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51.
S Schalla C Herskind KH H?ver WJ Lorenz EW Hahn 《Canadian Metallurgical Quarterly》1998,174(4):204-211
PURPOSE: The relative biological effectiveness (RBE) for inactivation of V79 cells was determined as function of dose at the Heidelberg 14-MeV (d + T) neutron therapy facility after irradiation with single doses in air and at different depths in a therapy phantom. Furthermore, to assess the reproducibility of RBE determinations in different experiments we examined the relationship between the interexperimental variation in radiosensitivity towards neutrons with that towards low LET 60Co photons. METHODS: Clonogenic survival of V79 cells was determined using the colony formation assay. The cells were irradiated in suspension in small volumes (1.2 ml) free in air or at defined positions in the perspex phantom. Neutron doses were in the range, Dt = 0.5-4 Gy. 60Co photons were used as reference radiation. RESULTS: The radiosensitivity towards neutrons varied considerably less between individual experiments than that towards photons and also less than RBE. However, the mean sensitivity of different series was relatively constant. RBE increased with decreasing dose per fraction from RBE = 2.3 at 4 Gy to RBE = 3.1 at 0.5 Gy. No significant difference in RBE could be detected between irradiation at 1.6 cm and 9.4 cm depth in the phantom. However, an approximately 20% higher RBE was found for irradiation free in air compared with inside the phantom. Combining the two effects, irradiation with 0.5 Gy free in air yielded an approximately 40% higher RBE than a dose of 2 Gy inside the phantom. CONCLUSION: The measured values of RBE as function of dose per fraction within the phantom is consistent with the energy of the neutron beam. The increased RBE free in air, however, is greater than expected from microdosimetric parameters of the beam and may be due to slow recoil protons produced by interaction of multiply scattered neutrons or to an increased contribution of alpha particles from C(n, alpha) reactions near the surface. An enhanced RBE in subcutaneous layers of skin combined with an increase in RBE at low doses per fraction outside the target volume could potentially have significant consequences for normal tissue reactions in radiotherapy patients treated with fast neutrons. 相似文献
52.
BK Berdiev KH Karlson B Jovov PJ Ripoll R Morris D Loffing-Cueni P Halpin BA Stanton TR Kleyman II Ismailov 《Canadian Metallurgical Quarterly》1998,75(5):2292-2301
The molecular composition of a core conduction element formed by the alpha-subunit of cloned epithelial Na+ channels (ENaC) was studied in planar lipid bilayers. Two pairs of in vitro translated proteins were employed in combinatorial experiments: 1) wild-type (WT) and an N-terminally truncated alphaDeltaN-rENaC that displays accelerated kinetics (tauo = 32 +/- 13 ms, tauc = 42 +/- 11 ms), as compared with the WT channel (tauc1 = 18 +/- 8 ms, tauc2 = 252 +/- 31 ms, and tauo = 157 +/- 43 ms); and 2) WT and an amiloride binding mutant, alphaDelta278-283-rENaC. The channels that formed in a alphaWT:alphaDeltaN mixture fell into two groups: one with tauo and tauc that corresponded to those exhibited by the alphaDeltaN-rENaC alone, and another with a double-exponentially distributed closed time and a single-exponentially distributed open time that corresponded to the alphaWT-rENaC alone. Five channel subtypes with distinct sensitivities to amiloride were found in a 1alphaWT:1alphaDelta278-283 protein mixture. Statistical analyses of the distributions of channel phenotypes observed for either set of the WT:mutant combinations suggest a tetrameric organization of alpha-subunits as a minimal model for the core conduction element in ENaCs. 相似文献
53.
T Haak E Haak E Jungmann K Kusterer KH Usadel 《Canadian Metallurgical Quarterly》1997,115(35-36):26-29
The development of diabetic microangiopathies is of decisive importance for the long-term prognosis of diabetes mellitus. For example, diabetic nephropathy is one of the the most common causes of terminal kidney failure. Primary prevention of diabetic nephropathy is best achieved by establishing good metabolic control. To ensure early pharmacological intervention of incipient diabetic nephropathy, screening for microalbuminuria is recommended at least once a year. A major element in the pathogenesis of diabetic nephropathy is a disordered microcirculation characterized by abnormal hemodynamics with elevated capillary pressure and microvascular resistance. Angiotensin converting enzyme inhibitors (ACE inhibitors) effectively act on these pathophysiological events by dilation of the vasa efferentia of the glomeruli. By means of videocapillaroscopy and laser doppler imaging also distinct changes in microcirculation can be detected. Investigations with these methods provided evidence that ACE inhibitors might also be useful in the primary prevention of diabetic nephropathy. Therefore, ACE inhibitors are useful pharmaceutical agents in the treatment of diabetic nephropathy. 相似文献
54.
