全文获取类型
收费全文 | 690501篇 |
免费 | 118045篇 |
国内免费 | 83682篇 |
专业分类
电工技术 | 70867篇 |
技术理论 | 2篇 |
综合类 | 78126篇 |
化学工业 | 84076篇 |
金属工艺 | 59309篇 |
机械仪表 | 44282篇 |
建筑科学 | 51409篇 |
矿业工程 | 34989篇 |
能源动力 | 20580篇 |
轻工业 | 74057篇 |
水利工程 | 24328篇 |
石油天然气 | 30447篇 |
武器工业 | 11532篇 |
无线电 | 80708篇 |
一般工业技术 | 67583篇 |
冶金工业 | 27511篇 |
原子能技术 | 10019篇 |
自动化技术 | 122403篇 |
出版年
2024年 | 5525篇 |
2023年 | 12231篇 |
2022年 | 24976篇 |
2021年 | 31413篇 |
2020年 | 26408篇 |
2019年 | 27018篇 |
2018年 | 29065篇 |
2017年 | 33245篇 |
2016年 | 30885篇 |
2015年 | 39331篇 |
2014年 | 44736篇 |
2013年 | 49224篇 |
2012年 | 58749篇 |
2011年 | 57638篇 |
2010年 | 54979篇 |
2009年 | 50598篇 |
2008年 | 50321篇 |
2007年 | 49067篇 |
2006年 | 41540篇 |
2005年 | 34429篇 |
2004年 | 28312篇 |
2003年 | 19500篇 |
2002年 | 18340篇 |
2001年 | 16531篇 |
2000年 | 13702篇 |
1999年 | 7698篇 |
1998年 | 4823篇 |
1997年 | 4212篇 |
1996年 | 3908篇 |
1995年 | 3901篇 |
1994年 | 3167篇 |
1993年 | 2974篇 |
1992年 | 2834篇 |
1991年 | 2047篇 |
1990年 | 1634篇 |
1989年 | 1572篇 |
1988年 | 1158篇 |
1987年 | 402篇 |
1986年 | 355篇 |
1985年 | 238篇 |
1984年 | 199篇 |
1983年 | 152篇 |
1982年 | 191篇 |
1981年 | 240篇 |
1980年 | 269篇 |
1979年 | 172篇 |
1976年 | 230篇 |
1975年 | 212篇 |
1972年 | 237篇 |
1960年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Silicon forms the backbone of the microelectronics industry, and possibly, of the optoelectronics industry, hitherto dominated by III/V materials. One of the remaining goals is to build an optical source in silicon. Erbium exhibits luminescent 1.54 μm intra-4f transitions in both silicon and porous silicon. This paper reviews the work which has been carried out in this field and discusses some possible additional applications of erbium-doped silicon in optoelectronics, such as a novel on-chip temperature sensor. 相似文献
82.
Z. -G. Fan Y. -X. Zhuang G. Yang R. Shao G. -F. Zhang 《Journal of Alloys and Compounds》1993,200(1-2):33-36
The oxygen absorption process in highly aligned YBa2Cu3Ox samples in air and in pure oxygen was studied at several constant temperatures. The process can be expressed in two steps, a chemical reaction controlled step and a diffusion controlled step. The kinetic equations are as follows respectively:
(1 − at) ln(1 − at) + at = kDt
The activation energy was calculated using an Arrhenius equation. The technical conditions of heat treatment for oxygen absorption of highly aligned YBa2Cu3Ox crystals are discussed. 相似文献
83.
The buckling of plain and discretely stiffened composite axisymmetric shell panels/shells made of repeated sublaminate construction is studied using the finite element method. In repeated sublaminate construction, a full laminate is obtained by repeating a basic sublaminate, which has a smaller number of plies. The optimum design for buckling is obtained by determining the layup sequence of the plies in the sublaminate by ranking, so as to achieve maximum buckling load for a specified thickness. For this purpose, a four-noded 48-dof quadrilateral composite thin shell element, together with fully compatible two-noded 16-dof composite meridional and parallel circle stiffener elements are used. 相似文献
84.
纳米聚N-异丙基丙烯酰胺微凝胶的光引发聚合 总被引:7,自引:0,他引:7
选择具有温敏性的高分子单体N-异丙基丙烯酰胺(N-isopropylacrylamide,NIPAM)为主单体,N,N′-亚甲基双丙烯酰胺(methylenebisacrylamide,MBA)为交联剂,运用光引发无皂乳液聚合的方法合成出粒径小于100nm的高分子微凝胶,并研究了在改变体系组成和条件时微凝胶粒径的变化。结果显示,在乳化剂临界胶束浓度以下,随着乳化剂浓度的提高,微凝胶粒子的粒径不断关小且趋向稳定;相比于热引发,产生的微凝胶具有较高的单分散性而且粒径较小。 相似文献
85.
