全文获取类型
收费全文 | 2739篇 |
免费 | 92篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 174篇 |
综合类 | 4篇 |
化学工业 | 965篇 |
金属工艺 | 78篇 |
机械仪表 | 60篇 |
建筑科学 | 84篇 |
矿业工程 | 2篇 |
能源动力 | 99篇 |
轻工业 | 298篇 |
水利工程 | 8篇 |
石油天然气 | 2篇 |
无线电 | 158篇 |
一般工业技术 | 472篇 |
冶金工业 | 157篇 |
原子能技术 | 66篇 |
自动化技术 | 210篇 |
出版年
2023年 | 12篇 |
2022年 | 37篇 |
2021年 | 58篇 |
2020年 | 36篇 |
2019年 | 37篇 |
2018年 | 48篇 |
2017年 | 45篇 |
2016年 | 67篇 |
2015年 | 37篇 |
2014年 | 88篇 |
2013年 | 162篇 |
2012年 | 122篇 |
2011年 | 176篇 |
2010年 | 105篇 |
2009年 | 151篇 |
2008年 | 150篇 |
2007年 | 138篇 |
2006年 | 104篇 |
2005年 | 122篇 |
2004年 | 105篇 |
2003年 | 93篇 |
2002年 | 95篇 |
2001年 | 66篇 |
2000年 | 48篇 |
1999年 | 48篇 |
1998年 | 65篇 |
1997年 | 56篇 |
1996年 | 49篇 |
1995年 | 36篇 |
1994年 | 48篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 17篇 |
1990年 | 22篇 |
1989年 | 22篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 29篇 |
1985年 | 33篇 |
1984年 | 29篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1977年 | 13篇 |
1976年 | 20篇 |
1974年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有2837条查询结果,搜索用时 16 毫秒
91.
Recent development of open-loop electric potential microscopy (OL-EPM) has enabled to measure local potential distribution at a solid/liquid interface. However, the operating environment of OL-EPM has been limited to a weak electrolyte solution (<1 mM). This has significantly limited its application range in biology and chemistry. To overcome this limitation, we have developed dual frequency (DF) mode OL-EPM. In the method, an ac bias voltage consisting of two frequency components at f(1) and f(2) is applied between a tip and sample. The local potential is calculated from the amplitudes of the f(1) and |f(1) - f(2)| components of the electrostatic force. In contrast to the conventional single frequency (SF) mode OL-EPM, the detection of the 2f(1) component is not required in DF mode. Thus, the maximum bias modulation frequency in DF mode is twice as high as that in SF mode. The high bias modulation frequency used in DF mode prevents the generation of electrochemical reactions and redistribution of ions and water, which enables to operate OL-EPM even in a strong electrolyte solution. In this study, we have performed potential measurements of nanoparticles on a graphite surface in 1 and 10 mM NaCl solution. The results demonstrate that DF mode OL-EPM allows measurements of local potential distribution in 10 mM electrolyte solution. 相似文献
92.
Yasuhiro Kodera Takeshi Yamamoto Naoki Toyofuku Manshi Ohyanagi Zuhair A. Munir 《Journal of Materials Science》2006,41(3):727-732
The ordering of stacking-disordered silicon carbide prepared from the elements by high energy ball milling was investigated
during sintering. A sharp increase in density in the temperature region 1700–1800°C was associated with a decrease in the
disorder. Samples which had low disorder density showed a more continuous sintering behavior with temperature. Highly dense
(up to 99% relative density) SiC can be obtained at 1900°C under a pressure of 70 MPa with no hold time. Similar results were
observed for structurally disordered carbon with 10 at% of boron. The sintering behavior exhibited an abrupt density increase
in the narrow temperature region of 1450–1600°C and was associated with disorder-order transformation. 相似文献
93.
