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   11758篇
  免费   1933篇
  国内免费   1180篇
电工技术   972篇
综合类   1591篇
化学工业   1050篇
金属工艺   232篇
机械仪表   586篇
建筑科学   709篇
矿业工程   230篇
能源动力   278篇
轻工业   448篇
水利工程   294篇
石油天然气   496篇
武器工业   224篇
无线电   2431篇
一般工业技术   1132篇
冶金工业   466篇
原子能技术   75篇
自动化技术   3657篇
  2024年   32篇
  2023年   272篇
  2022年   350篇
  2021年   507篇
  2020年   521篇
  2019年   486篇
  2018年   451篇
  2017年   488篇
  2016年   602篇
  2015年   659篇
  2014年   779篇
  2013年   890篇
  2012年   868篇
  2011年   965篇
  2010年   696篇
  2009年   688篇
  2008年   746篇
  2007年   813篇
  2006年   673篇
  2005年   571篇
  2004年   443篇
  2003年   408篇
  2002年   323篇
  2001年   301篇
  2000年   240篇
  1999年   208篇
  1998年   138篇
  1997年   111篇
  1996年   104篇
  1995年   108篇
  1994年   76篇
  1993年   59篇
  1992年   58篇
  1991年   36篇
  1990年   38篇
  1989年   27篇
  1988年   19篇
  1987年   21篇
  1986年   14篇
  1985年   14篇
  1984年   9篇
  1983年   11篇
  1982年   7篇
  1981年   5篇
  1980年   6篇
  1976年   3篇
  1963年   3篇
  1961年   2篇
  1959年   5篇
  1956年   2篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Various fermented whey-based beverages have been developed to reduce waste. However, approaches to increase the preference of whey-based beverages are required because of the low sensory acceptability of whey. Here, we identified the better starting material (whey type), between raw whey (RW) and demineralised whey (DMW), and determined the optimal initial concentration using multiple sensory evaluations to develop acceptable fermented beverages made from sole whey with pure cultured Kluyveromyces marxianus (i.e. without additional ingredients and processing methods). Acceptance tests showed that fermented beverages made from DMW were superior to RW as the starting material. The amounts of ethanol produced were 5.0%, 7.6% and 9.5% v/v from the different initial DMW concentrations of 10%, 15% and 20% w/v, respectively. We observed a significant positive correlation (rs = 0.32, P < 0.05) between the assessment attributes, strength of taste as alcohol beverage and overall acceptability, indicating that higher concentrations of DMW yielded a more desirable product.  相似文献   
52.
53.
通过对唐家河煤矿自然地形条件及外部条件分析,结合井下煤层赋存情况,设计提出三个工业场地选址方案和两个开拓布置方案,通过技术、经济比较,选择陈家湾场地立井开拓方式,减少了矿井初期投资及后期运营费。  相似文献   
54.
In this study, the colorimetric parameters (L*, a*, b*) and mass loss of heat‐treated bamboo were investigated, and the obtained results were modeled by using two methods: multiple linear regression (MLR) and artificial neural network (ANN). First, bamboo samples were exposed to heat treatment at different temperatures (110°C, 140°C, 170°C, and 200°C) and durations (15, 30, 45, 60, 75, 90, and 115 minutes) in a laboratory oven. Then, the colorimetric parameters (L*, a*, b*) and mass loss of each sample were measured after each period of heat treatment. All data were modeled by using two methods separately for each parameter and the performances of these proposed methods were compared. It was found that color change and mass loss increased with increasing temperature and duration of heat treatment. Mean absolute percentage error (MAPE) values of all obtained MLR ranged from 0.64% to 10.63%, while the all MAPE values of ANN were found to be lower than 1.5%. Based on these results, it can be said that MLR and ANN could be used to evaluate the changes on the selected properties of heat‐treated bamboo samples. On the other hand, it should be emphasized that the ANN gave more accurate results than the MLR method because of its learning capability.  相似文献   
55.
