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排序方式: 共有387条查询结果,搜索用时 171 毫秒
121.
D Billot-Klein D Shlaes D Bryant D Bell R Legrand L Gutmann J van Heijenoort 《Canadian Metallurgical Quarterly》1997,179(15):4684-4688
Analyses of the peptidoglycan nucleotide precursor contents of enterococci and staphylococci treated with ramoplanin, tunicamycin, or vancomycin were carried out by high-pressure liquid chromatography coupled with mass spectrometry (MS). In all cases, a sharp increase in the UDP-N-actetylmuramoyl-pentapeptide or -pentadepsipeptide pool was observed. Concomitantly, new peptidoglycan nucleotide peptides of higher molecular masses with hexa- or heptapeptide moieties were identified: UDP-MurNAc-pentapeptide-Asp or pentadepsipeptide-Asp in enterococci and UDP-MurNAc-pentapeptide-Gly or -Ala and UDP-MurNAc-pentapeptide-Gly-Gly or -Ala-Gly in staphylococci. These new compounds are derivatives of normal UDP-MurNAc-pentapeptide or -pentadepsipeptide precursors with the extra amino acid(s) linked to the lysine epsilon-amino group as established by various analytical procedures (MS, MS-MS fragmentation, chemical analysis, and digestion with R39 D,D carboxypeptidase). Except for tunicamycin-treated cells, it was not possible to ascertain whether these unusual nucleotides were formed by direct addition of the amino acids to UDP-MurNAc-pentapeptide (or -pentadepsipeptide) or whether they arose by reverse reactions from lipid I intermediates to which the amino acids had been added. 相似文献
122.
An optimization procedure using a genetic algorithm has been applied to define the optimum orientation of fibres in a uni-directional laminate in which the fibres were allowed to vary continuously across the domain. The domain was divided into two-dimensional finite elements and anisotropic properties corresponding to a carbon fibre laminate with all layers aligned in the zero element axis direction were applied to the laminate. The orientation of the material axis on each element was then prescribed as an independent variable for the genetic algorithm. 相似文献
123.
Mapping and load-balancing iterative computations 总被引:1,自引:0,他引:1
Legrand A. Renard H. Robert Y. Vivien F. 《Parallel and Distributed Systems, IEEE Transactions on》2004,15(6):546-558
We consider the mapping of iterative algorithms onto heterogeneous clusters. The application data is partitioned over the processors, which are arranged along a virtual ring. At each iteration, independent calculations are carried out in parallel, and some communications take place between consecutive processors in the ring. The aim is to determine how to slice the application data into chunks, and to assign these chunks to the processors, so that the total execution time is minimized. One major difficulty is to embed a processor ring into a network that typically is not fully connected, so that some communication links have to be shared by several processor pairs. We establish a complexity result that assesses the difficulty of this problem, and we design a practical heuristic that provides efficient mapping, routing, link- sharing, and data distribution schemes. 相似文献
124.
Galectin-3 is a galactose-binding lectin that has been found in several mammalian tissues. Galectin-3 gene is expressed in a wide range of normal and tumoral cells. In the case of myeloid cells, its expression correlates with the differentiation of monocytes to macrophages. In the case of cancer cell lines, its expression correlates with tumorigenicity and metastatic potential. The regulation of the expression of this gene is still largely unknown. The rabbit galectin-3 gene has been isolated and characterized. Its structure revealed an organization similar to that of the murine galectin-3 gene. The genomic sequences located upstream from its 5' end, upon insertion upstream from a promoter-free reporter gene, exhibited a strong promoter activity. This activity was upregulated upon treatment of transfected smooth muscle cells with phorbol 12-myristate 13-acetate (PMA) as well as upon transfection with a EJ/ras encoding plasmid. Conversely, it was downmodulated upon transfection with wild-type p53 but not with mutated p53. The regulatory sequences involved in the positive regulation of the gene were located upon serial deletion experiments. 相似文献
125.
