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排序方式: 共有958条查询结果,搜索用时 15 毫秒
71.
Leong P.H.W. Leung I.K.H. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2002,10(5):550-559
The implementation of a microcoded elliptic curve processor using field-programmable gate array technology is described. This processor implements optimal normal basis field operations in F(2/sup n/). The design is synthesized by a parameterized module generator, which can accommodate arbitrary n and also produce field multipliers with different speed/area tradeoffs. The control part of the processor is microcoded, enabling curve operations to be incorporated into the processor and hence reducing the chip's I/O requirements. The microcoded approach also facilitates rapid development and algorithmic optimization: for example, projective and affine coordinates were supported using different microcode. The design was successfully tested on a Xilinx Virtex XCV1000-6 device and could perform an elliptic curve multiplication over the field F(2/sup n/) using affine and projective coordinates for n=113,155, and 173. 相似文献
72.
In developing countries, urban water is often provided by public private partnership (PPP). However, PPPs remain highly contentious, with many contracts renegotiated or stalled. Prima facie, this stems from issues in the French model of contract design between two parties – the government and the private operator. Critics point out that in reality, the PPP is a tri-party exchange of promises, services and fees linking the interests of the private operator, the government and the people. We propose a game theoretic analysis comparing a two-party contracting model with a tri-party one, which is tested against a real-world experiment in the water utilities in Manila and Jakarta. Paradoxically, we ?nd that a tri-party contracting model, though analytically more faithful in separating the interest of the government from the consumers’ leads to sub-optimal outcomes. In practical terms, we ?nd that an independent regulator may not generate better outcomes. 相似文献
73.
For the pharmaceutical industry, powder segregation can occur in many processes such as blending and compression solid dose unit operations. Yet it is important that the high quality standards of drug product manufacture are maintained throughout the whole processes. Powder segregation has been identified by the pharmaceutical industry as a potential issue, and in some cases it may cause variability in tablet assay and uniformity throughout a compression run. Early studies suggested for certain Direct Compression (DC) products, the separation of Active Pharmaceutical Ingredient (API) from excipients could arise due to air-induced segregation of the powders discharging from an Intermediate Bulk Container (IBC) to the tablet press via a vertical chute.Segregation tests were carried out on trial powder blend materials supplied by GlaxoSmithKline (GSK), using a laboratory-scale air elutriation test facility at The Wolfson Centre. Particle size analysis of the virgin and segregated sub-samples clearly indicated that powder segregation occurred as a result of aerodynamic effects. Subsequent chemical assay results concurred with the particle size results. Flowability testing of the powder blends indicated them to be free-flowing materials; this in addition to the presence of large particle size differentials within the powder blends is the likely cause of the susceptibility to air-induced segregation. 相似文献
74.
Leong SL Pettersson OV Rice T Hocking AD Schnürer J 《International journal of food microbiology》2011,145(1):57-63
Little is known about the mould, Xeromyces bisporus, unique in its strong xerophilicity and ability to grow at water activity (aw) 0.62, lower than for any other known organism. The linear growth rates of one fast and one slow-growing strain of X. bisporus were assessed at 20, 25, 30 and 37 °C on solid agar media containing a mixture of glucose and fructose to reduce aw to 0.94, 0.88, 0.84, 0.80, 0.76 and 0.66. Growth rates of xerophilic species closely related to X. bisporus, viz. Chrysosporium inops, C. xerophilum and Monascus eremophilus, were also assessed. Optimal conditions for growth of both X. bisporus strains were approx. 0.84 aw and 30 °C, despite FRR 2347 growing two- to five-fold faster than CBS 185.75. X. bisporus FRR 2347 even grew well at 0.66 aw (0.48 mm/day). C. inops and C. xerophilum were more tolerant of high aw than X. bisporus, and could be differentiated from each other based on: the faster growth of C. xerophilum; its preference for temperatures ≥ 30 °C and aw ≥ 0.94 (c.f. ≤ 25 °C and ~ 0.88 aw for C. inops); and its ability to grow at 0.66 aw, which is the lowest aw reported to date for this species. M. eremophilus grew slowly (max. 0.4 mm/day) even in its optimal conditions of ~ 0.88 aw and 25 °C. To investigate the competitive characteristics of X. bisporus at low aw, both X. bisporus strains were grown in dual-culture with xerotolerant species Aspergillus flavus and Penicillium roqueforti, and xerophilic species A. penicillioides, C. inops, C. xerophilum and Eurotium chevalieri, on glucose-fructose agar plates at 0.94, 0.84, 0.80 and 0.76 aw and at 25 °C. Growth rates and types of interactions were assessed. Excretion of inhibitory substances acting over a long-range was not observed by any species; inhibitors acting over a short-range that temporarily slowed competitors' growth or produced a protective zone around the colony were occasionally observed for A. penicillioides, C. inops and C. xerophilum. Instead, rapid growth relative to the competitor was the most common means of dominance. The xerotolerant species, A. flavus and P. roqueforti were dominant over X. bisporus at 0.94 aw. E. chevalieri was often dominant due to its rapid growth over the entire aw range. At aw < 0.80, X. bisporus was competitive because it grew faster than the other species examined. This supports the concept that its ideal environmental niche is sugary foods with low aw. 相似文献
75.
