全文获取类型
收费全文 | 1860篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
综合类 | 2篇 |
化学工业 | 10篇 |
金属工艺 | 4篇 |
机械仪表 | 4篇 |
轻工业 | 12篇 |
石油天然气 | 2篇 |
无线电 | 1篇 |
一般工业技术 | 6篇 |
冶金工业 | 1817篇 |
自动化技术 | 8篇 |
出版年
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2013年 | 4篇 |
2012年 | 3篇 |
2011年 | 1篇 |
2009年 | 3篇 |
2008年 | 2篇 |
2006年 | 2篇 |
2005年 | 3篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2001年 | 1篇 |
1999年 | 49篇 |
1998年 | 613篇 |
1997年 | 339篇 |
1996年 | 186篇 |
1995年 | 126篇 |
1994年 | 98篇 |
1993年 | 106篇 |
1992年 | 13篇 |
1991年 | 31篇 |
1990年 | 26篇 |
1989年 | 28篇 |
1988年 | 25篇 |
1987年 | 25篇 |
1986年 | 20篇 |
1985年 | 17篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 13篇 |
1978年 | 5篇 |
1977年 | 23篇 |
1976年 | 72篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有1866条查询结果,搜索用时 15 毫秒
991.
CS Williams 《Canadian Metallurgical Quarterly》1998,56(3):673-681
PURPOSE: To compare subtracted and nonsubtracted gadolinium-enhanced magnetic resonance (MR) angiography and cardiac-synchronized time-of-flight MR angiography for help in detecting pelvic-region stenoses. MATERIALS AND METHODS: Twenty-eight patients with intermittent claudication underwent MR angiography with a 1.5-T system; two-dimensional cardiac-synchronized time-of-flight MR angiograms and three-dimensional MR angiograms (without and with gadolinium enhancement) were obtained. Subtracted images were obtained by subtracting unenhanced data from enhanced data of identical volumes, and maximum intensity projection images were constructed, which two observers independently evaluated in blinded fashion, with conventional angiographic results as the reference standard. RESULTS: Sensitivity and specificity for grading of hemodynamically significant stenoses (> or = 50% lumen reduction) on subtracted MR angiograms were 94% and 93%, respectively. Sensitivity of subtracted images was significantly higher compared with that of time-of-flight images (P < .05) but not with that of nonsubtracted images. Contrast-to-noise ratio on subtracted images was significantly higher compared with that on nonsubtracted images (P < .05) but not with that on time-of-flight images. There was good correlation between stenosis length measurements on gadolinium-enhanced MR angiograms and those on conventional angiograms. CONCLUSION: Subtracted MR angiography is superior to cardiac-synchronized time-of-flight MR angiography for imaging of iliac and upper femoral arteries and provides higher contrast-to-noise ratio, fewer artifacts, and easier image interpretability than nonsubtracted MR angiography. 相似文献
992.
Bacterial symbionts may be used as vehicles for expressing foreign genes in arthropods. Expression of selected genes can render an arthropod incapable of transmitting a second microorganism that is pathogenic for humans and is an alternative approach to the control of arthropod-borne diseases. We discuss the rationale for this alternative approach, its potential applications and limitations, and the regulatory concerns that may arise from its use in interrupting disease transmission in humans and animals. 相似文献
993.
994.
Tottering mice inherit a recessive mutation of the calcium channel alpha1A subunit that causes ataxia, polyspike discharges, and intermittent dystonic episodes. The calcium channel alpha1A subunit gene encodes the pore-forming protein of P/Q-type voltage-dependent calcium channels and is predominantly expressed in cerebellar granule and Purkinje neurons with moderate expression in hippocampus and inferior colliculus. Because calcium misregulation likely underlies the tottering mouse phenotype, calcium channel blockers were tested for their ability to block the motor episodes. Pharmacologic agents that specifically block L-type voltage-dependent calcium channels, but not P/Q-type calcium channels, prevented the inducible dystonia of tottering mutant mice. Specifically, the dihydropyridines nimodipine, nifedipine, and nitrendipine, the benzothiazepine diltiazem, and the phenylalkylamine verapamil all prevented restraint-induced tottering mouse motor episodes. Conversely, the L-type calcium channel agonist Bay K8644 induced stereotypic tottering mouse dystonic at concentrations significantly below those required to induce seizures in control mice. In situ hybridization demonstrated that L-type calcium channel alpha1C subunit mRNA expression was up-regulated in the Purkinje cells of tottering mice. Radioligand binding with [3H]nitrendipine also revealed a significant increase in the density of L-type calcium channels in tottering mouse cerebellum. These data suggest that although a P/Q-type calcium channel mutation is the primary defect in tottering mice, L-type calcium channels may contribute to the generation of the intermittent dystonia observed in these mice. The susceptibility of L-type calcium channels to voltage-dependent facilitation may promote this abnormal motor phenotype. 相似文献
995.
