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   418篇
  免费   16篇
  国内免费   1篇
电工技术   39篇
化学工业   87篇
金属工艺   7篇
机械仪表   9篇
建筑科学   9篇
能源动力   13篇
轻工业   14篇
石油天然气   2篇
无线电   44篇
一般工业技术   79篇
冶金工业   71篇
原子能技术   4篇
自动化技术   57篇
  2023年   11篇
  2022年   12篇
  2021年   17篇
  2020年   11篇
  2019年   10篇
  2018年   14篇
  2017年   8篇
  2016年   11篇
  2015年   7篇
  2014年   10篇
  2013年   29篇
  2012年   17篇
  2011年   22篇
  2010年   13篇
  2009年   10篇
  2008年   14篇
  2007年   18篇
  2006年   11篇
  2005年   7篇
  2004年   10篇
  2003年   9篇
  2002年   9篇
  2001年   6篇
  2000年   10篇
  1999年   9篇
  1998年   14篇
  1997年   15篇
  1996年   11篇
  1995年   3篇
  1994年   8篇
  1993年   6篇
  1992年   4篇
  1991年   3篇
  1990年   3篇
  1989年   3篇
  1988年   8篇
  1987年   4篇
  1986年   4篇
  1985年   5篇
  1984年   4篇
  1983年   5篇
  1982年   4篇
  1977年   3篇
  1976年   2篇
  1969年   2篇
  1967年   2篇
  1946年   1篇
  1945年   1篇
  1944年   1篇
  1942年   1篇
排序方式: 共有435条查询结果,搜索用时 15 毫秒
51.
Real-life appraisal interviews conducted by 92 manager-subordinate pairs were studied intensively. Reactions of subordinates were systematically obtained before and after their appraisal interviews and the proceedings in the actual interviews were carefully documented by trained Os. Measures of subsequent performance improvement realized as a result of the appraisal interviews were taken 12 wk. later. The results indicated that a manager's attempts to assist a subordinate by pointing up improvement needs were likely to be perceived by the subordinate as threatening to his self-esteem and to result in defensive behavior. The greater the threat, the less favorable the attitude toward the appraisal system and the less the subsequent constructive improvement in job performance realized. These reactions were strong to the extent that the subordinate had relatively low occupational self-esteem. Some practical implications for appraisal practices are cited. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
52.
The small intestine has a high rate of cell turnover under homeostatic conditions, and this increases further in response to infection or damage. Epithelial cells mostly die by apoptosis, but recent studies indicate that this may also involve pro-inflammatory pathways of programmed cell death, such as pyroptosis and necroptosis. Celiac disease (CD), the most prevalent immune-based enteropathy, is caused by loss of oral tolerance to peptides derived from wheat, rye, and barley in genetically predisposed individuals. Although cytotoxic cells and gluten-specific CD4+ Th1 cells are the central players in the pathology, inflammatory pathways induced by cell death may participate in driving and sustaining the disease through the release of alarmins. In this review, we summarize the recent literature addressing the role of programmed cell death pathways in the small intestine, describing how these mechanisms may contribute to CD and discussing their potential implications.  相似文献   
53.
Ca- and/or B-modified silicon oxycarbides were synthesized via pyrolysis of suitable polysilsesquioxane-based single-source precursors. Their polymer-to-ceramic transformation was investigated with thermogravimetric analysis, coupled with in situ evolved gas analysis. The prepared silicon oxycarbides were investigated with respect to their crystallization behavior, network architecture, and chemical compositions. The network connectivity in silicon oxycarbides can be affected/tuned upon using two different “tools”: (a) first, the use of network modifiers, such as Ca in our study, leads to a slight depolymerization of the network via generation of a small amount of Q3 sites; (b) second, the modification of silicon oxycarbide with B/Ca leads to a decrease of the carbon content in the network and thus to a significant decrease of its connectivity. Using these two different effects, the network connectivity in silicon oxycarbides can be finely tuned.  相似文献   
54.
Erythropoietin (EPO) downregulates hepcidin expression to increase the availability of iron; the downregulation of hepcidin is mediated by erythroferrone (ERFE) secreted by erythroblasts. Erythroblasts also express transferrin receptor 2 (TFR2); however, the possible role of TFR2 in hepcidin downregulation is unclear. The purpose of the study was to correlate liver expression of hepcidin with the expression of ERFE and TFR2 in murine bone marrow and spleen at 4, 16, 24, 48, 72 and 96 h following administration of a single dose of EPO. Splenic Fam132b expression increased 4 h after EPO injection; liver hepcidin mRNA was decreased at 16 h. In the spleen, expression of TFR2 and transferrin receptor (TFR1) proteins increased by an order of magnitude at 48 and 72 h after EPO treatment. The EPO-induced increase in splenic TFR2 and TFR1 was associated with an increase in the number of Tfr2- and Tfr1-expressing erythroblasts. Plasma exosomes prepared from EPO-treated mice displayed increased amount of TFR1 protein; however, no exosomal TFR2 was detected. Overall, the results confirm the importance of ERFE in stress erythropoiesis, support the role of TFR2 in erythroid cell development, and highlight possible differences in the removal of TFR2 and TFR1 from erythroid cell membranes.  相似文献   
55.
