全文获取类型
收费全文 | 18317篇 |
免费 | 1006篇 |
国内免费 | 468篇 |
专业分类
电工技术 | 649篇 |
技术理论 | 1篇 |
综合类 | 1669篇 |
化学工业 | 2520篇 |
金属工艺 | 445篇 |
机械仪表 | 746篇 |
建筑科学 | 1816篇 |
矿业工程 | 417篇 |
能源动力 | 367篇 |
轻工业 | 1693篇 |
水利工程 | 269篇 |
石油天然气 | 319篇 |
武器工业 | 73篇 |
无线电 | 799篇 |
一般工业技术 | 2773篇 |
冶金工业 | 917篇 |
原子能技术 | 138篇 |
自动化技术 | 4180篇 |
出版年
2024年 | 39篇 |
2023年 | 185篇 |
2022年 | 254篇 |
2021年 | 366篇 |
2020年 | 403篇 |
2019年 | 417篇 |
2018年 | 380篇 |
2017年 | 490篇 |
2016年 | 557篇 |
2015年 | 576篇 |
2014年 | 1058篇 |
2013年 | 1077篇 |
2012年 | 1273篇 |
2011年 | 1490篇 |
2010年 | 1130篇 |
2009年 | 1130篇 |
2008年 | 948篇 |
2007年 | 1149篇 |
2006年 | 968篇 |
2005年 | 815篇 |
2004年 | 723篇 |
2003年 | 636篇 |
2002年 | 542篇 |
2001年 | 417篇 |
2000年 | 344篇 |
1999年 | 323篇 |
1998年 | 278篇 |
1997年 | 232篇 |
1996年 | 170篇 |
1995年 | 187篇 |
1994年 | 122篇 |
1993年 | 112篇 |
1992年 | 86篇 |
1991年 | 67篇 |
1990年 | 69篇 |
1989年 | 79篇 |
1988年 | 79篇 |
1987年 | 45篇 |
1986年 | 45篇 |
1985年 | 59篇 |
1984年 | 76篇 |
1983年 | 92篇 |
1982年 | 90篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1979年 | 24篇 |
1978年 | 24篇 |
1977年 | 20篇 |
1973年 | 8篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
G. J. Scott 《Food Reviews International》2003,19(1):203-219
Identifying markets for new or improved products for minor crops threatened with extinction is one critical component of any strategy intended to enhance prospects for sustainable production and use. Typically, however, activities linked to the sustainability of these commodities avoid addressing questions associated with assessing their commercial potential. After a brief review of this avoidance syndrome, this article presents a sample of practical, low-cost procedures to help evaluate the market prospects and procedures for crops like quinoa, while citing references to other methodological materials covering similar topics. 相似文献
83.
Compositional data occur as natural realizations of multivariate observations comprising element proportions of some whole
quantity. Such observations predominate in disciplines like geology, biology, ecology, economics and chemistry. Due to unit
sum constraint on compositional data, specialized statistical methods are required for analyzing these data. Dirichlet distributions
were originally used to study compositional data even though this family of distribution is not appropriate (see Aitchison,
1986) because of their extreme independence properties. Aitchison (1982) endeavored to provide a viable alternative to existing
methods by employing Logistic Normal distribution to analyze such constrained data. However this family does not include the
Dirichlet class and is therefore unable to address the issue of extreme independence. In this paper generalized Liouville
family is investigated to model compositional data which includes covariates. This class permits distributions that admit
negative or mixed correlation and also contains non-Dirichlet distributions with non-positive correlation and overcomes deficits
in the Dirichlet class. Semiparametric Bayesian methods are proposed to estimate the probability density. Predictive distributions
are used to assess performance of the model. The methods are illustrated on a real data set. 相似文献
84.
活性炭的制备及应用新进展 总被引:32,自引:0,他引:32
综述了活性炭材料研究开发的新进展。重点介绍了煤、石油焦、沥青基活性炭的制备方法及针对不同用途的活性炭改性技术,为选择合适的活化方法和制备特殊功能的改性活性炭提供了参考。 相似文献
85.