Zs. ZSÓFI L. GÁL Z. SZILÁGYI E. SZCS M. MARSCHALL Z. NAGY B. BÁLO 《Australian Journal of Grape and Wine Research》2009,15(1):36-47
Background and Aims: A 3‐year study was carried out in order to evaluate the ecophysiology, yield and quality characteristics of Vitis vinifera L. cv. Kékfrankos (syn. Limberger) at Eger‐Nagyeged hill (steep slope) and at Eger‐K?lyuktet? (flat) vineyard sites located in the Eger wine region, Hungary. The aim of this paper was to analyse the effect of ‘vintage’ and ‘terroir’ on the seasonal changes of Kékfrankos ecophysiology and its possible relationship with yield and wine composition. Methods and Results: Grapevine physiological responses (midday‐ and pre‐dawn water potential, pressure–volume analysis and gas‐exchange), growing stages, yield and wine composition of each vineyard were studied. Lower grapevine water supply was detected at Eger‐Nagyeged hill in each season due to its steep slope and soil characteristics. Pressure‐volume curves indicated that there was no osmotic adjustment in the leaves of this variety. Higher osmotic concentration was measured at turgor loss and full turgor in the leaves of the unstressed vineyard (Eger‐K?lyuktet?) presumably due to higher photosynthetic activity. Differences in soil water content of the vineyards resulted in a slightly altered cell wall elasticity. Stomatal conductance, transpiration rate and photosynthetic production per unit leaf area were affected by water availability. Lower yield in Eger‐Nagyeged hill was partly associated with decreased photosynthetic production of the canopy. Improved wine quality of Eger‐Nagyeged hill was due to moderate water stress which induced higher concentration of anthocyanins and phenolics in the berries. The duration of the phenological stages was dependent on vintage temperature characteristics rather than on vineyard site. Conclusion: There was a close relationship between environmental conditions, Kékfrankos gas‐exchange, water relations, yield and wine composition. Water deficit plays an important role in creating a terroir effect, resulting in decreased yield, better sun exposure of leaves and clusters and thus higher concentration of phenolics and anthocyanins. Although quality is mainly influenced by vintage differences, vineyard characteristics are able to buffer unfavourable vintage effects even within a small wine region. Significance of the Study: Stomatal conductance, pre‐dawn water potential and climatic data may be reliable parameters for terroir classification, although variety–terroir interactions must always be considered. 相似文献
996.
Ray‐Yu Yang Samson CS Tsou Tung‐Ching Lee Wan‐Jan Wu Peter M Hanson George Kuo Liwayway M Engle Po‐Yung Lai 《Journal of the science of food and agriculture》2006,86(14):2395-2403
Epidemiological studies have demonstrated the protective effects of fruit and vegetable consumption on human health. A total of 150 edible plants representing 127 species were evaluated for Trolox equivalent antioxidant capacity (TEAC) and superoxide scavenging (SOS) activity. Distributions of vegetables for TEAC and SOS were not continuous but highly skewed. TEAC values on a dry weight basis ranged from 0 to 2105 µmol TE g−1 and SOS values ranged from 0 to 6206 µmol ascorbate equivalent (AE) g−1. The majority of vegetables clustered within 200 µmol TE g−1 and 400 µmol AE g−1. Vegetable species were grouped into six classes after natural logarithm transformation of TEAC and SOS values. Most highly consumed vegetables fell in the very low to medium classes. Species in the very high class for both TEAC and SOS included leaves of Cedrela sinensis (Chinese cedar), Oroxylum indicum (Damocles tree), Cassia siamea (cassod tree) and Cassia tora (sickle senna). Edible plants high in antioxidant activity (AOA) were mostly perennial and underutilised crops, while commonly consumed vegetables were generally low in AOA. There is great potential to increase dietary antioxidants and improve human health through consumption of diverse vegetable species, especially those high in AOA. Copyright © 2006 Society of Chemical Industry 相似文献
997.
A Cafolla F Dragoni G Girelli ME Tosti B Monarca R Kendall CS Scott 《Canadian Metallurgical Quarterly》1998,61(3):160-163
Diabetes mellitus is a lifelong condition which requires acceptance, understanding and some degree of lifestyle discipline in order to maintain glycaemic equilibrium. The situation is complicated by the fact that poor glycaemic control is not necessarily symptomatic. Routines recommended by health professionals may not always be acceptable to the recipients or may be difficult to translate into the individual's framework of daily living. Dramatic emergencies may arise from a complex interrelated multiplicity of actions or omissions, or for reasons outside the control of the patient. Most emergencies are technically preventable. An attempt should be made by Accident and Emergency (A & E) staff to determine the cause. Referral to the diabetes specialist team is usually indicated. 相似文献
998.
