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排序方式: 共有888条查询结果,搜索用时 15 毫秒
61.
The introduction of multiwall carbon nanotube (MWCNT)-polymer composites ushered in fresh opportunities for engineering new materials with high performance capabilities. The nanoscale dimensions and extraordinary properties of MWCNTs directly address the sub-micron damage mechanisms (such as crazing) that culminate during the fatigue failure of most polymers. The large traditional graphite fibers commonly used in composite materials do little to address these microscopic mechanisms of cyclic deformation; thus, MWCNTs offer new promise for improving the fatigue performance of polymer systems where the previous successes of traditional graphite fibers were limited. To test this theory, small amounts (0-10 wt%) of MWCNTs were added to methyl methacrylate-styrene copolymer (MMA-co-Sty), a chief component of commercial bone cement. The resulting nanocomposites were tested to failure in fully reversed tension-compression fatigue in a 37 °C saline environment. Testing at 20 MPa peak stress showed that adding 2 wt% and 5 wt% MWCNTs enhanced the fatigue performance of MMA-co-Sty by 565% and 592%, respectively. These results clearly demonstrate that MWCNTs can substantially enhance the fatigue performance of this polymer. Furthermore, a comparison of these results with the literature shows that MWCNTs are better candidates than traditional graphite fibers for improving the fatigue performance of polymer systems. 相似文献
62.
This article responds to "Coaching at the Top: Assisting A Chief Executive and His Team ' (M. M. Krajl, 2001 see record 2001-01213-005) by critiquing the article. It extends the discussion by focusing on the desired characteristics of a case study and how a professional literature can be derived from well constructed case studies. Applying these principles to Krajl's article, the author notes some issues concerning the intervention and preceding assessment, including the choice of the term coaching to describe complex and multifaceted interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
63.
64.
Mattison Richard E.; Handford H. Allen; Kales Helen C.; Goodman Amy L.; McLaughlin Rodney E. 《Canadian Metallurgical Quarterly》1990,2(2):169
Predictive value for the Children's Depression Inventory (CDI) was demonstrated through a 4-year follow-up study of 105 children who entered a private residential school for children who had lost one or both natural parents through death, divorce, or separation. At baseline, depressed and nondepressed groups were defined with the CDI. They were then reevaluated at the end of 1, 2, and 4 yrs. On the CDI, the Revised Children's Manifest Anxiety Scale, and the Internalizing scale of the Child Behavior Checklist, the original depressed group who remained at school all 4 years showed scores that were significantly higher than those of the nondepressed group after 1 and 2 years, and were also greater after the 4th year. They further showed significantly poorer academic performance, received significantly more counseling, and more often separated from the school under negative circumstances. The most pathological scores overall were demonstrated by the children in the original depressed group who separated from the school during the 4 years under negative circumstances. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
65.
Goodyear Rodney K.; Newcomb Michael D.; Allison Russell D. 《Canadian Metallurgical Quarterly》2000,47(1):116
In addressing teen pregnancy, researchers have given scant attention either to the male partners or to psychological variables that might affect incidence rates. This study examined the contribution of developmental and psychosocial factors to the number of teen pregnancies for which young Latino men had been responsible. Data from a community sample of 307 Latino men were used to test a mediated model that incorporated 5 classes of variables: (a) developmental, family-of-origin variables, including indicators of quality of childhood experience; (b) gender-related attitudes and emotionality, including masculine ideology and alexithymia; (c) dating characteristics; (d) sexual behavior; and (e) the number of teen pregnancies for which a Latino man had been responsible. Results indicated that men's involvement in teen pregnancy was mediated not only by sexual activity, but that it was also affected by both developmental factors and gender-related attitudes and emotionality. Implications for teen pregnancy prevention, intervention, and research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
66.
Rybarczyk Bruce; Lopez Martita; Benson Rodney; Alsten Christopher; Stepanski Edward 《Canadian Metallurgical Quarterly》2002,17(2):288
Older adults with comorbid insomnia and medical illness have been excluded from behavioral treatment research, but recent evidence suggested that such treatments would be effective with this population. In this study, 38 older adults with comorbid insomnia were randomized to 1 of 3 conditions: classroom cognitive-behavioral treatment (CBT), home-based audio relaxation treatment (HART), or delayed-treatment control. Compared to the control group, the CBT group had significant changes in 5 of 7 self-report measures of sleep at the 4-month follow-up. The HART group obtained significant outcomes on 3 of 7 measures. Wrist actigraphy measures and secondary-outcome measures did not yield significant findings for either treatment. Clinically significant changes at follow-up were obtained for 54% of patients in CBT, 35% in HART, and 6% in the control group when treatment dropouts were included. Although not as effective as in-person CBT, home interventions may have utility as a first-line, low-cost treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
67.
