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   685篇
  免费   5篇
电工技术   5篇
化学工业   44篇
金属工艺   4篇
机械仪表   9篇
建筑科学   15篇
矿业工程   3篇
能源动力   6篇
轻工业   26篇
水利工程   2篇
石油天然气   21篇
无线电   54篇
一般工业技术   76篇
冶金工业   321篇
原子能技术   8篇
自动化技术   96篇
  2018年   5篇
  2016年   4篇
  2014年   9篇
  2013年   12篇
  2012年   15篇
  2011年   9篇
  2010年   12篇
  2009年   9篇
  2008年   10篇
  2007年   15篇
  2006年   13篇
  2005年   11篇
  2004年   13篇
  2003年   15篇
  2002年   14篇
  2001年   11篇
  2000年   10篇
  1999年   11篇
  1998年   55篇
  1997年   33篇
  1996年   40篇
  1995年   27篇
  1994年   24篇
  1993年   25篇
  1992年   12篇
  1991年   15篇
  1990年   15篇
  1989年   11篇
  1988年   19篇
  1987年   11篇
  1986年   16篇
  1985年   14篇
  1984年   6篇
  1983年   12篇
  1982年   5篇
  1981年   14篇
  1980年   12篇
  1979年   11篇
  1978年   5篇
  1977年   11篇
  1976年   20篇
  1975年   9篇
  1974年   11篇
  1973年   4篇
  1972年   10篇
  1967年   7篇
  1966年   4篇
  1963年   3篇
  1962年   3篇
  1960年   3篇
排序方式: 共有690条查询结果,搜索用时 0 毫秒
91.
Previous quantitative reviews of research on the efficacy of psychotherapy for depression have included only a subset of the available research or limited their focus to a single outcome measure. The present review offers a more comprehensive quantitative integration of this literature. Using studies that compared psychotherapy with either no treatment or another form of treatment, this article assesses (1) the overall effectiveness of psychotherapy for depressed clients, (2) its effectiveness relative to pharmacotherapy, and (3) the clinical significance of treatment outcomes. Findings from the review confirm that depressed clients benefit substantially from psychotherapy, and these gains appear comparable to those observed with pharmacotherapy. Initial analysis suggested some differences in the efficacy of various types of treatment; however, once the influence of investigator allegiance was removed, there remained no evidence for the relative superiority of any 1 approach. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
92.
We describe the result of applying the ion evaporation theory to a series of amino acids. The very good correlation (r = 0.98) of the natural logarithms of protonated molecule intensities observed by electrospray with the difference between the hydration free energies of molecules and the gas-phase binding free energies of molecules and protons in amino acids is consistent with the ion evaporation model. It seems that the difference in the protonated molecule intensities of amino acids obtained by electrospray can be explained by a scheme in which protonated molecules in the liquid phase are extracted into the gas phase after a charged droplet is formed.  相似文献   
93.
Bacterial antibodies were studied in acute, intermediate and convalescent phase sera (mean duration from first to last sample 36 days) of 121 children hospitalized for acute lower respiratory tract infection. Antibody responses were observed in 45% of all cases and in 29% of the 21 children < 1 year old. A total of 15 responses to Streptococcus pneumoniae (pneumolysin), 20 to Haemophilus influenzae, 9 to Moraxella catarrhalis, 3 to chlamydiae and 8 to Mycoplasma pneumoniae were found. In 79 patients with 4 consecutive samples available, 52% of the 31 responses were measurable within 5 days from admission. Overall the responses were not associated with upper respiratory tract bacterial findings or acute otitis media. Significantly more responses were found in the 121 children with acute lower respiratory tract infection than in healthy controls (P < 0.007). We conclude that bacterial antibody assays provide a useful tool in the study of the etiology of acute lower respiratory tract infection in young children, even if the interval between paired serum samples is short.  相似文献   
94.
