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51.
A new curve-based approach to polyhedral machining 总被引:8,自引:0,他引:8
Cha-Soo JunAuthor Vitae Dong-Soo KimAuthor VitaeSehyung ParkAuthor Vitae 《Computer aided design》2002,34(5):379-389
This paper presents a new approach to three-axis NC tool path generation for sculptured surfaces. In the proposed curve-based approach, the gouge-free tool paths are generated from a polyhedral model of the STL (stereolithography) format. The polyhedral model is offset by a local-offsetting scheme. Then, the offset elements such as triangular facets, trimmed cylinders, and trimmed spheres are sliced by a series of drive planes. The curve segments on a drive plane are sorted, trimmed and linked, while the concave gouge is removed during the trimming process. The method is implemented on a PC, and some illustrative examples are provided in this paper. The main advantage of the proposed method is that the tool path can be generated from a polyhedral model without any concave and convex gouge, especially on an NC machine that supports NURBS interpolation. Other advantages and disadvantages of the proposed model are also discussed. 相似文献
52.
Administration (p.o.) of SKP-450, 2-[2"-(1",3"-dioxolane)]-2-methyl-4-(2'-oxo-1'-pyrrolidinyl)-6-nitro-2H- 1-benzopyran, a novel antihypertensive agent, to hypercholesterolemic Syrian hamsters led to a significant reduction in plasma lipids in a dose-dependent manner, i.e., a 10.8% to 29% reduction in low-density lipoprotein cholesterol at doses of 0.3 to 10 mg/kg of SKP-450. SKP-450 was found to specifically inhibit the hepatic microsomal lanosterol 14alpha-methyl demethylase (14alpha-DM) in a competitive manner (Ki:2.65 microM). Furthermore, a dose-dependent decrease in the 14alpha-DM activity by SKP-450 parallelled the cholesterol synthetic rate in vitro in both the rat hepatic S10 fractions (supernatants at 10,000 g; IC50:20 microM) and Chinese hamster ovary cells (IC50:23 microM). However, this phenomenon was not seen in AR45 cells, which are deficient in 14alpha-DM, suggesting that 14alpha-DM is the major target for the inhibitory action of SKP-450 in regard to cholesterol biosynthesis. 相似文献
53.
Dong-Soo?ParkEmail author Ji-Hyun?Lim Yeon-Gil?Jung 《Metals and Materials International》2003,9(6):613-618
α-Sialon powder was made from α-Si3N4, Si, Y2O3 and AIN powders by a SHS process under 3 MPa nitrogen pressure. Hot pressing of the α-Sialon powder with added 0–8 wt.% YAG
(Y3Al5O12) at 2223 K for 1.5 hr under 30 MPa resulted in α/β-Sialon composites. α-Sialon content of the hot pressed sample was decreased
as YAG content was increased. The number of elongated α- and β-Sialon grains was increased as the YAG content was increased.
Vickers hardness of the hot pressed α/β-Sialon composites was decreased as the YAG content was increased, while both the fracture
toughness and the flexural strength reached their maxima at 2 wt.% YAG addition. 相似文献
54.
Jong Hoo Paik Sahn Nahm Young Sik Kim Hyun Min Park Hwack Joo Lee Jae Dong Byun 《Journal of Materials Science》2003,38(3):621-628
The crystal structure of (Ba1–x
La
x
)[Mg(1 + x)/3Nb(2–x)/3]O3 (BLMN) ceramics with 0 x 1 was investigated using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). When the La content, x, was above 0.1, the 1:2 ordered hexagonal structure found in Ba(Mg1/3Nb2/3)O3 (BMN) was transformed into the 1:1 ordered cubic structure. The 1:1 ordered cubic structure was maintained up to x = 0.7. When x exceeded 0.7, however, BLMN exhibited a 1:1 ordered monoclinic structure, rather than a 1:1 ordered cubic structure. La(Mg2/3Nb1/3)O3 (LMN) has a 1:1 ordered monoclinic P21/n structure with a = 5.6004 Å, b = 5.6414 Å, c = 7.9346 Å, and = 89.9819°. The monoclinic LMN has the in-phase and the anti-phase tilt of oxygen octahedra. The anti-parallel shift of A-site cations was also found in LMN. 相似文献
55.
Data are presented on the externally received personal dose equivalent for radiation workers who used the Korea Radioisotope Association's personal monitoring and dose record keeping service since 1984, and provide initial statistics on Korean workers who have been exposed to ionising radiation in different occupations. The total number of workers registered during the period of 1984 to 1999 was 64,518. The number increased steadily and the accumulated dose also increased. The proportion of radiation workers by occupation was 38.4% for nuclear power plants, 20.3% for industrial organisations and 12.4% for non-destructive industry. The annual collective dose of radiation workers was 31.72 man.Sv in 1999. The mean annual dose by sex was 1.49 mSv for males and 0.56 mSv for females and the mean annual dose for a worker was 1.41 mSv with the highest mean dose being received by non-destructive industry (3.53 mSv). Very few workers (0.8%) received more than 20 mSv (2 rem) and only one more than 50 mSv, the legal limit for an annual dose increase. There has been a steady decline in the mean dose since 1984, showing a significant decrease in dose with time (p<0.001). The data showed that radiation protection in Korea was improving, though annual doses were still higher than other countries. 相似文献
56.
