全文获取类型
收费全文 | 3105篇 |
免费 | 51篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 111篇 |
综合类 | 6篇 |
化学工业 | 515篇 |
金属工艺 | 159篇 |
机械仪表 | 53篇 |
建筑科学 | 36篇 |
矿业工程 | 5篇 |
能源动力 | 72篇 |
轻工业 | 146篇 |
水利工程 | 15篇 |
石油天然气 | 1篇 |
无线电 | 410篇 |
一般工业技术 | 519篇 |
冶金工业 | 854篇 |
原子能技术 | 63篇 |
自动化技术 | 199篇 |
出版年
2023年 | 8篇 |
2022年 | 8篇 |
2021年 | 36篇 |
2020年 | 14篇 |
2019年 | 27篇 |
2018年 | 26篇 |
2017年 | 23篇 |
2016年 | 29篇 |
2015年 | 23篇 |
2014年 | 47篇 |
2013年 | 123篇 |
2012年 | 87篇 |
2011年 | 132篇 |
2010年 | 102篇 |
2009年 | 122篇 |
2008年 | 131篇 |
2007年 | 103篇 |
2006年 | 83篇 |
2005年 | 77篇 |
2004年 | 83篇 |
2003年 | 86篇 |
2002年 | 90篇 |
2001年 | 67篇 |
2000年 | 53篇 |
1999年 | 62篇 |
1998年 | 332篇 |
1997年 | 180篇 |
1996年 | 169篇 |
1995年 | 95篇 |
1994年 | 89篇 |
1993年 | 91篇 |
1992年 | 44篇 |
1991年 | 38篇 |
1990年 | 33篇 |
1989年 | 44篇 |
1988年 | 47篇 |
1987年 | 40篇 |
1986年 | 30篇 |
1985年 | 33篇 |
1984年 | 29篇 |
1983年 | 28篇 |
1982年 | 28篇 |
1981年 | 26篇 |
1980年 | 35篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1976年 | 33篇 |
1975年 | 8篇 |
1973年 | 4篇 |
排序方式: 共有3164条查询结果,搜索用时 15 毫秒
21.
H Ishiwata T Inoue K Yoshihira 《Zeitschrift für Lebensmittel-Untersuchung und -Forschung》1987,185(1):39-42
The content of tetramethylsuccinonitrile (TMSN), the main decomposition product of 2,2'-azobis-isobutyronitrile, in polyvinyl chloride (PVC) products used for food packaging, were examined as well as food-simulating solvents. The TMSN concentration in 17 PVC products ranged from below the detection limit, 0.05 mg/kg, up to 523 mg/kg. The release of TMSN from two PVC products into five kinds of food-simulating solvents at 60 degrees C for 30 min was observed, except for 1 +/- 1 micrograms/kg of TMSN in n-heptane from a PVC bottle containing 523 +/- 30.4 mg/kg of TMSN. The detection limit of TMSN in the food-simulating solvents was 1 micrograms/kg. When pieces of the bottle were stored in olive oil at 40 degrees C for 120 days, 5 +/- 1 micrograms/kg of TMSN was detected in the oil. The release of TMSN from the pieces of the bottle into olive oil between 80 and 140 degrees C depended on the formula ln y = 0.08786x-5.696, r = 0.9927, where y is the concentration (microgram/kg) of TMSN in olive oil, x is the temperature (degrees C), and r is the correlation coefficient. 相似文献
22.
For the purpose of remediation of soils polluted by heavy metals, the use of some strong synthetic chelating agents such as ethylenediaminetetraacetic acid (EDTA) has been proposed. However, EDTA would not be considered as the preferential choice for the remediation of soil polluted with heavy metals like copper because of its nonbiodegradability and permanent residence in the natural environment. In the present work, some novel environmentally benign chelating agents, glucosamine hydrochloride, chito-oligosaccharide and
-asparaginic-N,N-diacetic acid (ASDA) were screened to find alternatives to EDTA by investigating the elution of copper from vermiculite with these reagents and comparing their effectiveness with EDTA. The effects of suspension contact time, reagent concentration and equilibrium pH of the solution on the removal of copper were examined. A stoichiometric amount of EDTA can quantitatively remove copper in both acidic and neutral conditions. Chito-oligosaccharide was a slightly less-effective reagent under acidic conditions compared to EDTA, and an amount well in excess of stoichiometry is required to achieve the maximum removal of copper from vermiculite. Glucosamine hydrochloride shows a relatively weak ability for the liberation of copper. The elution behavior of ASDA was equivalent to EDTA in acidic and neutral media. It was concluded that ASDA is the best substitute for EDTA because of its similar high complexing ability and superior biodegradability. 相似文献
23.