JB Henshaw CA Olsen AR Farnbach KH Nielson JD Bell 《Canadian Metallurgical Quarterly》1998,37(30):10709-10721
Bilayers composed of phosphatidylcholine initially resist catalysis by phospholipase A2. However, after a latency period, they become susceptible when sufficient reaction products (lysolecithin and fatty acid) accumulate in the membrane. Temperature near the main bilayer phase transition and calcium concentration modulate the effectiveness of the reaction products. The purpose of this study was to examine the individual contributions of lysolecithin and palmitic acid to the susceptibility of dipalmitoylphosphatidylcholine vesicles and to rationalize the effects of temperature and calcium. Various fluorescent probes (Prodan, Laurdan, pyrene-labeled fatty acid, and dansyl-labeled phospholipid) were used to assess changes in the ability of the reaction products to perturb the bilayer and to affect the interactions with the enzyme. Un-ionized palmitic acid decreased bilayer polarity and perturbed the membrane surface exposing some of the Prodan to bulk water. Lysolecithin increased bilayer polarity and the rate of dipolar relaxation in response to the excited states of Laurdan and Prodan. A combination of the individual contributions of each product was observed when palmitic acid and lysolecithin were present together at low calcium, and the effects of lysolecithin dominated at high calcium. Palmitic acid, but not lysolecithin, promoted the binding of phospholipase A2 to the bilayer surface in the absence of calcium. Lysolecithin reduced the ability of fatty acid to enhance binding apparently by altering the structure of fatty acid domains in the membrane. Furthermore, increased temperature and ionization of the fatty acid tended to cause segregation of bound phospholipase A2 into domains poor in phospholipid content which presumably impeded bilayer hydrolysis. In contrast, un-ionized palmitic acid and lysolecithin promoted hydrolysis by augmenting a step distal to the adsorption of enzyme to the bilayer. This kinetic response to lysolecithin was calcium-dependent. A model accounting for these varied influences of the reaction products is presented. 相似文献
55.
Kell and Kx are two quantitatively minor proteins from the human erythrocyte membrane which carry blood groups antigens and are thought to be a metalloprotease and a membrane transporter, respectively. In the red cell membrane, these proteins form a complex stabilized by disulfide bond(s). Phosphorylation status of these proteins was studied, in the presence or absence of effectors of several kinases, either on intact cells incubated with [32P]-orthophosphate or on ghosts incubated with [gamma-32P]ATP. Purification of Kell-Kx complex, by immunochromatography on an immobilized human monoclonal antibody of Kell blood group specificity allowed to establish that (i) neither protein is phosphorylated on tyrosine; (ii) the Kell protein is a putative substrate for Casein Kinase II (CKII) and Casein Kinase I (CKI) but not for protein kinase C (PKC), whereas Kx protein is phosphorylated by CKII and PKC but not by CKI; (iii) Protein Kinase A neither phosphorylates the Kell nor the Kx proteins. 相似文献
56.
A Wild M Kalff-Suske A Vortkamp D Bornholdt R K?nig KH Grzeschik 《Canadian Metallurgical Quarterly》1997,6(11):1979-1984
Greig cephalopolysyndactyly syndrome (GCPS, MIM 175700) is a rare autosomal dominant developmental disorder characterized by craniofacial abnormalities and post-axial and pre-axial polydactyly as well as syndactyly of hands and feet. Human GLI3, located on chromosome 7p13, is a candidate gene for the syndrome because it is interrupted by translocation breakpoints associated with GCPS. Since hemizygosity of 7p13 resulting in complete loss of one copy of GLI3 causes GCPS as well, haploinsufficiency of this gene was implicated as a mechanism to cause this developmental malformation. To determine if point mutations within GLI3 could be responsible for GCPS we describe the genomic sequences at the boundaries of the 15 exons and primer pair sequences for mutation analysis with polymerase chain reaction-based assays of the entire GLI3 coding sequences. In two GCPS cases, both of which did not exhibit obvious cytogenetic rearrangements, point mutations were identified in different domains of the protein, showing for the first time that Greig syndrome can be caused by GLI3 point mutations. In one case a nonsense mutation in exon X generates a stop codon truncating the protein in the C-H link of the first zinc finger. In the second case a missense mutation in exon XIV causes a Pro-->Ser replacement at a position that is conserved among GLI genes from several species altering a potential phosphorylation site. 相似文献
57.
