首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2975篇
  免费   61篇
  国内免费   10篇
电工技术   125篇
综合类   10篇
化学工业   613篇
金属工艺   126篇
机械仪表   109篇
建筑科学   39篇
矿业工程   1篇
能源动力   134篇
轻工业   181篇
水利工程   3篇
石油天然气   1篇
无线电   302篇
一般工业技术   441篇
冶金工业   673篇
原子能技术   81篇
自动化技术   207篇
  2023年   12篇
  2022年   29篇
  2021年   46篇
  2020年   19篇
  2019年   21篇
  2018年   33篇
  2017年   22篇
  2016年   41篇
  2015年   37篇
  2014年   52篇
  2013年   125篇
  2012年   71篇
  2011年   123篇
  2010年   97篇
  2009年   125篇
  2008年   135篇
  2007年   113篇
  2006年   75篇
  2005年   98篇
  2004年   100篇
  2003年   94篇
  2002年   77篇
  2001年   83篇
  2000年   67篇
  1999年   80篇
  1998年   231篇
  1997年   187篇
  1996年   140篇
  1995年   85篇
  1994年   71篇
  1993年   63篇
  1992年   41篇
  1991年   34篇
  1990年   25篇
  1989年   26篇
  1988年   30篇
  1987年   30篇
  1986年   21篇
  1985年   28篇
  1984年   25篇
  1983年   17篇
  1982年   28篇
  1981年   22篇
  1980年   27篇
  1979年   28篇
  1978年   13篇
  1977年   22篇
  1976年   39篇
  1975年   11篇
  1974年   6篇
排序方式: 共有3046条查询结果,搜索用时 31 毫秒
1.
Background: Within the claudin (CLDN) family, CLDN12 mRNA expression is altered in various types of cancer, but its clinicopathological relevance has yet to be established due to the absence of specific antibodies (Abs) with broad applications. Methods: We generated a monoclonal Ab (mAb) against human/mouse CLDN12 and verified its specificity. By performing immunohistochemical staining and semiquantification, we evaluated the relationship between CLDN12 expression and clinicopathological parameters in tissues from 138 cases of cervical cancer. Results: Western blot and immunohistochemical analyses revealed that the established mAb selectively recognized the CLDN12 protein. Twenty six of the 138 cases (18.8%) showed low CLDN12 expression, and the disease-specific survival (DSS) and recurrence-free survival rates were significantly decreased compared with those in the high CLDN12 expression group. We also demonstrated, via univariable and multivariable analyses, that the low CLDN12 expression represents a significant prognostic factor for the DSS of cervical cancer patients (HR 3.412, p = 0.002 and HR 2.615, p = 0.029, respectively). Conclusions: It can be concluded that a reduced CLDN12 expression predicts a poor outcome for cervical cancer. The novel anti-CLDN12 mAb could be a valuable tool to evaluate the biological relevance of the CLDN12 expression in diverse cancer types and other diseases.  相似文献   
2.
Porous alumina with a highly textured microstructure was fabricated by pulse electric current sintering (PECS) using alumina platelets. Highly oriented porous alumina with a porosity of 3%–50% was obtained by a pressure-controlled method of PECS. The properties of the highly textured porous alumina were measured in two directions. The nitrogen gas permeance and thermal conductivity at room temperature were higher in the direction along the platelet length due to the higher continuity of pores and the connectivity of alumina platelets, respectively. The anisotropy of the thermal conductivity at room temperature was investigated and explained by the effect of grain size of platelets as well as morphology and orientation of pores. The bending strength was higher with the loading direction along the platelet thickness. The thermal shock strength was clearly different in the two directions. The difference in the thermal shock strength was investigated by the measurement of properties and thermal stress analysis.  相似文献   
3.
Cyclodextrins (CyDs) are water-soluble host molecules possessing a nanosized hydrophobic cavity. In the realm of molecular recognition, this cavity is used not only as a recognition site but also as a reaction medium, where a hydrophobic sensor recognizes a guest molecule. Based on the latter concept, we have designed a novel supramolecular sensing system composed of Zn(II)-dipicolylamine metal complex-based azobenzene (1-Zn) and 3A-amino-3A-deoxy-(2AS,3AS)-γ-cyclodextrin (3-NH2-γ-CyD) for sensing adenosine-5′-triphosphate (ATP). 1-Zn showed redshifts in the UV-Vis spectra and induced circular dichroism (ICD) only when both ATP and 3-NH2-γ-CyD were present. Calculations of equilibrium constants indicated that the amino group of 3-NH2-γ-CyD was involved in the formation of supramolecular 1-Zn/3-NH2-γ-CyD/ATP. The Job plot of the ICD spectral response revealed that the stoichiometry of 1-Zn/3-NH2-γ-CyD/ATP was 2:1:1. The pH effect was examined and 1-Zn/3-NH2-γ-CyD/ATP was most stable in the neutral condition. The NOESY spectrum suggested the localization of 1-Zn in the 3-NH2-γ-CyD cavity. Based on the obtained results, the metal coordination interaction of 1-Zn and the electrostatic interaction of 3-NH2-γ-CyD were found to take place for ATP recognition. The “reaction medium approach” enabled us to develop a supramolecular sensing system that undergoes multi-point interactions in water. This study is the first step in the design of a selective sensing system based on a good understanding of supramolecular structures.  相似文献   
4.
