全文获取类型
收费全文 | 2455篇 |
免费 | 92篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 45篇 |
综合类 | 5篇 |
化学工业 | 544篇 |
金属工艺 | 43篇 |
机械仪表 | 78篇 |
建筑科学 | 56篇 |
矿业工程 | 1篇 |
能源动力 | 88篇 |
轻工业 | 118篇 |
水利工程 | 8篇 |
石油天然气 | 3篇 |
无线电 | 466篇 |
一般工业技术 | 448篇 |
冶金工业 | 263篇 |
原子能技术 | 8篇 |
自动化技术 | 378篇 |
出版年
2023年 | 13篇 |
2022年 | 41篇 |
2021年 | 52篇 |
2020年 | 29篇 |
2019年 | 33篇 |
2018年 | 53篇 |
2017年 | 44篇 |
2016年 | 52篇 |
2015年 | 41篇 |
2014年 | 90篇 |
2013年 | 188篇 |
2012年 | 141篇 |
2011年 | 155篇 |
2010年 | 118篇 |
2009年 | 150篇 |
2008年 | 153篇 |
2007年 | 137篇 |
2006年 | 98篇 |
2005年 | 82篇 |
2004年 | 75篇 |
2003年 | 69篇 |
2002年 | 65篇 |
2001年 | 49篇 |
2000年 | 43篇 |
1999年 | 47篇 |
1998年 | 107篇 |
1997年 | 85篇 |
1996年 | 43篇 |
1995年 | 38篇 |
1994年 | 34篇 |
1993年 | 28篇 |
1992年 | 33篇 |
1991年 | 29篇 |
1990年 | 12篇 |
1989年 | 5篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1973年 | 6篇 |
1967年 | 3篇 |
排序方式: 共有2552条查询结果,搜索用时 15 毫秒
81.
Ssu-Han Chen Shih-Jiuan Chiu Teh-Min Hu 《International journal of molecular sciences》2012,13(11):13985-14001
Nitric oxide (NO) is an important molecule that exerts multiple functions in biological systems. Because of the short-lived nature of NO, S-nitrosothiols (RSNOs) are believed to act as stable NO carriers. Recently, sulfhydryl (SH) containing macromolecules have been shown to be promising NO carriers. In the present study, we aimed to synthesize and characterize a potential NO carrier based on bovine Cu,Zn-superoxide dismutase (bSOD). To prepare S-nitrosated bSOD, the protein was incubated with S-nitrosoglutathione (GSNO) under varied experimental conditions. The results show that significant S-nitrosation of bSOD occurred only at high temperature (50 °C) for prolonged incubation time (>2 h). S-nitrosation efficiency increased with reaction time and reached a plateau at ~4 h. The maximum amount of NO loaded was determined to be about 0.6 mol SNO/mol protein (~30% loading efficiency). The enzymatic activity of bSOD, however, decreased with reaction time. Our data further indicate that NO functionality can only be measured in the presence of extremely high concentrations of Hg2+ or when the protein was denatured by guanidine. Moreover, mildly acidic pH was shown to favor S-nitrosation of bSOD. A model based on unfolding and refolding of bSOD during preparation was proposed to possibly explain our observation. 相似文献
82.
Shih-Chieh Chang Shih-Jiuan Chiu Chih-Yuan Hsu Yung Chang Ying-Ling Liu 《Polymer》2012,53(20):4399-4406
Rhodamine B (RhB)-anchored amphiphilic poly(poly(ethylene glycol)methacrylate)-b-poly(glycidyl methacrylate) block copolymer (PPEGMA-b-PGMA/RhB) has been prepared by a sequential atom transfer radical polymerization and post-functionalization of RhB. The chemical structure of PPEGMA-b-PGMA/RhB is characterized with gel-permeation chromatography, Fourier-transform infrared spectroscopy, and 1H nuclear magnetic resonance spectroscopy. PPEGMA-b-PGMA/RhB has shown self-assembly behaviors in tetrahydrofuran and aqueous solutions. The RhB aggregation induced with the inter-molecular interaction of RhB results in the various core–shell structures of the assembled nanoparticles. The photoluminescent properties of the PPEGMA-b-PGMA/RhB nanoparticles are structure-dependent and exhibit yellow-light, blue-light, and white-light emissions. The fluorescent organic nanoparticles of PPEGMA-b-PGMA/RhB in aqueous solution show low cytotoxicity and have been used as a bio-dye for cell labelling. Internalization of PPEGMA-b-PGMA/RhB nanoparticles into HELA cells to exhibit fluorescent images has been demonstrated. 相似文献
83.
