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   7880篇
  免费   174篇
  国内免费   15篇
电工技术   121篇
综合类   6篇
化学工业   1237篇
金属工艺   124篇
机械仪表   102篇
建筑科学   381篇
矿业工程   60篇
能源动力   204篇
轻工业   699篇
水利工程   82篇
石油天然气   41篇
武器工业   1篇
无线电   692篇
一般工业技术   1082篇
冶金工业   2309篇
原子能技术   90篇
自动化技术   838篇
  2022年   54篇
  2021年   96篇
  2020年   56篇
  2019年   96篇
  2018年   103篇
  2017年   92篇
  2016年   121篇
  2015年   61篇
  2014年   132篇
  2013年   438篇
  2012年   225篇
  2011年   335篇
  2010年   281篇
  2009年   237篇
  2008年   348篇
  2007年   306篇
  2006年   292篇
  2005年   284篇
  2004年   233篇
  2003年   206篇
  2002年   170篇
  2001年   166篇
  2000年   149篇
  1999年   186篇
  1998年   414篇
  1997年   271篇
  1996年   213篇
  1995年   147篇
  1994年   167篇
  1993年   167篇
  1992年   110篇
  1991年   78篇
  1990年   125篇
  1989年   119篇
  1988年   111篇
  1987年   103篇
  1986年   94篇
  1985年   112篇
  1984年   113篇
  1983年   80篇
  1982年   97篇
  1981年   96篇
  1980年   86篇
  1979年   69篇
  1978年   69篇
  1977年   76篇
  1976年   93篇
  1975年   64篇
  1974年   42篇
  1973年   43篇
排序方式: 共有8069条查询结果,搜索用时 13 毫秒
151.
152.
Copper oxide nanoparticle mediated DNA damage in terrestrial plant models   总被引:2,自引:0,他引:2  
Engineered nanoparticles, due to their unique electrical, mechanical, and catalytic properties, are presently found in many commercial products and will be intentionally or inadvertently released at increasing concentrations into the natural environment. Metal- and metal oxide-based nanomaterials have been shown to act as mediators of DNA damage in mammalian cells, organisms, and even in bacteria, but the molecular mechanisms through which this occurs are poorly understood. For the first time, we report that copper oxide nanoparticles induce DNA damage in agricultural and grassland plants. Significant accumulation of oxidatively modified, mutagenic DNA lesions (7,8-dihydro-8-oxoguanine; 2,6-diamino-4-hydroxy-5-formamidopyrimidine; 4,6-diamino-5-formamidopyrimidine) and strong plant growth inhibition were observed for radish (Raphanus sativus), perennial ryegrass (Lolium perenne), and annual ryegrass (Lolium rigidum) under controlled laboratory conditions. Lesion accumulation levels mediated by copper ions and macroscale copper particles were measured in tandem to clarify the mechanisms of DNA damage. To our knowledge, this is the first evidence of multiple DNA lesion formation and accumulation in plants. These findings provide impetus for future investigations on nanoparticle-mediated DNA damage and repair mechanisms in plants.  相似文献   
153.
The extraction of nitrogenous material from Brewers' spent grain (BSG) by solvents (water, sodium chloride solution, aqueous alcohol, acidic and alkaline solutions) commonly used to extract cereal proteins, resulted in the relatively low (0·2 to 8·5%) recovery of the total nitrogen. The recovery of nitrogenous material by the use of aqueous alkaline solutions was increased from 3–4% to 41% when the BSG was subjected to cellulase incubation prior to extraction. Approximately 75% of the nitrogen was solubilized with trifluoracetic acid. Detergent solutions (acid, neutral) solubilized more than 80% of the total nitrogen of the BSG. The low solubility of the nitrogenous constituents by conventional protein solvents could be the result of association between cellulosic material and protein.  相似文献   
154.
The acidic and basic lectins of the winged bean were isolated from seed extracts by affinity chromatography on lactose-Sepharose 6B and melibiose Bio-Gel P150, respectively. The lectins isolated from six varieties of Psophocarpus tetragonolobus, collected from different regions of south-east Asia, showed no significant differences in their properties; their subunit Mr and amino acid compositions were the same as those of the acidic and basic lectins isolated by non-affinity methods. On isoelectric focusing the affinity purified acidic lectins showed two major protein components (isolectins) while the affinity purified basic lectins had four protein components. The acidic lectins showed a preference for β-D-galactosides and they agglutinated trypsinised human type A, B and O erythrocytes but not trypsinised rabbit erythrocytes. The basic lectins showed a preference for α-D-galactosides and they agglutinated trypsinised rabbit and human type A and B erythrocytes but not trypsinised human type O erythrocytes.  相似文献   
155.
