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991.
S. S. Cho B. S. Chun C. H. Won B. S. Lee H. K. Kim B. J. Song M. Ryu 《Advanced Performance Materials》1996,3(1):29-42
The Al-12Si-5Fe-3Cu-1Mg(wt%) alloy was rapidly solidified by centrifugal atomization. The microstructural characteristics of rapidly solidified powder and the microstructure changes with heat treatment were investigated in terms and related to powder size. The microstructures of the powder consisted of dendritic -Al, eutectic phase, Cu-rich phase, and needle-like intermetallic compounds. These phases were much finer than that of ingot cast structure and the size decreased with increasing cooling rate. The X-ray diffraction of the atomized powders revealed the presence of non-equilibrium 3-(AlFeSi) intermetallic phase. This phase appeared to transform to an equilibrium -(AlFeSi) phase by heating at temperatures above 470°C. The extruded rod which was hot extruded at 360°C with an extrusion ratio of 40:1 also revealed the presence of the -(AIFeSi) intermetallic phase. Using DSC, the exothermic peak due to precipitation from the supersaturated -Al matrix was observed in the range of 200–250°C during continuous heating of atomized powder, and the size of the peaks increased with decreasing powder size. 相似文献
992.
Characteristics of sol-gel derived PZT thin films with lead oxide cover layers and lead titanate interlayers 总被引:1,自引:0,他引:1
The sol-gel derived PbZr0.53Ti0.47O3 (PZT) films were fabricated on the bare Pt/Ti/SiO2/Si substrates or the same substrates coated by the PbTiO3 (PT) interlayers. The post-deposition annealing temperature and time were optimized when the PbO cover layers and PbO vapour-containing atmosphere were compared with each other and adopted as the method to diminish the lead-loss problem during the high-temperature post-deposition annealing. The X-ray diffraction patterns, microstructures, and electrical properties such as relative permittivity, r, remanent polarization, P
r, and coercive electrical field, E
c, were investigated in relation to the annealing conditions. The PZT films deposited on the bare Pt/Ti/SiO2/Si substrates under the PbO vapour-containing atmosphere showed better electrical properties. This indicates that the PbO vapour-containing atmosphere may be the better method of lead-loss-prevention to process the lead-containing films rather than the PbO cover layer method. The electrical characteristics of the PZT films, r=1150, a dissipation factor of 0.039, P
r=26 C cm–2, and E
c=40.5 kV cm–1 were measured at 1 kHz. When PZT films were deposited on substrates coated by the PT layers, PZT-PT films with single perovskite phase were derived by post-deposition annealing at 500 °C for 1 h. However, the relative electrical properties are very poor, i.e. E
r=160, P
r=2.0 C cm–2 and E
c=75 kVcm–1. The optimum combination for preparing PZT-PT films is a 40 nm PbTiO3 interlayer and annealing conditions of 6 h at 550 °C in a PbO vapour-containing atmosphere; the derived films exhibit electrical properties of E
r=885, P
r=21.5 C cm–2 and E
c=64 kV cm–1. The combination of inserting a PT interlayer and annealing in a PbO vapour-containing atmosphere can prevent the formation of electrical short paths. In this case, nearly pin-hole-free PZT films can be grown on the PT (interlayer) /Pt/Ti/SiO2/Si substrates. It is believed that it is possible to prepare the PZT films with nano-scale uniformity, reproducible quality, which may be worth considering for commercial applications. 相似文献
993.
Microstructural evolution of potassium titanate whiskers during the synthesis by the calcination and slow-cooling method 总被引:2,自引:0,他引:2
K2Ti6O13 whisker was synthesized by the calcination and slow-cooling method, and the microstructural evolution of whiskers, and the relations between the phase and the layer structure, were investigated. The amount of K2O in the starting powder mixture played a key role in forming a layer structure, which can be obtained by addition of excess K2O. During calcination, rod-like K2Ti6O13 particles with a layer structure were formed by reactions between K2O and TiO2. During slow-cooling, the K2O-rich liquid phase reacted with K2Ti6O13 layers near the boundary and k2Ti4O9 whiskers were produced by the splitting of layers within rod-like k2T6O13 particles. k2Ti4O9 whiskers were reformed into k2T6O13 whiskers by treatment in boiling water and reheating. The synthesized k2T6O13 whiskers had a clean surface and a length exceeding 100 m. 相似文献
994.
