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   1988篇
  免费   115篇
  国内免费   14篇
电工技术   29篇
综合类   6篇
化学工业   508篇
金属工艺   30篇
机械仪表   79篇
建筑科学   59篇
矿业工程   3篇
能源动力   183篇
轻工业   201篇
水利工程   13篇
石油天然气   35篇
无线电   180篇
一般工业技术   398篇
冶金工业   54篇
原子能技术   17篇
自动化技术   322篇
  2024年   11篇
  2023年   71篇
  2022年   135篇
  2021年   152篇
  2020年   107篇
  2019年   112篇
  2018年   131篇
  2017年   100篇
  2016年   133篇
  2015年   76篇
  2014年   134篇
  2013年   188篇
  2012年   109篇
  2011年   109篇
  2010年   84篇
  2009年   85篇
  2008年   61篇
  2007年   49篇
  2006年   47篇
  2005年   25篇
  2004年   25篇
  2003年   16篇
  2002年   16篇
  2001年   15篇
  2000年   7篇
  1999年   14篇
  1998年   18篇
  1997年   7篇
  1996年   13篇
  1995年   6篇
  1994年   9篇
  1993年   7篇
  1992年   7篇
  1991年   6篇
  1990年   4篇
  1989年   2篇
  1988年   2篇
  1987年   2篇
  1986年   4篇
  1985年   3篇
  1984年   3篇
  1983年   3篇
  1981年   2篇
  1979年   2篇
  1978年   2篇
  1977年   2篇
  1976年   1篇
排序方式: 共有2117条查询结果,搜索用时 12 毫秒
61.
Heat shock proteins are ubiquitous, induced under a number of environmental and metabolic stresses, with highly conserved DNA sequences among mammalian species. Camelus dromedaries (the Arabian camel) domesticated under semi-desert environments, is well adapted to tolerate and survive against severe drought and high temperatures for extended periods. This is the first report of molecular cloning and characterization of full length cDNA of encoding a putative stress-induced heat shock HSPA6 protein (also called HSP70B') from Arabian camel. A full-length cDNA (2417 bp) was obtained by rapid amplification of cDNA ends (RACE) and cloned in pET-b expression vector. The sequence analysis of HSPA6 gene showed 1932 bp-long open reading frame encoding 643 amino acids. The complete cDNA sequence of the Arabian camel HSPA6 gene was submitted to NCBI GeneBank (accession number HQ214118.1). The BLAST analysis indicated that C. dromedaries HSPA6 gene nucleotides shared high similarity (77-91%) with heat shock gene nucleotide of other mammals. The deduced 643 amino acid sequences (accession number ADO12067.1) showed that the predicted protein has an estimated molecular weight of 70.5 kDa with a predicted isoelectric point (pI) of 6.0. The comparative analyses of camel HSPA6 protein sequences with other mammalian heat shock proteins (HSPs) showed high identity (80-94%). Predicted camel HSPA6 protein structure using Protein 3D structural analysis high similarities with human and mouse HSPs. Taken together, this study indicates that the cDNA sequences of HSPA6 gene and its amino acid and protein structure from the Arabian camel are highly conserved and have similarities with other mammalian species.  相似文献   
62.
The effect of the type and the amount of hardeners, such as ammonium nitrate, ammonium carbonate and nitric acid on the molasses bonded briquettes prepared from anthracite fines or coke breeze were investigated. Amongst the hardener studied the best results were obtained with 2.5% ammonium nitrate hardener. The briquettes produced with this hardener were highly water resistant but not waterproof and their tensile strengths were not adequate to be used as a substitute for the metallurgical coke. Therefore, the briquettes were prepared with molasses containing 2.5% ammonium nitrate hardener and air blown coal tar pitch blended binder. When the blended binder was used for the production of anthracite fines or coke breeze briquettes, after curing at 200 °C for 2 h, they became waterproof and their tensile strengths were found to be sufficient to be used as a substitute for coke oven coke. The briquettes after curing could be directly charged into the blast furnace without carbonizing them at high carbonization temperatures. Since molasses and coal tar pitch, are relatively cheap and readily available materials, the process investigated could be economical way of producing high quality formed coke.  相似文献   
63.
