全文获取类型
收费全文 | 1826篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 20篇 |
综合类 | 2篇 |
化学工业 | 206篇 |
金属工艺 | 11篇 |
机械仪表 | 24篇 |
建筑科学 | 135篇 |
矿业工程 | 1篇 |
能源动力 | 50篇 |
轻工业 | 125篇 |
水利工程 | 14篇 |
石油天然气 | 4篇 |
无线电 | 136篇 |
一般工业技术 | 147篇 |
冶金工业 | 866篇 |
原子能技术 | 12篇 |
自动化技术 | 89篇 |
出版年
2022年 | 9篇 |
2021年 | 9篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 22篇 |
2013年 | 49篇 |
2012年 | 25篇 |
2011年 | 41篇 |
2010年 | 27篇 |
2009年 | 25篇 |
2008年 | 30篇 |
2007年 | 29篇 |
2006年 | 36篇 |
2005年 | 26篇 |
2004年 | 32篇 |
2003年 | 21篇 |
2002年 | 22篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 48篇 |
1998年 | 267篇 |
1997年 | 159篇 |
1996年 | 140篇 |
1995年 | 69篇 |
1994年 | 60篇 |
1993年 | 59篇 |
1992年 | 31篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 31篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 24篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 31篇 |
1982年 | 16篇 |
1981年 | 21篇 |
1980年 | 31篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 32篇 |
1976年 | 51篇 |
1975年 | 14篇 |
1974年 | 6篇 |
1973年 | 16篇 |
1969年 | 6篇 |
排序方式: 共有1842条查询结果,搜索用时 15 毫秒
31.
M Patel RF Kaltenbach DA Nugiel RJ McHugh PK Jadhav LT Bacheler BC Cordova RM Klabe S Erickson-Viitanen S Garber C Reid SP Seitz 《Canadian Metallurgical Quarterly》1998,8(9):1077-1082
Cyclic urea SD146, a potent HIV protease inhibitor bearing a flat resistance profile, possessed poor solubility and bioavailability, which precluded further development of the compound. In an effort to improve upon the pharmacokinetic profile of the compound, several analogs modified at the P1/P1' residues were prepared and evaluated. Several of those compounds displayed significant improvement of physical properties. 相似文献
32.
Mark A. Spalding Kun S. Hyun Steven R. Jenkins Donald E. Kirkpatrick 《Polymer Engineering and Science》1995,35(23):1907-1916
Previous research and this research indicate that the mechanical melting for poly(vinylidene chloride) copolymers (PVDC) is complex. Mechanical melting is defined as the melting (or devitrification) of a polymer when a significant portion of the thermal energy originates from a mechanical energy dissipative process. PVDC mechanically melted on a moving metal surface at temperatures of the test instrument that were considerably lower than the differential scanning calorimetry (DSC) onset melting temperature. PVDC formulated with low levels of high density polyethylene (HDPE), however, melted at metal temperatures near the DSC onset melting temperature. Two different mechanical melting mechanisms are proposed to explan the data, and the frictional data are discussed with respect to solids conveying in a single-screw, plasticating extruder. 相似文献
33.
Heidel D.F. Bapst U.H. Jenkins K.A. Geppert L.M. Zabel T.H. 《IEEE transactions on nuclear science》1993,40(2):127-134
An ion microbeam radiation test system has been built for studying radiation-induced charge collection and single event upsets in advanced semiconductor circuits. With this system, it is possible to direct an ion beam of a diameter as small as 1 μm onto a circuit or test structure with a placement accuracy of 1 μm. The components of the system and its operation are described. Applications are described which demonstrate the capabilities of the system 相似文献
34.
N-acetyltransferase (NAT) activity was determined by incubation of purified Enterobacter aerogenes enzyme with 2-aminofluorene (2-AF) as the substrate, followed by high pressure liquid chromatography assays. The NAT activity from E. aerogenes was 0.58 +/- 0.08 nmol/min/mg protein for 2-AF. The values of apparent K(m) and Vmax were 0.72 +/- 0.14 mM and 2.45 +/- 0.29 nmol/min/mg protein, respectively, for 2-AF. The optimal pH value for the enzyme activity was 7.5 for the 2-AF tested. The optimal temperature for enzyme activity was 37 degrees C for the 2-AF substrate. The molecular weight of NAT from E. aerogenes was 44.9 kD. Among a series of divalent cations and salts, Zn2+, Ca2+, and Fe2+ were demonstrated to be the most potent protease inhibitors, and only ethylenediaminetetraacetic acid significantly protected the NAT. Iodoacetamide, in contrast to other agents, markedly inhibited NAT. 相似文献
35.
