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   1008篇
  免费   5篇
电工技术   13篇
化学工业   78篇
金属工艺   14篇
机械仪表   6篇
建筑科学   9篇
能源动力   8篇
轻工业   12篇
水利工程   5篇
无线电   88篇
一般工业技术   78篇
冶金工业   645篇
原子能技术   3篇
自动化技术   54篇
  2022年   10篇
  2021年   10篇
  2020年   7篇
  2019年   4篇
  2018年   3篇
  2017年   6篇
  2016年   6篇
  2015年   4篇
  2014年   7篇
  2013年   18篇
  2012年   16篇
  2011年   24篇
  2010年   15篇
  2009年   14篇
  2008年   20篇
  2007年   18篇
  2006年   16篇
  2005年   8篇
  2004年   17篇
  2003年   12篇
  2002年   15篇
  2001年   17篇
  2000年   14篇
  1999年   28篇
  1998年   185篇
  1997年   113篇
  1996年   81篇
  1995年   49篇
  1994年   43篇
  1993年   34篇
  1992年   6篇
  1991年   5篇
  1990年   8篇
  1989年   11篇
  1988年   9篇
  1987年   4篇
  1986年   4篇
  1985年   5篇
  1984年   3篇
  1983年   6篇
  1982年   8篇
  1981年   7篇
  1980年   11篇
  1978年   4篇
  1977年   37篇
  1976年   48篇
  1975年   6篇
  1968年   3篇
  1966年   3篇
  1955年   2篇
排序方式: 共有1013条查询结果,搜索用时 17 毫秒
21.
Two month-old Wistar male albino rats were exposed during a 30-day period to a daily oral intake ad libitum of either 200 microg/mL Cd (as CdCl2), 0.1 microg/mL Se (as Na-selenite), or the same dosages of Cd + Se in drinking water. The daily intake from the water was calculated to be 15 mg Cd/kg and 7 microg Se/kg. Cadmium (Cd) accumulates in the heart (p < 0.005) and, in rats, decreases both body mass growth (p < 0.005) and heart mass (p < 0.02). Selenium (Se) significantly decreases the negative effect of Cd on body mass growth. In the hearts of Cd-treated rats, cadmium caused the decrease (p < 0.05) of selenium-dependent glutathione peroxidase (GSH-Px, EC 1.11.1.9) activity. At the same time, the activities of total superoxide dismutase (total SOD, EC 1.15.1.1), manganese-containing superoxide dismutase (Mn SOD), and copper-zinc-containing superoxide dismutase (CuZn SOD) were increased (p < 0.005). The activities of total SOD, CuZn SOD (p < 0.005), GSH-Px (p < 0.02), and glutathione-S-transferase (GST, p < 0.005) were increased in the hearts of Se-treated rats. However, by concomitant administration of Cd and Se, these changes were diminished (total SOD, GST) or were completely eliminated (Mn SOD, GSH-Px). These results indicate that Se only partly diminishes the effects of Cd cardiotoxicity.  相似文献   
22.
Critics of Kohlberg's moral theory today focus on the content of his theory and more specifically on its justice-orientated moral concept. This has led to the well-known 'justice-care debate'. The purpose of this article is to critically examine the validity of Kohlberg's moral theory for research in nursing ethics from a caring perspective (referring to the content) as well as from a cognitive-structural perspective (referring to the basic assumptions of the model). The analysis points to the usefulness and value of the cognitive-structural model to empirically study nurses' ethical behaviour; the content of Kohlberg's model, however, needs to be adapted by adding a caring perspective as well as some personal and situational variables. An adjusted version of Kohlberg's model is proposed and discussed.  相似文献   
23.
We used melanophores, cells specialized for regulated organelle transport, to study signaling pathways involved in the regulation of transport. We transfected immortalized Xenopus melanophores with plasmids encoding epitope-tagged inhibitors of protein phosphatases and protein kinases or control plasmids encoding inactive analogues of these inhibitors. Expression of a recombinant inhibitor of protein kinase A (PKA) results in spontaneous pigment aggregation. alpha-Melanocyte-stimulating hormone (MSH), a stimulus which increases intracellular cAMP, cannot disperse pigment in these cells. However, melanosomes in these cells can be partially dispersed by PMA, an activator of protein kinase C (PKC). When a recombinant inhibitor of PKC is expressed in melanophores, PMA-induced pigment dispersion is inhibited, but not dispersion induced by MSH. We conclude that PKA and PKC activate two different pathways for melanosome dispersion. When melanophores express the small t antigen of SV-40 virus, a specific inhibitor of protein phosphatase 2A (PP2A), aggregation is completely prevented. Conversely, overexpression of PP2A inhibits pigment dispersion by MSH. Inhibitors of protein phosphatase 1 and protein phosphatase 2B (PP2B) do not affect pigment movement. Therefore, melanosome aggregation is mediated by PP2A.  相似文献   
24.
