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   1840篇
  免费   41篇
  国内免费   8篇
电工技术   92篇
综合类   6篇
化学工业   516篇
金属工艺   53篇
机械仪表   33篇
建筑科学   29篇
能源动力   60篇
轻工业   136篇
水利工程   2篇
石油天然气   6篇
无线电   133篇
一般工业技术   404篇
冶金工业   253篇
原子能技术   50篇
自动化技术   116篇
  2023年   12篇
  2022年   12篇
  2021年   27篇
  2020年   11篇
  2019年   11篇
  2018年   24篇
  2017年   23篇
  2016年   20篇
  2015年   24篇
  2014年   38篇
  2013年   82篇
  2012年   46篇
  2011年   98篇
  2010年   64篇
  2009年   75篇
  2008年   89篇
  2007年   74篇
  2006年   72篇
  2005年   63篇
  2004年   47篇
  2003年   46篇
  2002年   64篇
  2001年   51篇
  2000年   35篇
  1999年   39篇
  1998年   121篇
  1997年   62篇
  1996年   55篇
  1995年   41篇
  1994年   28篇
  1993年   31篇
  1992年   24篇
  1991年   32篇
  1990年   23篇
  1989年   25篇
  1988年   20篇
  1987年   19篇
  1986年   28篇
  1985年   18篇
  1984年   22篇
  1983年   36篇
  1982年   25篇
  1981年   19篇
  1980年   19篇
  1979年   22篇
  1978年   14篇
  1977年   11篇
  1976年   18篇
  1974年   5篇
  1972年   8篇
排序方式: 共有1889条查询结果,搜索用时 15 毫秒
991.
The Paris Agreement calls for maintaining a global temperature less than 2°C above the pre-industrial level and pursuing efforts to limit the temperature increase even further to 1.5°C. To realize this objective and promote a low-carbon society, and because energy production and use is the largest source of global greenhouse-gas (GHG) emissions, it is important to efficiently manage energy demand and supply systems. This, in turn, requires theoretical and practical research and innovation in smart energy monitoring technologies, the identification of appropriate methods for detailed time-series analysis, and the application of these technologies at urban and national scales. Further, because developing countries contribute increasing shares of domestic energy consumption, it is important to consider the application of such innovations in these areas. Motivated by the mandates set out in global agreements on climate change and low-carbon societies, this paper focuses on the development of a smart energy monitoring system (SEMS) and its deployment in households and public and commercial sectors in Bogor, Indonesia. An electricity demand prediction model is developed for each device using the Auto-Regression eXogenous model. The real-time SEMS data and time-series clustering to explore similarities in electricity consumption patterns between monitored units, such as residential, public, and commercial buildings, in Bogor is, then, used. These clusters are evaluated using peak demand and Ramadan term characteristics. The resulting energy-prediction models can be used for low-carbon planning.  相似文献   
992.
Recovery from ischemic acute kidney injury requires the replacement of damaged tubular cells. This repair process involves epidermal growth factor (EGF) synthesized in medullary the thick ascending limbs (mTAL) of Henle. Atrial natriuretic peptide (ANP), a hormone synthesized by the cardiac atria, increases glomerular filtration rate and renal medullary blood flow. However, the effects of ANP on renal recovery after I/R-induced renal injury remain unclear. We therefore examined whether human ANP enhances recovery from I/R-induced renal injury by reducing damage to EGF-producing kidney cells in a rat model. Male Wistar rats weighing 200–240 g were observed for 48 h after reperfusion following 45-min renal ischemia. Rats were intravenously administered α-human ANP (α-hANP) at 0.2 μg/kg/min beginning immediately after ischemia and continuing for 2 h after reperfusion. Outer medullary blood flow (OMBF), EGF mRNA, serum blood urea nitrogen (BUN) and creatinine levels as indicators of glomerular function were measured, while urinary N-acetyl β-d-glucosaminidase (NAG) was used as a specific indicator of proximal tubular function. OMBF was increased by α-hANP after reperfusion and maintained significantly higher mRNA level of EGF in the kidney 24 h after reperfusion. I/R-induced increases in serum concentrations of BUN and creatinine and urinary concentrations of NAG were also reduced by α-hANP, with improved histopathological changes, including acute tubular necrosis at 24–48 h after reperfusion. This report is the first to demonstrate that α-hANP accelerates recovery following renal ischemic insult by reducing the damage to EGF-producing kidney cells.  相似文献   
993.
