全文获取类型
收费全文 | 631篇 |
免费 | 36篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 23篇 |
综合类 | 28篇 |
化学工业 | 46篇 |
金属工艺 | 26篇 |
机械仪表 | 11篇 |
建筑科学 | 24篇 |
矿业工程 | 7篇 |
能源动力 | 8篇 |
轻工业 | 17篇 |
水利工程 | 13篇 |
石油天然气 | 11篇 |
武器工业 | 4篇 |
无线电 | 40篇 |
一般工业技术 | 38篇 |
冶金工业 | 322篇 |
原子能技术 | 2篇 |
自动化技术 | 64篇 |
出版年
2024年 | 3篇 |
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 14篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 21篇 |
2012年 | 27篇 |
2011年 | 28篇 |
2010年 | 22篇 |
2009年 | 20篇 |
2008年 | 22篇 |
2007年 | 20篇 |
2006年 | 18篇 |
2005年 | 21篇 |
2004年 | 20篇 |
2003年 | 8篇 |
2002年 | 11篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 105篇 |
1997年 | 63篇 |
1996年 | 40篇 |
1995年 | 24篇 |
1994年 | 18篇 |
1993年 | 14篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 6篇 |
1976年 | 14篇 |
1955年 | 1篇 |
排序方式: 共有684条查询结果,搜索用时 272 毫秒
81.
82.
Three studies investigated the authenticity of prejudice-related discrepancies. A comprehensive discrepancy questionnaire was developed (Study 1), which yielded small as well as large discrepancy scores. Study 2 indicated that discrepancy scores were stable, and personality could not account for the relation between discrepancies and their affective consequences. In Study 3, low-prejudice participants responded to jokes about Blacks under high or low distraction. Behavioral validation for self-reported discrepancies was found, such that participants with larger discrepancies evaluated the jokes more favorably under high than low distraction, but participants with smaller discrepancies provided equally unfavorable evaluations in both distraction conditions. Implications for understanding people's abilities to avoid potentially prejudiced responses and their self-insight into such abilities are discussed. 相似文献
83.
To understand better the organisation of zona incerta of the thalamus, this study has examined the patterns of connections that this nucleus has with various nuclei of the brainstem. Injections of biotinylated dextran or cholera toxin subunit B were made into the dorsal raphe, midbrain reticular nucleus, pedunculopontine tegmental nucleus, periaqueductal grey matter, pontine reticular nucleus, substantia nigra, superior colliculus, and ventral tegmental area of Sprague-Dawley rats, and their brains were processed by using standard tracer-detection methods. In general, our results show that zona incerta forms the major zone in the thalamus where these ascending brainstem axons terminate and from which descending axons that travel back to these same brainstem centres originate. These incertal inputs and outputs are limited largely to a distinct sector of zona incerta, the dorsal sector. An exception to this pattern is evident in the incertal projection to the deep layers of the superior colliculus; this projection, unlike all of the others, arises from cells in the ventral sector of zona incerta. Our results also show little evidence for a well-defined topography of projection between the brainstem and the zona incerta. For instance, small injections into each brainstem nucleus result in labelled terminals and in cells spread throughout much of the dorsal sector of zona incerta, with no local zone of concentration within the sector. Again, an exception to this pattern is seen in the incertal projection to the superior colliculus. This projection, unlike the others, shows a clear topographical organisation: A medial-lateral shift in the injection site in the colliculus results in a lateral-medial shift in the position of labelled cells in zona incerta. Curiously, even though the incertal projection to the colliculus appears to be mapped, the collicular projection back to zona incerta is not mapped. In conclusion, then, a number of brainstem nuclei (except for the deep collicular layers) have strong and overlapping connections within the same sector of zona incerta. This convergence of many functionally diverse brainstem afferents within zona incerta places this nucleus in a strategic position to sample the general activity of the brainstem and, perhaps, acts as a relay of this information to higher centres, such as the dorsal thalamic relay nuclei and the cerebral hemispheres. 相似文献
84.
