全文获取类型
收费全文 | 3409篇 |
免费 | 120篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 77篇 |
化学工业 | 450篇 |
金属工艺 | 33篇 |
机械仪表 | 47篇 |
建筑科学 | 109篇 |
矿业工程 | 5篇 |
能源动力 | 84篇 |
轻工业 | 293篇 |
水利工程 | 23篇 |
石油天然气 | 16篇 |
无线电 | 418篇 |
一般工业技术 | 442篇 |
冶金工业 | 1125篇 |
原子能技术 | 55篇 |
自动化技术 | 361篇 |
出版年
2022年 | 23篇 |
2021年 | 50篇 |
2020年 | 25篇 |
2019年 | 52篇 |
2018年 | 53篇 |
2017年 | 60篇 |
2016年 | 71篇 |
2015年 | 36篇 |
2014年 | 65篇 |
2013年 | 166篇 |
2012年 | 87篇 |
2011年 | 116篇 |
2010年 | 100篇 |
2009年 | 93篇 |
2008年 | 132篇 |
2007年 | 113篇 |
2006年 | 86篇 |
2005年 | 80篇 |
2004年 | 64篇 |
2003年 | 72篇 |
2002年 | 67篇 |
2001年 | 83篇 |
2000年 | 60篇 |
1999年 | 85篇 |
1998年 | 284篇 |
1997年 | 180篇 |
1996年 | 120篇 |
1995年 | 71篇 |
1994年 | 82篇 |
1993年 | 94篇 |
1992年 | 40篇 |
1991年 | 29篇 |
1990年 | 51篇 |
1989年 | 46篇 |
1988年 | 54篇 |
1987年 | 45篇 |
1986年 | 39篇 |
1985年 | 54篇 |
1984年 | 33篇 |
1983年 | 32篇 |
1982年 | 27篇 |
1981年 | 32篇 |
1980年 | 37篇 |
1979年 | 25篇 |
1978年 | 34篇 |
1977年 | 41篇 |
1976年 | 62篇 |
1975年 | 36篇 |
1974年 | 14篇 |
1973年 | 16篇 |
排序方式: 共有3538条查询结果,搜索用时 546 毫秒
31.
McEvoy Cathy L.; Nelson Douglas L.; Holley Patricia E.; Stelnicki Glennda S. 《Canadian Metallurgical Quarterly》1992,7(3):401
Reports 2 cued recall experiments in which younger and older Ss studied target words varying in number of preexperimental associates. In Exp 1, targets were studied in either the absence or presence of meaning-related context cues, with recall always prompted by the cues. In the absence of context, words with smaller sets of associates were easier to recall than those with larger sets, but this effect was reduced for older Ss. The presence of a study context cue facilitated recall and eliminated the effect of associative set size for both ages. In Exp 2, targets were studied and tested in the presence of unrelated words. In this situation, words with smaller sets of associates were less likely to be recalled than words with larger sets; again the effect was reduced for older Ss. The results are interpreted as an age decrement in processing implicitly activated information. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
32.
S Uribe-Luna JD Quintana-Hau R Maldonado-Rodriguez M Espinosa-Lara KL Beattie D Farquhar JA Nelson 《Canadian Metallurgical Quarterly》1997,54(3):419-424
The stimulatory effect of phytin added to skim milk on acid production of Lactobacillus casei was examined. Phytin stimulated acid production of L. casei fairly well. The stimulatory effect of phytin on acid production was not shown when phytin was treated with Dowex 50 (H+) and neutralized by NaOH solution. The incinerated product of phytin maintained almost equal stimulatory effect on acid production as that before processing. The addition of Mn2+ in the amount contained in a reagent phytin augmented the stimulatory effect on acid production markedly. The further addition of Fe3+, Ca2+, Mg2+ and PO4(3-) in amounts corresponding to their contents in the preparation of phytin as well as Mn2+ increased the effect slightly. The four preparations of phytin contained 0.045-0.20% of Mn, and the greater the Mn content was, the greater the potentiation of acid production. 相似文献
33.
The surface of polyethylene was derivatized with ester, carboxylate, amino, hydroxyl, and phosphate functional groups. α, ω bifunctional alkanes, containing on one end a primary amine, were coupled to oxidized polyethylene through an amide linkage. Polyethylene was first oxidized with chromic acid, the carboxylate groups were converted to the acyl chloride with phosphorus pentachloride, and then reacted with a primary amine to give the covalently bound amide. The copposing ends of the bifunctional alkanes were the methyl, tertiary amine, ester, and hydroxyl groups. The ester was converted to the carboxylate by acid cleavage and the hydroxyl group converted to the phosphate by treatment first with phosphorus oxychloride and then aqueous base. Attenuated total reflection FTIR, XPS, and pH-dependent contact angle wetting were used to characterize the surfaces. The FTIR data were used to confirm the formation of the amide and to detect an undesired carboxylate/ammonium ion complex formed in the presence of trace amounts of water. XPS data were used to confirm expected changes in elemental composition and to provide quantitative estimates of the yields. Oxidation of the polyethylene introduced 5 × 1014 carboxylate groups/cm2 in the 25 Å XPS sampling depth. Of these, up to 98% could be converted to the amide. The advancing contact angle data confirmed the acid/base behavior of the functional groups. 相似文献
34.
35.