A multiresidue method using dual-injection, dual-column, and dual-micro electron capture detection gas chromatography (dual-column GC-μECD) was developed for the determination of PCB, organochlorine pesticides and chlordanes in marine products. The sample was extracted with hexane-acetone (2 : 1), and the extract was cleaned up by gel permeation chromatography(GPC)/solid-phase extraction (SPE). The GPC fraction was selectively collected, and loaded directly onto a graphitized carbon/PSA 2-layered column. After fractionation by 4% hydrated silica-gel column chromatography, each fraction was determined by dual-column GC-μECD. Recoveries of PCB, organochlorine pesticides and chlordanes were in the ranges of 84-109% (RSD ≤ 21.6%), 74-117% (RSD ≤ 14.6%) and 69-114% (RSD ≤ 12.9%), respectively. This method is superior to single chromatography for the determination of total PCB, and should be useful for monitoring of these pollutants in marine products.  相似文献   
994.
Erythritol is an important sugar alcohol industrially produced only by fermentation. The highly osmophilic yeast-like fungi, Trichosporonoides megachiliensis SN-G42, enables commercial production of erythritol with a high conversion from glucose to erythritol of more than 47%. However, the microbial production pathway of erythritol remains unclear. In the present study, the activities of enzymes in the pentose phosphate pathway of Trichosporonoides megachiliensis SN-G42 used for industrial erythritol production were measured under various culture conditions to examine the production mechanism and the key-enzymes.As a result, the various enzyme activities of this organism are revealed in the pentose phosphate pathway, i.e., those of hexokinase, glucose-6-phosphate dehydrogenase, gluconate dehydrogenase, transketolase, transaldolase, and erythrose reductase. In the cultures in which erythritol was produced after completion of cell growth, the enzyme activities of the pentose phosphate pathway were higher than those of the TCA cycle. In particular, transketolase activity was correlated with erythritol productivity under various production cultures with different agitation speeds and thiamine concentrations.These results suggest that erythritol may be produced mainly through the pentose phosphate pathway. In addition, the high activity of transketolase is required to produce abundant intermediates, which results in high erythritol productivity. As such, transketolase appears to be a key-enzyme for erythritol production in the organism studied.  相似文献   
995.
Using microplates as pressure and cultivation vessels, a high-throughput method was developed for analyzing the high-pressure inactivation kinetics of microorganisms. The loss of viability from a high-pressure treatment, measured based on the growth delay during microplate cultivation, showed reproducibility with the conventional agar plate method and was applicable for the kinetics analysis.  相似文献   
996.
Penicillium herquei IFO 4674 is a filamentous fungus that produces a large amount of hydrolases for fibrous polysaccharides. We purified two beta-xylosidases, S1 and S2. The molecular masses of S1 and S2 determined by MALDI-TOF-MS were 103,700 and 37,460 Da. The optimum pHs of S1 and S2 were 4.0 and 6.5, respectively. By several kinds of alcohols, especially glycerol, S1 was activated while S2 was unaffected or inhibited. S1 had a transxylosylation activity, while S2 did not. The s2 gene encoding xylosidase S2 was cloned by PCR with primers designed on the basis of partial amino acid sequences of S2. The s2 consisted of 1005 by encoding 335 amino acids (37,433 Da) and had no secretion signal sequence. The deduced amino acid sequence shows a high identity to that of Bacteroides ovatus xylosidase/arabinosidase (56%), which is a member of the family 43 glycoside hydrolase.  相似文献   
997.
