全文获取类型
收费全文 | 1936篇 |
免费 | 3篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 10篇 |
金属工艺 | 3篇 |
建筑科学 | 15篇 |
矿业工程 | 1篇 |
轻工业 | 6篇 |
水利工程 | 1篇 |
无线电 | 14篇 |
一般工业技术 | 9篇 |
冶金工业 | 1873篇 |
自动化技术 | 5篇 |
出版年
2023年 | 1篇 |
2021年 | 1篇 |
2018年 | 1篇 |
2017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 | 2篇 |
2009年 | 1篇 |
2008年 | 3篇 |
2007年 | 5篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 57篇 |
1998年 | 573篇 |
1997年 | 321篇 |
1996年 | 221篇 |
1995年 | 102篇 |
1994年 | 108篇 |
1993年 | 126篇 |
1992年 | 16篇 |
1991年 | 22篇 |
1990年 | 24篇 |
1989年 | 21篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 59篇 |
1976年 | 126篇 |
1975年 | 5篇 |
1974年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有1939条查询结果,搜索用时 31 毫秒
991.
RP Jankov CF Boerkoel J Hellmann WL Sirkin Z Tümer N Horn A Feigenbaum 《Canadian Metallurgical Quarterly》1998,87(12):1297-1300
OBJECTIVES: To estimate overdiagnosis (detection of latent carcinomas) as a consequence of screening for prostate cancer. DESIGN: Based on actual screen (first or repeat) detected and interval prostate cancer rates observed in the Florence screening pilot study, a scenario was simulated where males aged 60 years (or 65) had six biennal screens and were followed up for four years. Overdiagnosis was determined as the proportional excess of cancers detected by screening with respect to that expected in its absence. SETTING: City of Florence, Italy, from 1992 through 1995. POPULATION: 2,740 resident males, aged 60 to 74 years. RESULTS: Overdiagnosis was estimated to be 51% (95% confidence limits: 44%-55%) or 93% (85%-101%) for age 60 or 65 at entry. Comparison with other screening experiences obtaining higher detection rates suggests that a more aggressive screening approach could be associated with overdiagnosis estimates as big as 200%-250%. CONCLUSIONS: Screening for prostate cancer is associated with a relevant risk of overdioagnosis. As latent carcinomas can not be presently identified, this would lead to overtreatment in most overdiagnosed cases. The negative consequences of overdiagnosis (knowledge of having a cancer) and of overtreatment (impotence, incontinence, perioperatory death) may be extremely serious. In absence of any scientific evidence of screening benefits (if any) screening should not be recommended as a current practice, but should be limited to prospective controlled studies designed to assess its cost-effectiveness. 相似文献
992.
Alcohol has been reported to increase the urinary excretion of dolichols, and urinary dolichols are suggested to be derived from the lysosomes of the renal cells. In the present study we examined the effects of alcohol and glucagon on the biliary excretion of dolichols in rats. Chronic ethanol treatment decreased both biliary dolichol and beta-hexosaminidase excretion. The absolute amount of dolichol excreted into the bile correlated highly significantly with the absolute amount of biliary beta-hexosaminidase. Our results indicate that biliary dolichols are--at least in part--derived from hepatic lysosomes. Decreased biliary dolichol output during chronic alcohol administration suggests that urinary and biliary dolichol excretions are regulated independently of each other. 相似文献
993.
The aortic rupture in the pulmonary parenchyma or the bronchi rarely results in an haemoptysis. It means in most of the cases the rupture of an aortica aneurysm. We relate the observation of a aorto-bronchial fistula from a tuberculosa origin in an old woman case. Although the tuberculosa aortitis is becoming very exceptional, it still remains the cause of aorta rupture, with the formation of a false aneurysm which is rapidly fatal and so, it is important to search for it before any capricious haemoptysis. 相似文献
994.
