全文获取类型
收费全文 | 2644篇 |
免费 | 49篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 44篇 |
综合类 | 3篇 |
化学工业 | 448篇 |
金属工艺 | 78篇 |
机械仪表 | 53篇 |
建筑科学 | 127篇 |
矿业工程 | 10篇 |
能源动力 | 51篇 |
轻工业 | 158篇 |
水利工程 | 24篇 |
石油天然气 | 14篇 |
无线电 | 200篇 |
一般工业技术 | 389篇 |
冶金工业 | 669篇 |
原子能技术 | 22篇 |
自动化技术 | 407篇 |
出版年
2022年 | 23篇 |
2021年 | 23篇 |
2020年 | 20篇 |
2019年 | 26篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 39篇 |
2015年 | 35篇 |
2014年 | 55篇 |
2013年 | 152篇 |
2012年 | 78篇 |
2011年 | 114篇 |
2010年 | 75篇 |
2009年 | 75篇 |
2008年 | 132篇 |
2007年 | 91篇 |
2006年 | 87篇 |
2005年 | 85篇 |
2004年 | 79篇 |
2003年 | 71篇 |
2002年 | 76篇 |
2001年 | 46篇 |
2000年 | 47篇 |
1999年 | 53篇 |
1998年 | 75篇 |
1997年 | 38篇 |
1996年 | 51篇 |
1995年 | 43篇 |
1994年 | 59篇 |
1993年 | 35篇 |
1992年 | 54篇 |
1991年 | 32篇 |
1990年 | 42篇 |
1989年 | 37篇 |
1988年 | 36篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 34篇 |
1984年 | 43篇 |
1983年 | 41篇 |
1982年 | 41篇 |
1981年 | 29篇 |
1980年 | 32篇 |
1979年 | 27篇 |
1978年 | 32篇 |
1977年 | 30篇 |
1976年 | 33篇 |
1975年 | 23篇 |
1974年 | 29篇 |
1973年 | 27篇 |
排序方式: 共有2697条查询结果,搜索用时 15 毫秒
51.
In 2 studies, the authors examined autobiographical memories for the presence of 2 growth orientations that were expected to correspond differentially to maturity and well-being, which are considered to be key facets of "the good life" by L. A. King (2001). Mature participants emphasized integrative memories (conceptual integration and learning), whereas happy participants emphasized intrinsic memories (humanistic concerns). Both kinds of growth memories correlated more strongly with eudaimonic than with hedonic measures of well-being. Growth memories were largely independent of Big Five traits in relation to maturity and well-being. Finally, older participants were more likely than younger participants to have greater maturity (marginally) and well-being, but this was in part explained by older participants' greater tendency to have growth memories. The discussion considers the role of growth memories in the intentional cultivation of the good life. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
52.
Judges were asked to make numerical estimates (e.g., "In what year was the first flight of a hot air balloon?"). Judges provided high and low estimates such that they were X% sure that the correct answer lay between them. They exhibited substantial overconfidence: The correct answer fell inside their intervals much less than X% of the time. This contrasts with choices between 2 possible answers to a question, which showed much less overconfidence. The authors show that overconfidence in interval estimates can result from variability in setting interval widths. However, the main cause is that subjective intervals are systematically too narrow given the accuracy of one's information-sometimes only 40% as large as necessary to be well calibrated. The degree of overconfidence varies greatly depending on how intervals are elicited. There are also substantial differences among domains and between male and female judges. The authors discuss the possible psychological mechanisms underlying this pattern of findings. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
53.
