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   3615篇
  免费   217篇
  国内免费   6篇
电工技术   60篇
综合类   1篇
化学工业   792篇
金属工艺   86篇
机械仪表   71篇
建筑科学   80篇
矿业工程   10篇
能源动力   109篇
轻工业   494篇
水利工程   33篇
石油天然气   14篇
无线电   234篇
一般工业技术   502篇
冶金工业   961篇
原子能技术   24篇
自动化技术   367篇
  2024年   6篇
  2023年   34篇
  2022年   36篇
  2021年   143篇
  2020年   105篇
  2019年   107篇
  2018年   129篇
  2017年   132篇
  2016年   141篇
  2015年   88篇
  2014年   104篇
  2013年   236篇
  2012年   175篇
  2011年   199篇
  2010年   160篇
  2009年   161篇
  2008年   150篇
  2007年   119篇
  2006年   94篇
  2005年   61篇
  2004年   63篇
  2003年   72篇
  2002年   53篇
  2001年   44篇
  2000年   41篇
  1999年   52篇
  1998年   279篇
  1997年   201篇
  1996年   120篇
  1995年   66篇
  1994年   54篇
  1993年   70篇
  1992年   16篇
  1991年   28篇
  1990年   22篇
  1989年   31篇
  1988年   18篇
  1987年   18篇
  1986年   18篇
  1985年   27篇
  1984年   12篇
  1983年   17篇
  1982年   9篇
  1981年   11篇
  1980年   14篇
  1979年   5篇
  1978年   9篇
  1977年   25篇
  1976年   54篇
  1973年   3篇
排序方式: 共有3838条查询结果,搜索用时 125 毫秒
31.
The aim of the present study was to evaluate renal and liver distribution of two monoclonal immunoglobulin light chains. The chains were purified individually from the urine of patients with multiple myeloma and characterized as lambda light chains with a molecular mass of 28 kDa. They were named BJg (high amount of galactose residues exposed) and BJs (sialic acid residues exposed) on the basis of carbohydrate content. A scintigraphic study was performed on male Wistar rats weighing 250 g for 60 min after i.v. administration of 1 mg of each protein (7.4 MBq), as the intact proteins and also after carbohydrate oxidation. Images were obtained with a Siemens gamma camera with a high-resolution collimator and processed with a MicroDelta system. Hepatic and renal distribution were established and are reported as percent of injected dose. Liver uptake of BJg was significantly higher than liver uptake of BJs (94.3 vs 81.4%) (P < 0.05). This contributed to its greater removal from the intravascular compartment, and consequently lower kidney accumulation of BJg in comparison to BJs (5.7 vs 18.6%) (P < 0.05). After carbohydrate oxidation, there was a decrease in hepatic accumulation of both proteins and consequently a higher renal overload. The tissue distribution of periodate-treated BJg was similar to that of native BJs: 82.7 vs 81.4% in the liver and 17.3 vs 18.6% in the kidneys. These observations indicate the important role of sugar residues of Bence Jones proteins for their recognition by specific membrane receptors, which leads to differential tissue accumulation and possible toxicity.  相似文献   
32.
A multicenter, open-label prospective trial was performed to determine the clinical and microbiologic efficacy of ofloxacin (OFLX) otic solution in the treatment of subjects > or =12 years with chronic suppurative otitis media (CSOM) and a chronically perforated tympanic membrane in the infected ear(s). A total of 207 patients at 27 centers in the United States and Central America received OFLX 0.5 mL instilled ototopically twice daily for 14 consecutive days. The primary clinical end point was cure (dry ear) or failure (not dry ear). The primary microbiologic end point was eradication of baseline pathogens. Because there was no comparator and there were few data in the literature regarding clinical efficacy in patients treated with other regimens, the efficacy of OFLX was compared with data recorded in the clinical records of historical-practice control (HPC) or current-practice control (CPC) subjects. The incidence of clinical cure in clinically evaluable OFLX-treated patients (91%; 148 of 162 subjects) was significantly higher than in HPC subjects (67%; 124 of 185 subjects) or CPC subjects (70%; 38 of 54 subjects). OFLX eradicated all baseline pathogens isolated in microbiologically evaluable subjects. These pathogens were predominantly Staphylococcus aureus, Pseudomonas aeruginosa, and Proteus mirabilis. The most common treatment-related adverse event, bitter taste, occurred in 17% (35 of 207) of OFLX-treated subjects. Thus OFLX 0.5 mL administered twice daily for 14 days was effective in resolving the signs and symptoms of CSOM in subjects > or =12 years, was significantly more effective than therapies used to treat HPC or CPC subjects, and was well tolerated.  相似文献   
33.