The reactions of horse heart cytochrome c, hydrogen peroxide, and the spin trap 3,5-dibromo-4-nitrosobenzenesulfonic acid with a series of polypeptides were investigated using mass spectrometry. The mass spectra obtained from these reactions revealed that after a free radical has been generated on the heme-containing protein horse heart cytochrome c, it can be transferred to other biomolecules. In addition, the number of free radicals transferred to the target molecule could be determined. Recipient peptides/proteins that contained a tyrosine and/or tryptophan amino acid residue were most susceptible to free radical transfer. Using tandem mass spectrometry, the location of the 3,5-dibromo-4-nitrosobenzenesulfonic acid radical adduct on the nonapeptide RWIILGLNK was unequivocally determined to be at the tryptophan residue. We also demonstrated that the presence of an antioxidant in the reaction mixture not only inhibits free radical formation on horse heart cytochrome c, but also interferes with the transfer of the free radical, once it has been formed on cytochrome c. 相似文献
995.
RP Levin 《Canadian Metallurgical Quarterly》1997,128(12):1649-1651
You don't need an M.B.A. to know that to thrive in today's competitive market, you need to run your practice like a business. It's a matter of keeping productivity high, while holding the line on costs and stress. 相似文献
996.
A mathematical model of posttetanic processes launched by rhythmic stimulation of the excitatory and inhibitory inputs to the dendritic spine of a pyramidal neuron in hippocampal field CA3 was used to study conditions for modifying the efficiency of the inhibitory input. The level of dephosphorylation of GABAa and GABAb receptors, which determines the GABA sensitivity of these receptors, was shown to depend on the Ca(2+)-dependent ratio of active protein kinases and protein phosphatases; the level of dephosphorylation decreased monotonically as the intracellular Ca2+ increased. Posttetanic increases and decreases in the Ca2+ concentration, as compared with the level achieved during the previous stimulation, led to increases or decreases respectively in the number of dephosphorylated GABA receptors and to induction of long-term potentiation and depression, respectively, in the efficiency of inhibitory transmission. The extent of the modification effect depended on the ratio of the quantities of inhibitory and excitatory mediators in the synaptic cleft. At very low or very high GABA concentrations, modification of inhibitory transmission was insignificant. 相似文献
997.
YM Sun RP Millar H Ho MC Gershengorn N Illing 《Canadian Metallurgical Quarterly》1998,139(8):3390-3398
We report on the cloning of the full-length complementary DNA for the chicken TRH receptor. Although the TRH receptor has been cloned from several mammalian species, this is the first report from another vertebrate class. The ligand binding pocket, which is situated in the transmembrane helices of the mouse and rat TRH receptors, is completely conserved in the chicken receptor. Pharmacological studies (receptor binding and signaling) employing several TRH analogs revealed that there are no significant differences between the chicken and mouse receptors. These findings show that there have been considerable evolutionary constraints on TRH receptor structure and function. Several truncated forms of the chicken TRH receptor that appear to retain a part of an intron and are truncated in the putative third intracellular loop were also cloned, but were nonfunctional. This study provides a useful tool for further studies on the roles of TRH in avian growth and TSH regulation. 相似文献
998.
BV Kallakury CE Sheehan RA Ambros HA Fisher RP Kaufman JS Ross 《Canadian Metallurgical Quarterly》1997,80(4):753-763
BACKGROUND: Cyclin-dependent kinases (CDK) and cyclins constitute the subunits of the maturation-promoting factor that controls the process of cell division. High levels of these proteins have been reported in human malignancies of the stomach, colon, breast, and lung, and have been implicated in aberrant cell division and dysregulated tumor growth. METHODS: p34cdc2 CDK and cyclin D1 (D1) protein expression were evaluated in 140 radical prostatectomy specimens harboring adenocarcinoma (PAC), using the respective monoclonal antibodies on archival tissue sections. In each case, slides stained with hematoxylin and eosin were examined for evaluation of Gleason's grade and pathologic stage. The DNA content of the tumors was determined by the Feulgen method with the CAS200 Image Analyzer (Cell Analysis Systems, Lombard, IL). Nuclear immunoreactivity for the two proteins was semiquantitatively scored, and results were correlated with Gleason's grade, stage, ploidy, metastatic status, and disease