全文获取类型
收费全文 | 1554篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 26篇 |
化学工业 | 316篇 |
金属工艺 | 42篇 |
机械仪表 | 31篇 |
建筑科学 | 61篇 |
矿业工程 | 8篇 |
能源动力 | 20篇 |
轻工业 | 174篇 |
水利工程 | 17篇 |
石油天然气 | 18篇 |
无线电 | 155篇 |
一般工业技术 | 224篇 |
冶金工业 | 274篇 |
原子能技术 | 7篇 |
自动化技术 | 203篇 |
出版年
2021年 | 16篇 |
2020年 | 13篇 |
2019年 | 23篇 |
2018年 | 39篇 |
2017年 | 12篇 |
2016年 | 28篇 |
2015年 | 22篇 |
2014年 | 24篇 |
2013年 | 63篇 |
2012年 | 43篇 |
2011年 | 82篇 |
2010年 | 75篇 |
2009年 | 56篇 |
2008年 | 80篇 |
2007年 | 54篇 |
2006年 | 35篇 |
2005年 | 53篇 |
2004年 | 38篇 |
2003年 | 40篇 |
2002年 | 38篇 |
2001年 | 26篇 |
2000年 | 23篇 |
1999年 | 25篇 |
1998年 | 69篇 |
1997年 | 51篇 |
1996年 | 31篇 |
1995年 | 24篇 |
1994年 | 23篇 |
1993年 | 27篇 |
1992年 | 33篇 |
1991年 | 18篇 |
1990年 | 19篇 |
1989年 | 22篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 18篇 |
1977年 | 19篇 |
1976年 | 31篇 |
1974年 | 14篇 |
1971年 | 10篇 |
1970年 | 9篇 |
1969年 | 10篇 |
1955年 | 11篇 |
排序方式: 共有1576条查询结果,搜索用时 15 毫秒
1.
Maurice Kamen-Kaye 《Journal of Petroleum Geology》1985,8(3):323-329
Exploratory drilling on the Seychelles Bank, in a sector west of outcrop granite on Mahé Island, has revealed the presence of substantial Mesozoic colums. Their thicness approaches 3,000m; and total Phanerozoic down to true basement probably exceeds 4,500m. Still greater depths are possible, not only in this drilled NW-most sector of the island arc of the Mascarene Ridge, but also elsewhere along the arc, whose total cross-latitudinal dimension is more than 2,000km. Volcanics, like those in the African borderlands, repeatedly enter the Phanerozoic column of the Seychelles. The young "basaltic basement" of geodynamic theory, consequently, cannot exist on the Seychelles Bank. The same negative may hold true for the whole arc of the Mascarene Ridge and for its marginal waters westward as far back as the African borderlands themsleves. In the domain of exploration, the prime parameter of sedimentary volume is acceptable along much of the Mascarene Ridge, for which reason wells drilled to true basement merit consideration in future drilling. Such wells in central and southern sectors might recover basement rocks whose petrology could offer a strong challenge to present concepts of paleogeography in the whole back-arc area of the western Indain Ocean. 相似文献
2.
GA Iotti MC Olivei A Palo C Galbusera R Veronesi A Comelli JX Brunner A Braschi 《Canadian Metallurgical Quarterly》1997,23(4):399-405
OBJECTIVE: To investigate the mechanical effects of artificial noses. SETTING: A general intensive care unit of a university hospital. PATIENTS: 10 patients in pressure support ventilation for acute respiratory failure. INTERVENTIONS: The following three conditions were randomly tested on each patient: the use of a heated humidifier (control condition), the use of a heat and moisture exchanger without filtering function (HME), and the use of a combined heat and moisture exchanger and mechanical filter (HMEF). The pressure support level was automatically adapted by means of a closed-loop control in order to obtain constancy, throughout the study, of patient inspiratory effort as evaluated from airway occlusion pressure at 0.1 s (P0.1). Patient's ventilatory pattern, P0.1, work of breathing, and blood gases were recorded. MEASUREMENTS AND MAIN RESULTS: The artificial noses increased different components of the inspiratory load: inspiratory resistance, ventilation requirements (due to increased dead space ventilation), and dynamic intrinsic positive end-expiratory pressure (PEEP). The additional load imposed by the artificial noses was entirely undertaken by the ventilator, being the closed-loop control of P0.1 effective to maintain constancy of patient inspiratory work by means of adequate increases in pressure support level. CONCLUSIONS: The artificial noses cause unfavorable mechanical effects by increasing inspiratory resistance, ventilation requirements, and dynamic intrinsic PEEP. Clinicians should consider these effects when setting mechanical ventilation and when assessing patients' ability to breathe spontaneously. 相似文献
3.