Self-generated validity and other effects of measurement on belief, attitude, intention, and behavior. 总被引:7,自引:0,他引:7
Drawing from recent developments in social cognition, cognitive psychology, and behavioral decision theory, we analyzed when and how the act of measuring beliefs, attitudes, intentions, and behaviors affects observed correlations among them. Belief, attitude, or intention can be created by measurement if the measured constructs do not already exist in long-term memory. The responses thus created can have directive effects on answers to other questions that follow in the survey. But even when counterparts to the beliefs, attitudes, and intentions measured already exist in memory, the structure of the survey researcher's questionnaire can affect observed correlations among them. The respondent may use retrieved answers to earlier survey questions as inputs to response generation to later questions. We present a simple theory predicting that an earlier response will be used as a basis for another, subsequent response if the former is accessible and if it is perceived to be more diagnostic than other accessible inputs. We outline the factors that determine both the perceived diagnosticity of a potential input, the likelihood that it will be retrieved, and the likelihood that some alternative (and potentially more diagnostic) inputs will be retrieved. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
54.
In this work, we compared APPI and APCI for normal-phase LC/MS chiral analysis of five pharmaceuticals. Performance was compared both by FIA and by on-column analysis using a ChiralPak AD-H column under optimized conditions. By comparison, APPI generated more reproducible signals and was less susceptible to ion suppression than APCI. APPI generated higher peak area and lower baseline noise, and therefore much higher S/N ratios. APPI sensitivity (i.e., S/N ratio) was approximately 2-130 times higher than APCI by FIA and was approximately 2.6-530 times higher than APCI by on-column analysis depending on specific compounds. The better APPI sensitivity as compared to APCI was more dramatic by on-column analysis than by FIA. APCI sensitivity was degraded by ion suppression caused by LC column bleeding components and by elevated APCI baseline noise relative to APPI. On-column APPI LODs (at S/N = 3) were 83, 16, 17, 95, and 7 pg for enantiomer #1, and 104, 23, 19, 122, and 17 pg for enantiomer #2 for benzoin, naringenin, mianserin, mephenesin, and diperodon, respectively, on a Waters ZQ. APPI offers no concern of explosion hazard relative to APCI corona needle discharge or ESI high voltage discharge when flammable solvents (e.g., hexane) are used as mobile phases. Whether APPI dopants are required depends on the IP(s) of mobile-phase solvent(s) and solvent complexes, and photon energies of VUV lamps. Dopant was not necessary for hexane-based mobile phases due to their self-doping effects. Dopants did enhance Kr lamp APPI sensitivity when MeOH was used as the mobile phase. However, dopants became unnecessary for the MeOH mobile phase when the Ar lamp was used. 相似文献
55.
The vulnerability of water supplies to toxic contamination calls for fast and effective means for screening water samples for multiple threats. We describe the use of photoionization (PI) mass spectrometry (MS) for high-speed, high-throughput screening and molecular identification of chemical weapons (CW) threats and other hazardous compounds. The screening technology can detect a wide range of compounds at subacute concentrations with no sample preparation and a sampling cycle time of approximately 45 s. The technology was tested with CW agents VX, GA, GB, GD, GF, HD, HN1, and HN3, in addition to riot agents and precursors. All are sensitively detected and give simple PI mass spectra dominated by the parent ion. The target application of the PI MS method is as a routine, real-time early warning system for CW agents and other hazardous compounds in air and in water. In this work, we also present comprehensive measurements for water analysis and report on the system detection limits, linearity, quantitation accuracy, and false positive (FP) and false negative rates for concentrations at subacute levels. The latter data are presented in the form of receiver operating characteristic curves of the form of detection probability P(D) versus FP probability P(FP). These measurements were made using the CW surrogate compounds, DMMP, DEMP, DEEP, and DIMP. Method detection limits (3sigma) obtained using a capillary injection method yielded 1, 6, 3, and 2 ng/mL, respectively. These results were obtained using 1-microL injections of water samples without any preparation, corresponding to mass detection limits of 1, 6, 3, and 2 pg, respectively. The linear range was about 3-4 decades and the dynamic range about 4-5 decades. The relative standard deviations were generally <10% at CW subacute concentrations levels. 相似文献
56.
