全文获取类型
收费全文 | 2696篇 |
免费 | 34篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 13篇 |
综合类 | 4篇 |
化学工业 | 205篇 |
金属工艺 | 18篇 |
机械仪表 | 24篇 |
建筑科学 | 49篇 |
矿业工程 | 1篇 |
能源动力 | 16篇 |
轻工业 | 117篇 |
水利工程 | 9篇 |
石油天然气 | 6篇 |
无线电 | 136篇 |
一般工业技术 | 224篇 |
冶金工业 | 1779篇 |
原子能技术 | 19篇 |
自动化技术 | 116篇 |
出版年
2021年 | 13篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 23篇 |
2016年 | 18篇 |
2015年 | 14篇 |
2014年 | 31篇 |
2013年 | 60篇 |
2012年 | 36篇 |
2011年 | 40篇 |
2010年 | 27篇 |
2009年 | 35篇 |
2008年 | 35篇 |
2007年 | 52篇 |
2006年 | 26篇 |
2005年 | 36篇 |
2004年 | 37篇 |
2003年 | 27篇 |
2002年 | 37篇 |
2001年 | 33篇 |
2000年 | 27篇 |
1999年 | 64篇 |
1998年 | 482篇 |
1997年 | 309篇 |
1996年 | 240篇 |
1995年 | 94篇 |
1994年 | 108篇 |
1993年 | 114篇 |
1992年 | 31篇 |
1991年 | 29篇 |
1990年 | 38篇 |
1989年 | 43篇 |
1988年 | 34篇 |
1987年 | 30篇 |
1986年 | 24篇 |
1985年 | 29篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 25篇 |
1981年 | 16篇 |
1980年 | 30篇 |
1979年 | 14篇 |
1978年 | 27篇 |
1977年 | 55篇 |
1976年 | 141篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1972年 | 10篇 |
1968年 | 7篇 |
排序方式: 共有2736条查询结果,搜索用时 11 毫秒
81.
MJ Francis EE Jones ER Levy S Ponnambalam J Chelly AP Monaco 《Canadian Metallurgical Quarterly》1998,7(8):1245-1252
Menkes disease arises from a genetic impairment in copper transport. The gene responsible for the phenotype has been identified as a copper transporting ATPase ( ATP7A ). Recently, the protein encoded by the ATP7A gene has been localized to the Golgi complex. In order to investigate the role of the Menkes disease protein in copper transport, recombinant constructs containing both the full-length open reading frame and an alternatively spliced form have been successfully expressed and localized in mammalian cells. Other studies of a patient with occipital horn syndrome, an allelic variant of Menkes disease, have demonstrated that only this alternatively spliced isoform and not the full-length form is expressed in this patient. The milder form of this patient's phenotype suggests that the alternatively spliced isoform has some functional role in copper transport. In the present study the full-length recombinant Menkes protein was shown by immunofluorescence to localize to the Golgi apparatus and the alternatively spliced form, lacking sequences for transmembrane domains 3 and 4 encoded by exon 10, was shown to localize to the endoplasmic reticulum. Using sequences from exon 10 fused to a non-Golgi reporter molecule, a 38 amino acid sequence containing transmembrane domain 3 of the Menkes protein was found to be sufficient for localization to the Golgi complex. Therefore, the protein sequence encoded by exon 10 may be responsible for this differential localization and both isoforms may be required for comprehensive transport of copper within the cell. 相似文献
82.
The context-dependent nature in which mutations affect protein stability was investigated using the FK506-binding protein, FKBP12. Thirty-four mutations were made at sites throughout the protein, including residues located in the hydrophobic core, the beta-sheet, and the solvent-exposed face of the alpha-helix. Urea-induced denaturation experiments were used to measure the change in stability of the mutants relative to that of the wild type (Delta DeltaGU-F). The results clearly show that the extent of destabilization, or stabilization, is highly context-dependent. Correlations were sought in order to link Delta DeltaGU-F to various structural parameters. The strongest correlation found was between Delta DeltaGU-F and N, the number of methyl(ene) groups within a 6 A radius of the group(s) deleted. For mutations of buried hydrophobic residues, a correlation coefficient of 0.73 (n = 16,where n is the number of points) was obtained. This increased to 0.81 (n = 24) on inclusion of mutations of partially buried hydrophobic residues. These data could be superimposed on data obtained for other proteins for which similarly detailed studies have been performed. Thus, the contribution to stability from hydrophobic side chains, independent of the extent to which a side chain is buried, can be estimated quantitatively using N. This correlation appears to be a general feature of all globular proteins. The effect on stability of mutating polar and charged residues in the alpha-helix and beta-sheet was also found to be highly context-dependent. Previous experimental and statistical studies have shown that specific side chains can stabilize the N-caps of alpha-helices in proteins. Substitutions of Ile56 to Thr and Asp at the N-cap of the alpha-helix of FKBP12, however, were found to be highly destabilizing. Thus, the intrinsic propensities of an amino acid for a particular element of secondary structure can easily be outweighed by tertiary packing factors. This study highlights the importance of packing density in determining the contribution of a residue to protein stability. This is the most important factor that should be taken into consideration in protein design. 相似文献
83.
Interleukin-2 (IL-2) therapy often causes gastrointestinal side effects and at least 8 cases of bowel perforation have been reported. The patient reported here developed a colosplenic fistula, diagnosed by CT, with no neoplastic involvement of these organs. Awareness of these complications of IL-2 can help lead to earlier diagnosis. 相似文献
84.