S Rezaiguia C Garat C Delclaux M Meignan J Fleury P Legrand MA Matthay C Jayr 《Canadian Metallurgical Quarterly》1997,99(2):325-335
To study the rate and regulation of alveolar fluid clearance in acute pneumonia, we created a model of Pseudomonas aeruginosa pneumonia in rats. To measure alveolar liquid and protein clearance, we instilled into the airspaces a 5% bovine albumin solution with 1.5 microCi of 125I-human albumin, 24 h after intratracheal instillation of bacteria. The concentration of unlabeled and labeled protein in the distal airspaces over 1 h was used as an index of net alveolar fluid clearance. Since there was histologic evidence of alveolar epithelial injury, several methods were used to measure alveolar fluid clearance, including the use of experiments in rats with blood flow and the use of experiments in rats without blood flow, so that movement across the epithelial barrier would be minimized in the latter group. The results with each method were identical. We found that P. aeruginosa pneumonia increased alveolar liquid clearance over 1 h by 48% in studies with blood flow, and by 43% in rats without blood flow, compared with respective controls (P < 0.05). In both studies, this increase was inhibited with amiloride. However, propranolol had no inhibitory effect, thus ruling out a catecholamine-dependent mechanism to explain the increase in alveolar fluid clearance. An antitumor necrosis factor-alpha neutralizing antibody, instilled into the lung 5 min before bacteria, prevented the increase in alveolar liquid clearance in rats with pneumonia (P < 0.05). Also, TNFalpha (5 microg) instilled in normal rats increased alveolar liquid clearance by 43% over 1 h compared with control rats (P < 0.05). In normal rats instilled with TNFalpha, propranolol had no inhibitory effect. In conclusion, gram-negative pneumonia markedly upregulates net alveolar epithelial fluid clearance, in part by a TNFalpha-dependent mechanism. This finding provides a novel mechanism for the upregulation of alveolar epithelial sodium and fluid transport from the distal airspaces of the lung. 相似文献
126.
127.
128.
J. Legrand 《Canadian Metallurgical Quarterly》2002,128(11):1027-1031
Experimental data of pressure drop in flow through crushed rocks are reanalyzed with the capillary model in comparison with a model based on the square root of permeability as characteristic length. The capillary model is described by two parameters: the pore diameter and the tortuosity. The comparison leads to relationships between the structural parameters, Reynolds number, and friction factor of each model. The interest of the capillary model is that a single equation can predict all the experimental data expressed in terms of a pore friction factor as a function of pore Reynolds number. The equation, which is the sum of a viscous term and an inertial one, is valid for the whole Reynolds number domain. The equation can be used for the determination of the limits of the Darcy and turbulent flow regimes. According to the criterion used to neglect the viscous or the inertial term, the flow regimes limits can be expressed by a simple numerical value. 相似文献
129.
Dihydroceramide Δ4-desaturase 1 (DES1) catalyzes the last step of the de novo ceramide biosynthesis, which consists of the
introduction of a trans Δ4-double bond in the carbon chain of the dihydroceramide. It was previously observed that myristic acid binds DES1 through
N-myristoylation. This N-terminal modification significantly increased the activity of the recombinant DES1 in COS-7 cells
and targeted part of the enzyme initially present in the endoplasmic reticulum to the mitochondrial outer membrane, leading
to an increase in ceramide levels. Since these results were obtained in a recombinant COS-7 cell model with high expression
of rat DES1, the purpose of the present study was to investigate if the native DES1 enzyme was really upregulated by its N-myristoylation
in cultured rat hepatocytes. We first showed that DES1 was the main dihydroceramide desaturase isoform expressed in rat hepatocytes.
In this model, the wild-type myristoylable recombinant form of rat DES1 was found in both the endoplasmic reticulum and the
mitochondria whereas the mutated non-myristoylable recombinant form (N-terminal glycine replaced by an alanine) was almost
exclusively localized in the endoplasmic reticulum, which evidenced the importance of the myristoylation. Then, we showed
that compared to other fatty acids, myristic acid was the only one to increase native DES1 activity, in both total cell lysates
and mitochondrial fractions. The myristic acid-associated increase in DES1 activity was not linked to elevated mRNA or protein
expression but more likely to its N-terminal myristoylation. Finally, the myristic acid-associated increase in DES1 activity
slightly enhanced the number of apoptotic cells. 相似文献
130.
Sworowski M. Neuilly F. Legrand B. Summanwar A. Philippe P. Buchaillot L. 《Electron Device Letters, IEEE》2010,31(1):23-25
A new approach for the fabrication of large contour-mode single-crystal silicon resonators has been demonstrated without the use of SOI substrates. Twenty-four-megahertz disk resonators have been built thanks to industrial facilities dedicated to the integration of passive components on silicon and exhibit a good compromise between the quality factor higher than 50 000 and the motional resistance of a few kiloohms. 相似文献