KE Covinsky RM Palmer DM Kresevic E Kahana SR Counsell RH Fortinsky CS Landefeld 《Canadian Metallurgical Quarterly》1998,24(2):63-76
BACKGROUND: Hospitalization often marks the beginning, and may be partially responsible for, a downward trajectory characterized by declining function, worsening quality of life, placement in a long term care facility, and death. At the University Hospitals of Cleveland, an Acute Care for Elders (ACE) unit that reengineered the process of caring for older patients (> or = 70 years of age) to improve functional outcomes was established in September 1990. DESCRIPTION OF INTERVENTION: The general principles of ACE included an approach to care guided by the biopsychosocial model and recognition of the importance of fitting the hospital environment to the patient's needs. The design of the intervention was consistent with principles of comprehensive geriatric assessment and continuous quality improvement. Care, which focused on maintaining function, was directed by an interdisciplinary team that considered the patient's needs both at home and in the hospital. The major components of the ACE Unit intervention included patient-centered nursing care (daily assessment of functional needs by nursing, nursing-based protocols to improve outcomes, daily rounds by a multidisciplinary team), a prepared environment, planning for discharge, and medical care review. RESULTS: In a randomized trial comparing ACE with usual care, patients receiving ACE had improved functional outcomes at discharge. The costs to the hospital for ACE unit care were less than for usual care. The functional status of ACE and usual care patients was similar 90 days after discharge. FUTURE DIRECTIONS: The ACE unit intervention is being expanded to preserve the improvements observed during the hospitalization in the outpatient setting. In addition, needs other than function which are critical to patients' long-term quality of life are being considered. 相似文献
999.
C Cepeda CS Colwell JN Itri E Gruen MS Levine 《Canadian Metallurgical Quarterly》1998,10(11):3491-3497
Cell swelling induced by activation of excitatory amino acid receptors is presumably the first step in a toxic cascade that may ultimately lead to cell death. Previously we showed that bath application of N-methyl-D-aspartate (NMDA) or kainate (KA) produces swelling of neostriatal cells. The present experiments examined modulation of NMDA and KA-induced cell swelling by dopamine (DA) and its receptor agonists. Nomarski optics and infra-red videomicroscopy were utilized to visualize neostriatal medium-sized neurons in thick slices from rat pups (12-18 postnatal days). Increase in somatic cross-sectional area served as the indicator of swelling induced by bath application of glutamate receptor agonists. NMDA induced cell swelling in a dose-dependent manner. Activation of DA receptors in the absence of NMDA did not produce swelling. DA and the D1 receptor agonist SKF 38393, increased the magnitude of swelling produced by NMDA. This effect was reduced in the presence of the D1 receptor antagonist, SCH 23390. In contrast, activation of D2 receptors by quinpirole decreased the magnitude of NMDA-induced cell swelling. DA slightly attenuated cell swelling induced by activation of KA receptors. Quinpirole produced a significant concentration-dependent reduction in KA-induced swelling while SKF38393 increased KA-induced swelling, but only at a low concentration of KA. Together, these results provide additional support for the hypothesis that the direction of DA modulation depends on the glutamate receptor subtype, as well as the DA receptor subtype activated. One possible consequence of these observations is that endogenous DA may be an important contributing factor in the mechanisms of cell death in Huntington's disease. 相似文献
1000.
CM Lebreton PM Visscher CS Haley A Semikhodskii SA Quarrie 《Canadian Metallurgical Quarterly》1998,150(2):931-943
A novel method using the nonparametric bootstrap is proposed for testing whether a quantitative trait locus (QTL) at one chromosomal position could explain effects on two separate traits. If the single-QTL hypothesis is accepted, pleiotropy could explain the effect on two traits. If it is rejected, then the effects on two traits are due to linked QTLs. The method can be used in conjunction with several QTL mapping methods as long as they provide a straightforward estimate of the number of QTLs detectable from the data set. A selection step was introduced in the bootstrap procedure to reduce the conservativeness of the test of close linkage vs. pleiotropy, so that the erroneous rejection of the null hypothesis of pleiotropy only happens at a frequency equal to the nominal type I error risk specified by the user. The approach was assessed using computer simulations and proved to be relatively unbiased and robust over the range of genetic situations tested. An example of its application on a real data set from a saline stress experiment performed on a recombinant population of wheat (Triticum aestivum L. ) doubled haploid lines is also provided. 相似文献