全文获取类型
收费全文 | 4041篇 |
免费 | 279篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 71篇 |
综合类 | 2篇 |
化学工业 | 1063篇 |
金属工艺 | 107篇 |
机械仪表 | 97篇 |
建筑科学 | 117篇 |
矿业工程 | 10篇 |
能源动力 | 143篇 |
轻工业 | 647篇 |
水利工程 | 44篇 |
石油天然气 | 25篇 |
无线电 | 287篇 |
一般工业技术 | 637篇 |
冶金工业 | 508篇 |
原子能技术 | 30篇 |
自动化技术 | 541篇 |
出版年
2024年 | 9篇 |
2023年 | 52篇 |
2022年 | 115篇 |
2021年 | 196篇 |
2020年 | 136篇 |
2019年 | 157篇 |
2018年 | 168篇 |
2017年 | 174篇 |
2016年 | 184篇 |
2015年 | 120篇 |
2014年 | 149篇 |
2013年 | 315篇 |
2012年 | 253篇 |
2011年 | 274篇 |
2010年 | 213篇 |
2009年 | 216篇 |
2008年 | 198篇 |
2007年 | 144篇 |
2006年 | 117篇 |
2005年 | 76篇 |
2004年 | 78篇 |
2003年 | 80篇 |
2002年 | 59篇 |
2001年 | 52篇 |
2000年 | 50篇 |
1999年 | 45篇 |
1998年 | 143篇 |
1997年 | 133篇 |
1996年 | 76篇 |
1995年 | 47篇 |
1994年 | 40篇 |
1993年 | 40篇 |
1992年 | 14篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 24篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 16篇 |
1973年 | 4篇 |
排序方式: 共有4329条查询结果,搜索用时 15 毫秒
41.
MG Seves MJ Brito S Lamy PV Luiz G Bastos M Faleiro J Batista JF De Sousa 《Canadian Metallurgical Quarterly》1998,11(7):631-634
Hormone-refractory prostate cancer (HRPC) patients often have nonmeasurable disease. In such patients, predictive biomarkers other than tumor response may be required to compare therapeutic effects. We examined the predictive value for survival of various clinical and laboratory parameters, including prostate-specific antigen (PSA), in HRPC patients treated with suramin. Data from 103 HRPC patients were analyzed using various survival analyses, the likelihood ratio approach, and logistic regression analyses. When pretreatment factors, percentage decrease in PSA at 4 weeks from start of treatment (deltaPSA), and updated survival data were fit by a multivariate Cox proportional hazards model, acid phosphatase, lactate dehydrogenase, and deltaPSA were significant, with risk ratios close to 1. There was a decrease in likelihood ratio with increasing APSA. A logistic regression model was developed to predict the probability of <1 year of survival from the start of treatment. Hemoglobin and deltaPSA were found to be significant variables. However, in view of the complexities involving the relationship between PSA expression and prostate cancer growth and possible selective effect of treatment on PSA, further prospective testing is necessary. Therefore, deltaPSA cannot necessarily be used as a biomarker for survival response in individual patients during the evaluation of the therapeutic response of HRPC to new antineoplastic drugs. 相似文献
42.
The Eysenck Personality Profiler (EPP), a set of 21 scales measuring primary traits hypothesized to be definers of Neuroticism, Extraversion, and Psychoticism factors, was administered to 229 adults together with the Eysenck Personality Questionnaire--Revised (H. J. Eysenck & S. B. G. Eysenck, 1991) and the Revised NEO Personality Inventory (NEO-PI-R; P. T. Costa & R. R. McCrae, 1992b). Correlations of EPP scales with NEO-PI-R facet scales provided preliminary evidence supporting the convergent and discriminant validity of the EPP scales. However, varimax and targeted validimax factor analyses suggested that some EPP scales were misclassified and that EPP scales could better be understood in terms of the 5-factor model than the intended 3-factor model. 相似文献
43.
The role of psychosocial protective factors in adolescent health-enhancing behaviors--healthy diet, regular exercise, adequate sleep, good dental hygiene, and seatbelt use--was investigated among 1,493 Hispanic, White, and Black high school students in a large, urban school district. Both proximal (health-related) and distal (conventionality-related) protective factors have significant positive relations with health-enhancing behavior and with the development of health-enhancing behavior. In addition, in cross-sectional analyses, protection was shown to moderate risk. Key proximal protective factors are value on health, perceived effects of health-compromising behavior, and parents who model health behavior. Key distal protective factors are positive orientation to school, friends who model conventional behavior, involvement in prosocial activities, and church attendance. The findings suggest the importance of individual differences on a dimension of conventionality-unconventionality. Strengthening both proximal and distal protective factors may help to promote healthful behaviors in adolescence. 相似文献
44.
