全文获取类型
收费全文 | 335篇 |
免费 | 8篇 |
专业分类
电工技术 | 8篇 |
化学工业 | 47篇 |
金属工艺 | 1篇 |
机械仪表 | 3篇 |
建筑科学 | 27篇 |
矿业工程 | 1篇 |
能源动力 | 61篇 |
轻工业 | 34篇 |
水利工程 | 2篇 |
无线电 | 17篇 |
一般工业技术 | 49篇 |
冶金工业 | 19篇 |
原子能技术 | 9篇 |
自动化技术 | 65篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 4篇 |
2017年 | 6篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 8篇 |
2012年 | 14篇 |
2011年 | 22篇 |
2010年 | 20篇 |
2009年 | 13篇 |
2008年 | 21篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 10篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有343条查询结果,搜索用时 15 毫秒
1.
The structure of the nonlinear H∞-filter in the neighborhood of the estimated trajectory is investigated and a bound on the size of the neighborhood that allows this structure is determined, both for finite and infinite horizons. Riccati inequalities that depend on the estimated trajectory are derived for finding the filter gain matrix and an algorithm for calculating the bound on the size of the above neighborhood is presented. Explicit formulas are obtained in the infinite horizon case for the minimum achievable disturbance attenuation level, the size of the neighborhood, and the corresponding filter gain. 相似文献
2.
Alternative measures of pesticide use 总被引:2,自引:0,他引:2
C Barnard S Daberkow M Padgitt ME Smith ND Uri 《Canadian Metallurgical Quarterly》1997,203(3):229-244
tRNA (m5U54)-methyltransferase (RUMT) catalyzes the S-adenosylmethionine-dependent methylation of uridine-54 in the T psi C-loop of all transfer RNAs in E. coli to form the 54-ribosylthymine residue. However, in all tRNA structures, residue 54 is completely buried and the question arises as to how RUMT gains access to the methylation site. A 17-mer RNA hairpin consisting of nucleotides 49-65 of the T psi-loop is a substrate for RUMT. Homonuclear NMR methods in conjunction with restrained molecular dynamics (MD) methods were used to determine the solution structure of the 17-mer T-arm fragment. The loop of the hairpin exhibits enhanced flexibility which renders the conventional NMR average structure less useful compared to the more commonly found situation where a molecule exists in predominantly one major conformation. However, when resorting to softer refinement methods such as MD with time-averaged restraints, the conflicting restraints in the loop can be satisfied much better. The dynamic structure of the T-arm is represented as an ensemble of 10 time-clusters. In all of these, U54 is completely exposed. The flexibility of the T psi-loop in solution in conjunction with extensive binding studies of RUMT with the T psi C-loop and tRNA suggest that the specificity of the RUMT/ tRNA recognition is associated with tRNA tertiary structure elements. For the methylation, RUMT would simply have to break the tertiary interactions between the D- and T-loops, leading to a melting of the T-arm structure and making U54 available for methylation. 相似文献
3.
Noel D. Uri 《Applied Energy》1996,54(4):355-373
This study begins by asking whether fluctuations in the price of crude oil have affected agricultural employment in the USA. After reviewing previous assessments of the issue, the existence of an empirical relationship between agricultural employment and crude-oil price volatility is established using Granger causality. Subsequently, the nature of the relationship is estimated with the results suggesting that at least three full years are required before the measurable impacts of a percentage change in the real price of crude oil on the change in agricultural employment are exhausted. Finally, the structural stability of the functional relationship between the change in agricultural employment and the volatility of the price of crude oil, the percentage changes in expected net farm income, realized technological innovation, and the wage rate are examined. 相似文献
4.
We consider two multicriteria versions of the global minimum cut problem in undirected graphs. In the k-criteria setting,
each edge of the input graph has k non-negative costs associated with it. These costs are measured in separate, non-interchangeable,
units. In the AND-version of the problem, purchasing an edge requires the payment of all the k costs associated with it. In the OR-version, an edge can be purchased by paying any one of the k costs associated with it. Given k bounds b1,b2,. . . ,bk, the basic multicriteria decision problem is whether there exists a cut C of the graph that can be purchased using a budget
of bi units of the ith criterion, for 1 ≤ i ≤ k. We show that the AND-version of the multicriteria global minimum cut problem is
polynomial for any fixed number k of criteria. The OR-version of the problem, on the other hand, is NP-hard even for k = 2,
but can be solved in pseudo-polynomial time for any fixed number k of criteria. It also admits an FPTAS. Further extensions,
some applications, and multicriteria versions of two other optimization problems are also discussed. 相似文献
5.
