9篇
  1990年   17篇
  1989年   29篇
  1988年   21篇
  1987年   24篇
  1986年   18篇
  1985年   24篇
  1984年   24篇
  1983年   12篇
  1982年   23篇
  1981年   23篇
  1980年   17篇
  1979年   8篇
  1978年   11篇
  1977年   35篇
  1976年   65篇
  1975年   10篇
  1974年   15篇
  1973年   10篇
  1972年   11篇
  1971年   6篇
  1970年   6篇
  1966年   5篇
排序方式: 共有1545条查询结果,搜索用时 31 毫秒
991.
New thin layer densitometry and high performance liquid chromatography (HPLC) methods are described for quantitative determination of glafenine in dosage forms in the presence of its photo-degradation products and in serum in the presence of its metabolites. Mobile phases consisting of toluene-isopropyl alcohol-dimethylformamide-water (18:3:1:0.5) and methanol-water-phosphoric acid (80:120:0.5) are found to be efficient for reasonable separation and adequate resolution of glafenine from associated substances by thin layer chromatography (TLC) and HPLC techniques, respectively. The methods are used for the study of glafenine purity, stability, bioavailability, bioequivalence and tablet dissolution rate. The results obtained by TLC and HPLC techniques are in good agreement and offer the advantages of reproducibility and accuracy.  相似文献   
992.
Detection of Cr(V) in the reduction of Cr(VI) by whole live mice and its characterization were carried out by low frequency electron paramagnetic resonance (EPR). Intravenous injection of Cr(VI) to mice generated Cr(V). The Cr(V) was found predominantly in the liver with a small amount in the blood. Liver homogenates from Cr(VI) treated mice generated essentially the same Cr(V) spectrum as that obtained from the whole live mice. This Cr(V) species was identified to be a Cr(V)-nicotinamide adenine dinucleotide (NAD) (P)H complex with an oxygen bond to Cr(V). Pretreatment of the mice with ascorbic acid and glutathione reduced the Cr(V) formation, while pretreatment with reduced nicotinamide adenine dinucleotide (NADH) enhanced it. Metal chelators, ethylenediaminetetraacetic acid (EDTA), 1,10-phenanthroline, and diethylenetriaminepentaacetic acid (DTPA) inhibited the intensity of the Cr(V) signal. The results suggest that Cr(V) generated in the whole body of a live animal is a Cr(V)-NAD(P)H complex and NAD(P)H/flavoenzymes and not glutathione or ascorbate as the major one-electron Cr(VI) reductant responsible for observed formation of Cr(V)-NAD(P)H complex in vivo.  相似文献   
993.
Increased heat shock protein expression after stress in Japanese quail   总被引:1,自引:0,他引:1  
The health care received from first admission to a pediatric rheumatology clinic to 9-year follow-up was assessed in 109 patients with chronic inflammatory rheumatic diseases or chronic idiopathic musculoskeletal pain. Ninety-five of the patients had received hospital care after the first admission, of whom 53 patients > or = 18 years, 21 patients < 18 years, and 33 parents of patients < 18 years rated their degree of satisfaction with the health care from 0 to 10. Mean scores of satisfaction with different aspects of care ranged from 6.0 to 9.6. Among patients > or = 18 years, those with idiopathic pain were less satisfied than those with inflammatory rheumatic diseases on the availability of care (mean 6.4 vs. 8.5, p < 0.001), continuity of care (mean 6.5 vs. 8.4, p < 0.001), and empathy of the health care providers (mean 6.7 vs. 7.9, p <0.05). The diagnostic group and the occurrence of remission predicted the level of global satisfaction in patients > or = 18 years. In patients < 18 years, chronic family difficulties predicted patient satisfaction and physical disability and chronic family difficulties predicted parent satisfaction. In conclusion, most parents and patients with inflammatory rheumatic diseases were satisfied with the health care. However, some patients with idiopathic pain had unmet needs for care.  相似文献   
994.
Insulin, a classic vertebrate hormone, produces alterations in cellular metabolism and growth in the ciliate Tetrahymena pyriformis, as well as an increase in insulin binding upon subsequent exposure, a phenomenon known as hormonal imprinting. An antibody to a peptide corresponding to the alpha-subunit of the human insulin receptor (amino acid residues 657-670) was used to investigate the location and to partially characterize immunoreactive proteins in insulin-exposed and non-insulin-exposed cells (control). Confocal microscopy revealed immunofluorescent labeling of cilia, nuclei, vesicles and an oblong structure of unknown nature. Labeling of nuclei, mitochondria and ciliary microtubules was seen with immunoelectron microscopy. Labeling was absent on the cell and ciliary membranes by immunoelectron microscopy. Polyacrylamide gel electrophoresis revealed several differences in protein composition between control and insulin-exposed ciliary membrane extracts, especially in the 30-50 kDa range. Immunoblotting revealed 2 reactive proteins in whole cell lysates but none were detected in ciliary membrane extracts or wheat germ agglutinin affinity column eluates of T. pyriformis whole cell preparations. Based on these findings it is unlikely that a cell surface structure similar to a mammalian insulin receptor exists in T. pyriformis.  相似文献   
995.
Successful left ventricular support is dependent on adequate inflow drainage. We describe atrial cannulation using the dome of the left atrium, which in our experience has resulted in excellent inflow drainage.  相似文献   
996.
997.
