全文获取类型
收费全文 | 2714篇 |
免费 | 86篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 26篇 |
化学工业 | 531篇 |
金属工艺 | 30篇 |
机械仪表 | 45篇 |
建筑科学 | 97篇 |
矿业工程 | 11篇 |
能源动力 | 72篇 |
轻工业 | 259篇 |
水利工程 | 22篇 |
石油天然气 | 7篇 |
无线电 | 353篇 |
一般工业技术 | 358篇 |
冶金工业 | 634篇 |
原子能技术 | 23篇 |
自动化技术 | 334篇 |
出版年
2022年 | 17篇 |
2021年 | 48篇 |
2020年 | 34篇 |
2019年 | 30篇 |
2018年 | 53篇 |
2017年 | 34篇 |
2016年 | 39篇 |
2015年 | 37篇 |
2014年 | 47篇 |
2013年 | 129篇 |
2012年 | 79篇 |
2011年 | 116篇 |
2010年 | 75篇 |
2009年 | 108篇 |
2008年 | 104篇 |
2007年 | 126篇 |
2006年 | 84篇 |
2005年 | 80篇 |
2004年 | 84篇 |
2003年 | 74篇 |
2002年 | 71篇 |
2001年 | 53篇 |
2000年 | 55篇 |
1999年 | 57篇 |
1998年 | 138篇 |
1997年 | 102篇 |
1996年 | 66篇 |
1995年 | 60篇 |
1994年 | 47篇 |
1993年 | 62篇 |
1992年 | 47篇 |
1991年 | 40篇 |
1990年 | 32篇 |
1989年 | 29篇 |
1988年 | 31篇 |
1987年 | 41篇 |
1986年 | 31篇 |
1985年 | 29篇 |
1984年 | 29篇 |
1983年 | 30篇 |
1982年 | 22篇 |
1981年 | 40篇 |
1980年 | 27篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1977年 | 37篇 |
1976年 | 43篇 |
1975年 | 28篇 |
1974年 | 14篇 |
1973年 | 22篇 |
排序方式: 共有2802条查询结果,搜索用时 15 毫秒
101.
Analysis of samples taken at the Gentilly 2 (Québec) CANDU-PHW (CANadian Deuterium Uranium - Pressurized Heavy Water) plant after chlorination and demineralization revealed the presence of all four trihalomethanes (THMs) (CHCl3, CHBrCl2, CHBr2Cl and CHBr3) and other unidentified halogenated volatile compounds. Among the THMs, chloroform was the major contaminant. A study of its thermal stability in water at different temperatures confirmed the degradation of the CHCl3 molecule according to the equation CHCl3 + H2O → CO + 3 HCl. The reaction follow a first order kinetics and has an activation energy of 100 kJ/mol. The estimated half-life is six seconds at 260°C, the maximum temperature of the steam-condensate cycle. 相似文献
102.
The hexane-soluble fractions of hydroliquefied products from three Yallourn brown coal lithotypes have been separated into five fractions by combined silica-alumina packed column chromatography. Analyses of various fractions by g.c.-m.s. permitted the identification of ≈50 components in the saturate fraction and 40 components in the diaromatic fraction, together with 30 components in the monoaromatics. The components identified were quite similar among hexane-soluble portions of all three lithotypes. A marked predominance of even carbon number alkane (C23-C29) was observed in the hydrocarbon fractions from pale lithotype over , and medium light lithotype over both pure ZnCl2 and . However, medium dark lithotype over both melt catalysts produced a saturate fraction with an odd carbon number(C22-C28) preference. Based on spectral methods, Soxhlet extracts obtained from untreated lithotypes (hexane and benzene solubles) were characterized as complex mixtures of higher molecular weight(300–1000) aliphatic hydrocarbons, which were supposed to be a precursor of the saturates produced from the corresponding lithotype in the catalytic hydroliquefaction. 相似文献
103.
