全文获取类型
收费全文 | 3106篇 |
免费 | 121篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 23篇 |
综合类 | 2篇 |
化学工业 | 557篇 |
金属工艺 | 116篇 |
机械仪表 | 51篇 |
建筑科学 | 99篇 |
矿业工程 | 4篇 |
能源动力 | 125篇 |
轻工业 | 272篇 |
水利工程 | 26篇 |
石油天然气 | 6篇 |
无线电 | 258篇 |
一般工业技术 | 654篇 |
冶金工业 | 523篇 |
原子能技术 | 25篇 |
自动化技术 | 490篇 |
出版年
2024年 | 8篇 |
2023年 | 48篇 |
2022年 | 87篇 |
2021年 | 101篇 |
2020年 | 77篇 |
2019年 | 96篇 |
2018年 | 112篇 |
2017年 | 106篇 |
2016年 | 113篇 |
2015年 | 79篇 |
2014年 | 99篇 |
2013年 | 221篇 |
2012年 | 156篇 |
2011年 | 208篇 |
2010年 | 157篇 |
2009年 | 161篇 |
2008年 | 177篇 |
2007年 | 165篇 |
2006年 | 127篇 |
2005年 | 104篇 |
2004年 | 91篇 |
2003年 | 63篇 |
2002年 | 74篇 |
2001年 | 50篇 |
2000年 | 44篇 |
1999年 | 40篇 |
1998年 | 39篇 |
1997年 | 48篇 |
1996年 | 32篇 |
1995年 | 28篇 |
1994年 | 40篇 |
1993年 | 28篇 |
1992年 | 24篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 28篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1973年 | 7篇 |
1971年 | 5篇 |
排序方式: 共有3231条查询结果,搜索用时 15 毫秒
81.
Pavan Gangwar Rajiv Singh Ravi Pratap Tripathi Ashutosh Kumar Singh 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2019,41(15):1828-1837
Solar irradiance being considered as one of the most important alternative sources of energy can be harnessed in the form of electrical power using photovoltaic panels erected under the sun. Optimum conversion of power from solar panels can be obtained by using Maximum Power Point Tracking (MPPT), which involves continuously adjusting the angle of panels according to the change in the angle of falling irradiance. These trackers, however, use some amount of power for operation of MPPT equipment. Various techniques for arranging the solar panels in three dimensions have been suggested for optimizing the output power from them. The inspiration behind arranging the panels are often drawn from the natural trees where the branches and the leaves follow a particular pattern called phyllotaxy which is directly analogous to the Fibonacci number and Golden ratio. In this research work, the power output from two solar tree models based on 3/8 and 2/5 phyllotaxy pattern and solar conventional panel compared under similar irradiance conditions. There are so many phyllotaxy patterns like 1/3, 2/5, 3/8, etc. When the solar panels aligned in different phyllotaxies, then the orientation direction of solar panels are distinct. Each solar panel connected in solar trees is in a different direction, so that they received the maximum amount of sunlight throughout the day as compared to conventional panels which is oriented unidirectional. 相似文献
82.
Heather D. Ots Jovanna A. Tracz Katherine E. Vinokuroff Alberto E. Musto 《International journal of molecular sciences》2022,23(8)
Immune-inflammatory conditions in the central nervous system (CNS) rely on molecular and cellular interactions which are homeostatically maintained to protect neural tissue from harm. The CD40–CD40L interaction upregulates key proinflammatory molecules, a function best understood in the context of infection, during which B-cells are activated via CD40 signaling to produce antibodies. However, the role of CD40 in neurological disease of non-infectious etiology is unclear. We review the role of CD40–CD40L in traumatic brain injury, Alzheimer’s Disease, Parkinson’s Disease, stroke, epilepsy, nerve injury, multiple sclerosis, ALS, myasthenia gravis and brain tumors. We also highlight therapeutic advancements targeting the CD40 system to either attenuate the neuroinflammatory response or leverage the downstream effects of CD40 signaling for direct tumor cell lysis. 相似文献
83.
