全文获取类型
收费全文 | 671篇 |
免费 | 38篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 15篇 |
综合类 | 4篇 |
化学工业 | 125篇 |
金属工艺 | 8篇 |
机械仪表 | 7篇 |
建筑科学 | 56篇 |
能源动力 | 8篇 |
轻工业 | 83篇 |
水利工程 | 4篇 |
无线电 | 62篇 |
一般工业技术 | 123篇 |
冶金工业 | 63篇 |
原子能技术 | 2篇 |
自动化技术 | 154篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 28篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 15篇 |
2015年 | 22篇 |
2014年 | 21篇 |
2013年 | 42篇 |
2012年 | 33篇 |
2011年 | 40篇 |
2010年 | 25篇 |
2009年 | 32篇 |
2008年 | 35篇 |
2007年 | 30篇 |
2006年 | 19篇 |
2005年 | 35篇 |
2004年 | 25篇 |
2003年 | 14篇 |
2002年 | 19篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 21篇 |
1996年 | 22篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 4篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
排序方式: 共有714条查询结果,搜索用时 15 毫秒
91.
Algorithms for calculating the emitter hole and electron currents in the case of an n+n? epitaxial emitter have been published by Yu [2] and Rofail et al. [3]. Both algorithms are restricted to a small ratio of hole to electron current whereas Yu's algorithm is further restricted by the assumption of a constant electric field in the epilayer.In the present paper an algorithm is presented in which both restrictions have been removed and which is valid from low through high injection. The assumption of quasineutrality in the epilayer, which is used in the present algorithm, is veryfied using Adlers criterium [4]. Calculation results are presented for a structure treated by Poorter [1] and a comparison is made with his results. 相似文献
92.
Henk F. J. Hendriks Pieter J. A. M. Brekelmans Rien Buytenhek Adriaan Brouwer A. Margreet de Leeuw Dick L. Knook 《Lipids》1987,22(4):266-273
The neutral lipid and phospholipid compositions of purified sinusoidal (fat-storing, endothelial and Kupffer) cells, parenchymal
cells and liver homogenates were determined by thin layer chromatography. In addition, the retinoid content of the same purified
cell populations was determined by high performance liquid chromatography. From each cell type, both a lipid droplet fraction
and a pellet fraction (containing the majority of the remaining cell organelles) were prepared by differential centrifugation.
Electron microscopic analysis showed that lipid droplets isolated from fat-storing cells were larger (up to 8 μm) than those
isolated from parenchymal cells (up to 2.5 μm). Moreover, the parenchymal lipid droplets seemed to be surrounded by a membranous
structure, while the fat-storing lipid droplets seemed not to be. Both fat-storing and parenchymal cells contained high concentrations
of neutral lipids, 57.9 μg and 71.0 μg/106 cells, respectively, while endothelial and Kupffer cells contained only 8.6 μg and 13.8 μg/106 cells of neutral lipids, respectively. Sixty-five percent of fat-storing cell lipid droplet fractions comprised esters of
retinol and cholesterol. This combined ester fraction contained mainly retinyl esters. In addition, considerable quantities
(20%) of triglycerides were present. Parenchymal cell lipid droplet fractions comprised triglycerides (62%) and cholesteryl
esters (up to 30%). The pellet fractions prepared from all four cell types consisted mainly of cholesterol (41–67%) and free
fatt acids (20–28%). The phospholipid content was much higher in parenchymal cells than in the sinusoidal liver cell types.
The relative proportions of the four major phospholipid classes were comparable in all liver cell types analyzed. It is concluded
that parenchymal cell lipid droplets comprised mainly triglycerides and cholesteryl esters, which is in agreement with the
function of parenchymal cells in lipid metabolism. Fat-storing cell lipid droplets consisted of retinyl esters and triglycerides,
which correlates well with their function in retionid storage and metabolism. 相似文献
93.
94.
Summary Conventional time-temperature (t-T) superposition appears to be inappropriate to the viscoelastic behaviour of amorphous, peroxide cured EPDM networks. A phenomenological approach is presented that reduces these permanent elastomers to thermorheologically simple materials. Although the origin of the anomalous behaviour observed is not yet completely understood, it is attributed to an unusual variation of the equilibrium modulus with temperature.Presented at the 7th IUPAC Discussion Conference Polymer Networks, Karlovy Vary, CSSR, September 15–19, 1980 相似文献
95.
