全文获取类型
收费全文 | 1829篇 |
免费 | 11篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 64篇 |
金属工艺 | 3篇 |
机械仪表 | 7篇 |
建筑科学 | 13篇 |
矿业工程 | 4篇 |
能源动力 | 10篇 |
轻工业 | 49篇 |
水利工程 | 8篇 |
石油天然气 | 1篇 |
无线电 | 45篇 |
一般工业技术 | 49篇 |
冶金工业 | 1526篇 |
原子能技术 | 3篇 |
自动化技术 | 52篇 |
出版年
2021年 | 6篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 9篇 |
2014年 | 14篇 |
2013年 | 34篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 10篇 |
2009年 | 18篇 |
2008年 | 12篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 8篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 59篇 |
1998年 | 418篇 |
1997年 | 240篇 |
1996年 | 163篇 |
1995年 | 103篇 |
1994年 | 85篇 |
1993年 | 89篇 |
1992年 | 24篇 |
1991年 | 26篇 |
1990年 | 26篇 |
1989年 | 32篇 |
1988年 | 28篇 |
1987年 | 35篇 |
1986年 | 23篇 |
1985年 | 19篇 |
1983年 | 5篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 28篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 34篇 |
1976年 | 108篇 |
1975年 | 7篇 |
1971年 | 5篇 |
1967年 | 2篇 |
1958年 | 2篇 |
1955年 | 2篇 |
1906年 | 2篇 |
排序方式: 共有1841条查询结果,搜索用时 31 毫秒
91.
92.
93.
目前正在进行一场竞赛,以期找出下一个网站新秀,能够利用这种铺天盖地的所谓用户自创内容吸引庞大的受众群体;同时,人们也在竞相甄别下一个大趋势,这个趋势将会决定无数网民未来使用网络媒介的方式.5年前,谁会想到博客和社交网络会成为主流? 相似文献
94.
One hundred twenty-seven individuals who ranged in age from18 to 90 years were tested on a reading span test and on measures of on-line and off-line sentence processing efficiency. Older participants had reduced working-memory spans compared with younger participants. The on-line measures were sensitive to local increases in processing load, and the off-line measures were sensitive to the syntactic complexity of the sentences. Older and younger participants showed similar effects of syntactic complexity on the on-line measures. There was some evidence that older participants were more affected than younger participants by syntactic complexity on the off-line measures. The results support the hypothesis that on-line processes involved in recognizing linguistic forms and determining the literal, preferred, discourse-coherent meaning of sentences constitute a domain of language processing that relies on its own processing resource or working-memory system. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
95.
Ellen Y. Sun Paul F. Becher Kevin P. Plucknett Chun-Hway Hsueh Kathleen B. Alexander Shirley B. Waters Kiyoshi Hirao Manuel E. Brito 《Journal of the American Ceramic Society》1998,81(11):2831-2840
Significant improvements in the fracture resistance of self-reinforced silicon nitride ceramics have been obtained by tailoring the chemistry of the intergranular amorphous phase. First, the overall microstructure of the material was controlled by incorporation of a fixed amount of elongated ß-Si3 N4 seeds into the starting powder to regulate the size and fraction of the large reinforcing grains. With controlled microstructures, the interfacial debond strength between the reinforcement and the intergranular glass was optimized by varying the yttria-to-alumina ratio in the sintering additives. It was found that the steady-state fracture toughness value of these silicon nitrides increased with the Y:Al ratio of the oxide additives. The increased toughness was accompanied by a steeply rising R -curve and extensive interfacial debonding between the elongated ß-Si3 N4 grains and the intergranular glassy phase. Microstructural analyses indicate that the different fracture behavior is related to the Al (and O) content in the ß´-SiAlON growth layer formed on the elongated ß-Si3 N4 grains during densification. The results imply that the interfacial bond strength is a function of the extent of Al and Si bonding with N and O in the adjoining phases with an abrupt structural/chemical interface achieved by reducing the Al concentration in both the intergranular phase and the ß´-SiAlON growth layer. Analytical modeling revealed that the residual thermal expansion mismatch stress is not a dominant influence on the interfacial fracture behavior when a distinct ß´-SiAlON growth layer forms. It is concluded that the fracture resistance of self-reinforced silicon nitrides can be improved by optimizing the sintering additives employed. 相似文献
96.
97.
98.
99.
Simon P. Shone Brian R. Mace Tim P. Waters 《Mechanical Systems and Signal Processing》2009,23(2):405-414
A method for detecting damage in uniform waveguide structures from two or more point frequency response functions (FRFs) is described. Attention is focussed on bending waves in beams although the method can in principle be applied to any waveguide structure. The input FRF is the superposition of directly injected waves and waves reflected from the damage and from other scattering regions in the structure. The phase of this FRF modulates with wavenumber, with the period of modulation in wavenumber space being related to the distances between the excitation point and scattering locations. The phase spectrum of the input FRF is found: the phase is determined, dispersive effects are removed by transforming from the frequency domain to the wavenumber domain, and the inverse Fourier transform from the wavenumber to the space domain found. Peaks in this phase spectrum indicate the distance to the scatterer. Two (or more) input FRFs can be used to determine the location of the scatterer unambiguously. Signal processing issues are discussed. Numerical results for a uniform beam with a breathing crack are given and experimental results for beams with a slot cut into them are presented. The approach lies in the middle ground between low frequency, modal methods and high frequency, ultrasonic methods. It allows one to interrogate a region of a structure rather than the complete structure and there is no requirement for a validated model of the structure in order to locate damage, apart from an estimate of the dispersion relation. 相似文献
100.
Thymidylate synthase (TS) is a long-standing target for anticancer drugs and is of interest for its rich mechanistic features. The enzyme catalyzes the conversion of dUMP to dTMP using the co-enzyme methylenetetrahydrofolate, and is perhaps the best studied of enzymes that catalyze carbon-carbon bond formation. Arg 126 is found in all TSs but forms only 1 of 13 hydrogen bonds to dUMP during catalysis, and just one of seven to the phosphate group alone. Despite this, when Arg 126 of TS from Escherichia coli was changed to glutamate (R126E), the resulting protein had kcat reduced 2000-fold and Km reduced 600-fold. The crystal structure of R126E was determined under two conditions--in the absence of bound ligand (2.4 A resolution), and with dUMP and the antifolate CB3717 (2.2 A resolution). The first crystals, which did not contain dUMP despite its presence in the crystallization drop, displayed Glu 126 in a position to sterically and electrostatically interfere with binding of the dUMP phosphate. The second crystals contained both dUMP and CB3717 in the active site, but Glu 126 formed three hydrogen bonds to nearby residues (two through water) and was in a position that partially overlapped with the normal phosphate binding site, resulting in a approximately 1 A shift in the phosphate group. Interestingly, the protein displayed the typical ligand-induced conformational change, and the covalent bond to Cys 146 was present in one of the protein's two active sites. 相似文献