The effect of the charge fluctuation of dust particles on ion acoustic wave (IAW) excited through ionization instability was investigated. The hydrodynamic equations and linear time-dependent perturbation theory served as the starting point of theory, by which the dispersion relation and growth rate of the IAW were given. By comparing the results with the case of constant dust charges, it was found that the charge fluctuation of dust particles reduces the instability of the wave mode. 相似文献
86.
The dye-sensitized TiO2 complex films were prepared by the dye coat onto TiO2 surfaces,and the sensitizing mechanism and adsorption properties of the dye-sensitized TiO2 complex films were inverstigated.The influence of the application conditions of dye adsorbed on TiO2 films on the amount of dye adsorption was discussed.Experimental results show that the concentration,the temperature of dye solutions and the dipping time of TiO2 films in the dye solutions have a significant influence on the amount of dye adsorption.Cell test indicates that the conversion efficiency of light to electricity increases with the amount of dye adsorption. 相似文献
87.
K. Tsuzuki T. Banno A. Kinbara Y. Nakagawa T. Tsukada 《Journal of Nuclear Materials》1993,200(3):291-295
The self-bias potential (Vdc) induced on an RF-powdered electrode (153 mm Ø) in a plasma is measured using electrical probes which are buried in, de-insulated from, and RF-connected to the electrode. The configuration of the probes allows to study the distribution of Vdc discretely on the electrode. The potential is homogeneous in the absence of external magnetic field. In the presence of a homogeneous magnetic field parallel to the electrode, it is reduced and a monotonous gradient takes place in its distribution due to the plasma shift induced by E × B drift. When the magnetic field is rotated along the axis of the RF-electrode at a frequency less than 50 Hz, the distribution, which is almost identical to the one in a static field, rotates with the magnetic field. On the coordinate system rotating with the magnetic field, the probes are regarded to be rotating. The potential distribution is obtained as a continuous function of the azimuthal angle. Thus the rotation of the field provides information for the experimental interpolation. 相似文献
88.
Methods are described for forming coating specimens and testing them in pure bending. The proposed tester gives adequate accuracy in determining the elastic characteristics and strength for thin specimens (up to 0.1 mm) of brittle materials of powder-coating type.Translated from Problemy Prochnosti, No. 3, pp. 94–97, March, 1993. 相似文献
89.
Buffalo milk Cheddar cheese samples of different ages were analysed for compositional attributes (CA), ripening indices (RI) and Instron Textural Profile (ITP). All samples were compositionally alike, except for pH and salt-in-moisture (SM) contents. RI showed significant variations. CA and RI showed highly significant correlations within themselves and with each other, except for moisture with pH, SM with moisture, MNFS, Fat and FDM and Fat with MNFS. The ITPs of cheeses showed significant variations and had highly significant intercorrelations indicating their interdependence. CA (except moisture and MNFS) and RI showed a highly significant correlationship with ITPs. Moisture content showed a highly significant correlationship with all ITPs, except cohesiveness and springiness, where it was significant. MNFS content showed significant correlations only with hardness and brittleness. Stepwise regression analysis revealed that MI was the most predominant factor influencing cheese texture, followed by pH, SM, FDM and TVFA. Knowing Ca and RI, the textural properties of cheeses can be forecast through mathematical equations. Similarly the age of cheese can also be predicted if RI and/or textural properties are known. 相似文献
90.
J. M. Zaldivar E. Molga M. A. Al s H. Hern ndez K. R. Westerterp 《Chemical Engineering and Processing: Process Intensification》1995,34(6):543-559
Aromatic nitrations by mixed acid have been selected as a specific case of a heterogeneous liquid-liquid reaction. An extensive experimental programme has been followed using adiabatic and heat-flow calorimetry and pilot reactor experiments, supported by chemical analysis. A series of nitration experiments has been carried out to study the influences of different initial and operating conditions such as temperature, stirring speed and sulphuric acid concentration. In parallel, a mathematical model to predict the overall conversion rate has been developed. In this paper the mathematical modelling and the implementation and experimental validation for benzene, toluene and chlorobenzene mononitration in the kinetic control regime (slow liquid-liquid reaction) are presented and discussed. 相似文献