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41.
Friction surfacing is a solid-state process, which allows deposition welding at temperatures below the melting range. For this investigation coating layers of NiAl-bronze were deposited by friction surfacing on self-mating substrates, followed by microstructural characterisation. Further, cavitation tests were performed in order to investigate wear resistance. Cavitation erosion mechanisms were analysed by means of optical and electron microscopy. All coatings show incubation periods about twice as long as those of the substrate material, while their average rate of material loss is about one half of that of the substrate. The differences in cavitation erosion resistance are due to more ductile behaviour of the coatings, as well as corrosion increasing the wear of the as-cast material. 相似文献
42.
Persistent organic pollutants in Mediterranean seawater and processes affecting their accumulation in plankton 总被引:1,自引:0,他引:1
Berrojalbiz N Dachs J Del Vento S Ojeda MJ Valle MC Castro-Jiménez J Mariani G Wollgast J Hanke G 《Environmental science & technology》2011,45(10):4315-4322
The Mediterranean and Black Seas are unique marine environments subject to important anthropogenic pressures due to riverine and atmospheric inputs of organic pollutants. Here, we report the results obtained during two east-west sampling cruises in June 2006 and May 2007 from Barcelona to Istanbul and Alexandria, respectively, where water and plankton samples were collected simultaneously. Both matrixes were analyzed for hexaclorochyclohexanes (HCHs), hexachlorobenzene (HCB), and 41 polychlorinated biphenyl (PCB) congeners. The comparison of the measured HCB and HCHs concentrations with previously reported dissolved phase concentrations suggests a temporal decline in their concentrations since the 1990s. On the contrary, PCB seawater concentrations did not exhibit such a decline, but show a significant spatial variability in dissolved concentrations with lower levels in the open Western and South Eastern Mediterranean, and higher concentrations in the Black, Marmara, and Aegean Seas and Sicilian Strait. PCB and OCPs (organochlorine pesticides) concentrations in plankton were higher at lower plankton biomass, but the intensity of this trend depended on the compound hydrophobicity (K(OW)). For the more persistent PCBs and HCB, the observed dependence of POP concentrations in plankton versus biomass can be explained by interactions between air-water exchange, particle settling, and/or bioaccumulation processes, whereas degradation processes occurring in the photic zone drive the trends shown by the more labile HCHs. The results presented here provide clear evidence of the important physical and biogeochemical controls on POP occurrence in the marine environment. 相似文献
43.
Vertical stacks of (In, Ga)N insertions in GaN nanowires are grown by molecular beam epitaxy. The chemical composition and strain within the structure are probed by a combination of high-resolution x-ray diffraction, transmission electron microscopy, and geometrical phase analysis. The (In, Ga)N insertions are coherently strained. Finite-element simulations strongly support an ineffective [corrected] strain relaxation despite [corrected] the nanowire geometry, leading to high-quality (In, Ga)N/GaN nanowire heterostructures. An intense green photoluminescence emission is observed and attributed to an inter-well transition between the stacked (In, Ga)N insertions. 相似文献
44.
Heinemann S Heinemann C Jäger M Neunzehn J Wiesmann HP Hanke T 《ACS applied materials & interfaces》2011,3(11):4323-4331
A recently established materials concept of biomimetic composites based on silica, collagen, and calcium phosphates was adapted for the preparation of porous scaffolds suitable for tissue engineering applications. Mineralization was achieved by directed nucleation of silica on the templating organic phase during a sol-gel process with or without addition of hydroxyapatite. Both mineral phases (25 wt %, individually or combined in equal shares) influenced the scaffold's morphology at the nanoscale. Enhancement of apparent density and compressive strength was similar for silica or hydroxyapatite mineralization; however the stiffening effect of hydroxyapatite was much higher. All scaffold modifications provided proper conditions for adhesion, proliferation, and osteogenic differentiation of human bone marrow stromal cells. The open porosity allowed cells to migrate throughout the scaffolds while maintaining their viability, both confirmed by MTT staining and confocal laser scanning microscopy. Initial cell distributions were graduated due to collagen mineralization, but balanced out over the cultivation time of 28 days. RT-PCR analyses revealed higher gene expression of ALP but lower expression of BSP II and osteocalcin because of collagen mineralization. The results demonstrate that both silica and hydroxyapatite offer comparable possibilities to tailor mechanical properties of collagen-based scaffolds without being detrimental to in vitro biocompatibility. 相似文献
45.
46.