CE Pitsavos CI Stefanadis CG Stratos SG Lambrou KP Toutouzas ID Barbetseas PK Toutouzas 《Canadian Metallurgical Quarterly》1997,18(3):455-463
AIM: The reliability of Doppler echocardiography in determining the mitral valve area after balloon mitral valvuloplasty has been questioned, as discrepancies were noted between measurements obtained by the pressure half-time method and those derived haemodynamically, immediately following completion of the procedure. Recent investigations, however, have indicated that these discrepancies may be attributable to the over-estimation of the mitral valve area by haemodynamic measurements, caused by the presence of the iatrogenic atrial septal defect complicating transseptal catheterization. The aim of the present study was to further test this hypothesis. METHODS AND RESULTS: Measurements of the mitral valve area by the Doppler pressure half-time method and the Gorlin formula were obtained and compared in 238 consecutive patients before and immediately after retrograde non-transseptal balloon mitral valvuloplasty, which does not involve puncture and/or dilatation of the inter-atrial septum. No significant difference was found between Doppler- and Gorlin-derived measurements, neither before (1.04 +/- 0.23 vs 1.03 +/- 0.23 cm2, P = ns) nor immediately after (2.14 +/- 0.47 vs 2.12 +/- 0.49 cm2, P = ns) valvuloplasty. Linear regression analysis demonstrated a high degree of correlation between Doppler and Gorlin measurements before (r = 0.778) and after (r = 0.886) the procedure. Good agreement was confirmed by the Bland-Altman method. CONCLUSION: Doppler echocardiography yields accurate measurements of the mitral valve area immediately after retrograde non-transseptal balloon mitral valvuloplasty. This finding supports the hypothesis that the creation of an iatrogenic atrial septal defect during transseptal catheterization may contribute to the poor agreement between Doppler and Gorlin data after balloon mitral valvuloplasty. 相似文献
85.
86.
ST O'Keeffe T Smith R Valacio CI Jack JR Playfer M Lye 《Canadian Metallurgical Quarterly》1994,344(8937):1619-1620
The reported prevalence of absent ankle jerks in elderly people varies greatly. This variation may be due to differences in the method of testing. Eight physicians examined 12 patients for the presence of ankle jerks using two techniques: plantar strike and tendon strike. Both intra-observer agreement (kappa 0.47 vs 0.20; p = 0.01) and inter-observer agreement (0.57 vs 0.21; p < 0.001) were greater with plantar strike. Reliability of ankle jerk assessment was greater for more experienced examiners. Differences in technique may explain some of the discrepancy between studies examining the prevalence of absent ankle jerks in elderly people. 相似文献
87.
BACKGROUND: Hypertension, a known independent risk factor for end-stage renal failure, damages the kidney in multiple ways. It produces hemodynamic and mechanical stress, which may lead to glomerular endothelial dysfunction. Both of these mechanisms may lead to increased glomerular leakiness, hence proteinuria, which may damage the kidney further. Hypertension may also stimulate the production of vasoactive substances that, in turn, activate the production of cytokines and growth factors, leading to the production of extracellular matrix proteins. Thus, the progression of renal failure is related to both systemic and glomerular hemodynamic changes and to the activation of vasoactive hormones, growth factors and cytokines. THERAPY: To protect the kidney, we need to control or prevent the occurrence of these factors. Therapy with effective antihypertensive agents, such as angiotensin-converting enzyme inhibitors, has been shown to slow the progression of end-stage renal disease. 相似文献
88.
