全文获取类型
收费全文 | 1288篇 |
免费 | 28篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 99篇 |
综合类 | 3篇 |
化学工业 | 378篇 |
金属工艺 | 28篇 |
机械仪表 | 42篇 |
建筑科学 | 15篇 |
能源动力 | 185篇 |
轻工业 | 86篇 |
石油天然气 | 1篇 |
无线电 | 83篇 |
一般工业技术 | 168篇 |
冶金工业 | 137篇 |
原子能技术 | 25篇 |
自动化技术 | 67篇 |
出版年
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 18篇 |
2020年 | 6篇 |
2019年 | 15篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 24篇 |
2015年 | 16篇 |
2014年 | 36篇 |
2013年 | 66篇 |
2012年 | 38篇 |
2011年 | 79篇 |
2010年 | 50篇 |
2009年 | 52篇 |
2008年 | 63篇 |
2007年 | 56篇 |
2006年 | 41篇 |
2005年 | 44篇 |
2004年 | 48篇 |
2003年 | 52篇 |
2002年 | 37篇 |
2001年 | 21篇 |
2000年 | 25篇 |
1999年 | 23篇 |
1998年 | 76篇 |
1997年 | 52篇 |
1996年 | 46篇 |
1995年 | 25篇 |
1994年 | 28篇 |
1993年 | 25篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有1317条查询结果,搜索用时 15 毫秒
131.
Niisoe T Harada KH Hitomi T Watanabe T Hung NN Ishikawa H Wang Z Koizumi A 《Environmental science & technology》2011,45(7):2856-2862
Environmental ecological modeling (EEM), which unifies models simulating transport of chemicals and exposure of humans to chemicals, was used to simulate long-term trends of female adult human blood lead levels (BLLs) and historical exposure to the atmospheric lead in four East Asian countries: Japan, Korea, China, and Vietnam. Anthropogenic lead emissions to the atmosphere in Vietnam were estimated from energy statistics to be 1931 t yr(-1). Calculated BLLs generally agreed with those observed in samples collected in these countries as the error factors were less than 2. The model results revealed that BLLs decreased significantly in Tokyo (by 58%) and Seoul (by 45%) in recent decades and confirmed the effects of efforts to reduce environmental lead in Japan and Korea. The model results also revealed that BLLs in Beijing did not decrease in this decade as much as in Tokyo and Seoul, despite the phasing out of leaded gasoline, and that the contribution from the atmospheric component was increasing (43% in 2009). Finally, we applied EEM to simulate BLLs of children in Hanoi. The probability of children having BLLs greater than 50 μg L(-1) was 7.5%, which was greater than those observed in developed countries. 相似文献
132.
Vincent Lijo Heuy Dong Kim Toshiaki Setoguchi Shigeru Matsuo 《Journal of Mechanical Science and Technology》2011,25(2):341-347
When sonic nozzles of significantly smaller diameter are used as standard flow meters, the critical backpressure ratio is
affected by the boundary layer at the nozzle throat. It is known that, as the flow pathway is complicated in actual valves,
the critical pressure ratio differs from the ideal value. However, the effect of the boundary layer thickness on choking criteria
is still controversial. Choking phenomenon in a sonic nozzle fitted with a straight circular pipe of variable length is investigated
numerically and the results are compared with experimental and theoretical ones. The results show that the actual critical
pressure ratio is less than the ideal value and it decreases with increase in pipe length. The effect of boundary layer thickness
on main flow Mach number is also made clear in this work. In addition, sonic conductance and pressure loss in actual viscous
flows computed are compared with the ISO 6358 standard. 相似文献
133.
Experimental study on hysteresis phenomena of shock wave structure in an over-expanded axisymmetric jet 总被引:1,自引:0,他引:1
Shigeru Matsuo Toshiaki Setoguchi Junji Nagao Miah Md. Ashraful Alam Heuy Dong Kim 《Journal of Mechanical Science and Technology》2011,25(10):2559-2565
In recent studies on two-dimensional supersonic jets, it is reported that the hysteresis phenomenon for the reflection type of shock waves in the jet flow field is occurred under the quasi-steady flow condition and this phenomenon is affected by the transitional pressure ratio between the regular reflection and Mach reflection. However, so far, there are few researches on the hysteresis phenomenon for the transition of shock waves between regular and Mach reflection in over-expanded supersonic jets and the phenomenon has not been investigated satisfactorily. Therefore, the purpose of this study is to clarify the hysteresis phenomena for the reflection type of shock wave in the over-expanded axi-symmetric supersonic jet experimentally, and to discuss the relationship between hysteresis phenomenon and rate of the change of pressure ratio with time. Furthermore, the effect of Mach number at the nozzle exit on hysteresis loop was investigated for two kinds of nozzle. 相似文献
134.