Nelson Douglas L.; Keelean Patricia D.; Negrao Maura 《Canadian Metallurgical Quarterly》1989,15(3):388
In four experiments we evaluated aspects of the hypothesis that word-fragment completion depends on the results of lexical but not semantic search. Experiment 1 showed that the number of meaningful associates linked to a studied word does not affect its recovery when the test cue consists of letters and spaces for missing letters. Experiments 2 and 3 showed retroactive interference effects in fragment completion when words in a second list were lexically related to words in a first list but not when the words in the second list were meaningfully related. Experiment 4 indicated that for studied words, instructions to search at the word level facilitated completion performance and that instructions to generate letters to fill missing spaces had no effect. Other findings indicate that completion was affected by the number of words lexically related to the fragment and by the number of letters missing from the fragment. In general, experimental manipulations that focused on lexical characteristics were effective, and those that focused on semantic characteristics were ineffective. The findings support the conclusion that word fragments engender a lexical search process that does not depend on retrieving encoded meaning. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
36.
P. Ravirajan S.A. Haque J.R. Durrant D.D.C. Bradley J. Nelson 《Advanced functional materials》2005,15(4):609-618
We report a study of the effects of polymer optoelectronic properties on the performance of photovoltaic devices consisting of nanocrystalline TiO2 and a conjugated polymer. Three different poly(2‐methoxy‐5‐(2′‐ethylhexoxy)‐1,4‐phenylenevinylene) (MEH‐PPV)‐based polymers and a fluorene–bithiophene copolymer are compared. We use photoluminescence quenching, time‐of‐flight mobility measurements, and optical spectroscopy to characterize the exciton‐transport, charge‐transport, and light‐harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic‐device performance. We find that photocurrent is primarily limited by the photogeneration rate and by the quality of the interfaces, rather than by hole transport in the polymer. We have also studied the photovoltaic performance of these TiO2/polymer devices as a function of the fabrication route and device design. Including a dip‐coating step before spin‐coating the polymer leads to excellent polymer penetration into highly structured TiO2 networks, as was confirmed through transient optical measurements of the photoinduced charge‐transfer yield and recombination kinetics. Device performance is further improved for all material combinations studied, by introducing a layer of poly(ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonic acid) (PSS) under the top contact. Optimized devices incorporating the additional dip‐coated and PEDOT:PSS layers produced a short‐circuit current density of about 1 mA cm–2, a fill factor of 0.50, and an open‐circuit voltage of 0.86 V under simulated AM 1.5 illumination (100 mW cm–2, 1 sun). The corresponding power conversion efficiency under 1 sun was ≥ 0.4 %. 相似文献
37.
Shu-Chu Ren Nelson N. Hsu Donald G. Eitzen 《Journal of research of the National Institute of Standards and Technology》2002,107(5):445-473
Pulsed ultrasonic techniques can be and have been used to examine the interface conditions of a bonded structure. To provide a theoretical basis for such testing techniques we model the structure as a layer on top of a half-space, both of different elastic properties, with various interface bonding conditions. The exact dynamic Green’s tensor for such a structure is explicitly derived from the three-dimensional equations of motion. The final solution is a series. Each term of the series corresponds to a successive arrival of a “generalized ray” and each is a definite line integral along a fixed path which can be easily computed numerically. Willis’ method is used in the derivation. A new scheme of automatic generation of the arrivals and ray paths using combinatorial analysis, along with the summation of the corresponding products of reflection coefficients is presented. A FORTRAN code is developed for computation of the Green’s tensor when both the source and the detector are located on the top surface. The Green’s tensor is then used to simulate displacements due to pulsed ultrasonic point sources of known time waveform. Results show that the interface bonding conditions have a great influence on the transient displacements. For example, when the interface bonding conditions vary, some of the first few head waves and regular reflected rays change polarities and amplitudes. This phenomenon can be used to infer the quality of the interface bond of materials in ultrasonic nondestructive evaluation. In addition the results are useful in the study of acoustic microscopy probes, coatings, and geo-exploration. 相似文献
38.
在重点说明影响传输光纤设计的主要问题的同时,简要介绍了各种升级方式所面临的主要技术挑战,并详细说明这些挑战对传输光纤提出的技术要求。 相似文献
39.
The effects of processing conditions on the morphology of molecular composite films are examined by optical and electron microscopy. During coagulation processing from solutions in methanesulfonic acid (MSA), rigid-rod polymer, such as poly(p-phenylenebenzobisoxazole) (PBO), phase separates into undesirable aggregates. The coagulant and the method of its introduction have been found to exert a strong impact on the final film morphology. A quench of a PBO solution in MSA into a water bath results in a three dimensional interconnected network of PBO, while a slower introduction of water results in a more amorphous material. A computer simulation program of the coagulation process has been developed to better understand the different structures emerging from coagulation processing of molecular composites. The simulation results are in qualitative agreement with the experimental observations. 相似文献
40.
KR Porter PL Summers D Dubois B Puri W Nelson E Henchal JJ Oprandy CG Hayes 《Canadian Metallurgical Quarterly》1993,48(3):440-446
A polymerase chain reaction (PCR) assay was developed to rapidly detect and identify West Nile (WN) virus. The RNA from seven isolates of WN virus from six countries and four other flaviviruses (Kunjin, Japanese encephalitis, St. Louis encephalitis, and yellow fever viruses) was reverse-transcribed (RT) and amplified by PCR. The nucleotide sequences of the amplified products were determined by a rapid, automated DNA sequencing method. The WN virus RT/PCR assay detected the target gene segment of sequencing method. The WN virus RT/PCR assay detected the target gene segment of isolates from both the African-Middle Eastern group and the Indian group with a sensitivity of approximately 0.05 pg of viral RNA. Kunjin virus was the only other flavivirus tested that produced a band of the appropriate size. Five of seven WN virus isolates showed 92-98% homology in the nucleotide sequence of their PCR products. The sequence of one isolate was virtually identical to the published sequence of the Nigerian isolate (99.5% homology). No correlation was established between the degree of nucleotide homology, geographic location, time of isolation, or source of the isolates. 相似文献