AG Randall GN Kent P Garcia-Webb CI Bhagat DJ Pearce DH Gutteridge RL Prince G Stewart B Stuckey RK Will RW Retallack RI Price L Ward 《Canadian Metallurgical Quarterly》1996,11(8):1176-1184
We have compared the use of new markers of bone turnover in the assessment and treatment of Paget disease and made observations on the mechanisms of bone resorption. Urine hydroxyproline (Hyp) as a bone resorption marker and serum alkaline phosphatase (ALP) as a bone formation marker have traditionally been used to biochemically assess and monitor treatment of Paget disease. Hyp and total ALP were compared with total urine pyridinoline (Pyd) and deoxypyridinoline (Dpd), free urine Pyd and Dpd, urine type I collagen N-terminal cross-linked telopeptide (NTX), type I collagen C-terminal propeptide (PICP), serum osteocalcin, and bone ALP in Paget patients treated with pamidronate. Patients were divided into three biochemical severity-based treatment groups by their fasting urine hydroxyprolline excretion (HypE) levels (Le., group 1, HypE < 5.0 mumol/l of glomerular filtrate [GF]; group 2, HypE of 5.0-9.9 mumol/l of GF; group 3, HypE > 10 mumol/l of GF). Group 1 received one 60 mg intravenous infusion of pamidronate, and groups 2 and 3 received four and six 60 mg infusions at weekly intervals, respectively. Fasting serum and morning urine specimens were taken before and at 2, 6, 13, and 26 weeks after starting treatment. Baseline Z scores were used to compare separation of patient results from normal, and the difference in Z scores from baseline to 13 weeks was used to compare response to treatment. Baseline discrimination and response to treatment at all disease activity levels was greatest for NTX and was poor for osteocalcin, PICP, and C-terminal cross-linked telopeptide of type I collagen (ICTP). The other markers showed good discrimination and response at medium and high levels of disease activity. NTX, total Pyd and Dpd, free Pyd and Dpd, and ICTP are all pyridinoline cross-link-based markers, but discrimination and response by NTX was generally much greater than for the others. Determination of the mechanism of the difference between NTX and other cross-link measures is necessary for appropriate use of the markers and may also lead to a better understanding of the bone resorption process. It has been proposed that the greater sensitivity and discrimination of NTX is because it is more bone-specific than the other cross-link markers with significant amounts of free Pyd and Dpd coming from nonbone sources. We propose another model where the proportion of peptide-bound cross-links such as NTX may be increased in high bone turnover states partly due to a rate-limiting step in their degradation to free cross-links. Conditions with high bone resorption rates would have high levels of NTX that would decline rapidly when resorption rates fall to a level where the capacity to degrade NTX matches the rate of production. 相似文献
89.
LO Langer BJ Wolfson CI Scott CS Reid DV Schidlow EA Millar PF Borns JP Lubicky BL Carpenter 《Canadian Metallurgical Quarterly》1993,45(4):488-500
Further delineation of a generalized bone dysplasia which we call spondylo-meta-epiphyseal dysplasia, short limb-abnormal calcification type is presented. This dwarfing condition has several serious complications, with the most common cause of death being spinal cord damage secondary to atlantoaxial instability. It is a heritable condition with an autosomal recessive mode of transmission. Radiologic diagnostic criteria are developed on the basis of studies in 8 patients with the oldest being between 4 and 5 years old. The condition is clinically and radiographically apparent neonatally or in early infancy, and it is probable that all or almost all affected individuals will come to medical attention in the age range screened by this study. 相似文献
90.
WP Farrar S Bech-Nielsen JC Gordon SM Reed CI Pretzman CW Kohn 《Canadian Metallurgical Quarterly》1993,34(4):345-353
A sulfate-reducing bacterium using trinitrotoluene (TNT) as the sole nitrogen source was isolated with pyruvate and sulfate as the energy sources. The organism was able to reduce TNT to triaminotoluene (TAT) in growing cultures and cell suspensions and to further transform TAT to still unknown products. Pyruvate, H2, or carbon monoxide served as the electron donors for the reduction of TNT. The limiting step in TNT conversion to TAT was the reduction of 2,4-diamino-6-nitrotoluene (2,4-DANT) to triaminotoluene. The reduction proceeded via 2,4-diamino-6-hydroxylaminotoluene (DAHAT) as an intermediate. The intermediary formation of DAHAT was only observed in the presence of carbon monoxide or hydroxylamine, respectively. The reduction of DAHAT to triaminotoluene was inhibited by both CO and NH2OH. The inhibitors as well as DANT and DAHAT significantly inhibited sulfide formation from sulfite. The data were taken as evidence for the involvement of dissimilatory sulfite reductase in the reduction of DANT and/or DAHAT to triaminotoluene. Hydrogenase purified from Clostridium pasteurianum and carbon monoxide dehydrogenase partially purified from Clostridium thermoaceticum also catalyzed the reduction of DANT in the presence of methyl viologen or ferredoxin, however, as the main reduction product DAHAT rather than triaminotoluene was formed. The findings could explain the function of CO as an electron donor for the DANT reduction (to DAHAT) and the concomitant inhibitory effect of CO on triaminotoluene formation (from DAHAT) by the inhibition of sulfite reductase.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献