FM Loehrer CP Angst FP Brunner WE Haefeli B Fowler 《Canadian Metallurgical Quarterly》1998,13(3):656-661
BACKGROUND: Elevated homocysteine concentrations have been associated with premature arteriosclerosis and with impairment of key methylation reactions through accumulation of the homocysteine metabolite S-adenosylhomocysteine. In end-stage renal failure high homocysteine concentrations are commonly found but thus far the concentrations of related adenosylated metabolites in plasma have not been assessed. METHODS: In this prospective study we determined plasma homocysteine and related metabolites in 25 patients on regular haemodialysis, and in 40 healthy volunteers. Blood samples from patients were drawn immediately before and in 10 patients additionally after the dialysis session. RESULTS: Folic acid and vitamin B12 in plasma were similar in patients (mean +/- SEM 25+/-2 nmol/l and 400+/-41 pmol/l respectively) and controls (24+/-3 and 324+/-23 respectively). In patients plasma homocysteine, S-adenosylmethionine and S-adenosylhomocysteine were markedly elevated (36.6+/-3.6 micromol/l, 381+/-32nmol/l and 1074+/-55 nmol/l respectively) compared to the control values (6.8+/-0.4 micromol/l, 60+/-3 nmol/l and 24.4+/-1.1 nmol/l respectively) whereas the molar ratio of plasma S-adenosylmethionine and S-adenosylhomocysteine was significantly decreased (0.36+/-0.02 and 2.7+/-0.2 in patients and controls respectively). Haemodialysis failed to normalize the abnormal levels of these metabolites. CONCLUSION: Since the ratio of S-adenosylmethionine : S-adenosylhomocysteine is closely linked to the activity of numerous enzymatic methylation reactions, these results suggest that methylation may be impaired in these patients. 相似文献
4.
The protease-protected 30 kDa domain of SecA is largely inaccessible to the membrane lipid phase 总被引:2,自引:0,他引:2
SecA binds to the inner membrane of Escherichia coli through low affinity lipid interactions or with high affinity at SecYEG, the integral domain of preprotein translocase. Upon addition of preprotein and nucleotide, a 30 kDa domain of SecYEG-bound SecA is protected from proteolysis via membrane insertion. Such protection could result from some combination of insertion into the lipid phase, into a proteinaceous environment or across the membrane. To assess the exposure of SecYEG-bound SecA to membrane lipids, a radiolabeled, photoactivatable and lipid-partitioning crosslinker, 3-trifluoromethyl-3-(m[125I]iodophenyl) diazirine benzoic acid ester, was incorporated into inner membrane vesicles. The 30 kDa domain of SecYEG-bound SecA, inserted into the membrane in response to translocation ligands, is 18-fold less labeled than SecY, which is labeled effectively. In contrast, incorporation of the purified 30 kDa SecA fragment into crosslinker-containing detergent micelles or addition of detergent to crosslinker-containing membranes bearing the protease-protected SecA domain readily allows for labeling of this domain. We propose that the protease-inaccessible 30 kDa SecA domain is shielded from the fatty acyl membrane phase by membrane-spanning SecYEG helices and/or is largely exposed to the periplasm. 相似文献
5.
Trends in causative organisms and sources of infection were studied in a series of 288 episodes of bacteremia in neutropenic cancer patients observed in a single institution from 1986 to 1993. The incidence of bacteremia increased significantly from 20 episodes per 1000 admissions in 1986 to 50 episodes per 1000 admissions in 1993 (p = 0.00001). Over the study period, a continuous increment in gram-positive bacteremia, which reached 81% of episodes in 1993 (p = 0.000001), was observed. Conversely, the incidence of gram-negative bacteremia remained stable. Coagulase-negative staphylococci and viridans group streptococci were the most commonly isolated pathogens. Bacteremia caused by coagulase-negative staphylococci increased from 3 episodes per 1000 admissions to 19 episodes per 1000 admissions (p = 0.0001), and viridans group streptococci bacteremia increased from 0 episodes per 1000 admissions to 19 episodes per 1000 admissions (p = 0.000001). The upward trend in gram-positive bacteremia appeared to be related to a significant increase in both intravascular catheters (p = 0.003) and oral mucositis (p = 0.003) as sources of infection. Specific strategies to prevent chemotherapy-induced mucositis and catheter-related bacteremia merit further investigations. 相似文献
6.
