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   2473篇
  免费   50篇
  国内免费   2篇
电工技术   22篇
综合类   5篇
化学工业   962篇
金属工艺   39篇
机械仪表   41篇
建筑科学   237篇
矿业工程   6篇
能源动力   67篇
轻工业   194篇
水利工程   15篇
石油天然气   2篇
武器工业   4篇
无线电   140篇
一般工业技术   318篇
冶金工业   138篇
原子能技术   34篇
自动化技术   301篇
  2023年   25篇
  2022年   23篇
  2021年   63篇
  2020年   45篇
  2019年   43篇
  2018年   34篇
  2017年   25篇
  2016年   66篇
  2015年   56篇
  2014年   54篇
  2013年   104篇
  2012年   90篇
  2011年   120篇
  2010年   99篇
  2009年   101篇
  2008年   98篇
  2007年   84篇
  2006年   89篇
  2005年   80篇
  2004年   63篇
  2003年   44篇
  2002年   53篇
  2001年   45篇
  2000年   51篇
  1999年   63篇
  1998年   56篇
  1997年   57篇
  1996年   52篇
  1995年   53篇
  1994年   43篇
  1993年   29篇
  1992年   41篇
  1991年   40篇
  1990年   32篇
  1989年   41篇
  1988年   26篇
  1987年   32篇
  1986年   30篇
  1985年   24篇
  1984年   30篇
  1983年   27篇
  1981年   29篇
  1980年   25篇
  1979年   20篇
  1978年   21篇
  1977年   23篇
  1976年   18篇
  1975年   20篇
  1974年   21篇
  1973年   19篇
排序方式: 共有2525条查询结果,搜索用时 15 毫秒
61.
Oncostatin M (OSM), a member of the interleukin-6 family, functions as a major mediator of cardiomyocyte remodeling under pathological conditions. Its involvement in a variety of human cardiac diseases such as aortic stenosis, myocardial infarction, myocarditis, cardiac sarcoidosis, and various cardiomyopathies make the OSM receptor (OSMR) signaling cascades a promising therapeutic target. However, the development of pharmacological treatment strategies is highly challenging for many reasons. In mouse models of heart disease, OSM elicits opposing effects via activation of the type II receptor complex (OSMR/gp130). Short-term activation of OSMR/gp130 protects the heart after acute injury, whereas chronic activation promotes the development of heart failure. Furthermore, OSM has the ability to integrate signals from unrelated receptors that enhance fetal remodeling (dedifferentiation) of adult cardiomyocytes. Because OSM strongly stimulates the production and secretion of extracellular proteins, it is likely to exert systemic effects, which in turn, could influence cardiac remodeling. Compared with the mouse, the complexity of OSM signaling is even greater in humans because this cytokine also activates the type I leukemia inhibitory factor receptor complex (LIFR/gp130). In this article, we provide an overview of OSM-induced cardiomyocyte remodeling and discuss the consequences of OSMR/gp130 and LIFR/gp130 activation under acute and chronic conditions.  相似文献   
62.
Lipases that display high regioselectivities and broad substrate tolerance were used as catalysts for the efficient esterification of glycerol under the conditions of irreversible acyl transfer. A variety of unsaturated fatty acids, such as oleic, linoleic, erucic, ricinolic, hydroxystearic and coriolic acid, were used for this purpose in the form of their vinyl esters. Suitable biocatalysts were chosen on the basis of systematic screening experiments regarding their regioselectivities (RE) and substrate tolerances. Distinct differences were found and expressed in numerical RE values as a measure for differences of these biocatalysts as being specific, selective, and nonspecific. Based on these experiments, a variety of molecules were synthesized on a preparative scale (>150 mmol) in good yield (ca.85%) and with high regioisomerical purities (>95% RE).  相似文献   
63.
An analysis of the secondary fragments emerging from a target plate has shown that their mass distribution fits excellently to a formula established earlier by the author. This applies equally well to the secondary fragments of an explosive-formed fragment from a multi-P warhead, to those from the warhead's structural casing. and even to the fragments from the target plate itself, as well as to the sum of all of these 3 types of fragements. The correlation coefficient for the two constant parameters governing this formula (namely, the scaling factor B and the form factor λ) is always better than 0.99, when an optimum total mass Mo is southt and inserted, and when the first, large fragements are not included in the consideration, which means when one or two measured points are negiected. For secondary fragements, the form factor λ in the mass distribution is close to 1/2 = 0.5, whereas for the natural fragments of HE projectiles it is in the order of 2/3. namely, from 0.6 to 0.8.  相似文献   
64.
