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   969篇
  免费   0篇
  国内免费   3篇
化学工业   6篇
金属工艺   2篇
能源动力   3篇
冶金工业   960篇
原子能技术   1篇
  2012年   2篇
  2010年   1篇
  2009年   2篇
  2006年   1篇
  2003年   3篇
  2002年   1篇
  1999年   30篇
  1998年   301篇
  1997年   169篇
  1996年   101篇
  1995年   75篇
  1994年   44篇
  1993年   54篇
  1992年   6篇
  1991年   13篇
  1990年   6篇
  1989年   10篇
  1988年   9篇
  1987年   10篇
  1986年   2篇
  1985年   7篇
  1983年   2篇
  1982年   3篇
  1981年   9篇
  1980年   3篇
  1978年   5篇
  1977年   33篇
  1976年   65篇
  1975年   2篇
  1965年   1篇
  1955年   1篇
  1954年   1篇
排序方式: 共有972条查询结果,搜索用时 781 毫秒
31.
Blood samples from 740 Egyptian Nationals working in the tourism industry at two sites in the South Sinai governorate were screened for markers of infection with hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), and Treponema pallidum. Study subjects included 467 individuals from a rural seashore tourist village and 273 persons at two hotels in a well-established resort town. Subjects' ages ranged from 15 to 70 years; 99.3% were male. The prevalence of serologic markers for currently asymptomatic or past HBV infection alone was 20.7% (n = 153), of markers for past or chronic HCV infection alone was 7.4% (n = 55), and of markers for both HBV and HCV was 6.9% (n = 51). Of the 204 individuals positive for anti-HBV core antibody, 12 (5.9%) were also positive for hepatitis B surface antigen. Two individuals (0.3%) had a serologic market suggestive of an active syphilitic infection. No subject was found to be HIV-seropositive. History of prior injections and number of injections were associated with infection with HCV. Primary residence in the Nile delta and valley areas where schistosomiasis is highly endemic, was also a statistically significant risk factor for HCV, but not HBV infection.  相似文献   
32.
33.
Abstract DNA typing of four tetrameric repeat loci (HUMVWA, HUMTH0I, D21SII and HPRT) was carried out in a Chinese Han population from Shanghai (East China) and one from Guangzhou (South-East China) using a quadruplex PCR amplification and detection of the fluorescent-labeled alleles on the ALF DNA sequencer. All loci were in accordance with Hardy-Weinberg equilibrium except for D21S11 in the Guangzhou population. A test for population differentiation showed no statistical difference in the allele frequency distribution between the two populations. Comparison of the allele frequency data with other Chinese Han populations from North and South-West China for the STR loci HUMVWA and HUMTH01 revealed heterogeneity between Northern Chinese Han and Southern Chinese Han, which is in accordance with previous studies on the basis of protein markers.  相似文献   
34.
Amiodarone is a benzofuran derivative with a chemical structure similar to thyroxine. Originally introduced to treat angina pectoris, amiodarone was found to have antiarrhythmic properties, and in 1985, was approved in the United States for treatment of life-threatening ventricular arrhythmias. It is now used for various ventricular and supraventricular arrhythmias refractory to conventional first-line medications, and as a result, side effects have been observed with increased frequency. The most severe and potentially life-threatening of these side effects is the development of pulmonary toxicity. Typically, amiodarone pulmonary toxicity (APT) is manifested by acute pneumonitis and chronic fibrosis. Amiodarone-associated hemoptysis (AAH) is a rare occurrence. The authors describe a case of AAH successfully treated with cessation of drug and steroid therapy.  相似文献   
35.