Efficacy of an advanced sewage treatment plant in southeast Queensland, Australia, to remove estrogenic chemicals 总被引:1,自引:0,他引:1
Leusch FD Chapman HF Korner W Gooneratne SR Tremblay LA 《Environmental science & technology》2005,39(15):5781-5786
The estrogenicity profile of domestic sewage during treatment at a medium-sized (3800 EP) advanced biological nutrient removal plant in Queensland, Australia, was characterized using a sheep estrogen receptor binding assay (ERBA) and the MCF-7 breast cancer cell proliferation assay (E-Screen). The raw influent was highly estrogenic (20-54 ng/L EEq), and primary treatment resulted in a slight increase in estrogenicity that was detected in one of the assays (6-80 ng/L). Concurrent chemical analysis suggested that most of the estrogenicity in the influent was due to natural hormones (>48%). Secondary activated sludge treatment followed by nitrification/denitrification effectively removed > 95% of the estrogenic activity (to <0.75-2.6 ng/L), and estrogenicity of the final tertiary-treated effluent was below the detection limit of both assays (<0.75 ng/L). 相似文献
84.
Ponnachanna C Srinivasa Nuggenahalli S Susheelamma R Ravi Rudrapatnam N Tharanathan 《Journal of the science of food and agriculture》2004,84(8):818-824
Mango (Mangifera indica) cv ‘Alphonso’ fruits, harvested 40–50 days after flowering, were stored at 27 ± 1 °C and 65% RH under three conditions of packaging: (1) perforated plastic boxes, (2) wax lined cartons sealed with low‐density polyethylene (LDPE) film, and (3) wax lined cartons sealed with chitosan films. The weight loss, firmness, Hunter colour values and acidity were determined periodically during storage. Sensory analysis was carried out to determine colour, firmness, flavour qualities and also defective spots. Principal component analysis (PCA) of the results indicated that fruits stored in perforated plastic boxes and LDPE film‐sealed cartons differed significantly with respect to mango flavour, firmness and development of defective spots, while those in chitosan film sealed cartons retained the desirable qualities for a longer period (up to 20 days) without developing defective spots. The higher level of carbon dioxide and lower level of oxygen, or lower rate of oxygen transmission, associated with chitosan films delay ripening, and the higher water vapour transmission rate minimizes the rate of transpiration and prevents condensation of water droplets on the film. This helps in establishing equilibrium moisture content of mangoes in the cartons, which, in turn, extends the shelf life of fruits for a longer period. Copyright © 2004 Society of Chemical Industry 相似文献
85.
An improved HPLC method for single‐run analysis of the spectrum of hop bittering compounds usually encountered in beers 下载免费PDF全文
A single‐run reverse phase‐high performance liquid chromatography method for the quantification of humulinones, α‐acids, iso‐α‐acids and reduced iso‐α‐acids (where present) in commercial beer samples is presented. The method utilizes a binary solvent system consisting of (A) 1% v/v acetic acid and (B) 0.1% v/v orthophosphoric acid in acetonitrile. Separation was achieved on a Purospher® star RP‐18 column (250 × 46 mm, 3 µm) with a flow rate of 0.5 mL/min. The compounds of interest eluted within 32 min. The method was fully validated according to International Conference on Harmonization guidelines and subsequently applied to monitor degradation of hop acids in a storage trial where four lager beers were aged at 28 and 38 °C for 70 and 60 days, respectively. Results confirmed the widely reported degradation through storage of trans‐iso‐α‐acids whilst demonstrating that the HLPC method was sufficiently sensitive to monitor and model this degradation. One beer exhibited a significantly lower (P < 0.05) rate of trans‐iso‐α‐acid degradation than the other conventionally hopped beers in the study, which might have been linked to its higher pH (4.71 vs 4.36). The relative stability of reduced iso‐α‐acids during ageing was also confirmed. 相似文献
86.