B Sp?rri M Bickel A Limat ER Waelti T Hunziker UN Wiesmann 《Canadian Metallurgical Quarterly》1997,21(4):371-378
T cells adhere to human dermal fibroblasts (HDF). This cellular interaction leads to a pronounced secretion of the proinflammatory cytokines IL-6 and IL-8 via a juxtacrine stimulation induced by HDF-associated IL-1. Upon stimulation, fibroblasts express various surface proteins such as MCH-I molecules, which may interact with corresponding receptors on T cells. The present study was conducted to further investigate the mechanism of this complex interaction with regard to the secretion of IL-6 in cocultures of T cells and HDF. IL-6 was time- and dose-dependently upregulated in such cocultures. Spatial separation of the cells by microporous membranes resulted in a 90% reduction of IL-6 secretion, but when cells had limited cell contact IL-6 secretion was increased again. Allogeneic cocultures of T cells and HDF showed increased capacity of IL-6 stimulation as compared to autologous cultures. Our results suggest that MHC-I/T cell receptor interaction modulates IL-6 secretion in allogeneic and autologous cocultures. 相似文献
85.
The current study establishes the unprecedented involvement in the evolution and production of novel core–shell nanocomposites composed of nanosized titanium dioxide and aniline‐o‐phenylenediamine copolymer. TiO2@copoly(aniline and o‐phenylenediamine) (TiO2@PANI‐o‐PDA) core–shell nanocomposites were chemically synthesized in a molar ratio of 5:1 of the particular monomers and several weights of nano‐TiO2 via oxidative copolymerization. The construction of the TiO2@PANI‐o‐PDA core–shell nanocomposites was ascertained from Fourier transform IR spectroscopy, UV–visible spectroscopy and XRD. A reasonable thermal behavior for the original copolymer and the TiO2@PANI‐o‐PDA core–shell nanocomposites was investigated. The bare PANI‐o‐PDA copolymer was thermally less stable than the TiO2@PANI‐o‐PDA nanocomposites. The core–shell feature of the nanocomposites was found to have core and shell sizes of 17 nm and 19–26 nm, respectively. In addition, it was found that the addition of a high ratio of TiO2 nanoparticles increases the electrical conductivity and consequently lowers the electrical resistivity of the TiO2@PANI‐o‐PDA core–shell nanocomposites. The hybrid photocatalysts exhibit a dramatic photocatalytic efficacy of methylene blue degradation under solar light irradiation. A plausible interpretation of the photocatalytic degradation results of methylene blue is also demonstrated. Our setup introduces a facile, inexpensive, unique and efficient technique for developing new core–shell nanomaterials with various required functionalities and colloidal stabilities. © 2018 Society of Chemical Industry 相似文献
86.
87.
Georgina K. SuchAngus P.R. Johnston Kang LiangFrank Caruso 《Progress in Polymer Science》2012,37(7):985-1003
The synthesis of nanoengineered materials with precise control over material composition, architecture and functionality is integral to advances in diverse fields, including biomedicine. Over the last 10 years, click chemistry has emerged as a prominent and versatile approach to engineer materials with specific properties. Herein, we highlight the application of click chemistry for the synthesis of nanoengineered materials, ranging from ultrathin films to delivery systems such as polymersomes, dendrimers and capsules. In addition, we discuss the use of click chemistry for functionalizing such materials, focusing on modifications aimed at biomedical applications. 相似文献
88.
A novel electrodeposition technique is developed to estimate time‐averaged convective local mass transfer coefficients. This method is based on the diffusion‐controlled deposition rate of copper. With an electrolyte solution consisting of H2SO4 and CuSO4, copper is dissolved at the anode and deposited onto the nickel cathode. The thickness of the copper, measured with an optical microscope, provides an estimate of the time‐averaged local mass transfer coefficient for the given location, and by depositing multiple layers, the coefficients under different flow conditions can be obtained from one cathode. The results for laminar flow in a smooth, round pipe showed good agreement with those calculated from the analytical Leveque solution. Results were also obtained for turbulent flow and demonstrate the potential for acquiring convective local mass transfer coefficients for various flow configurations. 相似文献
89.
Reactive Laser Ablation Synthesis of Nanosize Alumina Powder 总被引:1,自引:0,他引:1
Gregory P. Johnston Ross Muenchausen Douglas M. Smith William Fahrenholtz Steve Foltyn 《Journal of the American Ceramic Society》1992,75(12):3293-3298
An aluminum (Al) target was laser ablated in an oxygen (O2 ) atmosphere, producing nanosize alumina (Al2 O3 ) powder. The powder surface area decreased (and the particle size increased) with both increasing oxygen pressure and laser fluence. All powders produced had surface areas between 135 and 250 m2 /g, corresponding to primary particle sizes ranging from 7 to 3 nm in radius. Phase evolution with temperature was studied via X-ray diffraction. These powders showed a direct transformation from γ- to α-alumina at approximately 1200°C, bypassing other transition alumina phases, while still maintaining small particle size ( 30 nm). Despite the nanosize particles, green densities equal to 54% of the skeletal density (i.e., true density of the solid phase) were obtained by uniaxial pressing at 40 MPa. 相似文献
90.
Gregory P. Johnston Ross E. Muenchausen Douglas M. Smith Steve R. Foltyn 《Journal of the American Ceramic Society》1992,75(12):3465-3468
An aluminum (Al) target was laser ablated in a nitrogen (N2 ) atmosphere, producing aluminum nitride (AlN) powder. These powders were calcined at 900°C for 2 h. Powders were produced at various nitrogen pressures, and the calcined powders were tested for unreacted aluminum content, using differential thermal analysis (DTA). The AlN powder, produced at a laser fluence of 12 J/cm2 and a nitrogen pressure of 10.0 kPa (75 torr), showed no evidence of unreacted aluminum by DTA and was phase-pure AlN by X-ray diffraction (XRD). The surface area of this powder is 82 m2 /g, corresponding to a particle size of ∼11 nm, which is in good agreement with TEM observations. 相似文献