A simple and convenient method for colorimetric determination of sulfite in foods based on its conversion to formaldehyde with sulfite oxidase and catalase was developed. Sulfite in a sample was extracted with water and then diluted with methanol. One mL of sample solution containing about 5-10 micrograms of sulfite was taken into a test tube with a ground-glass stopper, and 3 mL of 0.04 mol/L borate buffer (pH 8.7), 1 mL of 0.4% 3-methyl-2-benzothiazolinone hydrazone (MBTH) solution, 2,000 units of catalase solution and 1.0 units of sulfite oxidase were added. The mixture was incubated for 35 minutes at 37 degrees C. Then 0.15 mL of 1 mol/L hydrochloric acid and 5 mL of 0.2% iron(III) nitrate solution were added. The reaction mixture was transferred to a measuring flask after standing for 5 minutes at room temperature, and diluted to 20 mL with methanol. The absorbance of this solution was measured using a spectrophotometer at the wavelength of 635 nm. The calibration curve prepared with sodium sulfite showed linearity between 0 to 16 micrograms/mL as sulfur dioxide. The recoveries of sulfite in "Kanpyo" (dried gourd shavings) and "Konnyaku-seiko" (devil's-tongue fine powder) by the proposed method were 97-104%, and the coefficients of variation were below 6%. The sulfite values in these foods determined by the proposed method were reasonably consistent with those obtained by the bubbling distillation-alkaline titration method.  相似文献   
998.
To develop novel multi-component molten salt systems more effectively, we developed a simulative technique using the CALPHAD (Calculation of Phase Diagram and Thermodynamics) method to estimate the ionic conductivity and the melting point. The validity of this new simulative technique was confirmed by comparing the simulated ionic conductivities and melting points of typical high-temperature molten salts, such as LiF-LiCl-LiBr, LiF-LiBr-KBr, LiCl-LiBr-KBr, and LiCl-LiBr-LiI, with those reported data in the literature or experimentally obtained.This simulative technique was used to develop new quaternary molten salt systems for use as electrolytes in high-temperature molten salt batteries (called thermal batteries). The targets of the ionic conductivity and the melting point were set at 2.0 S cm−1 and higher at 500 °C, and in the range of 350-430 °C, respectively, to replace the LiCl-KCl system (1.85 S cm−1 at 500 °C) within the conventional design of the heat generation system for thermal batteries. Using the simulative method, six kinds of novel quaternary systems, LiF-LiCl-LiBr-MX (M = Na and K; X = F, Cl, and Br), which contain neither environmentally instable anions such as iodides nor expensive cations such as Rb+ and Cs+, were proposed. Experimental results showed that the LiF-LiCl-LiBr-0.10NaX (X = Cl and Br) and LiF-LiCl-LiBr-0.10KX (X = F, Cl, and Br) systems meet our targets of both the ionic conductivity and the melting point.  相似文献   
999.
3,4,5-Tricaffeoylquinic acid (TCQA) that is not found in intact plant of lettuce leaves was isolated from the cultured cells. The intact plant produced chicoric acid (dicaffeoyl tartaric acid: L-CCA) as well as chlorogenic acid (3-caffeoylquinic acid: 3-CQA) as the major metabolites. After subculturing of the cells for 40 days, the amount of 3,4,5-TCQA reached to 0.14 mg/g fresh weight. The inhibitory effect of 3,4,5-TCQA for human immunodeficiency virus (HIV) Type 1 integrase was assayed. Anti-HIV activity using HIV and MT-2 cells was 1.15 microM and IC(50) against HIV integrase was 0.063 microM whereas cell toxicity of this chemical was expressed as 5% death of all living cells to be 18.4 microM. The HIV inhibitory effect of 3,4,5-TCQA was the highest in values among L-CCA, and other dicaffeoylquinic acids. This data will provide a new possibility for creating a new drug design for HIV.  相似文献   
1000.
This paper reviews a part of the state of the art of nanobioscience in Japan. The importance of combination and integration of interdisciplinary principles is emphasized for the development of nanobioscience. Biomagnetics, biomechanics, nanomachining, self-replicating cell model, neuronal network, drug delivery system, and tissue engineering are discussed.  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