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   2478篇
  免费   61篇
  国内免费   4篇
电工技术   32篇
综合类   11篇
化学工业   515篇
金属工艺   77篇
机械仪表   53篇
建筑科学   49篇
能源动力   89篇
轻工业   137篇
水利工程   4篇
石油天然气   4篇
无线电   437篇
一般工业技术   439篇
冶金工业   295篇
原子能技术   16篇
自动化技术   385篇
  2023年   13篇
  2022年   55篇
  2021年   55篇
  2020年   20篇
  2019年   24篇
  2018年   33篇
  2017年   32篇
  2016年   49篇
  2015年   55篇
  2014年   79篇
  2013年   172篇
  2012年   117篇
  2011年   144篇
  2010年   139篇
  2009年   167篇
  2008年   136篇
  2007年   144篇
  2006年   103篇
  2005年   77篇
  2004年   82篇
  2003年   58篇
  2002年   71篇
  2001年   48篇
  2000年   44篇
  1999年   39篇
  1998年   123篇
  1997年   69篇
  1996年   60篇
  1995年   33篇
  1994年   37篇
  1993年   26篇
  1992年   25篇
  1991年   30篇
  1990年   20篇
  1989年   18篇
  1988年   10篇
  1987年   7篇
  1986年   11篇
  1985年   13篇
  1984年   16篇
  1983年   7篇
  1982年   11篇
  1981年   11篇
  1980年   9篇
  1979年   8篇
  1978年   5篇
  1977年   7篇
  1976年   6篇
  1973年   5篇
  1971年   4篇
排序方式: 共有2543条查询结果,搜索用时 15 毫秒
991.
Using the concept of prescribed arrays of point forces and point couples, the long range displacement, the stress and the interaction energy fields associated with an isolated volume defect in nonlocal micropolar continuum elasticity are calculated. It is shown that all the physically possible volume defects can be described by a distribution of body forces and body couples. Interestingly these forces and couples are not singular extending therefore the validity of the classical continuum treatment of defects. Line defects such as dislocations and disclinations can be analyzed in a similar way.  相似文献   
992.
A model is presented for a bubble switch based on the Y-bar propagation element. Good correlation of the predictions of the model with experimental results is found for 8 μ bubbles. The heuristically derived scaling law, which predicts that the switching current must remain constant as the bubble diameter decreases, is confirmed by direct calculation with the model. The model shows that it will be increasingly difficult to design switches as the bubble diameter is reduced below 1 μ.  相似文献   
993.
Examination of cooked pre-rigor muscle by TEM (transmission electron microscopy) and SEM (scanning electron microscopy) revealed that all cookery methods resulted in the development of supercontraction bands alternating with areas showing tissue fragmentation and tearing. Microwave cookery produced smaller and less dense supercontraction nodes in pre-rigor muscle with less tearing and fragmentation but more fibre separation. Although cold-shortened pre-rigor muscle cooked by all methods also exhibited supercontraction bands with some tearing and fragmentation in adjacent sarcomeres, the samples cooked by microwaves showed a more uniform repeating pattern of small stretched areas alternating with dense contracted areas. Cooking of muscle in full rigor resulted in myofibrillar protein coagulation and shrinkage but supercontraction nodes were absent. Cold-shortened bicarbonate treated muscle was relatively intact after cooking, exhibiting fusion of the myofibrils and an absence of intermyofibrillar spaces. Results are discussed in relation to possible effects upon tenderness.  相似文献   
994.
Methyl esters of dimeric fatty acids were prepared by fractionating a mixture of conjugated linoleic and oleic acids that was heated for 24 hr at 300 C in the absence of air. Rats fed diets containing less than 1% dimers showed no significant difference (P less than 0.05) in the growth rate, feed efficiency, liver:body weight ratio, and lipid:liver weight ratio from those fed normal diets. A lymph cannulation study using 14C labeled dimers showed that ca. 0.4% of the dimers fed were absorbed within 12 hr and were transported as free acids in the lymph. Within a 28 hr period, 2% of the labeled dimers fed by gastric intubation were oxidized to 14CO2, and 1% radioactivity was recovered from the urine. The metabolism of methyl oleate appeared normal for rats prefed diets containing dimers.  相似文献   
995.
