首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3123篇
  免费   202篇
  国内免费   6篇
电工技术   33篇
化学工业   546篇
金属工艺   43篇
机械仪表   73篇
建筑科学   100篇
矿业工程   7篇
能源动力   90篇
轻工业   267篇
水利工程   30篇
石油天然气   7篇
无线电   304篇
一般工业技术   619篇
冶金工业   799篇
原子能技术   17篇
自动化技术   396篇
  2023年   32篇
  2022年   33篇
  2021年   84篇
  2020年   62篇
  2019年   92篇
  2018年   102篇
  2017年   77篇
  2016年   93篇
  2015年   73篇
  2014年   111篇
  2013年   167篇
  2012年   155篇
  2011年   214篇
  2010年   142篇
  2009年   134篇
  2008年   173篇
  2007年   151篇
  2006年   117篇
  2005年   96篇
  2004年   77篇
  2003年   65篇
  2002年   61篇
  2001年   27篇
  2000年   36篇
  1999年   46篇
  1998年   162篇
  1997年   101篇
  1996年   61篇
  1995年   53篇
  1994年   55篇
  1993年   58篇
  1992年   26篇
  1991年   18篇
  1990年   26篇
  1989年   31篇
  1988年   24篇
  1987年   18篇
  1986年   16篇
  1985年   15篇
  1984年   26篇
  1983年   20篇
  1982年   17篇
  1981年   11篇
  1980年   12篇
  1979年   17篇
  1978年   14篇
  1977年   20篇
  1976年   34篇
  1974年   10篇
  1971年   13篇
排序方式: 共有3331条查询结果,搜索用时 15 毫秒
1.
2.
Effects of mushroom type, seasoning and health benefit information (HBI) on consumers’ saltiness expectation, sensory liking, elicited emotions and purchase intent (PI) of extruded snacks were investigated. Five snacks were evaluated: straw mushroom (Volvariella volvacea) extrudates without (SME) or with seasoning (SMES), phoenix mushroom (Pleurotus pulmonarius) extrudates without (PME) or with seasoning (PMES), and the control without mushroom and seasoning. Hedonic scores and positive emotions were generally higher for seasoned mushroom-containing snacks (SMES and PMES) with 65% and 75.83% of consumers reporting willingness to purchase, respectively, after receiving HBI. Bored, interested and satisfied were identified as significant emotional predictors for PI odds. Flavour, saltiness, overall liking, bored, good and interested were critical attributes, differentiating snacks. This study demonstrated that sensory liking and PI of extruded brown rice-based snacks containing mushroom could be improved through savoury seasoning addition, which also allowed saltiness expectations to be met.  相似文献   
3.
In this paper, we first re-examine the previous protocol of controlled quantum secure direct communication of Zhang et al.’s scheme, which was found insecure under two kinds of attacks, fake entangled particles attack and disentanglement attack. Then, by changing the party of the preparation of cluster states and using unitary operations, we present an improved protocol which can avoid these two kinds of attacks. Moreover, the protocol is proposed using the three-qubit partially entangled set of states. It is more efficient by only using three particles rather than four or even more to transmit one bit secret information. Given our using state is much easier to prepare for multiqubit states and our protocol needs less measurement resource, it makes this protocol more convenient from an applied point of view.  相似文献   
4.
5.
A continuous phase quadrature phase shift keyed (CPQPSK) modulation technique is presented. This method utilizes a conventional QPSK modulator and a phase trajectory converter to approximate M=4, h=1/4 continuous phase signal and allows low cost, low complexity, and high rate (>1 Gbit/s) CPM modem implementation for bandwidth efficient transmission through nonlinear satellite channels. Using a communications analysis computer program it has been found that CPQPSK has 99 percent out-of-band power of 0.8R (MSK has 99 percent out-of-band power of 1.2 R where R is defined as bit rate), continuous phase trajectories, and nearly constant envelope amplitude. Simulation of realistic hardware designs indicate that the CPQPSK will require an Eb/No of 14 dB to achieve a bit error rate (BER) of 10-6. Forward error correcting techniques using block codes with an overhead of 10 percent indicate that the Eb/No requirements can be reduced to 11.2 dB for 10-6 BER  相似文献   
6.
