首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   657篇
  免费   33篇
电工技术   2篇
综合类   8篇
化学工业   157篇
金属工艺   3篇
机械仪表   6篇
建筑科学   59篇
能源动力   15篇
轻工业   139篇
水利工程   8篇
无线电   16篇
一般工业技术   83篇
冶金工业   128篇
原子能技术   4篇
自动化技术   62篇
  2024年   2篇
  2023年   7篇
  2022年   11篇
  2021年   28篇
  2020年   9篇
  2019年   19篇
  2018年   13篇
  2017年   12篇
  2016年   13篇
  2015年   21篇
  2014年   18篇
  2013年   29篇
  2012年   38篇
  2011年   51篇
  2010年   29篇
  2009年   44篇
  2008年   40篇
  2007年   23篇
  2006年   34篇
  2005年   22篇
  2004年   33篇
  2003年   20篇
  2002年   21篇
  2001年   17篇
  2000年   11篇
  1999年   14篇
  1998年   18篇
  1997年   5篇
  1996年   15篇
  1995年   5篇
  1994年   8篇
  1993年   5篇
  1992年   7篇
  1991年   7篇
  1989年   6篇
  1988年   6篇
  1987年   2篇
  1986年   3篇
  1985年   3篇
  1984年   2篇
  1982年   4篇
  1980年   2篇
  1979年   1篇
  1977年   1篇
  1974年   1篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
  1964年   3篇
  1963年   2篇
排序方式: 共有690条查询结果,搜索用时 31 毫秒
91.
Cerebral palsy (CP) is a perinatally acquired nonprogressive brain damage resulting in motor impairment affecting mobility and posture. Early identification of infants with CP is desired to target early interventions and follow-up. During early infancy, distinct motion patterns occur which are highly predictive for later disability. These motor patterns can be observed and recorded. In this paper, a method to predict later CP based on early video recordings of the infants' spontaneous movements, applying optical flow and statistical pattern recognition, is presented. We extract motion information from video recordings of young infants using a total variation related optical flow method. By using wavelet analysis features from motion trajectories of points initiated on a regular grid were extracted and classified using a support vector machine.  相似文献   
92.
The removal of certain central nervous system (CNS) tissues (part of the bovine spongiform encephalopathy risk material) from the food chain is one of the highest priority tasks associated with avoiding contamination of the human food chain with the agent of bovine spongiform encephalopathy. A recently developed real-time PCR assay and three commercially available enzyme-linked immunosorbent assays (ELISAs) for the detection of CNS tissues in minced meat and three types of heat-treated sausages were evaluated. Bovine brain was used for spiking of internal reference material, and its detectability was examined during storage times of 12 months (for frozen minced meat and liver sausage) and 24 months (for sausages treated with medium and high heat). The real-time PCR method and both ELISA kits detected 0.1% CNS tissue in frozen minced meat and 0.1 or 1% CNS tissue in heat-treated meat products. The detectability of the amplified mRNA target region with the PCR assay was similar to the detectability of antigen by the ELISAs. Because the real-time PCR method also can be used to distinguish cattle, ovine, and caprine CNS tissues from porcine CNS tissues, it seems to be suitable as a routine diagnostic test for the sensitive and specific detection of CNS tissues in meat and meat products.  相似文献   
93.
Data regarding chewing gum consumption habits and attitudes were collected for 963 children and adolescents (aged 6–14) and 3150 adolescents and adults (aged 13 years+) in the United States (U.S.) using a dedicated online food frequency questionnaire. A total of 79.6% of children/adolescents reported using chewing gum in the last 3 months, whereas 61.8% of adolescents/adults chewed gum in the previous 6 months. The mean and 90th percentile of consumption among children/adolescents aged 6–14 were 1.95 and 4.71 g day?1, equivalent to 0.75 and 1.78 pieces per day, respectively. Stratification by gender and age brackets revealed that the consumption of chewing gum was more heavily reported in boys compared to girls. Among adolescents/adults aged 13 years and older, the mean and 90th percentile of consumption of chewing gum was estimated to be 2.98 and 7.67 g day?1, or 1.05 and 3.00 pieces per day, respectively. Stratification by gender and by age brackets in this cohort did not reveal any marked patterns although it was noted that there was a decrease in the percent consuming with age (from 87.0 to 34.5%). The most commonly reported chew frequency among all ages was ‘two or three times a week’ (23.7 to 26.8%). The average and high-level estimates reported herein provide up-to-date estimates of chewing gum consumption in the U.S. Comparisons of the calculated intake values with those reported from the National Health and Nutrition Examination Survey dataset suggests that national nutrition surveys may result in an under-reporting of the percent consumers, but similar estimates for the daily intakes in g day?1.  相似文献   
94.