Lactation records (n = 2362) of 1402 crossbred cows in 22 cooperating dairy herds in southeastern Brazil were evaluated. Cows were mixtures of Zebu (Gir, Guzera, and unknown) and European breeding (mostly Holstein). Lactation milk yields were expressed as total, 3050-d, or deviated 305-d yields, either adjusted or unadjusted for days in milk (DIM). Mean DIM was 280. Arithmetic means unadjusted for DIM were 1942, 1666, and 5 kg per record. Milk yields of daughters from sires of 6/8 and 7/8 European breeds were higher than yields of daughters from sires of 5/8 European breeds when data were either adjusted or unadjusted for DIM. The differences associated with breed group of sire were only slightly reduced when records were adjusted for DIM. There was no evidence of a decline in milk yield as the fraction of European breeding of the sire increased from 6/8 to 7/8. For a given breed group of sire, whether the grandsire was purebred or crossbred had no detectable effect. These results should be useful in determining strategies for crossbreeding of dairy cows in tropical areas, particularly when crossbred sires are used. 相似文献
45.
A Tocchi L Lepre G Costa G Liotta G Mazzoni N Agostini 《Canadian Metallurgical Quarterly》1996,17(6-7):345-348
Twenty-one patients undergoing colectomy for carcinoma of the splenic flexure from November 1996 throughout October 1993 were studied retrospectively. Clinical and prognostic features were compared with those of other colon cancers treated in the same period at the same Institution. No differences in symptoms at onset and stage distribution were found in the two groups. The complex removal of the cancer tissue was achieved with the resection of the major part of the transverse colon, splenic flexure, descending colon and its mesocolon. The splenic flexure cancer did not show a worse prognosis than other colon cancers. 相似文献
46.
D Matecka RB Rothman L Radesca BR de Costa CM Dersch JS Partilla A Pert JR Glowa FH Wojnicki KC Rice 《Canadian Metallurgical Quarterly》1996,39(24):4704-4716
The design, synthesis, and biological evaluation of compounds related to the dopamine (DA) uptake inhibitors: 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (1) and 1-[2-[bis-(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (2) (GBR 12395 and GBR 12909, respectively), directed toward the development and identification of new ligands interacting with high potency and selectivity at the dopamine transporter (DAT) is reported. The substitution of the piperazine ring in the GBR structure with other diamine moieties resulted in the retention of the high affinity of new ligands for the DAT. Some of the modified GBR analogs (e.g. 8, 10, (-)-49, or (-)-50) displayed substantially higher selectivity (4736- to 693-fold) for the dopamine (DA) versus the serotonin (5HT) reuptake site than the parent compounds. The bis(p-fluoro) substitution in the (diphenylmethoxy)ethyl fragment slightly increased the affinity of the ligands at the DA reuptake site but reduced their selectivity at this site (e.g. 9 and 8, 11 and 10, or 17 and 16, respectively). Congeners, such as the series of monosubstituted and symmetrically disubstituted piperazines and trans-2,5-dimethylpiperazines, which lack the (diphenylmethoxy)ethyl substituent lost the affinity for the DAT yet exhibited very high potency for binding to the sigma receptors (e.g.28). The chiral pyrrolidine derivatives of 1, (-)-49, and (+)-49, exhibited an enantioselectivity ratio of 181 and 146 for the inhibition of DA reuptake and binding to the DAT, respectively. 相似文献
47.
Carneiro Davide Pereira Jorge e Silva Eliana Costa 《Neural computing & applications》2021,33(14):8687-8707
Neural Computing and Applications - Grapes reception is a key process in wine production. The harvest days are extremely challenging days in managing the reception of the grapes, as the winery... 相似文献
48.
This reply clarifies that it is possible to change the plane of cut by filtering a tomogram, if the presence of the out-of-focus images is tolerated, because the (projected) images of all the layers are superimposed on the film and any filtering will process all these images simultaneously. 相似文献
49.
Joseph R. Fox P. Costa Kokoropoulos Gary H. Wiseman H. K. Bowen 《Journal of Materials Science》1987,22(12):4528-4531
Organosilanes of the general formula R
x
Si(OR)4–x
(where R is an alkyl group and R = CH3 or CH2CH3) were used to sterically stabilize hexane dispersions of submicrometre silica spheres. The dispersions were characterized according to sediment volume results. For 0.5m silica particles, the sediment density increased by more than a factor of three up to 50 to 55% of theoretical in the presence of organosilanes with 12 or more carbons in the R group. Solid-state13C nuclear magnetic resonance was used to characterize the powder-dispersant interaction; this technique can distinguish between carbons in the R group of the organosilane and residual organic groups in the silica. Scanning electron micrographs of filter compacts were used to further characterize the dispersions and indicated the presence of primary particles as well as small agglomerates. 相似文献