全文获取类型
收费全文 | 101639篇 |
免费 | 7562篇 |
国内免费 | 6284篇 |
专业分类
电工技术 | 8244篇 |
技术理论 | 2篇 |
综合类 | 7046篇 |
化学工业 | 20882篇 |
金属工艺 | 6340篇 |
机械仪表 | 7880篇 |
建筑科学 | 3846篇 |
矿业工程 | 1455篇 |
能源动力 | 3489篇 |
轻工业 | 6749篇 |
水利工程 | 658篇 |
石油天然气 | 4444篇 |
武器工业 | 930篇 |
无线电 | 12350篇 |
一般工业技术 | 10634篇 |
冶金工业 | 2578篇 |
原子能技术 | 1164篇 |
自动化技术 | 16794篇 |
出版年
2024年 | 283篇 |
2023年 | 1297篇 |
2022年 | 2258篇 |
2021年 | 2680篇 |
2020年 | 2383篇 |
2019年 | 2375篇 |
2018年 | 2227篇 |
2017年 | 2885篇 |
2016年 | 3150篇 |
2015年 | 3279篇 |
2014年 | 4707篇 |
2013年 | 5495篇 |
2012年 | 5876篇 |
2011年 | 7001篇 |
2010年 | 5791篇 |
2009年 | 6683篇 |
2008年 | 6467篇 |
2007年 | 7082篇 |
2006年 | 6842篇 |
2005年 | 5656篇 |
2004年 | 4959篇 |
2003年 | 4753篇 |
2002年 | 3893篇 |
2001年 | 3104篇 |
2000年 | 2741篇 |
1999年 | 2180篇 |
1998年 | 1560篇 |
1997年 | 1254篇 |
1996年 | 1157篇 |
1995年 | 1152篇 |
1994年 | 1019篇 |
1993年 | 845篇 |
1992年 | 653篇 |
1991年 | 394篇 |
1990年 | 251篇 |
1989年 | 250篇 |
1988年 | 168篇 |
1987年 | 114篇 |
1986年 | 112篇 |
1985年 | 85篇 |
1984年 | 71篇 |
1983年 | 47篇 |
1982年 | 50篇 |
1981年 | 56篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 23篇 |
1977年 | 20篇 |
1976年 | 26篇 |
1975年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Hui Gu Rowland M. Cannon Hans J. Seifert Michael J. Hoffmann Isao Tanaka 《Journal of the American Ceramic Society》2002,85(1):25-32
The nitrogen solubility in the SiO2 -rich liquid in the metastable binary SiO2 -Si3 N4 system has been determined by analytical TEM to be 1%–4% of N/(O + N) at 1973–2223 K. Analysis of the near edge structure of the electron energy loss peak indicates that nitrogen is incorporated into the silicate network rather than being present as molecular N2 . A regular solution model with a positive enthalpy of mixing for the liquid was used to match the data for the metastable solubility of N in the presence of crystalline Si3 N4 and to adjust the computed phase diagram. The solubility of Si3 N4 in fused SiO2 is far less than reported in liquid silicates also containing Al, Mg, and/or Y. Apparently, these cations act as modifiers that break anion bridges in the silicate network and, thereby, allow further incorporation of Si3 N4 without prohibitive amounts of network cross-linking. Finally, indications emerged regarding the diffuse nature of the Si3 N4 -SiO2 interface that leads to amorphous regions of higher N content. 相似文献
932.
Spectroscopic evidence for the interaction of hydroxyl groups and chromium ions was obtained using a catalyst prepared from chromyl chloride. A new OH peak, observed at 3705 cm–1 after pumping away CO gas, is attributed to the direct interaction of OH with the low-valent chromium. This peak shifts to 3590 cm–1 on contact with O2 at room temperature and it is assigned to a hydroxyl interacting with the oxidized chromium. New assignments are also proposed for IR bands of CO presorbed on the catalyst. The peak due to CO at 2188 cm–1 decreases as the OH intensity at 3705 cm–1 increases, suggesting that the former peak arises from adsorption on Cr(II) species to which two oxygen atoms are attached. 相似文献
933.
934.
C.?M.?SeubertEmail author M.?E.?Nichols A.?V.?Kucherov 《Journal of Coatings Technology and Research》2005,2(7):529-538
The long-term weathering performance of two UV-curable clearcoat systems was studied using in-plane microtomy in combination
with infrared spectroscopy, UV spectroscopy, and ESR spectroscopy. Oxygen transport characteristics were also studied using
the half-time method. The photooxidation versus depth profile was highly dependant on the presence of hindered amine light
stabilizers (HALS) for both coating systems. Ultraviolet light absorbers (UVA) had little effect on the photooxidation profile.
A photooxidation gradient was formed in both clearcoats due to a reduction in oxygen solubility when compared to standard
thermoset clearcoats. This gradient was only seen in formulations not containing HALS.
Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago,
IL. 相似文献
935.
