全文获取类型
收费全文 | 4677篇 |
免费 | 131篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 323篇 |
综合类 | 4篇 |
化学工业 | 1355篇 |
金属工艺 | 140篇 |
机械仪表 | 110篇 |
建筑科学 | 100篇 |
矿业工程 | 2篇 |
能源动力 | 159篇 |
轻工业 | 420篇 |
水利工程 | 14篇 |
石油天然气 | 6篇 |
无线电 | 289篇 |
一般工业技术 | 861篇 |
冶金工业 | 509篇 |
原子能技术 | 140篇 |
自动化技术 | 397篇 |
出版年
2023年 | 34篇 |
2022年 | 64篇 |
2021年 | 106篇 |
2020年 | 41篇 |
2019年 | 59篇 |
2018年 | 76篇 |
2017年 | 65篇 |
2016年 | 95篇 |
2015年 | 84篇 |
2014年 | 116篇 |
2013年 | 270篇 |
2012年 | 201篇 |
2011年 | 280篇 |
2010年 | 185篇 |
2009年 | 250篇 |
2008年 | 267篇 |
2007年 | 199篇 |
2006年 | 203篇 |
2005年 | 158篇 |
2004年 | 145篇 |
2003年 | 169篇 |
2002年 | 145篇 |
2001年 | 99篇 |
2000年 | 96篇 |
1999年 | 114篇 |
1998年 | 227篇 |
1997年 | 159篇 |
1996年 | 113篇 |
1995年 | 92篇 |
1994年 | 85篇 |
1993年 | 74篇 |
1992年 | 53篇 |
1991年 | 47篇 |
1990年 | 31篇 |
1989年 | 34篇 |
1988年 | 37篇 |
1987年 | 33篇 |
1986年 | 24篇 |
1985年 | 31篇 |
1984年 | 29篇 |
1983年 | 26篇 |
1982年 | 31篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 29篇 |
1978年 | 34篇 |
1977年 | 16篇 |
1976年 | 23篇 |
1975年 | 9篇 |
1969年 | 7篇 |
排序方式: 共有4829条查询结果,搜索用时 15 毫秒
91.
Thermal behaviors of a few kinds of poly(fluoroalkyl methacrylate) prepared by γ-or UV-ray polymerization were investigated by using thermogravimetric measurements with the intermittent analysis of the gaseous products. The degradation of fluoroalkyl methacrylate polymers, monomeric units of which were CH2=C(CH3)COOCH2(CF2CF2)nH, n = 1, 2, and 3, proceeded according to the depolymerization mechanism reproducing the pristine monomer exclusively, but the thermogram in inert atmosphere showed the features of a two-step reaction. Two species of polymer differing in the heat stability were supposed to exist in the polymeric substance produced by γ- or UV-ray irradiation, and the fraction of polymer having lower heat stability increased with the increasing length of the fluoroalkyl ester group. In air, however, the thermogram of poly(fluoroalkyl methacrylate) showed no such a stepwise weight decrease as was observed in inert atomsphere with the elevating temperature, and the temperatures at which the depolymerization was introduced shifted to a much higher region. The results were ascribed to the reaction of initiating polymer radicals produced on polymer having lower stability with oxygen to form hydroperoxide, which once stabilized the polymer radicals and obstructed the initiaition of the unzipping reaction till higher temperature. 相似文献
92.
Yoshikazu Suzuki Naoki Kondo Tatsuki Ohji Peter E. D. Morgan 《International Journal of Applied Ceramic Technology》2004,1(1):76-85
Uniformly porous composites with 3-D network structure (UPC-3D) have been recently developed via a pyrolytic reactive sintering process, which takes advantage of the evolved CO2 gas from a decomposing carbonate source (e.g., dolomite, CaMg(CO3 )2 ) and does not require any additional pore-forming agent nor long-time burning-out process. Through liquid formation via LiF doping, strong necks are formed between constituent particles before completion of the pyrolysis of carbonate, resulting in the formation of a strong 3-D network structure. The pore size distribution is very narrow (with typical pore size: ∼1 μm), and the porosity was controllable (∼30–60%) by changing the sintering temperature. This article presents the development details of UPC-3D, and reports the recent findings in CaZrO3 /MgAl2 O4 system, which will be one of the more promising systems for practical applications. 相似文献
93.
