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   1417篇
  免费   11篇
电工技术   6篇
化学工业   22篇
金属工艺   6篇
机械仪表   17篇
建筑科学   12篇
能源动力   9篇
轻工业   71篇
水利工程   4篇
无线电   14篇
一般工业技术   60篇
冶金工业   1177篇
原子能技术   1篇
自动化技术   29篇
  2023年   3篇
  2022年   5篇
  2021年   6篇
  2020年   5篇
  2019年   4篇
  2018年   5篇
  2017年   4篇
  2016年   5篇
  2015年   5篇
  2014年   10篇
  2013年   43篇
  2012年   15篇
  2011年   11篇
  2010年   13篇
  2009年   8篇
  2008年   16篇
  2007年   3篇
  2006年   3篇
  2005年   4篇
  2004年   5篇
  2003年   7篇
  2002年   2篇
  2001年   2篇
  2000年   3篇
  1999年   30篇
  1998年   388篇
  1997年   175篇
  1996年   137篇
  1995年   76篇
  1994年   59篇
  1993年   73篇
  1992年   9篇
  1991年   18篇
  1990年   9篇
  1989年   8篇
  1988年   15篇
  1987年   11篇
  1986年   13篇
  1985年   17篇
  1984年   3篇
  1983年   7篇
  1982年   6篇
  1981年   7篇
  1980年   13篇
  1979年   3篇
  1978年   10篇
  1977年   47篇
  1976年   102篇
  1975年   2篇
  1965年   2篇
排序方式: 共有1428条查询结果,搜索用时 15 毫秒
41.
A panel of colorimetric assays was assessed for sensitivity, reproducibility, and performance in the investigation of the biocompatibility of a representative range of orthopædic biomaterials, using a commercially available human osteosarcoma-derived cell line. The MTT assay was the most sensitive, with a detection limit of 4×102 cells per well against background, while the NR assay was the least sensitive, with no colour change until the cell density reached 2×104 per well. All of the assays investigated showed a highly significant edge effect when within-plate reproducibility was examined; between-plate reproducibility was good for all assays except the MTT assay. When the assays were tested on cells adherent on biomaterials, there was a wide variation in the results obtained; in particular, the MTS assay showed poor reproducibility in the presence of materials. The MTT and BrdU assays both showed sufficient precision to detect cells on two of the materials studied. The study demonstrates that colorimetric assays are potentially useful in biocompatibility assessment but must be fully validated for the application chosen.  相似文献   
42.
Treatment of an acetaminophen overdose with N-acetyl cysteine usually is based on the position of the 4-h acetaminophen (APAP) level on the Rumack-Matthew nomogram; however, there is disagreement on the level at which clinically relevant hepatotoxicity occurs. A retrospective review of all acute adult formulation APAP exposures reported to our poison center between 1986 and 1993 was performed and cases corresponding to the "possible risk or toxicity" range on the nomogram were identified. Our current poison center protocol for APAP poisoning does not recommend treatment with N-acetylcysteine (NAC) in low-risk patients if the 4-h serum APAP level or the extrapolated equivalent falls within the possible toxicity range on the nomogram. Seventeen cases met the inclusion criteria for the study and received no NAC; six additional patients met inclusion criteria but received one or two doses of NAC before therapy was discontinued. No patients in either group demonstrated clinical evidence of hepatotoxicity. This pilot study suggests that patients with no risk factors and APAP levels in the "possible risk" range may not require NAC therapy.  相似文献   
43.
One of the most significant difficulties with developing Service-Oriented Architecture (SOA) involves meeting its security challenges, since the responsibilities of SOA security are based on both the service providers and the consumers. In recent years, many solutions to these challenges have been implemented, such as the Web Services Security Standards, including WS-Security and WS-Policy. However, those standards are insufficient for the new generation of Web technologies, including Web 2.0 applications. In this research, we propose an intelligent SOA security framework by introducing its two most promising services: the Authentication and Security Service (NSS), and the Authorization Service (AS). The suggested autonomic and reusable services are constructed as an extension of WS-1 security standards, with the addition of intelligent mining techniques, in order to improve performance and effectiveness. In this research, we apply three different mining techniques: the Association Rules, which helps to predict attacks, the Online Analytical Processing (OLAP) Cube, for authorization, and clustering mining algorithms, which facilitate access control rights representation and automation. Furthermore, a case study is explored to depict the behavior of the proposed services inside an SOA business environment. We believe that this work is a significant step towards achieving dynamic SOA security that automatically controls the access to new versions of Web applications, including analyzing and dropping suspicious SOAP messages and automatically managing authorization roles.  相似文献   
44.
