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   41539篇
  免费   1560篇
  国内免费   144篇
电工技术   567篇
综合类   246篇
化学工业   7071篇
金属工艺   936篇
机械仪表   907篇
建筑科学   1487篇
矿业工程   117篇
能源动力   1213篇
轻工业   5525篇
水利工程   351篇
石油天然气   178篇
武器工业   6篇
无线电   3640篇
一般工业技术   6108篇
冶金工业   9132篇
原子能技术   407篇
自动化技术   5352篇
  2023年   184篇
  2022年   477篇
  2021年   1007篇
  2020年   657篇
  2019年   779篇
  2018年   904篇
  2017年   974篇
  2016年   967篇
  2015年   704篇
  2014年   1144篇
  2013年   2072篇
  2012年   1740篇
  2011年   2233篇
  2010年   1660篇
  2009年   1695篇
  2008年   1646篇
  2007年   1484篇
  2006年   1215篇
  2005年   1264篇
  2004年   1243篇
  2003年   1142篇
  2002年   1093篇
  2001年   984篇
  2000年   827篇
  1999年   853篇
  1998年   2953篇
  1997年   1921篇
  1996年   1371篇
  1995年   953篇
  1994年   749篇
  1993年   809篇
  1992年   375篇
  1991年   426篇
  1990年   367篇
  1989年   336篇
  1988年   337篇
  1987年   270篇
  1986年   273篇
  1985年   337篇
  1984年   239篇
  1983年   186篇
  1982年   191篇
  1981年   215篇
  1980年   210篇
  1979年   183篇
  1978年   125篇
  1977年   250篇
  1976年   378篇
  1975年   133篇
  1973年   109篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
131.
132.
The present studies demonstrated the moderation of self-construal orientation on mimicry. Recent research has indicated that an interdependent self-construal is associated with assimilation of the other to the self whereas an independent self-construal is associated with minimizing the influence of others on the self (H. R. Markus & S. Kitayama, 1991; D. Stapel & W. Koomen, 2001). Therefore, the authors hypothesized that an interdependent self-construal would be associated with more mimicry than an independent self-construal. When self-construal orientations were experimentally primed. as in Studies 1 and 2, independent self-construals produced less nonconscious mimicry than interdependent self-construals. When self-construals were examined as cultural differences with either a chronically dominant independent (Americans) or interdependent (Japanese) construal of the self, these results were replicated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
133.
Critical Shear Stress of Bimodal Sediment in Sand-Gravel Rivers   总被引:1,自引:0,他引:1  
A new model for the critical shear stress and the transport of graded sediment is presented. The model is based on the size distribution of the bed surface and can be used to compute sediment transport rates in numerical simulations with an active layer model. This model makes a distinction between unimodal and bimodal sediments. It is assumed that all size fractions of unimodal sediments have the same critical shear stress while there is selective transport for the gravel fractions of bimodal sediments. A recently published laboratory transport data set is used to calibrate our model.  相似文献   
134.
135.
W-35%Cu液相活化烧结工艺研究   总被引:11,自引:0,他引:11  
本文从钨铜两相迁移机制和固溶扩散的角度 ,实验研究了钨铜复合粉的活化和常规烧结 ,分析了钨铜复合粉液相活化烧结过程中球磨时间、烧结温度、保温时间和升温速度对材料致密度的影响。结果表明 ,短时间球磨的钨铜复合粉具有良好的烧结性能 ,烧结温度和保温时间对材料致密度影响很大 ,活化烧结能有效降低烧结温度 ,提高烧结致密度  相似文献   
136.
