全文获取类型
收费全文 | 501篇 |
免费 | 17篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 111篇 |
金属工艺 | 20篇 |
机械仪表 | 5篇 |
建筑科学 | 20篇 |
能源动力 | 6篇 |
轻工业 | 48篇 |
水利工程 | 6篇 |
石油天然气 | 2篇 |
无线电 | 19篇 |
一般工业技术 | 96篇 |
冶金工业 | 109篇 |
原子能技术 | 11篇 |
自动化技术 | 61篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 13篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 13篇 |
2015年 | 6篇 |
2014年 | 13篇 |
2013年 | 31篇 |
2012年 | 13篇 |
2011年 | 13篇 |
2010年 | 13篇 |
2009年 | 20篇 |
2008年 | 7篇 |
2007年 | 14篇 |
2006年 | 11篇 |
2005年 | 6篇 |
2004年 | 5篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 22篇 |
1997年 | 28篇 |
1996年 | 22篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 14篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1979年 | 2篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 13篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有518条查询结果,搜索用时 340 毫秒
91.
92.
93.
An ion beam milling system utilizing a Kaufman-type source to etch patterns in conductive, semiconductive and insulating materials was used to examine the surface morphology of resistive thick films, and to modify the surface topography of biomaterials. The ion beam sputter modification of the different materials presently used or under consideration for electronic and implant devices were studied. A Japan Electron Optics Laboratory, model JSM-35 scanning electron microscope was used to examine all the materials tested. 相似文献
94.
Lunayach R. Knick E. Kowalski G. 《Selected Areas in Communications, IEEE Journal on》1983,1(1):110-117
The advent of processing satellites which perform demodulation and remodulation of received signals has made it practical to consider satellite communication systems in which the up-link and down-link multiplexing/multiple-access schemes are different. This paper considers a satellite communication system in which channels are demand-assigned, and in which a hybrid time-division/frequencydivision multiple-access approach is employed for the up-link and pure time-division multiplexing is employed for the down-link. This scheme has significant advantage for systems which may be subject to electronic jamming. The user capacity is analyzed in general, and numerical results are given for some specific parameters of interest. Depending on the number of ground terminals in the network, it is found that the user capacity of the system can be limited by either the terminal's or the satellite's channel capacity. 相似文献
95.
Prof. Dr. Ing. Boleslaw Konorski 《Electrical Engineering (Archiv fur Elektrotechnik)》1956,42(7):381-397
Übersicht Geschlossene Ausdrücke für die Summe der durch gegenseitige Spiegelung an Kugelflächen entstandenen Ladungen. Kapazität der Systeme zweier Kugeln. Krafteinwirkungen bei Kugeln mit konstanten Potentialen und Ladungen (gleiche und verschiedene Vorzeichen). Elektrostatisches Gleichgewicht.Mit 13 Abbildungen 相似文献
96.
Sparse regression often uses ℓ
p
norm priors (with p < 2). This paper demonstrates that the introduction of mixed-norms in such contexts allows one to go one step beyond in signal
models, and promote some different, structured, forms of sparsity. It is shown that the particular case of the ℓ1,2 and ℓ2,1 norms leads to new group shrinkage operators. Mixed norm priors are shown to be particularly efficient in a generalized basis pursuit denoising approach, and
are also used in a context of morphological component analysis. A suitable version of the Block Coordinate Relaxation algorithm
is derived for the latter. The group-shrinkage operators are then modified to overcome some limitations of the mixed-norms.
The proposed group shrinkage operators are tested on simulated signals in specific situations, to illustrate and compare their
different behaviors. Results on real data are also used to illustrate the relevance of the approach. 相似文献
97.
Katarzyna A. Michalow Andre Heel Andri Vital Martin Amberg Giuseppino Fortunato Kazimierz Kowalski Thomas J. Graule Mieczyslaw Rekas 《Topics in Catalysis》2009,52(8):1051-1059
Effect of W doping as well as a thermal treatment on the structural and photocatalytic properties of TiO2 produced by flame spray synthesis (FSS) were the subject of investigation. Structural properties were studied by means of
X-ray diffraction (XRD), BET adsorption isotherm and transmission electron microscopy (TEM). The surface condition was investigated
by X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC) and differential thermal and thermogravimetric
analysis (DTA-TGA). The photocatalytic properties were studied by optical measurements and photodecomposition of methylene
blue under visible irradiation. It was found that the photoactivity in the visible region was enhanced significantly by the
W-doping as well as by additional thermal treatment of those nanopowders. The obtained TiO2-W nanopowders exhibited higher performance under visible light than P25. 相似文献
98.