Calbindin-D and parvalbumin are calcium binding proteins which are found in non-overlapping subpopulations of GABA-ergic interneurons in mammalian neocortex. We studied the development of these calcium-binding proteins in interneurons of cat striate and extrastriate cortical areas which have differing patterns of connectivity and follow different developmental timetables. We examined primary visual areas 17 and 18, secondary visual area 19, medial lateral suprasylvian and lateral suprasylvian areas (MLS and LLS) and association areas 7 and the splenial visual area from the day of birth (P0) through P101. Parvalbumin-immunoreactive (ir) interneurons followed the inside-out pattern of maturation of cortical laminae. They were located only in infragranular layers at the earliest ages and were not observed in the overlying cortical plate. At 3 weeks of age, when cortical lamination is mature, parvalbumin stained cells were found in all cortical layers except layer I. The number of stained secondary and tertiary dendrites in the parvalbumin-ir interneuronal population decreased with age. This change was associated with a shift in the molecular weight of parvalbumin detected on Western blots. During the first postnatal week, the area 17/18 border contained more parvalbumin-ir neurons than other visual areas. The developmental pattern of calbindin staining differed considerably from the parvalbumin staining pattern. Very few calbindin-ir interneurons were seen in area 17 during the first 2 weeks of life. In lateral cortical areas, calbindin-ir neurons were located in cortical plate, infragranular layers of cortex and white matter/subplate. Calbindin-ir neurons increased in supragranular layers of secondary cortical areas by P7 and in area 17 by P20. In the mature cortex, the calbindin staining pattern was bilaminar, with a dense band of calbindin-ir cells in layer II and a second band in layers V-VI. There was no difference in the distribution of calbindin-ir neurons among visual areas at maturity.  相似文献   
95.
The need for developing a clear and concise guide for designing, selecting, and using hand tools would minimize if not eliminate acute–chronic trauma exposure factors and help improve efficiency, well‐being, and morale. Despite several research efforts devoted to the exploration and understanding of the interrelation between human capabilities, task requirements, nature of tasks, and ergonomically designed hand tools, there appear to be several problems in utilizing existing knowledge in practical use. One of the most important barriers is the lack of interaction of several specialists from different backgrounds. In this article, TOOL‐EXPERT, a knowledge‐based system developed to assert the ergonomical nonpowered hand tool design, selection, and use, is explained, which will provide a guideline to several users from various backgrounds. The system is designed to run in any IBM‐compatible personal computer system. Knowledge from several domains was included. The type of knowledge used in the research was selected to be a declarative knowledge. Altogether it includes 423 goals, 35 questions, and 40 rules. © 2004 Wiley Periodicals, Inc. Hum Factors Man 14: 257–268, 2004.  相似文献   
96.
This article compares resident and faculty learning strategies and styles and considers implications for teaching. The Kolb Learning Style Inventory was administered to 17 pediatric residents and 22 faculty in a pediatric department of an urban university-affiliated public medical center in 1991. Four scales--concrete experience (CE), reflective observation (RO), abstract conceptualization (AC), and active experimentation (AE)--are derived from self-ranking groups of words. Combining strategies leads to one of four styles: accommodator, diverger, converger, or assimilator. Analysis of variance and chi-square statistics were used to analyze strongest strategies and styles and to compare groups. It was found that resident and faculty preferred learning strategies and styles were significantly different. Resident strategies were spread primarily between concrete experience (40.5%) and active experimentation (40.5%), whereas faculty clearly preferred abstract conceptualization (77%). Most residents had either an accommodator or diverger learning style (81%), whereas most faculty were either assimilators or convergers (73%). This knowledge of learning strategy preferences and styles may have implications for design and delivery of instruction to residents.  相似文献   
97.
PURPOSE: The characterization of recombinant MN gp120/alum vaccine requires the study of the gp120-alum interaction for the successful formulation of an alum-based HIV-1 vaccine. METHODS: Several observations suggest that the gp120-alum interaction is weak, wherein buffer counterions such as phosphate, sulfate, bicarbonate may cause the desorption of gp120 from alum. Comparison of gp120 with other proteins using particle mobility measurements shows that the weak binding of gp120 to alum is not an anomaly. Serum and plasma also cause desorption of gp120 from alum with a half-life of only a few minutes, wherein this half-life may be faster than the in-vivo recruitment of antigen presenting cells to the site of immunization. RESULTS: Immunization of guinea pigs, rabbits and baboons with gp120 formulated in alum or saline demonstrated that alum provides adjuvant activity for gp120, particularly after early immunizations, but the adjuvant effect is attenuated after several boosts. CONCLUSIONS: These observations indicate that both the antigen and the adjuvant require optimization together.  相似文献   
98.
