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   2903篇
  免费   8篇
  国内免费   1篇
电工技术   2篇
综合类   2篇
化学工业   29篇
金属工艺   13篇
机械仪表   8篇
建筑科学   16篇
能源动力   12篇
轻工业   60篇
水利工程   7篇
石油天然气   4篇
无线电   35篇
一般工业技术   66篇
冶金工业   2605篇
原子能技术   4篇
自动化技术   49篇
  2020年   3篇
  2019年   8篇
  2018年   5篇
  2016年   3篇
  2014年   5篇
  2013年   16篇
  2012年   7篇
  2011年   17篇
  2010年   11篇
  2009年   10篇
  2008年   21篇
  2007年   20篇
  2006年   18篇
  2005年   9篇
  2004年   12篇
  2003年   10篇
  2002年   13篇
  2001年   17篇
  2000年   10篇
  1999年   86篇
  1998年   791篇
  1997年   437篇
  1996年   316篇
  1995年   163篇
  1994年   136篇
  1993年   157篇
  1992年   22篇
  1991年   27篇
  1990年   33篇
  1989年   25篇
  1988年   28篇
  1987年   25篇
  1986年   20篇
  1985年   20篇
  1984年   7篇
  1983年   13篇
  1982年   23篇
  1981年   21篇
  1980年   31篇
  1979年   6篇
  1978年   14篇
  1977年   67篇
  1976年   189篇
  1975年   9篇
  1974年   2篇
  1973年   4篇
  1965年   3篇
  1964年   3篇
  1963年   2篇
  1955年   3篇
排序方式: 共有2912条查询结果,搜索用时 15 毫秒
31.
32.
Four patterns of inositol fermentation by different isolates of Klebsiellae are described. Inositol fermentation by some isolates may be modified by medium incorporation of acetoin and diacetyl. An inositol--hydrogen sulphide--motility medium, modified by reducing the pH value, increasing the inositol concentration, and the incorporation of acetoin, is described and evaluated as a means of detecting acid production by isolates showing different inositol fermentation patterns.  相似文献   
33.
Administered a revision of the Test Anxiety Scale for Children (TASC) on which there were separate comparative Self-Evaluation and Anxiety scales to 133 females and 131 males in Form 1 (equivalent to Grade 6). Ss also responded to self-report measures (self-concept of attainment, causal attribution, independent reading, and friendship choices), and teachers rated Ss on their classroom behavior. Findings indicate that correlations between Ss' TASC scores and variables that had been found to be related to the original scale and assumed to be affected by anxiety were generally higher for the Self-Evaluation scale than the Anxiety scales. It is suggested that many results with the TASC may be better interpreted in terms of self-evaluation than anxiety effects. Results with measures of causal attributions suggest that self-evaluation measures are more effective predictors of achievement behavior than anxiety measures because anxiety is but one of a number of possible consequences of poor self-evaluation that could mediate relatively unproductive achievement behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
34.
This study was undertaken to determine the relative effects of morphine and halothane anesthesia on coronary blood flow. Right heart bypass was instituted in 20 dogs by draining the vena cava blood into a cardiotomy reservoir and returning it to the main pulmonary artery. Coronary sinus drainage was measured by a right ventricular cannula. Group I (10 dogs) was sequentially given 0.5, 1, 1.5, 2.0, and 2.5% halothane. Group II (10 dogs) was given 1, 2, 3, 4, and 5 mg per kilogram of morphine intravenously. Arterial pressure, coronary sinus blood flow, cardiac output, arterial pH, PCO2, and PO2 were determined and repeated at each dose level of anesthesia and compared to the control values. Morphine significantly increased coronary flow at 3, 4, and 5 mg/kg without pressure adjustment and at 2 mg/kg after pressure adjustment. Coronary flow with halothane was unchanged from control values except for a decrease at 2.5%. Coronary flow was significantly greater with 3, 4, and 5 mg/kg of morphine than with 1.0 and 1.5% halothane.  相似文献   
35.
