全文获取类型
收费全文 | 7323篇 |
免费 | 419篇 |
国内免费 | 15篇 |
专业分类
电工技术 | 223篇 |
综合类 | 34篇 |
化学工业 | 1694篇 |
金属工艺 | 226篇 |
机械仪表 | 204篇 |
建筑科学 | 229篇 |
矿业工程 | 35篇 |
能源动力 | 272篇 |
轻工业 | 1044篇 |
水利工程 | 61篇 |
石油天然气 | 40篇 |
武器工业 | 1篇 |
无线电 | 458篇 |
一般工业技术 | 1668篇 |
冶金工业 | 228篇 |
原子能技术 | 94篇 |
自动化技术 | 1246篇 |
出版年
2023年 | 61篇 |
2022年 | 60篇 |
2021年 | 178篇 |
2020年 | 151篇 |
2019年 | 173篇 |
2018年 | 288篇 |
2017年 | 275篇 |
2016年 | 305篇 |
2015年 | 237篇 |
2014年 | 369篇 |
2013年 | 730篇 |
2012年 | 481篇 |
2011年 | 587篇 |
2010年 | 465篇 |
2009年 | 375篇 |
2008年 | 290篇 |
2007年 | 268篇 |
2006年 | 173篇 |
2005年 | 182篇 |
2004年 | 116篇 |
2003年 | 133篇 |
2002年 | 152篇 |
2001年 | 119篇 |
2000年 | 98篇 |
1999年 | 73篇 |
1998年 | 99篇 |
1997年 | 82篇 |
1996年 | 72篇 |
1995年 | 57篇 |
1994年 | 61篇 |
1993年 | 57篇 |
1992年 | 49篇 |
1991年 | 39篇 |
1990年 | 39篇 |
1989年 | 42篇 |
1988年 | 27篇 |
1986年 | 24篇 |
1985年 | 52篇 |
1984年 | 64篇 |
1983年 | 53篇 |
1982年 | 48篇 |
1981年 | 69篇 |
1980年 | 57篇 |
1979年 | 51篇 |
1978年 | 43篇 |
1977年 | 37篇 |
1976年 | 52篇 |
1975年 | 36篇 |
1974年 | 26篇 |
1973年 | 38篇 |
排序方式: 共有7757条查询结果,搜索用时 0 毫秒
41.
Phenolic and amino resins on the basis of α,β-unsaturated aldehydes were synthesized in bulk or solution. Catalysts were HCl, H3PO4, or formic acid, and in some cases NaOH. The course of the reactions was followed by GPC and NMR while the structure of the reaction products was determined by one- and two-dimensional NMR. The course of the reactions is influenced by experimental conditions: the type of monomers, their molar ratio, the type and quantity of the catalyst, the reaction time and temperature, and the reaction medium. At the beginning of the reaction the addition of a nucleophile to an aldehyde takes place through parallel 1,2-addition to and 1,4-addition to group. Oligomers with ? OH, , and ? CHO functional groups are able to add new monomer units or to react mutually to form higher molecular weight addition and condensation products. The overall rate constants for the beginning of the reactions were between 10?3 L/mol s for the high reactive mixtures and 10?7 L/mol s for the less reactive mixtures. The resins were cured by heating at temperatures above 135°C with the addition of hexamethylenetetramine. 相似文献
42.
The formation of oxide phases in the system (1 -x) Fe2O3 +xGd2O3 was investigated for 0 x 1. On the basis of XRD measurements the distribution of oxide phases, -Fe2O3, Gd3Fe5O12, GdFeO3 and Gd2O3 was determined, as a function ofx. No solid solutions were observed with certainty even at the very ends of the concentration range. This was also confirmed by57Fe Mössbauer spectroscopy. New accurate crystallographic data for Gd3Fe5O12 are given. The formation of oxide phases in the system Fe2O3- Gd2O3 is compared with the data for analogous system Fe2O3-Eu2O3. 相似文献
43.
