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   1544篇
  免费   0篇
电工技术   1篇
化学工业   8篇
轻工业   2篇
无线电   1篇
一般工业技术   4篇
冶金工业   1526篇
自动化技术   2篇
  2021年   1篇
  2020年   1篇
  2014年   1篇
  2013年   2篇
  2012年   1篇
  2011年   2篇
  2003年   1篇
  1999年   37篇
  1998年   464篇
  1997年   275篇
  1996年   174篇
  1995年   101篇
  1994年   71篇
  1993年   109篇
  1992年   12篇
  1991年   13篇
  1990年   12篇
  1989年   20篇
  1988年   24篇
  1987年   20篇
  1986年   28篇
  1985年   18篇
  1983年   1篇
  1982年   8篇
  1981年   8篇
  1980年   12篇
  1978年   2篇
  1977年   39篇
  1976年   84篇
  1975年   2篇
  1955年   1篇
排序方式: 共有1544条查询结果,搜索用时 15 毫秒
31.
32.
33.
The conserved residue Asp477 in yeast transketolase is located in the substrate channel of the enzyme and forms a hydrogen bond with the C2-hydroxyl group of the acceptor substrate. The significance of this interaction for the recognition of the preferred acceptor substrates, D-alpha-hydroxyaldehydes was investigated by site-directed mutagenesis. In the wild-type enzyme the kcat/KM values are by three to four orders of magnitude lower for 2-deoxyaldoses or substrates with L-configuration at the C2-atom. In the Asp477 Ala mutant, the kcat/KM values for D-alpha-hydroxyaldehydes are decreased by a thousandfold, while the kcat/KM values for substrates with L-configuration or 2-deoxyaldoses are similar to wild-type enzyme. These results indicate that Asp477 is involved in determining the enantioselectivity of transketolase.  相似文献   
34.
35.
The efficacy and safety of oral sildenafil, a potent inhibitor of phosphodiesterase type 5, were evaluated in men with diabetes mellitus and erectile dysfunction (ED). Twenty-one men (aged 42-65 years) were enrolled in a double-blind, placebo-controlled, three-way crossover study conducted in two parts. In part I, the effect of a single dose (25 mg or 50 mg) of sildenafil or placebo on penile rigidity was assessed by penile plethysmography during visual sexual stimulation. In part II, daily diary records of erectile activity and a global efficacy question were used to evaluate once-daily dosing with 25 mg or 50 mg of sildenafil or placebo for 10 days. After a single 50 mg dose of sildenafil, the adjusted geometric mean duration (min) of penile rigidity >60% at the base of the penis during visual sexual stimulation was significantly increased (10.1 min) compared with placebo (2.8 min; p = 0.0053). In part II, sildenafil significantly increased the number of erections considered sufficiently hard for vaginal penetration compared with placebo (p = 0.0005). Improved erections were reported by 50% and 52% of patients treated with 25 mg and 50 mg of sildenafil, respectively, compared with 10% of those receiving placebo (p values < 0.05). Adverse events were mostly mild or moderate in nature and included muscular pains, headache, and dyspepsia. Sildenafil is a well-tolerated and potentially efficacious oral treatment for ED in men with diabetes mellitus.  相似文献   
36.
The aim of this study was to compare the results of open retropubic (OC) and laparoscopic (LC) colposuspension to the Cooper's ligament (Burch operation). We matched retrospectively 72 LC and OC according to their ages, the type of associated operations and the clinical stages of their urinary incontinence. We excluded associated prolapsus, previous surgical procedure for urinary incontinence, maximal urethral closure pressure lower than 30 cms of water and instability of the detrusor. We estimated the comparability of our two series about the other criteria which have an effect upon the post operative results in literature. The mean follow up was 17 months for LC and 46 months for OC. LC operative time was longer than (Mean: LC: 89 minutes, OC: 42 minutes), women considered LC less aching than OC. They needed less postoperative analgesia, mostly given only just the day of the procedure. LC length of hospitalization and return to normal activity was shorter than OC (Mean: LC: 3 days--OC: 6, 7 days; LC: 15 days--OC: 21 days). The graphs of the subjective cure and improvement rates made according to the Kaplan-Meier method could be compared with the log rank test. (Cure after one year: LC 79%, OC 69%--Improvement after one year: LC 85%, OC 82%--Cure after two years: LC 68%--OC 64%--Improvement after two years: LC 80%--OC 75%).  相似文献   
37.
