全文获取类型
收费全文 | 826篇 |
免费 | 0篇 |
专业分类
化学工业 | 4篇 |
一般工业技术 | 3篇 |
冶金工业 | 819篇 |
出版年
2013年 | 1篇 |
2009年 | 1篇 |
2006年 | 1篇 |
2005年 | 1篇 |
2003年 | 6篇 |
1999年 | 23篇 |
1998年 | 260篇 |
1997年 | 136篇 |
1996年 | 85篇 |
1995年 | 40篇 |
1994年 | 37篇 |
1993年 | 57篇 |
1992年 | 8篇 |
1991年 | 16篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1978年 | 4篇 |
1977年 | 24篇 |
1976年 | 38篇 |
1975年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有826条查询结果,搜索用时 15 毫秒
31.
There has been little empirical study of risk factors for the development of late-life late-onset drinking problems. In the current prospective study, we compare two groups of older adults who, at a baseline assessment, were nonproblem drinkers: individuals who developed drinking problems over the course of the next 7 years (n = 77) and those who did not (n = 197). Late-onset problem drinkers reported mild to moderate drinking problems and spontaneous remission rates were high. Compared with stable nonproblem drinkers, late-onset problem drinkers at baseline were more likely to report incipient problems, heavier alcohol consumption, greater friend approval of drinking, more reliance on avoidance coping strategies, were more likely to smoke, and were less likely to have acute medical conditions that could potentially be complicated by alcohol consumption. Contrary to expectation, life stressors did not predict drinking problem onset. However, compared with stable nonproblem drinkers, late-onset problem drinkers were more likely to have a history of responding to stressors and negative affect with increased alcohol consumption. 相似文献
32.
KK Doak CE Haas KJ Dunnigan RA Reiss JR Reiser J Huntress JL Altavela 《Canadian Metallurgical Quarterly》1998,18(3):637-645
In the absence of E1B, the 289-amino acid product of human adenovirus type 5 13S E1A induces p53-independent apoptosis by a mechanism that requires viral E4 gene products (Marcellus, R.C., J.C. Teodoro, T. Wu, D.E. Brough, G. Ketner, G.C. Shore, and P.E. Branton. 1996. J. Virol. 70:6207-6215) and involves a mechanism that includes activation of caspases (Boulakia, C.A., G. Chen, F.W. Ng, J. G. Teodoro, P.E. Branton, D.W. Nicholson, G.G. Poirier, and G.C. Shore. 1996. Oncogene. 12:529-535). Here, we show that one of the E4 products, E4orf4, is highly toxic upon expression in rodent cells regardless of the p53 status, and that this cytotoxicity is significantly overcome by coexpression with either Bcl-2 or Bcl-XL. Conditional expression of E4orf4 induces a cell death process that is characterized by apoptotic hallmark features, such as externalization of phosphatidylserine, loss of mitochondrial membrane potential, cytoplasmic vacuolation, condensation of chromatin, and internucleosomal DNA degradation. However, the wide-spectrum inhibitor of caspases, tetrapeptide zVAD-fmk, does not affect any of these apoptogenic manifestations, and does not alter the kinetics of E4orf4-induced cell death. Moreover, E4orf4 expression does not result in activation of the downstream effector caspase common to most apoptosis-inducing events, caspase-3 (CPP32). We conclude, therefore, that in the absence of E1A, E4orf4 is sufficient by itself to trigger a p53-independent apoptosis pathway that may operate independently of the known zVAD-inhibitable caspases, and that may involve an as yet uncharacterized mechanism. 相似文献
33.
Influence of chemical treatments on glutathione S-transferases of maize with activity towards metolachlor and cinnamic acid 总被引:2,自引:0,他引:2
The subcellular distribution of glutathione S-transferase (GST) activity extracted from shoots of 3-day-old etiolated seedlings of maize (Zea mays L., Northrup-King 9283 hybrid) and the induction of soluble and membrane-bound GST activity by the safener benoxacor, the herbicide metolachlor and their combination (CGA-180937) were investigated. GST activity extracted from maize shoots was detected in both cytosolic and microsomal fractions and utilized 1-chloro-2,4-dinitrobenzene (CDNB), metolachlor, and trans-cinnamic acid (CA) as substrates. Soluble GST activity extracted from maize shoots was greater than microsomal with CDNB or metolachlor as substrate. Membrane-bound GST activity was greater than soluble with cinnamic acid as substrate. Washing the microsomal preparations from maize shoots with Triton X-100 increased GST(CA) activity. Pretreatment with the safener benoxacor or a formulated combination of the herbicide metolachlor with benoxacor induced soluble GST(CDNB), GST(metolachlor) and GST(CA) activities in maize shoots. Benoxacor and CGA-180937 induced also membrane-bound GST(CDNB) and GST(CA) activities in maize shoots, but did not affect membrane-bound GST(metolachlor) activity. These results confirm that maize contains multiple GST isozymes that differ in their substrate specificity and inducibility by safeners or other chemicals. 相似文献
34.
