全文获取类型
收费全文 | 1416篇 |
免费 | 23篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 53篇 |
化学工业 | 233篇 |
金属工艺 | 33篇 |
机械仪表 | 13篇 |
建筑科学 | 16篇 |
能源动力 | 27篇 |
轻工业 | 119篇 |
水利工程 | 3篇 |
石油天然气 | 2篇 |
无线电 | 190篇 |
一般工业技术 | 218篇 |
冶金工业 | 394篇 |
原子能技术 | 41篇 |
自动化技术 | 101篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 12篇 |
2019年 | 23篇 |
2018年 | 22篇 |
2017年 | 15篇 |
2016年 | 14篇 |
2015年 | 9篇 |
2014年 | 19篇 |
2013年 | 41篇 |
2012年 | 23篇 |
2011年 | 57篇 |
2010年 | 29篇 |
2009年 | 49篇 |
2008年 | 45篇 |
2007年 | 35篇 |
2006年 | 36篇 |
2005年 | 32篇 |
2004年 | 43篇 |
2003年 | 43篇 |
2002年 | 37篇 |
2001年 | 34篇 |
2000年 | 35篇 |
1999年 | 53篇 |
1998年 | 162篇 |
1997年 | 100篇 |
1996年 | 80篇 |
1995年 | 56篇 |
1994年 | 36篇 |
1993年 | 33篇 |
1992年 | 33篇 |
1991年 | 26篇 |
1990年 | 22篇 |
1989年 | 24篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1964年 | 3篇 |
排序方式: 共有1443条查询结果,搜索用时 15 毫秒
61.
Kondo A Kohda J Endo Y Shiromizu T Kurokawa Y Nishihara K Yanagi H Yura T Fukuda H 《Journal of Bioscience and Bioengineering》2000,90(6):600-606
Coexpression of two classes of folding accessory proteins, molecular chaperones and foldases, can be expected to improve the productivity of soluble and active recombinant proteins. In this study, horseradish peroxidase (HRP), which has four disulfide bonds, was selected as a model enzyme and overexpressed in Escherichia coli. The effects of coexpression of a series of folding accessory proteins (DnaK, DnaJ, GrpE, GroEL/ES, trigger factor (TF), DsbA, DsbB, DsbC, DsbD, and thioredoxin (Trx)) on the productivity of active HRP in E. coli were examined. Active HRP was produced by very mild induction with 1 microM isopropyl-beta-D-thiogalactopyranoside (IPTG) at 37 degrees C, whereas the amount of active HRP produced by the induction with 1 mM IPTG was negligibly small. Active HRP production was increased significantly by coexpression of DsbA-DsbB (DsbAB) or DsbC-DsbD (DsbCD), while coexpression of molecular chaperones did not improve active HRP production. The growth of E. coli cells was inhibited significantly by the induction with 1 mM IPTG in a HRP single expression system. In contrast, when HRP was coexpressed with DsbCD, the growth inhibition of E. coli was not observed. Therefore, coexpression of Dsb proteins improves both the cell growth and the productivity of HRP. 相似文献
62.
Sekiguchi K. Seki Y. Okitani N. Fukuda M. Critchley S. Habib W.G. Hartman D. Shaw K. 《Industry Applications, IEEE Transactions on》1996,32(3):608-616
The new coupled pickle line and cold mill (CPCM) has been processing steel since December 1991 at Dofasco Inc. in Hamilton, Ontario, Canada. This mill rolls both sheet and tin plate. The work rolls for the last stand are often textured by grit blasting to roll “matte” finished strip. A new computer-targeted control system was developed for the roll speeds and gaps, specifically for matte rolling. The new set-up system uses Stone's model, which is more appropriate for the limited reductions evident with the rougher rolls. Conventional automatic gauge control (AGC) systems using thickness measurements after the last stand are limited in performance by the effect of long transport delays. These limitations are particularly critical during mill acceleration and deceleration. The use of a thickness gauge before the stand with matte rolls allows the development of AGC systems using shorter control loops for final gauge control. The AGC system uses a Smith predictor for transport lag, (phase shift), and compensation. The combination of the shorter AGC loop and the Smith predictor allows higher gains to be used in the control system. This set-up and control system has contributed to Dofasco's position as a market leader in thickness performance 相似文献
63.