We used radiostereometric analysis to compare wear rates between uncemented porous sockets and cemented all-polyethylene sockets in a series of 102 hips randomised for either a Harris-Galante or a Charnley cup. Wear was evaluated in 95 hips at a mean of five years (2 to 7). All hips had a cemented, 22 mm head mono-bloc Charnley stem. The mean annual wear rate was 0.09 mm in the Charnley sockets and 0.10 mm in the Harris-Galante sockets, with no statistically significant differences in wear, migration or rotation. We conclude that, up to five years, the wear characteristics of the modular and porous Harris-Galante socket resemble that of the Charnley socket.  相似文献   
998.
p21waf1 has been shown to mediate the p53-dependent growth arrest induced by DNA-damaging agents. Several functions have been ascribed to p21waf1 that could be involved in this growth arrest. For one, p21waf1 is an efficient inhibitor of cyclin-dependent kinases (CDKs). Also, p21waf1 can interact with proliferating cell nuclear antigen (PCNA), and as such inhibit in vitro DNA-replication. Finally, p21waf1 has been reported to inhibit stress-activated protein kinases (SAPKs). In order to study these multiple functions of p21waf1 we have established U2OS-derived cell lines, in which the expression of p21waf1 can be regulated by the concentration of tetracycline in the culture medium. We observed a virtually complete, but reversible inhibition of cell growth upon induction of p21waf1-expression. Both [3H]thymidine-incorporation and CDK2-activity were strongly inhibited by p21waf1. Upon induction of p21waf1 cells accumulated with a 2N or 4N DNA content suggesting events in G1 and G2 can be inhibited by p21waf1. Indeed, kinase activity associated with cyclin B was reduced dramatically upon induction of p21waf1, although cyclin B continues to be expressed. In contrast, p21waf1 does not seem to inhibit the function of PCNA in ongoing DNA replication, since cells expressing high levels of p21waf1 apparently progressed normally through S-phase. Also, the activity of SAPKs was not substantially affected by the high levels of p21waf1. We conclude that, at least in these U2OS-derived cells, p21waf1 functions as an inhibitor of CDK-activity in G1 and G2, but not as an inhibitor of PCNA or SAPKs.  相似文献   
999.
BACKGROUND: Ventricular septal myotomy/myectomy (Morrow procedure) is the standard surgical option for severely symptomatic patients with hypertrophic cardiomyopathy (HCM) and marked basal obstruction to left ventricular outflow due to mitral valve systolic anterior motion. In some patients, however, congenital malformations of the mitral apparatus may be responsible for outflow obstruction; the failure to recognize this morphology before operation could have adverse consequences. METHODS AND RESULTS: We recently evaluated 2 patients with obstructive HCM operated on at Mayo Medical Center in 1997 who demonstrated direct anomalous papillary muscle insertion into the anterior mitral leaflet, producing muscular midcavity obstruction. This anomaly is potentially identifiable with echocardiography by exaggerated anterior displacement of hypertrophied papillary muscles within the left ventricular cavity and the direct continuity between papillary muscle and anterior leaflet associated with a rigid motion pattern of the mitral apparatus. Echocardiographic diagnosis, however, was confused in both patients by the association of systolic anterior motion of the mitral valve, probably produced by freely mobile margins of the mitral leaflet unencumbered by papillary muscle insertion, and in 1 patient probably representing a second and more basal level of obstruction. Because outflow tract morphology was judged unsuitable for conventional myotomy/myectomy, a novel surgical strategy was designed to remove the outflow gradient in which an extensive myectomy trough (wider at its apical than basal extent) was created within the ventricular septum to papillary muscle level; also, in 1 patient, attachment of anterolateral papillary muscle with the lateral free wall was partially severed to increase mobility of the mitral apparatus. After surgery, both patients reported substantial relief of symptoms and improved exercise tolerance and also showed reduced or abolished basal outflow obstruction. CONCLUSIONS: In HCM, outflow obstruction due to anomalous papillary muscle insertion directly into anterior mitral leaflet is challenging to identify but should always be contemplated before operative intervention. This important (but often unsuspected) congenital malformation may require alternative surgical strategies to standard myotomy/myectomy, similar to those described here.  相似文献   
1000.
OBJECTIVE: Recurrent coarctation is a complication which is seen at a consistent rate following all types of repair for coarctation of the aorta. Particularly disappointing late results are reported in younger infants, under 3 months of age. This retrospective analysis was undertaken to compare the outcomes on late follow-up between subclavian flap angioplasty and resection and end-to-end repair, in this age group. METHODS: Over a 12-year period, between 1982 and 1994, 86 infants under 3 months of age underwent surgical repair of coarctation (39 resections and end-to-end repair, and 47 subclavian flap angioplasty procedures). Operative mortality was not significantly different (P = 0.6) between resection and end-to-end repair (5.1%) and subclavian flap angioplasty (8.5%). All operative deaths (six patients) were in infants with associated ventricular septal defects. The mean follow-up for all patients was 7.95 years +/- 4.10 (range 0-14.5 years). The 5-year survival for resection and end-to-end repair was 87 +/- 5%, compared to 75 +/- 7% for subclavian flap angioplasty (P = 0.2). RESULTS: Recurrent coarctation occurred in nine patients who needed reoperation. The reoperation-free rates at both 5 and 10 years for resection and end-to-end anastomosis, and subclavian flap repair were 86 +/- 6% and 90 +/- 5%, respectively. The recurrence in the resection and end-to-end anastomosis group were due to constrictive scarring at the anastomosis, whereas periductal tissue and growth of posterior aortic ridge caused recurrence in the subclavian flap angioplasty group. There were no deaths during reoperation for recurrence. CONCLUSIONS: Both procedures are extremely effective for coarctation repair in young infants and run a similar risk of recurrence, which are due to completely different mechanisms. The surgeon's expertise is the major determinant of outcome.  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