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961.
在功率受限的机会频谱接入(OSA)研究中,大多使用完全可观测马尔可夫决策过程(MDP)对环境建模,以提高物理层或介质访问控制(MAC)层指标,但由于感知设备的限制,无法保证用户对环境完全感知。为解决该问题,提出一种基于部分可观测马尔可夫决策过程(POMDP)与Sarsa(λ)的跨层OSA优化设计方案。结合MAC层和物理层,采用POMDP对功率受限且有感知误差的次用户频谱感知和接入过程进行建模,并将其转换为信念状态MDP(BMDP),使用Sarsa(λ)算法对其进行求解。仿真结果表明,在功率受限条件下,该Sarsa(λ)-BMDP方案的有效传输容量、吞吐量和频谱利用率分别比完全可观测Q-MDP方案低9%、7%和3%左右,其误比特率比基于点的值迭代PBVI-POMDP方案低20%左右,比Q-MDP方案高16%左右。 相似文献
962.
在并行测试的研究中对于任务的测试次序一直是个研究重点及难题。用时间Petri网建立关于并行测试系统的模型,并首次用元胞遗传算法(CAGA)对模型中的变迁序列进行搜索,快速得到最好的测试序列。通过仿真结果表明,该算法展示了很好的收敛效果,并且与已有的研究成果相比更具优势。 相似文献
963.
Unique clay orientation in the injection-molded bar of isotactic polypropylene/clay nanocomposite 总被引:1,自引:0,他引:1
In this article, the injection-molded bars of isotactic polypropylene/organoclay nanocomposite with different clay contents have been obtained via dynamic packing injection molding (DPIM). The oriented microstructure including layered nanoparticles and PP lamellae has been inspected through 2D-WAXS analyses along the sample thickness of the molded bars. Depending on the clay content and sample thickness, various oriented clay structures with nanoparticles uniplanar-axially oriented parallel to the surface of molded bar, or partially tumbled around the flow axis of the molded bar, or even a random orientation, could be observed. The observed orientation behavior of nanoparticles could be temporarily elucidated as the results of the sensitive response of layered nanoparticles to shear deformation and the structural recovery of clay network assisted by the electrostatic attraction existing between adjacent nanoplatelets. 相似文献
964.
965.
High surface area carbon-supported platinum-based catalysts, Pt/C, PtWO
x
/C, PtRu/C and PtRuWO
x
/C, were prepared via a chemical reduction route using single metal precursor salts. The catalyst particles were found to
be in the nanoscale range, and the addition of Ru clearly decreased the particle size. The Ru was found to be partially incorporated
into the face centered cubic lattice of Pt and to form a single Ru catalyst component. X-ray diffraction and X-ray photon
spectroscopy did not provide evidence for electronic interactions between WO
x
and Pt as well as WO
x
and Ru. However, the addition of tungsten to the PtRuWO
x
/C catalyst resulted in a high degree of catalyst particle agglomeration. Both Ru containing catalysts showed significantly
higher activities for the CH3OH oxidation reaction in terms of Pt + Ru mass as well as electroactive Pt + Ru surface area than the Pt/C and PtWO
x
/C catalysts. The addition of tungsten appeared to mainly result in some ‘physical’ modification of the catalytically active
Pt and Ru surface components such as differences in electroactive surface area rather than promotion of the CH3OH oxidation reaction via a true catalytic mechanism. 相似文献
966.