Iterative optimization of high-affinity proteases inhibitors using phage display. 1. Plasmin 总被引:2,自引:0,他引:2
We generated a series of libraries having variants of the first Kunitz domain of human lipoprotein-associated coagulation inhibitor (LACI-D1, also known as tissue-factor pathway inhibitor-I) displayed on bacteriophage M13 as pIII-fusions. We varied LACI-DI iteratively in two regions: the P1 region (positions 10-21) and the "second loop", (positions 31-39), which together form one end of the domain. Display-phage library Lib#1 allows 31 200 amino-acid sequences in P1 region (residues 13, 16-19). Preliminary, we screened Lib#1 against human plasmin (PLA, EC 3.4.21.7) immobolized on agarose to enrich for phage displaying variants with PLA affinity. We introduced a 1600-fold increase in second-loop diversity (residues 31, 32, 34, 39) into the population of selectants from Lib#1, yielding Lib#2. Lib#2 (allowing approximately 50 million amino-acid sequences) was screened against PLA-agarose to isolate highest affinity binders. Protein EPI-P211, derived from the best isolate of Lib#2, inhibits PLA with Ki = 2 nM (at least 500-fold better than LACI-D1) and with high specificity. We used amino-acid sequences of PLA-binding selectants to design a PLA-biased library (Lib#3) which we screened against PLA. The protein EPI-P302 (derived from the best binder obtained from Lib#3) has Ki for PLA inhibition of 87 pM, which is 25-fold better than the first-round best binder and > or = 12 500-fold better than LACI-D1. EPI-P302 also shows very high specificity for PLA vs other human proteases and is resistant to inactivation by oxidants and extremes of temperature or pH. Thus, one can use selectants from one library to design target-tailored combinatorial libraries and obtain quite stable, highly specific, very high-affinity binding molecules while maintaining an essentially human framework. 相似文献
995.
Sunghak Lee Dongwoo Suh Dongil Kwon 《Metallurgical and Materials Transactions A》1996,27(12):3893-3901
A microstructural analysis of local microfracture of cast A356 Al-SiC
p
composites fabricated by permanent mold re-casting and squeeze-casting methods was made. Notch fracture toughness tests were
conducted on these composites to identify critical fracture parameters using a stress-modified critical-strain criterion.
The composite microstructure shows continuous networks of densely populated SiC and eutectic Si particles along the intercellular
regions. Squeeze casting produces a more homogeneous structure and larger spacing of brittle particles and increases the tensile
ductility and fracture toughness, while strength levels are almost identical to the re-casting case. The calculated values
of the microstructurally characteristic distancel* for the re-cast and squeeze-cast composites are about 40 μm, which is comparable to the average sizes of the intercellular
network. However, the reference critical strain
for squeeze casting is larger than that for re-casting, showing a trend to higher ductility and fracture toughness. 相似文献
996.
Heterozygous mutations in the gene for the Kit transmembrane receptor have been identified recently in human piebaldism and mouse "dominant spotting." Interestingly, all of the 14 known missense mutations that cause depigmentation in these species map to the tyrosine kinase domain of the receptor, whereas none have involved the extracellular ligand-binding domain. In an attempt to detect these uncommon mutations, we screened the nine exons encoding the extracellular portion of Kit for single-strand conformation polymorphisms (SSCP) in eight piebald subjects previously reported to be negative for kinase mutations. Four of these eight kindreds proved to carry novel mutations. The first mutation, found in two apparently unrelated probands with mild piebaldism and English ancestry, substitutes an arginine for a highly conserved cysteine at codon 136. This substitution disrupts a putative disulfide bond required for formation of the second Ig-like (D2) loop of the Kit ligand-binding domain. The second mutation, detected in a piebald kindred characterized by unusually limited depigmentation, substitutes a threonine for an alanine at codon 178, a site just proximal to conserved cysteines at codons 183 and 186. The third mutation, occurring in a kindred with more extensive depigmentation, is a novel four-base insertion in exon 2 that results in a proximal frameshift and premature termination. The data strongly suggest that piebaldism can result from missense mutations in the Kit ligand-binding domain, although the resulting phenotype may be milder than that observed for null or kinase mutations. The apparent clustering of these uncommon mutations at or near the conserved cysteines for the D2 Ig-like loop further suggests a critical role for this region in Kit receptor function. 相似文献
997.