Pulsed plasma thrusters (PPTs) have the advantages of mechanical simplicity and robustness compared to other electric propulsion systems. However the thrust power ratio of PPTs is lower than that of other electric propulsion systems. To enhance the thrust performance of the PPT, we propose to use several combustible solid chemicals as coaxial PPT propellants to replace Teflon® (Polytetrafluoroethylene: PTFE). With the design, the force obtained thermodynamically is expected to augment the PPT thrust power ratio with the help of the chemical energy contained in the propellants. As a result, the thrust power ratio is increased using hydroxyl-terminated polybutadiene-ammonium perchlorate (HTPB-AP)-based propellants compared to the case of ordinary Teflon. The discharge current and voltage waveform does not change even when the propellant is changed. These findings could indicate that the impulse bits by gasdynamic contribution are lager in the case of chemical solid propellants than in the case of Teflon. 相似文献
94.
Yasuhiro Konishi Takeshi TsukiyamaKaori Ohno Norizoh SaitohToshiyuki Nomura Shinsuke Nagamine 《Hydrometallurgy》2006
Microbial reduction and intracellular precipitation of gold was achieved at 25 °C and pH 7 by using the mesophilic anaerobic bacterium Shewanella algae with H2 as the electron donor. The reductive precipitation of gold by S. algae was a fast process: 0.1–1 mol/m3 AuCl4− ions were completely reduced to insoluble gold within 30 min. The biogenic precipitates were crystalline gold nanoparticles of 10–20 nm present in the periplasmic space. The reducing power of S. algae at 3.2 × 1015 cells/m3 and 25 °C was comparable to that of aqueous citric acid solution (chemical reductant) at 20 mol/m3 and 50 °C. The intracellular recovery of gold is potentially attractive as an environmentally friendly alternative to conventional methods. 相似文献
95.
Takeshi Kubota 《国际钢铁研究》2005,76(6):464-470
Control of crystalline orientation and consequent enhancement of magnetic properties are important for decreasing core loss of non‐oriented silicon steel as well as grain‐oriented silicon steel. Through the development of special process techniques to produce clean refined steel, it is now possible to use any element to improve the crystalline texture control of steel without producing harmful effects. Utilization of these effects have actually lowered the core loss and raised the magnetic flux density of the products, and a product series of high‐efficiency non‐oriented silicon steel has been developed. Recently, demand has grown for non‐oriented silicon steel with particular properties, such as lower core loss at high frequencies or high strength, as high‐speed motors have progressed in regard to high efficiency and miniaturization. In response to this trend, non‐oriented thin gauge silicon steel with a thickness of 0.20 and 0.15mm and high strength non‐oriented thin gauge silicon steel with the same thickness but a yield strength of more than 570MPa and 780MPa have been developed. 相似文献
96.
Kazunori Yamamoto Takatsugu Wakahara Takeshi Akasaka 《Progress in Nuclear Energy》2005,47(1-4):616-623
A carbon nanoencapsulate has a polyhedral outer shell of nested, concentric layers of carbon. The shell defines an internal cavity where a metal is encapsulated. Although the rare-earth carbides readily hydrolyze in moist air, the carbides in these carbon shells did not degrade after exposure to air for considerable lengths of time. This means that the carbide particle is physically enclosed within the carbon cavity completely, and the cavity protects it perfectly against attack of water molecules. Considering intrinsic chemical stability of carbon under oxygen free condition, this structure may be a perfect barrier to extremely long-term release of radionuclides. Because encapsulation of LaC2 within carbon nanoparticles increased drastically from by-product to major product, it would be possible to find the optimized condition that complete encapsulation is achieved. Intrinsic stability of carbon and carbon coated waste nanoparticles may provide an improved barrier to radionuclide release by groundwater. 相似文献
97.