Contamination of groundwaters with geogenic arsenic poses a major health risk to millions of people. Although the main geochemical mechanisms of arsenic mobilization are well understood, the worldwide scale of affected regions is still unknown. In this study we used a large database of measured arsenic concentration in groundwaters (around 20,000 data points) from around the world as well as digital maps of physical characteristics such as soil, geology, climate, and elevation to model probability maps of global arsenic contamination. A novel rule-based statistical procedure was used to combine the physical data and expert knowledge to delineate two process regions for arsenic mobilization: "reducing" and "high-pH/ oxidizing". Arsenic concentrations were modeled in each region using regression analysis and adaptive neuro-fuzzy inferencing followed by Latin hypercube sampling for uncertainty propagation to produce probability maps. The derived global arsenic models could benefit from more accurate geologic information and aquifer chemical/physical information. Using some proxy surface information, however, the models explained 77% of arsenic variation in reducing regions and 68% of arsenic variation in high-pH/oxidizing regions. The probability maps based on the above models correspond well with the known contaminated regions around the world and delineate new untested areas that have a high probability of arsenic contamination. Notable among these regions are South East and North West of China in Asia, Central Australia, New Zealand, Northern Afghanistan, and Northern Mali and Zambia in Africa.  相似文献   
95.
The apparent particle density of particulate matter with aerodynamic diameter < 2.5 microm (rho2.5) was determined at an urban site in Augsburg, Germany and its correlation with chemical composition and meteorological conditions was investigated. rho2.5 showed strong day-to-day variation from 1.05 to 2.36 g cm(-3) (5 to 95% percentile), and nearly 64% of the daily variability could be explained by a multiple variable regression model. A minimum in the morning and afternoon (about 1.5 g cm(-3)), and a maximum (near 1.8 g cm(-3)) during midday was observed. The minima represent fresh primary aerosol emissions, which were related to traffic soot particles with low density due to their agglomerate structure, especially observed in the early morning hours of weekdays. The maximum is likely due to increased secondary particle production and the presence of more aged particles with the built-up of the convectively mixed boundary layer. rho2.5 has the potential to serve as a crude tracer for chemical composition and atmospheric processing and might play an important role when considering the associations between health effects and ambient particles.  相似文献   
96.
The chemical composition of three essential oils obtained from the barks of three endemic Boswellia species namely, Boswellia dioscorides, Boswellia elongata and Boswellia socotrana which were collected from the Soqotra Island (Yemen), was investigated. In parallel to that evaluation of their antimicrobial and antioxidant activities was also carried out. The investigation led to the identification of 72, 70 and 67 constituents for B.dioscorides, B. elongata, and B. socotrana, respectively. The B. dioscorides oil was found to have a high content of monoterpene hydrocarbons (32.8%) with α-thujene (9.3%) and α-pinene (8.3%) as main components. Whereas, the essential oil of B. elongata was characterised by high diterpene content (31.7%), in which incensol (14.8%) was found to be the major constituent. On the other hand, the oil obtained from the B. socotrana was found to be predominated of monoterpene hydrocarbons (26.4%) and oxygenated monoterpenes (30.7%) with p-cymene (13.0%), 2-hydroxy-5-methoxy-acetophenone (16.3%) and camphor (11.6%). All essential oils possessed antimicrobial activity especially against Gram-positive bacteria with MIC-values between 1.8 and 17.2 mg/ml. Furthermore, the DPPH-radical scavenging assay exhibited only weak antioxidant activities (28%) at 1.0 mg/ml.  相似文献   
97.
The P2X7 receptor is a promising target for the treatment of various diseases due to its significant role in inflammation and immune cell signaling. This work describes the design, synthesis, and in vitro evaluation of a series of novel derivatives bearing diverse scaffolds as potent P2X7 antagonists. Our approach was based on structural modifications of reported (adamantan-1-yl)methylbenzamides able to inhibit the receptor activation. The adamantane moieties and the amide bond were replaced, and the replacements were evaluated by a ligand-based pharmacophore model. The antagonistic potency of the synthesized analogues was assessed by two-electrode voltage clamp experiments, using Xenopus laevis oocytes that express the human P2X7 receptor. SAR studies suggested that the replacement of the adamantane ring by an aryl-cyclohexyl moiety afforded the most potent antagonists against the activation of the P2X7 cation channel, with analogue 2-chloro-N-[1-(3-(nitrooxymethyl)phenyl)cyclohexyl)methyl]benzamide ( 56 ) exhibiting the best potency with an IC50 value of 0.39 μM.  相似文献   
98.
99.
Objective: Patients with rheumatoid arthritis (RA) have accelerated atherosclerosis, but there is limited information about the genetic contribution to atherosclerosis in this population. Therefore, we examined the association between selected genetic polymorphisms and coronary atherosclerosis in patients with RA. Methods: Genotypes for single-nucleotide polymorphisms (SNPs) in 152 candidate genes linked with autoimmune or cardiovascular risk were measured in 140 patients with RA. The association between the presence of coronary artery calcium (CAC) and SNP allele frequency was assessed by logistic regression with adjustment for age, sex, and race. To adjust for multiple comparisons, a false discovery rate (FDR) threshold was set at 20%. Results: Patients with RA were 54 ± 11 years old and predominantly Caucasian (89%) and female (69%). CAC was present in 70 patients (50%). A variant in rs2073618 that encodes an Asn3Lys missense substitution in the osteoprotegerin gene (OPG, TNFRSF11B) was significantly associated with the presence of CAC (OR = 4.09, p < 0.00026) and withstands FDR correction. Conclusion: Our results suggest that a polymorphism of the TNFRSF11B gene, which encodes osteoprotegerin, is associated with the presence of coronary atherosclerosis in patients with RA. Replication of this finding in independent validation cohorts will be of interest.  相似文献   
100.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号