首页 | 官方网站   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   969篇
  免费   18篇
工业技术   987篇
  2023年   2篇
  2022年   7篇
  2021年   24篇
  2020年   16篇
  2019年   7篇
  2018年   12篇
  2017年   13篇
  2016年   23篇
  2015年   10篇
  2014年   39篇
  2013年   41篇
  2012年   43篇
  2011年   65篇
  2010年   35篇
  2009年   45篇
  2008年   43篇
  2007年   53篇
  2006年   44篇
  2005年   32篇
  2004年   30篇
  2003年   28篇
  2002年   32篇
  2001年   23篇
  2000年   24篇
  1999年   13篇
  1998年   59篇
  1997年   49篇
  1996年   20篇
  1995年   26篇
  1994年   26篇
  1993年   17篇
  1992年   11篇
  1991年   5篇
  1990年   5篇
  1989年   9篇
  1988年   6篇
  1987年   1篇
  1986年   3篇
  1985年   4篇
  1984年   3篇
  1983年   4篇
  1982年   4篇
  1981年   3篇
  1980年   6篇
  1979年   8篇
  1978年   2篇
  1977年   3篇
  1976年   3篇
  1975年   3篇
  1974年   2篇
排序方式: 共有987条查询结果,搜索用时 140 毫秒
81.
This paper describes three circuit techniques for a DDR1/DDR2-compatible chip architecture designed for both high-speed and high-density DRAMs: 1) a dual-clock input-latch scheme, which reduces the excessive timing margin for random input commands by using a pair of latch circuits controlled by dual-phase one-shot clock signals, achieves a 0.9-ns reduction in cycle time from 3.05 to 2.15 ns; 2) a hybrid multi-oxide output buffer reduces the area penalty of the output buffer caused by compatible chip design from 1.35% to 0.3%; and 3) a quasi-shielded distributed data transfer scheme enables a 2.6-ns reduction in access time to 10.25 ns in both 2-b and 4-b prefetch operations. By using these techniques, we developed a 175.3-mm/sup 2/ 1-Gb SDRAM that operates as an 800-Mb/s/pin DDR2 or 400-Mb/s/pin DDR1.  相似文献   
82.
Members of the mammalian long-chain acyl-CoA synthetase (ACSL) family are key enzymes for cellular fatty acid metabolism that catalyze the initial step in activation of long-chain fatty acids. However, the specificity of individual isoforms of ACSL to the lipid metabolic process is not well studied. In addition, the regulation of expression of individual ACSL isoforms under hyperlipidemic conditions is largely unknown. We cloned the hamster ACSL3 cDNA coding region and generated specific antibodies recognizing the ACSL3 protein. We next observed the changes in ACSL3 mRNA and protein expression in hamsters fed a standard chow diet or a high fat and high cholesterol (HFHC) diet. HFHC feeding significantly increased ACSL3 mRNA and protein expression in liver and to a lesser extent in muscle but not in adipose, brain, heart, or testis. Additionally, ACSL3 mRNA abundance was differentially regulated by the nutritional status in different tissues with liver, muscle, and adipose being the most sensitive tissues. Importantly, the hepatic ACSL3 mRNA expression pattern in response to fasting and refeeding in hyperlipidemic hamsters differed from that observed in normal chow-fed hamsters. Together, these results provide the first in vivo evidence of altered regulation of hepatic ACSL3 expression under hyperlipidemic conditions and suggest important regulatory roles for this enzyme in lipid metabolism.  相似文献   
83.
We synthesized new polymers with both photocrosslinkability and biocompatibility by a random copolymerization of 4‐(4‐methoxycinnamoyl)phenyl methacrylate and 2‐methacryloyloxyethyl phosphorylcholine. These polymers were used as prepolymers to make a hydrogel by photoirradiation. Gelation began with 5 s of photoirradiation and reached an equilibrium state after 360 s of photoirradiation. The absorption maximum at 347 nm, attributed to the cinnamoyl group, disappeared with the photoirradiation time. That is, dimerization between cinnamoyl groups in the polymer proceeded and formed a hydrogel. The equilibrium water concentration of the hydrogels was more than 90%. Moreover, we succeeded in making a microshape hydrogel on glass by photoirradiation through a photomask. The window shape of the photomask was transferred to the hydrogel that was formed. We concluded that these photocrosslinkable polymers could be useful in preparing microfluidic devices for separating or immobilizing biomolecules and cells. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 44–50, 2007  相似文献   
84.
This paper describes three circuit technologies indispensable for high-bandwidth multibank DRAM's. (1) A clock generator based on a bidirectional delay (BDD) eliminates the output skew. The BDD measures the cycle time as the quantity charged or discharged of an analog quantity, and replicates it in the next cycle. This achieves a 0.18-mm 2, two-cycle-lock clock generator operating from 25 to 167 MHz with a 30-ps resolution. (2) A quad-coupled receiver eliminates the internal skew caused by the difference between a rise input and a fall input by 40%. (3) An interbank shared redundancy scheme (ISR) with a variable unit redundancy (VUR) efficiently increases yield in multibank DRAM's. The ISR allows redundancy match circuits to be shared with two or more banks. The VUR allows the number of units replaced to be variable. These circuit technologies achieved a 250-Mb/s/pin, 8-bank, 1-Gb double-data-rate synchronous DRAM  相似文献   
85.
