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   2495篇
  免费   46篇
  国内免费   1篇
电工技术   19篇
综合类   1篇
化学工业   531篇
金属工艺   23篇
机械仪表   37篇
建筑科学   80篇
矿业工程   2篇
能源动力   104篇
轻工业   415篇
水利工程   27篇
石油天然气   9篇
无线电   209篇
一般工业技术   447篇
冶金工业   122篇
原子能技术   12篇
自动化技术   504篇
  2024年   40篇
  2023年   44篇
  2022年   114篇
  2021年   116篇
  2020年   80篇
  2019年   114篇
  2018年   124篇
  2017年   103篇
  2016年   108篇
  2015年   78篇
  2014年   122篇
  2013年   177篇
  2012年   165篇
  2011年   201篇
  2010年   130篇
  2009年   108篇
  2008年   109篇
  2007年   97篇
  2006年   88篇
  2005年   61篇
  2004年   70篇
  2003年   41篇
  2002年   37篇
  2001年   16篇
  2000年   17篇
  1999年   17篇
  1998年   43篇
  1997年   26篇
  1996年   21篇
  1995年   13篇
  1994年   14篇
  1993年   9篇
  1992年   3篇
  1991年   2篇
  1990年   2篇
  1989年   5篇
  1988年   4篇
  1987年   3篇
  1984年   3篇
  1982年   1篇
  1981年   2篇
  1980年   2篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1971年   1篇
  1970年   1篇
  1953年   1篇
排序方式: 共有2542条查询结果,搜索用时 0 毫秒
991.
Translation in fluent bilinguals requires comprehension of a stimulus word and subsequent production, or retrieval and articulation, of the response word. Four repetition-priming experiments with Spanish–English bilinguals (N = 274) decomposed these processes using selective facilitation to evaluate their unique priming contributions and factorial combination to evaluate the degree of process overlap or dependence. In Experiment 1, symmetric priming between semantic classification and translation tasks indicated that bilinguals do not covertly translate words during semantic classification. In Experiments 2 and 3, semantic classification of words and word-cued picture drawing facilitated word-comprehension processes of translation, and picture naming facilitated word-production processes. These effects were independent, consistent with a sequential model and with the conclusion that neither semantic classification nor word-cued picture drawing elicits covert translation. Experiment 4 showed that 2 tasks involving word-retrieval processes—written word translation and picture naming—had subadditive effects on later translation. Incomplete transfer from written translation to spoken translation indicated that preparation for articulation also benefited from repetition in the less-fluent language. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
992.
This study examined the social organization of Guatemalan Mayan fathers' engagement with school-age children in a group problem-solving task. Twenty-nine groups of Mayan fathers varying in extent of Western schooling and 3 related school-age children (ages 6-12 years) constructed a puzzle together. Groups with fathers with 0 to 3 grades more often constructed the puzzle through shared multiparty collaboration involving a common agenda, whereas groups with fathers with 12 or more grades more often structured their contributions through a division of labor. Groups involving fathers with 6 to 9 grades demonstrated patterns of coordination that fell between the other two types of schooling groups. Fathers with greater schooling were also found to propose more explicit division-of-labor plans to children than were fathers with no to little schooling. The results indicate that Western schooling may be gradually transforming the collaborative social organization of group problem solving of indigenous Mayan families. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
993.
We evaluated combinations of telazol, ketamine, and xylazine (TKX), telazol and xylazine (TX), telazol, xylazine, and xylazine (T2X), and ketamine and xylazine (KX) for chemical restraint and anesthesia induction in swine. Forty healthy mixed-breed pigs were randomly assigned to the four treatment groups with 10 pigs in each group. For TKX, TX, and T2X combinations, anesthetics were premixed by adding xylazine and ketamine, sterile water and xylazine, or xylazine alone directly into the telazol vial. For KX, anesthetic agents were drawn up separately, then mixed in the same syringe immediately before injection. All anesthetics were given as a single intramuscular injection. All four anesthetic combinations induced a rapid onset of sternal recumbency within 1.55 +/- 0.5 min and lateral recumbency within 2.27 +/- 0.6 min in pigs after intramuscular injection. There was no significant difference among treatments in these regards. The T2X combination induced a significantly longer duration of analgesia than did either TKX, TX, or KX. The T2X combination also induced a significantly longer duration of tolerance for endotracheal intubation and duration of lateral recumbency. Heart and respiratory rates were not significantly different among the four treatment groups. Vomiting was not observed in any of the treated pigs throughout the procedure. Recovery quality and duration from time of drug administration to recovery of pig walking unassisted were similar in three treatment groups but was shorter in KX-treated pigs. We concluded that all four anesthetic combinations were suitable for chemical restraint but that only TKX, TX, and T2X were suitable for anesthesia induction in pigs.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
994.