Circular dichroism studies on leghaemoglobins from snake bean, lupin, serradella and other plants show that, in common with soybean (reported earlier) they have a similar overall polypeptide chain conformation and haem environment and orientation. Immunochemical studies, on the other hand, suggest that the antigenic determinants on the surface of the leghaemoglobins vary considerably. Thus, firstly the alpha-helix content of the leghaemoglobins as a class is very similar (60-65%) and approaches that of the myoglobins, secondly, the sign, magnitude and shape of their circular dichroism spectra in the near ultraviolet, Soret and visible regions suggest close similarities in the environment and orientation of a structurally important tryptophan residue and of the haem moiety, and thirdly, there is comparatively weak haem-protein interaction. The extent of immuno cross-reactivity was found to be best deomonstrated using the Farr radioimmunoassay procedure. The results were (a) 5 leghaemoglobins from one plant (soybean) crossreacted completely but with varying affinities. (b) The extent of cross reactivity between leghaemoglobins from different plants was compared to that within a single plant; the reaction of antiserum to a soybean leghaemoglobin with a serradella leghaemoglobin was weak, with a snake bean leghaemoglobin still weaker (and incomplete) while lupin leghaemoglobins showed no cross reactivity at all. (c) The "rapid" attenuation of cross reactivity among different plant leghaemoglobins is explicable in terms of the extensive amino acid substitutions which have been demonstrated in the literature and in the present studies. (d) In view of this rapid divergence it is not surprising that sperm whale and horse heart myoglobins showed no cross reactivity with soybean leghaemoglobins. In summary, amino acid substitutions in the leghaemoglobin family are conformationally but not immunochemically conservative.  相似文献   
36.
Comparison of changes in temperature, moisture content, infestation and germination were made in six aerated 20 t bins of malting barley. Two were at about 13.5% moisture content, three at about 15.5% moisture content, and one at about 16.5% moisture content. The grain started at between 20–25°C and, during aeration, fell at a rate dependent on the moisture content, damper grain being cooler, presumably due to evaporative cooling. The ‘high’ moisture content grain was often over 5°C cooler at 1m and 2m than the ‘low’ moisture content bins. Moisture uptake at the surface was related to bulk moisture content and trends in mite population changes were related to moisture content. Mite population achieved highest numbers at the grain surface but usually before the moisture content absorption was at its peak. They were commonest in the ‘high’ moisture content bin and least numerous in the ‘low’ moisture content bins. There were no apparent differences between bins in the numbers of insects trapped, for instance they were not less numerous in the coolest ‘high’ moisture content bin. However, the trends of numbers trapped followed a similar pattern in all bins; normally O. surinamensis and S. granarius only began to decline after nine weeks storage in December when temperatures fell below 10°C. Germination loss at the surface of the dampest bin was sufficient to cause rejection of the entire bulk for malting. Micromalting indicated that yield of extract and friability were particularly affected by the changes at the surface of the dampest barley.  相似文献   
37.
An overview of a microprocessor-based online accident location system is given. The system, designed mainly for emergency medical services, is not only capable of displaying all accident occurrences at a given location, intersection or street, but can also be used for accident report management and as a tool for guiding lost vehicles. The highway reference system used for this system is LORAN-C.  相似文献   
38.
A high performance liquid chromatography/ultraviolet method developed for the simple and direct determination of β-hydroxy-β-methylbutyrate (HMB) in liquid nutritional products and dietary supplements is described. Method suitability was defined by experimental assessments of linearity (r 2 > 0.9999), precision (day-to-day RSD <1.5%), accuracy (spike recoveries = 98.1–102.4%, n = 28), selectivity (peak purity average = 99.8 ± 0.8%, n = 10; absence of interference verified by placebo analysis), and quantitation limit (90 mg/kg or 0.8 mM). The method provides for a simple, accurate, and precise quantification of HMB, when present at millimolar concentrations in liquid nutritional products and dietary supplements.  相似文献   
39.
Ready-to-eat (RTE) meats (low-fat pastrami, Strassburg beef, export sausage, and Cajun beef) were pressure treated at 600 MPa, 20 degrees C, for 180 s to evaluate the feasibility of using high-pressure processing (HPP) for the safe shelf-life extension of these products. After processing, samples were stored at 4 degrees C for 98 days during which time microbiological enumeration and enrichments were performed. Additionally, sensory analyses were undertaken to determine consumer acceptability and purchase intent over the duration of storage. Counts of aerobic and anaerobic mesophiles, lactic acid bacteria, Listeria spp., staphylococci, Brochothrix thermosphacta, coliforms, and yeasts and molds revealed that there were undetectable or low levels for all types of microorganisms throughout storage. Comparison of consumer hedonic ratings for unprocessed and processed meats revealed no difference in consumer acceptability, and no deterioration in the sensory quality was evident for any of the products tested during the study. Additionally, inoculated pack studies were conducted to determine if HPP could be used as a postlethality treatment to reduce or eliminate Listeria monocytogenes and thus assess the potential use of HPP in a hazard analysis critical control point plan for production of RTE meats. Inoculated samples (initial level of 10(4) CFU/g) were pressure treated (600 MPa, 20 degrees C, for 180 s) and stored at 4 degrees C, and survival of L. monocytogenes was monitored for 91 days. L. monocytogenes was not detected by plating methods until day 91, but selective enrichments showed sporadic recovery in three of the four products examined. The results show that HPP at 600 MPa, 20 degrees C, for 180 s can extend the refrigerated shelf life of RTE meats and reduce L. monocytogenes numbers by more than 4 log CFU/g in inoculated product.  相似文献   
40.
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