Chronic diseases have become the medical challenge of the 21st century because of their high incidence and mortality rates. Modulation of diet and lifestyle habits is considered as the best strategy for the prevention of these disorders. Health promoting benefits beyond their nutritional effects have been described for multiple dietary compounds. Among these compounds, the peptide lunasin is considered as one of the most promising. Naturally present in soybean, lunasin has been extensively studied in the last two decades because of its potential against chronic diseases such as cancer, cardiovascular and immunological disorders. The purpose of this article is to summarise the evidence on the presence of lunasin in soybean and derived foods, and its bioavailability once it is orally ingested. The protective and therapeutic effects of this peptide against cancer, oxidative stress, inflammation, and high cholesterol levels as well as the molecular mechanisms of action involved in these effects are also described in this review. © 2017 Society of Chemical Industry  相似文献   
996.
The thermal conductivities of molten polypropylene and its glass fiber composites were measured by the compensating hot wire method. The testing apparatus empolyed was designed and tested in our laboratory. The measurements were carried out with temperatures ranging from 170 to 230°C and pressures from 1 to 2000 kg/cm2. The results show that the thermal conductivity increases with increasing pressure and glass fiber content, but is almost independent of temperature. The thermal conductivity data were fitted satisfactorily with a proposed empirical equation for polypropylene and Lewies-Nielsen equation for the composites, respectively.  相似文献   
997.
An experimental investigation of the effect of lignin content of wood fibers on pulp screening is conducted. A non-uniform lignin distribution may exist in wood pulp due to variations in wood chip characteristics, and/or cooking conditions in a digester. Pulp screening was conducted in a modified Williams Freeness tester at different fiber lignin contents and pulp consistencies. The study indicated a large drop in pulp accepts fraction, thus a substantial fiber loss, with an increase in lignin content. The fiber loss was more significant at higher consistencies of pulp. This study suggests that the fiber lignin content should be considered an important process variable affecting the efficiency of pulp screening processes.  相似文献   
998.
Synthesis of poly(phenylene acetylene) from poly(phenylene vinylene)   总被引:1,自引:0,他引:1  
Summary The objective of this work was to prepare films of poly(phenylene acetylene) from films of a precursor polymer, namely poly(a, a-dibromoxylylene). This polymer was obtained by selective bromination of the vinylene groups of poly(phenylene vinylene) films in bromine/CHCl3. Pyrolytic dehydrobromination of the brominated films under argon atmosphere gave dark yellow films which showed about 65 wt% of desired phenylene acetylene units.  相似文献   
999.
Abstract:   Maximizing transport diversity is critical to the equitable achievement of stakeholder needs. Resource allocation policies help planners decide when and how to invest transportation infrastructure and services. However, policies for improving transport diversity are difficult to design, implement, and quantify because of the uncertainty, feedback interaction, and complexity of system relationships. This study proposes a hybrid model integrating system dynamics, cognitive maps, and a sensitivity model to tackle the problems. The model application is illustrated through an empirical study to enhance the managerial implications in the Taipei metropolitan area.  相似文献   
1000.
Time-dependent measurements of pressure drop in different flow fields on the cathode of a PEM fuel cell with different operating conditions of mass flow rates and cell temperatures on water accumulation were conducted. The results show that, among four flow fields studied herein, the interdigitated flow channel has the biggest pressure drop as well as the largest water accumulation at an early phase (?30 min) compared to those of the other three channels. In addition, the more water produced, the bigger the pressure drop that occurs. Similarly, the effects of mass flow rates at a fixed cell temperature were also examined and discussed.  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