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   281篇
  免费   7篇
电工技术   6篇
化学工业   30篇
金属工艺   13篇
机械仪表   9篇
建筑科学   13篇
矿业工程   1篇
能源动力   3篇
轻工业   14篇
水利工程   2篇
无线电   52篇
一般工业技术   38篇
冶金工业   68篇
原子能技术   2篇
自动化技术   37篇
  2022年   6篇
  2021年   5篇
  2020年   4篇
  2019年   6篇
  2018年   2篇
  2017年   6篇
  2016年   4篇
  2015年   2篇
  2014年   4篇
  2013年   8篇
  2012年   14篇
  2011年   11篇
  2010年   11篇
  2009年   6篇
  2008年   10篇
  2007年   15篇
  2006年   10篇
  2005年   6篇
  2004年   7篇
  2003年   6篇
  2002年   10篇
  2001年   5篇
  2000年   3篇
  1999年   5篇
  1998年   18篇
  1997年   10篇
  1996年   7篇
  1995年   4篇
  1994年   6篇
  1993年   12篇
  1991年   5篇
  1990年   2篇
  1989年   5篇
  1988年   1篇
  1987年   1篇
  1986年   4篇
  1985年   8篇
  1984年   5篇
  1983年   5篇
  1982年   4篇
  1981年   1篇
  1980年   1篇
  1979年   6篇
  1978年   2篇
  1976年   4篇
  1975年   4篇
  1974年   1篇
  1971年   1篇
  1968年   1篇
  1966年   1篇
排序方式: 共有288条查询结果,搜索用时 10 毫秒
81.
Efficient algorithms for the continuous representation of a discrete signal in terms of B-splines (direct B-spline transform) and for interpolative signal reconstruction (indirect B-spline transform) with an expansion factor m are described. Expressions for the z-transforms of the sampled B-spline functions are determined and a convolution property of these kernels is established. It is shown that both the direct and indirect spline transforms involve linear operators that are space invariant and are implemented efficiently by linear filtering. Fast computational algorithms based on the recursive implementations of these filters are proposed. A B-spline interpolator can also be characterized in terms of its transfer function and its global impulse response (cardinal spline of order n). The case of the cubic spline is treated in greater detail. The present approach is compared with previous methods that are reexamined from a critical point of view. It is concluded that B-spline interpolation correctly applied does not result in a loss of image resolution and that this type of interpolation can be performed in a very efficient manner  相似文献   
82.
Past Pygmalion research has been susceptible to interpersonal contrast effects, rendering it uncertain whether raising managers' expectations toward subordinates can improve performance without reference to control Ss in the same group. Twenty-nine platoons in the Israel Defense Forces were randomly assigned to Pygmalion or control conditions to test the hypothesis that raising manager expectations boosts performance without contrast effects. Leaders of the Pygmalion platoons were informed that their subordinates on average had unusually high command potential. Platoon-level analysis of performance showed that Pygmalion platoons significantly outscored control platoons, confirming the Pygmalion hypothesis. Manager expectation effects are not dependent on interpersonal contrast effects; in addition, the Pygmalion approach appears well suited to applications involving whole groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
83.
The electromigration behaviour of various metallization systems has been tested on Si, GaAs and GaInAs substrates. Lifetime dependence on temperature and current density has been measured by accelerated lifetime tests. Linewidth was between 0.45 μm and 2 μm. The best electromigration resistance was found for electroplated gold lines, however also the system Al on Ti showed a as much as 40 times better performance than standard Al metallization. For linewidths of 0.45 μm a steep increase in stability has been found.  相似文献   
84.
