全文获取类型
收费全文 | 12928篇 |
免费 | 852篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 130篇 |
综合类 | 8篇 |
化学工业 | 2691篇 |
金属工艺 | 431篇 |
机械仪表 | 567篇 |
建筑科学 | 272篇 |
矿业工程 | 10篇 |
能源动力 | 391篇 |
轻工业 | 1161篇 |
水利工程 | 37篇 |
石油天然气 | 21篇 |
无线电 | 1593篇 |
一般工业技术 | 2349篇 |
冶金工业 | 2936篇 |
原子能技术 | 131篇 |
自动化技术 | 1073篇 |
出版年
2023年 | 96篇 |
2022年 | 169篇 |
2021年 | 280篇 |
2020年 | 207篇 |
2019年 | 262篇 |
2018年 | 298篇 |
2017年 | 344篇 |
2016年 | 401篇 |
2015年 | 352篇 |
2014年 | 498篇 |
2013年 | 775篇 |
2012年 | 661篇 |
2011年 | 826篇 |
2010年 | 594篇 |
2009年 | 562篇 |
2008年 | 561篇 |
2007年 | 435篇 |
2006年 | 352篇 |
2005年 | 326篇 |
2004年 | 318篇 |
2003年 | 303篇 |
2002年 | 262篇 |
2001年 | 213篇 |
2000年 | 196篇 |
1999年 | 273篇 |
1998年 | 927篇 |
1997年 | 592篇 |
1996年 | 385篇 |
1995年 | 253篇 |
1994年 | 247篇 |
1993年 | 268篇 |
1992年 | 122篇 |
1991年 | 111篇 |
1990年 | 103篇 |
1989年 | 117篇 |
1988年 | 80篇 |
1987年 | 74篇 |
1986年 | 64篇 |
1985年 | 83篇 |
1984年 | 68篇 |
1983年 | 49篇 |
1982年 | 47篇 |
1981年 | 49篇 |
1980年 | 50篇 |
1979年 | 39篇 |
1978年 | 36篇 |
1977年 | 89篇 |
1976年 | 187篇 |
1975年 | 41篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Nanocomposites based on poly(butylene terephthalate) (PBT) and an organoclay (Cloisite 30B) were prepared by melt blending using a twin‐screw extruder. Two kinds of PBTs, ie PBT‐A and PBT‐B, with different inherent viscosities (ηinh), were used for this study (ηinh of PBT‐A and PBT‐B were 0.74 and 1.48, respectively). Dispersion of the clay layers in the PBT nanocomposites was characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and dynamic mechanical properties and non‐isothermal crystallization temperatures of the nanocomposites were also examined. Nanocomposites based on the higher‐viscosity PBT (PBT‐B) showed a higher degree of exfoliation of the clay and a higher reinforcing effect when compared to the composites based on the lower‐viscosity PBT (PBT‐A). The clay nanolayers dispersed in PBT matrices lead to increases in the non‐isothermal crystallization temperatures of the PBTs, with such increases being more significant for the PBT‐B nanocomposites than for the PBT‐A nanoocomposites. Copyright © 2004 Society of Chemical Industry 相似文献
2.
The transmission mode of holographic polymer‐dispersed liquid crystals (HPDLCs) was developed an under electric field. It is reported that orientation of LC molecules under an electric field induces orientation of oligomer molecules giving rise to low off‐state diffraction and small grating shrinkage. Copyright © 2005 Society of Chemical Industry 相似文献
3.
Young Sil Jeon Jing Lei Ji-Heung Kim 《Journal of Industrial and Engineering Chemistry》2008,14(6):726-731
This study examined the removal of some basic dyes, such as Methylene Blue, Malachite Green and Methyl Orange, using alginate or alginate/polyaspartate composite gel beads. The adsorption of dyes from aqueous solutions at 25 °C was examined using a batch sorption technique. The effects of CaCl2 and the dye concentration on the adsorption were examined. Type-S adsorption isotherms were obtained, which is characteristic of a weak solute–solid interaction. The ionic interaction between the dye molecule and gel matrix appears to be responsible for the efficient adsorption of cationic dyes in this system. These results suggest that an alginate/polyaspartate gel can be used as an effective sorbent for water pollutants such as dyes, and the immobilization of these organic contaminants in the hydrogels from wastewater can solve one of the most important environmental problems in the related industry. 相似文献
4.
