全文获取类型
收费全文 | 4479篇 |
免费 | 134篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 25篇 |
综合类 | 17篇 |
化学工业 | 761篇 |
金属工艺 | 90篇 |
机械仪表 | 63篇 |
建筑科学 | 222篇 |
矿业工程 | 32篇 |
能源动力 | 52篇 |
轻工业 | 444篇 |
水利工程 | 16篇 |
石油天然气 | 27篇 |
武器工业 | 1篇 |
无线电 | 306篇 |
一般工业技术 | 584篇 |
冶金工业 | 1507篇 |
原子能技术 | 17篇 |
自动化技术 | 455篇 |
出版年
2022年 | 47篇 |
2021年 | 59篇 |
2020年 | 44篇 |
2019年 | 67篇 |
2018年 | 53篇 |
2017年 | 47篇 |
2016年 | 71篇 |
2015年 | 63篇 |
2014年 | 88篇 |
2013年 | 233篇 |
2012年 | 128篇 |
2011年 | 177篇 |
2010年 | 133篇 |
2009年 | 134篇 |
2008年 | 141篇 |
2007年 | 143篇 |
2006年 | 136篇 |
2005年 | 111篇 |
2004年 | 119篇 |
2003年 | 97篇 |
2002年 | 114篇 |
2001年 | 63篇 |
2000年 | 85篇 |
1999年 | 117篇 |
1998年 | 277篇 |
1997年 | 190篇 |
1996年 | 147篇 |
1995年 | 93篇 |
1994年 | 108篇 |
1993年 | 107篇 |
1992年 | 67篇 |
1991年 | 59篇 |
1990年 | 85篇 |
1989年 | 58篇 |
1988年 | 66篇 |
1987年 | 63篇 |
1986年 | 55篇 |
1985年 | 39篇 |
1984年 | 48篇 |
1983年 | 53篇 |
1982年 | 42篇 |
1981年 | 34篇 |
1980年 | 47篇 |
1979年 | 46篇 |
1978年 | 41篇 |
1977年 | 35篇 |
1976年 | 71篇 |
1975年 | 40篇 |
1972年 | 25篇 |
1970年 | 27篇 |
排序方式: 共有4619条查询结果,搜索用时 15 毫秒
111.
Carl Miller Helen Austin Larry Posorske Jesus Gonzlez 《Journal of the American Oil Chemists' Society》1988,65(6):927-931
The lipase-catalyzed synthesis of ester bonds has been well-documented lately and is of much current commercial interest.
Immobilization of a fungal lipase on a unique macroporous support allows not only the ability to operate in non-aqueous media
but to catalyze ester synthesis in quantitative yields, employing attractive commercial conditions. Catalyst dose and process
configurations will be illustrated. The capability of the catalyst to operate efficiently in reverse under a variety of unnatural,
hostile, solvent-containing environments will be discussed. The range of substrates for this immobilized lipase, Lipzome,
has been investigated. The enzyme will catalyze ester synthesis with saturated, unsaturated and a variety of branched carboxylic
acids. The alcohol specificity for this enzyme also is equally broad. A wide variety of straight-chain, branched and polar
alcohols can be substrates. In addition, some examples of alcohol specificity for kinetic isomer resolution will be cited.
Presented at the symposium “The Biology, Biotechnology and Technology of Lipases” at the 78th annual meeting of the American
Oil Chemists’ Society held May 17–21, 1987, in New Orleans, Louisiana. 相似文献
112.
The effect of microstructural changes on the ductile-brittle transition temperature (DBTT) was studied in a titanium-getter ed Fe-8Ni-2 Mn-0.15 Ti alloy. A fairly strong grain size dependence of the transition temperature, 8°C/mm?1/2, was found. Grain size refinement from 38 μm (ASTM #6.5) to 1.5 μm (ASTM #15.5) through a four-step thermal treatment lowered the transition temperature by 162°C. A small amount of retained austenite was introduced into this grain-refined microstructure, and the transition temperature was reduced by an additional 120 ~ 150°C. The reduction of the DBTT due to retained austenite was smaller when the austenite was in a large-grained structure (64°C). The distribution and stability of retained austenite were also studied. 相似文献
113.
