全文获取类型
收费全文 | 899篇 |
免费 | 38篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 30篇 |
综合类 | 1篇 |
化学工业 | 245篇 |
金属工艺 | 13篇 |
机械仪表 | 28篇 |
建筑科学 | 22篇 |
能源动力 | 30篇 |
轻工业 | 65篇 |
石油天然气 | 2篇 |
无线电 | 81篇 |
一般工业技术 | 154篇 |
冶金工业 | 143篇 |
原子能技术 | 18篇 |
自动化技术 | 107篇 |
出版年
2023年 | 10篇 |
2022年 | 7篇 |
2021年 | 23篇 |
2020年 | 14篇 |
2019年 | 18篇 |
2018年 | 24篇 |
2017年 | 13篇 |
2016年 | 26篇 |
2015年 | 24篇 |
2014年 | 32篇 |
2013年 | 46篇 |
2012年 | 49篇 |
2011年 | 47篇 |
2010年 | 35篇 |
2009年 | 32篇 |
2008年 | 36篇 |
2007年 | 32篇 |
2006年 | 28篇 |
2005年 | 28篇 |
2004年 | 17篇 |
2003年 | 25篇 |
2002年 | 14篇 |
2001年 | 9篇 |
2000年 | 12篇 |
1999年 | 17篇 |
1998年 | 57篇 |
1997年 | 34篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 3篇 |
1977年 | 10篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有939条查询结果,搜索用时 46 毫秒
101.
An end-to-end packet delay in the Internet is an important performance parameter, because it heavily affects the quality of real-time applications. In the current Internet, however, because the packet transmission qualities (e.g., transmission delays, jitters, packet losses) may vary dynamically, it is not easy to handle a real-time traffic. In UDP-based real-time applications, a smoothing buffer (playout buffer) is typically used at a client host to compensate for variable delays. The issue of playout control has been studied by some previous works, and several algorithms controlling the playout buffer have been proposed. These studies have controlled the network parameters (e.g., packet loss ratio and playout delay), not considered the quality perceived by users. In this paper, we first clarify the relationship between Mean Opinion Score (MOS) of played audio and network parameters (e.g., packet loss, packet transmission delay, transmission rate). Next, utilizing the MOS function, we propose a new playout buffer algorithm considering user's perceived quality of real-time applications. Our simulation and implementation tests show that it can enhance the perceived quality, compared with existing algorithms. 相似文献
102.
Masahiro Nagae Yasunori Koyama Seita Yasutake Tetsuo Yoshio Kohei Oda 《Journal of the American Ceramic Society》2006,89(11):3550-3553
The corrosion behavior of sialon ceramics was investigated in supercritical water at 450°C under 45 MPa for 2–50 h. α-sialon exhibited better corrosion resistance than β-sialon and α/β-sialon. Pitting corrosion with the formation of corrosion products was observed in the case of β-sialon and α/β-sialon. By contrast, the corrosion behavior of α-sialon was characterized by uniform corrosion with the formation of corrosion products. The degree of strength deterioration was strongly dependent on the corrosion morphology. The bending strength of α-sialon after corrosion for 30 h was about 90% of its initial strength, while the strength of β-sialon decreased to 65% of its original strength. 相似文献
103.
104.
Hidero Unuma Koh Miura Tsuyoshi Furusaki Kohei Kodaira 《Journal of the American Ceramic Society》1991,74(6):1291-1295
Crystallization of Li-Al-Si-O-N oxynitride glasses based on the β-spodumene composition and the properties of the resultant glass-ceramics have been studied. The onset of the precipitation of metastable high-quartz solid solution and its transformation to β-spodumene shift to higher temperatures with increasing nitrogen content of the oxynitride glasses. Nitrided glass-ceramics crystallized at 1200°C have negative thermal expansion coefficients, since high-quartz structure is maintained up to 1000° and 1200°C. Knoop hardness and density of the glass-ceramics increase with increasing nitrogen content. There was evidence that part of the nitrogen atoms were incorporated into the high-quartz solid-solution structure and that a small amount of the minor phase of Si2 N2 O was precipitated in highly nitrided glass-ceramics. 相似文献
105.
A human RNA helicase gene, DBP1, was cloned by PCR methodsusing degenerate oligonucleotide primers corresponding to highly conserved motifs among known members of the DEAH-box protein family. The full-length DBP1 contains 3028 nucleotides and codes for a protein of 813 amino acids with a calculated mol. wt. of 92723 daltons. The predicted amino acid sequence shares extensive homology with Prp2, Prp16, and Prp22 proteins, which are required to splice mRNA precursors in budding yeast. The protein encoded by DBP1 has RGD, RD, and HS(A/T) repeat motifs close to the N-terminus. Southern blot analysis suggested the presence of a homologue of the DBP1 genes in other species, and Northern blot analysis showed that DBP1 is expressed ubiquitously in various human organs investigated. The DBP1 gene was found to be on chromosome 4p15.3 and encodes a putative nuclear ATP-dependent RNA helicase. 相似文献
106.