Removing low ppb level perchlorate, RDX, and HMX from groundwater with cetyltrimethylammonium chloride (CTAC) pre-loaded activated carbon 总被引:4,自引:0,他引:4
Perchlorate contaminates vast amounts of groundwater throughout the United States which could potentially be used as potable water. Activated carbon pre-loaded with cetyltrimethylammonium chloride has been shown in this research to be an effective adsorbent for removing perchlorate from three low conductivity (50-66 microS/cm) groundwaters containing perchlorate (ClO(4)(-)) concentrations of 0.85, 1.0, and 5.6 parts per billion (ppb), respectively. In rapid small-scale column tests (RSSCTs), the virgin granular activated carbon (GAC) (used as a control) treated between 20,000 and 40,000 bed volumes (BV) of water. In contrast, the activated carbon that was pre-loaded with CTAC processed 170,000-270,000 BV before perchlorate was detected above 0.25 ppb in the effluent. Though this pre-loading significantly increased the capacity for perchlorate, it also diminished the GAC's capacity to remove organics. The groundwater containing 1 ppb ClO(4)(-) also contained the nitro-organics HMX (0.6 ppb) and RDX (5.5-6.6 ppb). RDX was detected in the effluent from the CTAC-pre-loaded bed after only 8000 BV had been processed whereas 308,000 BV could be processed through the virgin bed before RDX was detected. Likewise, HMX breakthrough was observed after 116,000 BV in the CTAC-pre-loaded bed while the virgin RSSCT exhibited no breakthrough of HMX during a test that was operated for 309,000 BV. However, by combining a CTAC-pre-loaded bed followed by a virgin GAC bed in series, both perchlorate and RDX could be removed for the same length of time. 相似文献
87.
88.
For grading different types of renewable energy based electricity generation systems, a figure of merit has been proposed and evaluated. The figure of merit has been obtained by analyzing total energy utilization in constructing and installing the systems and by their respective electricity generation. The gross carbon emission has also been estimated for evaluation of figure of merit. This figure of merit clearly indicates that wind power is the most sustainable source for electricity generation, followed by small hydropower and solar photovoltaics. 相似文献
89.
Prediction of surface heating rates is of prime importance for the hypersonic flow regime. Experimental and conventional computational efforts overlook the heat transfer phenomenon in the solid due to the rigid assumptions involved in the solution methodologies. In order to address this fact, conjugate heat transfer (CHT) studies are carried out using various coupling techniques to examine their implementation abilities. Three types of solution methodologies are adopted, namely, decoupled, strongly coupled, and loosely coupled analysis. This study is also focused on looking into the effect of a hypersonic flow field on wall heat flux for a finite thickness insulating cylinder at moderately large time scales. Increase in wall temperature and decrease in surface heat flux have been noticed using strong and loose coupling techniques with an increase in simulation time. Decoupled fluid and solid domain analysis is found to be useful for typical shock tunnel test durations (~1 ms) while investigations with loose coupling techniques are advisable for time scales corresponding to flight testing (~1 s). Efforts are also made to reason the discrimination in prediction of stagnation point heat flux using conventional computational and experimental analysis. 相似文献
90.
Sunil K. Ravi 《Critical reviews in food science and nutrition》2019,59(18):2999-3018
ABSTRACTAlzheimer's disease (AD) is characterized by a massive neuronal death causing memory loss, cognitive impairment and behavioral alteration that ultimately lead to dementia and death. AD is a multi-factorial pathology controlled by molecular events such as oxidative stress, protein aggregation, mitochondrial dysfunction and neuro inflammation. Nowadays, there is no efficient disease-modifying treatment for AD and epidemiological studies have suggested that diet and nutrition have a significant impact on the development of this disorder. Indeed, some nutrients can protect all kind of cells, including neurons. As prevention is better than cure, life style improvement, with a special emphasis on diet, should seriously be considered as an anti-AD track and intake of nutrients promoting neuronal health is the need of the hour. Diets rich in unsaturated fatty acids, polyphenols and vitamins have been shown to protect against AD, whereas saturated fatty acids-containing diets deprived of polyphenols promote the development of the disease. Thus, Mediterranean diets, mainly composed of fruits, vegetables and omega-3 fatty acids, stand as valuable, mild and preventive anti-AD agents. This review focuses on our current knowledge in the field and how one can fight this devastating neurodegenerative disorder through the simple proper modification of our life style. 相似文献