全文获取类型
收费全文 | 30919篇 |
免费 | 3046篇 |
国内免费 | 1462篇 |
专业分类
电工技术 | 426篇 |
综合类 | 1595篇 |
化学工业 | 11548篇 |
金属工艺 | 1279篇 |
机械仪表 | 1456篇 |
建筑科学 | 653篇 |
矿业工程 | 461篇 |
能源动力 | 934篇 |
轻工业 | 6328篇 |
水利工程 | 173篇 |
石油天然气 | 1794篇 |
武器工业 | 220篇 |
无线电 | 2213篇 |
一般工业技术 | 3862篇 |
冶金工业 | 1026篇 |
原子能技术 | 640篇 |
自动化技术 | 819篇 |
出版年
2024年 | 156篇 |
2023年 | 603篇 |
2022年 | 770篇 |
2021年 | 1205篇 |
2020年 | 1222篇 |
2019年 | 1253篇 |
2018年 | 1153篇 |
2017年 | 1250篇 |
2016年 | 1368篇 |
2015年 | 1255篇 |
2014年 | 1782篇 |
2013年 | 2155篇 |
2012年 | 2150篇 |
2011年 | 2102篇 |
2010年 | 1459篇 |
2009年 | 1520篇 |
2008年 | 1289篇 |
2007年 | 1718篇 |
2006年 | 1554篇 |
2005年 | 1347篇 |
2004年 | 1136篇 |
2003年 | 1017篇 |
2002年 | 893篇 |
2001年 | 797篇 |
2000年 | 718篇 |
1999年 | 614篇 |
1998年 | 521篇 |
1997年 | 467篇 |
1996年 | 343篇 |
1995年 | 313篇 |
1994年 | 225篇 |
1993年 | 226篇 |
1992年 | 184篇 |
1991年 | 110篇 |
1990年 | 90篇 |
1989年 | 72篇 |
1988年 | 63篇 |
1987年 | 43篇 |
1986年 | 32篇 |
1985年 | 58篇 |
1984年 | 51篇 |
1983年 | 33篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Tadashi Hano Michiaki Matsumoto Takahisa Kawazu Takaaki Ohtake 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,62(1):60-63
The extraction equilibria of various di- and tripeptides with di-2-ethylhexylphosphoric acid (D2EHPA) were studied at low pH values. The complex extracted to organic phase consisted of one molecule of peptide and two molecules of D2EHPA dimer. The extraction constants of the peptides correlated well with the distribution coefficients of peptides between 1-octanol and water, which is a measure of hydrophobicity. The permeation rates of peptides through an emulsion liquid membrane were examined by using D2EHPA as a carrier, Span 80 as an emulsifier and kerosene as a diluent. The rates varied considerably with peptide type, depending upon the hydrophobicity. 相似文献
12.
Crystalline Behavior and Magnetic Properties of Nd60Fe30-x Al10Cox(x = 0,5,10) Bulk Amorphous Alloys
Crystalline behavior and magnetic properties of Nd60Fe30-xAl10Cox( x = 0, 5, 10) bulk amorphous alloys were investigated by differential scanning calorimeter (DSC), X-ray diffraction (XRD) and the vibrating sample magnetometer (VSM). Neither glass transition nor supercooled liquid region before crystallization was observed for the as-cast Nd60Fe30-xAl10Cox ( x = 0,5,10) bulk amorphous alloys. The glass forming ability can be improved significantly by the addition of Co. The as-cast Nd60Fe30-xAl10Cox (x = 0,5,10) alloys show hard magnetic behavior. With the addition of Co content, intrinsic coercivity (iHc) increases while the saturation magnetization(σs) and remanence (σr) decrease. The Curie temperature for the as-cast Nd60Fe30-xAl10Cox alloys increases from 451 K for x =0 to 468 K for x = 10. Some pre-cipitation of crystalline phases does not affect the hard magnetic properties of Nd60Fe30-xAl10Cox(x = 0,5,10) alloys, while the hard magnetic behavior disappears quickly after the alloys being completely crystallized. 相似文献
13.
Francisco Jos Alguacil Concepcin Caravaca María Isabel Martín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(10):1048-1053
The transport of chromium(VI) through a flat‐sheet supported liquid membrane containing Cyanex 921 as a carrier has been investigated. The permeation of the metal is investigated as a function of various experimental variables: hydrodynamic conditions, concentration of chromium(VI) and HCl in the feed phase, carrier concentration and diluent in the membrane and strippant concentration in the stripping phase. The mass transfer coefficient and the thickness of the aqueous boundary layer were calculated from the experimental data. Furthermore, the selectivity of Cyanex 921‐based flat‐sheet supported liquid membrane towards different metal ions and the behaviour of the system against other carriers are presented. Copyright © 2003 Society of Chemical Industry 相似文献
14.