The farnesoid X receptor (FXR, NR1H4) has been recognized as an attractive therapeutic target because it is a nuclear hormone
receptor that controls the expression level of cholesterol-7α-hydroxylase, which in turn regulates bile acid production and
cholesterol excretion. To compare receptor activity between each domain and the full-length protein, human FXR cDNA was cloned
from a human liver cDNA library. Three human FXR cDNA, designated FXR20, FXR33, and FXR53 cDNA, were subcloned and ligated into a pET28a expression vector. Each protein was expressed in Escherichia coli (BL21) and purified by nickel-nitrilotriacetic acid column chromatography. Approximately 5 mg of FXR33 (1–182 amino acids deleted from FXR, 37 kDa) and 2 mg of FXR53 (the full-length protein of FXR, 59 kDa) was purified from 1 L of Luria-Bertani culture, achieving at least 90% purity. The
coactivator recruitment assay for FXR activation was carried out with the three variants of the FXR protein by using dissociation-enhanced
lanthanide fluoroimmunoassay-europium-N1-labeled anti-His antibody. From an optimized assay, a saturated hyperbolic fluorescence signal curve was produced when 250
nM of FXR33 and 100 nM of steroid receptor coactivator-1 peptide, a coactivator of FXR consisting of 26 amino acids, were used with a
concentration dependence on chenodeoxycholic acid (from 0 to 200 μM). The ligand-binding domain of FXR (FXR33) was the most suitable protein for studying the activation of FXR with a fluorescence-based assay, because it showed better
structural stability than either the full length of FXR (FXR53) or the DNA-binding domain of FXR (FXR20). 相似文献
967.
968.
Won Seok Lyoo Han Do Ghim Hee‐Sam Kim Joon Ho Kim Sam Soo Kim Won Sik Yoon Jinwon Lee Sang‐Seob Lee 《应用聚合物科学杂志》2002,86(14):3667-3672
N‐Vinylcarbazole (VCZ) was solution‐polymerized in tetrahydrofuran (THF) at ?20, 0, and 20°C using the photoinitiation method; the effects of the amount of solvent, polymerization temperature, and photoinitiator concentration were investigated. On the whole, the experimental results corresponded to predicted ones. Low polymerization temperature using photoinitiation proved to be successful in obtaining poly(N‐vinylcarbazole) (PVCZ) of a high molecular weight with a smaller temperature rise during polymerization; nevertheless of free radical polymerization by 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN). The photo‐solution polymerization rate of VCZ in THF was proportional to the 0.47 power of ADMVN concentration. The molecular weight was higher and the molecular weight distribution was narrower with PVCZ polymerized at lower temperatures. For PVCZ prepared in THF at ?20°C using a photoinitiator concentration of 0.00005 mol/mol of VCZ, a weight‐average molecular weight of 510,000 was obtained, with a polydispersity index of 1.73, and a degree of lightness converged to about 99%. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3667–3672, 2002 相似文献
969.
A novel bio‐based composite material, suitable for electronic as well as automotive and aeronautical applications, was developed from soybean oils and keratin feather fibers (KF). This environmentally friendly, low‐cost composite can be a substitute for petroleum‐based composite materials. Keratin fibers are a hollow, light, and tough material and are compatible with several soybean (S) resins, such as acrylated epoxidized soybean oil (AESO). The new KFS lightweight composites have a density ρ ≈ 1 g/cm3, when the KF volume fraction is 30%. The hollow keratin fibers were not filled by resin infusion and the composite retained a significant volume of air in the hollow structure of the fibers. Due to the retained air, the dielectric constant, k, of the composite material was in the range of 1.7–2.7, depending on the fiber volume fraction, and these values are significantly lower than the conventional silicon dioxide or epoxy, or polymer dielectric insulators. The coefficient of thermal expansion (CTE) of the 30 wt % composite was 67.4 ppm/°C; this value is low enough for electronic application and similar to the value of silicon materials or polyimides used in printed circuit boards. The water absorption of the AESO polymer was 0.5 wt % at equilibrium and the diffusion coefficient in the KFS composites was dependent on the keratin fiber content. The incorporation of keratin fibers in the soy oil polymer enhanced the mechanical properties such as storage modulus, fracture toughness, and flexural properties, ca. 100% increase at 30 vol %. The fracture energy of a single keratin fiber in the composite was determined to be about 3 kJ/m2 with a fracture stress of about 100–200 MPa. Considerable improvements in the KFS composite properties should be possible by optimization of the resin structure and fiber selection. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1524–1538, 2005 相似文献
970.