T. Okano J. Tanabe M. Fukuda M. Tanaka 《Journal of the American Oil Chemists' Society》1992,69(1):44-46
The surface-active properties and emulsification ability of sodium α-sulfonated fatty acid esters, CmH2m+1CH-(SO3Na)COOCnH2n+1, were studied as a function of the hydrophobic alkyl chainlength in the fatty acid (m=8−16) and the alcohol (n=8−18). As
a result, it was discovered that sodium α-sulfonated fatty acid esters have a structural effect on the Krafft point different
from that of amphiphiles with short alkyl chains. Moreover, some of the α-sulfonated fatty acid esters have quite low interfacial
tensions, as well as non-foaming properties, which depend upon the total (m+n) number of carbon atoms in the alkyl chains. 相似文献
64.
65.
Kakui M. Kato T. Kashiwada T. Nakazato K. Fukuda C. Onishi M. Nishimura M. 《Electronics letters》1995,31(1):51-52
Based on system optimisation through theoretical model simulations, 2.4 Gbit/s repeaterless transmission over 306 km nondispersion-shifted fibre has been demonstrated with no power penalty, using a directly modulated DFB laser with a bulk active layer and dispersion-compensating fibres 相似文献
66.
It is experimentally demonstrated that the increase in residual spectral linewidth during device degradation is due to an increase in 1/f noise in a multiple quantum-well (MQW) distributed-feedback (DFB) laser. The origin of 1/f noise and its influence on device characteristics is discussed and clarified by observing the degradation behavior of the spectral linewidth 相似文献
67.
CONTEXT: Physical activity and fitness are believed to reduce premature mortality, but whether genetic factors modify this effect is not known. OBJECTIVE: To investigate leisure physical activity and mortality with respect to familial aggregation of health habits during childhood and factors that may enable some individuals to achieve higher levels of fitness. DESIGN: Prospective twin cohort study. SETTING: Finland. SUBJECTS: In 1975, at baseline, 7925 healthy men and 7977 healthy women of the Finnish Twin Cohort aged 25 to 64 years who responded to a questionnaire on physical activity habits and known predictors of mortality. Those who reported exercising at least 6 times per month with an intensity corresponding to at least vigorous walking for a mean duration of 30 minutes were classified as conditioning exercisers, those who reported no leisure physical activity were classified as sedentary, and other subjects were classified as occasional exercisers. MAIN OUTCOME MEASURES: All-cause mortality and discordant deaths among same-sex twin pairs from 1977 through 1994. RESULTS: Among the entire cohort, 1253 subjects died. The hazard ratio for death adjusted for age and sex was 0.71 (95% confidence interval [CI], 0.62-0.81) in occasional exercisers and 0.57 (95% CI, 0.45-0.74) in conditioning exercisers, compared with those who were sedentary (Pfor trend <.001). Among the twin pairs who were healthy at baseline and discordant for death (n=434), the odds ratio for death was 0.66 (95% CI, 0.46-0.94) in occasional exercisers and 0.44 (95% CI, 0.23-0.83) in conditioning exercisers compared with those who were sedentary (P for trend, .005). The beneficial effect of physical activity remained after controlling for other predictors of mortality. CONCLUSION: Leisure-time physical activity is associated with reduced mortality, even after genetic and other familial factors are taken into account. 相似文献
68.
The modal and relative intensity noise of InGaAsP/InP lasers are monitored before and after degradation. These noise levels under VHF modulation are scarely affected by laser degradation and are almost determined by VHF modulation, although the noise levels under DC bias increase after degradation. 相似文献
69.
70.
Yamaji H Sakai K Joho T Izumoto E Fukuda H 《Journal of Bioscience and Bioengineering》2004,98(6):487-489
When recombinant Chinese hamster ovary cells were treated with pertussis toxin or genistein, not only lysophosphatidic acid (LPA) but also phosphatidic acid (PA) failed to stimulate progression through the cell cycle in serum-free culture, suggesting that PA and LPA induce cell growth through the same signal transduction pathway. Cell cycle analysis also indicates that cell growth promoted by PA results in enhanced protein production. 相似文献