全文获取类型
收费全文 | 23478篇 |
免费 | 687篇 |
国内免费 | 114篇 |
专业分类
电工技术 | 1619篇 |
综合类 | 150篇 |
化学工业 | 4487篇 |
金属工艺 | 609篇 |
机械仪表 | 440篇 |
建筑科学 | 978篇 |
矿业工程 | 116篇 |
能源动力 | 698篇 |
轻工业 | 1463篇 |
水利工程 | 364篇 |
石油天然气 | 220篇 |
武器工业 | 4篇 |
无线电 | 1581篇 |
一般工业技术 | 3505篇 |
冶金工业 | 4646篇 |
原子能技术 | 194篇 |
自动化技术 | 3205篇 |
出版年
2022年 | 127篇 |
2021年 | 250篇 |
2020年 | 203篇 |
2019年 | 281篇 |
2018年 | 308篇 |
2017年 | 365篇 |
2016年 | 376篇 |
2015年 | 306篇 |
2014年 | 490篇 |
2013年 | 1305篇 |
2012年 | 803篇 |
2011年 | 1162篇 |
2010年 | 841篇 |
2009年 | 847篇 |
2008年 | 947篇 |
2007年 | 1032篇 |
2006年 | 835篇 |
2005年 | 813篇 |
2004年 | 1187篇 |
2003年 | 794篇 |
2002年 | 741篇 |
2001年 | 500篇 |
2000年 | 440篇 |
1999年 | 594篇 |
1998年 | 559篇 |
1997年 | 482篇 |
1996年 | 422篇 |
1995年 | 397篇 |
1994年 | 336篇 |
1993年 | 428篇 |
1992年 | 360篇 |
1991年 | 236篇 |
1990年 | 282篇 |
1989年 | 290篇 |
1988年 | 270篇 |
1987年 | 263篇 |
1986年 | 290篇 |
1985年 | 302篇 |
1984年 | 297篇 |
1983年 | 292篇 |
1982年 | 235篇 |
1981年 | 266篇 |
1980年 | 257篇 |
1979年 | 254篇 |
1978年 | 228篇 |
1977年 | 233篇 |
1976年 | 209篇 |
1975年 | 198篇 |
1974年 | 176篇 |
1973年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Kinetics of the reaction between bis(4-isocyanatocyclohexyl)methane, H-MDI, and n-butanol was studied in toluene at 100°C. Effects of various catalysts, such as Hg(CH3COO)2, Zn(CH3COO)2 · 2H2O, SnCl4 · 5H2O, and dibutyltindilaurate on the reaction rate and kinetics were also investigated. Reactions were followed by determining the unreacted isocyanate as a function of reaction time, using the standard dibutylamine back titration method. All catalysts seem to be very effective in increasing of the rate of the reaction compared to the uncatalyzed system. Depending on the initial stoichiometric ratio of (NCO) and (OH) and the concentration of the catalyst used, it seems possible to have preferential catalysis of the primary reaction between (NCO) and (OH) over the side reactions. 相似文献
42.
Graduates of clinical training programs were surveyed to determine the degree to which they have found various graduate school experiences useful in their professional work. Samples of academic clinical psychologists and practicing clinical psychologists reported time allocation and preference for various professional activities, perceived usefulness of various theoretical orientations, and the influence on their current professional work of 19 different graduate training topics. Results suggest that where differences exist, academic clinical psychologists are generally more satisfied with Boulder-model-inspired scientific training than are clinical practitioners. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
43.
44.
This letter presents some further results on the local stability in equilibrium for Internet congestion control algorithm proposed by Low et al., (IEEE/ACM Transactions on Networking, 1999). The propagation delay d(t) is assumed to be time-varying and have maximum and minimum delay bounds (i.e., d/sub m//spl les/d(t)/spl les/d/sub M/), which is more general than the assumption (0相似文献
45.
Butler Emily A.; Egloff Boris; Wlhelm Frank H.; Smith Nancy C.; Erickson Elizabeth A.; Gross James J. 《Canadian Metallurgical Quarterly》2003,3(1):48
At times, people keep their emotions from showing during social interactions. The authors' analysis suggests that such expressive suppression should disrupt communication and increase stress levels. To test this hypothesis, the authors conducted 2 studies in which unacquainted pairs of women discussed an upsetting topic. In Study 1, one member of each pair was randomly assigned to (a) suppress her emotional behavior, (b) respond naturally, or (c) cognitively reappraise in a way that reduced emotional responding. Suppression alone disrupted communication and magnified blood pressure responses in the suppressors' partners. In Study 2, suppression had a negative impact on the regulators' emotional experience and increased blood pressure in both regulators and their partners. Suppression also reduced rapport and inhibited relationship formation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
46.
47.
Digant Gupta Christopher G Lis Sadie L Dahlk Jessica King Pankaj G Vashi James F Grutsch Carolyn A Lammersfeld 《Nutrition journal》2008,7(1):19
Background
Bioelectrical Impedance (BIA) derived phase angle is increasingly being used as an objective indicator of nutritional status in advanced cancer. Subjective Global Assessment (SGA) is a subjective method of nutritional status. The objective of this study was to investigate the association between BIA derived phase angle and SGA in advanced colorectal cancer. 相似文献48.
49.
Interfacial hybridization kinetics of oligonucleotides immobilized onto fused silica surfaces 总被引:3,自引:0,他引:3
Jiang Zeng Amer Almadidy James Watterson Ulrich J. Krull 《Sensors and actuators. B, Chemical》2003,90(1-3):68-75
Fused silica optical fibers have been used in an intrinsic mode optical configuration as biosensors for fluorescence based detection of hybridization of nucleic acids. In this work, the kinetics of hybridization of single-stranded oligonucleotides that were covalently immobilized were studied. The probe DNA was dT20, and the target was Fluorescein-labeled non-complementary (dT20) or complementary (dA20) oligonucleotide. Chronofluorimetric monitoring of the adsorption and hybridization processes was used to investigate oligonucleotide films of different density, in different salt concentrations, at temperatures of 25 and 40 °C, with the concentration of the target DNA being 0.005–0.1 μM. Mathematical models based on first- and second-order Langmuir adsorption have been examined to describe both the adsorption and the hybridization processes. Experimental data were processed using the models, and the hybridization kinetics were calculated. Hybridization kinetics on these optical fiber DNA sensors was found to be up to three orders faster than results presented for a number of other experiments using different immobilization chemistries. 相似文献
50.
The technique of analytical pyrolysis has been used to characterize 40 similar mid-rank western Kentucky coals of widely differing ASTM Gieseler plasticity. Certain pyrolysis/g.c. variables were shown to correlate well with both ASTM Gieseler and isothermal plasticity. Highly plastic coals were shown to exhibit certain characteristic peaks in the 450 °C pyrogram which were absent in the pyrogram of the non-plastic coals. Two coals, representing the two extremes in plasticity, were selected for further study. After extraction with solvents such as DMF the characteristic peaks were absent in the 450 °C pyrogram of the extraction residue of the highly plastic coal. These peaks were also shown to decrease with increasing severity of air oxidation of the plastic coal. This technique appears to be a useful tool for the analysis of mid-rank plastic coals and supports the view that the substances contained in the bitumen fraction of these coals are involved in the development of the plastic state. 相似文献