全文获取类型
收费全文 | 654篇 |
免费 | 19篇 |
专业分类
电工技术 | 4篇 |
综合类 | 1篇 |
化学工业 | 167篇 |
金属工艺 | 2篇 |
机械仪表 | 8篇 |
建筑科学 | 31篇 |
矿业工程 | 2篇 |
能源动力 | 14篇 |
轻工业 | 94篇 |
水利工程 | 26篇 |
石油天然气 | 1篇 |
无线电 | 45篇 |
一般工业技术 | 117篇 |
冶金工业 | 96篇 |
原子能技术 | 3篇 |
自动化技术 | 62篇 |
出版年
2024年 | 19篇 |
2023年 | 24篇 |
2022年 | 28篇 |
2021年 | 51篇 |
2020年 | 31篇 |
2019年 | 27篇 |
2018年 | 30篇 |
2017年 | 27篇 |
2016年 | 22篇 |
2015年 | 20篇 |
2014年 | 25篇 |
2013年 | 35篇 |
2012年 | 39篇 |
2011年 | 42篇 |
2010年 | 26篇 |
2009年 | 21篇 |
2008年 | 25篇 |
2007年 | 25篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 12篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 7篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 5篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1969年 | 3篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1961年 | 1篇 |
1960年 | 2篇 |
1958年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有673条查询结果,搜索用时 15 毫秒
141.
142.
The relation between age and altruism was examined in 2 experiments conducted in naturalistic settings. In both studies, individuals from 5 to over 75 years of age had opportunities to donate money to a charity concerned with the welfare of infants with birth defects. The effect of a variable designed to evoke the needs rule was also observed by using both pregnant and nonpregnant charitable solicitors. Results of both studies yielded a significant main effect of solicitor condition on donations. Study 1 yielded a linear increase with age in numbers of people donating; however, retired persons generally donated less money than did younger adults. In Study 2, which controlled for financial costs, elderly persons proved to be the most generous. These results underscore the importance of personal resources and helping opportunities in influencing altruism among older persons. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
143.
Batson C. Daniel; Kobrynowicz Diane; Dinnerstein Jessica L.; Kampf Hannah C.; Wilson Angela D. 《Canadian Metallurgical Quarterly》1997,72(6):1335
Across 3 small studies, 80 female undergraduates were confronted with the dilemma of deciding whom—themselves or another research participant—to assign to a positive consequences task, leaving the other to do a dull, boring task. In Study 1, where morality was not mentioned, 16 of 20 assigned themselves to the positive consequences task, even though in retrospect only 1 said this was moral. In Studies 2 and 3, a moral strategy was suggested: either flipping a coin or accepting task assignment by the experimenter. In Study 2, 10 of 20 participants flipped a coin, but of these, 9 assigned themselves the positive consequences task. In Study 3, participants were significantly more likely to accept the experimenter's assignment when it gave them the positive consequences task. Overall, results suggested motivation to appear moral yet still benefit oneself. Such motivation is called moral hypocrisy. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
144.
Temperature lability of ADP-glucose pyrophosphorylase (AGP; glucose-1-phosphate adenylyltransferase; ADP: alpha-D-glucose-1-phosphate adenylyltransferase, EC 2.7.7.27), a key starch biosynthetic enzyme, may play a significant role in the heat-induced loss in maize seed weight and yield. Here we report the isolation and characterization of heat-stable variants of maize endosperm AGP. Escherichia coli cells expressing wild type (WT) Shrunken2 (Sh2), and Brittle2 (Bt2) exhibit a reduced capacity to produce glycogen when grown at 42 degreesC. Mutagenesis of Sh2 and coexpression with WT Bt2 led to the isolation of multiple mutants capable of synthesizing copious amounts of glycogen at this temperature. An increase in AGP stability was found in each of four mutants examined. Initial characterization revealed that the BT2 protein was elevated in two of these mutants. Yeast two-hybrid studies were conducted to determine whether the mutant SH2 proteins more efficiently recruit the BT2 subunit into tetramer assembly. These experiments showed that replacement of WT SH2 with the heat-stable SH2HS33 enhanced interaction between the SH2 and BT2 subunits. In agreement, density gradient centrifugation of heated and nonheated extracts from WT and one of the mutants, Sh2hs33, identified a greater propensity for heterotetramer dissociation in WT AGP. Sequencing of Sh2hs33 and several other mutants identified a His-to-Tyr mutation at amino acid position 333. Hence, a single point mutation in Sh2 can increase the stability of maize endosperm AGP through enhanced subunit interactions. 相似文献
145.