This study examines whether a catheter mounted left intraventricular balloon may prevent left ventricular (LV) dysfunction following acute experimental myocardial infarction. In 10 anesthetized pigs, multiple coronary arterial ligations were applied around the apex of the heart. LV end-diastolic pressure (LVEDP), aortic flow (AF), and LV long and short axis fractional shortening (FS) were measured before and at 15 min intervals after ligations. At the 60th min after ligation, the LV long axis FS and AF decreased by 7.2 +/- 2.6% (p < 0.05) and 13.25 +/- 2.68% (p < 0.01), respectively, and the LVEDP increased by 4.3 +/- 1.1 mm Hg (p < 0.01) while no change was noted in the LV short axis FS. An intraventricular catheter mounted nonpulsating balloon was positioned over the endocardium of the infarcted area at the LV apex. Inflation of the nonpulsating balloon to an optimal volume, which was found to be equal to 8-10% of the LV end-diastolic volume, resulted in a reduction (by 3.8 +/- 1.2 mm Hg, p < 0.01) of the already increased LVEDP and in an increase (by 6.6 +/- 2.1%, p < 0.05) in the LV short axis FS while no statistically significant change was noted in the AF and LV long axis FS. It is concluded that an intraventricular catheter mounted balloon patch positioned over the endocardium of the infarcted area may ameliorate early LV dysfunction, possibly by interfering with the functional geometry of the LV contraction.  相似文献   
36.
The effect of various concentrations of ofloxacin, ciprofloxacin and lomefloxacin on the morphokinetic parameters of the cellular elements of the lung tissue of intact animals (mice, guinea pigs and dogs) was studied under the conditions of the tissue culture. It was shown that in a concentration of 100 micrograms/ml and the exposure time of 24 hours the drugs had no effect on the mobility and structure of the lung tissue cellular elements. When the drugs were used in a concentration of 100 micrograms/ml the mobility rate of the lymphocytes and macrophages proved to by markedly retarded by the end of the 24th hour. In a concentration of 1000 micrograms/ml the drugs killed the cell culture. There were detected no specific differences in the effect of the fluoroquinolones on the cellular elements of the lung tissue of the intact animals.  相似文献   
37.
Bioaccumulation of non-, mono-, and di-ortho-substituted chlorobiphenyls (CBs) was investigated in four species of mustelids (weasel, stoat, polecat, and otter) and their preys, from a restricted area in the northern part of The Netherlands. Diets of these mustelids ranged from terrestrial (weasel, stoat, and polecat) to aquatic (otter). Diet-specific biomagnification factors (BMFs), CB in diet relative to CB in mustelids, were calculated for the sum of 28 congeners (SigmaCB), for the sum of the toxic equivalent concentration (SigmaTEQ) and on an individual congener basis. Biotransformation was studied in relation to structural CB properties (vicinal H-atom substitution). In addition, the methylsulphonyl CB-metabolites were determined. The concentration of SigmaCB on lipid weight basis increased in the order weasel < stoat < polecat < otter. On the basis of SigmaTEQ, the order changed to weasel < polecat < stoat < otter. Most of the differences in BMFs between the CBs could be explained by the vicinal H-atom structure-activity rules. For all mustelids, the lowest BMFs were found for congeners with vicinal H-atoms in the meta, para position. Indications were found that all mustelid species can metabolize these congeners. For some of the CBs, their methylsulphonyl-CB metabolites were determined and found to be present in concentrations up to 350-fold higher than those of the parent compounds. In addition, the non-ortho CBs 126 and 169 are selectively retained in the liver of weasel, stoat, and otter. These CBs had the highest BMFs of all congeners. However, rather surprisingly, in polecat the highest BMFs were found for di-ortho-substituted CBs. This animal was able to metabolize all congeners with vicinal H-atoms in the ortho and meta position (non- and mono-ortho CBs). The information concerning the differences in bioaccumulation of CBs for closely related mustelid species increased the understanding of reported differences in PCB toxicity between mink and ferrets, and suggest that weasel, stoat, and otter are at least as sensitive to CBs as are mink, while polecats are less sensitive. As otter is exposed to much higher concentrations of CBs trough their diet than weasel and stoat, the toxic threat of CBs will be the greatest for this animal.  相似文献   
38.
