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   2889篇
  免费   47篇
  国内免费   3篇
电工技术   20篇
综合类   1篇
化学工业   341篇
金属工艺   76篇
机械仪表   37篇
建筑科学   91篇
矿业工程   10篇
能源动力   31篇
轻工业   190篇
水利工程   9篇
石油天然气   24篇
无线电   242篇
一般工业技术   362篇
冶金工业   1225篇
原子能技术   17篇
自动化技术   263篇
  2021年   24篇
  2019年   20篇
  2018年   19篇
  2016年   30篇
  2015年   24篇
  2014年   35篇
  2013年   101篇
  2012年   53篇
  2011年   60篇
  2010年   70篇
  2009年   69篇
  2008年   79篇
  2007年   72篇
  2006年   77篇
  2005年   53篇
  2004年   56篇
  2003年   57篇
  2002年   65篇
  2001年   43篇
  2000年   58篇
  1999年   74篇
  1998年   256篇
  1997年   173篇
  1996年   115篇
  1995年   69篇
  1994年   91篇
  1993年   88篇
  1992年   52篇
  1991年   51篇
  1990年   65篇
  1989年   44篇
  1988年   58篇
  1987年   55篇
  1986年   44篇
  1985年   32篇
  1984年   37篇
  1983年   43篇
  1982年   34篇
  1981年   26篇
  1980年   45篇
  1979年   37篇
  1978年   33篇
  1977年   33篇
  1976年   68篇
  1975年   32篇
  1974年   14篇
  1972年   19篇
  1971年   14篇
  1970年   21篇
  1969年   12篇
排序方式: 共有2939条查询结果,搜索用时 15 毫秒
21.
Haze measurements have been obtained for suspensions of polystyrenelatex particles of known diameter using two light scattering instruments which measure at angles of 90° and 13° respectively. The results agree well with the theory of light scattering and demonstrate the significant effects of particle size and angle of detection upon the instrumental values for haze. This information has been used to correlate the particle size distributions of a number of beers, as measured by Coulter Counter, with the corresponding, measured haze values.  相似文献   
22.
Mutations in the p53 tumour suppressor gene are amongst the most frequent genetic abnormalities acquired in tumours. Recent studies in vitro suggest that mutant p53 destabilises the genome and facilitates development of aneuploidy. Here, in a study of 83 colorectal carcinomas, we demonstrate that alterations in p53 (detected by immunocytochemical stabilisation) precede and apparently facilitate divergence of aneuploid sub-clones. Aneuploidy in these tumours (but not those with normal p53) is predominantly in the subtetraploid range, suggesting that endoreduplication is important in its origin. This association with a specific phase of carcinoma progression is not shared by other commonly acquired genetic abnormalities in these tumours. These observations highlight the critical role of p53 in the regulation of abnormal chromosome replication and afford an explanation for the association between p53 abnormalities, aneuploidy and biological aggression in cancer.  相似文献   
23.
Comments on the article by S. T. Fiske et al (see record 1992-07509-001) praising the American Psychological Association's (APA's) amicus brief intended to inform the Supreme Court of current scientific thinking regarding gender stereotyping. A balanced perspective, it is argued, should include both research supporting an argument and findings that are inconsistent with that argument. The APA brief gave no indication of contradictory findings. Moreover, review of the research cited indicates that more than half of the studies do not support the argument for which they were cited. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
24.
The last decade has seen the development of a number of approaches for estimating those variables which are difficult to measure on-line in industrial process situations. Whilst a range of techniques is available, a common element is the use of process knowledge in the form of a system model. In the case of bioprocess systems, although a large range of models has been presented in the literature, their use in estimation schemes on an industrial scale has been limited. A number of reasons can be identified for their low level of utilisation. Of particular significance is the uncertainty which exists in quantifying system performance and the process-model mismatch which inevitably results. The level of ‘pre-defined model’ uncertainty, together with the knowledge gained during the course of the fermentation, serves to dictate estimator structure. The paper considers a range of estimation strategies and contrasts, through industrial applications, their performance characteristics and utility.  相似文献   
25.
Hemispheric priming was examined in 3 language-trained chimpanzees (Pan troglodytes) using a simple reaction time (RT) paradigm. Ss were required to hold down a response button until the occurrence of a response cue. A warning stimulus was presented to either the left visual field or the right visual field (RVF) before the response cue occurred. No warning stimulus was presented on control trials. The warning stimuli were geometric communicative symbols from 2 semantic categories: food and tools. A 3rd set of warning stimuli were familiar geometric symbols. Dependent measures included RT and the number of false-positive responses. RT data indicated an RVF advantage in priming when the warning stimuli were food or tool symbols. No significant visual half-field differences were found for familiar symbols, but a trend toward an RVF advantage was observed. These effects were enhanced when Ss responded with their left hand. False-positive data also indicated an RVF advantage for the food and tool warning stimuli. The data indicate that hemispheric asymmetries for processing communicative symbols are present in language-trained chimpanzees. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
26.