Frozen storage is chosen to be the preferred method in meat preservation. However, multiple freeze-thaw (F-T) cycles will occur during the transfers or distribution processes under poor cold-chain conditions. This study investigated the effects of multiple freeze-thaw (F-T) cycles on water mobility, microstructure damage, protein oxidation and lipid oxidation in rabbit meat during seven F-T cycles through 56 days. Scanning electron microscopy results indicated that the increase of F-T cycles induced the rupture of endomysia and the increase of gaps between fibres. Low-field nuclear magnetic resonance (LF-NMR) results showed that the peak area of T21 and T22 decreased with increasing number of repeated F-T cycles, indicating that immobile water shifted to free water, and free water mobility increased. During repeated freeze-thaw process, the peroxide value, thiobarbituric acid-reactive substances, non-haem iron content and carbonyl groups of rabbit meat gradually increased, whereas haem content, haem iron content and sulfhydryl content of rabbit meat gradually decreased. In addition, the results of Fourier transform infrared, sodium dodecyl sulphate polyacrylamide gel electrophoresis, and intrinsic fluorescence spectroscopy indirectly proved that multiple F-T cycles could cause α-helix structure disruption, protein aggregation and degradation, and tryptophan oxidation of rabbit meat myofibrillar protein (MP). Overall, multiple repeated F-T cycles changed moisture migration, damaged microstructure and promoted lipid and protein oxidation of rabbit meat.  相似文献   
56.
In this study, unique fibrous silica ZSM-5 was successfully synthesized by using three type of alcohol possessing different alkyl-chain length as the co-surfactant. The effect of diverse co-surfactant was observed in the changes of physical properties, such as crystallinity, inter-dendrimer distances and pore properties. According to the IR and temperature programmed desorption of ammonia (NH3-TPD) analyses, all catalysts exhibited different acid strengths which could be triggered by the different amount of additional silica species. All catalysts exhibited high catalytic performance in the hydrocracking of 1,3,5-triisopropylbenzene due to the absence of diffusion limitation. However, FZSM5C3 exhibited the highest catalytic activity which corresponded to its high number of Brønsted acid sites. It was observed that different length of co-surfactant alkyl-chain has resulted in different degree of oil penetration into the microemulsion system which subsequently triggered in various inter-dendrimer distances and amount of incorporated silica species. Hence, the altered physicochemical properties led to the difference in catalytic performance due to the presence of different number of Brønsted acid sites.  相似文献   
57.
Mann-Whitney and Signed-Rank control charts are two well-known nonparametric charts used for controlling the center of the process when the distribution of the process parameter is unknown or nonnormal. Considering the effect of measurement error on the performance of control charts, the mentioned effect with additive model is investigated on Mann-Whitney and Signed-Rank charts. Furthermore, a comparison is made between the two charts and a Shewhart-type X¯ chart (as a parametric one) in the presence of the error. To do so, a simulation program is used and average run length (ARL) of the charts are calculated under three distributions. The results for all three distributions show that the existence of measurement error weakens the performances of both nonparametric charts and larger values of the variance of the error will increase the effect. A numerical example is also discussed to show the effect on the performance of the charts. Multiple measurements is used as a way to decrease the effect of measurement error. Knowing the fact that it requires extra time and money, it can be used in real cases depending on the financial limitations of the user.  相似文献   
58.