The synovitis of rheumatoid arthritis (RA) is one of few pathological lesions in which B lymphocyte accumulation progresses to the extent of germinal centre formation. The present study was designed to assess the ability of synovial fibroblasts to express molecules implicated in B lymphocyte survival and differentiation, both in vivo, and in response to cytokines in vitro. Normal and diseased synovia were examined by indirect immunofluorescence. In all tissues synovial intimal fibroblasts showed co-expression of vascular cell adhesion molecule-1 (VCAM-1) and complement decay-accelerating factor (DAF) comparable to that of follicular dendritic cells (FDC), but not complement receptor 2 (CR2). In rheumatoid synovia, subintimal cells showed variable expression of VCAM-1 and DAF, with bright co-expression of VCAM-1, DAF and CR2 in lymphoid follicle centres. B lymphocytes, some of which were proliferating cell nuclear antigen-positive, were present in contact with subintimal cells expressing VCAM-1 with or without DAF or CR2. B lymphocytes were rarely present in the intimal layer, and, where present, showed fragmentation. In vitro, synovial fibroblasts exposed to tumour necrosis factor-alpha (TNF-alpha) in combination with interferon-gamma (IFN-gamma) showed enhanced expression of VCAM-1, in comparison with fibroblasts from skin and lung and, unlike skin and lung fibroblasts, also expressed DAF and CR2. These findings support the hypothesis that synovial targeting in RA involves an enhanced ability of synovial fibroblasts to support B lymphocyte survival. This appears to be dependent, not on the constitutive expression of VCAM-1 and DAF on intimal cells, but on the increased ability of subintimal cells to respond to proinflammatory cytokines, perhaps critically in the expression of VCAM-1.  相似文献   
86.
Tested D. S. Olton's (1978) hypothesis that the gerbil's ability to easily learn the radial maze task is due to a natural "win-shift" foraging strategy, a tendency to avoid recently visited food sites. 25 Mongolian gerbils at weaning were put in 1 of 2 environments—one in which the source of food and water was always located in the same place and the other in which the source changed location from day to day—until they were 60 days of age. They then were tested in a 17-arm radial maze. Ss reared in the environment with variable locations of food and water learned the maze task more quickly than Ss reared in the other environment. Results are consistent with Olton's hypothesis. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
87.
The convergence performance of typical numerical schemes for geometric fitting for computer vision applications is compared. First, the problem and the associated KCR lower bound are stated. Then, three well-known fitting algorithms are described: FNS, HEIV, and renormalization. To these, we add a special variant of Gauss-Newton iterations. For initialization of iterations, random choice, least squares, and Taubin's method are tested. Simulation is conducted for fundamental matrix computation and ellipse fitting, which reveals different characteristics of each method.  相似文献   
88.
A phase diagram of the EuCl2---NaCl system was determined by differential scanning calorimetry (DSC) and the activity coefficients of EuCl2 and NaCl in this system were estimated under some assumptions. According to DSC measurement, it was found that there were two phase transitions at 1123.9 K and 1016.8 K. In order to specify the melting point of EuCl2 we did Raman spectroscopy experiments. Thus, the melting point of EuCl2 was evaluated to be 1016.8 K which was detected as the lower peak in the DSC curve. Raman spectroscopy of this system suggested that complex species were not formed clearly in the EuCl2 poor system and the estimated activity coefficients of EuCl2 also supported this suggestion.  相似文献   
89.
A novel technique was developed to recognize ice crystals in biological materials and to analyze their three-dimensional morphology using a Cryogenic Micro-Slicer Spectral Imaging System with a micro-slicer unit and a near-infrared spectral imaging unit. Consecutive cross-sections of a frozen sample were exposed by the multi-slicing operations with a minimum thickness of 1 µm, and their images were taken by the imaging unit. Spectroscopic analysis using a near-infrared spectrum meter showed an absorption peak at 1460 nm for pure water. Based on the observations of the absorption band of ice crystals in the wavelength range of 1450–1570 nm and its peak at 1495 nm, a commodity-type bandpass filter with a central wavelength of 1500 nm was adopted to identify ice crystals in near-infrared images. The absorption peak of water exhibited a tendency to move toward longer wavelengths with decreasing sample temperature from 25 °C to ?15 °C. The filtered images of ice crystals in frozen samples were darker than the other components at the peak wavelength of ice crystals. The three-dimensional reconstructed morphology of ice crystals revealed that they were formed along the direction of heat transfer while freezing. The proposed method provides a novel tool to investigate the effects of freezing conditions on the size, morphology and distribution of ice crystals.  相似文献   
90.
Periodontal disease is caused by dental plaque biofilms, and the removal of these biofilms from the root surface of teeth plays a central part in its treatment. The conventional treatment for periodontal disease fails to remove periodontal infection in a subset of cases, such as those with complicated root morphology. Adjunctive antimicrobial photodynamic therapy (aPDT) has been proposed as an additional treatment for this infectious disease. Many periodontal pathogenic bacteria are susceptible to low-power lasers in the presence of dyes, such as methylene blue, toluidine blue O, malachite green, and indocyanine green. aPDT uses these light-activated photosensitizer that is incorporated selectively by bacteria and absorbs a low-power laser/light with an appropriate wavelength to induce singlet oxygen and free radicals, which are toxic to bacteria. While this technique has been evaluated by many clinical studies, some systematic reviews and meta-analyses have reported controversial results about the benefits of aPDT for periodontal treatment. In the light of these previous reports, the aim of this review is to provide comprehensive information about aPDT and help extend knowledge of advanced laser therapy.  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-23

京公网安备 11010802026262号