BACKGROUND: Transillumination of the soft tissue of the neck using a lighted stylet (lightwand) is an effective and safe intubating technique. A newly designed lightwand (Trachlight) incorporates modifications to improve the brightness of the light source as well as flexibility. The goal of this study was to determine the effectiveness and safety of this device in intubating the trachea of elective surgical patients. METHODS: Healthy surgical patients were studied. Patients with known or potential problems with intubation were excluded. During general anesthesia, the tracheas were intubated randomly using either the Trachlight or the laryngoscope. Failure to intubate was defined as lack of successful intubation after three attempts. The duration of each attempt was recorded as the time from insertion of the device into the oropharynx to the time of its removal. The total time to intubation (TTI), an overall measure of the ease of intubation, was defined as the sum of the durations of all (as many as three) intubation attempts. Complications, such as mucosal bleeding, lacerations, dental injury, and sore throat, were recorded. RESULTS: Nine hundred fifty patients (479 in the Trachlight group and 471 in the laryngoscope group) were studied. There was a 1% failure rate with the Trachlight, and 92% of intubations were successful on the first attempt, compared with a 3% failure rate and an 89% success rate on the first attempt with the laryngoscope (P not significant). All failures were followed by successful intubation using the alternate device. The TTI was significantly less with the Trachlight compared with the laryngoscope (15.7 +/- 10.8 vs. 19.6 +/- 23.7 s). For laryngoscopic intubation, the TTI was longer for patients with limited mandibular protrusion and mentohyoid distance, with a larger circumference of the neck, and with a high classification according to Mallampatti et al. However, there was no relation between the TTI and any of the airway parameters for Trachlight. There were significantly fewer traumatic events in the Trachlight group than in the laryngoscope group (10 vs. 37). More patients complained of sore throat in the laryngoscope group than in the Trachlight group (25.3% vs. 17.1%). CONCLUSIONS: In contrast to laryngoscopy, the ease of intubation using the Trachlight does not appear to be influenced by anatomic variations of the upper airway. Intubation occasionally failed with the Trachlight but in all cases was resolved with direct laryngoscopy. The failures of direct laryngoscopy were resolved with Trachlight. Thus the combined technique was 100% successful in intubating the tracheas of all patients.  相似文献   
27.
Examination of the assumptions underlying consistency perspectives in social and personality psychology reveals that they are based on an independent, individualistic view of the self. If the self is constructed as relational or interdependent with others, consistency may be less important in social behavior and well-being. Using a variety of measures of well-being, the studies showed that there is a weaker relation between consistency and well-being for individuals with a highly relational self-construal than for those with a low relational self-construal. Study 3 examined the association between the self-construal, consistency, authenticity, and well-being. These findings reveal the importance of a cultural analysis of theories of the self, personality, and well-being for further theory development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
28.
如果企业能更深入地了解他们的终端顾客,那么他们将获得真正的收益。  相似文献   
29.
Theorists have predicted that repetition blindness (RB) should be absent for nonwords because they do not activate preexisting mental types. The authors hypothesized that RB would be observed for nonwords because RB can occur at a sublexical level. Four experiments showed that RB is observed for word-nonword pairs (noon noof), orthographically similar nonwords (glome glame), and identical repetitions (plass plass). More RB was found for words than for nonwords. Prior researchers may have failed to find RB for nonwords because display conditions that allow 2 words to be reliably encoded are insufficient for nonwords, or because observers coped with low ability to encode nonwords by using guessing strategies that do not require creating a mental type or tokenizing it. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
30.
We prepared a series of oligosaccharides from king crab cartilage chondroitin sulfate K after exhaustive digestion with testicular hyaluronidase, and determined the structures of four tetrasaccharides and a pentasaccharide by fast atom bombardment mass spectrometry, high performance liquid chromatography analysis of chondroitinase AC-II digests, and 500-MHz 1H NMR spectroscopy. The tetrasaccharides shared the common core structure GlcAbeta1-3GalNAcbeta1-4GlcAbeta1-3GalNAc with various sulfation profiles. One structure was GlcAbeta1-3GalNAc(4S)beta1-4GlcAbeta1-3GalNAc(4S), whereas three of them have the following hitherto unreported structures including a novel glucuronate 3-O-sulfate: GlcA(3S)beta1-3GalNAc(4S)beta1-4GlcAbeta1-3GalNAc(4S), GlcAbeta1-3GalNAc(4S)beta1-4GlcA(3S)beta1-3GalNAc(4S), and GlcA(3S)beta1-3GalNAc(4S)beta1-4GlcA(3S)beta1-3GalNAc(4S), where 3S or 4S represents 3-O- or 4-O-sulfate, respectively. The structure of the pentasaccharide was determined as GlcA(3S)beta1-3GalNAc(4S)beta1-4GlcA(3S)beta1- 3GalNAc(4S)beta1-4GlcA. Chondroitinase ABC digestion of the tetrasaccharides with GlcA(3S) at the internal position destroyed the disaccharide unit containing GlcA(3S) derived from the reducing side and resulted in only the disaccharide unit from the non-reducing side. In contrast, these tetrasaccharides remained totally resistant to chondroitinase AC-II. The results indicated that it is necessary to reevaluate the disaccharide composition of chondroitin sulfate poly- or oligosaccharides purified from various biological sources, since they were usually determined after chondroitinase ABC digestion. It is probable that the structures containing GlcA(3S) would not have been detected.  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