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   577篇
  免费   0篇
化学工业   8篇
轻工业   1篇
一般工业技术   1篇
冶金工业   566篇
原子能技术   1篇
  2020年   1篇
  2013年   1篇
  2006年   1篇
  2005年   1篇
  1999年   8篇
  1998年   141篇
  1997年   94篇
  1996年   53篇
  1995年   44篇
  1994年   31篇
  1993年   40篇
  1992年   6篇
  1991年   10篇
  1990年   7篇
  1989年   8篇
  1988年   5篇
  1987年   7篇
  1986年   8篇
  1985年   10篇
  1983年   1篇
  1982年   2篇
  1981年   5篇
  1980年   5篇
  1978年   5篇
  1977年   18篇
  1976年   59篇
  1975年   3篇
  1973年   1篇
  1964年   1篇
  1955年   1篇
排序方式: 共有577条查询结果,搜索用时 62 毫秒
71.
PURPOSE: To quantify the risks of intrauterine antiepileptic drug (AED) exposure in monotherapy and polytherapy. METHODS: Data from five prospective European studies totaling 1,379 children were pooled and reanalyzed. Data were available for 1,221 children exposed to AED during pregnancy and for 158 children of unexposed control pregnancies. RESULTS: Overall, when comparing a subgroup of 192 children exposed to AED with 158 children of matched nonepileptic controls, there was an increased risk of major congenital malformations (MCA) in children exposed to AED during gestation [relative risk (RR) 2.3; 95% confidence interval (CI): 1.2-4.7]. A significant increase in risk was found for children exposed to valproate (VPA) (RR 4.9; 95% CI: 1.6-15.0) or carbamazepine (CBZ) (RR 4.9; 95% CI: 1.3-18.0) in monotherapy. When comparing different AED regimens during all 1,221 pregnancies, risks of MCA were significantly increased for the combination of phenobarbital (PB) and ethosuximide (RR 9.8; 95% CI: 1.4-67.3) and the combination of phenytoin, PB, CBZ, and VPA (RR 11.0; 95% CI: 2.1-57.6). Offspring of mothers using > 1,000 mg VPA/day were at a significantly increased risk of MCA, especially neural tube defects, compared to offspring exposed < or =600 mg VPA/day (RR 6.8; 95% CI: 1.4-32.7). No difference in risk of MCA was found between the offspring exposed to 601-1,000 mg/day and < or =600 mg/day. CONCLUSIONS: This reanalysis shows that VPA is consistently associated with an increased risk of MCA in babies born to mothers with epilepsy. Significant associations were also observed with CBZ. Larger prospective population-based studies are needed to evaluate the risks of many other less frequently prescribed treatment regimens, including newly marketed AEDs.  相似文献   
72.
We evaluated the influence of urine pH on the proportion of urinary benzidine (BZ) and N-acetylbenzidine present in the free, unconjugated state and on exfoliated urothelial cell DNA adduct levels in 32 workers exposed to BZ in India. Postworkshift urine pH was inversely correlated with the proportions of BZ (r = -0.78; P < 0.0001) and N-acetylbenzidine (r = -0.67; P < 0.0001) present as free compounds. Furthermore, the average of each subject's pre- and postworkshift urine pH was negatively associated with the predominant urothelial DNA adduct (P = 0.0037, adjusted for urinary BZ and metabolites), which has been shown to cochromatograph with a N-(3'-phosphodeoxyguanosin-8-yl)-N'-acetylbenzidine adduct standard. Controlling for internal dose, individuals with urine pH < 6 had 10-fold higher DNA adduct levels compared to subjects with urine pH > or = 7. As reported previously, polymorphisms in NAT1, NAT2, and GSTM1 had no impact on DNA adduct levels. This is the first study to demonstrate that urine pH has a strong influence on the presence of free urinary aromatic amine compounds and on urothelial cell DNA adduct levels in exposed humans. Because there is evidence that acidic urine has a similar influence on aromatic amines derived from cigarette smoke, urine pH, which is influenced by diet, may be an important susceptibility factor for bladder cancer caused by tobacco in the general population.  相似文献   
73.
74.
LNA (Locked Nucleic Acids, 1, X = O, Y = O) is a novel oligonucleotide analogue capable of recognizing complementary DNA and RNA with unprecedented thermal affinities. Synthesis of the first chemically modified LNA analogues is reported. A 9-mer phosphorothioate-LNA containing three LNA thymine monomers (1, X = O, Y = S, Base = thymin-1-yl) and 9-mer LNAs containing one, three or five 2'-thio-LNA monomers (1, X = S, Y = O, Base = uracil-1-yl) were able to recognize both complementary DNA and RNA with thermal affinities comparable to those of parent LNA.  相似文献   
75.
76.
Samples of connective tissue obtained from the hoof of six laminitic and eight non-laminitic adult horses were analysed zymographically to investigate whether connective tissue matrix metalloproteinases are activated or induced during laminitis. The activity or matrix metalloproteinases was substantially greater in the tissues from the laminitic horses than in the tissues from the non-laminitic horses. A comparison of the collagenolytic activity in the laminitic and control tissues showed that collagenolytic activities corresponding to the 92 kDa (P < 0.001), 72 kDa (P < 0.01) and 66 kDa (P < 0.01) bands were induced in the laminitic tissues.  相似文献   
77.