Titanium oxides were reduced to metallic titanium using the liquid calcium floating on the molten CaCl2. A part of Ca dissolved into CaCl2 and reacted with TiO2 settled below CaCl2. The by-product CaO also dissolved by about 20 mol pct into CaCl2, which was effective in reducing the oxygen concentration in the obtained Ti particles. The compositional region in the Ca-CaCl2-CaO system was examined for the less oxygen contamination in Ti and the better handling in leaching. A large amount of the
residual calcium oxidized the titanium powder in leaching. The metallic Ti powder less than 1000 mass ppm oxygen could be
obtained only for 3.6 ks using 5 to 7 mol pct Ca-CaCl2 at 1173 K. The powder was slightly sintered like sponge, and contained approximately 1500 ppm Ca. The anatase phae, the intermediate
product in the refining process of TiO2, could be also supplied as raw material as well as rutile. 相似文献
24.
State- and time-dependent routing in the NTT network 总被引:1,自引:0,他引:1
The purpose of state- and time-dependent routing (STR) is to achieve high performance despite unpredictable real-time traffic fluctuations, with minimum changes to existing switching software and operations systems. STR uses an appropriate combination of the two kinds of control, centralized and distributed. The article gives an overview of STR and its advanced call-level routing, describes the current STR network and the performance of STR with two examples from the NTT network, and addresses a dimensioning method for STR 相似文献
25.
Brushless three-phase synchronous motor involving a rotating ac exciter on the same shaft as the motor and with the windings linked through a shaft-mounted rectifier is widely used as medium and large capacity machines. However, the motor needs to fit with damping windings for self-starting outside of the field winding in the rotor and needs to equip discharge resistance with complex electronic device to dispose of electromagnetic force induced in the field winding at starting. Therefore, the rotor structure is very complex, and there are disadvantages, especially for the robust and highly reliable motor that is desired. To solve the problem found in traditional motors, the authors proposed a brushless three-phase synchronous induction motor with two stators and one wound rotor. This problem is solved because the proposed motor is of two-stators structure: the rotor winding operates as a secondary winding of induction motor at starting and as the field winding at synchronous operation. The motor can self-start as a wound-rotor induction motor without external secondary resistance. Therefore, discharge resistance is not necessary; the starting equipment is very simple and the rotor structure is robust. It is possible to start with high torque. In this paper, the basic constitution of the proposed motor and the principles of operation are described in detail. The experimental results at starting and pulling into synchronism are shown for confirming the principles of operation and the experimental and numerical results of the starting characteristics. The load ones and the generating ones are shown and then the practical use of the proposed motor is confirmed. 相似文献
26.
Y Asano Y Tokunaga Y Inoue H Gondo T Miyamoto Y Niho 《Canadian Metallurgical Quarterly》1998,39(6):460-462
We report on a case of adenovirus hemorrhagi cystitis that developed in a 49-year-old woman during intensive chemotherapy for adult T-cell leukemia. Although rapid etiologic diagnosis is essential for the effective management of viral hemorrhagic cystitis, the isolation of adenovirus from urine is often too time-cousuming. We detected the adenovirus antigen in the patient's urine using an Adenoclone direct sandwich ELISA kit (Cambridge Bio Science), which is commonly employed for the diagnosis of adenovirus conjunctivitis. Treatment consisted of intravenous vidarabine and bladder irrigation, which resulted in prompt clinical improvement. The Adenoclone kit was useful for the rapid etiologic diagnosis of adenovirus hemmorrhagic cystitis. 相似文献
27.
A broadband power meter calibration system based on a newly constructed coaxial calorimeter has been developed in the frequency region 10 MHz-40 GHz. The RF power is measured as the difference of DC power supplied to the calorimeter built-in heater in the RF load, when RF is turned off and on, holding an isothermal control between the RF load and a temperature reference. To minimize the error due to the adiabatic coaxial waveguide, we devised a new method utilizing its output port as a test port. The evaluations showed a calibration uncertainty of (0.28-2.2)% expressed by one standard deviation at the 1 mW level in the full band 相似文献
28.
Hirokazu Ikeda Chikara Fukunaga Yutaka Saitoh Masahiro Inoue Junko Yamanaka 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,380(3):618-622
The radiation tolerance for prototype front-end chips designed for a silicon micro-strip detector was examined with a 60Co irradiation source to establish an allowable range of the radiation dose. The irradiated front-end chips were SMA2SH-64A, a 64-channel preamplifier array; SMA2SH-1, a single-channel preamplifier circuit with a comparator; and Control-C, a digital-control chip for the preamplifiers. 相似文献
29.
Taking into consideration the knock-on cascade mechanism and the free volume theory, the cooling condition dependentR
s (ion etching rate) is investigated for a liquid-quenched Fe-10at%Si-15at%B alloy glass. A highR
s is found in a slow cooled glass. 相似文献
30.
Gain saturation dependence on signal wavelength in a 1.5 ?m InGaAsP travelling-wave semiconductor laser amplifier is experimentally studied. Saturation output powers were 6.9dBm, 8.3dBm and 10.6dBm for signal wavelengths of 1490 nm, 1510 nm and 1540 nm, respectively. This saturation dependence on wavelength, i.e. higher saturation output power for longer signal wavelength, results from signal gain peak shift towards longer wavelength with increasing input power. 相似文献