全文获取类型
收费全文 | 28627篇 |
免费 | 1954篇 |
国内免费 | 1054篇 |
专业分类
电工技术 | 1641篇 |
综合类 | 938篇 |
化学工业 | 7076篇 |
金属工艺 | 1106篇 |
机械仪表 | 1190篇 |
建筑科学 | 358篇 |
矿业工程 | 220篇 |
能源动力 | 7994篇 |
轻工业 | 2772篇 |
水利工程 | 55篇 |
石油天然气 | 129篇 |
武器工业 | 56篇 |
无线电 | 2896篇 |
一般工业技术 | 2983篇 |
冶金工业 | 747篇 |
原子能技术 | 331篇 |
自动化技术 | 1143篇 |
出版年
2024年 | 78篇 |
2023年 | 645篇 |
2022年 | 1729篇 |
2021年 | 2008篇 |
2020年 | 1176篇 |
2019年 | 1116篇 |
2018年 | 887篇 |
2017年 | 1069篇 |
2016年 | 952篇 |
2015年 | 904篇 |
2014年 | 1574篇 |
2013年 | 1734篇 |
2012年 | 1740篇 |
2011年 | 2542篇 |
2010年 | 1857篇 |
2009年 | 1594篇 |
2008年 | 1625篇 |
2007年 | 1525篇 |
2006年 | 1239篇 |
2005年 | 1016篇 |
2004年 | 801篇 |
2003年 | 612篇 |
2002年 | 587篇 |
2001年 | 465篇 |
2000年 | 376篇 |
1999年 | 293篇 |
1998年 | 267篇 |
1997年 | 218篇 |
1996年 | 173篇 |
1995年 | 157篇 |
1994年 | 128篇 |
1993年 | 106篇 |
1992年 | 82篇 |
1991年 | 61篇 |
1990年 | 50篇 |
1989年 | 49篇 |
1988年 | 39篇 |
1987年 | 22篇 |
1986年 | 24篇 |
1985年 | 28篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
This paper is a summary of an extensive research program carried out by the authors on the structure of rapidly solidified aluminum alloys; and a comparison with the work of others also involved in this field. The paper discusses the changes in the dendritic and non-dendritic structure of the matrix at cooling rates from 10–3 to 1010 K/s and discusses the hetergeneity of the structure caused by interdendritic-segretion during solidification. 相似文献
22.
This paper focuses on the microscopic damage and progressive failure of a composite reinforced by plain-weave glass cloth under tensile fatigue loading. The fatigue process was divided into three stages like that of multi-directional laminates. It was found that the internal damage at each stage (matrix cracks, debonds in the weft, successive debonds in the warp and ‘metadelaminations’ between warps and wefts) occurred near the cross-over point of the fabric. The modulus decay mechanism was explained by considering the progression of this internal damage. From the end of the first stage to the beginning of the middle stage, a characteristic damage state (CDS) (called a ‘meta-CDS’) was observed. It was found that woven composites have a unit area of damage accumulation (called a ‘unit cell’) and the damage of each unit cell and its distribution control the total fatigue damage of the material. 相似文献
23.
A. Benati M.A. Butturi C. Capperdoni M.C. Carotta G. Martinelli M. Merli L. Passari G. Sartori R. Van Steenwinkel G.M. Youssef 《Solar Energy Materials & Solar Cells》1996,43(2):183
The newly developed ingot growing techniques, as the three-grain and the columnar multigrain ingot processes, are now offering the possibility of slicing thinner wafers (≤ 100 μm). In this paper we present the results obtained on p type large area (≥ 100 cm2) and 100 μm thick wafers by using both conventional and reverse cell manufacturing technologies.The conventional cells are provided with aluminium or boron BSF plus screen-printed silver mirror or a silver-aluminium net; the reverse cells have a FSF and the deep back junction completely covered by a screen-printed or CVD silver layer.The constructing parameters have been chosen on the base of one and two dimensions modeling and both raw material and devices have been completely characterized.This work shows that very thin wafers do not introduce serious problems for the conventional manufacturing of solar cells. The efficiencies of the normal and of the reverse cells are found to be comparable and are of the same order than those of thicker cells, however at a significant lower cost. The main obtained result has to be related to the demonstration of a cell manufacturing feasibility starting from very thin wafers. 相似文献
24.
本文从无线电通信基本要素出发 ,阐述上行信号和下行信号的无线传播 ,得出上下行信号平衡链路方程 ,并以我国普遍使用的TACS系统和GSM系统为例 ,着重讨论了信号平衡与蜂窝小区设计之间的关系。 相似文献
25.
26.
J G De Nobel F M Klis A Ram H Van Unen J Priem T Munnik H Van Den Ende 《Yeast (Chichester, England)》1991,7(6):589-598
To study cell-cycle-related variations in wall permeability of Saccharomyces cerevisiae, two approaches were used. First, an asynchronous culture was fractionated by centrifugal elutriation into subpopulations containing cells of increasing size. The subpopulations represented different stages of the cell cycle as judged by light microscopy. Cell wall porosity increased when these subpopulations became enriched with budded cells. Secondly, synchronous cultures were obtained by releasing MATa cells from alpha-factor induced G1-arrest. These cultures grew synchronously for at least two generations. The cell wall porosity increased sharply in these cultures, shortly before buds became visible and was maximal during the initial stages of bud growth. It decreased in cells which had completed nuclear migration and before abscission of the bud had occurred. The porosity reached its lowest value during abscission and in unbudded cells. We examined the incorporation of mannoproteins into the wall during the cell cycle. SDS-extractable mannoproteins were incorporated continuously. However, the incorporation of glucanase-extractable mannoproteins, which are known to affect cell wall porosity, showed cyclic oscillations and reached its maximum after nuclear migration. This coincided with a rapid decrease in cell wall porosity, indicating that glucanase-extractable mannoproteins might contribute to this decrease. 相似文献
27.
Vero细胞在微载体上迁移和多层生长现象 总被引:1,自引:1,他引:0
本文通过对电子显微镜观察了Vero细胞有微载体增减过程中的迁移民政部发现在不同增减阶段,Vro细胞迁移方式不同;在分泌形成的细胞外基质,上,Vero细胞迁移是通过 层粘连蛋白介导进行的,被层粘连蛋白抗体抑制;这种迁移导致Vero细胞在微载体上形成多层生长现象。 相似文献
28.
Johan M. Thevelein 《Yeast (Chichester, England)》1994,10(13):1753-1790
29.
30.
Janne Halme Minna Toivola Antti Tolvanen Peter Lund 《Solar Energy Materials & Solar Cells》2006,90(7-8):872-886
Electrochemical impedance spectroscopy was used to determine the effective charge transfer resistances of porous dye-sensitized solar cell counter electrodes prepared by low-temperature spray deposition and compression of conductive carbon and platinized Sb-doped SnO2 powders on indium tin oxide-coated plastic substrates. The charge transfer resistances were 0.5–2 and 8–13 Ω cm2, respectively, when using 3-methoxypropionitrile as the electrolyte solvent. The manufacturing method used lends itself to produce mechanically stable and even-quality electrodes in an easy and fast manner. 相似文献