A granular cell tumor is one of the rare tumors of the esophagus. We present the case of a 65-year-old male patient, who was admitted to our hospital for an elective cholecystectomy. In the routine diagnostic gastroscopy an intramural tumor in the distal esophagus was incidentally found. Repeated endoscopic biopsies did not reveal the histologic diagnosis, although endoscopic ultrasound invasion to the tunica muscularis could not be excluded. After indicating the operative therapy, the tumor was removed through a thoracoscopic approach. The histologic specimen showed a granular cell tumor of the esophagus (tumor of Abrikossoff). Since the tumor grade was unknown, our therapy seemed to be justified because of the low risk involved in minimally invasive operative procedures. There has been much discussion and controversy in the literature on this subject, including the potential for malignancy and the correct therapy regime, with a general shift to conservative or minimally invasive treatment. The case is discussed with a review of the literature. 相似文献
47.
To investigate the mechanism of nitric oxide (NO) inhibition of aldosterone release, this study compared the effects of type A natriuretic peptide and heat-stable enterotoxin to a nitric oxide donor, deta nonoate, on cGMP production and angiotensin II-stimulated aldosterone synthesis ill primary cultures of bovine adrenal zona glomerulosa cells. Type A natriuretic peptide (10(-10)-10(-6) M) and deta nonoate (10(-6)-10(-3) M) stimulated concentration-related increases in cGMP production. Heat-stable enterotoxin (10(-6) M) failed to stimulate cGMP synthesis in zona glomerulosa cells. Type A natriuretic peptide and deta nonoate attenuated angiotensin II-stimulated aldosterone production over the same concentration range that stimulated cGMP production. Heat-stable enterotoxin (10(-6) M) was without effect on aldosterone release. To further test the hypothesis that cGMP mediated the inhibition of aldosterone synthesis, the selective inhibitor of soluble guanylyl cyclase, 1H-(1,2,4)oxadiazolo [4,3-a]quinoxalin-1-one (ODQ) was used. ODQ pretreatment (10(-5) M) completely prevented deta nonoate-stimulated cGMP production without altering the inhibitory effect of deta nonoate on angiotensin II-stimulated steroidogenesis. Consistent with its selectivity for inhibiting soluble guanylyl cyclase, ODQ did not block type A natriuretic peptide-stimulated cGMP synthesis or type A natriuretic peptide inhibition of steroidogenesis. Deta nonoate completely blocked 25-hydroxycholesterol- and progesterone-stimulated aldosterone synthesis in zona glomerulosa cells and inhibited the conversion of 25-hydroxycholesterol to pregnenolone in mitochondrial fractions from bovine adrenal cortex. Deta nonoate-derived NO gave an absorbance maximum of the mitochondrial cytochrome P450 of 453 nm and inhibited the absorbance at 450 nm caused by carbon monoxide binding to the enzyme. These results suggest that deta nonoate reduces steroidogenesis independent of guanylyl cyclase activation and that NO has a direct effect to inhibit the activity of cytochrome P450, probably by binding to the heme groups of the cytochrome. 相似文献
48.
Entwicklung einer Versuchseinrichtung zur gleichzeitigen Bestimmung der Höhenänderung und der Abgaszusammensetzung sowie des Gefügezustandes einer Erz- oder Sinterprobe. Darstellung der Ergebnisse in Form von Thermogrammen. Versuche an verschiedenen Erzen und einem Sinter zur Erläuterung der Zweckmäßigkeit und Aussagekraft solcher Schaubilder. 相似文献
49.
Sophia Schmitt Julia Hümmer Saskia Kraus Alexander Welle Sylvain Grosjean Maximilian Hanke‐Roos Axel Rosenhahn Stefan Bräse Christof Wöll Cornelia Lee‐Thedieck Manuel Tsotsalas 《Advanced functional materials》2016,26(46):8455-8462
The ability to control the structure and surface chemistry of biomaterials on a molecular level is crucial for optimizing their performance. Here, a novel type of nanoporous organic framework that is suited for the fabrication of thin films is described. These surface‐grafted gels (SURGELs) are prepared and functionalized using two orthogonal, metal‐free click chemistries. The SURGELs are shown to be cytocompatible and to efficiently mediate adhesion of osteoblast‐like cells. This process can be further enhanced by surface modification. In addition, the use of light‐triggered reactions in combination with photomasks allows a patterned functionalization of the substrates. The potential to vary and exactly adjust the parameters within the SURGEL polymer network (including porosity and exact network topology on the nanometer scale as well as addressable functional groups) combined with the ability to functionalize their surfaces with any clickable biomolecule of choice in any desired pattern allow the targeted design of novel SURGEL‐based biomaterials for applications in nanomedicine, tissue engineering scaffolds, wound dressing,and medical implants. 相似文献
50.