A poor response to L-DOPA in addition to parkinsonian, cerebellar, and autonomic signs is commonly regarded as indicative of clinical multiple system atrophy (MSA). We compared the motor response to a single oral administration of 250 mg L-DOPA/25 mg carbidopa in eight MSA patients and eight Parkinson's disease (PD) patients with the "on-off" phenomenon, evaluating L-DOPA peripheral pharmacokinetics. Motor response was consistently good in all PD patients, but only four MSA patients had a (moderate) response. Pharmacokinetic parameters did not differ between the groups. The varying extent of putaminal damage could be responsible for the differing motor response to L-DOPA in MSA patients.  相似文献   
45.
A bioactive material, capable of active stimulation of osteogenesis, has been produced by adsorbing human growth hormone onto calcium phosphate ceramics. These materials can be used to deliver growth hormone at the bone-ceramic interface. The elution of the hormone occurs in two phases, with an initial rapid release followed by a slow continuous release for up to 25 days. Tricalcium phosphate was found to release growth hormone better than hydroxyapatite, probably due to the higher solubility of the ceramic.In vivo studies using a rabbit model were used to demonstrate osteointegration at the ceramic interface.  相似文献   
46.
Harry  EL Casco 《中华手工》2014,(8):66-67
<正>不必质疑卡司克的精密、耐用和可靠程度,因为孕育它的母体可是战争中那把直接致命的武器——左轮手枪。"我打赌你以前没有拿过枪。"面对着正在把玩.32口径左轮手枪的乔恩·索洛萨巴尔(Jon Solozabal),很难相信这句话竟是一位文具制造商的开场白。对乔恩和他的这座超过90岁的企业王国而言,手枪所代表的不仅是一段历史,更是一笔宝贵的遗产。  相似文献   
47.
48.
We report on the recent progress of the Multicolor Submillimeter (kinetic) Inductance Camera, or MUSIC. MUSIC will use antenna-coupled Microwave Kinetic Inductance Detectors to observe in four colors (150 GHz, 230 GHz, 290 GHz and 350 GHz) with 2304 detectors, 576 per band, at the Caltech Submillimeter Observatory. It will deploy in 2012. Here we provide an overview of the instrument, focusing on the array design. We have also used a pathfinder demonstration instrument, DemoCam, to identify problems in advance of the deployment of MUSIC. In particular, we identified two major limiters of our sensitivity: out-of-band light directly coupling to the detectors (i.e. not through the antenna), effectively an excess load, and a large 1/f contribution from our amplifiers and electronics. We discuss the steps taken to mitigate these effects to reach background-limited performance (BLIP) in observation.  相似文献   
49.
Luenberger observer theory is extended to distributed parameter systems. This extension is based on the consideration of sensors. For systems with infinite dimensional state spaces, it is possible to construct the state vector asymptotically (or a part of the state vector) by a ‘good’ choice of sensors. We show that the link between detectability and sensor structure may be of some interest in the construction of observers.  相似文献   
50.
Plasma ignition threshold of nanoparticle-based and bulk silver targets was measured in air. The plasma was initiated by a Nd:YAG laser at wavelengths of 355, 532, and 1064 nm. The plasma ignition was monitored utilizing the prominent Ag I line at 546.5 nm. Lower ignition thresholds of the nanoparticle-based silver target were estimated at 0.4?±?0.02, 0.34?±?0.04, and 0.27?±?0.035 J cm~(-2) coupled with the different laser wavelengths, respectively. In contrast, the bulk silver target plasma exhibited an order of magnitude higher ignition threshold. A three orders of magnitude enhanced emission intensity from the nano-based target over the bulk target was achieved at lower levels of laser irradiation. A reduction of the thermal diffusion length of the nanosilver was assumed in order to theoretically predict this reduction in the plasma threshold. In addition, the effect of self-reversal on the resonance lines was taken into consideration.  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