全文获取类型
收费全文 | 493篇 |
免费 | 1篇 |
专业分类
电工技术 | 3篇 |
综合类 | 8篇 |
化学工业 | 3篇 |
金属工艺 | 1篇 |
机械仪表 | 2篇 |
建筑科学 | 2篇 |
矿业工程 | 1篇 |
能源动力 | 1篇 |
轻工业 | 1篇 |
无线电 | 18篇 |
一般工业技术 | 8篇 |
冶金工业 | 439篇 |
原子能技术 | 1篇 |
自动化技术 | 6篇 |
出版年
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 3篇 |
2010年 | 5篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 8篇 |
1998年 | 123篇 |
1997年 | 90篇 |
1996年 | 48篇 |
1995年 | 30篇 |
1994年 | 15篇 |
1993年 | 29篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 7篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 10篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 16篇 |
1976年 | 51篇 |
1970年 | 1篇 |
排序方式: 共有494条查询结果,搜索用时 15 毫秒
41.
TV Ellerbrock PE Harrington TJ Bush SA Schoenfisch MJ Oxtoby JJ Witte 《Canadian Metallurgical Quarterly》1995,86(3):400-404
OBJECTIVE: To investigate why women who use crack cocaine are at increased risk of human immunodeficiency virus (HIV) infection. METHODS: One thousand one hundred fifty-two (99.7%) of 1155 consecutive prenatal patients attending a rural public health clinic were interviewed about drug use and sexual practices and tested for HIV infection and other sexually transmitted diseases. RESULTS: Fifty-one (4.7%) of 1096 pregnant women reported ever using crack cocaine, but only five (10%) of the crack cocaine users had ever injected drugs. Eighteen (35%) of the crack users were HIV infected compared with 22 (2%) of the 1045 women who reported never using crack (odds ratio 25, 95% confidence interval 12-52; P < .001). Crack users were more likely to have had a known HIV-infected sex partner, exchanged sex for money or drugs, and tested positive for syphilis than were non-crack users (for each comparison, P < .001). Before using crack, 18% of crack users had exchanged sex for money or drugs and 8% had averaged three or more sex partners per month; in contrast, after beginning to use crack, 76% of crack users exchanged sex for money or drugs and 63% averaged three or more sex partners per month (for both comparisons, P < .001). Crack users who were not HIV infected were more likely to have almost always used condoms and/or had fewer than three sex partners per month than were HIV-infected crack users (P < .01). CONCLUSION: Women who reported using crack cocaine were at an increased risk of HIV infection because crack use was associated with a significant increase in unprotected sexual contact. 相似文献
42.
Microscopy is a basic tool for cell biologists. Recent progress of electronics and computer science made powerful methodologies for digital processing of microscopic images easily available. These methods allowed impressive increase of the power of conventional microscopy. Dramatic image enhancement may be achieved by combination of filtering techniques, computer-based deblurring and contrast enhancement. Quantitative treatment of digitized images allows absolute determination of the density of different components of the observed sample, including antigens, intracellular calcium and pH. Morphometric studies are also greatly facilitated by image processing techniques. The capture of fast phenomena may be performed by transfer of small portion of microscopic images into computer memory as well as particular use of confocal microscopy. Finally, improved display of experimental data through coded colors or other procedures may enhance the amount of information that can be conveyed by visual examination of microscopical images. The purpose of the present review is to describe the basic principles of image processing and exemplify the power of this approach with a variety of illustrated applications to conventional, fluorescence or electron microscopy as well as confocal microscopy. 相似文献
43.