PURPOSE: We describe a protocol designed to evaluate the use of twice daily radiation used together with cisplatin and 5 fluorouracil (5-FU) in the treatment of operable transitional cell carcinoma of the bladder with potential bladder preservation. MATERIALS AND METHODS: A total of 18 consecutive patients with T2-T4a bladder tumors underwent as complete a transurethral resection as possible, which was visibly complete in 14 cases. They then received twice daily radiation and infusion cisplatin and 5-FU during an induction phase. No therapy was given for 3 weeks, following which patients were reevaluated cystoscopically. Cases of clinical complete response by biopsy and cytology were consolidated with further chemotherapy/radiation using the same chemotherapeutic agents and radiation schedule. Patients who had incomplete responses were advised to undergo an immediate radical cystectomy. Of the 18 patients 15 subsequently received 3 cycles of adjuvant chemotherapy, consisting of methotrexate, cisplatin and vinblastine. Median followup for the entire group is 32 months. RESULTS: Of the 18 patients 14 had no detectable tumor after induction therapy. Of the 4 patients with persistent tumor 2 underwent radical cystectomy and 2 refused cystectomy, 1 of whom was treated with partial cystectomy and the other with consolidation chemotherapy/radiation. The actuarial overall survival at 3 years was 83%. The chance of a patient being alive at 3 years with a native bladder was 78%. No patient required cystectomy for hematuria or bladder shrinkage. Three patients in whom superficial tumors developed were treated successfully with bacillus Calmette-Guerin. Small bowel obstruction in 1 case was corrected surgically. CONCLUSIONS: This pilot study demonstrates a high rate of response to this combined chemotherapy/radiation regimen in conjunction with a visibly complete transurethral resection. Reevaluation after a short induction phase allows for the early selection of patients with persistent disease for radical cystectomy.  相似文献   
39.
To investigate the role of the sympathetic nervous system in angiotensin II (AngII)-stimulated medial and neointimal smooth muscle cell (SMC) replication, we sympathectomized rats with 6-hydroxydopamine (6-OHDA) in which the left carotid artery was injured by a balloon catheter. Balloon injury is associated with a loss of specific [3H]-prazosin binding. AngII (250 ng/kg/min), infused 2 weeks after balloon injury of the rat left carotid artery, increased systolic blood pressure by approximately 70 mm Hg. There was no effect of 6-OHDA on this pressor response. AngII increased the cumulative 5-bromo-2'-deoxyuridine (BrdU) labeling fraction (LF) in the uninjured right carotid media and the injured left carotid neointima as compared to controls (5.7+/-1.6% vs. 0.4+/-0.1%, p<0.05; 10.6+/-0.9% vs. 5.0+/-0.8%, p<0.05, respectively). 6-OHDA decreased the AngII-induced increase in LF in the media of the uninjured right carotid artery (AngII/6-OHDA 0.9+/-0.2% vs. AngII 5.7+/-1.6%, p < 0.05). 6-OHDA did not decrease the AngII-induced increase in LF in both the injured left carotid media and neointima at 4 weeks after balloon injury. The effects of chemical sympathectomy were comparable with those obtained 12 weeks after balloon injury. Thus, the data show that the sympathetic nervous system mediates the AngII-induced increase in SMC DNA synthesis, but only in the uninjured carotid media. This indicates a differential regulation of AngII-induced SMC replication in injured and uninjured vessels.  相似文献   
40.
Selectins are adhesion receptors that normally recognize certain vascular mucin-type glycoproteins bearing the carbohydrate structure sialyl-Lewisx. The clinical prognosis and metastatic progression of many epithelial carcinomas has been correlated independently with production of tumor mucins and with enhanced expression of sialyl-Lewisx. Metastasis is thought to involve the formation of tumor-platelet-leukocyte emboli and their interactions with the endothelium of distant organs. We provide a link between these observations by showing that P-selectin, which normally binds leukocyte ligands, can promote tumor growth and facilitate the metastatic seeding of a mucin-producing carcinoma. P-selectin-deficient mice showed significantly slower growth of subcutaneously implanted human colon carcinoma cells and generated fewer lung metastases from intravenously injected cells. Three potential pathophysiological mechanisms are demonstrated: first, intravenously injected tumor cells home to the lungs of P-selectin deficient mice at a lower rate; second, P-selectin-deficient mouse platelets fail to adhere to tumor cell-surface mucins; and third, tumor cells lodged in lung vasculature after intravenous injection often are decorated with platelet clumps, and these are markedly diminished in P-selectin-deficient animals.  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