全文获取类型
收费全文 | 2392篇 |
免费 | 5篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 6篇 |
综合类 | 5篇 |
化学工业 | 58篇 |
金属工艺 | 26篇 |
机械仪表 | 19篇 |
建筑科学 | 7篇 |
矿业工程 | 4篇 |
能源动力 | 1篇 |
轻工业 | 25篇 |
石油天然气 | 6篇 |
武器工业 | 1篇 |
无线电 | 150篇 |
一般工业技术 | 45篇 |
冶金工业 | 2026篇 |
自动化技术 | 35篇 |
出版年
2021年 | 3篇 |
2016年 | 3篇 |
2014年 | 3篇 |
2013年 | 17篇 |
2011年 | 25篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 14篇 |
2006年 | 22篇 |
2005年 | 19篇 |
2004年 | 42篇 |
2003年 | 26篇 |
2002年 | 20篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 59篇 |
1998年 | 574篇 |
1997年 | 302篇 |
1996年 | 218篇 |
1995年 | 126篇 |
1994年 | 102篇 |
1993年 | 136篇 |
1992年 | 34篇 |
1991年 | 44篇 |
1990年 | 38篇 |
1989年 | 49篇 |
1988年 | 47篇 |
1987年 | 38篇 |
1986年 | 37篇 |
1985年 | 25篇 |
1984年 | 5篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 27篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 61篇 |
1976年 | 143篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1961年 | 3篇 |
1959年 | 2篇 |
1958年 | 3篇 |
1956年 | 3篇 |
1955年 | 4篇 |
排序方式: 共有2414条查询结果,搜索用时 821 毫秒
71.
抗弹陶瓷的特殊耗能机制研究 总被引:6,自引:2,他引:4
黄良钊 《兵器材料科学与工程》2001,24(5):3-6
以刚玉系抗弹陶瓷为研究对象 ,测定其防护系数和相关性能 ,通过结构分析研究其抗弹机理 ,并提出陶瓷的特殊耗能机制 ,试图揭示陶瓷具有优良抗弹能力的本质 相似文献
72.
Richard C. Morey Donna L. Retzlaff-Roberts David J. Fine 《International Transactions in Operational Research》1994,1(3):285-292
One of the focal points of discussion among firms in the service sector concerns the level of service delivered and its value. In the hospital sector, an important aspect of the level of service relates to the level of quality of care delivered. We undertake an empirical study of 300 U.S. hospitals to evaluate their relative ‘service efficiency’ using the techniques of so-called allocative efficiency. This method estimates the potential improvement in service, estimates the ideal cost shares of the various resources, and provides the ‘peer group’ members to which the unit is being compared. Utilizing this information, the method proposed for units to improve involves two chief mechanisms. The first is a reallocation of cost shares among the various resource or input types (e.g. no increase in hospital budget). The second involves adopting the management practices used by peer group members. Over all 300 hospitals, a marked improvement potential was found for well over half. Of the poorest performers there appears to be some indication that a larger cost share was needed for face-to-face contact with patients (nursing) and a smaller share for personnel who do not deal with patients directly (lab technicians, non-physician administrators, etc.). 相似文献
73.
A study was conducted to investigate the effectiveness of three air purification systems in reducing the exposure of children to air contaminants inside nine classrooms of three Southern California schools. Continuous and integrated measurements were conducted to monitor the indoor and outdoor concentrations of ultrafine particles (UFPs), fine and coarse particulate matter (PM2.5 and PM10, respectively), black carbon (BC), and volatile organic compounds. An heating, ventilating, and air conditioning (HVAC)‐based high‐performance panel filter (HP‐PF), a register‐based air purifier (RS), and a stand‐alone air cleaning system (SA) were tested alone and in different combinations for their ability to remove the monitored pollutants. The combination of a RS and a HP‐PF was the most effective solution for lowering the indoor concentrations of BC, UFPs, and PM2.5, with study average reductions between 87% and 96%. When using the HP‐PF alone, reductions close to 90% were also achieved. In all cases, air quality conditions were improved substantially with respect to the corresponding baseline (preexisting) conditions. Data on the performance of the gas‐absorbing media included in the RS and SA unit were inconclusive, and their effectiveness, lifetime, costs, and benefits must be further assessed before conclusions and recommendations can be made. 相似文献
74.
Trentacosta Christopher J.; Izard Carroll E.; Mostow Allison J.; Fine Sarah E. 《Canadian Metallurgical Quarterly》2006,21(2):148
The current study examined the relations between two aspects of emotional competence--emotion knowledge and emotion expression, and children's attentional competence during one school year. Participants were 263 first- and second-grade students at two rural elementary schools. A multiple regression analysis showed that emotion knowledge predicted attentional competence while controlling for age, gender, verbal ability, and initial levels of attentional competence. Multiple regression analyses examining predictors of peer nominations of emotion expression showed that attentional competence predicted peer nominations of happiness, sadness, and anger expression, and emotion knowledge predicted peer nominations of anger expression. Potential improvements for prevention programs and the importance of the findings for school personnel are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
75.
