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   1747篇
  免费   45篇
电工技术   6篇
综合类   5篇
化学工业   298篇
金属工艺   32篇
机械仪表   11篇
建筑科学   22篇
能源动力   8篇
轻工业   117篇
水利工程   7篇
石油天然气   2篇
无线电   101篇
一般工业技术   177篇
冶金工业   916篇
原子能技术   9篇
自动化技术   81篇
  2023年   9篇
  2022年   10篇
  2021年   19篇
  2020年   19篇
  2019年   12篇
  2018年   17篇
  2017年   14篇
  2016年   18篇
  2015年   23篇
  2014年   20篇
  2013年   35篇
  2012年   36篇
  2011年   52篇
  2010年   39篇
  2009年   40篇
  2008年   33篇
  2007年   37篇
  2006年   40篇
  2005年   23篇
  2004年   24篇
  2003年   33篇
  2002年   34篇
  2001年   33篇
  2000年   31篇
  1999年   53篇
  1998年   276篇
  1997年   168篇
  1996年   120篇
  1995年   73篇
  1994年   49篇
  1993年   56篇
  1992年   16篇
  1991年   18篇
  1990年   24篇
  1989年   23篇
  1988年   20篇
  1987年   10篇
  1986年   7篇
  1985年   15篇
  1984年   6篇
  1983年   8篇
  1982年   15篇
  1981年   7篇
  1980年   14篇
  1979年   8篇
  1978年   11篇
  1977年   30篇
  1976年   52篇
  1975年   6篇
  1966年   7篇
排序方式: 共有1792条查询结果,搜索用时 250 毫秒
51.
52.
A recently introduced hierarchy of necessary and sufficient conditions for non-classicality of a quantum state [Th. Richter and W. Vogel, Phys. Rev. Lett. 89 283601 (2002)] is applied to the characterization of phase-insensitive quantum states. Even under such conditions it may be important to analyse the relation between different phase values in the quadrature distributions in order to demonstrate the non-classical nature of the state under study.  相似文献   
53.
In addition to the development of materials and technologies for smart HARMST applications the analysis of the thermo-mechanical material properties seems to be necessary to describe the photosensitive polymers applied. To do this, a microtensile analysis system has been developed to determine stress–strain curves, Young’s modulus and Poisson’s ratio. The results are compared with those of dynamical mechanical thermal analysis and discussed.  相似文献   
54.
The effects of the extrusion rate on the morphological changes of poly(lactic acid) (PLA)/poly(vinyl alcohol) (PVA) blend through a capillary die were investigated. In this study, the extrusion rate or mass flow rate is altered from 0.5 g min?1 to 2 g min?1 with an increment of 0.5 g min?1. The PLA/PVA blend with a composition of 30/70 (wt %) exhibits a particle matrix morphology with dispersed PLA droplets within the PVA matrix. It is found that, the spherical or ellipsoidal dispersed PLA droplets are elongated and coalesced into rod‐like or longer ellipsoidal droplets when they pass through the capillary die. When the extrusion rate increases, the coalescence between the large PLA droplets occurs more intense. However, the changes of the extrusion rate have no strong effect on the coalescence of small droplets having diameter less than about 150 nm. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44257.  相似文献   
55.
Herein, we report—for the first time—on the additive‐free bulk synthesis of Ti3SnC2. A detailed experimental study of the structure of the latter together with a secondary phase, Ti2SnC, is presented through the use of X‐ray diffraction (XRD), and high‐resolution transmission microscopy (HRTEM). A previous sample of Ti3SnC2, made using Fe as an additive and Ti2SnC as a secondary phase, was studied by high‐temperature neutron diffraction (HTND) and XRD. The room‐temperature crystallographic parameters of the two MAX phases in the two samples are quite similar. Based on Rietveld analysis of the HTND data, the average linear thermal expansion coefficients of Ti3SnC2 in the a and c directions were found to be 8.5 (2)·10?6 K?1 and 8.9 (1)·10?6 K?1, respectively. The respective values for the Ti2SnC phase are 10.1 (3)·10?6 K?1 and 10.8 (6)·10?6 K?1. Unlike other MAX phases, the atomic displacement parameters of the Sn atoms in Ti3SnC2 are comparable to those of the Ti and C atoms. When the predictions of the atomic displacement parameters obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Sn atoms. In the case of the Ti and C atoms, the agreement is more qualitative. We also used first principles to calculate the elastic properties of both Ti2SnC and Ti3SnC2 and their Raman active modes. The latter are compared to experiment and the agreement was found to be good.  相似文献   
56.