Pertussis toxin (PTX) is a required co-adjuvant for experimental autoimmune encephalomyelitis (EAE) induced by immunization with myelin antigen. However, PTX’s effects on EAE induced by the transfer of myelin-specific T helper cells is not known. Therefore, we investigated how PTX affects the Th17 transfer EAE model (Th17-EAE). We found that PTX significantly reduced Th17-EAE by inhibiting chemokine-receptor-dependent trafficking of Th17 cells. Strikingly, PTX also promoted the accumulation of B cells in the CNS, suggesting that PTX alters the disease toward a B-cell-dependent pathology. To determine the role of B cells, we compared the effects of PTX on Th17-EAE in wild-type (WT) and B-cell-deficient (µMT) mice. Without PTX treatment, disease severity was equivalent between WT and µMT mice. In contrast, with PTX treatment, the µMT mice had significantly less disease and a reduction in pathogenic Th17 cells in the CNS compared to the WT mice. In conclusion, this study shows that PTX inhibits the migration of pathogenic Th17 cells, while promoting the accumulation of pathogenic B cells in the CNS during Th17-EAE. These data provide useful methodological information for adoptive-transfer Th17-EAE and, furthermore, describe another important experimental system to study the pathogenic mechanisms of B cells in multiple sclerosis.  相似文献   
59.
Ammonia borane is a promising chemical hydrogen storage material to the hydrogen economy in the future. However, efficient and inexpensive catalyst for realizing this process remains challenging. Herein, the interfaces of copper nanoparticles (NPs) and nickel metal-organic framework (MOF) with different Cu/Ni ratios (Cu@Nix-MOF) have been constructed by Cu NPs in situ growth in Ni-MOF via a facile one-step solvothermal method. The Cu@Nix-MOF composites show much higher catalytic activity than their monometal counterparts and the optimized Cu@Ni6-MOF catalyst achieves a turnover frequency of 69.1 min?1 for ammonia borane hydrolysis, superior to most reported Ni-based catalysts. Density functional theory simulation and in situ Raman spectroscopy analysis propose that this remarkable enhanced activity of Ni-based catalysts is induced by a synergetic effect of Cu–Ni2+ dual active sites at their interfaces. This study shows that the strategy of dual active sites hold great promise to achieve efficient non-noble metal catalysts toward heterogeneous catalysis.  相似文献   
60.
《Journal of dairy science》2022,105(11):9240-9252
The small intestine is the primary site of nutrient digestion and absorption, which plays a key role in the survival of neonatal calves. A comprehensive assessment of the phosphoproteomic changes in the small intestine of neonatal calves is unavailable; therefore, we used phosphopeptide enrichment coupled with liquid chromatography-tandem mass spectrometry to investigate the changes in the phosphoproteome profile in the bovine small intestine during the first 36 h of life. Twelve neonatal male calves were assigned to one of the following groups: (1) calves not fed colostrum and slaughtered approximately 2 h postpartum (n = 3), (2) calves fed colostrum at 1 to 2 h and slaughtered 8 h postpartum (n = 3), (3) calves fed 2 colostrum meals (at 1–2 and 10–12 h) and slaughtered 24 h postpartum (n = 3), (4) calves fed 3 colostrum meals (at 1–2, 10–12, and 22–24 h) and slaughtered 36 h postpartum (n = 3). Mid-duodenal, jejunal, and ileal samples of the calves were collected after slaughter. We identified 1,678 phosphoproteins with approximately 3,080 phosphosites, which were mainly Ser (89.9%), Thr (9.8%), and Tyr (0.3%) residues; they belonged to the prodirected (52.9%), basic (20.4%), acidic (16.6%), and Tyr-directed (1.7%) motif categories. The regional differentially expressed phosphoproteins included zonula occludens 2, sorting nexin 12, and protein kinase C, which are mainly associated with developmental processes, intracellular transport, vesicle-mediated transport, and immune system process. They are enriched in the endocytosis, tight junction, insulin signaling, and focal adhesion pathways. The temporal differentially expressed phosphoproteins included occludin, epsin 1, and bridging integrator 1, which were mainly associated with macromolecule metabolic process, cell adhesion, and growth. They were enriched in the spliceosomes, adherens junctions, and tight junctions. The observed changes in the phosphoproteins in the tissues of small intestine suggest the protein phosphorylation plays an important role in nutrient transport and immune response of calves during early life, which needs to be confirmed in a larger study.  相似文献   
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