Evaluation of abundantly available agro-industrial by-products for their bioactive compounds and biological activities is beneficial in particular for the food and pharmaceutical industries. In this study, rapeseed meal, cottonseed meal and soybean meal were investigated for the presence of bioactive compounds and antioxidant, anti-inflammatory, xanthine oxidase and tyrosinase inhibitory activities. Methanolic extracts of rapeseed meal showed significantly (P < 0.01) higher phenolics and flavonoids contents; and significantly (P < 0.01) higher DPPH and nitric oxide free radical scavenging activities when compared to that of cottonseed meal and soybean meal extracts. Ferric thiocyanate and thiobarbituric acid tests results showed rapeseed meal with the highest antioxidant activity (P < 0.01) followed by BHT, cotton seed meal and soybean meal. Rapeseed meal extract in xanthine oxidase and tyrosinase inhibitory assays showed the lowest IC(50) values followed by cottonseed and soybean meals. Anti-inflammatory assay using IFN-γ/LPS stimulated RAW 264.7 cells indicated rapeseed meal is a potent source of anti-inflammatory agent. Correlation analysis showed that phenolics and flavonoids were highly correlated to both antioxidant and anti-inflammatory activities. Rapeseed meal was found to be promising as a natural source of bioactive compounds with high antioxidant, anti-inflammatory, xanthine oxidase and tyrosinase inhibitory activities in contrast to cotton and soybean meals.  相似文献   
64.
In this paper, a study on the development of a numerical modeling of the detonation of C H N O‐based gaseous explosives is presented. In accordance with the numerical model, a FORTRAN computer code named GasPX has been developed to compute both the detonation point and the detonation properties on the basis of Chapman–Jouguet (C‐J) theory. The determination of the detonation properties in GasPX is performed in chemical equilibrium and steady‐state conditions. GasPX has two improvements over other thermodynamic equilibrium codes, which predict steady‐state detonation properties of gaseous explosives. First, GasPX employs a nonlinear optimization code based on Generalized Reduced Gradient (GRG) algorithm to compute the equilibrium composition of the detonation products. This optimization code provides a higher level of robustness of the solutions and global optimum determination efficiency. Second, GasPX can calculate the solid carbon formation in the products for gaseous explosives with high carbon content. Detonation properties such as detonation pressure, detonation temperature, detonation energy, mole fractions of species at the detonation point, etc. have been calculated by GasPX for many gaseous explosives. The comparison between the results from this study and those of CEA code by NASA and the experimental studies in the literature are in good agreement.  相似文献   
65.
Propylsulfonic acid-functionalized partially crystalline silicalite-1 materials were synthesized via one step co-condensation technique by varying the molar ratio of organosilane source, 3-mercaptopropyltrimethoxysilane (3MP) to tetraethylorthosilicate (TEOS) in the range of 0.05–0.30, and subsequent oxidation of thiol group to propylsulfonic acid using hydrogen peroxide (H2O2). These materials were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and nitrogen adsorption–desorption method. The structure of these materials was determined by Fourier transform infrared spectroscopy (FT-IR) and 29Si and 13C solid state NMR. XRD results show that % crystallinity of the materials decreased with the increase in 3MP concentration in the synthesis mixture. Selected area electron diffraction (SAED) showed the presence of crystalline and amorphous phases in the samples. An amorphous phase was formed when 3MP concentration was 30 mol% of the total silica source. After elimination of the structure directing agent (SDA) by calcination at 420 °C, thermogravimetric analysis (TGA) shows that the structure was thermally stable up to 550 °C. Ammonia temperature-programmed desorption (NH3-TPD) shows that the acid capacity of these materials was in the range of 1.19–1.83 mmol H+/g, which shows that these materials could be used as potential heterogeneous acid catalyst.  相似文献   
66.
In this study, polysulfone (PSF) hollow fiber membranes with enhanced performance for humic acid removal were prepared from a dope solution containing PSF/DMAc/PVP/TiO2. The main reason for adding titanium oxide during dope solution preparation was to enhance the antifouling properties of membranes prepared. In the spinning process, air gap distance was varied in order to produce different properties of the hollow fiber membranes. Characterizations were conducted to determine membrane properties such as pure water flux, molecular weight cut off (MWCO), humic acid (HA) rejection and resistance to fouling tendency. The results indicated that the pure water flux and MWCO of membranes increased with an increase in air gap distance while HA retention decreased significantly with increasing air gap. Due to this, it is found that the PSF/TiO2 membrane spun at zero air gap was the best amongst the membranes produced and demonstrated > 90% HA rejection. Analytical results from FESEM and AFM also provided supporting evidence to the experimental results obtained. Based on the anti-fouling performance investigation, it was found that membranes with the addition of TiO2 were excellent in mitigating fouling particularly in reducing the fouling resistances due to concentration polarization, cake layer formation and absorption.  相似文献   
67.