Acid-mine drainage (AMD) is difficult and costly to treat. We investigated a new approach to AMD treatment using fuel cell technologies to generate electricity while removing iron from the water. Utilizing a recently developed microbial fuel cell architecture, we developed an acid-mine drainage fuel cell (AMD-FC) capable of abiotic electricity generation. The AMD-FC operated in fed-batch mode generated a maximum power density of 290 mW/m2 at a Coulombic efficiency greater than 97%. Ferrous iron was completely removed through oxidation to insoluble Fe(III), forming a precipitate in the bottom of the anode chamber and on the anode electrode. Several factors were examined to determine their effect on operation, including pH, ferrous iron concentration, and solution chemistry. Optimum conditions were a pH of 6.3 and a ferrous iron concentration above approximately 0.0036 M. These results suggest that fuel cell technologies can be used not only for treating AMD through removal of metals from solution, but also for producing useful products such as electricity and recoverable metals. Advances being made in wastewater fuel cells will enable more efficient power generation and systems suitable for scale-up.  相似文献   
156.
Biomolecular interaction analysis mass spectrometry (BIA-MS) was applied to detection of bacterial toxins in food samples. This two-step approach utilizes surface plasmon resonance (SPR) to detect the binding of the toxin(s) to antibodies immobilized on a surface of a sensor chip. SPR detection is then followed by identification of the bound toxin(s) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Staphylococcal enterotoxin B (SEB) was readily detected in milk and mushroom samples at levels of 1 ng/ml. In addition, non-specific binding of food components to the immobilized antibody and to the sensor chip surface was detected. To evaluate the applicability of BIA-MS in the analysis of materials containing multiple toxic components, sample containing both SEB and toxic-shock syndrome toxin-1 was analyzed. Both toxins were successfully and simultaneously detected through the utilization of multiaffinity sensor chip surfaces.  相似文献   
157.
Cells of Escherichia coli O157:H7 on uninjured and injured surfaces of green pepper were inactivated by 0·15–1·2 mg l−1ClO2gas treatments. A membrane-surface-plating method was used for resuscitation and enumeration of E. coli O157:H7 treated with ClO2. The location and viability ofE. coli O157:H7 on uninjured and injured green pepper surfaces after ClO2gas treatments were visualized using confocal laser scanning microscopy (CLSM). Live and dead cells of E. coli O157:H7 on pepper surfaces were labeled with a fluorescein isothiocyanate-labeled antibody and propidium iodide, respectively. A 7·27 log reduction of E. coli O157:H7 on uninjured green pepper surfaces was obtained with a 0·60 mg l−1ClO2gas treatment for 30 min at 20°C under 90–95% relative humidity. For injured surfaces, a 6·45 log reduction was achieved with a 1·2 mg l−1ClO2gas treatment. Each ClO2gas treatment (0·15–1·2 mg l−1ClO2) for inoculated bacteria on uninjured surfaces showed significantly more reductions (1·23–4·24 log) than for those on injured surfaces (P<0·05). The microphotographs of CLSM showed that bacteria preferentially attached to injured surfaces and those bacteria could be protected from bacterial reduction by the injuries. This study indicates that ClO2gas treatment can be a potential effective method of pathogen reduction for fresh fruits and vegetables.  相似文献   
158.
Ion-exchange experiments were performed to evaluate the formation of the uranium-citrate and uranium-iron-citrate complexes over a wide concentration range; i.e., environmentally relevant concentrations (e.g., 10(-6) M in metal and ligand) and concentrations useful for spectroscopic investigations (e.g., 10(-4) M in metal and ligand). The stability of the well-known uranium-citrate complex was determined to validate the computational and experimental methods applied to the more complex system. Values of the conditional stability constants for these species were obtained using a chemical equilibrium model in FITEQL. At a pH of 4.0, the stability constant for uranium-citrate complex (log beta1,1) was determined to be 8.71+/-0.6 at I = 0. Analysis of the results of ion-exchange experiments for the U-Fe-citric acid system indicates the formation of the 1:1:1 and 1:1:2 ternary species with stability constants (log beta) of 17.10+/-0.41 and 20.47+/-0.31, respectively, at I= 0.  相似文献   
159.
Natural organic matter (NOM) in drinking water supplies can provide precursors for disinfectant byproducts, molecules that impact taste and odors, compounds that influence the efficacy of treatment, and other compounds that are a source of energy and carbon for the regrowth of microorganisms during distribution. NOM, measured as dissolved organic carbon (DOC), was monitored daily in the White River and the Indiana-American water treatment plant over 22 months. Other parameters were either measured daily (UV-absorbance, alkalinity, color, temperature) or continuously (turbidity, pH, and discharge) and used with stepwise linear regressions to predict DOC concentrations. The predictive models were validated with monthly samples of the river water and treatment plant effluent taken over a 2-year period after the daily monitoring had ended. Biodegradable DOC (BDOC) concentrations were measured in the river water and plant effluent twice monthly for 18 months. The BDOC measurements, along with measurements of humic and carbohydrate constituents within the DOC and BDOC pools, revealed that carbohydrates were the organic fraction with the highest percent removal during treatment, followed by BDOC, humic substances, and refractory DOC.  相似文献   
160.
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