全文获取类型
收费全文 | 90332篇 |
免费 | 4729篇 |
国内免费 | 1188篇 |
专业分类
电工技术 | 2310篇 |
技术理论 | 4篇 |
综合类 | 1648篇 |
化学工业 | 16651篇 |
金属工艺 | 3580篇 |
机械仪表 | 4702篇 |
建筑科学 | 2892篇 |
矿业工程 | 810篇 |
能源动力 | 3287篇 |
轻工业 | 6209篇 |
水利工程 | 691篇 |
石油天然气 | 1218篇 |
武器工业 | 147篇 |
无线电 | 15105篇 |
一般工业技术 | 15919篇 |
冶金工业 | 8360篇 |
原子能技术 | 1000篇 |
自动化技术 | 11716篇 |
出版年
2024年 | 150篇 |
2023年 | 977篇 |
2022年 | 1668篇 |
2021年 | 2560篇 |
2020年 | 1897篇 |
2019年 | 1794篇 |
2018年 | 2203篇 |
2017年 | 2234篇 |
2016年 | 2481篇 |
2015年 | 2337篇 |
2014年 | 3389篇 |
2013年 | 5523篇 |
2012年 | 5080篇 |
2011年 | 6131篇 |
2010年 | 4740篇 |
2009年 | 4945篇 |
2008年 | 4704篇 |
2007年 | 4115篇 |
2006年 | 3741篇 |
2005年 | 3138篇 |
2004年 | 2886篇 |
2003年 | 2860篇 |
2002年 | 2998篇 |
2001年 | 2435篇 |
2000年 | 1992篇 |
1999年 | 1859篇 |
1998年 | 3102篇 |
1997年 | 2065篇 |
1996年 | 1746篇 |
1995年 | 1404篇 |
1994年 | 1104篇 |
1993年 | 994篇 |
1992年 | 736篇 |
1991年 | 706篇 |
1990年 | 635篇 |
1989年 | 598篇 |
1988年 | 489篇 |
1987年 | 420篇 |
1986年 | 377篇 |
1985年 | 362篇 |
1984年 | 306篇 |
1983年 | 226篇 |
1982年 | 222篇 |
1981年 | 188篇 |
1980年 | 207篇 |
1979年 | 150篇 |
1978年 | 153篇 |
1977年 | 179篇 |
1976年 | 234篇 |
1975年 | 121篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
A multi-channel continuous toxicity monitoring system developed in our laboratory, based on two-stage mini-bioreactors, was successfully implemented in the form of computer-based data acquisition. The multi-channel system consists of a series of a two-stage minibioreactor systems connected by a fiber optic probe to a luminometer, and uses genetically engineered bioluminescent bacteria for the detection of the potential toxicity from the soluble chemicals. This system can be stably and continuously operated due to the separation of the culture reactor from the test reactor and accomplish easy and long-term monitoring without system shut down by abrupt inflows of severe polluting chemicals. Four different recombinant bioluminescent bacteria were used in different channels so that the modes of the samples toxicities can be reasonably identified and evaluated based upon the response signature of each channel. The bioluminescent signatures were delivered from four channels by switching one at once, while the data is automatically logged to an IBM compatible computer. We also achieved the enhancement of the system through the manipulation of the dilution rate and the use of thermo-lux fusion strains. Finally, this system is now being implemented to a drinking water reservoir and river for remote sensing as an early warning system. 相似文献
42.
The influence of liquid penetration at grain boundary regions on the rate of advance of the solid-liquid interface during
isothermal solidification of transient liquid phase (TLP) brazed nickel joints has been examined. The test samples used in
this study were Ohno-cast nickel with a grain size of >4 mm and a fine-grained nickel with a grain size of around 40 μm. Both
Ni-base materials had the same chemical composition. The rate of isothermal solidification was greater when fine-grained nickel
was employed during TLP brazing using Ni-11 wt pct P filler metal at 1200 °C. Liquid penetration at grain boundaries accelerates
the isothermal solidification process by increasing the effective solid-liquid interfacial area and increasing the rate of
solute diffusion into the base material. An analysis of electron channeling patterns has confirmed that random high-angle
boundaries have a greater influence on the rate of isothermal solidification than ordered boundaries including small-angle
or twin boundaries.
