全文获取类型
收费全文 | 2744篇 |
免费 | 98篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 665篇 |
金属工艺 | 26篇 |
机械仪表 | 24篇 |
建筑科学 | 148篇 |
矿业工程 | 5篇 |
能源动力 | 55篇 |
轻工业 | 510篇 |
水利工程 | 20篇 |
石油天然气 | 6篇 |
无线电 | 107篇 |
一般工业技术 | 419篇 |
冶金工业 | 585篇 |
原子能技术 | 8篇 |
自动化技术 | 254篇 |
出版年
2023年 | 20篇 |
2022年 | 49篇 |
2021年 | 84篇 |
2020年 | 45篇 |
2019年 | 39篇 |
2018年 | 60篇 |
2017年 | 50篇 |
2016年 | 62篇 |
2015年 | 47篇 |
2014年 | 70篇 |
2013年 | 171篇 |
2012年 | 176篇 |
2011年 | 188篇 |
2010年 | 166篇 |
2009年 | 147篇 |
2008年 | 159篇 |
2007年 | 155篇 |
2006年 | 108篇 |
2005年 | 121篇 |
2004年 | 92篇 |
2003年 | 98篇 |
2002年 | 89篇 |
2001年 | 48篇 |
2000年 | 37篇 |
1999年 | 46篇 |
1998年 | 42篇 |
1997年 | 54篇 |
1996年 | 52篇 |
1995年 | 33篇 |
1994年 | 32篇 |
1993年 | 25篇 |
1992年 | 29篇 |
1991年 | 17篇 |
1990年 | 27篇 |
1989年 | 22篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 19篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1948年 | 3篇 |
排序方式: 共有2844条查询结果,搜索用时 15 毫秒
991.
Catherine Everett 《Network Security》2004,2004(1):1
Emails that use social engineering techniques to manipulate people into opening infected attachments will become increasingly prevalent this year, after first rearing their ugly heads in 2003. 相似文献
992.
Tomas Hudlicky Fan Rulin Toshiya Tsunoda Hector Luna Catherine Andersen John D. Price 《Israel journal of chemistry》1991,31(3):229-238
Bacterial oxygenation of halogenated aromatic compounds yields arene cis-diols of type 2 of high enantiomeric purity. Further oxygenation of these extremely versatile synthetic intermediates provides for stereo- and regioselective introduction of additional functionalities such as hydroxyl groups. Several rational methods of oxygenation (epoxidation, osmylation, singlet oxygen addition, and ozonolysis) are used to produce, in short synthetic routes, cyclitol derivatives of medicinal importance. Proper symmetry considerations lead to the development of enantiodivergent synthetic design of target compounds from a single enantiomer of a starting diol. These principles are illustrated on the short syntheses of (+)- and (-)-pinitol. Stereocontrolled oxidative transformation of diols of type 2 are exemplified in the synthesis of conduritol C and dihydroconduritol C. Full experimental details are provided for all compounds. A guide to the stereorational design of any stereoisomer of cyclohexane (poly)ols or carbohydrates is provided at the end of the paper. 相似文献
993.
The high-performance liquid chromatographic separation and quantitation of conjugated bile salts from pig bile is reported.
Synthetic standards and bile samples were chromatographed on a C18 reversed phase column using acetonitrile/water/tetrabutyl ammonium phosphate as an isocratic mobile phase at a flow rate
of 1 mL/min. Detection of the ion-pairs was at 214 nm. The method permits efficient separation of all conjugated pig biliary
bile salts without prior modification or treatment of the samples. Analysis of 12 pig biles showed that 85% of the bile salts
are conjugated to glycine. The three main conjugated bile salts were glyco-3α,6α,7α-trihydroxy-5β-cholanoic acid (GHC), glyco-3α,7α-dihydroxy-5β-cholanoic
acid (GCDC), and glyco-3α,6α-dihydroxy-5β-cholanoic acid (GHDC). Glyco-3α-hydroxy-6-oxo-5β-cholanoic acid (G3α6oxo), tauro-3α,7α-dihydroxy-5β-cholanoic
acid (TCDC), tauro-3α,6α,7α-trihydroxy-5β-cholanoic acid (THC), and tauro-3α,6α-dihydroxy-5β-cholanoic acid (THDC) were found
to contribute each for 4 to 5% ot the total. An excellent correlation was found between the sum of conjugated bile salts quantitated
by high-performance liquid chromatography (HPLC) and values obtained by conventional enzymatic assay. Simplicity, efficiency
and relative rapidity of the method render it suitable for routine analyses. 相似文献
994.