Kobayashi M Ohtsuka K Tamura Y Tomizawa S Kamijo K Iwakoshi K Kageyama Y Nagayama T Takano I 《Shokuhin eiseigaku zasshi. Journal of the Food Hygienic Society of Japan》2011,52(2):121-129
A survey of pesticide residues in 595 imported frozen products on the Tokyo market from April 1989 to March 2008 was carried out. Forty three kinds of pesticides, including organophosphorus, organochlorine, carbamate, pyrethroid and others, were detected between levels of trace (below 0.01 ppm) and 4.6 ppm from 162 samples. Chlorpyrifos, cypermethrin and omethoate were frequently detected in green vegetables (komatsuna leaf and spinach), cypermethrin and methamidophos were detected in pods and seeds (green soybean and string pea), chlorpropham (CIPC) was detected in potato, and captan and carbaryl were detected in berries (blueberry, raspberry and strawberry). The hydrophilic pesticide methamidophos was detected in flesh of lychee. Residue levels of these pesticides were calculated as between less than 0.5% and 30% of their ADI values according to the daily intake of frozen products. Therefore, these frozen products should be safe when they were eaten in customary amounts. 相似文献
135.
BACKGROUND: Fructose-sorbitol (F-S) mixtures can provoke symptoms in irritable bowel syndrome (IBS) patients, and a proportion of IBS patients also have enteric hypersensitivity to distension. We hypothesized, therefore, that sugar malabsorption and fermentation to produce hydrogen gas may provoke symptoms to a greater extent in IBS patients hypersensitive to distension than in those patients without such hypersensitivity. Our aims were therefore to compare, in IBS patients, symptoms and breath hydrogen responses after F-S, on the basis of jejunal sensitivity and jejunal motor function. METHODS: Fifteen female IBS patients (44 +/- 15 years) underwent, on separate occasions, 3-h breath hydrogen analyses after ingesting 10 g lactulose and 25 g fructose with 5 g sorbitol. Jejunal sensitivity and motor function were determined by balloon distension and 24-h manometry studies, respectively. Cumulative symptom scores and breath hydrogen production were analysed on the basis of the presence or absence of jejunal hypersensitivity and dysmotility. RESULTS: Four and seven patients had jejunal hypersensitivity for initial perception and pain, respectively. Eleven, nine, and nine patients had jejunal dysmotility for fasting phase 3, phase 2, and fed motor activity, respectively. Of the patients with symptom provocation after F-S (n = 8 within 3 h, n = 12 within 12 h) or with F-S malabsorption (n = 10), the relative proportion did not differ on the basis of the presence or absence of jejunal hypersensitivity or of motor dysfunction. Symptom scores and hydrogen production also were not different in these subgroups. CONCLUSIONS: Although carbohydrate malabsorption can provoke symptoms in some IBS patients, there is no consistent association between such a phenomenon and the presence of either jejunal hypersensitivity or dysmotility. 相似文献
136.
Koike H. Matsuoka F. Ohtsuka H. Kakumu M. 《Semiconductor Manufacturing, IEEE Transactions on》1996,9(4):489-494
Process simplification and turnaround time reduction for deep submicrometer CMOS fabrication are discussed. Process step analysis is carried out for standard 1Poly/1Metal CMOS structure, and consequently, both isolation and gate formation processes are extracted as items for process simplification. A combination of shallow trench isolation with retrograde well structure and single mask step well/gate doping technique is proposed for deep submicrometer CMOS fabrication. This simplified CMOS process can achieve a reduction of five mask steps and eliminates both well drive-in annealing and field oxidation without performance deterioration. As a result, a 10% process step reduction and a 20% manufacturing turnaround time reduction have been realized in comparison to the standard 1Poly/1Metal CMOS process with LOCOS isolation 相似文献
137.