A psychrotrophic yeast, Rhodotorula glutinis KUJ 2731, isolated from soil, effectively produced an extracellular endo-beta-glucanase (EC 3.2.1.4). The enzyme was monomeric, and the molecular mass was about 40,000 Da. The N-terminal amino acid sequence was H-Ser-Leu-Pro- Lys-Leu-Gly-Gly-Val-Asp-Leu-Ala-Gly-Leu-Asp-Ile-Gly-Lys-Asp-Lys-Asn-. alpha-Helix content was calculated to be about 32.6%. The isoelectric point was 8.57. The activation energy was 20.9 kJ/mol, which was much smaller than that of mesophilic enzymes. The enzyme was active at temperatures from 0 to 70 degrees C, with a highest initial velocity at 50 degrees C similar to other psychrotrophic enzymes. The enzyme was inhibited by Hg2+. The enzyme catalyzed hydrolysis of carboxymethyl cellulose with an apparent K(m) of 1.1% and Vmax of 556 mumol/min/mg. Products from the enzymatic hydrolysis of carboxymethyl cellulose by the enzyme were glucose, cellobiose, and cellotriose. The enzyme also catalyzed the transglycosylation of p-nitrophenyl-beta-cellotrioside to cellotetraose.  相似文献   
25.
The medical management of Crohn's disease has changed in recent years, but the mainstay of treatment is still prednisone. A substantial fraction of steroid-treated patients are refractory to therapy and addition of azathioprine or methotrexate has a corticosteroid-sparing effect and increases duration of remission. Controlled ileal release budesonide (9 mg daily) induces clinical remission in 60-70% of patients with Crohn's ileitis or right-sided colitis, and continued budesonide treatment has a finite effect on the duration of remission. The efficacy of mesalazine in active Crohn's disease is limited and high doses are required (4000 mg/day). The role of mesalazine in Crohn's disease in remission is disputed, and there is no evidence of a corticosteroid-sparing effect.  相似文献   
26.
High-computing speed and modularity have made RNS-based arithmetic processors attractive for a long time, especially in signal processing, where additions and multiplications are very frequent. The VLSI technology renewed this interest because RNS-based circuits are becoming more feasible; however, intermodular operations degradate their performance and a great effort results on this topic. In this paper, we deal with the problem of performing the basic operationX(modm), that is the remainder of the integer divisionX/m, for large values of the integerX, following an approximating and correcting approach, which guarantees the correctness of the result. We also define a structure to computeX(modm) by means of few fast VLSI binary multipliers, which is exemplified for 32-bit long numbers, obtaining a total response time lower than 200 nsec. Furthermore, such a structure is evaluated in terms of VLSI complexity and area and time figuresA=?(n 2 T m 2 ) andT=?(T M ) for the parameterT M in \([\log n,\sqrt n ]\) are derived. A simple positional-to-residue converter is finally presented, based on this structure; it improves some complexity results previously obtained by authors.  相似文献   
27.
Neural Computing and Applications - In this paper, we present the novel Deep-MEG approach in which image-based representations of magnetoencephalography (MEG) data are combined with ensemble...  相似文献   
28.
29.
To overcome the problems relevant to the low processbility and scarce mechanical properties of polyaniline, in a previous work we have proposed the synthesis of elastomeric conducting copolymers prepared by grafting polyaniline (EB) or sulfonated polyaniline (SPAN) chains to the backbone of a carboxylated segmented polyurethane (PEUA). In the present work the physical and chemical‐physical properties of the copolymers are investigated. As evidenced by thermal (DSC) and dynamo‐mechanical (DMTA) characterization, the introduction of EB or SPAN in the matrix enhances the hard‐soft phase segregation effect, because of the strong tendency of the conductive polymer chains to aggregate. Moreover, the EB and SPAN chains, grafted to the polyurethane backbone, acting as reinforcing filler, give rise, compared with the mechanical properties of the insulating matrix, to an increase of the Young modulus and a decrease of the tensile set. When the copolymers are HCl doped their electrical conductivity increases many orders of magnitude, reaching values of about 10?3 Ω?1 cm?1. The conductivity, measured along the deformation direction, may be further increased by stretching the copolymer films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1259–1264, 2002  相似文献   
30.
The spreading of multicast technology enables the development of group communication and so dealing with digital streams becomes more and more common over the Internet. Given the flourishing of security threats, the distribution of streamed data must be equipped with sufficient security guarantees. To this aim, some architectures have been proposed, to supply the distribution of the stream with guarantees of, e.g., authenticity, integrity, and confidentiality of the digital contents. This paper shows a formal capability of capturing some features of secure multicast protocols. In particular, both the modeling and the analysis of some case studies are shown, starting from basic schemes for signing digital streams, passing through protocols dealing with packet loss and time-synchronization requirements, concluding with a secure distribution of a secret key. A process-algebraic framework will be exploited, equipped with schemata for analysing security properties and compositional principles for evaluating if a property is satisfied over a system with more than two components.  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