TV Nasedkina AE Kuz'minova SA Surkov NM Pleskach VV Prokof'eva IM Spivak VM Mikhel'son AI Poletaev 《Canadian Metallurgical Quarterly》1997,39(9):809-821
Lymphoblastoid cell lines from patients with xeroderma pigmentosum (2 forms) and progeria (unusual form) were established using transformation of peripheral blood lymphocytes by Epstein--Barr virus. The influence of different UV doses on cell vitality, proliferation and cell cycle progression was studied by means of flow cytometry. The cell vitality was determined after incubation of cells with etidium bromide and FDA. We used cytograms with two logarithmic signals (log green/log red) to discriminate the cell cycle status. Cell cultures were used with density of 500,000 cells per 1 ml, previously synchronized at G-phase by the incubation in a medium with low serum content. The effect of UV irradiation was followed during 72 h. Among four analysed cell lines only line XP2SP demonstrated enhanced UV sensitivity, expressed by decreasing of the amount of living cells after the UV dose of 2.5 J/m2 and higher. The cell cycle studies showed that cells were blocked in S-phase and simultaneously the amount of apoptotic cells with both reduced DNA content and ability to bind FDA was seen increased. Similar events were observed in the control line only after the dose of 20 J/m2 and higher. 相似文献
44.
KB Aslanidi OV Aslanidi DM Vachadze OA Mornev TV Potapova LM Chailakhyan EG Shtemanetyan 《Canadian Metallurgical Quarterly》1997,11(3):349-365
To describe electrical phenomena observed in growth of Neurospora crassa hyphae, a theoretical model was developed considering the hypha as a one-dimensional electric cable with non-uniform longitudinal distribution of current sources reflecting the activity of proton pumps. A profile of the density of the pump current along the hypha is proposed, at which the results of simulation quantitatively coincide with the results of physiological experiments. The model values of energy coupling in the growth zones were estimated. The experimental dependence of the elongation rate of regenerating apical hypha fragments on their lengths was determined. Based on the comparison of these experimental results with the results of analysis of the model, the contribution of the axial metabolite transport, from the distal parts of the hypha to the apical part, to the dynamics of the apical cell growth was estimated. The possibility of evaluating the intensity of high-molecular-weight syntheses and/or accumulation of substances in granules was demonstrated. The growth rate of the regenerating hypha fragments was shown to correlate with the electric current flowing into the apical fragment 0.2-mm in length. 相似文献
45.
JA Asensio D Demetriades JD Berne A Falabella H Gomez J Murray EE Cornwell G Velmahos H Belzberg W Shoemaker TV Berne 《Canadian Metallurgical Quarterly》1997,174(1):54-60
OBJECTIVE: It is necessary to have thorough knowledge of the survival of extreme low birth weight infants (ELBWI) in order to make it easier for obstetricians, neonatologists and the family to make a decision. PATIENTS AND METHODS: A revision of the 100 ELBWI in our service between 1988 and 1995, considering live births, those deceased in the same birthing room and those followed until their discharge from the hospital, was performed. The differences between the periods before and after the introduction of pulmonary surfactant in 1992 were analyzed. RESULTS: The total survival was 37% for those with a birth weight superior to 750 g or 26 weeks gestation. There were 44.2% males and 28.9% females. The total survival improved from 26.1% during 1988-1991 to 46.3% during the period of 1992-1995. During this period (1992-1995), the newborns weighing more than 750 g had a survival rate of 72.4% and for those of 26 weeks gestation it was 73.3%. Those born at 28 weeks gestation and those with 25 weeks of gestation and weighing more than 750 g, the total survival was 63% and the survival rate in the last four years was 75.9%. CONCLUSIONS: The mortality of the ELBWI descends in similar proportion to the remainder fo the ELBWI. In order to predict the prognosis, it would be necessary to carry out a correct ultrasound estimation of the gestational age and weight. It is necessary to offer a mother in the process of childbirth with a fetus of 28 weeks gestation or with 25 weeks gestation and a fetus with an ultrasound weight greater than 750 g, intrapartum fetal monitoring and to finish by Cesarean section in case of acute fetal distress, as well as intense and immediate neonatal attention as indicated by the index of survival reached in the group mentioned during the later years. 相似文献
46.