Surfactant convertase is required for conversion of heavy density (H) natural surfactant to light density (L) subtype during cycling in vitro, a technique that reproduces surfactant metabolism. To study mechanisms of H to L conversion, we prepared liposomes of dipalmitoylphosphatidylcholine (DPPC) and phosphatidylglycerol (PG), or the phospholipids (PL) in combination with either surfactant protein A (SP-A), surfactant protein B (SP-B), or both SP-A and SP-B. Phospholipids alone showed time-dependent conversion from heavy to light subtype on cycling in the absence of convertase, which was decreased by adding SP-B, but not SP-A, to phospholipids (p < 0.01 for PL+SP-B, or PL+SP-A+SP-B vs. PL, or PL+SP-A). The ultrastructure, surface activity, buoyant density, and L subtype generation on cycling PL+SP-A+SP-B with partially purified convertase or with phospholipase D were similar to those of natural TM. In conclusion, a reconstituted surfactant mimics the behavior of natural surfactant on cycling, and reveals that interaction of SP-B with phospholipids decreases L subtype generation. In addition, esterase/ phospholipase D activity is required for conversion of heavy to light subtype on cycling.  相似文献   
78.
A cigarette which heats rather than burns tobacco (Premier) was introduced in 1988, but was unacceptable due to unpleasant taste and low nicotine intake. We examined availability of nicotine from a new version (Eclipse), in the same four subjects as our earlier Premier study. Average blood nicotine boosts of 23.7 and 17.8 ng/ml were obtained from smoking a first and second Eclipse. This substantially exceeds intake from Premier (boost 13 ng/ml) and that obtained by heavy smokers from conventional brands (boost 12-15 ng/ml). Eclipse (or similar product) may be the best option for averting Peto's dire warnings of rising millions of annual smoking deaths in the 2020s, and its potential for large-scale, long-term switching warrants further study.  相似文献   
79.
BACKGROUND: We evaluated the safety and efficacy of transurethral electrovaporization of the prostate (TVP) as a new alternative treatment for patients with benign prostatic hyperplasia. METHODS: A total of 22 patients with symptomatic benign prostatic hyperplasia, including 4 with urinary retention, underwent TVP. If enough of a cavity was not created after 60 minutes of vaporization, transurethral resection of the prostate (TURP) was performed successively. International Prostate Symptom Score (I-PSS) with quality-of-life index, maximum flow rate, and postvoid residual volume were measured at baseline and at 2 weeks, 1, 3, and 6 months. A pressure-flow study was performed at baseline and at 3 or 6 months after surgery. RESULTS: TURP was required in 10 of 22 patients. At 6 months, mean I-PSS decreased from 20.0 to 5.2, quality-of-life index decreased from 4.6 to 1.1, mean maximum flow rate increased from 6.9 to 16.7 mL/s, and postvoid residual volume decreased from 152 to 32 mL. Detrusor pressure at maximum flow decreased from 108 to 39 cm H2O, with a significant relief of bladder outlet obstruction in 93% of the patients. Mean decrease in hematocrit was 4.4%, and in serum sodium, 4.8 mEq/L. None of the patients required transfusions or had TUR syndrome. A urethral stricture and a severe stress incontinence developed in 1 patient. CONCLUSION: TVP seems to be a safe and effective alternative to a standard TURP associated with fewer intraoperative complications. Although preliminary clinical results have been promising, further study is necessary to establish long-term efficacy and safety of this procedure.  相似文献   
80.
The mammalian pulmonary toxin 4-ipomeanol (IPO) is activated by the cytochrome P450 system in bronchial Clara cells in animals. The resulting metabolites bind rapidly to macromolecules, producing localized cytotoxicity. IPO has in vitro and in vivo antitumor activity in non-small cell lung cancer (NSCLC) and thus was proposed as a lung cancer-specific antitumor agent. We have completed a directed Phase I trial in patients with NSCLC. Forty-four patients (34 men and 10 women) with NSCLC were treated with IPO. All but two patients had an Eastern Cooperative Oncology Group performance status of 0 or 1. They received 91 courses of therapy with i.v. IPO; 82 courses were administered daily for five days, and 9 were single bolus doses. The dose-limiting toxicity of elevated serum transaminases was observed in three of seven patients at 922 mg/m2/day. The maximum tolerated dose was 693 mg/m2/day on 5 consecutive days every 3 weeks. One patient developed grade 4 pulmonary toxicity at 167 mg/m2/day. There was no significant hematological or renal toxicity. No objective antitumor responses were observed. Pharmacokinetic analysis of 39 patients from day 1 of IPO administration showed biexponential elimination with mean half-lives of 8.6 (alpha half-life) and 76 min (beta half-life). There was a linear relationship between the area under the plasma drug concentration-time curve and the dose of IPO. There was no significant difference between the pharmacokinetic parameters measured on day 1 and day 5. Using a 4-day in vitro cytotoxicity assay, two tumor cell lines established from patients treated at 693 mg/m2/day had IC50s of approximately 6 mM, a concentration more than 75-fold higher than the plasma levels measured in these patients. Thus, although the total amount of drug administered per cycle on a daily times five dose schedule is more than 2.5-fold higher than the recommended single daily dose, IPO is unlikely to be a useful drug for patients with lung cancer.  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