Scientometrics - This country case study describes how science policy instruments are designed to shape publication patterns and identifies the changes in researchers’ productivity that can...  相似文献   
56.
The austemperability of seven high silicon cast steels with different alloy contents was characteri sed. The maximum round bar diameter that can be fully austempered changed from about 10?mm for an unalloyed steel to more than 70?mm for a low-alloy steel. The austemperability was calculated by applying a procedure based on a standard Jominy test and the characterisation of the microstructure along the Jominy sample. The method, which was validated experimentally, creates a relatively simple procedure to measure austemperability. Processing factors such as the ability of the salt bath to extract heat and the austempering temperature are accounted for the method. The metallographic study revealed the influence of microsegregation on hardenability, which is particularly important for cast steels.  相似文献   
57.
The suggestion of writing, for some problems, nonlinear state equations not as dx/dt = F(x,u,t), but as dx/dt = [A(t,x)]x + [B(t,x)]u(t), which is more ‘constructive’ as re system perception and possible structural generalizations, is considered, supported by arguments related to the classification of switched circuits as linear and nonlinear. The point of the distinction is mainly that when solving dx/dt = F(x,u,t), one immediately dwells into the analytical problems related to pure mathematics, whereas for dx/dt = [A(t,x)]x + [B(t,x)]u(t), considering first a constant matrix [A], one introduces the system's physical structure and considering then [A(x)] sees the nonlinearity of the system as a dependence of the structure on the processes in it or on system's input. (This might be named structural response). The thinking in terms of structure better observes the engineering and physical degrees of freedom, which are relevant regarding applications. Some electronic systems and physical systems (e.g., hydrodynamic) are considered in these terms. The logical side is always the focus, and the pedagogical (even philosophical) side is not ignored. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
58.
External magnetic fields affect various electrochemical processes and can be used to enhance the efficiency of the electrochemical water splitting reaction. However, the driving forces behind this effect are poorly understood due to the analytical challenges of the available interface-sensitive techniques. Here, we present a set-up based on magneto- and electro-optical probing, which allows to juxtapose the magnetic properties of the electrode with the electrochemical current densities in situ at various applied potentials and magnetic fields. On the example of an archetypal hydrogen evolution catalyst, Pt (in a form of Co/Pt superlattice), we provide evidence that a magnetic field acts on the electrochemical double layer affecting the local concentration gradient of hydroxide ions, which simultaneously affects the magneto-optical and magnetocurrent response.  相似文献   
59.
In this work, we report the production of a layer-by-layer (LbL) film of gold nanoparticles stabilized with carrageenan (carr-AuNPs) interspersed with a conductive polyaniline (PANI) layer. Conventionally, PANI has poor electroactivity in physiological buffers, limiting its using in electrochemical biosensors. The films were prepared on low cost and easy to manufacture flexible gold electrodes (FEAu). Two adsorption sequences were tested for production of the films—PANI/carr-AuNP and carr-AuNP/PANI. The gold nanoparticle size and colloidal stability were characterized. The films were characterized by cyclic voltammetry, UV–visible spectroscopy and atomic force microscopy. The results showed the synergistic effects of the carr-AuNPs (120 nm) and PANI, which improved both the electrochemical response and the stability of the conductive polymer in physiological medium by three times. The presence of the carr-AuNPs in the film caused a significant increase in roughness of the FEAu-modified electrode compared to that of an unmodified electrode, resulting in an increased active electrode area. Studies of film growth by UV–Vis spectroscopy indicated that the deposition mechanisms of both films involved an auto-regulating adsorption process, with the same amount of material adsorbed in each coating step. The PANI/carr-AUNP film showed considerable improvement in stability and conductivity compared to PANI-only films in the physiological environment, which confers advantages for use as a biosensor.  相似文献   
60.
Modifications to a finite element program developed in a prior study were extended for an initial-strain analysis of horizontal bending moments and hoop tension developed during bisymmetrical eccentric discharge. The results obtained by the newly developed initial-strain method, by the prior study, and those required by ACI Standard 313-77, were compared for a circular concrete silo.Although a significant difference in bending moment was obtained by the initial-strain and linear analysis methods, the steel reinforcement required was nearly the same at the lower elevation. However, at the upper elevation, approximately 50% more reinforcement was required for the initial-strain analysis. The reinforcement required by ACI Standard 313-77 was comparable to that for the initial-strain method at the higher elevation, and greater for the lower elevation.  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