The catalytic behavior of the novel MCM-22 zeolite for the continuous alkylation of isobutane with 2-butene has been investigated at a temperature of 50°C, 2.5 MPa total pressure, and a variety of olefin space velocities. At high olefin conversions the MCM-22 zeolite showed a very high initial cracking activity attributable to strong Brønsted acid sites, as well as to the existence of strong diffusional restrictions of the TMP's (formed inside the zeolite) to exit through the channels. At short times on stream (TOS), TMP's account for ca. 40% of the C8 fraction. The olefin conversion and the cracking activity rapidly decline with TOS, while the alkylate product became richer in dimethylhexenes, indicating a predominance of 2-butene dimerization and a loss of hydrogen transfer activity as the catalyst aged. Moreover, MCM-22 gives less TMP's than large-pore zeolites (USY, beta, mordenite), but more than the mediumpore ZSM-5 at similar 2-butene conversion. The latter catalyst was much more selective for olefin dimerization than for isobutane alkylation, presumably because formation of the bulkier TMP's was strongly impeded in its smaller pores. 相似文献
936.
Phosphorus modification of ZSM-5 leads to extra framework P5+ and probably incorporation of +3 valence state of P in the framework. The resulting system has increased Brønsted acidity. Theoretical calculations also favour the postulate that phosphorus in +3 valence state can be incorporated into the lattice. 相似文献
937.
Host Plant Volatiles Synergize Response to Sex Pheromone in Codling Moth, Cydia pomonella 总被引:1,自引:0,他引:1
Plant volatile compounds synergize attraction of codling moth males Cydia pomonella to sex pheromone (E,E)-8,10-dodecadien-1-ol (codlemone). Several apple volatiles, known to elicit a strong antennal response, were tested in a wind tunnel. Two-component blends of 1 pg/min codlemone and 100 pg/min of either racemic linalool, (E)-beta-farnesene, or (Z)-3-hexen-1-ol attracted significantly more males to the source than codlemone alone (60, 58, 56, and 37%, respectively). In comparison, a blend of codlemone and a known pheromone synergist, dodecanol, attracted 56% of the males tested. Blends of pheromone and plant volatiles in a 1:100 ratio attracted more males than 1:1 or 1:10,000 blends. Adding two or four of the most active plant compounds to codlemone did not enhance attraction over blends of codlemone plus single-plant compounds. Of the test compounds, only farnesol was attractive by itself; at a release rate of 10,000 pg/min, 16% of the males arrived at the source. However, attraction to a 1:10,000 blend of codlemone and farnesol (42%) was not significantly different from attraction to codlemone alone (37%). In contrast, a codlemone mimic, (E)-10-dodecadien-1-ol, which attracted 2% males by itself, had a strong antagonistic effect when blended in a 1:10,000 ratio with codlemone. 相似文献
938.
Hydrophobically modified alkali-soluble emulsion (HASE) polymers are an important class of rheology modifiers for waterborne
coatings applications. They are typically prepared as terpolymers by emulsion polymerization of ethyl acrylate (EA), methacrylic
acid (MAA), and an associative macromonomer. The viscosity development and shear responses of HASE solutions depend on a number
of factors. This article presents rheological data reflecting the impacts of three key variables: hydrophobe size, acid content,
and molecular weight, on model HASE thickening and rheological performance. The relative contributions of hydrophobic association,
chain expansion, and polymer chain length are discussed.
In steady shear flow, all thickener solutions approached some constant low-shear viscosity at small deformation rates. At
the same molar composition, larger hydrophobe size resulted in higher viscosity development and greater shear thinning behavior.
The amount of acid monomer in HASE polymers can influence the balance between hydrophobic attraction and electrostatic repulsion
forces. It was found that a minimum of 15 wt% MAA was required to effect dissolution and thickening of the model HASE polymers.
Increasing the MAA level yielded higher zero-shear viscosity and storage modulus G’ with maximal values being obtained at
40% MAA.
The molecular weight of the model thickeners was controlled by the amount of chain transfer agent (CTA) added during polymerization.
When the CTA level was below 0.1 wt% based on total monomers, the polymer solutions displayed shear-thinning behavior. A small
increase in CTA concentration beyond 0.1% resulted in a dramatic change to Newtonian flow, and the solution viscosity was
nearly two orders of magnitude lower.
The model thickeners were also tested in a vinyl acrylic architectural paint formulation. The effects of each individual factor
on paint thickener efficiency, high-shear, and low-shear properties are discussed and compared with solution rheology for
predictive relationships.
Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 11–12, 2003, in Philadelphia,
PA. 相似文献
939.
基于嵌入式的CAN-Ethernet网关的设计 总被引:2,自引:0,他引:2
提出基于"现场总线 以太网 MODBUS/TCP"方案的网络结构、协议转换的设计思路及网络模型,应用OPC技术解决I/O硬件设备以及软件之间的互操作性问题.在此基础上介绍嵌入式网卡硬件平台的设计及软件开发方法. 相似文献
940.