J Hayashi K Yamamoto M Sugawara Y Fujita S Nakazawa F Oguma S Tsuchida H Miyamura S Eguchi 《Canadian Metallurgical Quarterly》1992,40(10):1866-1870
Between January 1980 and August 1991, 99 patients underwent operation for mitral valve regurgitation (MR). The ages of the patients ranged from 12 to 67 years, (49.4 +/- 11.9 years), and there were 39 males and 60 females. Pathological cause of regurgitation, which was determined by intraoperative inspection and histological findings of excised leaflets, was rheumatic in 46, degenerative in 38, infective endocarditis in 9, ischemic in 4 and unknown in 2 patients. Cardiac rhythm was atrial fibrillation in 73, normal sinus rhythm in 24 and junctional rhythm in 2 patients. Our principles for valve repair were (1) excision of responsible segment and repair for prolapsed leaflet due to torn chordae, (2) shortening of elongated chordae, (3) annuloplasty, and (4) repair of perforated leaflet. Finally, 19 patients endured plastic operation, and 80 patients underwent prosthetic valve replacement. The rate of plastic procedure was 62.5% (10/16) in degenerative MR with mural chordal lesions, 42.9% (3/7) in rheumatic MR without stenosis, 22.2% (2/9) in infective endocarditis and 100% (2/2) in MR with unknown etiology. Mitral valve repair was failed both in rheumatic MR associated with stenosis (39 patients) and in ischemic MR (4 patients). A ten-year survival rate after operation was 92.2 +/- 3.1% in patients with valve replacement and 83.6 +/- 10.0% with valve repair (N.S.), and a proportion of event-free survival in patients with valve replacement was similar to valve. Late postoperative cardiac catheterization revealed decreased left ventricular volume indices and increased left ventricular end-systolic stress/volume ratio in both groups compared to preoperative values, respectively.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
107.
The antitumor effects of toremifene were studied in vitro using 10 anaplastic thyroid carcinoma cell lines and were compared with those of tamoxifen. The antitumor effect of toremifene was dose-dependent and the IC50 values for these cell lines ranged 20.1-58.5 microM. Although the cell lines expressed multidrug resistance gene mRNA, multidrug resistance-associated protein gene mRNA and insulin-like growth factor-1 (IGF-1) receptor mRNA to various degrees, nine of them lacked estrogen receptor expression as evaluated by immunocytochemistry. These data indicate that toremifene, as well as tamoxifen, is cytolytic at relatively high doses for multidrug-resistant anaplastic thyroid carcinoma cell lines. 相似文献
108.
Hailong Hu Dian Zhang Weiming Yu Katsuyasu Sugawara Tailiang Guo 《Journal of Electronic Materials》2014,43(7):2548-2552
We report on a two-step wet chemical route for producing Cu@Ni core–shell particles with multiple needle-like branches on the surface. Using the usual synthesis process, urchin-like Ni shells were formed on the surface of spherical Cu cores and monodisperse particles were obtained. Under the direction of a static magnetic field, one-dimensional, well-aligned Cu@Ni particles were assembled through cross-linking the branched Ni shells. The monodisperse Cu@Ni particles show stable and uniform field electron emission, having a low turn-on field of 3.3 V/μm and a large current density of 1 mA/cm2 under an applied field of about 5.33 V/μm. 相似文献
109.
Kohei Okita Ryuta Narumi Takashi Azuma Shu Takagi Yoichiro Matumoto 《Computational Mechanics》2014,54(4):1023-1033
High-intensity focused ultrasound (HIFU) has been used clinically and is under clinical trials to treat various diseases. An advanced HIFU system employs ultrasound techniques for guidance during HIFU treatment instead of magnetic resonance imaging in current HIFU systems. A HIFU beam imaging for monitoring the HIFU beam and a localized motion imaging for treatment validation of tissue are introduced briefly as the real-time ultrasound monitoring techniques. Numerical simulations have a great impact on the development of real-time ultrasound monitoring as well as the improvement of the safety and efficacy of treatment in advanced HIFU systems. A HIFU simulator was developed to reproduce ultrasound propagation through the body in consideration of the elasticity of tissue, and was validated by comparison with in vitro experiments in which the ultrasound emitted from the phased-array transducer propagates through the acrylic plate acting as a bone phantom. As the result, the defocus and distortion of the ultrasound propagating through the acrylic plate in the simulation quantitatively agree with that in the experimental results. Therefore, the HIFU simulator accurately reproduces the ultrasound propagation through the medium whose shape and physical properties are well known. In addition, it is experimentally confirmed that simulation-assisted focus control of the phased-array transducer enables efficient assignment of the focus to the target. Simulation-assisted focus control can contribute to design of transducers and treatment planning. 相似文献
110.