Machado VS Knauer WA Bicalho ML Oikonomou G Gilbert RO Bicalho RC 《Journal of dairy science》2012,95(3):1349-1357
The objectives were (1) to evaluate the association of uterine lavage sample optical density (ULSOD) with uterine health, and (2) to estimate and evaluate a threshold value that will maximize the accuracy of ULSOD as a diagnostic tool for clinical endometritis. The study enrolled 1,742 cows from 3 dairy farms located near Ithaca, New York. The samples were collected at 35 ± 3 d in milk (DIM) by using low-volume uterine lavage. Cows with a purulent or mucopurulent secretion in the sample were diagnosed with clinical endometritis, whereas a subgroup of all studied cows was examined for cytological evidence of inflammation by endometrial cytology. Data for ULSOD measured at different wavelengths (200, 352, 620, 790, 860, and 960 nm) were available for 554 cows; all 1,742 cows had data for ULSOD measured at 620 nm (ULSOD(620)). Incidences of clinical endometritis, metritis, and retained placenta were 10, 15.2, and 5.6%, respectively. The ULSOD(620) was associated with clinical endometritis. Receiver operating characteristic (ROC) analysis of the accuracy of optical density in the detection of clinical endometritis was conducted for ULSOD measured at different wavelengths; ULSOD(620) was selected for further analysis because it presented the best ROC curve to detect clinical endometritis. The recommended threshold for ULSOD(620) ROC was 0.058, where the sensitivity and specificity were 76.3 and 78.3%, respectively. The ROC analysis of the accuracy of optical density in the detection of endometritis defined as a percentage of neutrophils in the uterine lavage samples higher than 18% was conducted for ULSOD(620). The recommended threshold was 0.059, where the sensitivity and specificity were 100 and 82.2%, respectively. Cows with ULSOD(620) ≤ 0.058 were 1.21 times more likely to conceive than cows with ULSOD(620) >0.058; moreover, the median calving-to-conception interval for cows that had ULSOD(620) ≤ 0.058 was 122 d compared with 148 d for cows that had ULSOD(620) >0.058. Cows that were positive for Arcanobacterium pyogenes, diagnosed with metritis, or had retained placenta had 4.0, 1.4, and 1.7 times higher odds of having ULSOD(620) >0.058, respectively. Cows with ULSOD(620) >0.058 had a higher percentage of neutrophils in the uterine lavage samples than cows with ULSOD(620) ≤ 0.058. Uterine lavage sample optical density measured at 620 nm can be used as an objective indicator of uterine health in dairy cows, principally for clinical endometritis. 相似文献
104.
Nicolas RousselLucile Lallemant Bernard Durand Sophie GuillemetJean-Yves Chane Ching Gilbert Fantozzi Vincent Garnier Guillaume Bonnefont 《Ceramics International》2011,37(8):3565-3573
A slurry of α-Al2O3 was doped with Mg, Zr and La nitrates or chlorides, in various amounts in the range 150-500 wt ppm and then freeze-dried to produce nanosized doped powder (∼150 nm). The powder was sintered by SPS to yield transparent polycrystalline alpha alumina. The influence of the nature of the doping element and the starting salt, the thermal treatment before sintering and the sintering temperature on the transparency of the ceramics were investigated. The transparency of the ceramics of nanosized Al2O3 was shown to depend mainly on the way the powder was prepared, the nature of the doping salt also had an effect. Finally, a high real inline transmittance, reaching 48.1% was achieved after optimization. 相似文献
105.
William J. R. Gilbert Stephen J. Johnson Jyun‐Syung Tsau Jenn‐Tai Liang Aaron M. Scurto 《应用聚合物科学杂志》2017,134(10)
Polyacrylamides are often used in water‐based hydraulic fracturing for natural gas and oil production. However, residual polymer remaining in the fractured rock can limit production. A novel approach for degrading partially hydrolyzed polyacrylamide (HPAM) was investigated using hydrogen peroxide and horseradish peroxidase (HRP). This sustainable HRP/H2O2 system degraded the polymer in solution, reducing its viscosity in both pure water and brine solutions. Molecular weight measurements confirmed that the viscosity reduction was due to a significant degradation of the polymer backbone and not primarily by other mechanisms such as amide hydrolysis or rearrangement, and so forth. The reduction in viscosity and molecular weight was first order with respect to H2O2 concentration. The kinetics of viscosity reduction and molecular weight are closely correlated which would allow the quicker and simpler viscosity method to help engineer future processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44560. 相似文献
106.