Thermal behaviors of a few kinds of poly(fluoroalkyl methacrylate-co-methyl methacrylate) prepared by γ-ray copolymerization were investigated by using thermogravimetric measurements together with the intermittent analysis of the gaseous products. The thermal degradation of copolymers composed of one of fluoroalkyl methacrylates of the following structures: CH2?C(CH3)COOCH2(CF2CF2)nH, where n = 1,2, and 3, and methyl methacrylate proceeded according to the depolymerization mechanism reproducing the pristine component comonomers exclusively, but their thermograms in inert atmosphere showed the feature of a two-step reaction. In air, however, thermograms of copolymers did not show such a stepwise decrease in weight with the elevating temperature, and temperatures at which depolymerization was introduced shifted to a much higher region. The overall aspects of depolymerization of copolymers seemed to be much similar to that of fluoroalkyl methacrylate homopolymer previously reported, and the retardation of depolymerization by air was considered to be due mainly to the stabilization of once-formed polymer radicals by oxygen. 相似文献
94.
Effects of dietary lipids on daunomycin-induced nephropathy in mice: comparison between cod liver oil and soybean oil 总被引:3,自引:0,他引:3
Although it is well known that dietary lipids affect the course of glomerulonephritis in rats and humans, the precise mechanisms
involved have not been fully elucidated. The aim of this study was to investigate the effects of different types of dietary
lipids (fish oil and vegetable oil) on daunomycin (DM)-induced nephropathy in mice fed on soybean oil (SO) or cod liver oil
(CLO). Urinary protein excretion, serum albumin, creatinine, total cholesterol, and TG were measured, and glomerular histological
changes were evaluated. Antioxidant enzymes were also measured, along with the levels of lipid peroxide, GSH, thromboxane
(Tx) B2′ and 6-keto prostaglandin F1α in renal cortical tissue. Dietary CLO significantly reduced urinary albumin excretion and ameliorated the histological changes
induced by DM. The increase of tissue lipid peroxide levels seen in SO-fed mice was suppressed in CLO-fed mice, whereas CLO-fed
mice showed higher GSH levels than SO-fed mice throughout the experiment. In addition, renal tissue GSH peroxidase activity
was significantly higher at 72 h after DM injection in CLO-DM mice than in SO-DM mice. Both renal cortical TxB2 and 6-keto PGF1α levels were significantly lower in CLO-DM mice than in SO-DM mice. These results suggest that inhibition of oxidative damage
by dietary CLO played an important role in the prevention of DM nephropathy in this mouse model. The effect of CLO was closely
associated with the inhibition of Tx synthesis. 相似文献
95.
Yoshiyuki Sakamoto Tomoyoshi Motohiro Shinichi Matsunaga Kohei Okumura Tomoyuki Kayama Kiyoshi Yamazaki Toshiyuki Tanaka Yoshimi Kizaki Naoki Takahashi Hirofumi Shinjoh 《Catalysis Today》2007,121(3-4):217-225
The release and reduction of NOx in a NOx storage-reduction (NSR) catalyst were studied with a transient reaction analysis in the millisecond range, which was made possible by the combination of pulsed injection of gases and time resolved time-of-flight mass spectrometry. After an O2 pulse and a subsequent NO pulse were injected into a pellet of the Pt/Ba/Al2O3 catalyst, the time profiles of several gas products, NO, N2, NH3 and H2O, were obtained as a result of the release and reduction of NOx caused by H2 injection. Comparing the time profiles in another analysis, which were obtained using a model catalyst consisting of a flat 5 nmPt/Ba(NO3)2/cordierite plate, the release and reduction of NOx on Pt/Ba/Al2O3 catalyst that stored NOx took the following two steps; in the first step NO molecules were released from Ba and in the second step the released NO was reduced into N2 by H2 pulse injection. When this H2 pulse was injected in a large amount, NO was reduced to NH3 instead of N2.
A only small amount of H2O was detected because of the strong affinity for alumina support. We can analyze the NOx regeneration process to separate two steps of the NOx release and reduction by a detailed analysis of the time profiles using a two-step reaction model. From the result of the analysis, it is found that the rate constant for NOx release increased as temperature increase. 相似文献
96.
Koji Matsui Kenji Tanaka Takanori Yamakawa Masato Uehara Naoya Enomoto Junichi Hojo 《Journal of the American Ceramic Society》2007,90(2):443-447
The shrinkage behavior of fine zirconia powders containing 2.9 and 7.8 mol% Y2 O3 was investigated to clarify the effect of Y2 O3 concentration on the initial sintering stage. The shrinkage of powder compact was measured under both conditions of constant rates of heating (CRH) and constant temperatures. CRH measurements revealed that when the Y2 O3 concentration of fine zirconia powder increased, the starting temperature of shrinkage shifted to a high temperature. Isothermal shrinkage measurements revealed that the increase in Y2 O3 concentration causes the shrinkage rate to decrease. The values of activation energy ( Q ) and frequency-factor term (β0 ) of diffusion at initial sintering were estimated by applying the sintering-rate equation to the isothermal shrinkage data. When the Y2 O3 concentration increases, both Q and β0 of diffusion increase. It is, therefore, concluded that the increase in Y2 O3 concentration of fine zirconia powder decreases the shrinkage rate because of increasing Q of diffusion at the initial stage of sintering. 相似文献
97.
