全文获取类型
收费全文 | 4166篇 |
免费 | 1篇 |
专业分类
化学工业 | 18篇 |
金属工艺 | 1篇 |
建筑科学 | 1篇 |
矿业工程 | 1篇 |
能源动力 | 4篇 |
轻工业 | 4篇 |
无线电 | 1篇 |
一般工业技术 | 4篇 |
冶金工业 | 4124篇 |
自动化技术 | 9篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2018年 | 2篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2013年 | 3篇 |
2011年 | 3篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 1篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 12篇 |
1999年 | 122篇 |
1998年 | 1228篇 |
1997年 | 762篇 |
1996年 | 453篇 |
1995年 | 255篇 |
1994年 | 208篇 |
1993年 | 249篇 |
1992年 | 32篇 |
1991年 | 37篇 |
1990年 | 53篇 |
1989年 | 47篇 |
1988年 | 69篇 |
1987年 | 46篇 |
1986年 | 44篇 |
1985年 | 44篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 19篇 |
1981年 | 29篇 |
1980年 | 40篇 |
1978年 | 4篇 |
1977年 | 123篇 |
1976年 | 245篇 |
1975年 | 5篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1961年 | 1篇 |
1955年 | 5篇 |
1954年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有4167条查询结果,搜索用时 0 毫秒
961.
The results of the treatment of 316 patients with various injuries of abdomen are summarized. 144 (45.6%) of the patients were operated on vital indications (internal bleeding, peritonitis). Additional instrumental examination was necessary in 172 (54.4%) of the patients. Urgent diagnostic laparoscopy was performed in 118 of them. This procedure is indicated in patients with the absence of the symptoms of "acute abdomen" hospitalised in less than 2 hours from the moment of penetrating injury. It is also indicated in case of a doubtful diagnosis in a blunt injury of abdomen, and in alcoholic intoxication. Three groups of the patients were distinguished: 1) patients with indications for urgent surgery (38.1%); 2) patients with indications for conservative treatment (17.8%); 3) patients with indications for out-patient follow-up (44.1%). This policy made it possible to decrease the number of diagnostic laparotomies to 11%, the period of limited disability by 5.8 + 0.3 days, decrease lethality to 6%. 相似文献
962.
H Pircher K Brduscha U Steinhoff M Kasai T Mizuochi RM Zinkernagel H Hengartner B Kyewski KP Müller 《Canadian Metallurgical Quarterly》1993,23(3):669-674
The cellular requirements of T cell tolerance induction in the thymus by clonal deletion was investigated by using an in vitro assay: thymocytes from mice expressing a transgenic TcR specific for lymphocytic choriomeningitis virus (LCMV) and H-2Db were co-cultured with various H-2b cell types as antigen-presenting cells in the presence of the antigenic LCMV peptide. The results revealed that all cell lines examined including embryonic and transformed fibroblasts, melanoma cells, cortical thymic epithelial cells, lymphomas and neuronal cells induced an antigen dose-dependent deletion of CD4+8+ thymocytes. Similarly, highly enriched accessory cell populations from thymus and spleen (macrophages, dendritic and cortical epithelial cells, i.e. thymic nurse cells) could induce antigen-specific depletion of immature CD4+8+ thymocytes. Depending on the cell type examined micromolar to picomolar concentration of LCMV peptide were required to induce deletion. The effectiveness of deletion by the different cell types did not correlate with their major histocompatibility class I expression level; it was, however, influenced by the presence of ICAM-1 adhesion molecules. 相似文献
963.