OBJECTIVES: This study investigated the ability of on-line vectorcardiography (VCG) to detect myocardial ischaemia as assessed by dobutamine stress echocardiography after an episode of unstable coronary artery disease. DESIGN: Dobutamine stress test (incrementally infused doses of 5, 10, 20, 30 and 40 microg kg(-1) per minute) was performed during simultaneous VCG monitoring. QRS vector difference (QRS-VD), ST vector magnitude (ST-VM), ST change vector magnitude (STC-VM) and T change vector magnitude (TC-VM) were monitored. A new wall motion abnormality or worsening of abnormal wall motion was regarded as indicating a positive dobutamine stress test. SUBJECTS: Fifty-five patients with unstable angina pectoris and 16 patients with an acute non-Q-wave myocardial infarction were studied 5-8 days after admission. RESULTS: A positive dobutamine stress test was observed in 37 patients (52%). The sensitivity, specificity and total accuracy of identifying patients with a positive dobutamine stress test by VCG were: 38%, 91% and 63% for QRS-VD; 59%, 88% and 73% for ST-VM; 84%, 79% and 82% for STC-VM; and 86%, 23% and 56% for TC-VM. Patients with a positive dobutamine stress test showed higher maximum VCG values than patients with a negative dobutamine stress test (QRS-VD, P < 0.01; ST-VM, P < 0.001; STC-VM, P < 0.001). The maximum VCG values were related to the number of segments showing new or worsening wall motion abnormality (QRS-VD: r=0.41, P < 0.001; ST-VM: r=0.44, P < 0.001; STC-VM: r=0.57, P < 0.001). CONCLUSION: STC-VM and ST-VM seem to be the best VCG variables for detection of myocardial ischaemia as assessed by dobutamine stress echocardiography. 相似文献
146.
Bono Joyce E.; Foldes Hannah Jackson; Vinson Gregory; Muros John P. 《Canadian Metallurgical Quarterly》2007,92(5):1357
In this experience sampling study, the authors examined the role of organizational leaders in employees' emotional experiences. Data were collected from health care workers 4 times a day for 2 weeks. Results indicate supervisors were associated with employee emotions in 3 ways: (a) Employees experienced fewer positive emotions when interacting with their supervisors as compared with interactions with coworkers and customers; (b) employees with supervisors high on transformational leadership experienced more positive emotions throughout the workday, including interactions with coworkers and customers; and (c) employees who regulated their emotions experienced decreased job satisfaction and increased stress, but those with supervisors high on transformational leadership were less likely to experience decreased job satisfaction. The results also suggest that the effects of emotional regulation on stress are long lasting (up to 2 hr) and not easily reduced by leadership behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
147.
In 2001 Marc Prensky coined the phrase ‘digital natives’ to refer to the new generation of students who have grown up surrounded by technology. His companion papers spurred large amounts of research, debating changes that are required to curricula and pedagogical models to cater for the changes in the student population. This article reports on a study conducted in 2009 of more than 290 first year students at two South African universities. In this study, students were asked about their access to and use of technology. The results portrayed a heterogeneous student population, with varying levels of access to and use of most technologies. One of Prensky’s key features of a digital native is their excitement with Web 2.0 based technologies. Participants in this study however, appear not to use such technologies, and to not be interested in using them in their studies. One tool that students had high levels of access to (98.1%), and use of is the mobile phone. Out of all uses of technology surveyed, tasks involving the mobile phone were ranked in the top two positions. Also when asked to rank different uses of technology particularly for their studies, three of the top five uses relied on a mobile phone. 相似文献
148.
149.