TV Korneenko NB Pestov MB Egorov MV Ivanova MB Kostina MI Shakhparonov 《Canadian Metallurgical Quarterly》1997,23(10):800-804
The N-terminal fragment of ATP1AL1, the possible catalytic subunit of human ouabain-sensitive H+,K(+)-ATPase, was expressed in Escherichia coli cells as two recombinant proteins: the Ser14-Ile104 fragment or the same fragment containing His6 sequence at its N-end. The second protein was purified by metal-affinity chromatography and used as an antigen to construct two hybridoma lines producing antibodies of the IgM class. These monoclonal antibodies were shown to recognize not only the starting antigen but also the full-size recombinant ATP1AL1 protein and do not react with Na+,K(+)-ATPase. 相似文献
47.
TV Lasukova EV Uskina SA Afanas''iev IV Ponomarenko NV Naryzhnaia AM Cherniavski? IuB Lishmanov 《Canadian Metallurgical Quarterly》1997,60(5):51-53
Comparative study of the cardioprotective effect of antioxidants emoxipin and hystochrom was conducted in patients with chronic ICD during and after operation for aorto-coronary shunting. Both drugs effectively inhibited LPO activation and reduced the reperfusion damage to the myocardium recorded according to the release of MB-PCK into the blood. The new antioxidant hystochrom proved to be more effective. Its prevalent effect is associated with its higher antioxidant activity. 相似文献
48.
INTRODUCTION: Comprehensive emergency medical services and helicopter aeromedical transport systems have been developed based on the principle that early definitive care improves outcome. The purpose of this study was to compare outcomes between patients transported by helicopter and those transported by ground. METHODS: Data were obtained from the North Carolina Trauma Registry for the period between 1987 and 1993 on all patients transported by helicopter and ground admitted to one of the eight state designated trauma centers. Study patients included only those who were transported directly from the scene of injury to the trauma center (interhospital transfers were excluded). Mortality (outcome) was compared after patient stratification by injury severity and transport time, using Cochran-Mantel-Haenszel statistics and logistic regression-derived probabilities of survival. RESULTS: One thousand three hundred forty-six patients (7.3% of the total) were transported from scene to trauma center by helicopter and 17,144 were transported by ground. In patients transported by helicopter, the mean Trauma Score was lower (12 +/- 3.6) versus 14.3 +/- 3.6 (p < 0.001) and the mean Injury Severity Score was higher (17 +/- 11.1) versus 10.8 +/- 8.4 (p < 0.001). A trend toward increased survival was observed among patients transported by helicopter with a higher Injury Severity Score. Statistical significance was achieved only for patients with a Trauma Score between 5 and 12 and Injury Severity Score between 21 and 30. CONCLUSION: The large majority of trauma patients transported by both helicopter and ground ambulance have low injury severity measures. Outcomes were not uniformly better among patients transported by helicopter. Only a very small subset of patients transported by helicopter appear to have any chance of improved survival based on their helicopter transport. This study suggests that further effort should be expended to try to better identify patients who may benefit from this expensive and risky mode of transport. 相似文献
49.
50.
O Fernandes RP Souto JA Castro JB Pereira NC Fernandes AC Junqueira RD Naiff TV Barrett W Degrave B Zingales DA Campbell JR Coura 《Canadian Metallurgical Quarterly》1998,58(6):807-811
Traditional molecular and biochemical methods, such as schizodeme analysis, karyotyping, DNA fingerprinting, and enzyme electrophoretic profiles, have shown a large variability among Trypanosoma cruzi isolates. In contrast to those results, polymerase chain reaction (PCR) amplification of sequences from the 24S alpha ribosomal RNA gene and from the mini-exon gene nontranscribed spacer indicated a dimorphism among T. cruzi isolates, which enabled the definition of two major parasite lineages. In the present study, 86 T. cruzi field stocks (68 isolated from humans with defined presentations of Chagas' disease and 18 from triatomines) derived from four Brazilian geographic areas were typed by the PCR assay based on the DNA sequences of the mini-exon and 24S alpha rRNA genes. These stocks were ordered into the two major T. cruzi lineages. Lineage 1 was associated mainly with human isolates and lineage 2 with the sylvatic cycle of the parasite. 相似文献