This paper discusses the need for interface management within construction, with particular reference to building facade interfaces. It categorizes the three different types of interface management—physical, contractual, and organizational. The implication of interface management in construction contracting is discussed; it is explained how the U.K. procurement trends have changed, affecting the interface management within projects. U.K. cladding procurement is very fragmented, and the paper maps the development of a typical cladding system showing the complexities of interface management. Finally, the paper discusses CladdISS, a U.K. government funded research project to develop a standardized strategy for the design and management of window and cladding interfaces. It explains the principles of CladdISS with reference to process maps, action plans, management strategy, bibliography, advice on standards, materials, maintenance, joints, movement, and tolerances. This will enable strategies to be developed to avoid the endemic interface problems occurring on-site. It will also guide the management of the interfaces throughout the project. 相似文献
86.
87.
Recently, efficient scheduling algorithms based on Lagrangian relaxation have been proposed for scheduling parallel machine
systems and job shops. In this article, we develop real-world extensions to these scheduling methods. In the first part of
the paper, we consider the problem of scheduling single operation jobs on parallel identical machines and extend the methodology
to handle multiple classes of jobs, taking into account setup times and setup costs. The proposed methodology uses Lagrangian
relaxation and simulated annealing in a hybrid framework. In the second part of the paper, we consider a Lagrangian relaxation
based method for scheduling job shops and extend it to obtain a scheduling methodology for a real-world flexible manufacturing
system with centralized material handling.
This research was supported in part by the Office of Naval Research and the Department of Science and Technology grant N00014-93-1017. 相似文献
88.
A. S. S. R. Reddy 《Canadian Metallurgical Quarterly》1992,5(1):70-78
The dynamic analysis and control system design of large space structures involve the solution of the large‐dimensional generalized matrix eigenvalue problem. The computational effort involved is proportional to the third power of the dimension of the matrices involved. To minimize the computational time a graph‐theory approach to reduce a matrix to lower‐ordered submatrices is proposed. The matrix‐reduction algorithm uses the Boolean matrices corresponding to the original numerical matrices and, thus, the computational effort to reduce the original matrix is nominal. The computational savings directly depend upon the number of submatrices into which the original matrix is reduced. A free‐free square plate is considered as an example to illustrate the technique. In this example a matrix of 16th order is reduced to three scalars corresponding to three rigid‐body modes, and three matrices of order three and one matrix of order four. 相似文献
89.
设计IIR数字滤波器的遗传优化算法 总被引:2,自引:0,他引:2
提出了IIR数字滤波器设计的遗传优化法。这是一种模拟自然遗传和达尔文进化理论的随机并行优化算法。首先,详细描述了遗传算法并给出了计算步骤,然后将遗传算法用于IIR数字滤波器的优化设计,最后给出了模拟计算结果。 相似文献
90.
Reconstruction of a discontinuous function from a few fourier coefficients using bayesian estimation
Alex Solomonoff 《Journal of scientific computing》1995,10(1):29-80
The goal of this paper is the application of spectral methods to the numerical solution of conservation law equations. Spectral methods furnish estimates of the firstn Fourier coefficients of the solution. But since the solutions of conservation law equations can have discontinuities, the estimate of the solution by summing the firstn terms of the Fourier series will haveO(1/n) error, even if the Fourier coefficients are known to high accuracy. But if the solution could be accurately reconstructed from its Fourier coefficients, spectral methods could be used effectively in these problems. A method for doing this is to assume a probability distribution for functions. Functions which are smooth away from the discontinuity are assumed to be likely, and those which are not smooth away from the discontinuity are assumed to be unlikely. Then a reconstruction algorithm is chosen by minimizing the expected error over all algorithms. It is possible to put the smoothness assumptions mentioned earlier into an infinite-dimensional Gaussian probability distribution, and then the minimum-error algorithm is well-known and fairly simple to construct and apply. If the Fourier coefficients of the reconstructed function are known exactly, then this approach gives very good results. But when used with Fourier coefficients obtained from a spectral approximation to Burgers' equation, the results were much less impressive, probably because the coefficients were not known very accurately. It is possible to construct filters that reconstruct a function using Legendre or Chebyshev coefficients for information instead Fourier coefficients. It is found that the performance of these filters is similar to the Fourier case. 相似文献