It is shown that liquid crystal polyester can be extruded and drawn from the melt into fine fibres which possess stiffnesses up to 68 GPa. Thicker fibres with smaller draw ratios have correspondingly lower stiffnesses, which are correlated with molecular alignments characterized by flat plate X-ray diffraction. Fibres with a range of diameters were heat-treated over a range of temperatures to determine the effect of annealing on preferred orientation and stiffness. Heat-treatment of as-spun fibres produced maxima in axial stiffness at 170° C, corresponding to an increase in preferred orientation, and 270° C, corresponding to the development of quasi-crystalline order which is analysed. Scanning electron microscopy showed the existence of needle-like domains of approximately circular cross section up to 0.8 m in diameter. These were aligned in the direction of drawing in contrast to being haphazardly arranged in a hot rolled specimen displaying no preferred orientation. 相似文献
36.
Robert K. Jenkins 《应用聚合物科学杂志》1967,11(2):171-177
Arbitrary cure times and glass transition temperatures are reported for an epoxy resin cocrosslinked by various weight fractions of hexamethylenediamine (HMDA) and m-phenylenediamine (m-PLDA). The glass transition temperatures of the epoxy resin systems studied yielded an excellent fit to an empirical equation developed by Dyvik for copolymers. The cure time parameters were found to be a linear function of the weight fractions of each crosslinking agent present. The mechanical properties of the epoxy resins were measured by an in situ dynamic modulus technique which employed the use of a resin-coated metallic substrate. 相似文献
37.
Chlorination of a low molecular weight polystyrene in the α position was studied by following changes in the infrared spectrum, glass transition temperature, and molecular weights of the polymer. The logarithm of the absorbance ratio at 2920 and 1500 cm?1 as a function of mole per cent chlorination was linear. The glass transition temperatures, determined by use of a differential scanning calorimeter (DSC), were found to obey an equation developed by Dyvik for copolymers. The molecular weight of the chlorinated polystyrene decreased as a function of chlorination. 相似文献
38.
The property changes of Epon 828 crosslinked by either diethylenetriamine or m-phenylenediamine at several temperatures have been studied by two in situ techniques. The mechanical property changes were followed by continuously monitoring the changes in the fundamental frequency of vibration during cure of a resin-coated substrate acting as a cantilever reed. The disappearance of the reactive epoxy group was followed in situ by continuously monitoring the absorbance of the infrared epoxide band at 915 cm.?1. Correlation of the two techniques was accomplished by normalizing both the mechanical property and infrared data. The apparent energy of activation was calculated to be 10.4 and 11.4 kcal. /mole, respectively, for the m-phenylenediamine and diethylenetriamine systems by the mechanical technique, and 11.0 kcal./mole for the m-phenylenediamine crosslinked system by the infrared technique. 相似文献
39.
Mamballykalathil N. Menon Ho T. Fang David C. Wu Michael G. Jenkins Mattison K. Ferber Karren L. More Camden R. Hubbard Theodore A. Nolan 《Journal of the American Ceramic Society》1994,77(5):1217-1227
Cylindrical buttuohead specimens of an advanced silicon nitride were tested in uniaxial tension at temperatures between 1422 and 1673 K. In the range 1477 to 1673 K, creep deformation was reliably measured using high-temperature contact probe extensometry. Extensive scanning and transmission electron microscopy has revealed the formation of lenticular cavities at two-grain junctions at all temperatures (1422–1673 K) and extensive triple-junction cavitation occurring at the higher temperatures (1644–1673 K). Cavitation is believed to be part of the net creep process. The stress rupture data show stratification of the Monkman–Grant lines with respect to temperature. Failure strain increased with increase in rupture time or temperature, or decrease in stress. Fractography showed that final failure occurred by subcritical crack growth in all specimens. 相似文献
40.
Semih Eser Robert G. Jenkins Guangquan Wei Harold H. Schobert Joseph T. Joseph 《Fuel》1991,70(12):1445-1455
High pressure microdilatometer experiments were performed on a subbituminous (Wyodak) and a bituminous (Illinois no. 6) coal in helium and hydrogen atmospheres with and without added tetralin. Wyodak coal samples showed no swelling but contractions ranging between 24 and 40 vol% upon heating at 20 and 100 °C min− 1 under helium or hydrogen pressures between 150 and 1000 psig (˜1.0–6.9 MPa). Under the same conditions, Illinois no. 6 coals displayed contractions (25–60 vol%) prior to swelling up to 117 vol%. Upon tetralin addition (at 35–190 wt% of the coal), Wyodak coal samples did not swell but showed an increasing contraction with increasing helium or hydrogen pressure due to a slight softening and fusion of the coal particles. In contrast, addition of tetralin at much lower concentrations (5–35 wt%) had a marked effect on the contraction and swelling behaviour of Illinois no. 6. A maximum swelling of 200 vol% was obtained at a tetralin addition of 30 wt%. The increased swelling results from more extensive softening and fusion of coal particles in the presence of tetralin. Both coals showed a decreasing char yield with increasing tetralin concentration. The substantially lower extent of interaction observed between Wyodak coal samples and tetralin compared to Illinois no. 6 coal can be attributed to the differences in pore structure and/or chemical constitution of the two coal samples. Examination of the resultant solids by optical microscopy revealed the microstructural changes produced by thermal treatment in dilatometer experiments. 相似文献