全文获取类型
收费全文 | 42992篇 |
免费 | 3514篇 |
国内免费 | 2371篇 |
专业分类
电工技术 | 2595篇 |
技术理论 | 1篇 |
综合类 | 2377篇 |
化学工业 | 5926篇 |
金属工艺 | 2941篇 |
机械仪表 | 2430篇 |
建筑科学 | 3038篇 |
矿业工程 | 868篇 |
能源动力 | 1359篇 |
轻工业 | 2744篇 |
水利工程 | 776篇 |
石油天然气 | 1572篇 |
武器工业 | 339篇 |
无线电 | 5589篇 |
一般工业技术 | 7205篇 |
冶金工业 | 2998篇 |
原子能技术 | 589篇 |
自动化技术 | 5530篇 |
出版年
2024年 | 188篇 |
2023年 | 614篇 |
2022年 | 1163篇 |
2021年 | 1688篇 |
2020年 | 1215篇 |
2019年 | 1072篇 |
2018年 | 1283篇 |
2017年 | 1281篇 |
2016年 | 1186篇 |
2015年 | 1538篇 |
2014年 | 1972篇 |
2013年 | 2719篇 |
2012年 | 2649篇 |
2011年 | 3032篇 |
2010年 | 2730篇 |
2009年 | 2725篇 |
2008年 | 2562篇 |
2007年 | 2480篇 |
2006年 | 2259篇 |
2005年 | 1818篇 |
2004年 | 1521篇 |
2003年 | 1418篇 |
2002年 | 1511篇 |
2001年 | 1394篇 |
2000年 | 1073篇 |
1999年 | 899篇 |
1998年 | 1039篇 |
1997年 | 750篇 |
1996年 | 634篇 |
1995年 | 470篇 |
1994年 | 358篇 |
1993年 | 300篇 |
1992年 | 223篇 |
1991年 | 180篇 |
1990年 | 151篇 |
1989年 | 136篇 |
1988年 | 108篇 |
1987年 | 67篇 |
1986年 | 62篇 |
1985年 | 49篇 |
1984年 | 53篇 |
1983年 | 45篇 |
1982年 | 32篇 |
1981年 | 25篇 |
1980年 | 26篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 17篇 |
1974年 | 13篇 |
1970年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
气凝胶──一种结构可控的新型功能材料 总被引:2,自引:0,他引:2
气凝胶是一种结构可控的新型轻质纳米多孔性非晶固态材料,具有许多特殊性质,因而蕴藏着广阔的应用前景。本文综述了气凝胶材料的制备方法、结构控制原理、性质和各种可能的应用。 相似文献
132.
从供应商受益角度研究国际供应链合作关系 总被引:11,自引:1,他引:10
首先指出从供应商受益角度对国际供应链合作关系进行研究的重要意义,接着对国际供应链合作关系的起源及其概念界定进行了综合分析;其次对国际供应链战略伙伴关系下的供应商受益进行了相关研究结论的综合,并对我国供应商参与国际供应链合作的实际受益进行分析,然后将两者进行了比较,最后综合全文探讨得出本文研究的结论。 相似文献
133.
Tetrahedrally close-packed structures with juxtaposed pentagonal antiprisms, such as the μ, C14 Laves and the newly found C phases, were studied by means of HREM and SAD. It was found that each bright spot in the structural image corresponds to an antiprism. Differently oriented domains of these phases intergrow frequently with a fairly good match at the interphase boundary. All diffraction patterns of these phases show a fivefold distribution of spot-pairs, and it is shown that this fivefold symmetry comes from the pentagons and spot-pairs from two pentagonal prisms superposed in antisymmetrical positions. 相似文献
134.
135.
AC hot-carrier effects in n-MOSFETs with thin (~85 Å) N2O-nitrided gate oxides have been studied and compared with control devices with gate oxides grown in O2. Results show that furnace N2O-nitrided oxide devices exhibit significantly reduced AC-stress-induced degradation. In addition, they show weaker dependences of device degradation on applied gate pulse frequency and pulse width. Results suggest that the improved AC-hot-carrier immunity of the N2O-nitrided oxide device may be due to the significantly suppressed interface state generation and neutral electron trap generation during stressing 相似文献
136.
K Shannon P Stapleton X Xiang A Johnson H Beattie F El Bakri B Cookson G French 《Canadian Metallurgical Quarterly》1998,36(10):3105-3110
Representative isolates from 10 distinct extended-spectrum beta-lactamase-producing strains of Klebsiella pneumoniae that caused hospital outbreaks in the United Kingdom from 1991 to 1994 were examined for relationships between their enzymes and plasmids. The beta-lactamases were identified by a combination of isoelectric focusing and gene sequencing. SHV-2 beta-lactamase was produced by isolates from four outbreaks, SHV-5 was involved in three, and SHV-4, TEM-15, and TEM-26 were involved in one outbreak each. All of the extended-spectrum beta-lactamases were encoded by self-transmissible plasmids, with sizes ranging from about 70 to 160 kb. No similarities between the restriction digest patterns of the extended-spectrum beta-lactamase-encoding plasmids were detected, except to some extent between those that produced TEM-15 and TEM-26. Thus, outbreaks of hospital infection with these organisms in the United Kingdom from 1991 to 1994 involved distinct organisms and resistance plasmids and appeared to be unrelated. 相似文献
137.