Cleavage motifs of the yeast 20S proteasome beta subunits deduced from digests of enolase 1 总被引:3,自引:0,他引:3
AK Nussbaum TP Dick W Keilholz M Schirle S Stevanovi? K Dietz W Heinemeyer M Groll DH Wolf R Huber HG Rammensee H Schild 《Canadian Metallurgical Quarterly》1998,95(21):12504-12509
The 436-amino acid protein enolase 1 from yeast was degraded in vitro by purified wild-type and mutant yeast 20S proteasome particles. Analysis of the cleavage products at different times revealed a processive degradation mechanism and a length distribution of fragments ranging from 3 to 25 amino acids with an average length of 7 to 8 amino acids. Surprisingly, the average fragment length was very similar between wild-type and mutant 20S proteasomes with reduced numbers of active sites. This implies that the fragment length is not influenced by the distance between the active sites, as previously postulated. A detailed analysis of the cleavages also allowed the identification of certain amino acid characteristics in positions flanking the cleavage site that guide the selection of the P1 residues by the three active beta subunits. Because yeast and mammalian proteasomes are highly homologous, similar cleavage motifs might be used by mammalian proteasomes. Therefore, our data provide a basis for predicting proteasomal degradation products from which peptides are sampled by major histocompatibility complex class I molecules for presentation to cytotoxic T cells. 相似文献
76.
77.
The actin cytoskeleton in budding yeast consists of cortical patches and cables, both of which polarize toward regions of cell growth. Tropomyosin localizes specifically to actin cables and not cortical patches. Upon shifting cells with conditionally defective tropomyosin to restrictive temperatures, actin cables disappear within 1 min and both the unconventional class V myosin Myo2p and the secretory vesicle-associated Rab GTPase Sec4p depolarize rapidly. Bud growth ceases and the mother cell grows isotropically. When returned to permissive temperatures, tropomyosin-containing cables reform within 1 min in polarized arrays. Cable reassembly permits rapid enrichment of Myo2p at the focus of nascent cables as well as the Myo2p- dependent recruitment of Sec4p and the exocyst protein Sec8p, and the initiation of bud emergence. With the loss of actin cables, cortical patches slowly assume an isotropic distribution within the cell and will repolarize only after restoration of cables. Therefore, actin cables respond to polarity cues independently of the overall distribution of cortical patches and are able to directly target the Myo2p-dependent delivery of secretory vesicles and polarization of growth. 相似文献
78.
79.
T Skarzynski DH Kim WJ Lees CT Walsh K Duncan 《Canadian Metallurgical Quarterly》1998,37(8):2572-2577
MurA (UDP-GlcNAc enolpyruvyl transferase), the first enzyme in bacterial peptidoglycan biosynthesis, catalyzes the enolpyruvyl transfer from phosphoenolpyruvate (PEP) to the 3'-OH of UDP-GlcNAc by an addition-elimination mechanism that proceeds through a tetrahedral ketal intermediate. The crystal structure of the Cys115-to-Ala (C115A) mutant of Escherichia coli MurA complexed with a fluoro analogue of the tetrahedral intermediate revealed the absolute configuration of the adduct and the stereochemical course of the reaction. The fluorinated adduct was generated in a preincubation of wild-type MurA with (Z)-3-fluorophosphoenolpyruvate (FPEP) and UDP-GlcNAc and purified after enzyme denaturation. The fluorine substituent stabilizes the tetrahedral intermediate toward decomposition by a factor of 10(4)-10(6), facilitating manipulation of the adduct. The C115A mutant of MurA was utilized to avoid the microheterogeneity that arises in the wild-type MurA from the attack of Cys115 on C-2 of FPEP in competition with the formation of the fluorinated adduct. The crystal structure of the complex was determined to 2.8 A resolution, and the absolute configuration at C-2 of the adduct was found to be 2R. Thus, addition of the 3'-OH of UDP-GlcNAc is to the 2-si face of FPEP, corresponding to the 2-re face of PEP. Given the previous observation that, in D2O, the addition of D+ to C-3 of PEP proceeds from the 2-si face [Kim, D. H., Lees, W. J., and Walsh, C. T. (1995) J. Am. Chem. Soc. 117, 6380-6381], the addition across the double bond of PEP is anti. Also, because the overall stereochemical course has been shown to be either anti/syn or syn/anti [Lees, W. J., and Walsh, C. T. (1995) J. Am. Chem. Soc. 117, 7329-7337], it now follows that the stereochemistry of elimination of H+ from C-3 and Pi from C-2 of the tetrahedral intermediate of the reaction is syn. 相似文献
80.
Based upon all of the available data relating to the natural history, chemical course, and response to therapy of HCV, the following recommendations are made: 1) The primary end point for HCV therapy should be HCV clearance from all tissue sites, eg plasma, liver and others 2) Therapy should be provided for patients with early infections as they have the best chance of achieving a virologic response 3) Therapy should be offered to patients with cirrhotic disease, as prevention of hepatic decompensation and degeneration to hepatic cancer is possible 4) End stage decompensated disease should be treated, particularly if liver transplantation is being considered, in an effort to either eliminate or ameliorate disease recurrence 5) Combination therapies are preferable to monotherapy as they enhance the likelihood of a therapeutic response. Some of these include agents that reduce the frequency of IFN-induced untoward events (NSAIDs) 6) The approach to HCV infection should be to view it as an infectious disease. In this way, multi-agent therapy could be used to prevent the emergence of drug resistant mutants as well as to obtain earlier clearance of the infection than is possible with monotherapy. 相似文献