WR Chitwood CL Wixon JR Elbeery JF Moran WH Chapman RM Lust 《Canadian Metallurgical Quarterly》1997,114(5):773-80; discussion 780-2
OBJECTIVE: This study was done to determine the potential benefits of minimally invasive mitral surgery performed with intraoperative video assistance. METHODS: From May 1996 until March 1997, a minithoracotomy and video assistance were used in 31 consecutive patients undergoing mitral repair (n = 20) and replacement (n = 11). Their ages ranged from 18 to 77 years (59 +/- 2.6 years; mean +/- standard error of the mean). Ejection fractions were 35% to 62% (55% +/- 1.5%). Operations were done with either antegrade/retrograde (n = 10) or antegrade (n = 19) cold blood cardioplegia and a new transthoracic crossclamp or with ventricular fibrillation (n = 2). Peripheral arterial cannulation (n = 28) and pump-assisted right atrial drainage (n = 26) were used most often. RESULTS: No hospital deaths occurred, but the 30-day mortality was 3.2%. Complications included deep venous thrombosis and a phrenic nerve palsy in one patient each. No patient had a stroke or required reoperation for bleeding. Postoperative echocardiography showed excellent valve function in all but one patient. Cardiopulmonary bypass and arrest times averaged 183 +/- 7.2 and 136 +/- 5.5 minutes, respectively. Compared with 100 patients having conventional mitral valve operations, these patients had significantly shorter hospitalization times (8.6 +/- 0.5 vs 5.1 +/- 0.9 days, p = 0.05). Moreover, 81% of the later cohort were discharged between day 3 and 5 (3.6 +/- 0.2 days). Hospital charges (decreases 27%, p = 0.05) and costs (decreases 34%, p < 0.05) were less than in conventional operations. Patient follow-up suggested minimal perioperative pain and rapid recovery. CONCLUSIONS: Early results suggest that video-assisted minimally invasive mitral operations can be done safely. These methods may benefit patients through less morbidity, earlier discharge, and lower cost. 相似文献
964.
VR Kshettry TJ Kroshus MI Hertz DW Hunter SJ Shumway RM Bolman 《Canadian Metallurgical Quarterly》1997,63(6):1576-1583
BACKGROUND: Airway anastomosis complications continue to be a source of morbidity for lung transplant recipients. METHODS: This study analyzes incidence, treatment, and follow-up of airway anastomotic complications occurring in 127 consecutive lung transplant airway anastomoses (77 single lung and 25 bilateral sequential lung). Complications were categorized as stenosis (11), granulation tissue (8), infection (7), bronchomalacia (5), or dehiscence (3). Follow-up after treatment ranged from 6 months to 4 years. RESULTS: Nineteen airway anastomosis complications (15.0%) occurred in 18 patients. Telescoping the airway anastomosis reduced the complication rate to 12 of 97 (12.4%), compared with 7 of 30 (23.3%) for omental wrapping, (p = 0.15). Complications developed in 13 of 77 single-lung airway anastomoses (16.9%) versus 6 of 50 bilateral sequential lung recipients (12.0%). Treatment consisted of stenting (9 airway anastomoses), bronchodilation (8), laser debridement (4), rigid bronchoscopic debridement (2), operative revision (2), and growth factor application (2). There was no difference in actuarial survival between patients with or without airway anastomosis complications (p = 1.0). CONCLUSIONS: Airway anastomosis complications can be successfully managed in the immediate or late postoperative period with good outcome up to 4 years after intervention. 相似文献
965.
OBJECTIVE: To measure responses of cows to supplemental Se intake in excess of nutritional requirements, but lower than recognized toxic dosages. ANIMALS: 24 healthy adult Holstein cows. PROCEDURE: Cows were allotted to 4 groups and fed sodium selenite to provide 0, 3, 20, or 50 mg of Se/cow/d for 90 days. Subsequently, the dosage for the group receiving 50 mg/cow/d was increased to 100 mg/cow/d for 28 d. Blood, liver specimens, feces, and urine were obtained at points during the trial. RESULTS: Serum and blood Se concentrations in groups receiving 20 or 50 mg/cow/d increased over time, compared with controls (P < 0.01). Increasing supplemental Se intake to 100 mg/cow/d further increased serum and blood Se concentrations (P < 0.05). Urine, fecal, and liver Se concentrations increased more markedly in response to treatment than did those of serum or blood. No effect of Se treatment was seen on blood cell counts or serum activities of hepatocellular enzymes. Likewise, neither titer response to rabies vaccination nor lymphocyte blastogenic response to nonspecific mitogens was affected by Se treatment. Objective or subjective physical signs of Se toxicosis were not observed at any Se dosage. CONCLUSIONS: Inorganic Se intakes of up to 50 mg/d for 90 days or 100 mg/d for 28 days by adult Holstein cows do not affect the variables measured. CLINICAL RELEVANCE: Intakes of Se as sodium selenite in amounts 10 to 30 times the nutritional requirements are unlikely to cause health problems in adult cows. Urine and feces are good test samples for detection of Se supplementation greater than requirements. 相似文献
966.
967.