The effect of Al2O3 and Nb2O5 additions on the microstructure and thermal expansion behavior of tantalum (V) oxide has been studied. Both singly doped
and co-doped compositions were examined. Compositions with 3 wt% Al2O3 (or greater), contained AlTaO4 as a second phase. Complete solubility was observed for Nb2O5 contents in the range 1–5 wt%. It was found that doping with Al2O3 results in a decrease of the coefficient of thermal expansion (CTE), such that increasing amounts of Al2O3 (1–5 wt%) cause a successive decrease in the CTE value. In the case of Nb2O5 additions, the result is an increase in the CTE of the tantalum (V) oxide. However, in the range 1–5 wt% Nb2O5, the CTE value is relatively insensitive to the amount of Nb2O5 added. Due to the countervailing influences of these two additive oxides, it was demonstrated that co-doping with Al2O3 and Nb2O5 is an effective strategy for tailoring the CTE of tantalum (V) oxide. 相似文献
114.
Love John M.; Kisker Ellen Eliason; Ross Christine; Raikes Helen; Constantine Jill; Boller Kimberly; Brooks-Gunn Jeanne; Chazan-Cohen Rachel; Tarullo Louisa Banks; Brady-Smith Christy; Fuligni Allison Sidle; Schochet Peter Z.; Paulsell Diane; Vogel Cheri 《Canadian Metallurgical Quarterly》2005,41(6):885
Early Head Start, a federal program begun in 1995 for low-income pregnant women and families with infants and toddlers, was evaluated through a randomized trial of 3,001 families in 17 programs. Interviews with primary caregivers, child assessments, and observations of parent-child interactions were completed when children were 3 years old. Caregivers were diverse in race-ethnicity, language, and other characteristics. Regression-adjusted impact analyses showed that 3-year-old program children performed better than did control children in cognitive and language development, displayed higher emotional engagement of the parent and sustained attention with play objects, and were lower in aggressive behavior. Compared with controls, Early Head Start parents were more emotionally supportive, provided more language and learning stimulation, read to their children more, and spanked less. The strongest and most numerous impacts were for programs that offered a mix of home-visiting and center-based services and that fully implemented the performance standards early. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
115.
Rod Morris 《Computer Fraud & Security》2003,2003(1):11-13
Uncovering a computer user’s past activities is one of the most common tasks for a computer forensics investigator. Often, this task is straightforward and can be accomplished primarily through a detailed analysis of the relevant data and application files present on a system. However, a tremendous amount of information can also be discovered which might otherwise be thought lost or hidden. By discovering data on a computer which a suspect has tried to hide or destroy, or by uncovering information in the depths of the operating system (or even in areas no longer used by the operating system) an investigator may be able to gain vital evidence. This article describes some of the methods used by investigators to uncover these types of data on Windows systems. 相似文献
116.
Howard Bowman Helen Cameron Peter King Simon Thompson 《Formal Methods in System Design》2003,22(1):5-38
This paper explores a formalism for describing a wide class of multimedia document constraints, based on an interval temporal logic. We describe the requirements that arise from the multimedia documents application area, and we illustrate these requirements using several examples. Then we present the temporal logic formalism that we use. This logic extends existing interval temporal logic with a number of new features: actions, framing of actions, past operators, a projection-like operator called filter and a new handling of interval length. The notation is applied to the specification of the examples, and in particular a set of logical manipulations, providing feedback to an author, is presented. A model theory, logic and satisfaction relation are defined for the notation. 相似文献
117.