Miae Woo Sang-Tae Kim Jong-Ho Paik Hyoung-Kyu Song Young-Hwan You 《Broadcasting, IEEE Transactions on》2007,53(3):678-684
A combination of orthogonal frequency division multiplexing (OFDM) with frequency-division multiple access (FDMA) called orthogonal frequency-division multiple access (OFDMA) is regarded as a promising solution for improving the performance of interactive wireless broadcasting systems. This paper presents our investigation into reducing the multiple access interference (MAI) introduced by symbol timing misalignment in an OFDMA uplink system. To combat the MAI, we provide a new OFDMA symbol frame employing a simple symbol repetition coupled with a cyclic time shift for typical OFDMA uplink scenarios. Theoretical analysis and computer simulations are used to assess the performance of the proposed OFDMA uplink system. It is found that this scheme can decrease the probability of destroying the orthogonality among the users and provide the MAI-free reception. 相似文献
57.
Myung Jin Yim Chang-Kyu Chung Kyung Wook Paik 《Electronics Packaging Manufacturing, IEEE Transactions on》2007,30(4):306-312
This paper describes how the material properties of conductive particles in anisotropic conductive films (ACFs) affect the electrical conductivity and the reliability of ACF interconnections for chip-on-glass (COG) applications. For the conductive particles, Au/Ni-coated polymer particles with a 5-diameter were used. Two different types of conductive particles were characterized with respect to their mechanical and electrical properties, such as ball hardness, recovery behavior, and electrical resistance. In addition, two ACFs were fabricated in the form of a double-layered structure, in which the thickness of the ACF and a nonconductive film (NCF) layer were optimized to have as many conductive particles as possible on the bump after COG bonding. The electrical contact resistance of an ACF interconnection in a COG structure depends mainly on the electrical properties of conductive particles in the ACF. The electrical reliability of an ACF interconnection in a COG structure also depends more on the electrical properties than the mechanical properties of conductive particles under a high-temperature and humid condition. Conductive particles with a lower electrical resistance, higher mechanical hardness, and lower recovery rate show better reliability than conductive particles with a higher electrical resistance, lower mechanical hardness, and higher recovery rate. Cross-sectional scanning electron microscopic (SEM) pictures of a COG interconnection show the deformation of two different conductive particles after the reliability tests. The ACF interconnections in the edge or corner of a driver IC show less reliable joints due to high absorption of moisture. 相似文献
58.
59.
Jong-Jin Choi Joo-Hee Lee Dong-Soo Park Byung-Dong Hahn Woon-Ha Yoon Hua-Tay Lin 《Journal of the American Ceramic Society》2007,90(6):1926-1929
Conductive La0.8 Sr0.2 MnO3 (LSM) and La0.6 Sr0.4 Co0.2 Fe0.8 O3 (LSCF) layers with a thickness of ∼10 μm were deposited on ferritic stainless steel (SS) by the aerosol deposition method, for use as an oxidation resistance-coating layer in the metallic interconnector of a solid oxide fuel cell. The coated layers were fairly dense without pores or cracks, and maintained good adhesion even after oxidation at 800°C for 100 h. The surface of the bare SS after annealing at 800°C for 100 h was covered with Cr2 O3 and Fe3 O4 oxide scales, and the electrical conductivity was sharply decreased. However, the LSM- and LSCF-coated SSs showed a surface microstructure with almost no oxidation and maintained good electrical conductivity after annealing at 800°C for 100 h. The area-specific resistance (ASR) of LSM- and LSCF-coated alloys after 100 h of oxidation at 800°C was 20.6 and 11.7 mΩ·cm2 , respectively. 相似文献
60.
Sang-Wook Park Hyun-Bum Cho Dong-Soo Suh Chan-Woo Kim 《Korean Journal of Chemical Engineering》1999,16(2):221-228
Experiments were performed on the esterification of lauric acid with isopropyl alcohol by tricaprylylmethylammonium chloride
in a stirred vessel with a flat liquid-liquid interface. The observed initial rate of reaction was used to analyze the reaction
mechanism combined with the catalyst, and to evaluate the several kinds of reaction rate constant, from which equilibrium
constants were expressed as a function of reaction temperature. The analysis of reaction kinetics indicated that the reaction
was between a very slow and slow reaction regime. 相似文献