The aim of this study was to determine the effect of docosahexaenoic acid-rich algae (DHA-RA) supplementation in milk replacer (MR) on performance, selected cytokine expression in lymphocytes, and blood immunoglobulin concentration in newborn dairy calves. Forty female Holstein-Friesian calves (8.6 ± 0.8 d old and 41.1 ± 4.3 kg; mean ± standard deviation) were blocked by date of birth and allocated into 4 experimental groups (10 animals/group): (1) not supplemented with DHA-RA, (2) supplemented with 9 g of DHA-RA/d in MR, (3) supplemented with 18 g of DHA-RA/d in MR, and (4) supplemented with 27 g of DHA-RA/d in MR. Milk replacer was fed in an amount equal to 900 g of MR powder/d (as fed), 2 times a d, for 49 d. Starter mixture (SM) was fed ad libitum beginning on d 15 of the study. Each calf was in the study over a period of 49 d. The MR and SM intake and fecal score were recorded daily and body weight was recorded weekly. Blood samples were collected before the morning feeding, at the beginning of the study, every consecutive week, and at the end of the study for morphology and smear analysis, serum immunoglobulin level (IgG, IgA, and IgM), and lymphocyte isolation. The mRNA isolated from lymphocytes was checked for TNFα, IL-1β, IL-6, and p65 expression. Average daily gain between d 1 to 14 of the study increased quadratically with increasing dose of DHA-RA. However, average daily gain between d 15 to 49 of the study tended to linearly decrease and over the whole study linearly decreased with increasing dose of DHA-RA. The MR intake decreased linearly between d 1 to 14 of the study and over the whole study, and mean SM intake decreased quadratically with increasing dose of DHA-RA. Feed efficiency increased quadratically and fecal score decreased quadratically during the first 14 d of the study. Increasing dose of DHA-RA led to cubic changes in feed efficiency and fecal score between d 15 and 49 of the study. Overall, over the whole study period a tendency was observed for lower fecal score for the DHA-RA supplemented groups. Interleukin-1β mRNA expression decreased linearly, whereas the mRNA expression of p65 and TNFα as well as serum IgG concentration tended to decrease linearly with increasing dose of supplemental DHA-RA. No effect of group was found on IgA and IgM serum level and the majority of blood parameters. Altogether, treatment worsened production variables but seemed to have a beneficial effect on the immune system of calves. 相似文献
99.
Dr. Eric M. Lewandowski Dr. Łukasz Szczupak Dr. Aleksandra Kowalczyk Dr. Gracia Mendoza Prof. Manuel Arruebo Lian M. C. Jacobs Prof. Paweł Stączek Prof. Yu Chen Prof. Konrad Kowalski 《Chembiochem : a European journal of chemical biology》2020,21(15):2187-2195
The conjugation of organometallic groups to current β-lactam antibiotics is a field of increasing study due to the ability of certain organometallic groups to enhance the antibiotic potency of these drugs. Herein, we report the antibacterial properties of two metallocenyl (ferrocenyl and ruthenocenyl) 7-aminocephalosporanic acid (7-ACA) antibiotic conjugates. Continuing a trend we found in our previous studies, the ruthenocenyl conjugate showed greater antibacterial activity than its ferrocenyl counterpart. Compared with the previously published 7-aminodesacetoxycephalosporanic acid (7-ADCA) conjugates, the 3-acetyloxymethyl group significantly improved the compounds’ activity. Furthermore, the Rc-7-ACA compound was more active against clinical Staphylococcus aureus isolates than the ampicillin reference. Noticeably, neither of the two new compounds showed an undesirable toxic effect in HeLa and L929 cells at the concentrations at which they displayed strong antibacterial effects. The antibacterial activity of the two metallocenyl 7-ACA derivatives was further confirmed by scanning electron microscopy (SEM). SEM micrographs showed that bacteria treated with metallocenyl 7-ACA derivatives feature cell wall damage and morphology changes. Using a CTX-M-14 β-lactamase competition assay based on nitrocefin hydrolysis, we showed that the Rc-7-ACA bound more favorably to CTX-M-14 than its ferrocenyl counterpart, again confirming the superiority of the ruthenocenyl moiety over the ferrocenyl one in interacting with proteins. We also report a 1.47 Å resolution crystal structure of Rc-7-ACA in complex with the CTX-M-14 E166A mutant, an enzyme sharing a similar active site configuration with penicillin-binding proteins, the molecular target of β-lactam antibiotics. These results strengthen the case for the antibacterial utility of the Rc and Fc groups. 相似文献
100.
C Kowalski S Zahler BF Becker A Flaucher PF Conzen E Gerlach K Peter 《Canadian Metallurgical Quarterly》1997,86(1):188-195
BACKGROUND: Polymorphonuclear neutrophils (PMNs) contribute to postischemic reperfusion damage in many organs and tissues, a prerequisite being adhesion of PMNs to vascular endothelial cells. Because adhesion processes involve orderly interactions of membrane proteins, it appeared possible that "membrane effects" of volatile anesthetics could interfere. We investigated the effects of halothane, isoflurane, and sevoflurane on postischemic adhesion of human PMNs in the intact coronary system of isolated perfused guinea pig hearts. METHODS: The hearts (n = 7-10 per group) were perfused in the "Langendorff" mode under conditions of constant flow (5 ml/min) using modified Krebs-Henseleit buffer equilibrated with 94.4% oxygen and 5.6% carbon dioxide. Global myocardial ischemia was induced by interrupting perfusion for 15 min. In the second minute of reperfusion (5 ml/min), a bolus dose of 6 x 10(5) PMNs was injected into the coronary system. The number of cells reemerging in the coronary effluent was expressed as a percentage of the total number of applied PMNs. Halothane, isoflurane, and sevoflurane, each at 1 and 2 minimal alveolar concentration (MAC), were vaporized in the gas mixture and applied from 14 min before ischemia until the end of the experiment. RESULTS: Under nonischemic conditions, 24.7 +/- 1.3% of the injected neutrophils did not reemerge from the perfused coronary system. Subjecting the hearts to global ischemia augmented retention (36.4 +/- 2.8%, P < .05). Application of halothane reduced adhesion of neutrophils to 22.6 +/- 2.1% and 24.2 +/- 1.8% at 1 and 2 MAC, respectively (P < .05). Exposure to 1 and 2 MAC isoflurane was similarly effective, whereas basal adhesion was not significantly influenced. Sevoflurane-treated hearts (1 and 2 MAC) also showed decreased adhesion of PMNs (23 +/- 2.3% and 24.8 +/- 1.8%, respectively; P < .05) and an identical reduction resulted when sevoflurane (1 MAC) was applied only with the onset of reperfusion. CONCLUSIONS: Although the mechanism of action of volatile anesthetics remains unclear in these preliminary studies, their inhibitory effect on ischemia-induced adhesion of PMNs may be beneficial for the heart during general anesthesia. 相似文献