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   1281篇
  免费   92篇
  国内免费   2篇
电工技术   9篇
化学工业   478篇
金属工艺   19篇
机械仪表   26篇
建筑科学   33篇
能源动力   36篇
轻工业   295篇
水利工程   8篇
石油天然气   4篇
无线电   52篇
一般工业技术   178篇
冶金工业   83篇
原子能技术   9篇
自动化技术   145篇
  2024年   4篇
  2023年   24篇
  2022年   85篇
  2021年   103篇
  2020年   40篇
  2019年   43篇
  2018年   36篇
  2017年   39篇
  2016年   51篇
  2015年   52篇
  2014年   53篇
  2013年   99篇
  2012年   69篇
  2011年   88篇
  2010年   73篇
  2009年   80篇
  2008年   72篇
  2007年   48篇
  2006年   35篇
  2005年   26篇
  2004年   30篇
  2003年   21篇
  2002年   15篇
  2001年   19篇
  2000年   12篇
  1999年   13篇
  1998年   13篇
  1997年   9篇
  1996年   7篇
  1995年   7篇
  1994年   6篇
  1993年   12篇
  1992年   10篇
  1991年   9篇
  1990年   9篇
  1989年   4篇
  1988年   3篇
  1987年   8篇
  1986年   4篇
  1985年   4篇
  1983年   5篇
  1982年   5篇
  1981年   9篇
  1980年   5篇
  1979年   4篇
  1977年   4篇
  1976年   2篇
  1975年   2篇
  1971年   1篇
  1955年   1篇
排序方式: 共有1375条查询结果,搜索用时 8 毫秒
241.
Epigenetic regulation is an essential process for the normal functioning of genes. Therefore, targeting epigenetic dysregulation in cancer may be a valid therapeutic approach for the treatment of this severe disease. Histone deacetylases (HDACs) are enzymes involved in the regulation of epigenetic post-translational modifications; because they are overexpressed in many types of cancer, HDACs are valuable targets for the development of new anticancer agents. A large series of 2-aminobenzanilides linked at the 4'-position to α-amino acid amides, arenes, and heteroarenes through a methylene bridge were designed, synthesized, and tested as novel HDAC inhibitors. Several compounds showed IC(50) values in the two-digit nanomolar range in hrHDAC1 inhibition assays, lower than that of the reference compound MS-275. They also showed interesting selectivity profiles, as confirmed by western blot assays.  相似文献   
242.
Acivicin analogues with an increased affinity for CTP synthetase (CTPS) were designed as potential new trypanocidal agents. The inhibitory activity against CTPS can be improved by increasing molecular complexity, by inserting groups able to establish additional interactions with the binding pocket of the enzyme. This strategy has been pursued with the synthesis of α‐amino‐substituted analogues of Acivicin and N1‐substituted pyrazoline derivatives. In general, there is direct correlation between the enzymatic activity and the in vitro anti‐trypanosomal efficacy of the derivatives studied here. However, this cannot be taken as a general rule, as other important factors may play a role, notably the ability of uptake/diffusion of the molecules into the trypanosomes.  相似文献   
243.