Seth S. Berbano Jing Guo Hanzheng Guo Clive A. Randall 《Journal of the American Ceramic Society》2017,100(5):2123-2135
The recently developed technique of cold sintering process (CSP) enables densification of ceramics at low temperatures, i.e., <300°C. CSP employs a transient aqueous solvent to enable liquid phase‐assisted densification through mediating the dissolution‐precipitation process under a uniaxial applied pressure. Using CSP in this study, 80% dense Li1.5Al0.5Ge1.5(PO4)3 (LAGP) electrolytes were obtained at 120°C in 20 minutes. After a 5 minute belt furnace treatment at 650°C, 50°C above the crystallization onset, Li‐ion conductivity was 5.4 × 10?5 S/cm at 25°C. Another route to high ionic conductivities ~10?4 S/cm at 25°C is through a composite LAGP ‐ (PVDF‐HFP) co‐sintered system that was soaked in a liquid electrolyte. After soaking 95, 90, 80, 70, and 60 vol% LAGP in 1 M LiPF6 EC‐DMC (50:50 vol%) at 25°C, Li‐ion conductivities were 1.0 × 10?4 S/cm at 25°C with 5 to 10 wt% liquid electrolyte. This paper focuses on the microstructural development and impedance contributions within solid electrolytes processed by (i) Crystallization of bulk glasses, (ii) CSP of ceramics, and (iii) CSP of ceramic‐polymer composites. CSP may offer a new route to enable multilayer battery technology by avoiding the detrimental effects of high temperature heat treatments. 相似文献
107.
Dichlorophenylacrylonitriles as AhR Ligands That Display Selective Breast Cancer Cytotoxicity in vitro 下载免费PDF全文
Jennifer R. Baker Dr. Jayne Gilbert Prof. Stefan Paula Dr. Xiao Zhu Dr. Jennette A. Sakoff Prof. Adam McCluskey 《ChemMedChem》2018,13(14):1447-1458
Knoevenagel condensation of 3,4‐dichloro‐ and 2,6‐dichlorophenylacetonitriles gave a library of dichlorophenylacrylonitriles. Our leads (Z)‐2‐(3,4‐dichlorophenyl)‐3‐(1H‐pyrrol‐2‐yl)acrylonitrile ( 5 ) and (Z)‐2‐(3,4‐dichlorophenyl)‐3‐(4‐nitrophenyl)acrylonitrile ( 6 ) displayed 0.56±0.03 and 0.127±0.04 μm growth inhibition (GI50) and 260‐fold selectivity for the MCF‐7 breast cancer cell line. A 2,6‐dichlorophenyl moiety saw a 10‐fold decrease in potency; additional nitrogen moieties (‐NO2) enhanced activity (Z)‐2‐(2,6‐dichloro‐3‐nitrophenyl)‐3‐(2‐nitrophenyl)acrylonitrile ( 26 ) and (Z)‐2‐(2,6‐dichloro‐3‐nitrophenyl)‐3‐(3‐nitrophenyl)acrylonitrile ( 27 ), with the corresponding ‐NH2 analogues (Z)‐2‐(3‐amino‐2,6‐dichlorophenyl)‐3‐(2‐aminophenyl)acrylonitrile ( 29 ) and (Z)‐2‐(3‐amino‐2,6‐dichlorophenyl)‐3‐(3‐aminophenyl)acrylonitrile ( 30 ) being more potent. Despite this, both 29 (2.8±0.03 μm ) and 30 (2.8±0.03 μm ) were found to be 10‐fold less cytotoxic than 6 . A bromine moiety effected a 3‐fold enhancement in solubility with (Z)‐3‐(5‐bromo‐1H‐pyrrol‐2‐yl)‐2‐(3,4‐dichlorophenyl)acrylonitrile 18 relative to 5 at 211 μg mL?1. Modeling‐guided synthesis saw the introduction of 4‐aminophenyl substituents (Z)‐3‐(4‐aminophenyl)‐2‐(3,4‐dichlorophenyl)acrylonitrile ( 35 ) and (Z)‐N‐(4‐(2‐cyano‐2‐(3,4‐dichlorophenyl)vinyl)phenyl)acetamide ( 38 ), with respective GI50 values of 0.030±0.014 and 0.034±0.01 μm . Other analogues such as 35 and 36 were found to have sub‐micromolar potency against our panel of cancer cell lines (HT29, colon; U87 and SJ‐G2, glioblastoma; A2780, ovarian; H460, lung; A431, skin; Du145, prostate; BE2‐C, neuroblastoma; MIA, pancreas; and SMA, murine glioblastoma), except compound 38 against the U87 cell line. A more extensive evaluation of 38 ((Z)‐N‐(4‐(2‐cyano‐2‐(3,4‐dichlorophenyl)vinyl)phenyl)acetamide) in a panel of drug‐resistant breast carcinoma cell lines showed 10–206 nm potency against MDAMB468, T47D, ZR‐75‐1, SKBR3, and BT474. Molecular Operating Environment docking scores showed a good correlation between predicted binding efficiencies and observed MCF‐7 cytotoxicity. This supports the use of this model in the development of breast‐cancer‐specific drugs. 相似文献
108.