BACKGROUND: The human health effects of exposure to indoor nitrogen dioxide (NO2) are unclear, and few studies have examined the effects of short-term peak levels of exposure. METHODS: The association between indoor exposure to NO2 and respiratory illness was examined in 388 children aged 6-11 years. The NO2 levels were monitored during winter in 41 classrooms, from four schools with unflued gas heating and four schools with electric heating. Each classroom was monitored daily with 6-hour passive diffusion badge monitors over nine alternate weeks, and with hourly monitors over two of those weeks. Children living in homes with unflued gas appliances were also monitored daily over four evenings during times of gas use. RESULTS: Exposure to NO2 at hourly peak levels of the order of > or = 80 ppb, compared with background levels of 20 ppb, was associated with a significant increase in sore throat, colds and absences from school. An increase in cough with phlegm was marginally significant. Significant dose-response relationships were demonstrated for these four measures with increasing levels of NO2 exposure. CONCLUSIONS: Short-term peak levels of exposure are important to consider in relation to adverse respiratory effects associated with NO2 exposure. 相似文献
968.
Pulsed photoacoustic spectroscopy was used to study the penetration of sunscreen chromophores into human skin. This study focuses on basic solutions containing single typical filter molecules, as used in current sunscreens, dissolved in mineral oil. The pulsed form of the photoacoustic technique was preferred because it provides more detailed information on the filter distribution within the different layers of human skin. A new methodology provides better insight into the diffusion process through signal analysis in the time and frequency domains, allowing for global and depth-related characterization. The penetration of the chromophore influences the response signal by inducing changes in the optical and thermal properties at different depths within the medium. The light scattering effect of titanium dioxide was demonstrated by the same technique. 相似文献
969.
Local chemical gradients can have a significant impact on bacterial population distributions within subsurface environments by evoking chemotactic responses. These local gradients may be created by consumption of a slowly diffusing nutrient, generation of a local food source from cell lysis, or dissolution of nonaqueous phase liquids trapped within the interstices of a soil matrix. We used a random walk simulation algorithm to study the effect of a local microscopic gradient on the swimming behavior of bacteria in a porous medium. The model porous medium was constructed using molecular dynamics simulations applied to a fluid of equal-sized spheres. The chemoattractant gradient was approximated with spherical symmetry, and the parameters for the swimming behavior of soil bacterium Pseudomonas putida were based on literature values. Two different mechanisms for bacterial chemotaxis, one in which the bacteria responded to both positive and negative gradients, and the other in which they responded only to positive gradients, were compared. The results of the computer simulations showed that chemotaxis can increase migration through a porous medium in response to microscopic-scale gradients. The simulation results also suggested that a more significant role of chemotaxis may be to increase the residence time of the bacteria in the vicinity of an attractant source. 相似文献
970.
T Chishima M Yang Y Miyagi L Li Y Tan E Baranov H Shimada AR Moossa S Penman RM Hoffman 《Canadian Metallurgical Quarterly》1997,94(21):11573-11576
Metastasis is the ultimate life-threatening stage of cancer. The lack of accurate model systems thwarted studies of the metastatic cell's basic biology. To follow continuously the succeeding stages of metastatic colony growth, we heritably labeled cells from the human lung adenocarcinoma cell line ANIP 973 with green fluorescent protein (GFP) by transfection with GFP cDNA. Labeled cells were then injected intravenously into nude mice, where, by 7 days, they formed brilliantly fluorescing metastatic colonies on mouse lung [Chishima, T., Miyagi, Y., Wang, X., Yang, M., Tan, Y., Shimada, H., Moossa, A. R. & Hoffman, R. M. (1997) Clin. Exp. Metastasis 15, 547-552]. The seeded lung tissue was then excised and incubated in the three-dimensional sponge-gel-matrix-supported histoculture that maintained the critical features of progressive in vivo tumor colonization while allowing continuous access for measurement and manipulation. Tumor progression was continuously visualized by GFP fluorescence in the same individual cultures over a 52-day period, during which the tumors spread throughout the lung. Histoculture tumor colonization was selective for lung cancer cells to grow on lung tissue, because no growth occurred on histocultured mouse liver tissue, which was also observed in vivo. The ability to support selective organ colonization in histoculture and visualize tumor progression by GFP fluorescence allows the in vitro study of the governing processes of metastasis [Kuo, T.-H., Kubota, T., Watanbe, M., Furukawa, T., Teramoto, T., Ishibiki, K., Kitajima, M., Moossa, A. R., Penman, S. & Hoffman, R. M. (1995) Proc. Natl. Acad. Sci. USA 92, 12085-12089]. The results presented here provide significant, new opportunities to understand and to develop treatments that prevent and possibly reverse metastasis. 相似文献