JH Kim JA Kang Y Lee KH Lee JH Lee EC Choi BK Kim 《Canadian Metallurgical Quarterly》1998,42(4):527-530
Rotavirus (RV) strains infecting newborns often have unique neutralization antigens (P serotypes) on their outer capsids that are distinct from those found on RV strains that cause diarrhea in older children. We examined the hypothesis that unusual RV strains preferentially infect newborns because the newborns lack maternal neutralizing antibodies to these strains. To test this hypothesis, sera and saliva samples collected from neonates infected with 116E-like (P[11]G9) strains in the maternity ward of the All India Institute of Medical Sciences (AIIMS) hospital in New Delhi were tested for neutralizing antibodies against common RV strains and those infecting newborns and these titers were compared with those of newborns who did not become infected (controls). The infected neonates had significantly lower levels of cord blood neutralizing antibodies to 116E than the controls, suggesting that immunity to neonatal RV infection is acquired transplacentally through maternal antibodies. Further, this study confirmed the immunogenicity of the AIIMS neonatal strain 116E, a vaccine candidate, in its ability to evoke a potent RV-specific immunoglobulin A and neutralizing antibody response in serum and saliva among the infected babies. Our findings have important implications for the development of an effective RV vaccine. In India, where G9 strains are common in the community, the use of 116E as a vaccine, together with the rhesus tetravalent vaccine, may provide a broader protection against all the circulating RV serotypes, including serotype G9, which is not represented in the current rhesus RV tetravalent vaccine (G1-G4). 相似文献
58.
Koo LS Shafiee HR Hsu DK Wormley SJ Thompson DO 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1990,37(3):148-158
It is shown that the (normalized) area function based on the Born approximation offers a simple connection between the ultrasonic scattering response and the monochromatic ray sum in X-ray CT (computerized tomography). Because of this simple association, it is possible to apply the ultrasonic signals in the computationally direct and efficient parallel-beam X-ray CT algorithm to reproduce the vertical thickness function of an ultrasonic scatterer. The development of this imaging methodology is demonstrated for flaws of simple geometry; theoretical as well as experimental results for two model scatterers using this imaging technique are reported. Specifically, the area functions for a two-to-one spheroid and a circular cylinder are calculated and applied to a filtered backprojection algorithm of X-ray CT to obtain the vertical thickness function images. These images are then compared with the true vertical thickness functions of the targets based on their geometry. With theoretical data, this method was found to work very well. Even when experimental data containing creeping waves were used, the method produced satisfactory results for objects with continuously smooth surface. 相似文献
59.
Knowledge and Information Systems - Given sequential news watch logs of users, how can we accurately recommend news articles? Compared to other items (e.g., movies and e-commerce products) for a... 相似文献
60.
Koo Hyun Lee Ki Suk Nam Youl Min Park Pyung Woo Shin Deuk Yong Lee Yo-Seung Song 《Metals and Materials International》2002,8(4):381-385
Plasma nitrocarburized AISI 1020 steels were oxidized for 15, 30 and 60 min to evaluate their corrosion and microstructural properties. After plasma nitrocarburizing for 3 h at 570°C in a gas mixture comprising 85 vol.% N2, 12vol.% H2 and 3 vol.% CH4, the compound layer composed of ɛ-Fe2–3(N,C) and γ’-Fe4(N,C) phases and the diffusion layer above the matrix were observed. The top oxide layer, consisting mainly of magnetite (Fe2O4) and hematite (Fe2O3) phases, forms after post-oxidation treatment at 500°C. However, the oxide layer was severely degraded by spallation as a result of increases in post-oxidizing time. The difference in corrosion resistance should be attributed to the thickness of the top oxide layer, which was governed by post-oxidizing time. 相似文献