全文获取类型
收费全文 | 218066篇 |
免费 | 2635篇 |
国内免费 | 599篇 |
专业分类
电工技术 | 3685篇 |
综合类 | 158篇 |
化学工业 | 33602篇 |
金属工艺 | 10525篇 |
机械仪表 | 7292篇 |
建筑科学 | 4449篇 |
矿业工程 | 2183篇 |
能源动力 | 4863篇 |
轻工业 | 14356篇 |
水利工程 | 3014篇 |
石油天然气 | 7753篇 |
武器工业 | 22篇 |
无线电 | 22786篇 |
一般工业技术 | 46895篇 |
冶金工业 | 37291篇 |
原子能技术 | 6774篇 |
自动化技术 | 15652篇 |
出版年
2021年 | 2226篇 |
2019年 | 2153篇 |
2018年 | 3874篇 |
2017年 | 3905篇 |
2016年 | 4225篇 |
2015年 | 2369篇 |
2014年 | 4033篇 |
2013年 | 9311篇 |
2012年 | 6107篇 |
2011年 | 7752篇 |
2010年 | 6280篇 |
2009年 | 6897篇 |
2008年 | 7075篇 |
2007年 | 6958篇 |
2006年 | 5941篇 |
2005年 | 5489篇 |
2004年 | 4930篇 |
2003年 | 4846篇 |
2002年 | 4631篇 |
2001年 | 4748篇 |
2000年 | 4452篇 |
1999年 | 4492篇 |
1998年 | 11102篇 |
1997年 | 7758篇 |
1996年 | 5943篇 |
1995年 | 4461篇 |
1994年 | 3865篇 |
1993年 | 4115篇 |
1992年 | 3136篇 |
1991年 | 3131篇 |
1990年 | 3029篇 |
1989年 | 2988篇 |
1988年 | 2995篇 |
1987年 | 2609篇 |
1986年 | 2675篇 |
1985年 | 3006篇 |
1984年 | 2789篇 |
1983年 | 2646篇 |
1982年 | 2368篇 |
1981年 | 2359篇 |
1980年 | 2435篇 |
1979年 | 2448篇 |
1978年 | 2429篇 |
1977年 | 2594篇 |
1976年 | 3024篇 |
1975年 | 2240篇 |
1974年 | 2109篇 |
1973年 | 2223篇 |
1972年 | 1974篇 |
1971年 | 1781篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
G Franzosi E Battistel I Gagliardi W Van der Goes 《Canadian Metallurgical Quarterly》1995,43(3):508-513
A screening of microorganisms producing glutaryl-7ADCA acylase, an enzyme able to hydrolyse glutaric acid selectively from glutaryl-3-deacetoxy-7-aminocephalosporanic acid (glutaryl-7ADCA), has been carried out in soil samples. Five microorganisms expressing acylase activity were isolated and classified as Bacillus cereus, Achromobacter xylosooxidans, Bacillus sp., Pseudomonas sp. and Pseudomonas paucimobilis. The screening was carried out by preparing enrichment cultures containing glutaryl-7-ADCA or cephalosporin C as the selective carbon source. Four model compounds (adipoyl-, glutamyl- and glutaryl-p-nitroanilide and glutarylcoumarin), mimicking the glutaryl-7ADCA beta-lactam moiety, were synthesized as substrates suitable for the rapid screening of the microorganisms (2500) isolated from the enrichment cultures. A total of 300 strains were active on the model substrates and only 5 displayed acylase activity on glutaryl-7ADCA. The fermentation parameters, such as pH and inducer concentration, for the optimal acylase expression and acylase specificity towards the model substrates were different for each strain. 相似文献
992.
Propagation of Isothermal Flame in the Low-Pressure Thermal Decomposition of Nitrogen Trichloride 总被引:1,自引:0,他引:1
The inhibition and promotion of isothermal NCl3 flame by NOCl and H2, respectively, are explained. The crossover from the isothermal mode of flame propagation to the thermal one is analyzed for NCl3–He mixtures. Calculations based on a kinetic mechanism taking into account energy chain branching are performed, and qualitative agreement between the calculated and observed data is demonstrated. The one-dimensional problem of chain–thermal flame propagation by a chain reaction involving a nonlinear-branching step has two solutions corresponding, one corresponding the isothermal mode of flame propagation and the other corresponding to the chain–thermal one. Nonlinear chain branching shortens the time needed for thermal ignition and increases the flammability of the combustible mixture. 相似文献
993.