In this paper, the threshold voltage instability characteristics of HfO2 high-k dielectric are discussed. The results from various stress bias conditions including DC and AC with variations of frequency, duty cycle, and polarity provide additional insights into the intrinsic behavior and the trapping dynamics of high-k materials. A reduced threshold voltage shift was observed at higher frequency and lower duty cycle under AC positive unipolar stress compared to DC stress. Similarly, the degradation of maximum transconductance was also reduced with AC stress. However, subthreshold swing changes were found to be negligible and fairly independent of stress frequencies and duty cycles under AC positive unipolar stress.When different polarity of stress, such as positive, negative, and bipolar stress was applied, it was observed that frequency and duty cycle dependencies were still valid in all three conditions. In contrast to positive stress, negative stress showed a decrease in the threshold voltage shift. Bipolar stress resulted in the highest threshold voltage instability, but the degradation in transconductance and subthreshold swing was actually smaller than those in negative unipolar stress. The bulk trap of HfO2 dielectric, which is proportional to its physical thickness, is believed to be the primary factor for threshold voltage shift. AC unipolar operation would allow a higher 10-year lifetime operating voltage than the DC condition. In addition to experimental results, a plausible mechanism has been proposed. 相似文献
57.
Soragia Athina Gkazi Emma Gravett Carla Bautista Jack Bartram Sara Ghorashian Stuart Paul Adams 《International journal of molecular sciences》2022,23(14)
Chimeric antigen receptor (CAR) T cell therapy is an innovative immunotherapy for treating cancers in both children and adults with proven utility in numerous clinical trials. Significantly, some CAR T cell therapies have now been approved by relevant national regulatory bodies across numerous countries for clinical therapeutic use outside of clinical trials. One such recently licensed product is tisagenlecleucel, a CAR T therapy approved for the treatment of B-cell acute lymphoblastic leukemia (B-ALL) using autologous T cells from the patient. The genetically engineered T cells target a protein called CD19, common to B cells, through a CAR incorporating a 4-1BB costimulatory domain to improve response. Since tisagenlecleucel is now a standard of care treatment for B-ALL, it is clinically essential to be able to accurately monitor these CAR T cells in patients. Assessment of the copy number variant (CNV) of the CAR T cell products allows this within a clinically acceptable timeframe for optimal patient benefit. However, no standardized method with high reproducibility and efficiency has been described within a routine clinical laboratory setting. Here, we demonstrated a novel digital droplet PCR (ddPCR)-based methodology for the study of CNV (ddPCR-CNV) in 4-1BB CD19-specific CAR T cells with universal applicability across clinical diagnostic laboratories. 相似文献
58.
Sung Kim Jack Surek James Baker-Jarvis 《Journal of research of the National Institute of Standards and Technology》2011,116(3):655-669
To augment current methods for the evaluation of reinforcing bar (rebar) corrosion within concrete, we are exploring unique features in the dielectric and magnetic spectra of pure iron oxides and corrosion samples. Any signature needs to be both prominent and consistent in order to identify corrosion within concrete bridge deck or other structures. In order to measure the permittivity and propagation loss through concrete as a function of temperature and humidity, we cut and carefully fitted samples from residential concrete into three different waveguides. We also poured and cured a mortar sample within a waveguide that was later measured after curing 30 days. These measurements were performed from 45 MHz to 12 GHz. Our concrete measurements showed that the coarse granite aggregate that occupied about half the sample volume reduced the electromagnetic propagation loss in comparison to mortar. We also packed ground corrosion samples and commercially available iron-oxide powders into a transmission-line waveguide and found that magnetite and corrosion sample spectra are similar, with a feature between 0.5 GHz and 2 GHz that may prove useful for quantifying corrosion. We also performed reflection (S11) measurements at various corrosion surfaces and in loose powders from 45 MHz to 50 GHz. These results are a first step towards quantifying rebar corrosion in concrete. 相似文献
59.
60.