In an experiment on the effects of different feedback conditions on motivationally relevant variables, R. Butler (see record 1988-21628-001) tested the hypothesis that the effects of feedback on intrinsic motivation would depend on whether that feedback promotes a task-involving or ego-involving orientation. She interpreted the findings as they relate to J. G. Nicholls's (see record 1984-28719-001) theory of task/ego involvement and our cognitive evaluation theory (E. L. Deci and R. M. Ryan, 1985). Although the data were very interesting, Butler failed to review a series of highly relevant studies, she misportrayed cognitive evaluation theory, and she drew conclusions that were not necessarily warranted given her experimental manipulations and data. This article provides a commentary on that research and presents a discussion of the relation between the two theories that Butler claimed to have tested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
7.
Plagiarism in the classroom has changed since the period of 1997 to 2002, during which the author saw predominately word-for-word plagiarism in papers in his classes. Some came from single sources, but more often they came from two or more. With that kind of plagiarism, it was fairly easy, although time-consuming, to detect copying. Most students engaging in such behaviors believed their professors knew little about the World Wide Web, and many believed that few, if any, professors spent the time needed to check for plagiarism. The development of widely available plagiarism-detection tools also helped raise awareness and make it easier to check papers against online sources.  相似文献   
8.
9.
The very late antigen-4 (VLA-4) integrin expressed on the surface of lymphocytes and macrophages can regulate their migration to inflammatory sites as well as control cellular activation. The role of VLA-4 in the establishment of autoimmune diabetes is not easily predicted given the multiplicity of adhesion pathways and their differential use by various cell types. The contribution of VLA-4 to insulin-dependent diabetes mellitus was investigated by administration of VLA-4-specific monoclonal antibodies (MoAb) in an adoptive transfer model of disease in NOD mice. This study shows that VLA-4-specific MoAbs profoundly inhibit the development of diabetes with protection sustained by repeated MoAb exposure. Insulitis was completely inhibited during treatment and progressed to a severe degree once MoAb treatment was suspended, yet approximately 40% of treated recipients failed to become diabetic during 1-2 months post-treatment. Although we cannot rule out depletion of a relatively minor subpopulation of cells by prolonged anti-VLA-4 MoAb exposure, this inhibition of diabetes onset by treatment with MoAbs to VLA-4 supports a dependence on VLA-4 for cellular functions leading to diabetes and demonstrates that a significant disease modifying effect can be mediated by targeting the VLA-4 integrin.  相似文献   
10.
Theoretical treatments forecast that bistable CMOS devices using electronic charge as a state variable will operate at their maximum thermal dissipation limit possibly as early as 2012. The problem is further compounded by increasing manufacturing challenges associated with the ever decreasing logic switch dimensions. These challenges require the development of new fabrication strategies that replace or complement current top-down lithography with bottom-up protocols using controlled self-assembly of nanomaterial building blocks. To answer some of these issues, this paper focuses on a new device paradigm consisting of an arene-metal-arene conformational switch, addressable through capacitive, inductive, or resonant-tunneling field coupling. The operating principle is based on voltage-tunable modulation in quantum electron transmission. The switch is open (off) when the metal ion is displaced to a position at a C-H bond on the arene ring due to an externally applied bias. Conversely, when the external bias is removed, the metal ion moves to an axis- symmetric position on the arene ring, and the switch is closed (on). The paper presents a summary of the architecture, operating principle, and advantages of the conformational switch, along with associated findings from proof-of-concept theoretical and experimental studies of its target specifications and performance. The paper also discusses opportunities and challenges related to the integration of conformational switches into hybrid CMOS-molecular and monolithic (all molecular) circuits.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号