含氚废水水泥固化实验研究 总被引:2,自引:0,他引:2
研究用水泥固化处理氚废水,并选择了最佳配方:水与灰的重量比=0.45~0.5,水泥与石膏重量比=5∶1。用IAEA推荐的方法做浸出实验。为了减少水泥固化体中氚的浸出量,实验了几种涂层材料。沥青涂层可将固化体氚的浸出率降低1~2个量级。 相似文献
15.
16.
Polyurethanes were prepared from pure 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butane diol (BDO) or 1,2-ethane diol (EDO) and α,ω-hydroxyl poly(propylene oxide) (PPO) by reaction injection moulding (RIM). Hard segment (MDI + BDO or EDO) level was 45–50 wt%. The PPO had about 20% ethylene oxide copolymerized in at the chain ends to provide 80% primary OH end groups. Mn was varied from 2000 to 4000. Dibutyl tin dilaurate catalyst and mould temperature were varied. Dynamic mechanical, wide-angle X-ray, differential scanning calorimeter, molecular weight and tensile elongation measurements were made on the RIM polyurethanes. At low reaction rates (low catalyst or temperature) highly crystalline, well phase separated but low molecular weight polymers were produced. At high catalyst or temperature levels more poorly phase separated but high molecular weight, tough polymers resulted. Higher Mn PPO gave better phase separation and EDO gave higher melting temperatures. Preventing hard segment crystallinity by substituting asymmetric MDI or glycols resulted in phase compatibility. 相似文献
17.
18.
The electroclinic effect in the smectic A phase of ferroelectric liquid crystals is a sensitive probe for measuring the soft
mode response near the A-C* transition point. It is possible to evaluate several coefficients of the Landau theory describing
the A-C* transition by simultaneously measuring the frequency dependence of both the optical signal and the current through
the sample. We have made such measurements on a couple of homologous series [2S,3S]-4′-(2-chloro-3-methyl pentanoyloxy) phenyl-trans-4″-n alkoxy cinnamates synthesized in our labortory. The results show that the Landau meanfield theory is adequate to describe
the A-C* phase transition in these compounds.
Presented at the 15th International Liquid Crystal Conference, Budapest, 3–8 July 1994. 相似文献
19.
A new unsymmetrical chiral thioindigo dopant 6‐[(R,R)‐2,3‐difluorooct‐1‐yloxy]‐5′‐nitro‐6′‐[(R)‐2‐octyloxy]thioindigo ( 4 ) designed to photoinvert the sign of spontaneous polarization (PS) in a ferroelectric chiral smectic C (SmC*) liquid crystal was prepared using a synthetic approach previously developed in our laboratory. In this new “ambidextrous” design, the (R)‐2‐octyloxy side‐chain is sterically coupled to the thioindigo core and induces a positive PS, whereas the (R,R)‐2,3‐difluorooctyloxy side‐chain is decoupled from the core and induces a larger negative PS. In the trans form, this dopant induces a negative polarization in the SmC host (+)‐4‐(4‐methylhexyloxy)phenyl 4‐decyloxybenzoate ( PhB ). Irradiation of a 1 mol‐% mixture of 4 in PhB at λ = 510 nm caused a sign inversion of PS, from –0.88 to +0.42 nC cm–2 at T – TC = –5 °C, which is consistent with an increase in the polarization power of the coupled 2‐octyloxy/thioindigo unit over that of the 2,3‐difluorooctyloxy unit, due to the increase in transverse dipole moment of the thioindigo core upon trans–cis photoisomerization. The PS sign inversion was confirmed by a surface‐stabilized ferroelectric liquid crystal photoswitching experiment. Spectroscopic measurements on films of the doped liquid crystal mixtures showed that trans–cis photoisomerization is gradually suppressed with increasing dopant mole fraction, possibly as a result of increased dopant aggregation. 相似文献
20.
建立了高放废液中~(147)Pm的测定方法。用HDEHP萃取稀土,再用HDEHP萃淋树脂柱分离AM和稀土。然后用高效液相色谱法将~(147)Pm从Eu、Ce等其它稀土中分离出来,用液体闪烁法测量~(147)Pm的放射性活度。 相似文献