Glycosylation affects various biological functions of proteins (e.g., protein binding, inter- or intracell signaling, etc.), and it can serve as an indicator of disease. Therefore, characterization of the glycosylation in proteins is one important step in developing a comprehensive understanding of the biological significance of glycosylation and in facilitating disease diagnosis. Glycopeptide-based MS analysis has proven to be a viable tool for glycopeptide analysis. However, when glycopeptides coexist with peptides, glycopeptide signals are usually suppressed by the strongly ionizing peptides. Toward this end, it would be desirable to seek methods to improve glycopeptide detection. Herein, we performed an in-depth study of maximizing glycosylation coverage on model glycoproteins by optimizing all the aspects of glycopeptide-based analysis, including sample preparation methods, mass spectral techniques, and data analysis strategies. For sample preparation, several approaches, including reversed-phase high-performance liquid chromatography, lectin-based affinity, and hydrophilic affinity using a carbohydrate-based resin, were compared and tested individually as well as in parallel. For mass spectral techniques, profiling glycopeptides in both positive and negative ion mode is essential to obtain complete glycan profiles. For data analysis, incorporating variable modifications in the database search of GlycoPep DB enhances glycopeptide coverage. In addition, the use of PNGase F helps to confirm the presence of weakly ionized glycopeptides when they coelute with strongly ionizing species. In doing so, we created a work flow that is designed specifically to optimize the coverage of glycosylation heterogeneity in terms of the number of glycosylation sites detected and their corresponding glycan profiles. To test the effectiveness of this approach, a glycoprotein with 27 potential glycosylation sites, and an unknown glycosylation profile, was analyzed; on this protein, more than 300 glycoforms from 23 detected glycosylation sites were identified. This work demonstrates that these strategies significantly improve the glycopeptide detection, thereby, facilitating understanding the functional properties of glycans on the glycoproteins.  相似文献   
85.
It is often beneficial to modify surfaces to gain desirable properties such as improved wear and friction resistance. Self-lubricating coatings can improve the performance of contacting surfaces and extend component lifetimes by reducing the coefficient of friction and/or improving resistance to specific wear modes. With these goals in mind, self-lubricating coatings of hexagonal boron nitride (hBN) particles in a deposited nickel matrix were investigated and optimized for friction and wear. These self-lubricating coatings were created via high-velocity particle consolidation or cold spray using micrometer-sized hBN powder encapsulated by nickel and nickel phosphorous alloys. Relatively thick nickel encapsulation via electrolesss Ni plating was required to aid in coating bonding/formation by “tricking” the hBN into acting as monolithic Ni during deposition. Once deposited on aluminum substrates, the coatings were analyzed and found to exhibit enhanced mechanical and tribological properties such as high bond strength and microhardness, a relatively low coefficient of friction, and improved reciprocating wear behavior relative to pure cold-sprayed Ni coatings. Furthermore, the encapsulation process was found to be both scalable and amenable to relatively small hBN particles.  相似文献   
86.
The aim of transit-oriented development (TOD) is to create a livable urban environment by improving the integration between land-use and transportation systems. The capital city of Ethiopia, Addis Ababa, aims to promote a sustainable transportation system by launching its first light rail transit (LRT) network to control the current pattern of increased congestion and the need for mass transport. Planning for TOD around existing transit stations helps achieve improved transit choice and encourages local economic development. Therefore, this article proposes a methodology to quantitatively measure the existing TOD in terms of a TOD index within the walkable distance of transit nodes by measuring the criteria that define TOD levels. The TOD index is calculated for areas of 22 stations on the East-West LRT line of Addis Ababa. Depending on the value of the TOD index, certain stations are identified to have a potential TOD but poor transit accessibility. With these results, the recommendation to improve TOD planning can become accurate for each station, depending on its relevant factors. Such results also help identify each station's potential for TOD planning and its improvements toward future local developments.  相似文献   
87.
Wriedt  Gunter  de Vries  Dieter  Eden  Tanja  Federolf  Christian 《Grundwasser》2019,24(1):27-41
Grundwasser - Zur Nitratbelastung im Grundwasser besteht aufgrund der intensiven Agrarwirtschaft in Niedersachsen ein besonderer Informationsbedarf. Die Auswertung von Punktdaten soll...  相似文献   
88.
