首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2692篇
  免费   45篇
  国内免费   5篇
电工技术   80篇
综合类   2篇
化学工业   467篇
金属工艺   68篇
机械仪表   46篇
建筑科学   38篇
能源动力   72篇
轻工业   218篇
水利工程   7篇
石油天然气   3篇
无线电   341篇
一般工业技术   368篇
冶金工业   816篇
原子能技术   65篇
自动化技术   151篇
  2023年   7篇
  2022年   19篇
  2021年   37篇
  2020年   20篇
  2019年   20篇
  2018年   34篇
  2017年   15篇
  2016年   23篇
  2015年   23篇
  2014年   43篇
  2013年   112篇
  2012年   65篇
  2011年   81篇
  2010年   74篇
  2009年   62篇
  2008年   102篇
  2007年   69篇
  2006年   75篇
  2005年   77篇
  2004年   84篇
  2003年   62篇
  2002年   64篇
  2001年   55篇
  2000年   54篇
  1999年   66篇
  1998年   291篇
  1997年   210篇
  1996年   133篇
  1995年   83篇
  1994年   79篇
  1993年   81篇
  1992年   44篇
  1991年   37篇
  1990年   41篇
  1989年   29篇
  1988年   29篇
  1987年   32篇
  1986年   20篇
  1985年   31篇
  1984年   37篇
  1983年   23篇
  1982年   30篇
  1981年   31篇
  1980年   26篇
  1979年   20篇
  1978年   15篇
  1977年   14篇
  1976年   28篇
  1975年   9篇
  1972年   7篇
排序方式: 共有2742条查询结果,搜索用时 15 毫秒
71.
Ohtake T  Kimura M  Takemura H  Hishida A 《Lipids》2002,37(4):359-366
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 F 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 PGF 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   
72.
The alumina–carbon composite fibers were obtained from poly[(acyloxy)aloxane] (PAA) with 3-ethoxypropanoic (EPA) and m-anisic acids (m-AA) legands. This preceramic polymer can be dissolved in p-xylene-methanol-EPA mixed solvent, and the concentrated solution exhibited an excellent spinnability. During the pyrolysis and sintering processes, aliphatic carboxylate in the side groups was easily decomposed and eliminated. The aromatic carboxylate, however, seems to be converted and migrated to a carbon domain in the alumina matrix into which aloxane repetition was converted. The fibers pyrolyzed up to 800 and 1000°C have electrical conductivities that monotonically increase with increasing temperature. The fiber pyrolyzed up to 1200°C showed the electrical conductivity in a rather complicated manner.  相似文献   
73.
74.
75.
The phase behaviors for the blends of poly(3‐hydroxypropionate) (PHP), poly(L ‐lactide) (PLLA), poly(D ‐lactide) (PDLA), and poly(D,L ‐lactide) (PDLLA) with catechin were investigated by differential scanning calorimetry. In PLLA/catechin, PDLA/catechin, and PDLLA/catechin blends, two glass transitions were detected when the catechin content was ≥40 wt %, whereas in PHP/catechin blends only one glass transition was observed over the whole range of blend compositions. The former and the latter results should reflect the inhomogeneous and the homogeneous nature of the blends, respectively, in the amorphous phase. These different phase behaviors should arise from the differences in the chemical structures between PHP and PLLA/PDLA/PDLLA, which dominates the strength and the number of intermolecular hydrogen‐bonding interactions between the ester carbonyl groups of polyesters and the phenol groups of catechin. As detected by FTIR spectroscopy, in comparison with PHP, the steric hindrance of side‐chain methyl groups of PLLA, PDLA, and PDLLA might restrain the formation of hydrogen bonds between their ester carbonyl groups and the phenol hydroxyl groups of catechin, even weakening the strength of such hydrogen bonds. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3565–3573, 2004  相似文献   
76.
BACKGROUND: In this study, the inductive effect of salinity on nitrite accumulation in a down‐flow hanging sponge (DHS) reactor, developed as a novel and cost‐effective wastewater treatment process, was evaluated by conducting a long‐term continuous experiment lasting more than 1400 days. RESULTS: The influent salinity was controlled by adding NaCl at concentrations ranging from 0 to 25 g Cl? L?1. The effluent nitrite increased with increases in salinity, i.e. the fraction of nitrite to total nitrogen in the effluent increased from 1.6% at 0 g Cl? L?1 to 87.6% at 25 g Cl? L?1. Fluorescence in situ hybridization (FISH) analysis revealed that as salinity increased, the nitrifying bacterial community in the DHS changed markedly at the species level. In particular, the dominant nitrite‐oxidizing bacteria changed from Nitrospira‐sublineage I at 0 g Cl? L?1 to Nitrobacter spp. at 15 g Cl? L?1. At 25 g Cl? L?1, no nitrite‐oxidizing bacteria were detected. CONCLUSION: Our findings suggest that the DHS reactor is suitable for cost‐effective nitrite production processes and that salinity control using NaCl is an effective method for inducing nitrite accumulation. Copyright © 2012 Society of Chemical Industry  相似文献   
77.