The antimic robial activities of caseicin A and B antimicrobial peptides (AMPs) were assessed against a selection of verocytotoxigenic Escherichia coli (VTEC) strains (n = 11), other bacterial pathogenic and spoilage bacteria (n = 7), using a model broth system. The ability of the AMPs to retain their antimicrobial activities against a strain of E. coli O157:H7 380-94 under various test conditions (pH, temperature, water activity, sodium chloride concentrations, inoculum size and the presence of competitive microflora) was assessed and the minimum inhibitory concentrations (MIC) and number of surviving E. coli O157:H7 calculated. The mean number of VTEC surviving after exposure to 2 mg/ml caseicin A and B was reduced by 4.96 and 4.19 log10 cfu/ml compared to the respective controls. The susceptibility of E. coli O157:H7 to the caseicin AMPs decreased as temperature, pH, water activity and inoculum size were reduced. The presence of sodium chloride (0.5-2.5%) did not affect the activity of caseicin A (p > 0.05), however it did inhibit the activity of caseicin B. The presence of a competitive microflora cocktail did not significantly (p > 0.05) affect the activities of the AMPs for the majority of the concentrations tested. Using a quantitative PCR assay, the levels of verotoxins (vt1 and vt2) expressed by E. coli O157:H7 following exposure to a sub-inhibitory concentration (0.5 mg/ml) of caseicin A showed that the verotoxin levels did not differ from the levels produced by the control cultures. The antimicrobial activity of caseicin A against E. coli O157:H7 was also tested in a model rumen system, however concentrations of ≥ 2 mg/ml did not significantly (p > 0.05) reduce E. coli O157:H7 numbers in the model system over a 24 h period. The application of caseicin AMPs in food and/or animal production may be valuable in combination with other antimicrobials although further research is required.  相似文献   
244.
Effectiveness of trimming external carcass surfaces from subprimals during fabrication to reduce Escherichia coli O157:H7 surrogates was evaluated. Carcass sides (n = 10 sides) were inoculated along the hide pattern opening before entering the blast chill cooler with a gelatin slurry containing a bacterial cocktail of three rifampicin-resistant, nonpathogenic E. coli biotype I strains. Following a 48 h chill, sides were fabricated to produce eight subprimals. Microbiological samples were taken from the original carcass fat surface area, initial lean surface area, trimmed fat surface area (where applicable), and trimmed lean surface area (where applicable). Newly exposed lean surfaces had lower (P < 0.05) counts of rifampicin-resistant E. coli than did the external fat surfaces. However, fat and lean surfaces that were not inoculated became contaminated during the fabrication process. Trimming external surfaces reduced levels of pathogens, but under normal fabrication processes, pathogens were still spread to newly exposed surfaces.  相似文献   
245.
A reliable and predictive model of an existing structure entails the use of model updating techniques, which are usually performed on the basis of operational modal analysis campaigns. In this paper, a new model calibration strategy is proposed that adopts a multiphysics approach to exploit data collected by both static and dynamic monitoring systems. More specifically, mechanical and temperature data are assimilated into the model through a thermoelastic updating. The proposed scheme is validated with numerical simulations and applied on the Sanctuary of Vicoforte, a complex historical building that is subjected to both static and dynamic monitoring.  相似文献   
246.
Promoting the adoption of improved technologies among smallholder farmers is a challenge faced by agricultural scientists and extension personnel around the world. In the southern Philippines, Phytophthora diseases severely affect the yields of durian and jackfruit. A limited understanding of these diseases among farmers and extension professionals compromises their effective management and significantly reduces yields. Recommended management interventions were rarely validated in field trials. A participatory research approach was used to collect information on current farming practices, identify industry constraints, and to develop and promote management strategies for smallholder durian and jackfruit growers. Farmers identified the development of effective disease management strategies as the highest priority so information on the biology, epidemiology and management of the suspected pathogen, Phytophthora, and other pests and diseases, was presented and discussed. Participants were then asked to propose and design research trials to diagnose the pathogen and to test simple management interventions on their crops. The trials were established and managed by participants and monitored by the group of growers, researchers and extension staff over 3 years. Responsibility for the on-farm trials encouraged participants to become directly involved in the research process, improving their skills in developing and critically assessing solutions for management of their orchards, and in decision-making processes. Results from the Participatory Action Research (PAR) trials were subjected to simple benefit-cost analyses and used to formulate a series of low-, medium- and high-input disease management packages. The low-input options included sanitation and manual pruning and weeding, and other activities requiring relatively low levels of time and financial investment. Medium- and high-input options required greater investment of time, resources and finances and included application of soil amendments, water management through construction of drainage channels and mounding, and the application of pesticides. The availability of a range of options facilitates the adoption of improved management by farmers from diverse backgrounds, resources and capacity.  相似文献   
247.