Feng-Yi Chou Chao-Ming Shih Meng-Chao Tsai Wen-Yen Chiu Shingjiang Jessie Lue 《Polymer》2012,53(14):2839-2846
This paper reports a novel method to synthesize magnetic, stimuli-sensitive latex nanoparticles made with magnetite/poly(N-isopropylacrylamide-co-acrylic acid) (Fe3O4/P(NIPAAm-co-AAc)). To form a stabilized suspended core, iron oxide (Fe3O4) was functionalized with AAc such that further polymerization with NIPAAm and AAc monomers could occur. The P(NIPAAm-co-AAc) shell layer exhibited thermosensitive properties. The inclusion of Fe3O4 into the latex nanoparticles was confirmed using transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, thermogravimetric analyzer (TGA), and superconducting quantum interference device magnetometer. The NIP–(AAc2.6–Fe) latex nanoparticles contained 2.25% Fe3O4 (by weight), as determined by TGA analysis. The particle diameters measured approximately 160–240 nm with a lower critical solution temperature of 35 °C. These novel magnetic stimuli-responsive latex nanoparticles have potential applications in numerous fields, such as catalyst supports, protein immobilization, cancer therapy, target drug delivery systems, and other biomedical applications. 相似文献
84.
Jia-Wun Li Yung-Hsin Cheng Hsun-Tsing Lee Chyung-Chyung Wang Chih-Wei Chiu Maw-Cherng Suen 《应用聚合物科学杂志》2020,137(36):49062
This study successfully incorporated a short-segment fluorine-containing chain extender (2,2,3,3-tetrafluoro-1,4-butanediol [TF]) into castor oil-based polyurethane (COPU) to synthesize TF/COPUs. The interactions between TF and COPU components were identified by Fourier transform infrared and X-ray photoelectron spectroscopies, the results revealed that the increase in the TF content increased the van der Waals forces in C F…CO and the hydrogen bonding force in C F…H N. Atomic force microscopy indicated that the addition of more TF contributed to a higher level of microphase separation in the TF/COPUs. Thermogravimetric analysis showed that the TF component can enhance the thermal resistance of TF/COPUs. Differential scanning calorimetry and dynamic mechanical analysis indicated that the glass transition temperature (Tg) of TF/COPUs increased with the TF content. The stress–strain testing showed that the tensile strength and elongation at break values decreased with the TF content. This tensile behavior may be due to the molecular weight of a TF/COPU decreased with the TF content as evidenced by the gel permeation chromatography results. The hydrolytic degradation tests of dipping TF/COPUs in 3 wt% NaOH solution indicated that TF could lower the surface free energy and enhance the degradation stability of TF/COPUs. 相似文献
85.
Jia‐Wei Li Yu‐Jing Chiu Chia‐Jui Chang Hung‐Chieh He Yi‐Hsuan Tu Kuan‐Ting Lin Yu‐Liang Lin Tzu‐Hsun Kao Hsun‐Hao Hsu Hsiao‐Fan Tseng Tien‐Chang Lu Jiun‐Tai Chen 《大分子材料与工程》2020,305(1)
Polyimides (PIs) possess excellent mechanical properties, thermal stability, and chemical resistance and can be converted to carbon materials by thermal carbonization. The preparation of carbon nanomaterials by carbonizing PI‐based nanomaterials, however, has been less studied. In this work, the fabrication of PI nanofibers is investigated using electrospinning and their transformation to carbon nanofibers. Poly(amic acid) carboxylate salts (PAASs) solutions are first electrospun to form PAAS nanofibers. After the imidization and carbonization processes, PI and carbon nanofibers can then be obtained, respectively. The Raman spectra reveal that the carbon nanofibers are partially graphitized by the carbonization process. The diameters of the PI nanofibers are observed to be smaller than those of the PAAS nanofibers because of the formation of the more densely packed structures after the imidization processes; the diameters of the carbon nanofibers remain similar to those of the PI nanofibers after the carbonization process. The thermal dissipation behaviors of the PI and carbon nanofibers are also examined. The infrared images indicate that the transfer rates of thermal energy for the carbon nanofibers are higher than those for the PI nanofibers, due to the better thermal conductivity of carbon caused by the covalent sp2 bonding between carbon atoms. 相似文献
86.
Chiu HP Grünewald J Hao X Brock A Okach L Uno T Geierstanger BH 《Chembiochem : a European journal of chemical biology》2012,13(3):364-366
Sticky residue: Pyrroline-carboxy-lysine (Pcl) can be readily incorporated into proteins expressed in E. coli and mammalian cells by using the pyrrolysyl tRNA/tRNA synthetase pair. Pcl can be used as a single amino acid purification tag and can be site-specifically modified with functional probes during the elution process. 相似文献
87.