In polyolefin processes the melt index (MI) is the most important control variable indicating product quality. Because of
the difficulty in the on-line measurement of MI, a lot of MI estimation and correlation methods have been proposed. In this
work a new dynamic MI estimation scheme is developed based on system identification techniques. The empirical MI estimation
equation proposed in the present study is derived from the 1
st
-order dynamic models. Effectiveness of the present estimation scheme was illustrated by numerical simulations based on plant
operation data including grade change operations in high density polyethylene (HDPE) processes. From the comparisons with
other estimation methods it was found that the proposed estimation scheme showed better performance in MI predictions. The
virtual sensor model developed based on the estimation scheme was combined with the virtual on-line analyzer (VOA) to give
a quality control system to be implemented in the actual HDPE plant. From the application of the present control system, significant
reduction of transition time and the amount of off-spec during grade changes was achieved 相似文献
5.
Many engineering problems can be shown to be equivalent to solving semidefinite programs (SPs), i.e., convex optimization problems involving linear matrix inequalities (LMIs). Powerful computation tools are available for such problems in the finite-dimensional case. However, the problems arising in optimal and robust control theory are often infinite dimensional, and so adequate computation tools are not available. The key to tackling such problems with finite computation tools is to have a primal-dual formulation of the problem without duality gap. In this paper we study infinite-dimensional SPs and present a lifting technique to recast SPs as parameterized linear programs (LPs). This enables the wealth of theoretical tools available for infinite-dimensional LPs to be extended to infinite-dimensional SPs. In particular, we develop some new sufficient conditions for the lack of a duality gap for infinite-dimensional SPs and give an exact characterization of the primal and dual problems for these cases. Both primal and dual problems are formed as infinite-dimensional SP problems, with finite truncations to each giving upper and lower bounds, respectively, on the exact solution to the infinite-dimensional problem. Thus, these results can form the basis of practical computation schemes for infinite-dimensional problems, which require only finite-dimensional computation tools. To illustrate the power of these tools we apply the results to two previously unsolved optimization problems, namely minimizing the l1 norm of a closed-loop system subject to bounds on the frequency response magnitude at a finite number of points and/or bounds on the H2 norm 相似文献
6.
7.
The deactivation characteristics of Pd/SiO2 in the selective hydrogenation of acetylene were correlated with changes in the amount of the C4 species produced. The amounts of butenes produced changed in parallel with the catalyst activity, indicating that the rate limiting step for butene production was the same as that for acetylene hydrogenation. On the other hand, the amount of 1,3-butadiene produced changed, showing a maximum with catalyst deactivation because 1,3-butadiene is an intermediate in the sequential reaction process which involves both the production and consumption of 1,3-butadiene. This was verified by a simultaneous TG/reaction experiment showing that 1,3-butadiene was a precursor of green oil. The catalyst showed a self-regenerative behavior in its activity and the amounts of C4 species produced during the early stage of deactivation because two opposite factors, which contributed to either the lowering or the promotion of activity, were involved in the process. A specific type of polymer species, produced during the initial period of deactivation, is proposed to be responsible for the promotion of catalyst activity. 相似文献
8.
R Albrecht TC Awes C Baktash P Beckmann F Berger R Bock G Claesson G Clewing L Dragon A Eklund RL Ferguson A Franz S Garpman R Glasow HA Gustafsson HH Gutbrod J Idh P Jacobs K Kampert BW Kolb P Kristiansson IY Lee H Loehner I Lund FE Obenshain A Oskarsson I Otterlund T Peitzmann S Persson F Plasil AM Poskanzer M Purschke H Ritter S Saini R Santo HR Schmidt T Siemiarczuk SP Sorensen E Stenlund ML Tincknell GR Young 《Canadian Metallurgical Quarterly》1991,44(6):2736-2752
9.
10.
Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO2 for NO reduction by NH3 was examined in a fixed-bed flow reactor. The deactivation of the catalyst was strongly dependent on reaction temperature. At high reaction temperatures over 300°C, the catalyst did not lose its initial activity up to 50 h of operation, regardless of SO2 feed concentration from 500 to 20,000 ppm. However, at low reaction temperatures near 250°C, apparent deactivation did occur. Changes in the physicochemical properties such as surface area and sulfur content of deactivated catalyst well correlated with catalyst activity, depending upon reaction temperatures. The deactivation was due to pore blocking and/or filling by deactivating agents, which plugged and/or filled the pores of catalyst. The deactivating agents deposited on the catalyst surface were presumed to be (NH4)2SO4 and/or (NH4)HSO4 from the results of TGA and ion-chromatography measurement. 相似文献