Microdischarge arrays: a new family of photonic devices   总被引:4,自引:0,他引:4  
The optical and electrical characteristics of microdischarge devices and arrays fabricated in semiconductors and metal/polymer structures are described. Devices as small as (10 μm)2 in emitting area (nanoliters in volume) and arrays as large as 30 × 30 have been demonstrated and operated at gas pressures up to and exceeding one atmosphere. This new generation of microoptical sources is capable of producing photons from the infrared to the vacuum ultraviolet and beyond and is well suited for integration with microoptoelectronic, fluidic, and mechanical systems  相似文献   
89.
Despite the growing number of dam removals, few have been studied to understand their impacts on stream fish communities. An even smaller proportion of dam removal studies focus on the impacts of low-head dam removals, although they are the most common type of dam. Instead, the majority of removal studies focus on the impacts of larger dams. In this study, two previously impounded Illinois Rivers were monitored to assess the impacts of low-head dam removal on the functional assemblage of stream fishes. Study sites were sampled each fall from 2012–2015 (pre-dam removal) and 2018–2020 (post-dam removal) in three locations: the tailrace, impoundment, and river channel. Fishes were aggregated into habitat and reproductive guilds, relating community changes to habitat, environmental metrics, and stream quality. Prior to removal, the slackwater guild was the most prevalent habitat guild throughout both rivers, while nest builders and benthic spawners were the most abundant reproductive guilds. During the two years following removal, fish assemblage throughout both rivers shifted to a more evenly distributed representation of habitat and reproductive guilds, while restoration of lotic habitat conditions increased, as surface water temperatures decreased and QHEI, IBI, and dissolved oxygen increased. This shift in environmental metrics and increase in overall stream quality increased, particularly in the formerly impounded reaches, indicate diminished habitat homogeneity, and a shift towards natural habitat diversity. This habitat diversification likely led to the restoration of a range of potential niches, thereby increasing the array of guild types inhabiting these rivers, while simultaneously preventing single-guild dominance.  相似文献   
90.
Complexometric titrations are the primary source of metal speciation data for aquatic systems, yet their interpretation in waters containing humic and fulvic acids remains problematic. In particular, the accuracy of inferred ambient free metal ion concentrations and parameters quantifying metal complexation by natural ligands has been challenged because of the difficulties inherent in calibrating common analytical methods and in modeling the diverse array of ligands present. This work tests and applies a new method of modeling titration data that combines calibration of analytical sensitivity (S) and estimation of concentrations and stability constants for discrete natural ligand classes ([Li]T and Ki) into a single step using nonlinear regression and a new analytical solution to the one-metal/two-ligand equilibrium problem. When applied to jointly model data from multiple titrations conducted at different analytical windows, it yields accurate estimates of S, [Li]T, Ki, and [Cu2+] plus Monte Carlo-based estimates of the uncertainty in [Cu2+]. Jointly modeling titration data at low-and high-analytical windows leads to an efficient adaptation of the recently proposed "overload" approach to calibrating ACSV/CLE measurements. Application of the method to published data sets yields model results with greater accuracy and precision than originally obtained. The discrete ligand-class model is also re-parametrized, using humic and fulvic acids, L1 class (K1 = 10(13) M(-1)), and strong ligands (L(S)) with K(S) > K1 as "natural components". This approach suggests that Cu complexation in NW Mediterranean Sea water can be well represented as 0.8 +/- 0.3/0.2 mg humic equiv/L, 13 +/- 1 nM L1, and 2.5 +/- 0.1 nM L(S) with [CU]T = 3 nM. In coastal seawater from Narragansett Bay, RI, Cu speciation can be modeled as 0.6 +/- 0.1 mg humic equiv/L and 22 +/- 1 nM L1 or approximately 12 nM L1 and approximately 9 nM L(S), with [CU]T = 13 nM. In both waters, the large excess (approximately 10 nM) of high-affinity, Cu-binding ligands over [CU]T results in low equilibrium [Cu2+] of 10(-14.5 +/- 0.2) M and 10(-13.3 +/- 0.4) M, respectively.  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