Izard Carroll E.; Fantauzzo Christina A.; Castle Janine M.; Haynes O. Maurice; Rayias Maria F.; Putnam Priscilla H. 《Canadian Metallurgical Quarterly》1995,31(6):997
Four studies examined aspects of the differential emotions theory (DET) hypothesis of expressive behavior development. In Study 1, facial-expressive movements of 108 2.5–9-mo-old infants were video recorded in positive and negative mother–infant interactions (conditions). As expected, Max-specified full-face and partial expressions of interest, joy, sadness, and anger were morphologically stable between the 2 ages. Studies 1 and 2 confirmed predicted differential responding to mother sadness and anger expressions and to composite positive and negative conditions. Discrete negative expressions exceeded negative blends, and the amount of both expression types remained stable across ages. Studies 3 and 4 provided varying degrees of support for the social validity of Max-specified infant negative affect expressions. Conclusions include revisions and clarifications of DET. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
Meta-accuracy, knowing how others view the self, was examined using the Social Relations Model. 15 groups of 4–6 acquainted individuals gave self-ratings, perceptions of other group members, and estimated others' perceptions of self (metaperceptions) on the Big Five and Interesting. Individuals also rated liking and metaperceptions of liking. Trait perceptions were consensual, and self–other agreement emerged for most traits. Affect judgments were entirely relational; individuals differentiated among targets. Trait metaperceptions were dominated by perceiver variance. Individuals differed in the impression they believed others generally held about them. Affect metaperceptions, however, were relational in nature. Correlations between perceptions and metaperceptions assessed 2 types of meta-accuracy. Generalized meta-accuracy was obtained for some trait ratings. Affect judgments revealed significant dyadic meta-accuracy. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
Choice between a variable and a fixed food source was studied in pigeons. The variable source yielded different durations of access to food (changed across experimental conditions) uniquely associated with equiprobable delays of either 20 sec or 60 sec, timed from the choice point. A comparison, elapsing alternative (time-left procedure [J. Gibbon and R. M. Church; see PA, Vol 67:2812]), was associated with fixed access to feeder after a 60-sec delay, timed from the beginning of the trial. Preference was best characterized as reflecting an average of the 2 local rates of reinforcement in the variable alternative (the average of the ratio of each standard amount and its associated delay). The averaging rule characterized initial choice link data well, but terminal link responding showed that Ss also remembered the 2 delay–amount combinations separately. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
Crook Thomas H.; Youngjohn James R.; Larrabee Glenn J.; Salama Maurice 《Canadian Metallurgical Quarterly》1992,6(2):123
Performance on computer-simulated, everyday memory tasks was found to deteriorate with age in 434 Belgian (aged 14–88 yrs) and 434 American Ss matched on gender and age. This age-related memory decline was reasonably consistent across samples. Difficulties in cross-cultural research and the advantages of ecologically valid measurement instruments are discussed. Instruments included a grocery list selective reminding test, the Wechsler Memory Scale, the Benton Visual Retention Test, and the Wechsler Adult Intelligence Scale (WAIS). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
Maurice Depey 《电信纪事》1991,46(9-10):501-506
A practical work on design of analog bipolar integrated circuits is presented. The designed circuits are fabricated by Thomson composants militaires et spatiaux(TCMS,) and subsequently measured by the students. The semi-custom technique of pre-diffused array allows no prerequisite knowledge on technology. The process used(HF2C) has a large field of applications due to high performance of the available components (ft = 3 GHz for theNPN transitors). TheCAD tools involved areSPICE for circuit simulation and Princess (Silvar Lisco) as the layout editor. After being experimented atENSERG, this possibility is extended to a national level within the frame of the French multi chip project (CMP). 相似文献