The pET(scF11) plasmid was constructed comprising the gene of a single-chain antibody against human ferritin. This plasmid encodes the leader peptide pelB followed by the heavy chain variable V(H) domain, (Gly4Ser)3 linker peptide, and light chain variable V(L) domain. The correctly processed scF11 antibody was expressed in Escherichia coli as an insoluble protein without the leader peptide. Purified soluble scF11 was obtained after solubilization in 6 M GdnHCl followed by a sequential dialysis against decreasing urea concentrations and ion-exchange chromatography. ScF11 demonstrated only a approximately 8-fold decrease in the affinity (Ka = 5.1 x 10(8) M(-1) in RIA and 1.8 x 10(8) M(-1) in ELISA) vs. the parent IgG2a/kappa monoclonal antibody F11. The emission maximum of intrinsic fluorescence strongly suggests a compact conformation with tryptophanyl fluorophores buried in the protein interior, consistent with the functionality of the protein. However, scF11 demonstrated (i) the lack of denaturant-induced fluorescence 'dequenching' effect characteristic of the completely folded parent antibody, and (ii) prominent binding, under physiological conditions, of a hydrophobic probe 8-anilino-1-naphthalenesulfonate (ANS) recognizing partially structured states of a protein. These findings are indicative of an incomplete tertiary fold that gives ANS access to the protein hydrophobic core. This work provides the first indication that the functional single-chain antibody scF11 displays some properties of a partially structured state and therefore may possess incomplete folding.  相似文献   
38.
39.
40.
OBJECTIVE: This study aims to evaluate the risk of esophagectomy in the elderly compared with younger patients and to determine whether results of esophagectomy in the elderly have improved in recent years. SUMMARY BACKGROUND DATA: An increased life expectancy has led to more elderly patients presenting with carcinoma of the esophagus in recent years. Esophagectomy for carcinoma of the esophagus is associated with significant morbidity and mortality, and advanced age is often considered a relative contraindication to esophagectomy despite advances in modern surgical practice. METHODS: The perioperative outcome and long-term survival of 167 elderly patients (70 years or more) with esophagectomy for carcinoma of the esophagus were compared with findings in 570 younger patients with esophagectomy in the period 1982 to 1996. Changes in perioperative outcome and survival between 1982 to 1989 and 1990 to 1996 were separately analyzed. RESULTS: The resection rate in the elderly was 48% (167/345), lower than the 65% (570/874) resection rate in younger patients (p < 0.001). There were significantly more preoperative risk factors and postoperative medical complications in the elderly, but no significant differences were observed in surgical complications. The 30-day mortality rate was higher in the elderly (7.2%) than in younger patients (3.0%) (p = 0.02), but the hospital mortality rate was not significantly different in the elderly (18.0%) and younger age groups (14.4%) (p = 0.27). The long-term survival after curative resection in elderly patients was worse than younger patients (p = 0.01). However, when deaths from unrelated medical conditions were excluded from analysis, survival was similar between the two age groups (p = 0.23). A comparison of data for the periods 1982 to 1989 and 1990 to 1996 revealed that the resection rate had increased from 44% to 54% in the elderly, with significantly fewer postoperative complications and lower 30-day and hospital mortality rates. Long-term survival has also improved, although this has not reached a statistically significant level. CONCLUSIONS: With current surgical management, esophagectomy for carcinoma of the esophagus can be carried out with acceptable risk in the elderly, but intensive perioperative support is required. The improved results of esophagectomy in the elderly in recent years are attributed to increased experience and better perioperative management. Long-term survival was similar to that of younger patients, excluding deaths caused by unrelated medical conditions.  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