M Kai T Todo M Wada H Ryo C Masutani H Kobayashi H Morioka E Ohtsuka F Hanaoka K Sakaguchi 《Canadian Metallurgical Quarterly》1998,1397(2):180-188
Airborne substances can stimulate both the olfactory and the trigeminal nerve in the nose, giving rise to odor and pungent (irritant) sensations, respectively. Nose, eye, and throat irritation constitute common adverse effects in indoor environments. We measured odor and nasal pungency thresholds for homologous aliphatic aldehydes (butanal through octanal) and carboxylic acids (formic, acetic, butanoic, hexanoic, and octanoic). Nasal pungency was measured in subjects lacking olfaction (i.e., anosmics) to avoid odor biases. Similar to other homologous series, odor and pungency thresholds declined (i.e., sensory potency increased) with increasing carbon chain length. A previously derived quantitative structure-activity relationship (QSAR) based on solvation energies predicted all nasal pungency thresholds, except for acetic acid, implying that a key step in the mechanism for threshold pungency involves transfer of the inhaled substance from the vapor phase to the receptive biological phase. In contrast, acetic acid - with a pungency threshold lower than predicted - is likely to produce threshold pungency through direct chemical reaction with the mucosa. Both in the series studied here and in those studied previously, we reach a member at longer chain-lengths beyond which pungency fades. The evidence suggests a biological cut-off, presumably based upon molecular size, across the various series. 相似文献
138.
Kei Ohtsuka Makoto Nishida Yasuo Morioka Kenji Yachida 《Electrical Engineering in Japan》1996,116(5):61-74
A decentralized control system is studied for stabilizing multimachine power systems. A longitudinal power system with three areas, each having one machine, is considered in this study. A decentralized control design method is proposed, which is based on the optimal regulator theory. First a centralized control system is designed without any consideration on whether state variables are all available or not. Second a pseudo-decentralized control system is designed by omitting control gains corresponding to state variables which give hardly any effects on the power system stability. It is found that only one variable of phase angle of each machine is absolutely necessary for the pseudo-decentralized control system. This leads to an idea based on power system engineering, that is to say, new variables of tieline power flow are introduced in the decentralized control system design to substitute for the phase angle of each machine. Thus a decentralized control system for power system stability can be designed using the new variables of tieline power flow. It is demonstrated from simulation studies that the decentralized control system improves even longitudinal power system stability as well as the centralized control system. 相似文献
139.
Toshiaki Rokunohe Yoshitaka Yagihashi Fumihiro Endo Kenji Aoyagi Hitoshi Saitoh Takashi Oomori 《Electrical Engineering in Japan》2006,157(4):13-23
SF6 gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas‐insulated switchgear (GIS). However, use of SF6 gas has become regulated under agreements set at the 1997 COP3. Thus, investigation and development for GIS with a lower amount of SF6 gas are being carried out worldwide. Presently, SF6‐free GIS has been commercialized for the 24‐kV class. Air or N2 gas is used as the insulation gas for this GIS. On the other hand, SF6‐free GIS has not been commercialized for the 72‐kV‐class GIS. The dielectric strengths of air and N2 gas are approximately one‐third that of SF6 gas. To enhance the insulation performance of air and N2 we have investigated a hybrid gas insulation system which has the combined features of providing an insulation coating and suitable insulation gas. We have developed the world's first 72‐kV SF6‐free GIS. This paper deals with key technologies for SF6‐free GIS, such as the hybrid insulation structure, a bellows for the high‐pressure vacuum circuit breaker, a newly designed disconnector and spacer, and prevention of particle levitation. Test results of the 72‐kV high‐pressure air‐insulated GIS with the vacuum circuit breaker are described. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 13–23, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20451 相似文献
140.
This paper proposes a newly developed, highly precise cross-polarization interference canceller (XPIC), utilizing digitalized transversal filters. Performance of the digitalized XPIC is solely determined by quantization and tap numbers and is not affected by any circuit imperfection. Moreover, it can be universally applied to different bit rates and various modulation schemes. Performance of the XPIC is analytically estimated for various modulation schemes and various interference conditions. Then, the digitalized XPIC is realized and applied to a 12.5 MB 256 QAM digital radio system. Experimental results have closely conformed with theoretical estimations and it is confirmed that the XPIC is a powerful countermeasure against multipath fading for a future digital radio. 相似文献