This paper studies the behavior of motions of large-scale (LS) semistate systems (SSS) governed byP
i
(t)x
i
=M
i
(t,x
i
)x
i
+f
i
(t)+h
i
(t, x), i=1,2,...,s, =(x
1
T
x
2
T
x
s
T
)T, where matricesP
i
(t) are singular. Using Lyapunov's approach and the tools for LS system analysis, a variant of attractivity and ultimate boundedness of appropriate time-variable sets are investigated. The results are based on a specific choice of the aggregate functions. It is assumed that the reduction of equations to a normal form of lower order is inconvenient. The aggregation-decomposition approach used in this paper reduces the dimensionality of an aggregate matrix of the system to the number of its systems. Motion properties of LS systems are deduced from the properties of its isolated subsystems, the character of interconnections, and the conditions imposed on the system aggregate matrix. Sufficient algebraic conditions for the above-mentioned motion properties are developed. 相似文献
44.
The magnetic structure of a vortex in the presence of an anisotropic inhomogeneity distribution is calculated within the London model. The anisotropic supercurrent pattern consists of closed current loops, superimposed on a backflow pattern. The nonvanishing current density at the vortex core gives rise to an intrinsic Lorentz force identical with the pinning force resulting from the spatial variation of the vortex self-energy. 相似文献
45.
Pori Maja Arčon Iztok Dasireddy Venkata D. B. C. Likozar Blaž Orel Zorica Crnjak Marinšek Marjan 《Catalysis Letters》2021,151(11):3114-3134
Catalysis Letters - Industrial Cu/ZnO/Al2O3 or novel rate catalysts, prepared with a photochemical deposition method, were studied under functional CH3OH synthesis conditions at the set temperature... 相似文献
46.
应用有限元成形分析软件,对轮辐翻边成形过程进行了模拟分析,探讨了不同冲模斜角对翻边变形的影响,以控制变形冲力和轮辐变形区应变分布为目标,对冲模斜角参数进行优化。 相似文献
47.
Summary The effect of tert-butyl chloride in the polymerizations of isobutylene carried out in the presence of SnCl4 in dichloromethane at temperatures-20°C and-78°C was investigated. Synthesized polyisobutylene samples showed a bimodal molecular
weight distribution (MWD) and it was found that the weight content of the lowermolecular weight (LMW) fraction increased with
increasing t-BuCl concentration in the polymerization mixture. The effect of ageing of the initiation mixture t-BuCl/SnCl4 in CH2Cl2 prepared in advance on MWD of the PIB samples was also studied. Ageing of the initiation system supports the formation of
the LMW fraction and this oily PIB is the only product of the polymerization at-20°C,
. 相似文献
48.
49.
Oliver R. Ilić 《Journal of Intelligent Manufacturing》2014,25(3):617-628
Manufacturing cell formation is the first step in the design of cellular manufacturing system. The primary objective of this step is to cluster machines into machine cells and parts into part families so that the minimum of intercell trips will be achieved. This paper will be focused on the configuration of machine cells considering three types of initial machine-part matrix: binary (zero-one) matrix, production volume matrix, and operation time matrix. The similarity measure uses only information from these types of matrix. A pure combinatorial programming formulation will be developed to maximize the sum of similarity coefficients between machine/part pairs. An e-Learning tool/application to help industrial students and engineers for enhancing their cell formation capability is proposed. This tool is designed to include a novel similarity coefficient-based heuristic algorithm for solving the cell formation problem. To determine the performance of the proposed tool, comparison is made with a well-known tool along a case study. 相似文献
50.
Dalibor Petković Shahaboddin Shamshirband Hadi Saboohi Tan Fong Ang Nor Badrul Anuar Nenad D. Pavlović 《Applied Intelligence》2014,41(3):887-896
The prerequisite for new versatile grippers is the capability to locate and perceive protests in their surroundings. It is realized that automated controllers are profoundly nonlinear frameworks, and a faultless numerical model is hard to get, in this way making it troublesome to control utilizing tried and true procedure. Here, a design of an adaptive compliant gripper is presented. This design of the gripper has embedded sensors as part of its structure. The use of embedded sensors in a robot gripper gives the control system the ability to control input displacement of the gripper and to recognize specific shapes of the grasping objects. Since the conventional control strategy is a very challenging task, soft computing based controllers are considered as potential candidates for such an application. In this study, the polynomial and radial basis function (RBF) are applied as the kernel function of Support Vector Regression (SVR) to estimate and predict optimal inputs displacement of the gripper according to experimental tests and shapes of grasping objects. Instead of minimizing the observed training error, SVR poly and SVR rbf attempt to minimize the generalization error bound so as to achieve generalized performance. The experimental results show that an improvement in predictive accuracy and capability of generalization can be achieved by the SVR approach compared to other soft computing methodology. 相似文献