recurrence after radical prostatectomy. RESULTS: p34cdc2 was expressed in 84 of 140 PACs (60%) and correlated with high Gleason's grade (P = 0.0001), advanced pathologic stage (P = 0.01), nondiploid DNA content (P = 0.0001), and metastases (P = 0.04). On multivariate analysis using the Cox proportional hazards model, p34cdc2 immunoreactivity (P = 0.0001) and high Gleason's grade (P = 0.01) each independently predicted disease recurrence. When tumors were of low Gleason's grade and lacked p34cdc2 expression, 4 of 39 PACs (10%) recurred, as compared with 18 of 47 (38%) that recurred when tumors were of high Gleason's grade and expressed p34cdc2 protein. D1 was positive in 31 of 140 PACs (22%) and showed a trend (P = 0.07) of high Gleason's grade, but it did not reach statistical significance with any of the prognostic variables. In the majority of PACs expressing both p34cdc2 and D1 proteins, the adjacent benign prostate acini showed focal, scattered nuclear positivity of the basal and secretory epithelial cells. CONCLUSIONS: p34cdc2 is expressed in a majority of PACs and correlates with high Gleason's grade, advanced pathologic stage, nondiploid DNA content, and metastases. On multivariate analyses high Gleason's grade and p34cdc2 immunoreactivity predict disease recurrence independently of the pathologic stage. Thus, p34cdc2 appears to play a critical role in the evolution, proliferation, and spread of PACs and may be of prognostic value when applied to initial prostate tissue samples taken by needle biopsy. 相似文献
999.
L Yang G Morriello Y Pan RP Nargund K Barakat K Prendergast K Cheng WW Chan RG Smith AA Patchett 《Canadian Metallurgical Quarterly》1998,8(7):759-764
The purpose of the present study was to compare in untreated patients suffering from moderate to severe periodontitis the efficacy of dental floss (DF) and interdental brushes (IDB) in the reduction of plaque, gingival inflammation, and probing depth in a 6-week period prior to subgingival debridement. Twenty-six patients (12 female, 14 male; mean age 37.4 years; range 27 to 72 years) were instructed to use DF for one side of the dentition and IDB for the other side as an adjunct to the daily toothbrushing for 6 weeks. Oral hygiene instructions for toothbrushing and the use of the two devices were given at baseline and at week 3. Measurements were carried out at baseline and at 6 weeks including plaque scores, probing depth, and 2 bleeding scores (periodontal pocket bleeding index and angulated bleeding index). With the IDB, the approximal plaque score at baseline of 3.09 reduced to 2.15 at 6 weeks and with DF from 3.10 to 2.47, respectively. IDB proved to remove significantly more plaque than DF. Baseline probing depth of 5.84 mm for IDB sites and 5.59 mm for DF sites was reduced to 5.01 mm at 6 weeks for both regimens. Analysis showed that the use of IDB resulted in a greater pocket reduction. Both bleeding indices were slightly reduced with IDB and DF, but no differences between devices were found. In relation to patient acceptance, more problems were observed with DF, and IDB were felt to be more efficacious. In conclusion, the results of the present study indicate that in combination with a manual toothbrush, the use of interdental brushes is more effective in removal of plaque and results in a larger reduction of probing depth than the use of dental floss. Although the differences were small, they indicate, in combination with patient preferences, that interdental brushes are to be considered preferable to floss for interdental plaque removal in patients suffering from moderate to severe periodontitis. 相似文献
1000.
The mechanical behavior of calf pericardium employed in the manufacture of cardiac bioprostheses was assessed according to the region from which it was selected. For this purpose, selected samples of the tissue were sewn with different types of commercially available sutures and subjected to tensile testing, the results of which were compared with the findings in selected, but not sutured, tissue used as a control. The results confirm a loss of resistance--that is, a reduction of the capacity of sutured samples of the biomaterial to withstand breakage stress compared with control samples. Taking into account the marked resistance to breakage of the suture thread, this phenomenon can only be explained as a consequence of the deleterious mechanical interaction between the suture and chemically treated pericardium. This interaction is illustrated by the shearing force which is responsible for the loss of resistance in the tested samples. These trials demonstrate that the results can be improved and the deleterious interaction diminished, although not eliminated, when the pericardium is selected from a given region. 相似文献