V Douzdjian SS Bhaskar PK Baliga KK Gugliuzza PR Rajagopalan 《Canadian Metallurgical Quarterly》1997,20(8):1310-1314
OBJECTIVE: The racial impact on graft outcome is not well defined in diabetic recipients. The purpose of this study is to analyze our experience with kidney-alone (A) and kidney-pancreas (KP) transplantation in type 1 diabetic recipients and evaluate the impact of racial disparity on outcome. RESEARCH DESIGN AND METHODS: The records of 217 kidney transplants (118 KA, 99 KP) performed on type 1 diabetic patients between 1985 and 1995 at the Medical University of South Carolina and the University of Texas Medical Branch were reviewed. RESULTS: A total of 53 (31%) white patients and 15 (33%) black patients experienced at least one episode of biopsy-proven acute rejection of the renal graft (NS). Patient survival at 1, 2, and 5 years was similar in white (92, 87, 69%) and black (91, 91, 69%) patients (NS). Kidney graft survival at 1, 2, and 5 years in the KA group was 72, 62, and 42% in blacks, compared with 79, 76, and 53% in whites (NS). Kidney graft survival at 1, 2, and 5 years in the KP group was 92, 92, and 74% in blacks, compared with 83, 77, and 58% in whites (NS). Pancreas graft survival at 1, 2, and 5 years was 81, 81, and 81% in blacks, compared with 81, 75, and 62% in whites (NS). Cox regression analysis revealed that donor age > or = 40 years increased the risk of renal graft failure 6.2-fold (P = 0.0001), whereas the addition of a pancreas transplant to a kidney and a living-related transplant decreased the risk of failure of the kidney graft 0.2 (P = 0.005) and 0.1 times (P = 0.005). CONCLUSIONS: Our results suggest that when compared with whites, there may be a trend toward an improved kidney and pancreas graft outcome in blacks undergoing KP transplants. These findings suggest that diabetes may override the risk factors that account for the pronounced disparity in outcome observed between nondiabetic white and black recipients. 相似文献
35.
259 patients with primary proliferative polycythaemia (PPP) and idiopathic thrombocythaemia (IT) have been treated with 32P over the last 15 years. Complete follow-up data were obtained in 238 patients. PPP was the diagnosis in 183 patients and 76 patients had IT. The sex ratio in PPP was male/female 1.1:1 and in IT 1:1.4. Patients' ages ranged from 28 to 95 years (median 72 years). The number of 32P administrations per patient ranged from 1 to 13 (median 2) and the total administered activity per patient ranged from 81.4 to 4162 MBq (median 496 MBq). The outcome showed a normalization of the full blood count in 50% of patients after a single administration of 32P and in 73% after two treatments. 13 patients (5.5%) developed myelofibrosis; 18 (7.6%) developed leukaemia while other cancers arose in 19 patients (8%). 32P therapy proved to be of particular value in the elderly. 32P is easy to administer and is cost effective, compared with the alternative of chemotherapy where good compliance and frequent hospital visits are required. 相似文献
36.