In the present work, the composition of H- 13 tool steel was modified with respect to the vanadium content to include an addition of niobium to obtain improved austenite grain size control without altering the tempering response of the steel. Optical metallography and transmission electron microscopy (TEM) observation of extraction replicas showed that the new steel had a smaller austenite grain size and a finer carbide size distribution than the vanadium steel, which indicates a higher potential toughness.  相似文献   
34.
35.
Mean-square stability for discrete systems requires that uniform convergence is preserved between input and state correlation sequences. Such a convergence preserving property holds for an infinite-dimensional bilinear system if and only if the associate Lyapunov equation has a unique strictly positive solution.  相似文献   
36.
Summary Polymer composites have recently received a considerable amount of scientific and technological interest, because their properties can be properly controlled, choosing the adequate doped particles, their size and concentrations, and the synthesis conditions. In this work we report the synthesis and characterization of a polystyrene (PS) matrix doped with different concentrations of iron nanoparticles. X-ray diffraction and transmission electron microscopy were used to characterize the structure of the samples. The behaviour of the d.c. electrical conductivity (σdc) and the complex permittivity (ε*=ε-iε′′) as a function of frequency (100 Hz–10 MHz) reflects the important effect of the iron nanoparticles concentration in the sample properties. A percolation threshold in the conductivity was observed at a critical concentration of iron nanoparticles. A noticeable increase in the saturation magnetization and coercivity is observed with the rise of the iron nanoparticles concentration, being thisbehaviour also noticed in the remanent magnetization. A rise of the initial a.c. susceptibility with the iron concentration is also observed.  相似文献   
37.
The objective of this paper is to present an analysis on the scale‐up procedure of two‐dimensional spouted beds. The task was carried out with three different beds measuring 0.15, 0.30 and 0.80 in width. The conditions of scale‐up were studied through geometrical similitude analysis. Some parameters of scale were adimensionalised, tested and validated in order to propose relationships capable of predicting values of dependent properties. Those relationships should be followed in a prototype of an equipment of industrial scale. The study permitted the development of correlations to predict values of maximum pressure drop, minimum spout velocity and maximum height of spouting.  相似文献   
38.
The authors report 3 picture-word interference experiments in which they explore some properties of the agreement process in speech production. In Experiment 1, Croatian speakers were asked to produce utterances in which the noun's gender value had an impact on the selection of gender-marked freestanding morphemes (pronouns) while ignoring the presentation of same- or different-gender distractor words. In Experiments 2 and 3, Croatian speakers were asked to name the same pictures using noun phrases in which the noun's gender value surfaced as an inflectional suffix. Different-gender distractors interfered more than same-gender distractors (the gender congruency effect) in Experiment 1, but not in Experiments 2 and 3. These contrasting results show that the cause of the gender congruency effect is not at the level where lexical-grammatical information is selected but at the level of selection of freestanding morphemes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
39.
40.
OBJECTIVES: A randomized trial was conducted to evaluate the effectiveness of a work-site health promotion program in reducing obesity and the prevalence of cigarette smoking. METHODS: Thirty-two work sites were randomized to treatment or no treatment for 2 years. Treatment consisted of health education classes combined with a payroll-based incentive system. Evaluation was based on cohort and cross-sectional surveys. RESULTS: Of 10,000 total employees in treatment work sites, 2041 and 270 participated in weight control and smoking cessation programs, respectively. Weight losses averaged 4.8 lbs, and 43% of smoking participants quit. Net 2-year reductions in smoking prevalence in treatment vs control work sites were 4.0% and 2.1% in cross-sectional and cohort surveys, respectively. No treatment effect was found for weight. Treatment effects for smoking prevalence and weight were both positively correlated with participation rates in the intervention programs (r = .45 for smoking and r = .55 for weight). CONCLUSIONS: This work-site health promotion program was effective in reducing smoking prevalence at a cost that is believed to make the investment worthwhile.  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