Copoly(amide-ethers) containing two types of tertiary amine units were made as antistatic modifiers for poly(ethylene terephthalate) (PET) fibers. The filaments of the copolymers were melt-spun and reacted with three alkylating agents in order to quaternize the tertiary amine into a sulfo-betaine, a carbobetaine, and an ammonium ion. The apparent electric resistivity of the filaments was greatly reduced by this reaction, being in the range of 106 to 108 Ω/cm. However, because these quaternized copolymers incurred decomposition during blend spinning with PET, a blend PET fiber containing one type of copoly(amide-ether) was melt-spun and subjected to quaternization of the amino groups as well as to surface crosslinking with various alkylating and epoxy agents. The quaternized blend fibers obtained showed improved antistatic properties compared with the original blend fiber. Particularly, the fibers crosslinked with epoxy compounds were found to have the best antistatic properties that had ever been attained with this type of modification. The antistatic properties were retained even after dyeing, because both hydrophilic and ionic groups had been effectively immobilized on the surface. Since this quaternization and crosslinking could be conducted on-line with spinning and drawing within a short reaction time, this modification technique is called “spin-finishing method”, which should be superior to the conventional methods in terms of cost performance and productivity.  相似文献   
78.
A new technique for imparting antistatic properties to poly(ethylene terephthalate) (PET) fiber has been developed. In this technique, blend polyester fibers containing poly(ethylene terephthalate/5-sulfoisophthalate) (SIP-PET) were prepared by blend spinning and then treated with various cationic surfactants in the process of dyeing. The surfactants could effectively be immobilized on the fiber as the counter cations of the sulfonate groups of the 5-sulfoisophthalate (SIP) units and aid the release of static electrons formed in the fiber. Thus, the half-life time (t1/2) of leakage of static charge and the surface resistivity (Rs) of the blend PET fibers became much lower after treating. The best result was obtained with a methylated quaternary ammonium salt of a stearylamine-ethylene oxide (EO) adduct or hydrochloride of a laurylamine-EO adduct as the surfactant of which the number of EO units was around ten. Even after five washing cycles the t1/2 value of the fibers treated with these surfactants was kept lower than 30 s with the Rs value maintained in the order of 1013 Ω cm-2. Therefore, the present technique could be useful for practical production of polyester fibers with “semi-permanent” antistatic properties which can be recovered by re-treatment even if they were lost.  相似文献   
79.
Y-Si-O films were prepared by laser chemical vapor deposition (LCVD) with a Nd:YAG laser using TEOS (tetraethyl orthosilicate) and Y(dpm)3 precursors. The effects of laser power (PL), deposition temperature (Tdep) and total chamber pressure (Ptot) on the phase, microstructure and deposition rate of Y-Si-O films were investigated. At PL < 102 W (Tdep < 1140 K), amorphous Y-Si-O films were obtained independent of Ptot. At Ptot = 0.6 kPa, mixture phase films of Y2SiO5 (the X1 phase) and Y2Si2O7 (the α, β, δ and y phases) were obtained at PL = 102 W (Tdep = 1210 K), while single phase X1-Y2SiO5 films were prepared at PL > 139 W (Tdep > 1280 K). Y2Si2O7 mixture phase films were obtained at Ptot = 3.5 kPa and Y2Si2O7 and Y2SiO5 (the X2 phase) mixture phase films were obtained at Ptot = 7.5 kPa independent of Tdep. Amorphous Y-Si-O films showed a dense, glassy microstructure. Faceted columnar grains grew on the Y-Si-O films at Ptot = 0.6 kPa, whereas rounded cauliflower-like grains grew at Ptot = 7.5 kPa. The Rdep increased with increasing PL and Tdep and reached a maximum of 430 μm h1 at Ptot = 0.6 kPa, PL = 186 W and Tdep = 1310 K.  相似文献   
80.
The n-type thermoelectric properties of the half-Heusler compound ZrNiSn can be converted to p-type by the addition of Co and Ir. We found that Co and Ir atoms preferably occupy the vacancy sites instead of substituting at Ni sites. This implies that the phase stability of the compound gradually changes towards that of the Heusler compound Zr(Ni,M)2Sn, where M is Co and/or Ir. The occupation of vacancy sites by Co and Ir atoms leads to a drastic reduction in lattice thermal conductivity owing to the enhancement of phonon scattering by the solid solution effect.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号