Formerly Visiting Scientist, Department of Metallurgy and Materials Science, University of Toronto.
Formerly Postdoctoral Fellow, Department of Metallurgy and Materials Science, University of Toronto 相似文献
43.
Jong-Hwan Kim Yeon-Chan Hong Sung-Jun Lee Keh-Kun Choi 《Industrial Electronics, IEEE Transactions on》1989,36(3):361-364
A direct adaptive control scheme is proposed for nonminimum-phase systems in which controller parameters are estimated from the recursive least-squares algorithm and additional auxiliary parameters are obtained from the proposed polynomial identity. A local convergence is guaranteed without any extra condition. Integral action is incorporated into the adaptive controller to eliminate the steady-state error and to satisfy a condition of the unique solution for the polynomial identity. The control law used in this scheme is based on the set-point-on-I-only proportional-integral-derivative (PID) structure 相似文献
44.
45.
46.
47.
The effects of gallia additions on the sintering behavior of gadolinia-doped ceria were systematically investigated from the following aspects: the variation in sintered density, the variation in grain size, and the existing forms of Ga2O3 in CeO2.Sintered density increased with increasing Ga2O3 content up to 5 mol.% and then it decreased with further addition of Ga2O3. Grain size also increased with increasing Ga2O3 content up to 5 mol.% and then decreased with further addition of Ga2O3. Decrease in grain size was caused by a pinning effect of Ga2O3 precipitation at grain boundaries. Lattice constant decreased with increasing Ga2O3 content up to 5 mol.%. This decrease will be due to the substitution of smaller Ga3+ ions for Ce4+ ions in the CeO2 structure. According to the results obtained from scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, the solubility limit of Ga2O3 in Ce0.8Gd0.2O1.9 ceramics can be estimated to be nearly 5 mol.%. The addition of Ga2O3 up to the solubility limit was found to promote the sintering properties of Gd2O3-doped CeO2. 相似文献
48.
Junho Lee Hyungsoo Kim Joungho Kim 《Microwave and Wireless Components Letters, IEEE》2005,15(8):505-507
We experimentally demonstrated the great advantages of a high dielectric constant thin film electromagnetic bandgap (EBG) power distribution network (PDN) for the suppression of power/ground noises and radiated emissions in high-performance multilayer digital printed circuit boards (PCBs). Five-layer test PCBs were fabricated and their scattering parameters measured. The power plane noise and radiated emissions were measured, investigated and related to the PDN impedance. This successfully demonstrated that the bandgap of the EBG was extended more than three times, covering a range of hundreds of MHz using a 1-cm /spl times/ 1-cm EBG cell, the SSN was reduced from 170 mV to 10 mV and the radiated emission was suppressed by 22 dB because of the high dielectric constant thin film EBG power/ground network. 相似文献
49.
We obtain a necessary and sufficient condition for a discrete-time nonlinear system to be locally state equivalent to the nonlinear observer form. The result looks similar to the continuous counterpart except for the fact that Ad-operation is utilized instead of ad-operation. 相似文献
50.
Human facial gestures often exhibit such natural stochastic variations as how often the eyes blink, how often the eyebrows and the nose twitch, and how the head moves while speaking. The stochastic movements of facial features are key ingredients for generating convincing facial expressions. Although such small variations have been simulated using noise functions in many graphics applications, modulating noise functions to match natural variations induced from the affective states and the personality of characters is difficult and not intuitive. We present a technique for generating subtle expressive facial gestures (facial expressions and head motion) semi‐automatically from motion capture data. Our approach is based on Markov random fields that are simulated in two levels. In the lower level, the coordinated movements of facial features are captured, parameterized, and transferred to synthetic faces using basis shapes. The upper level represents independent stochastic behavior of facial features. The experimental results show that our system generates expressive facial gestures synchronized with input speech. 相似文献