BS Goldman DL Beckman A Bali EM Monika KK Gabbert RG Kranz 《Canadian Metallurgical Quarterly》1997,268(4):724-738
The helABC genes are predicted to encode an ATP-binding cassette (ABC) transporter necessary for heme export for ligation in bacterial cytochrome c biogenesis. The recent discoveries of homologs of the helB and helC genes in plant mitochondrial genomes suggest this is a highly conserved transporter in prokaryotes and some eukaryotes with the HelB and HelC proteins comprising the transmembrane components. Molecular genetic analysis in the Gram-negative bacterium Rhodobacter capsulatus was used to show that the helABC and helDX genes are part of an operon linked to the secDF genes. To facilitate analysis of this transporter, strains with non-polar deletions in each gene, epitope and reporter-tagged HelABCD proteins, and antisera specific to the HelA and HelX proteins were generated. We directly demonstrate that this transporter is present in the cytoplasmic membrane as an HelABCD complex. The HelB and HelC but not HelD proteins are necessary for the binding and stability of the HelA protein, the cytoplasmic subunit containing the ATP-binding region. In addition we show that the HelA protein co-immunoprecipitates with either the HelC or HelD proteins. Thus, the HelABCD heme export complex is distinguished by the presence of four membrane-associated subunits and represents a unique subfamily of ABC transporters. 相似文献
37.
We describe two cases of congenital chylothorax in siblings with important differences from previously described familial cases. Our findings support the likelihood of an autosomal recessive inheritance in some cases of this condition, rather than X-linked recessive inheritance, which has also been suggested. Autopsy findings from one of these cases and others previously described suggest that the pathophysiological mechanisms involved may be variable. 相似文献
38.
OBJECTIVE: The purpose of this study was to evaluate a hydroxylapatite-based material and calcium sulfate when each was used under a resin-modified glass ionomer cement to repair furcation perforations. STUDY DESIGN: Perforations of pulp chamber floors were made in 72 teeth of 9 dogs. Perforations were divided into 3 equal-sized groups and repaired with resin-modified glass ionomer either alone or over an artificial floor. The artificial floor was either a hydroxylapatite-based material or calcium sulfate. Three dogs were killed at each of 3 intervals (1, 3, and 6 months). The tissue response to the tested materials was evaluated clinically, radiographically, and histologically. RESULTS: The hydroxylapatite-based material showed the highest radiographic success; this was followed by calcium sulfate and glass ionomer. From histologic evaluation, the average success rate was found to be 67% for calcium sulfate, 62% for the hydroxylapatite-based material, and 59% for glass ionomer. However, there was no statistical significant difference with the resin-modified glass ionomer when it was used alone and when it was used over a barrier. There was also no significant difference between the hydroxylapatite-based material and the calcium sulfate when they were used as artificial floors. CONCLUSION: The use of an artificial floor may not be necessary when flowable resin-modified glass ionomer cements are used. 相似文献
39.
The feasibility of generating substituted phenyl radicals and biradicals (with a charged substituent) in the gas phase by laser photolysis was examined by using a Fourier-transform ion cyclotron resonance mass spectrometer. The precursors were generated by ipso-substitution of a halogen atom in the radical cation of a di- or trihalobenzene by various nucleophiles. Photolytic cleavage of the remaining carbon-halogen bond(s) with 266-nm radiation was found to produce many substituted phenyl radicals in greater yields than the earlier employed method, sustained off-resonance irradiated collision-activated dissociation (SORI-CAD). Furthermore, ion generation by photolysis leads to isomerization less often than collisional activation. Finally, not only phenyl-bromine and phenyl-iodine but also certain phenyl-chlorine bonds can be cleaved by photolysis, whereas the synthetic utility of SORI-CAD appears to be largely limited to the cleavage of phenyl-iodine bonds. Hence, laser photolysis greatly expands the variety of substituted phenyl radicals and biradicals that can be synthesized inside a mass spectrometer. 相似文献
40.
By using a mRNA differential display technique to search for salicylate suppressible genes, we identified a cDNA in human foreskin fibroblasts, which by GenBankTM DNA data base search shows sequence homology to the recently reported cullin/Cdc53 (CUL) family genes, especially CUL-3. We have cloned the full-length human CUL-3 (Hs-CUL-3) cDNA. It encodes a 768-amino acid polypeptide and has a predicted molecular weight of 88,939. The amino acid sequence of Hs-CUL-3 shows 46% homology to that of its Caenorhabditis elegans ortholog, Ce-CUL-3, and 27 and 23% to that of Hs-CUL-1 and Hs-CUL-2, respectively. Northern blot analysis showed that phorbol 12-myristate 13-acetate increased the expression of Hs-CUL-3 mRNA in a concentration- and time-dependent manner, and this increase was inhibited by sodium salicylate. Hs-CUL-3 widely expressed in human tissues and its expression in cultured COLO205 colon cancer cells was increased when compared with that in normal colon cells. It is likely that Hs-CUL-3 is involved in cell proliferation control. 相似文献