Asaf Shabtai Author Vitae Uri Kanonov Author Vitae Author Vitae 《Journal of Systems and Software》2010,83(8):1524-1537
In this paper, a new approach for detecting previously unencountered malware targeting mobile device is proposed. In the proposed approach, time-stamped security data is continuously monitored within the target mobile device (i.e., smartphones, PDAs) and then processed by the knowledge-based temporal abstraction (KBTA) methodology. Using KBTA, continuously measured data (e.g., the number of sent SMSs) and events (e.g., software installation) are integrated with a mobile device security domain knowledge-base (i.e., an ontology for abstracting meaningful patterns from raw, time-oriented security data), to create higher level, time-oriented concepts and patterns, also known as temporal abstractions. Automatically-generated temporal abstractions are then monitored to detect suspicious temporal patterns and to issue an alert. These patterns are compatible with a set of predefined classes of malware as defined by a security expert (or the owner) employing a set of time and value constraints. The goal is to identify malicious behavior that other defensive technologies (e.g., antivirus or firewall) failed to detect. Since the abstraction derivation process is complex, the KBTA method was adapted for mobile devices that are limited in resources (i.e., CPU, memory, battery). To evaluate the proposed modified KBTA method a lightweight host-based intrusion detection system (HIDS), combined with central management capabilities for Android-based mobile phones, was developed. Evaluation results demonstrated the effectiveness of the new approach in detecting malicious applications on mobile devices (detection rate above 94% in most scenarios) and the feasibility of running such a system on mobile devices (CPU consumption was 3% on average). 相似文献
6.
Uri Zwick 《Algorithmica》2006,46(2):181-192
We present an
-time algorithm for the All Pairs Shortest Paths (APSP) problem for directed graphs with real edge lengths. This slightly
improves previous algorithms for the problem obtained by Fredman, Dobosiewicz, Han, and Takaoka. 相似文献
7.
A theory is developed for the construction of carry-save networks with minimal delay, using a given collection of carry-save adders each of which may receive inputs and produce outputs using several different representation standards.The construction of some new carry-save adders is described. Using these carry-save adders optimally, as prescribed by the above theory, we get {, , }-circuits of depth 3.48 log2
n and {, , }-circuits of depth 4.95 log2
n for the carry-save addition ofn numbers of arbitrary length. As a consequence we get multiplication circuits of the same depth. These circuits put out two numbers whose sum is the result of the multiplication. If a single output number is required then the depth of the multiplication circuits increases respectively to 4.48 log2
n and 5.95 log2
n.We also get {, , }-formulae of sizeO (n
3.13) and {, }-formulae of sizeO (n
4.57) for all the output bits of a carry-save addition ofn numbers. As a consequence we get formulae of the same size for the majority function and many other symmetric Boolean functions. 相似文献
8.
Uri Cohen 《Journal of Electronic Materials》1977,6(6):607-643
Electrodeposition of both epitaxial and polycrystalline continuous films of dense, coherent, and well-adherent silicon coatings
was achieved from molten fluorides. A dissolving Si anode and an operating temperature of about 750 C were utilized. Silicon
electrocrystallization epitaxy (ECE) produced films with the (111) orientation on Si substrates of the same orientation. The
unintentionally doped films were of p-type character with a resistivity in the range 0.05 - 0.10 Ω-cm. Polycrystalline Si
films were similarly electroplated onto various polycrystalline metal substrates. Uniform coherent, and well-adherent coatings
with grain diameters as large as 40 – 50 μm were obtained. The useful rate of electrodeposition of Si could be significantly
increased by the application of an alternating square wave pulse (ASWP)2technique. Cathodic current pulses as high as 300 mA/cm2 (growth rate of about 5 μm/min) were demonstrated. The cathodic current efficiencies, for all modes of growth, were about
70 – 100%. The effects of the various operating parameters, and some prospective applications to the fabrication of solar
cells, are discussed.
This was paper A-6 in the 18th Annual Electronic Materials Conference, Salt Lake City, June 23–25, 1976. 相似文献
9.
Market power and the deregulation of special access service by the Federal Communications Commission
In 1999, the Federal Communications Commission adopted an order granting complete deregulation of the rates for special access service for specific metropolitan statistical areas based on an objective showing that there was potential competition in that market. This was done in an environment where the local exchange carriers (LECs) subject to price caps were earning a rate of return in excess of 22% with the rate of return on an upward trend. By 2002, the average rate of return across all price cap LECs topped 35%. The questions investigated in this article are whether the price cap LECs have market power in supplying special access service and whether they have taken advantage of this. The data clearly show that this is the case. Given the prevailing situation, there is a clear need to revisit the pricing flexibility order. First, the product market for special access service needs to be more carefully examined and, second, the metrics used to define the potential for competition need to be revamped. 相似文献
10.
Molten salt reactors (MSR) have many non-proliferation attributes. They can operate on the thorium-uranium fuel cycle which protects the fissile material by the daughter products of the inseparable U-232. MSRs can completely fission all plutonium and HEU, and as desired, ‘convert’ them to U-233. This also results in high, and efficient resource utilization, while diminishing the plutonium stock. On line processing, when applied, could free the waste from all fissile material. The fuel in the reactor stays protected by the intense radiation of the fission products. Fuel can also be protected in the reactor as well as outside the reactor by denaturing with natural uranium. A wide variety of MSRs are available, from ‘once through’ minimum processing reactors to ones with fuel processing which can breed fuel for converters. MSRs are extremely safe and simple reactors with good economic potential. 相似文献