This study was focused on chemical characterisation of liverwort Scapania nemorea extracts and their antimicrobial activity against pathogenic and food-spoiling yeasts and bacteria. The chemical composition of three different extracts of the liverwort S. nemorea was determined by solid phase microextraction gas chromatography-mass spectrometry (SPME GC–MS). The dominant compounds in extracts were sesquiterpenes β-bazzanene (11%, 17.9% and 14.6%), isobazzanene (10.2%, 15.8% and 11.7%) and aromadendrene (8.8%, 12.9% and 10.6%) in the methanol, ethanol and ethyl acetate extracts, respectively. Antimicrobial potential of S. nemorea extracts against food spoiling yeasts and bacteria was determined in vitro by microdilution method. The Minimum Inhibitory Concentration (MIC) varied from 0.5 to 3 mg/mL for bacteria, and from 0.2 to 1 mg/mL for yeasts. Moreover, the combined effects of dry methanol extract of S. nemorea and heat processing on the survival and growth of a spoilage yeast in an apple/orange-based beverage, have been assessed through a Central Composite Design. Changes in color and flavor of the beverages were considered acceptable also after one week of storage at 25 °C. The results provide evidence of antimicrobial potential of S. nemorea extracts and suggest its potential as natural antimicrobial agent for food preservation.  相似文献   
248.
The development of a mechatronic tactile stimulation platform for touch studies is presented. The platform was developed for stimulation of the fingertip using textured surfaces, providing repeatable tangential sliding motion of stimuli with controlled indentation force. Particular requirements were addressed to make the platform suitable for neurophysiological studies in humans with particular reference to electrophysiological measurements, but allowing a variety of other studies too, such as psychophysical, tribological and artificial touch ones. The design of the mechatronic tactile stimulator is detailed, as well as the performance in tracking reference trajectories. Using microneurography, we recorded from human tactile afferents and validated the platform compatibility with the exacting demands of electrophysiological methods, comprising the absence of spurious vibrations and the lack of relevant electromagnetic interference.  相似文献   
249.
A Monte Carlo (MC) simulation is described and used to calculate the energy distribution spectra of backscattered electrons from Al and Si. For the simulations, elastic scattering cross sections are calculated by numerically solving the Dirac equation in a central field. Inelastic scattering cross sections are computed within the dielectric response theory developed by Ritchie, and by Tung et al. Extension from the optical case to non-zero momentum transfer is done according to Ritchie and Howie. To evaluate surface and bulk contributions to the spectra, the Monte Carlo model treats the surface excitations according to the Werner differential surface and volume excitation probability theory. The Monte Carlo calculations are compared with the experimental reflection electron energy loss (REEL) spectra acquired in our laboratory.  相似文献   
250.
Nutritional and health-related compounds of alfalfa, wheat and soybean seeds dried by new drying process called the DIC process (controlled instantaneous pressure release) were evaluated, before and after sprouting. Vitamins (A, B1, B2, B6, C and E), minerals (Fe, Mg, Ca, K, Mn, Na, Cu and Zn) and phytoestrogens (genistein and daidzein ) content were determined. Alfalfa, soybean and wheat seeds dried by DIC showed similar content of biological compounds to seeds dried by traditional processes. Sprouting DIC-seeds significantly increased the levels of vitamins, minerals and phytoestrogens, improving their nutrititional value and health quality compared to fresh products. The increase of 1250-fold and 10-fold of the initial vitamin A and vitamin C content, respectively, of alfalfa seeds due to sprouting is remarkable. Sprouts from DIC-seeds showed a significantly higher vitamin A content than sprouts obtained from seeds dried by other methods. Soybean sprouts obtained from DIC-seeds showed a significant increase in free phytoestrogens, quantified as genistein (70.34LJ.8 mg kg-1 d.w.) and daidzein (109.17.3ᆥ.3 mg kg-1 d.w.).  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