Leonidas Lymberopoulos Emil Lupu Morris Sloman 《Journal of Network and Systems Management》2003,11(3):277-303
This paper presents a framework for specifying policies for the management of network services. Although policy-based management has been the subject of considerable research, proposed solutions are often restricted to condition-action rules, where conditions are matched against incoming traffic flows. This results in static policy configurations where manual intervention is required to cater for configuration changes and to enable policy deployment. The framework presented in this paper supports automated policy deployment and flexible event triggers to permit dynamic policy configuration. While current research focuses mostly on rules for low-level device configuration, significant challenges remain to be addressed in order to:a) provide policy specification and adaptation across different abstraction layers; and, b) provide tools and services for the engineering of policy-driven systems. In particular, this paper focuses on solutions for dynamic adaptation of policies in response to changes within the managed environment. Policy adaptation includes both dynamically changing policy parameters and reconfiguring the policy objects. Access control for network services is also discussed. 相似文献
118.
In this paper a visual approach to querying in spatial databases is presented. A filter flow methodology is used to consistently express different types of queries in these systems. Filters are used to represent operations on the database and pictorial icons are used throughout the language for filters, operators and spatial relations. Different granularities of the relations are presented in a hierarchical fashion for spatial constraints. The language framework and functions are described and examples are used to demonstrate its capabilities in representing different levels of queries, including spatial joins and composite spatial joins. Here, the primary focus is on the query language itself but an overview of the implemented interface of the language is also provided. 相似文献
119.
Continuous cast (CC) AA5182 Al alloy with the precipitation of Mg2Al3 and of MnAl6 was cold rolled to 70% reduction and then isothermally annealed in a salt bath at three temperatures (316, 343, and 371 °C) for different times. Texture evolution during recrystallization was investigated. It was found that the recrystallization textures of the material with intense Mg2Al3 precipitation along the grain boundaries exhibited weaker Cube, Goss and R/β fiber components than those of the material with the more uniform fine MnAl6 precipitates. The opposite was true in the cold rolled condition, i.e. the material with MnAl6 precipitation had weaker Cube, Goss, and R/β fiber components in the cold rolled condition than the material with intense Mg2Al3 precipitation. Thus, recrystallization textures of material with Mg2Al3 precipitation were weaker than material with MnAl6 precipitation. This is due to the fact that large Mg2Al3 particles favor the nucleation of randomly oriented grains. When subjected to formability tests, the material with prior Mg2Al3 precipitation displayed a lower anisotropy in tensile yield strength, ultimate tensile strength, elongation, and strain hardening exponent than material with prior MnAl6 precipitation. This is in accord with the texture results which indicated that the recrystallization textures of material with an initial Mg2Al3 precipitation were closer to those of a perfectly random sample than those of material with an initial MnAl6 precipitation. On the other hand, the elongation and Olsen values were lower and the surface quality after bending tests was worse for material with Mg2Al3 precipitation. This is due to the non-uniform distribution of Mg2Al3 particles which precipitated primarily along the grain boundaries and caused an earlier formation and coalescence of the microvoids around the grain boundary precipitates. The forming limit diagrams (FLD) correlated well with the tensile, Olsen and bending results. 相似文献
120.
Silk Jennifer S.; Sessa Frances M.; Sheffield Morris Amanda; Steinberg Laurence; Avenevoli Shelli 《Canadian Metallurgical Quarterly》2004,18(1):135
This study explored the moderating effects of children's neighborhoods on the link between hostile parenting and externalizing behavior. Participants were 1st- or 2nd-grade children in an urban northeastern community. Children were administered the Parenting and Neighborhood scales of the Child Puppet Interview, and mothers completed questionnaires on neighborhood quality and parenting practices. Census tract measures of neighborhood quality and teachers' reports of children's externalizing behavior also were obtained. Results indicated that children's and mothers' perceptions of neighborhood involvement-cohesion buffered the link between hostile parenting and externalizing problems. Children's externalizing behavior was unrelated to census tract variables. Findings highlight the protective effect of neighborhood social cohesion and the utility of including young children's perspectives in research on neighborhoods and families. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献