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   598篇
  免费   31篇
电工技术   7篇
化学工业   75篇
金属工艺   8篇
机械仪表   9篇
建筑科学   35篇
能源动力   14篇
轻工业   73篇
水利工程   12篇
石油天然气   1篇
无线电   57篇
一般工业技术   96篇
冶金工业   180篇
原子能技术   8篇
自动化技术   54篇
  2022年   8篇
  2021年   11篇
  2020年   7篇
  2019年   6篇
  2018年   14篇
  2017年   8篇
  2016年   10篇
  2015年   14篇
  2014年   19篇
  2013年   23篇
  2012年   35篇
  2011年   34篇
  2010年   29篇
  2009年   15篇
  2008年   31篇
  2007年   25篇
  2006年   16篇
  2005年   15篇
  2004年   23篇
  2003年   15篇
  2002年   10篇
  2001年   6篇
  2000年   6篇
  1999年   9篇
  1998年   36篇
  1997年   27篇
  1996年   16篇
  1995年   13篇
  1994年   18篇
  1993年   14篇
  1992年   4篇
  1991年   6篇
  1990年   9篇
  1989年   5篇
  1988年   11篇
  1987年   6篇
  1986年   10篇
  1985年   5篇
  1984年   5篇
  1983年   3篇
  1982年   4篇
  1980年   5篇
  1979年   7篇
  1978年   3篇
  1977年   4篇
  1976年   9篇
  1974年   5篇
  1972年   3篇
  1970年   2篇
  1969年   3篇
排序方式: 共有629条查询结果,搜索用时 62 毫秒
131.
The relations between infant attractiveness and maternal behavior were examined by observing mothers feeding and playing with their firstborn infants while they were still in the hospital after giving birth (N?=?144) and again when the infants were 3 months of age (N?=?115). The attitudes of the mothers toward their infants were also assessed. Mothers of more attractive infants were more affectionate and playful compared with mothers of less attractive infants. In contrast, the mothers of less attractive infants were more likely to be attentive to other people rather than to their infant and to engage in routine caregiving rather than affectionate behavior. The attitudes of the mothers of less attractive infants were also more negative than those of mothers of more attractive infants, but the number of differences in attitudes was not as great as the behavioral differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
132.
133.
Gammage  N. Casey  L. 《Software, IEEE》1985,2(3):9-19
XMS creates a single, powerful system from loosely coupled microcomputers. Programs work together across nodes, making systemwide resource management transparent and distributed-system design simpler.  相似文献   
134.
The development of new techniques in sequencing nuclei acids has produced a great amount of sequence data and has led to the discovery of new relationships. In this paper, we study a method for parallelizing the algorithm WORDUP, which detects the presence of statistically significant patterns in DNA sequences. WORDUP implements an efficient method to identify the presence of statistically significant oligomers in a non-homologous group of sequences. It is based on a modified version of the Boyer-Moore algorithm, which is one of the fastest algorithms for string matching available in the literature. The aim of the parallel version of WORDUP presented here is to speed up the computational time and allow the analysis of a greater set of longer nucleotide sequences, which is usually impractical with sequential algorithms.  相似文献   
135.
Both trigeminal and spinal ganglion neurons show a strong potentiation of responses to the irritant capsaicin in an acidic environment. The present study revealed that there is also a strong interaction between protons and piperine, another vanilloid irritant. We studied the mechanism of the interaction between protons and piperine. Whole-cell patch clamp recordings were performed on cultured adult rat trigeminal ganglion (TG) neurons voltage-clamped near their resting membrane potential (-60 mV). Piperine (10 microM) caused a sustained net inward current associated with either an increase or decrease in membrane conductance. When protons and piperine were co-applied, the membrane currents evoked in piperine-sensitive TG neurons far exceeded the algebraic sum of the responses to the two stimuli applied in isolation. Capsazepine blocked the response of TG neurons to piperine at both physiological and acidic pH. In the presence of capsazepine, responses to the mixture of piperine and protons resembled the response to the low pH stimulus applied alone. Capsazepine had no effect on the sustained proton-induced current. These findings suggest that protons enhance the piperine current by altering the vanilloid receptor/channel complex or increasing the length constant of the space clamp.  相似文献   
136.
The purpose of the present study was to determine whether gender differences exist in the forebrain cerebral activation patterns of the brain during pain perception. Accordingly, positron emission tomography (PET) with intravenous injection of H2(15)O was used to detect increases in regional cerebral blood flow (rCBF) in normal right-handed male and female subjects as they discriminated differences in the intensity of innocuous and noxious heat stimuli applied to the left forearm. Each subject was instructed in magnitude estimation based on a scale for which 0 indicated 'no heat sensation'; 7, 'just barely painful' and 10, 'just barely tolerable'. Thermal stimuli were 40 degrees C or 50 degrees C heat, applied with a thermode as repetitive 5-s contacts to the volar forearm. Both male and female subjects rated the 40 degrees C stimuli as warm but not painful and the 50 degrees C stimuli as painful but females rated the 50 degrees C stimuli as significantly more intense than did the males (P=0.0052). Both genders showed a bilateral activation of premotor cortex in addition to the activation of a number of contralateral structures, including the posterior insula, anterior cingulate cortex and the cerebellar vermis, during heat pain. However, females had significantly greater activation of the contralateral prefrontal cortex when compared to the males by direct image subtraction. Volume of interest comparison (t-statistic) also suggested greater activation of the contralateral insula and thalamus in the females (P < 0.05). These pain-related differences in brain activation may be attributed to gender, perceived pain intensity, or to both factors.  相似文献   
137.
Unforeseen interactions of dams and declining water availability have formed new obstacles to recovering endemic and endangered big‐river fishes. During a recent trend of drying climate and declining reservoir water levels in the Southwestern United States, a large waterfall has formed on two separate occasions (1989–1995 and 2001–present) in the transition zone between the San Juan River and Lake Powell reservoir because of deposited sediments. Since recovery plans for two large‐bodied endangered fish species, razorback sucker (Xyrauchen texanus) and Colorado pikeminnow (Ptychocheilus lucius), include annual stockings in the San Juan River, this waterfall potentially blocks upstream movement of individuals that moved downstream from the river into the reservoir. To quantify the temporal variation in abundance of endangered fishes aggregating downstream of the waterfall and determine population demographics, we remotely monitored and sampled in spring 2015, 2016, and 2017 when these fish were thought to move upstream to spawn. Additionally, we used an open population model applied to tagged fish detected in 2017 to estimate population sizes. Colorado pikeminnow were so infrequently encountered (<30 individuals) that population estimates were not performed. Razorback sucker captures from sampling (335), and detections from remote monitoring (943) showed high abundance across all 3 years. The razorback sucker population estimate for 2017 alone was 755 individuals and, relative to recent population estimates ranging from ~2,000 to ~4,000 individuals, suggests that a substantial population exists seasonally downstream of this barrier. Barriers to fish movement in rivers above reservoirs are not unique; thus, the formation of this waterfall exemplifies how water development and hydrology can interact to cause unforeseen changes to a riverscape.  相似文献   
138.
Case studies suggest a relationship between Asperger syndrome (AS) and computer hacking. The current study examined whether characteristics associated with AS were significantly related to hacking, cyberbullying, identity theft, and virus writing. Two hundred and ninety-six university undergraduate students completed an Internet-based anonymous survey measuring self-reported computer deviant behaviour and characteristics associated with AS (autism-spectrum quotient; AQ). Of the 296 university students, 179 (60%) engaged in some form of computer deviant behaviour, but only 2 (0.01%) yielded clinically significant scores according to the AQ. Contrary to the authors' expectations, hackers did not score higher on the AQ compared to non-computer hackers. However, virus writers, identity thieves, and cyberbullies scored higher on the AQ compared to their computer non-deviant counterparts. In addition, individuals who engaged in hacking, identity theft, cyberbullying, and virus writing scored higher on the AQ and reported poorer social skills, poorer communication, and poorer imagination compared to all other individuals engaging in computer deviant behaviours. Considerations for future research and study limitations are discussed.  相似文献   
139.
Thirteen beef carcasses and twenty-seven pig carcasses were analysed for collagen content. The beef carcasses were drawn from four breeds and four levels of fatness. They were dissected into ten joints: from the forequarter; shin, brisket, Jacob's ladder, clod, sticking, fore-rib, chuck: from the hindquarter; leg, thin flank and other joints. Samples of each joint were analysed for fat, moisture and collagen. Samples of the total forequarter and hindquarter meat were also analysed.

