全文获取类型
收费全文 | 103742篇 |
免费 | 1658篇 |
国内免费 | 453篇 |
专业分类
电工技术 | 1014篇 |
综合类 | 2339篇 |
化学工业 | 15523篇 |
金属工艺 | 5216篇 |
机械仪表 | 3425篇 |
建筑科学 | 3131篇 |
矿业工程 | 665篇 |
能源动力 | 1806篇 |
轻工业 | 5326篇 |
水利工程 | 1437篇 |
石油天然气 | 423篇 |
无线电 | 10777篇 |
一般工业技术 | 19767篇 |
冶金工业 | 6355篇 |
原子能技术 | 381篇 |
自动化技术 | 28268篇 |
出版年
2023年 | 132篇 |
2022年 | 239篇 |
2021年 | 384篇 |
2020年 | 287篇 |
2019年 | 306篇 |
2018年 | 14763篇 |
2017年 | 13665篇 |
2016年 | 10347篇 |
2015年 | 962篇 |
2014年 | 767篇 |
2013年 | 1506篇 |
2012年 | 3991篇 |
2011年 | 10569篇 |
2010年 | 9076篇 |
2009年 | 6383篇 |
2008年 | 7715篇 |
2007年 | 8626篇 |
2006年 | 913篇 |
2005年 | 1970篇 |
2004年 | 1748篇 |
2003年 | 1728篇 |
2002年 | 1098篇 |
2001年 | 464篇 |
2000年 | 513篇 |
1999年 | 408篇 |
1998年 | 483篇 |
1997年 | 374篇 |
1996年 | 426篇 |
1995年 | 350篇 |
1994年 | 339篇 |
1993年 | 306篇 |
1992年 | 302篇 |
1991年 | 207篇 |
1990年 | 254篇 |
1989年 | 231篇 |
1988年 | 211篇 |
1987年 | 190篇 |
1986年 | 177篇 |
1985年 | 218篇 |
1984年 | 218篇 |
1983年 | 182篇 |
1982年 | 193篇 |
1981年 | 184篇 |
1980年 | 158篇 |
1979年 | 181篇 |
1978年 | 143篇 |
1977年 | 137篇 |
1976年 | 184篇 |
1975年 | 137篇 |
1973年 | 123篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Friendship affects individual and organizational well-being through direct relations, social positions, and complex network structures. In this study, the authors use longitudinal data from 2 groups of master's of business administration students to increase understanding of how friendship networks develop. The authors propose and test a dynamic model in which attribute similarity facilitates dyadic friendship ties, as well as similar network centrality and social position; early friendship increases later similarity in structural position and centrality; and early structural similarity enhances the likelihood of future friendship. Findings largely supported the model, demonstrating how homophily and early social contacts can jointly shape maturing friendship networks. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
92.
A fully-dense Cu-75 vol pct ZrW2O8 metal matrix composite was fabricated by hot isostatic pressing of Cu-coated ZrW2O8 particles. A small amount of the high-pressure γ-ZrW2O8 phase was created during the cooldown and depressurization following densification; near complete transformation to γ-ZrW2O8 was achieved by subsequent cold isostatic pressing. The thermal expansion behavior of the composite between 25°C and 325°C
was altered by the cold isostatic pressing treatment, and also depended on the length of time that had passed between thermal
cycles. The measured thermal expansion coefficients within specific temperature ranges varied from −6·10−6 K−1 to far above the thermal expansion coefficient of the copper matrix. The complex temperature-dependent expansion/contraction
behavior could be justified by considering the evolution of phase transformations taking place in the ZrW2O8 phase, which were observed by in-situ synchrotron X-ray diffraction measurements. 相似文献
93.
Nicolas Clauvelin Basile Audoly Sébastien Neukirch 《Scientific Modeling and Simulation》2007,14(1):95-101
The DNA molecule is modeled as an elastic rod with bending and twisting rigidities, subjected to external tension and twist applied at one end, the other end being clamped. We study the plectonemic equilibrium of such a rod, taking into account the impenetrability constraint. Numerical solutions of this boundary value problem have previously shown that purely elastic models can reproduce the supercoiling response of the DNA molecule. Using a variational approach, we derive analytical formulae for the elastic response of the filament, and extend former numerical results. 相似文献
94.
95.
Like any other domain of human activity, psychology has its fads and fashions. One consequence of fads is an overconcentration of resources on specific problems or approaches, which leaves other important problems or approaches (holes) underappreciated and understudied. This article is primarily about different factors (such as negativity bias, polarization of positions, focus on internal causes of behavior, dedication to a narrow view of what science is) that result in holes and about explorations of some of these holes that have interested the author. Psychologists should look more in the holes left behind by current enthusiasms. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
96.
Learning Organizations in Construction 总被引:1,自引:0,他引:1
The transformation of organizations from production-oriented entities to proactive learning entities that continuously leverage the knowledge of the workforce is a primary objective of management researchers. This focus has significant relevance to the construction industry where production-related research has predominantly overshadowed organizational development research. As one effort to change this emphasis, the writers present a research effort designed to study current organization learning techniques and technologies fielded by organizations both inside and outside of the construction industry. Through a series of exploratory case studies, the writers developed a maturity model together with the Construction Industry Institute that provides construction organizations with a framework for developing a learning organization culture. The maturity model focuses on learning organization characteristics of leadership, processes and infrastructure, communication/collaboration, education, and culture at the organization, community, and individual levels. This paper introduces the results of that effort including a presentation of the learning organization maturity model, framework application, and the overall characteristics of a learning organization. 相似文献
97.
98.
We show new upper bounds for problems in the W-hierarchy of fixed-parameter complexity. A crucial ingredient of our proofs
is an extension to the W-RAM model, which permits more-powerful operations but remains equivalent to the original. We use
the extended model to give new upper bounds for Subsetsum, Maximum Irredundant Set, and various problems concerning intersection
of finite-state machines. 相似文献
99.
Daniel Meister 《Theory of Computing Systems》2007,41(2):257-289
A finite recurrent system over sets of natural numbers of dimension n is a pair composed of n n-ary functions over sets of
natural numbers and an n-tuple of singleton sets of natural numbers. Every function is applied to the entries of the tuple
and computes a set of natural numbers, that may also be empty. The results are composed into another tuple, and the process
is started anew. Thus, a finite recurrent system defines an infinite sequence of n-tuples containing sets of natural numbers.
The last entry of a generated n-tuple is called the output of a step, and the union of the output sets of all steps is the
set defined by the finite recurrent system. Membership problems ask whether a given number is in a specified output set or
in some output set. We study membership problems for special finite recurrent systems, whose functions are built from the
set operations union, intersection and complementation and the arithmetical operations addition and multiplication. Sum and
product of two sets of natural numbers are defined elementwise. We restrict the set of operations from which functions are
built and determine the impact on the complexity of the membership problems. We focus on PSPACE-decidable membership problems
and show completeness results for the complexity classes NL, NP and PSPACE. 相似文献
100.
Dynamic complexity investigates the required effort to maintain knowledge about a property of a structure under changing operations.
This article introduces a refined notion of dynamic problems which takes the initial structure into account. It develops the
basic structural complexity notions accordingly. It also shows that the dynamic version of the LOGCFL-complete problem D2LREACH(acyclic) can be maintained with first-order updates. 相似文献