We examined 1,159 consecutive patients who underwent adenosine stress dual isotope single-photon emission computed tomography (SPECT) and had follow-up performed at a mean of 27.5 +/- 9.1 months (94% complete) for hard events (cardiac death and myocardial infarction) and referral to cardiac catheterization after nuclear testing. During follow-up, 120 hard events occurred (11.0% hard event rate; 72 cardiac deaths [6.7% cardiac death rate] and 57 myocardial infarctions [5.3% myocardial infarction rate]). Cox proportional hazards analysis revealed that nuclear testing added incremental value after adjusting for clinical and historical variables (global chi-square increased 13 to 98 for cardiac death as the end point, global chi-square increased 19 to 105 for hard events as the end point; p <0.0001 for both). Kaplan-Meier analysis demonstrated that after clinical risk stratification of the patient population, the results of nuclear testing were further able to significantly stratify both low- and intermediate- to high-risk patients. Patients with both normal and mildly abnormal scans were at low risk of cardiac death (<1% cardiac death per year of follow-up) and the risk of events increased significantly with worsening scan result. Multivariable analysis revealed that the only predictor of referral to catheterization was the extent and severity of reversible defect present on the scan. Referral rates to early catheterization were very low in patients with normal scans and increased significantly as a function of worsening scan results. In patients who underwent myocardial perfusion SPECT using adenosine stress, the results of nuclear testing yielded incremental prognostic information and clinically relevant risk stratification. Referring physicians predominantly utilized nuclear information when referring patients to catheterization after nuclear testing and do so at rates comparable with those after exercise SPECT despite the higher risk of events in patients undergoing pharmacologic stress.  相似文献   
99.
BACKGROUND: Optometry has experienced a dramatic upward shift in the percentage of women entering the profession during the past 20 years. Our survey assessed the mechanisms for sustaining balance in professional and personal roles used by women optometrists and how these mechanisms may differ from those of their male colleagues. METHODS: A survey questionnaire was mailed to a large nationwide random sample of optometrists, composed of equal numbers of men and women. RESULTS: Data were analyzed from 353 men and 358 women; margin of error was +4%. Most of the respondents indicated they derived personal satisfaction from their career. A majority of both groups did not indicate that lack of time for their career was a source of frustration. However, significantly more women than men indicated some frustration in pursuing those activities that lead to career advancement. There were significant differences in response patterns of men and women about the effect of family, child care, and household work on their careers. CONCLUSIONS: Both men and women optometrists are satisfied with their careers and neither group feels compelled to choose between career and family. Optometrists do not fit into one pattern, but instead make individualized career choices on the basis of needs.  相似文献   
100.
The effect of H. pylori infection on gastric motility and sensation is unclear. Our hypothesis is that H. pylori infection increases gastric sensation and reduces gastric accommodation and emptying. In eight H. pylori-positive and eight H. pylori-negative asymptomatic subjects, infection was proven by antral histology or culture. We evaluated: (1) gastric emptying of solids, (2) proximal gastric compliance, (3) fasting and postprandial proximal gastric tone and phasic contractions, (4) gastric sensation during balloon inflations or ingestion of cold water, and (5) abdominal vagal function. H. pylori infection was associated with lower gastric accommodation (median 75% postprandial increase in barostat balloon volume compared to fasting) when compared to the accommodation in uninfected volunteers (median 211% change from fasting). One H. pylori-positive subject had an abnormal abdominal vagal function test and her gastric accommodation response was reduced. Other motor and sensory functions in the two groups were similar. In asymptomatic volunteers, H. pylori infection and gastritis result in reduced accommodation (diastolic dysfunction) but no change in overall sensation or motor functions of the stomach.  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