994.
N. F. Bondarenko E. Z. Gak M. Z. Gak 《Journal of Engineering Physics and Thermophysics》2002,75(5):1234-1247
This paper gives an overview of the experimental results obtained by the method of MHD modeling in thin electrolyte layers and used to solve problems connected with the appearance of monotonic and vibrational instabilities. Primary consideration is given to the generation and interaction of transient vortex processes. As examples, the results of the investigations of flows in systems of two, three, and four vortices and periodic vortex structures, as well as of flows in the presence of obstacles of different permittivity modeling plants or technogenic screening devices intended to protect objects against pollution are presented. We consider the ways of using the results obtained in studying natural phenomena and in solving engineering-technical problems connected with mass and heat transfer and electrotransmission. 相似文献
995.
The conventional application of reduction factors to response spectrum analysis results is inappropriate for the abutment shear forces, which are based on elastic action. On the other hand, adopting the unreduced values from the elastic dynamic analysis does not achieve equilibrium among the abutment shear forces, deck inertia forces, and reduced pier forces. A simplified method is here proposed for the assessment of the shear on the abutments, documented by comparison with response spectrum and time history nonlinear analyses for several bridge configurations. For the analyzed configuration of the bridge with an internal movement joint, the response spectrum analysis underestimates the shear on the abutment for low values of the abutment flexibility and overestimates it when the stiffness of the abutments becomes higher than that of the piers. In all the case studies analyzed, the proposed method approximates the time history results better than the response spectrum. 相似文献
996.
Erp Implementation Failure: A Case Study 总被引:5,自引:0,他引:5
While it is true that successful implementation of an enterprise resource planning (ERP) system is a task of Herculean proportions, it is not impossible. If your organization is to reap the benefits of ERP, it must first develop a plan for success. But “prepare to see your organization reengineered, your staff disrupted, and your productivity drop before the payoff is realized.” Implementing ERP must be viewed and undertaken as a new business endeavor and a team mission, not just a software installation. Companies must involve all employees, and unconditionally and completely sell them on the concept of ERP for it to be a success. A successful implementation means involving, supervising, recognizing, and retaining those who have worked or will work closely with the system. Without a team attitude and total backing by everyone involved, an ERP implementation will end in less than an ideal situation. This was the situation for a soft drink bottler that tried to cut corners and did not recognize the importance of the people so heavily involved and depended on. 相似文献
997.
N Melvin 《Canadian Metallurgical Quarterly》1995,10(3):152-159
Using the goodness-of-fit theoretical framework, an intervention study designed to help parents assess and understand the implications of their child's temperament is described. Examples of temperament strategies designed to be consistent with the child's needs are included. 相似文献
998.
A Van Aarem M Wagenaar AJ Pinckers PL Huygen EM Bleeker-Wagemakers BJ Kimberling CW Cremers 《Canadian Metallurgical Quarterly》1995,16(4):151-158
Thirty-seven patients, comprising 24 familial cases and 13 isolated patients with Usher syndrome type II (USH2), underwent ophthalmologic examination. Based on the degree of hearing loss, normal vestibular function, and gene-linkage analysis, familial cases were assumed to have USH2A. An analysis of genetic heterogeneity failed to reveal the presence of a second locus in the Dutch population. Although the patients appear to belong to a genetically homogeneous group, remarkable ophthalmologic variability was found. Corrected visual acuity decreased with age and remarkable differences in visual acuity were found within one family. Fundoscopic findings were classified as type A if attenuated vessels and bone corpuscles in all quadrants were found or as type B if findings other than these were found. The prevalence of type A significantly increased with age. 相似文献
999.
1000.
This study examines the ways in which therapists function as attachment figures for patients. Patients in long-term psychoanalytic therapy answered questionnaires about their feelings about their therapists and their closest personal relationships. Components of attachment prominent in the therapeutic relationships were looking up to the therapist and feeling the therapist was responsive to emotional needs. Stronger attachment to therapists was associated with greater frequency and duration of therapy, a stronger working alliance, and greater security of the patients' attachment style, as well as with the gender of the patient and therapist. Using attachment theory to understand psychoanalytic relationships emphasizes the unique importance of a therapist to a patient and can offer new perspectives on both therapeutic and attachment processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献