Past research has shown that creative behavior is associated with a higher risk for depression. The authors hypothesized that a 3rd underlying factor, namely, self-reflective rumination, may explain the connection. This hypothesis was examined in a sample of 99 undergraduate college students, using path analysis. The authors found that self-reported past depressive symptomatology was linked to increased self-reflective rumination. Rumination, in turn, was related to current symptomatology and to self-rated creative interests and objectively measured creative fluency, originality, and elaboration. No direct link existed between currently depressed mood and either creative interest or creative behavior. These results suggest that the association between depression and creativity is solely the result of rumination. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
68.
Salo Rodney W. Wallner Thomas G. Pederson Brian D. 《IEEE transactions on bio-medical engineering》1986,(2):189-195
The most widely used equation, V = pL2/R, is developed for the computation of ventricular volume from catheter based impedance measurements. The assumptions implicit in this derivation are examined and found to be generally invalid. An empirical discrete resistor model is described which includes the impedance of the myocardial tissue and the adjoining ventricular blood volume. Once the parameters of this model are determined for individual canine hearts, the model predicts stroke volume from measured impedances. Due to the difficulty involved in determining the parameters of the empirical model, a numerical model is developed which solves the equation V ?a V U + F = 0 in a three-dimensional volume. This model is then used to determine the effect of parallel tissue resistance, catheter position, and contraction of the other ventricle on volumes computed by intracardiac impedance. Parallel tissue resistance is found to have the greatest impact on absolute volume measurements. However, stroke volume computations are relatively unaffected by any of the three factors. 相似文献
69.
Summary Attribute grammars are a value-oriented, non-procedural extension to context-free grammars that facilitate the specification of translations whose domain is described by the underlying context-free grammar. Just as parsers for context-free languages can be automatically constructed from a context-free grammar, so can translators, called attribute evaluators, be automatically generated from an attribute grammar. A major obstacle to generating efficient attribute evaluators is that they typically use large amounts of memory to represent the attributed parse tree. In this report we investigate the problem of efficient representation of the attributed parse tree by analyzing and comparing the strategies of two systems that have been used to automatically generate a translator from an attribute grammar: the GAG system developed at the Universitat de Karlsruhe and the LINGUIST-86 system written at Intel Corporation. Our analysis will characterize the two strategies and highlight their respective strengths and weaknesses. Drawing on the insights given by this analysis, we propose a strategy for storage optimization in automatically generated attribute evaluators that not only incorporates the best features of both GAG and LINGUIST-86, but also contains novel features that address aspects of the problem that are handled poorly by both systems.This research was partially supported by the National Science Foundation under grant DCR-83-10930, and partially supported by the Defense Advanced Research Projects Agency under contract number N00039-84-C-0165 相似文献
70.
Fibrous Monolithic Ceramics 总被引:2,自引:0,他引:2
Desiderio Kovar Bruce H. King Rodney W. Trice John W. Halloran 《Journal of the American Ceramic Society》1997,80(10):2471-2487
Fibrous monolithic ceramics are an example of a laminate in which a controlled, three-dimensional structure has been introduced on a submillimeter scale. This unique structure allows this all-ceramic material to fail in a nonbrittle manner. Materials have been fabricated and tested with a variety of architectures. The influence on mechanical properties at room temperature and at high temperature of the structure of the constituent phases and the architecture in which they are arranged are discussed. The elastic properties of these materials can be effectively predicted using existing models. These models also can be extended to predict the strength of fibrous monoliths with an arbitrary orientation and architecture. However, the mechanisms that govern the energy absorption capacity of fibrous monoliths are unique, and experimental results do not follow existing models. Energy dissipation occurs through two dominant mechanisms—delamination of the weak interphases and then frictional sliding after cracking occurs. The properties of the constituent phases that maximize energy absorption are discussed. 相似文献