It has been reported in the technical literature that whiskers of rodlike single crystals can be used in order to generate shish‐kebab structures or other different lamellae morphologies during isothermal or dynamic crystallization of sheared or presheared polymer melts. The expected advantage of the changed crystalline structure is a reinforcing effect of the composite. A lot of papers reported about the application of inorganic and organic whiskers such as cellulose and chitin whiskers. This study reports on an attempt to use acicular PCC as appropriate whisker for improving mechanical properties of polypropylene. In this article special attention is given to demonstrate the effect of flow induced crystallization under varying shear conditions in order to improve the mechanical properties. The effects were demonstrated using rheology, thermal analysis, tensile testing, and transmission electron microscopy. POLYM. ENG. SCI., 54:2057–2063, 2014. © 2013 Society of Plastics Engineers  相似文献   
57.
58.
Ageing or obesity are risk factors for protein aggregation in the endoplasmic reticulum (ER) of chondrocytes. This condition is called ER stress and leads to induction of the unfolded protein response (UPR), which, depending on the stress level, restores normal cell function or initiates apoptotic cell death. Here the role of ER stress in knee osteoarthritis (OA) was evaluated. It was first tested in vitro and in vivo whether a knockout (KO) of the protein disulfide isomerase ERp57 in chondrocytes induces sufficient ER stress for such analyses. ER stress in ERp57 KO chondrocytes was confirmed by immunofluorescence, immunohistochemistry, and transmission electron microscopy. Knee joints of wildtype (WT) and cartilage-specific ERp57 KO mice (ERp57 cKO) were analyzed by indentation-type atomic force microscopy (IT-AFM), toluidine blue, and immunofluorescence/-histochemical staining. Apoptotic cell death was investigated by a TUNEL assay. Additionally, OA was induced via forced exercise on a treadmill. ER stress in chondrocytes resulted in a reduced compressive stiffness of knee cartilage. With ER stress, 18-month-old mice developed osteoarthritic cartilage degeneration with osteophyte formation in knee joints. These degenerative changes were preceded by apoptotic death in articular chondrocytes. Young mice were not susceptible to OA, even when subjected to forced exercise. This study demonstrates that ER stress induces the development of age-related knee osteoarthritis owing to a decreased protective function of the UPR in chondrocytes with increasing age, while apoptosis increases. Therefore, inhibition of ER stress appears to be an attractive therapeutic target for OA.  相似文献   
59.
The use of two-dimensional Nuclear Magnetic Resonance (NMR) spectroscopy as applied to studies of starch, starch products and glycogen is reported. The use of both homonuclear correlation (COSY, relay-COSY and HOHAHA) and heteronuclear correlation (HMQC, HETCOR) experiments is discussed. This approach makes it possible to obtain complete assignments of the proton NMR spectra of these polysaccharides. This is not possible from 1-D spectra due to excessive overlap of the non-anomeric proton signals. The resulting assignments are useful in obtaining structural information regarding starch and related products. Moreover, the greater inherent resolution of the two-dimensional spectra can reveal the presence of low molecular weight carbohydrates (glucose, maltose etc.) in dextrin samples, thus providing information about carbohydrate composition.  相似文献   
60.
A review is given of recent publications on the absorption of carbohydrates especially in relation to calcium. Starch and sucrose are hydrolyzed in mammals by enzymes attached to the wall of the jejunum to glucose and fructose. These are rapidly absorbed via carrier mediated mechanisms in adjoining epithelial cells. Feeding relatively high levels of lactose, sugar alcohols or modified starches to rodents leads to enhanced calcium absorption in the ileum. This results in increased urinary calcium, which may lead to lesions of the kidneys and adrenals in rats or to the formation of bladder stones in mice. If not hydrolyzed to absorbable moieties in the small intestine, carbohydrates pass to the cecum where they are fermented by microbial flora. This fermentation leads to cecal enlargement, diarrhoea and a decrease in urinary pH. All these effects, mainly caused by substantially overfeeding the rodents with these carbohydrates, are of no significance to humans consuming a balanced diet.  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