65.
All high explosives, at least the ones used in military applications, have a specific minimum detonation radius, Rmin with which the detonation can change its direction through 90° or 180°. It is to be emphasized that this applies not only to thc so-called insensitive high explosives, but the sensitive explosives of course have smaller radii than the insensitive ones. The corner-turning distance, As, determined in the radial test, also corresponds to the minimum radius, Rmin for the detonation wave to invert its direction through 180°. The radial test is a simple method, with regard to both design and analysis, that is suitable for determining the 90°-distance, or the minimum detonation radius, Rmin.  相似文献   
66.
We report about the dynamic behavior of a nanometer-scale amorphous intergranular film (IGF) in a Si3N4 ceramic by an in situ heating experiment in a high-resolution transmission electron microscopy (HRTEM). During the experiment the IGF gradually vanishes at 820 °C accompanied by the formation of crystal planes within the IGF. The IGF reappears after cooling back to room temperature. The results cannot be explained within the framework of a force balance model. We argue that the dynamic behavior of the IGF in our experiment originates from the open system observed.  相似文献   
67.
68.
Rice straw (Rs)/polypropylene (PP) composites were prepared in the different ratio of 5 : 95, 10 : 90, 15 : 85, 20 : 80, 25 : 75, and 30 : 70 (Rs wt % : PP wt %) by an injection molding process. This work investigated the tensile strength (TS), bending strength (BS), and impact strength (IS) of the composites. From the results, it is observed that Rs20 : PP80 mixture composite showed better performance with mechanical properties (TS = 26.2 MPa, BS = 58 N/mm2, and IS = 1.7 KJ/mm2) among the composites prepared. Two hybrid composites were also fabricated using 20% Rs, 10% seaweed with 70% PP and 20% Rs, 30% seaweed with 70% PP. In between the two hybrid composites, superior mechanical behavior showed by the hybrid composite in ratio of Rs20 : Sw10 : PP70 with enhanced results such as TS = 28 MPa, BS = 68 N/mm2, and IS = 2.5 KJ/mm2. Water uptake, simulating weathering, and soil degradation test of different composites were also performed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   
69.
70.
The alkane monooxygenase AlkBGT from Pseudomonas putida GPo1 constitutes a versatile enzyme system for the ω‐oxyfunctionalization of medium chain‐length alkanes. In this study, recombinant Escherichia coli W3110 expressing alkBGT was investigated as whole‐cell catalyst for the regioselective biooxidation of fatty acid methyl esters to terminal alcohols. The ω‐functionalized products are of general economic interest, serving as building blocks for polymer synthesis. The whole‐cell catalysts proved to functionalize fatty acid methyl esters with a medium length alkyl chain specifically at the ω‐position. The highest specific hydroxylation activity of 104 U gCDW−1 was obtained with nonanoic acid methyl ester as substrate using resting cells of E. coli W3110 (pBT10). In an optimized set‐up, maximal 9‐hydroxynonanoic acid methyl ester yields of 95% were achieved. For this specific substrate, apparent whole‐cell kinetic parameters were determined with a Vmax of 204±9 U gCDW−1, a substrate uptake constant (KS) of 142±17 μM, and a specificity constant Vmax/KS of 1.4 U gCDW−1 μM −1 for the formation of the terminal alcohol. The same E. coli strain carrying additional alk genes showed a different substrate selectivity. A comparison of biocatalysis with whole cells and enriched enzyme preparations showed that both substrate availability and enzyme specificity control the efficiency of the whole‐cell bioconversion of the longer and more hydrophobic substrate dodecanoic acid methyl ester. The efficient coupling of redox cofactor oxidation and product formation, as determined in vitro, combined with the high in vivo activities make E. coli W3110 (pBT10) a promising biocatalyst for the preparative synthesis of terminally functionalized fatty acid methyl esters.  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