Ingrid H. Holmøy Ingrid Toftaker Carsten Kirkeby Olav Østerås Hannah J. Jørgensen Ane Nødtvedt 《Journal of dairy science》2019,102(9):8385-8399
The primary objective of the present study was to estimate the effect of Streptococcus agalactiae intramammary infection on milk production and somatic cell count (SCC) in Norwegian dairy cows. A secondary objective was to assess differences in the effect of common Strep. agalactiae sequence types (ST) found in Norwegian dairy herds. We performed a cohort study combining registry data with sequence-type data from Strep. agalactiae isolates. Herds in which Strep. agalactiae had been detected in individual animals (bacteriological culture or quantitative PCR) between 2012 and 2015 were included. We accessed monthly test-day milk yield records for the entire period to compare milk yield and SCC between cows that were Strep. agalactiae positive and all other cows, within each herd. The study sample consisted of 150 herds, 15,757 cows, 30,850 lactations, and 204,126 test days. We evaluated the effects of Strep. agalactiae on test-day milk yield and SCC using mixed linear regression models, controlling for clustering by herd, cow, and lactation. Multilocus sequence typing of Strep. agalactiae was available for isolates from 86 herds. Additional models were fit to a subset of herds (n = 59) in which ST1, ST23, ST103, and ST196 had been found, to compare the effects of ST on milk production and SCC. In the period 3 to 2 mo before diagnosis, Strep. agalactiae-positive cows produced an average of 1.3 kg more DIM-adjusted milk/d than their negative herd mates. At the time of diagnosis, production was on average 0.13 kg less DIM-adjusted milk/d in Strep. agalactiae-positive cows than in negative cows; 2 to 3 mo after diagnosis, they produced 1.24 kg less DIM-adjusted milk/d than negative cows. Losses persisted for the rest of the investigated period. Cows with ST23, ST103, and ST196 followed a similar pattern as the overall analysis with respect to milk production, whereas ST1-affected cows produced similar amounts of milk before diagnosis as the negative cows. Cows with ST1 experienced the largest milk loss 1 to 2 mo after diagnosis but then recovered to some extent; for cows with ST103, the severe milk loss persisted for the rest of the investigation period. The cow-associated ST103 elicited a lower response in peak SCC compared with ST23, ST103, and ST196. The results indicate an effect of Strep. agalactiae on milk production and SCC. Production was lowest 2 to 3 mo after a positive sample. Peak SCC was reached the month before diagnosis, with notable differences between sequence types. 相似文献
150.
Elena S. George Skye Marshall Hannah L Mayr Gina L. Trakman Oana A. Tatucu-Babet Annie-Claude M. Lassemillante 《Critical reviews in food science and nutrition》2019,59(17):2772-2795
AbstractThe polyphenol fraction of extra-virgin olive oil may be partly responsible for its cardioprotective effects. The aim of this systematic review and meta-analysis was to evaluate the effect of high versus low polyphenol olive oil on cardiovascular disease (CVD) risk factors in clinical trials. In accordance with PRISMA guidelines, CINAHL, PubMed, Embase and Cochrane databases were systematically searched for relevant studies. Randomized controlled trials that investigated markers of CVD risk (e.g. outcomes related to cholesterol, inflammation, oxidative stress) were included. Risk of bias was assessed using the Jadad scale. A meta-analysis was conducted using clinical trial data with available CVD risk outcomes. Twenty-six studies were included. Compared to low polyphenol olive oil, high polyphenol olive oil significantly improved measures of malondialdehyde (MD: ?0.07µmol/L [95%CI: ?0.12, ?0.02µmol/L]; I2: 88%; p?=?0.004), oxidized LDL (SMD: ?0.44 [95%CI: ?0.78, ?0.10µmol/L]; I2: 41%; P?=?0.01), total cholesterol (MD 4.5 mg/dL [95%CI: ?6.54, ?2.39 mg/dL]; p<0.0001) and HDL cholesterol (MD 2.37 mg/dL [95%CI: 0.41, 5.04 mg/dL]; p?=?0.02). Subgroup analyses and individual studies reported additional improvements in inflammatory markers and blood pressure. Most studies were rated as having low-to-moderate risk of bias. High polyphenol oils confer some CVD-risk reduction benefits; however, further studies with longer duration and in non-Mediterranean populations are required. 相似文献