DW Hunt H Jiang DJ Granville AH Chan S Leong JG Levy 《Canadian Metallurgical Quarterly》1999,41(1):31-44
Silencing of the cryptic mating-type loci HMR and HML requires the recognition of DNA sequence elements called silencers by the Sir1p, one of four proteins dedicated to the assembly of silenced chromatin in Saccharomyces cerevisiae. The Sir1p is thought to recognize silencers indirectly through interactions with proteins that bind the silencer DNA directly, such as the origin recognition complex (ORC). Eight recessive alleles of SIR1 were discovered that encode mutant Sir1 proteins specifically defective in their ability to recognize the HMR-E silencer. The eight missense mutations all map within a 17-amino-acid segment of Sir1p, and this segment was also required for Sir1p's interaction with Orc1p. The mutant Sir1 proteins could function in silencing if tethered to a silencer directly through a heterologous DNA-binding domain. Thus the amino acids identified are required for Sir1 protein's recognition of the HMR-E silencer and interaction with Orc1p, but not for its ability to function in silencing per se. The approach used to find these mutations may be applicable to defining interaction surfaces on proteins involved in other processes that require the assembly of macromolecular complexes. 相似文献
76.
Nagarajan Raghavan Kin Leong Pey Wenhu LiuXing Wu Xiang LiMichel Bosman 《Microelectronic Engineering》2011,88(7):1124-1128
We present electrical evidence on asymmetric metal-insulator-semiconductor (MIS) based test structures in support of the presence of two different independent switching mechanisms in a resistive random access memory (RRAM) device. The valid mechanism for switching depends on the compliance capping (Igl) for forming/SET transition. Our results convincingly show that low compliance based switching only involves reversible oxygen ion drift to and from oxygen gettering gate electrodes, while high compliance switching involves formation and rupture of conductive metallic nanofilaments, as verified further by our physical analysis investigations. We have observed this unique dual mode switching mechanism only in NiSi-based gate electrodes, which have a moderate oxygen solubility as well as relatively low melting point. 相似文献
77.
Leong Hou U Kyriakos Mouratidis Nikos Mamoulis 《The VLDB Journal The International Journal on Very Large Data Bases》2010,19(2):141-160
Consider a set of servers and a set of users, where each server has a coverage region (i.e., an area of service) and a capacity (i.e., a maximum number of users it can serve). Our task is to assign every user to one server subject to the coverage and
capacity constraints. To offer the highest quality of service, we wish to minimize the average distance between users and
their assigned server. This is an instance of a well-studied problem in operations research, termed optimal assignment. Even though there exist several solutions for the static case (where user locations are fixed), there is currently no method
for dynamic settings. In this paper, we consider the continuous assignment problem (CAP), where an optimal assignment must be constantly maintained between mobile users and a set of servers. The fact that
the users are mobile necessitates real-time reassignment so that the quality of service remains high (i.e., their distance
from their assigned servers is minimized). The large scale and the time-critical nature of targeted applications require fast
CAP solutions. We propose an algorithm that utilizes the geometric characteristics of the problem and significantly accelerates
the initial assignment computation and its subsequent maintenance. Our method applies to different cost functions (e.g., average
squared distance) and to any Minkowski distance metric (e.g., Euclidean, L
1 norm, etc.). 相似文献
78.
J. C. Leong L. C. Tsao C. J. Fang C. P. Chu 《Journal of Materials Science: Materials in Electronics》2011,22(9):1443-1449
The effects of nano-TiO2 particles on the interfacial microstructures and bonding strength of Sn3.5Ag0.5Cu composite solder joints in ball grid array
packages with immersion Sn surface finishes have been investigated. Metallography reveals that addition of nano-TiO2 particle retarded wicker-Cu6Sn5 IMC formed in the Sn3.5Ag0.5Cu composite solder joints. The thickness of the interfacial intermetallic compounds of the solder
joint was reduced with increased additions of nano-TiO2 particles (0.25–1.0 wt%), but further additions up to 1.25 wt% decreased the beneficial influence. This indicates that the
presence of a small amount of nano-TiO2 particles is effective in suppressing the growth of the intermetallic compounds layer. In addition, the shear strength of
the soldered joints was improved by larger nano-TiO2 particle additions, with the peak shear strength occurring at 1.0 wt% of nano-TiO2 particles into the Sn3.5Ag0.5Cu solder. The fracture mode also changed with increased amounts of nano-TiO2 particles. 相似文献
79.
80.
Satellite on-board digital signal processing (DSP) offers the potential for significantly improved performance in certain satellite communications system scenarios in terms of system capacity and link quality. On-board DSP functions include digital beamforming, frequency multiplexing and demultiplexing, interference suppression, signal level control and, in a regenerative system, modems. The authors review the status of DSP in communications satellite payloads, focusing on the system advantages, some basic algorithms, and application specific IC implementation issues. As a specific illustrative example an advanced land mobile system is described which features digital beamforming and associated digital signal processing to achieve significant gains in power efficiency (and hence capacity), frequency reuse and flexibility to response to changing traffic scenarios 相似文献