96.
de Boer AR Alcaide-Hidalgo JM Krabbe JG Kolkman J van Emde Boas CN Niessen WM Lingeman H Irth H 《Analytical chemistry》2005,77(24):7894-7900
The potential of high-temperature liquid chromatography (HTLC) was investigated in an on-line combination with a screening system for bioactive compounds against the enzyme cathepsin B. Samples were separated by HTLC and subsequently analyzed by an on-line continuous-flow enzymatic assay. Detection was performed by electrospray ionization mass spectrometry, revealing both the bioactivity and the molecular mass of the bioactive compounds. Compared to conventional reversed-phase liquid chromatography, the amount of methanol necessary for separation could be decreased to only 10%, which improved the compatibility of LC with a biochemical assay. Sufficient preheating of the mobile phase prior to the separation and postcolumn cooling to prevent deactivation of the enzyme, even at column temperatures as high as 208 degrees C, was achieved as indicated by the reliable peak shapes obtained. The sensitivity was comparable with previously described systems operating at ambient temperatures as similar IC50 values were obtained. Exposing the inhibitors to high temperatures did not lead to thermal decomposition. The separation of inhibitors and the subsequent biochemical assay was performed either isothermally at various temperatures or by applying various temperature gradients as well as at various flow rates. The results obtained clearly show the compatibility of HTLC with an enzymatic screening assay. 相似文献
97.
Wil?A.?M.?van Loon Jozef?P.?H.?LinssenEmail author Aagje?Legger Ruud?M.?H.?Heijmans Henk?C.?van Deventer Maurits?J.?M.?Burgering Bas?L.?van Drooge Alphons?G.?J.?Voragen 《European Food Research and Technology》2005,221(6):779-786
A new, energy efficient production process for French fries was developed and evaluated. Superheated steam (SHS) was used
for evaporation of water instead of pre-drying with air and par-frying with oil. The product was frozen by vacuum cooling.
Unfortunately, with this process it was not possible to reach the quality of conventional French fries. Sensory analysis indicated
that the main quality defect was a tough crust with a fatty appearance. Confocal Scanning Laser Microscopy showed that this
was caused by skin formation on the surface during both SHS drying and vacuum cooling. A frying step was necessary to obtain
a porous crust. A satisfactory product quality was feasible after drying with SHS instead of air. Due to the concessions made
for the product quality, the final energy reduction was limited. Nevertheless, this study has gained more insight into how
processing affects potato tissue on micro-scale and it has shown that a porous structure is essential for good quality French
fries. 相似文献
98.
Ground surface conditions on construction sites have an important influence on the health and safety of workers and their productivity. The development of an expert-based "working conditions evaluation" system is described, intended to assist site managers in recognising unsatisfactory ground conditions and remedying these. The system was evaluated in the period 2002-2003. The evaluation shows that companies recognize poor soil/ground conditions as problematic, but are not aware of the specific physical workload hazards. The developed methods allow assessment of the ground surface quality and selection of appropriate measures for improvement. However, barriers exist at present to wide implementation of the system across the industry. Most significant of these is that responsibility for a site's condition is not clearly located within contracting arrangements, nor is it a topic of serious negotiation. 相似文献
99.
The objective of this qualitative study was to assess whether a hypothesised sequential order of behavioural change phases would be fulfilled in different groups of stakeholders involved at the start of a process to implement ergonomic [corrected] measures in bricklaying teams. The measures include trestles, bricklaying scaffolds, mast climbing work platforms [corrected] and cranes. The behavioural change phases were: (1) being aware of measures, (2) understanding measures, (3) wanting measures, (4) intention to buy or hire measures, (5) ability to use measures, (6) using measures (experience), and (7) continuing to use measures. Structured interviews were conducted to examine the change phases in two groups of stakeholders (employers/work planners (n=11) [corrected] and foremen/bricklayers (n=9) [corrected] from nine companies) thought to be relevant in the decision to adopt and use the ergonomic [corrected] measures. The results show that the fulfilled behavioural change phases differ between individual stakeholders, groups of stakeholders, companies and also between ergonomic measures. The hypothesised order of fulfilled consecutive behavioural change phases for individual stakeholders has not been confirmed by this study. The relationship between [corrected] fulfilled and unfulfilled change phases by each stakeholder (group) and actual use of each ergonomic measure requires further study, so as to improve the selection of suitable implementation strategies [corrected] 相似文献
100.
Given a nonlinear system we determine a relation at an equilibrium between controllability distributions defined for a nonlinear system and a Taylor series approximation of it. The value of such a relation is appreciated if we recall that the solvability conditions as well as the solutions to some control synthesis problems can be stated in terms of geometric concepts like controlled invariant (controllability) distributions. The relation between these distributions at the equilibrium will help us to decide when the solvability conditions of this kind of problems are equivalent for the nonlinear system and its approximation 相似文献