68.
BACKGROUND: The aim of this work is to enhance the production of terpolyester poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate‐co‐4‐hydroxybutyrate) (P(3HB‐co‐3HV‐co‐4HB)) produced by a locally isolated bacterium, Cupriavidus sp. USMAA2‐4. The monomer composition was varied by supplementing different carbon precursors and by manipulating the culture condition through one‐stage cultivation. The effect of C/N ratio and different concentrations of carbon source and precursors were investigated in order to produce higher content of this terpolyester. Although research on this biodegradable polyester is abundant, studies on terpolyester P(3HB‐co‐3HV‐co‐4HB) are still limited. RESULTS: Supplementation of oleic acid in accumulation medium increased the bacterial growth and polyhydroxyalkanoate (PHA) accumulation. It was also shown that medium consisting of assorted carbon precursors at C/N 20 gave relatively high dry cell weight and P(3HB‐co‐3HV‐co‐4HB) content. Various compositions of terpolyester were obtained when the concentration of oleic acid and 4HB precursors were manipulated. The combination of oleic acid with γ‐butyrolactone and 1‐pentanol was found to be the best combination to produce high PHA content (81 wt%). The composition of monomer in P(3HB‐co‐3HV‐co‐4HB) was produced in the range 8–13 mol% for 3HV and 9–24 mol% for 4HB, respectively. CONCLUSIONS: The production of P(3HB‐co‐3HV‐co‐4HB) in shake‐flasks successfully produced 81 wt% of PHA content. This manipulated culture condition can be used at larger scale to provide modeling for the production of terpolyester in a bioreactor. Copyright © 2012 Society of Chemical Industry  相似文献   
69.
The samples of sliced and mashed apples were freeze-dried by controlling their surface temperatures over the usual pressure range of commercial operations. The surface of sliced samples could not be maintained at above 10°C in order to prevent the frozen layer from melting, while that of mashed samples was allowed to heat up to 70°C.

Thermal conductivities and permeabilities were determined by applying the uniformly-retreating-ice front model to the dried layer of the samples undergoing freeze-drying. The values of permeability for the mashed samples were found to depend on the ice-crystallization time during freezing. The results indicated that the drying rate of sliced samples was limited by the transfer rate of water vapor flowing through the dried layer. A cellular structural model is proposed for predicting the permeability of the dried layer, based on the resistance of the cell membrane to molecular transfer of water vapor.  相似文献   
70.
The general blueprint for the design of monoamine oxidase-B (MAO-B) inhibitors has been based on two phenyl or heteronuclei linked via a spacer of appropriate length. In this study, 1-[4-(morpholin-4-yl)phenyl]-5-phenylpenta-2,4-dien-1-one (MO10) was prepared by the condensation of 4′-morpholinoacetophenone and cinnamaldehyde in basic alcoholic medium. MO10 was assessed for inhibitory activity against two human MAO isoforms, MAO-A and MAO-B. Interestingly, MO10 showed a remarkable inhibition against MAO-B with an IC50 value of 0.044 μM along with a selectivity index of 366.13. The IC50 value was better than that of lazabemide (IC50 value of 0.063 μM), which was used as a reference. Kinetics studies revealed that MO10 acted as a competitive inhibitor of MAO-B, with a Ki value of 0.0080 μM. The observation of recovery of MAO-B inhibition, compared to reference levels showed MO10 to be a reversible inhibitor. MTT assays showed that MO10 was nontoxic to normal VERO cells with an IC50 value of 195.44 μg/mL. SwissADME predicted that MO10 provided advantageous pharmacokinetics profiles for developing agents acting on the central nervous system, that is, high passive human gastrointestinal absorption and blood–brain barrier permeability. Molecular docking simulations showed that MO10 properly entered the aromatic cage formed by Y435, Y398, and FAD of the active site of MAO-B. On the basis of these results, MO10 can be considered a promising starting compound in development of agents for the treatment of various neurodegenerative disorders.  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