When molten plastic is extruded, the upper limiting throughput is often dictated by fine irregular distortions of the extrudate surface. Called sharkskin melt fracture, plastics engineers spike plastics formulations with processing aids to suppress these distortions. Sharkskin melt fracture is not to be confused with gross melt fracture, a larger scale distortion arising at throughputs higher than the critical throughput for sharkskin melt fracture. Sharkskin melt fracture has been attributed to a breakdown of the no slip boundary condition in the extrusion die, that is, adhesive failure at the die walls, where the fluid moves with respect to the wall. In this article, we account for the frictional heating at the wall, which we call slip heating. We focus on slit flow, which is used in film casting, sheet extrusion, curtain coating, and when curvature can be neglected, slit flow is easily extended to pipe extrusion and film blowing. In slit flow, the magnitude of the heat flux from the slipping interface is the product of the shear stress and the slip speed. We present the solutions for the temperature rise in pressure‐driven slit flow and simple shearing flow, each subject to constant heat generation at the adhesive slip interface, with and without viscous dissipation in the bulk fluid. We solve the energy equation in Cartesian coordinates for the temperature rise, for steady temperature profiles. For this simplest relevant nonisothermal model, we neglect convective heat transfer in the melt and use a constant viscosity. We arrive at a necessary dimensionless condition for the accurate use of our results: Pé?1. We find that slip heating can raise the melt temperature significantly, as can viscous dissipation in the bulk. We conclude with two worked examples showing the relevance of slip heating in determining wall temperature rise, and we show how to correct wall slip data for this temperature rise. POLYM. ENG. SCI., 55:2042–2049, 2015. © 2014 Society of Plastics Engineers 相似文献
109.
Daniel Spinks Emma J. Shanks Laura A. T. Cleghorn Stuart McElroy Deuan Jones Daniel James Alan H. Fairlamb Julie A. Frearson Paul G. Wyatt Ian H. Gilbert 《ChemMedChem》2009,4(12):2060-2069
There is an urgent need for new drugs for the treatment of tropical parasitic diseases such as human African trypanosomiasis, which is caused by Trypanosoma brucei. The enzyme trypanothione reductase (TryR) is a potential drug target within these organisms. Herein we report the screening of a 62 000 compound library against T. brucei TryR. Further work was undertaken to optimise potency and selectivity of two novel‐compound series arising from the enzymatic and whole parasite screens and mammalian cell counterscreens. Both of these series, containing either a quinoline or pyrimidinopyrazine scaffold, yielded low micromolar inhibitors of the enzyme and growth of the parasite. The challenges of inhibiting TryR with druglike molecules is discussed. 相似文献
110.
Maria Albareda-Sambola Elena Fernández Gilbert Laporte 《Computers & Operations Research》2009,36(2):597-611
This article introduces a new problem called the Capacity and Distance Constrained Plant Location Problem. It is an extension of the discrete capacitated plant location problem, where the customers assigned to each plant have to be packed in groups that will be served by one vehicle each. The constraints include two types of capacity. On the one hand plants are capacitated, and the demands of the customers are indivisible. On the other hand, the total distance traveled by each vehicle to serve its assigned customers in round trips plant–customer–plant is also limited. The paper addresses different modeling aspects of the problem. It describes a tabu search algorithm for its solution. Extensive computational tests indicate that the proposed heuristic consistently yields optimal or near-optimal solutions. 相似文献