The pig carcasses were drawn from three weight groups and three levels of fatness. Samples from each carcass were analysed for fat, moisture and collagen. Six selected pigs were dissected into five joints: hand, collar, back, streak and ham. Samples of each joint were analysed as described above.

Results from beef carcasses showed that collagen in the forequarter (3·2% wet fat-free) was significantly higher than in the hindquarter (2·7% wet fat-free). Within the forequarter collagen in the shin (4·8% wet fat-free) was significantly higher than in the other six joints. Within the hindquarter percentage collagen was significantly highest in the leg (4·2% wet fat-free). There were no significant breed differences.

Results from pig carcasses showed an overall mean value for collagen of 2·3% wet fat-free. Percentage collagen was significantly highest in the hand (2·9% wet fat-free).  相似文献   

140.
The differential uptake and targeting of intravenously infused [1-14C]palmitic ([1-14C] 16∶0) and [1-14C]arachidonic ([1-14C]20∶4n−6) acids into heart lipid pools were determined in awake adult male rats. The fatty acid tracers were infused (170 μCi/kg) through the femoral vein at a constant rate of 0.4 mL/min over 5 min. At 10 min postinfusion, the rats were killed using pentobarbital. The hearts were rapidly removed, washed free of exogenous blood, and frozen in dry ice. Arterial blood was withdrawn over the course of the experiment to determine plasma radiotracer levels. Lipids were extracted from heart tissue using a two-phase system, and total radioactivity was measured in the nonvolatile aqueous and organic fractions. Both fatty acid tracers had similar plasma curves, but were differentially distributed into heart lipid compartments. The extent of [1-14C]20∶4n−6 esterification into heart phospholipids, primarily choline glycerophospholipids, was elevated 3.5-fold compared to [1-14C]16∶0. The unilateral incorporation coefficient, k *, which represents tissue radioactivity divided by the integrated plasma radioactivity for heart phospholipid, was sevenfold greater for [1-14C]20∶4n−6 than for [1-14C]16∶0. In contrast, [1-14C]16∶0 was esterified mainly into heart neutral lipids, primarily triacylglycerols (TG), and was also found in the nonvolatile aqueous compartment. Thus, in rat heart, [1-14C]20∶4n−6 was primarily targeted for esterification into phospholipids, while [1-14C]16∶0 was targeted for esterification into TG or metabolized into nonvolatile aqueous components.  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