Summary This article deals with the handy synthesis of sulfonyl resins, which were produced by the treatment of a commercial sulfonic resin (Lewatit VPOC1812® based at divinylbenzene (DVB) and styrene (STY). The preliminary chemical modification was based on the reaction of the Lewatit VPOC1812® with thionyl chloride aiming to produce the sulfonyl chloride groups. The best conditions to obtain the sulfonyl chloride groups were: SOCl2/SO3H (molar ratio) =13 at 79 °C during 72 h. The resin chlorinated was afterward treated with urea, thiourea or guanidine. The functionalized resins with urea, thiourea or guanidine were produced with 56, 68 and 93% yield, respectively. The commercial and modified resins were characterized by apparent density, swelling degree, elemental analysis (CHNS), FTIR, optical microscopy (OM) and scanning electron microscopy (SEM).  相似文献   
137.
138.
139.
Umbilical cord blood (UCB) and mobilized peripheral blood (MPB) provide an alternate source to bone marrow for transplantation. Expansion in vitro of stem/progenitor cell populations from these sources may provide adult-sized grafts otherwise not attainable because of the limited cell numbers available in the case of UCB or because of numerous rounds of apheresis required for sufficient MPB cells. We asked whether continuous perfusion culture could be employed in ex vivo expansion to produce clinically relevant numbers of stem/progenitor cells from these sources. To evaluate MPB, 1-10 million leukocytes, from patients who had received either granulocyte colony-stimulating factor (G-CSF) or cyclophosphamide and granulocyte-macrophage colony-stimulating factor (GM-CSF), were inoculated into bioreactors, with or without irradiated, allogeneic stroma. The growth factor combination in the perfusion medium consisted of interleukin-3 (IL-3), stem cell factor (SCF), GM-CSF and erythropoietin (Epo). Under the best conditions tested, total cell numbers, granulocyte-macrophage colony-forming units (CFU-GM), and long-term culture-initiating cell (LTC-IC) populations were expanded by about 50-, 80-, and 20-fold, respectively, over 14 days. At low cell inocula (1 million), the presence of stroma enhanced the expansion of total cells and CFU-GM but not of LTC-IC. When SCF was not included in the medium, both total cells and CFU-GM expanded to a much lesser extent, but again the expansion of LTC-IC was not affected. At the higher cell inoculum (10 million), expansions of total cells and CFU-GM were equivalent with or without stroma. To evaluate UCB, cells were placed into bioreactors with or without irradiated, allogeneic stroma, and the bioreactors were perfused with medium containing the four standard growth factors. After 6-14 days, in several independent experiments, 20-24 million cells were harvested from bioreactors perfused with SCF-containing medium, irrespective of the presence or absence of preformed stroma. Similarly, in reactors perfused with SCF-containing medium (with or without stroma), an average 40- to 60-fold expansion of CFU-GM was obtained, yielding an average of 1.5-1.8 x 10(5) CFU-GM per reactor. Harvested cells were thus up to 40-fold enriched in CFU-GM in comparison to the inoculum. In the absence of SCF, cell expansions averaged 1.5- to 2-fold, and CFU-GM were expanded only 10- to 14-fold by day 14. As before, the presence of preformed stroma did not affect either cell or CFU-GM yields, provided the cell inoculum was at least 4.5 million cells.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
140.
Immunisation practices were examined at 6 hospitals in the western Cape during the latter half of 1992 to determine whether these practices had improved subsequent to the February 1991 resolution of the Health Matters Committee (HMC) on immunisation in hospitals, and since a similar study was undertaken in 1990. Exit interviews were conducted with the escorts of all children aged 3-59 months who attended the study hospitals on the days designated for the study. In the second study, 88 of the 311 children studied (28.3%) were in need of immunisation on arrival, but only 12 of the 88 (13.6%) were immunised during the hospital visit. There was no evidence of an increase in requests to see children's Road-to-Health cards (37.1% compared with 35.2% previously). The incidence of missed opportunities for measles immunisation in children aged 6-59 months remained unacceptably high (51.4% compared with 63.7% previously, when a strict definition was used; and 15.7% compared with 18.1% previously, when a lenient definition was used). Health authorities at all levels need to take urgent action to address the problem of missed opportunities for immunisation at hospitals.  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