Endothelial dysfunction is associated with atherogenesis and oxidative stress in humans. In rat and rabbit blood vessels, wine polyphenol antioxidants induce vascular relaxationin vitro through the NO-cGMP pathway. To assess the effect of a regular high-fat diet (HFD) and moderate red wine consumption on endothelial function (EF), a study was performed in healthy male volunteers. EF was measured as flow-mediated dilatation of the brachial artery, employing high-resolution ultrasound after an overnight fast. Other clinical and biochemical parameters related to EF were also measured. Six volunteers received a control diet, rich in fruits and vegetables (27% calories as fat) and five volunteers received an HFD (39.5% calories as fat). Measurements were done twice on each volunteer: after a period of 30 d with diet plus 240 mL of red wine/d, and after a period of 30 d with diet, without wine. In the absence of wine, there is a reduction of EF with HFD when compared to the control diet (P=0.014). This loss of EF is not seen when both diets are supplemented with wine for 30 d (P=0.001). Plasma levels ofn−3 fatty acids (R 2=0.232,P=0.023) and lycopene (R 2=0.223,P=0.020) show a positive correlation with individual EF measurements, but they do not account for the significant differences observed among dietary groups or after wine supplementation. These results help elucidate the deleterious effect of a high-fat diet and the protective role of wine, n−3 fatty acids and dietary antioxidants in cardiovascular disease.  相似文献   
995.
996.
    
A parallel array of frequency modulated light sheets results in a scanning-less light sheet microscope capable of fast volumetric imaging.  相似文献   
997.
    
Coffee plays a key role in the generation of rural employment in Colombia. More than 785,000 workers are directly employed in this activity, which represents the 26% of all jobs in the agricultural sector. Colombian coffee growers estimate the production of cherry coffee with the main aim of planning the required activities, and resources (number of workers, required infrastructures), anticipating negotiations, estimating, price, and foreseeing losses of coffee production in a specific territory. These important processes can be affected by several factors that are not easy to predict (e.g., weather variability, diseases, or plagues.). In this paper, we propose a non-destructive time series model, based on weather and crop management information, that estimate coffee production allowing coffee growers to improve their management of agricultural activities such as flowering calendars, harvesting seasons, definition of irrigation methods, nutrition calendars, and programming the times of concentration of production to define the amount of personnel needed for harvesting. The combination of time series and machine learning algorithms based on regression trees (XGBOOST, TR and RF) provides very positive results for the test dataset collected in real conditions for more than a year. The best results were obtained by the XGBOOST model (MAE = 0.03; RMSE = 0.01), and a difference of approximately 0.57% absolute to the main harvest of 2018.  相似文献   
998.
Synthetic (Z)-13-hexadecen-11-ynyl acetate has been shown to be highly active in catchingThaumetopoea pityocampa (Denis and Schiff.) males in field trials carried out in different parts of Spain. A variety of formulations containing antioxidants or solid paraffin were tested. Formulations containing 3 and 10% ofE isomer showed a decrease of activity compared with those prepared with pureZ isomer. Dodecyl acetate, also found in the virgin female gland, did not show any synergistic effect when tested in a 9∶1 mixture with the synthetic pheromone. The product exhibited a remarkable persistence of activity under the field conditions even in the absence of stabilizer.  相似文献   
999.
Forty-five marasmic infants were studied for plasma zinc and copper levels. They were selected from those children admitted to a nutritional recovery center. The mean plasma zinc level was 92.4 +/- 24 micrograms/dl (mean +/- SD); 7% of the infants had low zinc values as defined by zinc less than 70 micrograms/dl. Median copper was 90 micrograms/dl (range 27-172) and 49% of the children had copper levels below 90 micrograms/dl (established as our normal limit). Birth weight, breast feeding and prior hospitalization for acute diarrhea with dehydration were studied as antecedents related to low Cu and Zn. Children with prior diagnosis of acute diarrhea and hospitalization had lower copper levels than those sent from primary care centers. Breast feeding was associated with higher Cu levels. No relationship was found between zinc levels and those antecedents, but differences were found in regard to the degree of malnutrition, season of the year and Zn status. In this investigation no Zn deficiency was found in marasmus cases. Hypocupremia, however, is a very significant problem in marasmic infants, especially when associated with early weaning and the presence of previous hospitalization for acute diarrhea.  相似文献   
1000.
Constant-curl Laplacian equation is a new approach to study the behaviour of flows around bodies that do not present boundary-layer separation. It owns the simplicity and linearity of a potential analysis but also includes the rotational effects induced by a rotational displacement of the body such as turbine blades, manoeuvring aircrafts, etc. It assumes that this rotation is constant so that complex curved trajectories should be treated approximating the original path by a series of circular tracks. The idea is based upon a kinematic scheme that states the nullity of the velocity field Laplacian, imposing simultaneously the conditions of incompressibility and constant curl for velocity. We use 9-nodes isoparametric finite elements interpolating velocities and imposing the constant-curl condition by a modified penalty method and incompressibility by a classical one. The numerical results were compared satisfactorily against experimental data for aerodynamic forces and wake constitution on wind-turbine blades.  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