Yukio Tachibana Shigeaki Nakagawa Takeshi Takeda Akio Saikusa Takayuki Furusawa Kuniyoshi Takamatsu Kazuhiro Sawa Tatsuo Iyoku 《Nuclear Engineering and Design》2003,224(2):1010-197
Safety demonstration tests using the High Temperature Engineering Test Reactor (HTTR) will be conducted for the purpose of demonstrating inherent safety features of High Temperature Gas-cooled Reactors (HTGRs) as well as providing the core and plant transient data for validation of HTGR safety analysis codes. The first phase safety demonstration test items include the reactivity insertion test and the coolant flow reduction test. In the reactivity insertion test, which is the control rod withdrawal test, one pair out of 16 pairs of control rods is withdrawn, simulating a reactivity insertion event. The coolant flow reduction test consists of the partial loss of coolant flow test and the gas circulators trip test. In the partial loss of coolant flow test, primary coolant flow rate is slightly reduced by control system. In the gas circulators trip test one and two out of three gas circulators are run down, simulating coolant flow reduction events. The gas circulators trip tests, in which position of control rods are kept unchanged, are simulation tests of anticipated transients without scram (ATWS). 相似文献
98.
Takeshi Tokuyama 《Algorithmica》1997,18(2):229-245
We consider theorthgonal clipping problem in a set of segments: Given a set ofn segments ind-dimensional space, we preprocess them into a data structure such that given an orthogonal query window, the segments intersecting
it can be counted/reported efficiently.
We show that the efficiency of the data structure significantly depends on a geometric discrete parameterK named theProjected-image complexity, which becomes Θ(n
2) in the worst case but practically much smaller. If we useO(m) space, whereK log4d−7
n≥m≥n log4d−7
n, the query time isO((K/m)1/2 logmax{4, 4d−5}
n). This is near to an Ω((K/m)1/2) lower bound. 相似文献
99.
Daniella B. Mosqueda-Jimenez Roberto M. Narbaitz Takeshi Matsuura 《Canadian Metallurgical Quarterly》2004,130(12):1450-1459
New polyethersulfone (PES) based membranes for ultrafiltration (UF) were developed by blending a surface-modifying macromolecule (SMM) in the casting solution, in an attempt to minimize the impact of fouling. Fouling was evaluated using concentrated Ottawa River water (CORW), either unfractionated or fractionated via UF. These membranes also included some polyvinylpyrrolidone (PVP), a pore forming additive. A statistical analysis was conducted to evaluate the impact of some variables on the treatment of the surface water. The independent variables included PVP/PES ratio in the casting solution, with and without SMM, and the nature of the feed CORW [low molecular weight (LMW) fraction, unfractionated, high molecular weight (HMW) fraction]. The performance variables studied were total organic carbon (TOC) removal, the foulant accumulation at the membrane surface after filtration, the flux reduction, and the final permeate flux. The most important variable was the feed water. Filtration of LMW had a higher final flux, less fouling, but slightly lower TOC removal. The SMM did not significantly impact the membrane performance. TOC removal was high, compared with results reported in the literature for UF membranes. 相似文献
100.
Etsuro Shibata Takashi Nakamura Takeshi Nishida Mitsunori Endo Hideyuki Itou Tomio Takasu 《国际钢铁研究》2004,75(5):308-313
The flux of the CaO‐Al203‐BaO‐CeO2‐MgO system as a desulphurization flux containing no fluorine for the secondary metallurgy process was evaluated in this study. The flux composition was designed using the eutectic compositions of the binary systems. The melting and desulphurization abilities of the fluxes were evaluated by measuring their liquidus temperatures and the distribution ratios of sulphur between the fluxes and the carbon‐saturated iron or stainless steel. The lowest liquidus temperature of 1325°C was obtained by adding 5.7 mass% MgO to the 80mass%A‐20mass%B flux. (A: 12CaO‐7Al2O3, B: BaCeO3+12mass%Al2O3). The distribution ratios of sulphur and sulphide capacities of the fluxes in this study were higher than those of the commercial product of calcium aluminate flux. This means that the CaO‐Al2O3‐BaO‐CeO2‐MgO fluxes developed in this study have higher desulphurization and melting abilities compared with the commercial product of calcium aluminate flux. 相似文献