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   315558篇
  免费   5242篇
  国内免费   1344篇
电工技术   5688篇
综合类   1307篇
化学工业   48962篇
金属工艺   10974篇
机械仪表   9876篇
建筑科学   9325篇
矿业工程   1249篇
能源动力   8113篇
轻工业   31873篇
水利工程   2897篇
石油天然气   3078篇
武器工业   18篇
无线电   40892篇
一般工业技术   57801篇
冶金工业   54317篇
原子能技术   3989篇
自动化技术   31785篇
  2022年   4603篇
  2021年   6171篇
  2020年   4590篇
  2019年   5716篇
  2018年   4188篇
  2017年   3690篇
  2016年   3793篇
  2015年   2991篇
  2014年   4633篇
  2013年   13789篇
  2012年   8253篇
  2011年   12461篇
  2010年   9556篇
  2009年   10561篇
  2008年   10498篇
  2007年   10466篇
  2006年   9788篇
  2005年   8956篇
  2004年   9751篇
  2003年   9459篇
  2002年   9001篇
  2001年   8913篇
  2000年   7623篇
  1999年   7914篇
  1998年   17684篇
  1997年   12424篇
  1996年   9404篇
  1995年   7296篇
  1994年   6574篇
  1993年   6247篇
  1992年   4611篇
  1991年   4203篇
  1990年   4057篇
  1989年   3978篇
  1988年   3761篇
  1987年   3009篇
  1986年   3017篇
  1985年   3663篇
  1984年   3147篇
  1983年   3011篇
  1982年   2775篇
  1981年   2728篇
  1980年   2460篇
  1979年   2328篇
  1978年   2236篇
  1977年   2588篇
  1976年   3099篇
  1975年   1920篇
  1974年   1745篇
  1973年   1733篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Clean Technologies and Environmental Policy - Food production and consumption is one of the major causes of global environmental degradation. One way to address environmental impacts in the food...  相似文献   
2.
ABSTRACT

Bacteriocin is a proteinaceous biomolecule produced by bacteria (both Gram-positive and Gram-negative) that exhibits antimicrobial activity against closely related species, and food-borne pathogens. It has recently gained importance and attracted the attention of several researchers looking to produce it from various substrates and bacterial strains. This ushers in a new era of food preservation where the use of bacteriocin in food products will be an alternative to chemical preservatives, and heat treatment which are understood to cause unwanted side effects, and reduce sensory and nutritional quality. However, this new market depends on the success of novel downstream separation schemes from various types of crude feedstocks which are both effective and economic. This review focuses on the downstream separation of bacteriocin from various sources using both conventional and novel techniques. Finally, recommendations for future interesting areas of research that need to be pursued are highlighted.  相似文献   
3.
Abstract

This article discusses different approaches to materiality and material expressions of cultural identity in contemporary Bahrain, a small Arab Gulf state. Various Islamic traditions have different understandings of materiality and its ontological qualities. In the contemporary Gulf this difference is often understood as a sectarian difference between Sunni and Shia Muslims, a division that has gained increasing political importance in recent years. In this article I discuss how these traditions view materiality in religion, in particular focusing on the role of material mediation for Shia Muslims, exemplified by the use and meaning of the turba prayer stone. With this as a point of departure I discuss two other forms of materiality—political graffiti and martyr images—that in the wake of the uprising in 2011 have also been imbued with sectarian meanings, but where this is less clear. I therefore argue that vernacular understandings of material culture show ambiguous identifications that challenge the clear dichotomies with which people—locally and analytically —often operate.  相似文献   
4.
5.
6.

Stability constants and formation enthalpies of supramolecular complexes of crown ethers and their cyclic and acyclic analogues are determined on the basis of experimental data obtained by different physicochemical methods in the terms of a general approach developed and implemented in the ChemEqui software package. The established regularities of variation of stability of complexes are discussed as dependent on the ligand structure, nature of the cation, solvent, and anion. The applicability of the suggested method of determining complexation selectivity is shown for multicomponent equilibria in solutions.

  相似文献   
7.
8.
Cable‐shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable‐shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable‐shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil‐type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical‐electrochemical stability. The CASECs show excellent charge–discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm−3), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets.  相似文献   
9.

To increase the efficiency of designing systems intended for monitoring surface cracks in aluminum structures during their working life, we have analyzed a two-dimensional symmetric problem on uniaxial extension of an Al-polyimide-Cu layered structure with ideal adhesion between layers and a model crack in the aluminum base. The problem has been first solved for a sample with the crack modeled by a zero-thickness notch using the ANSYS engineering simulation program package. It is shown that this setting of the problem can lead to inadequate results as manifested, in particular, by significantly overstated mechanical stresses in aluminum in the region of crack emergence on the surface. In order to eliminate this difficulty, we propose to use the structure with a model defect in the form of a notch of nonzero thickness in the initial unstressed state of the structure. Recommendations for selecting the thickness of a notch used in the model structure are given.

  相似文献   
10.
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