全文获取类型
收费全文 | 378953篇 |
免费 | 4285篇 |
国内免费 | 1125篇 |
专业分类
电工技术 | 6588篇 |
综合类 | 280篇 |
化学工业 | 56628篇 |
金属工艺 | 17025篇 |
机械仪表 | 12086篇 |
建筑科学 | 8357篇 |
矿业工程 | 3154篇 |
能源动力 | 9261篇 |
轻工业 | 28144篇 |
水利工程 | 4800篇 |
石油天然气 | 10571篇 |
武器工业 | 28篇 |
无线电 | 41689篇 |
一般工业技术 | 78730篇 |
冶金工业 | 68032篇 |
原子能技术 | 10330篇 |
自动化技术 | 28660篇 |
出版年
2021年 | 3396篇 |
2019年 | 3306篇 |
2018年 | 5746篇 |
2017年 | 5856篇 |
2016年 | 6244篇 |
2015年 | 3744篇 |
2014年 | 6286篇 |
2013年 | 16587篇 |
2012年 | 9922篇 |
2011年 | 13189篇 |
2010年 | 10615篇 |
2009年 | 11968篇 |
2008年 | 12176篇 |
2007年 | 12166篇 |
2006年 | 10400篇 |
2005年 | 9659篇 |
2004年 | 8971篇 |
2003年 | 8826篇 |
2002年 | 8370篇 |
2001年 | 8514篇 |
2000年 | 8184篇 |
1999年 | 8357篇 |
1998年 | 20567篇 |
1997年 | 14512篇 |
1996年 | 11332篇 |
1995年 | 8368篇 |
1994年 | 7481篇 |
1993年 | 7487篇 |
1992年 | 5814篇 |
1991年 | 5679篇 |
1990年 | 5367篇 |
1989年 | 5388篇 |
1988年 | 5257篇 |
1987年 | 4573篇 |
1986年 | 4544篇 |
1985年 | 5196篇 |
1984年 | 4851篇 |
1983年 | 4550篇 |
1982年 | 4086篇 |
1981年 | 4164篇 |
1980年 | 4076篇 |
1979年 | 4148篇 |
1978年 | 4137篇 |
1977年 | 4520篇 |
1976年 | 5685篇 |
1975年 | 3693篇 |
1974年 | 3524篇 |
1973年 | 3633篇 |
1972年 | 3111篇 |
1971年 | 2872篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Self-induced effects in a passive polarization-independent vertical-cavity semiconductor gate are investigated numerically and experimentally. We demonstrate all-optical seed-pulse extraction for synchronization of differential phase-shift keying and ON-OFF keying packets at 10 Gb/s. Our results provide evidence that vertical-cavity gates, exploiting saturable absorption in semiconductor quantum-wells, exhibit attractive performances in terms of efficiency, power consumption, and polarization independency. 相似文献
102.
103.
Seidel A.R. Bisogno F.E. Pinheiro H. do Prado R.N. 《Industrial Electronics, IEEE Transactions on》2003,50(6):1267-1274
This paper presents a simple alternative for an electronic ballast operating in self-sustained oscillating mode with dimming capability for fluorescent lamps. A simple modification in one of the gate drivers side circuit allows the lamp to dim without compromising the simplicity, reliability, and low cost which characterize the self-oscillating electronic ballast (SOEB). A qualitative analysis is presented to explain the behavior of the proposed self-oscillating electronic ballast with dimming feature. In addition, the stability and the key equations for the design are derived using the extended Nyquist criterion and describing function method. Experimental results from two 40-W electronic ballasts are presented to demonstrate the performance and to validate the analysis carried out. 相似文献
104.
A series of novel thermoplastic elastomers, based on poly(dimethylsiloxane) (PDMS) as the soft segment and poly(butylene terephthalate) (PBT) as the hard segment, were synthesized by catalyzed two‐step, melt transesterification reactions of dimethyl terephthalate and methyl esters of carboxypropyl‐terminated poly(dimethylsiloxane)s (M?n = 550–2170 g mol?1) with 1,4‐butanediol. The lengths of both the hard and soft segments were varied while the weight ratio of the hard to soft segments in the reaction mixture was maintained constant (57/43). The molecular structure, composition and molecular weights of the poly(ester–siloxane)s were examined by 1H NMR spectroscopy. The effectiveness of the incorporation of the methyl‐ester‐terminated poly(dimethylsiloxane)s into the copolymer chains was verified by chloroform extraction. The effect of the segment length on the transition temperatures (Tm and Tg) and the thermal and thermo‐oxidative degradation stability, as well as the degree of crystallinity and hardness properties of the synthesized TPESs, were studied. Copyright © 2003 Society of Chemical Industry 相似文献
105.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves. 相似文献
106.
The continuing progression of Moore's Law has enabled the miniaturisation and dramatic cost reduction in electronics over the last ten years. For a truly pervasive communications environment the challenges of hiding key hardware technologies from the user are rapidly being overcome. This paper reviews the status of these hardware technology developments in the pervasive space and briefly discusses other contributing factors that will enable the pervasive vision to be realised. 相似文献
107.
N.S. Chen S.F. Yu 《Photonics Technology Letters, IEEE》2004,16(7):1610-1612
The effect of external optical feedback on the transient response of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) is studied. It can be shown that the proper design of ARROW can suppress the excitation of high-order transverse leaky mode as well as increase the critical feedback strength so that stable high-power single-mode operation of VCSELs can be obtained even under the influence of strong external optical feedback. 相似文献
108.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
109.
J. B. Quinn G. E. Schumacher L. W. Schultheis 《Journal of Failure Analysis and Prevention》2004,4(1):41-46
Several days after heart surgery, a patient discovered his upper right canine tooth had broken at the root. Such tooth damage,
recognized post-operatively, is usually assumed to be caused by blunt mechanical force from an instrument used by the anesthesiologist
during placement of a breathing tube at the start of surgery.
In this case, the patient had saved the crown portion of the broken tooth, and it was possible to examine the root fracture
characteristics. The curvature and direction of the crack path and natural tooth situation suggested that failure could be
described through a cantilever beam model. This was confirmed when a whole extracted sample tooth was embedded and broken
by a measured force in a manner consistent with the model. The resulting fracture surface matched that of the patient’s broken
canine tooth. However, the high load and force direction necessary to fracture the root was inconsistent with forces applied
during the anesthesia procedure. The failure analysis and further investigation indicated tooth clenching on the breathing
tube during recovery was the likely cause of fracture.
This paper presents an alternate explanation for intubation-related dental injury, demonstrates the practicality of fractographic
analysis of biological materials, and introduces a methodology for simulating in vitro tooth settings for mechanical testing. 相似文献
110.
Mathematical models of thermomechanical processes which are based on the laws of rational thermodynamics of irreversible processes are treated. Singular features of the unsteady-state behavior of a continuous medium are demonstrated within different models, such as a medium with internal parameters of state, a medium with memory, and a medium of the velocity type. 相似文献