A-band and Z-line/I-band lattice spacings were measured by small-angle X-ray diffraction from relaxed and isometrically-contracting whole frog sartorius muscles with lattice spacings reduced or swollen by changing the osmolarity of the bathing solution. A-band spacing increased by approximately 3% upon isometric contraction at reduced lattice spacings (245-356 mOsm) and decreased by approximately 1% at swollen spacings (172 mOsm), similarly to the behaviour of skinned muscles upon changing from the relaxed state to rigor. The Z/I lattice underwent a significant lattice expansion (3-8%) upon isometric contraction at all osmolarities, in qualitative agreement (but quantitative disagreement) with results from electron microscopy on mammalian skeletal muscle. Lattice areas calculated for the Z/I and A-band lattices indicate a barrel-shaped sarcomere in the resting state, which may provide a partial explanation for how longitudinal forces produced in the A-band can produce a radial expansive force in the Z-line during contraction. The radial component of cross-bridge stiffness was calculated from the A-band data for contracting muscle, using a lattice stability model incorporating structural, osmotic and electrostatic forces. The calculations gave a radial cross-bridge stiffness during contraction of about 9 x 10(5) N m-2, and outward radial force per thick filament in normal Ringer's solution of 6 x 10(-9) N, corresponding to a radial force per cross-bridge of 10(-11) N. 相似文献
138.
Summary Motions of hyperelastic materials involving surfaces of strain or stress discontinuities are generally dissipative in the sense that, in any portion of the body that is traversed by a moving singular surface, the rate of work of the external forces differs from the rate of storage of the total energy (the strain energy and the kinetic energy) by the rate of work done in moving the singular surface. Hence, the corresponding continuum theory is capable of modeling dissipative behavior associated with phase transformations which has potential applications in the design ofadaptive structures. The present work indicates that this dissipative behavior is characterized by a material function, called the driving-traction-response function, which is uniquely determined by the strain energy potential of the material. The driving-traction-response function vanishes identically if and only if the Piola-Kirchhoff stress-response function depends upon the deformation gradient linearly. 相似文献
139.
Z. S. Peng Z. Q. Hua Y. N. Li J. Di J. Ma Y. M. Chu W. N. Zhen Y. L. Yang H. J. Wang Z. X. Zhao 《Journal of Superconductivity》1998,11(6):749-754
Bi-based superconductors are of great interest in high-temperature superconductors. We describe what is believed to be the first synthesis of these materials using the Pechini process, a low-temperature synthetic method that often yields inorganic oxide of excellent phase purity and well-controlled stoichiometry. Using this process, it has been possible to synthesize phase-pure Bi-2223 phase by calcining the appropriate polymeric precursors in air at 800°C for several hours. The superconductivity studies show that the Pechini-synthesized materials appear to offer high-quality performance. 相似文献
140.
GH Fan J Zhao YL Wu LG Lou Z Zhang Q Jing L Ma G Pei 《Canadian Metallurgical Quarterly》1998,53(4):684-690
The effects of N-methyl-D-aspartate (NMDA) on opioid receptor-mediated G protein activation were explored in neuroblastoma X glioma hybrid (NG108-15) cells. Treatment of the cells with NMDA resulted in a remarkable attenuation of [35S]guanosine-5'-O-(3-thio)triphosphate binding stimulated by [D-Pen2,D-Pen5]-enkephalin (DPDPE), a delta-opioid receptor agonist. The effects of NMDA were dose and time dependent with an IC50 value of 5 nM and could be blocked by NMDA receptor antagonists. After NMDA treatment, the DPDPE dose-response curve shifted to the right (EC50 value increased approximately 7-fold, from 6 to 40 nM), and the maximal response induced by DPDPE was reduced by approximately 60%. The effects of NMDA were reversible, and the DPDPE response could recover within 60 min. The functional responses of delta-, mu-, and kappa-opioid receptors in primarily cultured neurons also were attenuated significantly by NMDA treatment. The inhibitory effects of NMDA on opioid receptor-mediated G protein activation could be blocked by coadministration of the protein kinase C (PKC) inhibitors or by elimination of the extracellular Ca2+. Correspondingly, NMDA treatment of NG108 cells significantly elevated cellular PKC activity and stimulated Gialpha2 phosphorylation. Transient transfection into NG108-15 cells of the wild-type Gialpha2 and a mutated Gialpha2 (Ser144Ala) resulted in a 2-fold increase in DPDPE-stimulated G protein activation. The DPDPE responses were greatly inhibited by NMDA treatment in the wild-type Gialpha2-transfected cells but much less affected in the mutant Gialpha2-transfected cells. In summary, NMDA attenuates opioid receptor/G protein coupling, and this process requires activation of PKC. 相似文献