Satoru Sano Noriko Saito Shin-ichi Matsuda Naoki Ohashi Hajime Haneda You Arita Minoru Takemoto 《Journal of the American Ceramic Society》2006,89(2):568-574
Forsterite (Mg2 SiO4 ) ceramics were prepared using Mg(OH)2 and SiO2 as precursors, and the effect of powder characteristics of Mg(OH)2 on calcination and sintering was investigated. The use of highly dispersed Mg(OH)2 powder (HD powder) resulted in a lower calcination temperature. Forsterite powder of high homogeneity and small particle size prepared from the HD powder enabled synthesis of high-density forsterite ceramics by ordinary sintering without applying external pressure. Moreover, transparent forsterite ceramics were successfully synthesized through addition of excess Mg to the precursors to compensate for Mg evaporated during the sintering process. Subsequent dielectric measurements revealed that the transparent forsterite ceramics had a very low dielectric loss (tan δ<10−4 ). 相似文献
98.
Tsuneo Okubo 《Polymer Bulletin》1990,23(2):211-218
Summary The adsorption of synthetic polyelectrolytes on the surfaces of monodisperse polystyrene spheres and colloidal silica spheres
is studied by electrophoretic mobility measurements. Electrolytes used are NaCl, CaCl2, LaCl3, Na2SO4, sodium poly(ethylenesulfonate) (NaPES), sodium poly(styrenesulfonate) (NaPSS), polybrene? (PB), poly-4-vinyl-N-ethylpyridinium bromide (C2PVP), poly-4-vinyl-N-benzylpyridinium chloride (BzPVP), and copolymer of
4-vinyl-N-benzylpyridinium chloride (95%) and 4-vinyl-N-n-hexadecylpyridinium bromide (5%) (C16BzPVP). Electrophoretic velocity
(u) and the effective charge number (α) of a colloidal sphere increase in the presence of PB, C2PVP, BzPVP, and C16BzPVP,
and turn to the positive from the negative values in their absence. Addition of NaPES and NaPSS further decreases u and α
values. Adsorption of the polymers on the colloidal spheres are explained by the hydrophobic and/or dipoledipole interactions
in addition to the electrostatic forces. Weak adsorption of simple electrolytes on the colloidal spheres is deduced from the
electrophoretic measurements. 相似文献
99.
The effect of sodium thiosulfate on the graft copolymerization of methyl methacrylate to cellulose in the hydrogen peroxide initiator system was investigated. The addition of sodium thiosulfate in general was effective for decreasing the per cent grafting and the average molecular weight of grafts and increasing the formation of homopolymer, and the effects became pronounced with increasing hydrogen peroxide concentration. Moreover, the addition of sodium thiosulfate slightly suppressed the formation of grafts at a hydrogen peroxide concentration of 3 mmole/l., but greatly promoted it at 20 mmole/l. Traces of metallic ions present in cellulose could not be eliminated sufficiently by treatment with 3N hydrochloric acid. Such ions were found to interact with hydrogen peroxide and thus participate directly in the initiation and termination of the polymerization reaction. EDTA, the chelating agent, was highly effective for suppressing such participation of metallic ions. In the hydrogen peroxide initiator system applied to the EDTA-treated samples, sodium thiosulfate caused an effective initiation of graft formation. 相似文献
100.
K. Wakui K. Satoh G. Sawada K. Shiozawa K. Matano K. Suzuki T. Hayakawa Y. Yoshimura K. Murata F. Mizukami 《Catalysis Letters》2002,81(1-2):83-88
Dehydrogenative cracking reaction of n-butane was studied using HZSM-5 catalyst modified with various metal oxides. Alkaline earth (magnesium), transition metal (cobalt) and rare earth (lanthanum) elements are used for the modification. The selectivity of the products was studied at low conversion (20%). Methane, ethane, ethylene, propylene, butenes and butadiene were the main products. With the use of the cobalt- or magnesium-containing HZSM-5, dehydrogenative cracking was observed and the selectivity of ethylene was much larger than that of ethane. On the other hand, the selectivity of ethylene and ethane were almost the same in the reaction using the lanthanum-containing HZSM-5. It is considered that the cobalt- and magnesium-loaded sites on HZSM-5 played an important role in the dehydrogenative cracking. 相似文献