This study presents a method that uses a standing surface acoustic wave (SSAW) to continuously separate particles in a size-gradient
manner in a microchannel flow. The proposed method was applied to a colloidal suspension containing poly dispersed particles
with three different sizes (1, 5, and 10 μm) but the same density and compressibility. Particle suspension was focused hydrodynamically
at an entrance region, and particles were forced actively toward the side wall where SSAW-pressure nodes were generated by
two interdigital transducers (IDTs) across the channel. The particles placed in the middle stream, in which the shear rate
was minimized, were separated successfully in a size-gradient manner by acoustic force. In addition, this study further developed
an analytical model to predict the displacement of particles in microchannel flow by considering viscous, acoustic, and diffusive
forces. The predicted values of particle displacement showed excellent agreement with the experimental results, and diffusion
was found to be important and not negligible. The advantage of this method is to minimize the shear rate on particles, which
would be useful for potential applications of shear-dependent cells such as platelets. 相似文献
998.
We demonstrate a microfluidic continuous-flow protein separation process in which silica-coated superparamagnetic nanoparticles
interact preferentially with hemoglobin in a mixture with bovine serum albumin, and the resulting hemoglobin-nanoparticle
aggregates are recovered online using magnetophoresis. We present detailed modeling and analysis of this process yielding
quantitative estimates of the recovery of both proteins, validated by experiments. While several previous studies utilize
an average particle size in modeling magnetophoretic particle trajectories or process design, in this study we emphasize the
importance of accounting for particle size distributions in calculating particle recovery, and therefore in estimating separation
efficiency. We combine experimentally measured size distributions of protein-nanoparticle aggregates with simulations of particle
trajectories and provide a simple analytical method to calculate the efficiency of separation at various flow speeds, which
fully accounts for heterogeneity in particle sizes. Our method can potentially be used for affinity based biomolecular separations
at both analytical and preparative scales by exploiting well-established techniques to functionalize nanoparticle surfaces
with selective ligands. Further, the modeling methodology presented here may be applied to provide better estimates of particle
recovery in a broad range of magnetophoretic separation processes involving heterogeneity in particle sizes. 相似文献
999.
Woo Young Kwon Il Hong Suh Sanghoon Lee 《International Journal of Control, Automation and Systems》2011,9(2):328-338
Reinforcement learning (RL) has been widely used as a mechanism for autonomous robots to learn state-action pairs by interacting
with their environment. However, most RL methods usually suffer from slow convergence when deriving an optimum policy in practical
applications. To solve this problem, a stochastic shortest path-based Q-learning (SSPQL) is proposed, combining a stochastic
shortest path-finding method with Q-learning, a well-known model-free RL method. The rationale is, if a robot has an internal
state-transition model which is incrementally learnt, then the robot can infer the local optimum policy by using a stochastic
shortest path-finding method. By increasing state-action pair values comprising of these local optimum policies, a robot can
then reach a goal quickly and as a result, this process can enhance convergence speed. To demonstrate the validity of this
proposed learning approach, several experimental results are presented in this paper. 相似文献
1000.
Sul Gee Park Ho Cheol Jeong Jeong Won Kim Dong-Hwan Hwang Sang Jeong Lee 《International Journal of Control, Automation and Systems》2011,9(2):276-284
This paper proposes a magnetic compass fault detection method for GPS/INS/Magnetic compass integrated navigation systems.
The fault is assumed to be caused by the hard iron and soft iron effect and modeled as an abrupt change in the magnetic compass
output. In order to detect the fault, a test statistic related with only azimuth error measurement is determined. When a fault
is detected, the GPS/INS/Magnetic compass integrated navigation system is changed into a GPS/INS integrated navigation system
mode. In order to show the validity of the proposed method, computer simulation and van testing are carried out. The simulation
and van test results show that the proposed navigation system gives more accurate outputs than the GPS/INS/Magnetic compass
without the proposed method. 相似文献