This study was addressed to the influence of an electric field strength applied at fabrication process and matrix properties, such as the dielectric constant and the Young's modulus, on “pseudo‐1‐3 piezoelectric ceramic/polymer composite” in order to further enhance the piezoelectricity of that. The pseudo‐1‐3 piezoelectric ceramic/polymer composite consists of linearly ordered piezoelectric ceramic particles in polymer material. Silicone gel, silicone rubber, urethane rubber, and poly‐methyl‐methacrylate, which exhibit different dielectric constants and Young's modulus, were used as matrices to evaluate the matrix influence. The piezoelectricity of the pseudo‐1‐3 piezoelectric ceramic/polymer composite was evaluated using the piezoelectric strain constant d33. The d33 is one of the indices of the piezoelectric properties for piezoelectric materials. As a result, it was confirmed that d33 of the pseudo‐1‐3 piezoelectric ceramic/polymer composite increased with the increase of the electric filed strength applied at fabrication process, though, it reached a constant value at a certain strength value. Further it was confirmed that dielectric constant of the matrix had a small influence on d33 of the pseudo‐1‐3 piezoelectric ceramic/polymer composite, however, in case of matrix of lower Young's modulus, d33 was increase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41817.  相似文献   
5.
Niobium- or vanadium-doped anatase sols were prepared by hydrothermal treatment of 0.1 mol/dm3 peroxotitanium complex aqueous solutions dissolving 0–10 mol% niobium or vanadium at 100°C for 8 h. Niobium-doping caused the increase of lattice constants of anatase and the shape change of anatase crystal from spindle-like to cubic-like structure, but no change of the optical absorbance. Vanadium-doping caused the decrease of lattice constant of c -axis, the miniaturization of anatase crystal and the increase of optical absorbance at the wavelength from 350–700 nm.  相似文献   
6.
Deformation behavior of stoichiometric blends made from poly(styrene-co-styrenesulfonic acid) (SPS) and poly(styrene-co-4-vinylpyridine) (SVP) was investigated by TEM observation of strained thin films. An FTIR investigation revealed that ionic cross-links were formed between the component polymers upon blending due to intermolecular ion-ion interactions, which arose from proton transfer from sulfonic acid groups to pyridine groups. TEM observations indicate that the deformation mode of the blends changed from crazing only to crazing plus shear deformation, with the shear contribution becoming larger, as the ion content in the blends increased. Such changes in deformation mode can be understood as arising from an increase in the ‘effective’ strand density due to the formation of ionic cross-links upon blending. It was also found that the ionic cross-links via pyridinium cation/sulfonate anion ion pairs were more effective in inducing the transition of deformation mode than ionic cross-links via -SO3/Na+ or -SO3/Ca2+ ion pairs.  相似文献   
7.
Characteristic power-law dependence of junction conductance on temperature was confirmed at low temperatures fora,b-axis oriented Au/PrBa2Cu3O7−x /YBa2Cu3O7−y junctions with a PrBa2Cu3O7−x layer thinner than 30 nm, indicating that current transport via a small number of localized states was predominant. The radius and the density of the localized states were estimated to be 1.1 nm and 5.0x1019 eV−1 cm−3, respectively. Transport measurement at 1.7 K in a magnetic field of up to 6 T revealed no indication of on-site Coulomb repulsion of electrons in the localized states. These results support the possibility of resonant tunneling of Cooper pairs in superconductor-insulator-superconductor junctions with a thin PrBa2Cu3O7−x tunnel barrier.  相似文献   
8.
By employing an electrochemical technique involving stabilized zirconia as solid electrolyte and Mo + MoO2 mixture as reference electrode, the equilibrium oxygen partial pressures for three-phase assemblages of CaSiO3(s) + Ca3Si2O7(s) + {CaO + SiO2 + FexO} melt and Ca3Si2O7(s) + Ca2SiO4(s) + {CaO + SiO2 + FexO} melt were determined as: - log {PO2 (CS + C3S2 + L)/bar} = - 3.22 13000/(T/K) ± 0.05 - log {PO2 (C3S2 + C2S + L)/bar} = - 0.92 16400/ (T/K) ± 0.04. respectively, where CS, C3S2 and C2S indicate CaSiO3(s), Ca3Si2O7(s). and Ca2SiO4(s), respectively.  相似文献   
9.
There are several damping phenomena in quantum optics. Such phenomena have been usually explained by open systems. In statistical physics, open system dynamics have been used to study the irreversibility and the approach to equilibrium. In this paper, the dynamical change of the mutual entropy for an open system, frequently studied in the quantum optics literature, is rigorously computed through a model of quantum Markov chain. In particular, the concrete formula of Stinespring expression for such a model is obtained and applied to the derivation of the mutual entropy, and some computational results are presented.  相似文献   
10.
OBJECTIVE: To evaluate what nursing home medical directors actually do, what they and other nursing home personnel believe would be desirable to do, and what problems and deficiencies are perceived. DESIGN: Mail survey with follow-up telephone interview when necessary. SETTING: Forty-five nursing facilities in upstate New York. PARTICIPANTS: The medical directors, administrators, and directors of nursing of the 45 facilities. MEASUREMENTS: Inventory of what medical directors reported as to their actual activities and time spent, and of what they, the administrators, and the directors of nursing felt should be their responsibilities and activities under ideal circumstances. RESULTS: For part-time medical directors, self-reported time spent on medical directorship activities averaged 12 hours per month; of all directors, 45% spent 8 hours or less per month. Proportion of time spent on various specific activities varied widely. There was general agreement that substantially more time should be spent, in particular, on evaluating and addressing problems of adequacy and quality of care, communicating with attending physicians about problems, and assisting with inservice training programs. CONCLUSIONS: To fill the role adequately, more time should be spent by many part-time medical directors, which will require greater financial commitment by facilities and reimbursement systems. Efforts need to made to better coordinate the expectations of medical directors and facility staff.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号