Lin CL Chen RF Chen JY Chu YC Wang HM Chou HL Chang WC Fong Y Chang WT Wu CY Chiu CC 《International journal of molecular sciences》2012,13(5):6236-6245
Caffeic acid (CA), a natural phenolic compound, is abundant in medicinal plants. CA possesses multiple biological effects such as anti-bacterial and anti-cancer growth. CA was also reported to induce fore stomach and kidney tumors in a mouse model. Here we used two human lung cancer cell lines, A549 and H1299, to clarify the role of CA in cancer cell proliferation. The growth assay showed that CA moderately promoted the proliferation of the lung cancer cells. Furthermore, pre-treatment of CA rescues the proliferation inhibition induced by a sub-IC(50) dose of paclitaxel (PTX), an anticancer drug. Western blot showed that CA up-regulated the pro-survival proteins survivin and Bcl-2, the down-stream targets of NF-κB. This is consistent with the observation that CA induced nuclear translocation of NF-κB p65. Our study suggested that the pro-survival effect of CA on PTX-treated lung cancer cells is mediated through a NF-κB signaling pathway. This may provide mechanistic insights into the chemoresistance of cancer calls. 相似文献
88.
Novel hydrogen-bonded acidic fluorinated poly(amide-imide-silica) hybrid materials, FPAI-SiO2 (6E and 6F) series, were synthesized by a sol-gel process. The structures and spin relaxation of the hybrids were characterized by infrared (IR), and 29Si and 13C nuclear magnetic resonance (NMR) spectroscopy. The abundant Q4 structures implied that in free catalyst the degree of condensation of tetramethoxysilane was enhanced by hydrogen-bonded acidic fluorinated poly(amide-imide). The dynamics on the local mobility of the hybrids was investigated by the time constant for energy exchange between 1H and 29Si spin system (TSiH) and spin-diffusion path length (L) measurements. It was found that the faster TSiH of 6E and 6F hybrids compared with the previous study of similar 6C and 6D hybrids implied that 6E and 6F hybrids had more aggregated structures even though the organic terminal segment changed from rigid imide to more flexible amide. The interactions of the charge transfer between donor and acceptor molecules or π-π aromatic stacking may be the dominant factors to affect the structures of 6E and 6F hybrids. Moreover, M1 and D2 segments of 6F hybrids had the same level mobility and the mobility of the 6F hybrids was little improved as the soft and flexible 1,3-bis(3-aminopropyl)-tetramethyl-disiloxane segment was incorporated in the dense structures of 6F hybrids. All of the L values of 6E and 6F hybrids were on the scale of 3.5-4.0 nm. The result also suggested that 6E and 6F hybrids had similar denser structures as 6D hybrids. 相似文献
89.
Polymeric composites with conductivities ranging from 10–4 to 1 S cm–1 were prepared by electrochemically polymerizing pyrrole in a matrix of polyurethane. The polypyrrole/polyurethane alloy films obtained were characterized by element analysis, electron microscopy and electrical conductivity measurements. The morphology of the films depended on the solvent, the electrolyte and the current density. The mechanism of the electrochemical polymerization showed that PPy grew in a treelike structure, with molecular chains extending from the electrode surface into the solution. The transition temperature of the PPy/PU increased with the PPy content. 相似文献
90.
The physical properties of 5 wt% poly(NIPAM) (Mv=3.22×105) semi-dilute solutions in H2O, D2O, and THF (tetrahydrofuran) solvents were studied using dynamic light scattering (DLS) and dynamic shear viscosity (DSV) measurements. The DLS data showed that there were poly(NIPAM) slow mode inter-polymer chains associations in H2O and D2O solvents. However, no DLS slow mode was observed in poly(NIPAM)/THF solutions. The DSV data showed that there are shear thickening behavior in these three poly(NIPAM) solutions, resulting in a maximum shear viscosity ηpeak in the viscosity η′(ω) versus shear frequency ω curve. The slow mode hydrodynamic radius 〈Rhs〉 of DLS measurements and the zero shear rate viscosity η0 and maximum viscosity ηpeak data of DSV measurements from poly(NIPAM)/H2O and poly(NIPAM)/D2O solutions show two critical transition temperatures with Tcr1=30-32 °C and Tcr2=32-34 °C. Poly(NIPASM)/D2O has higher Tcr1 and Tcr2 than poly(NIPASM)/H2O. However, no transition temperatures of poly(NIPAM)/THF solution were observed. The different temperature dependencies of these three solutions were attributed to the ‘solubility’ and ‘hydrogen bonding’ effects between poly(NIPAM) with H2O, D2O, and THF solvents. Without considering the polymer-solvent hydrogen bonding, the solubility of poly(NIPAM) in solvents decreases in the following sequence: THF>H2O>D2O and the degree of polymer-solvent hydrogen bonding increases in the following sequence: THF<H2O<D2O. The effects of the degree of ‘hydrogen bonding’ and the ‘solubility’ of polymer in solvents on the physical properties of poly(NIPAM) solutions are discussed. 相似文献