Heppner Mary J.; Multon Karen D.; Gysbers Norman C.; Ellis Carrie A.; Zook Catherine E. 《Canadian Metallurgical Quarterly》1998,45(4):393
This investigation examined the role of counselor trainees' self-efficacy on measures of career counseling process, "small o" outcome, and outcome with actual clients. Twenty-four counselor trainees saw 55 clients in 3 to 12 individual sessions. Results indicated that (a) career counseling self-efficacy increased by a standard deviation from prepracticum to postpracticum; (b) client scores significantly improved from pretest to posttest across multiple career outcome measures; (c) clients' working alliance, goal attainment, and decidedness indicated significant growth; (d) the significant growth on the process variable and small o outcome variables did not appear to be related to career counseling self-efficacy; and (e) career counseling self-efficacy apparently related to certain career counseling outcome measures in a manner suggesting much greater complexity than the "more self-efficacy is better" philosophy would imply. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
996.
Catherine Gauthier Anthony Bonnet Roger Gaertner Henry Sautereau 《Polymer International》2004,53(5):541-549
Polymer blends based on intractable, high temperature‐resistant thermoplastic polyetherimide (PEI) and epoxy‐amine (EA) were processed by dissolution of the thermoplastic into the epoxy‐amine precursors, followed by subsequent reaction. Because the PEI concentration was higher than the critical concentration, phase separation produced a dispersion of crosslinked thermoset (EA) in a PEI matrix. The creep behaviour of the blends were investigated in the temperature range near the glass transition of the thermoset phase. To account for the experimental data, two ways of modelling were explored, assuming (1) perfect coupling between phases (2) total debonding. Comparison between experimental data and modelling results indicates that a strong debonding process takes place even at low stress. This conclusion is in fair agreement with the low value of the estimated interfacial adhesion at the PEI matrix–EA particles interface. Copyright © 2004 Society of Chemical Industry 相似文献
997.
Dobkin Patricia L.; Tremblay Richard E.; Sacchitelle Catherine 《Canadian Metallurgical Quarterly》1997,65(1):86
Sons of male alcoholics (SOMAs) are said to be at risk for alcoholism. The present study examined 4 groups of 13-year-old boys: SOMAs with and without disruptive behaviors, disruptive boys who were not SOMAs, and control participants. The classification of disruptive was based on 7-year longitudinal data, and father's alcoholism was determined by standardized tests. Mothers' nurturance and promotion of autonomy were assessed in a laboratory setting; boys' substance abuse was measured by self-report methods in the same year as the observation. Boys with disruptive behaviors showed the most substance abuse; no effect of father's alcoholism was found. Disruptive boys' mothers were significantly less nurturant and demanded obedience rather than promoted autonomy. A multiple regression analysis revealed that the boys' disruptive behavior and the mother's lack of nurturance predicted early-onset substance abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
Robert M. Yadrick J. Wesley Regian Linda Robertson-Schule Catherine Connolly Gomez 《Computers in human behavior》1996,12(4):527-548
In this paper, we conceptualize computer-based instruction (CBI) as involving both a primary task, learning a particular domain, and several secondary tasks centered around learning to use the instructional approach and manipulate the interface efficiently. We argue that the complexity and compatibility of the domain, instructional approach, and system interface separately and interactively influence the ease with which students are able to learn the subject matter. Examples show how looking at CBI in this way provides a framework for better understanding the results of some previous studies of CBI and CBI-related interface design. We also describe an experiment that attempted to dissociate the separate effects of these components on domain learning. The experiment examined the pretest-posttest performance differences of remedial subjects who learned to solve mathematics word problems. 相似文献
999.
1000.
Campbell Patrick E.; Batsche Catherine J.; Batsche George M. 《Canadian Metallurgical Quarterly》1972,81(2):360
Trained 56 male Charles River hooded rats in a runway with either small- or large-reward magnitude. Both small and large rewards were presented in single- or multiple-pellet form. 1 training trial was given each day for 120 days. Early in training, the large-reward Ss ran faster than those receiving small reward, and the effect was more pronounced in the multiple-pellet condition. Later in training, the small-reward Ss equaled the performance of Ss receiving large reward and even ran somewhat faster in the run section of the alley. The typical extinction effect of greater persistence for small-reward Ss was observed, but only in the goal section. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献