全文获取类型
收费全文 | 458617篇 |
免费 | 43355篇 |
国内免费 | 23959篇 |
专业分类
电工技术 | 24528篇 |
技术理论 | 53篇 |
综合类 | 48588篇 |
化学工业 | 68392篇 |
金属工艺 | 32517篇 |
机械仪表 | 23975篇 |
建筑科学 | 51145篇 |
矿业工程 | 19421篇 |
能源动力 | 19641篇 |
轻工业 | 27849篇 |
水利工程 | 16379篇 |
石油天然气 | 17547篇 |
武器工业 | 4513篇 |
无线电 | 43527篇 |
一般工业技术 | 51782篇 |
冶金工业 | 25696篇 |
原子能技术 | 5811篇 |
自动化技术 | 44567篇 |
出版年
2024年 | 1131篇 |
2023年 | 5872篇 |
2022年 | 10152篇 |
2021年 | 14319篇 |
2020年 | 12925篇 |
2019年 | 11074篇 |
2018年 | 10776篇 |
2017年 | 13296篇 |
2016年 | 15683篇 |
2015年 | 17155篇 |
2014年 | 27130篇 |
2013年 | 26262篇 |
2012年 | 30619篇 |
2011年 | 32235篇 |
2010年 | 25118篇 |
2009年 | 25930篇 |
2008年 | 23935篇 |
2007年 | 31337篇 |
2006年 | 29520篇 |
2005年 | 25780篇 |
2004年 | 21730篇 |
2003年 | 19361篇 |
2002年 | 16169篇 |
2001年 | 13382篇 |
2000年 | 11341篇 |
1999年 | 9029篇 |
1998年 | 7031篇 |
1997年 | 6133篇 |
1996年 | 5554篇 |
1995年 | 4674篇 |
1994年 | 4122篇 |
1993年 | 3173篇 |
1992年 | 2763篇 |
1991年 | 2067篇 |
1990年 | 1777篇 |
1989年 | 1497篇 |
1988年 | 1092篇 |
1987年 | 737篇 |
1986年 | 578篇 |
1985年 | 503篇 |
1984年 | 509篇 |
1983年 | 362篇 |
1982年 | 336篇 |
1981年 | 225篇 |
1980年 | 210篇 |
1979年 | 138篇 |
1978年 | 79篇 |
1977年 | 87篇 |
1962年 | 93篇 |
1959年 | 101篇 |
排序方式: 共有10000条查询结果,搜索用时 288 毫秒
41.
为研究金针菇多糖(polysaccharide from Flammulina velutipes,FVP)对微冻大黄鱼及鱼片在贮藏期间肌原纤维蛋白性质的变化及水分分布的影响,实验分别选用0.03、0.06、0.09 g/L FVP浸渍处理大黄鱼和鱼片,以无菌水处理为对照组,分析微冻贮藏期间样品的感官指标得分、总挥发性盐基氮含量、总巯基含量、Ca2+-ATPase活性、蛋白流变学性质以及水分迁移变化规律。结果表明:FVP可有效抑制整鱼总挥发性盐基氮含量上升和感官得分的下降;减缓整鱼及鱼片在微冻过程中总巯基含量、Ca2+-ATPase活性下降和水分流失;此外FVP还能够延缓大黄鱼因腐败而出现的蛋白凝胶能力减弱。在本实验选取的多糖浓度范围内,0.09 g/L FVP处理组保鲜效果较强。该研究结果可为FVP用于水产品贮运保鲜提供理论参考。 相似文献
42.
43.
44.
An electrolyte Equation of State is presented by combining the Cubic Plus Association Equation of State,Mean Spherical Approximation and the Born equation.This new model uses experimental relative static permittivity,intend to predict well the activity coefficients of individual ions (ACI) and liquid densities of aqueous solutions.This new model is applied to model water + NaCl binary system and water + gas +NaCl ternary systems.The cation/anion-water interaction parameters of are obtained by fitting the exper-imental data of ACI,mean ionic activity coefficients (MIAC) and liquid densities of water + NaCl binary system.The cation/anion-gas interaction parameters are obtained by fitting the experimental data of gas solubilities in aqueous NaCl solutions.The modeling results show that this new model can correlate well with the phase equilibrium and volumetric properties.Without gas,predictions for ACI,MIAC,and liquid densities present relative average deviations of 1.3%,3.6% and 1.4% compared to experimental ref-erence values.For most gas-containing systems,predictions for gas solubilities present relative average deviations lower than 7.0%.Further,the contributions of ACI,and salting effects of NaCl on gases are ana-lyzed and discussed. 相似文献
45.
46.
Jiangyou Long Qingfa Peng Gaopan Chen Yuliang Zhang Xiaozhu Xie Guoshun Pan Xiaofeng Wang 《Ceramics International》2021,47(16):23134-23143
Femtosecond (fs) lasers have been proved to be reliable tools for high-precision and high-quality micromachining of ceramic materials. Nevertheless, fs laser processing using a single-mode beam with a Gaussian intensity distribution is difficult to obtain large-area flat and uniform processed surfaces. In this study, we utilize a customized diffractive optical element (DOE) to redistribute the laser pulse energy from Gaussian to square-shaped Flat-Top profile to realize centimeter-scale low-damage micromachining on single-crystal 4H–SiC substrates. We systematically investigated the effects of processing parameters on the changes in surface morphology and composition, and an optimal processing strategy was provided. Mechanisms of the formation of surface nanoparticles and the removal of surface micro-burrs were discussed. We also examined the distribution of subsurface defects caused by fs laser processing by removing a thin surface layer with a certain depth through chemical mechanical polishing (CMP). Our results show that laser-induced periodic surface structures (LIPSSs) covered by fine SiO2 nanoparticles form on the fs laser-processed areas. Under optimal parameters, the redeposition of SiO2 nanoparticles can be minimized, and the surface roughness Sa of processed areas reaches 120 ± 8 nm after the removal of a 10 μm thick surface layer. After the laser processing, micro-burrs on original surfaces are effectively removed, and thus the average profile roughness Rz of 2 mm long surface profiles decreases from 920 ± 120 nm to 286 ± 90 nm. No visible micro-pits can be found after removing ~1 μm thick surface layer from the laser-processed substrates. 相似文献
47.
Cell surface and secreted proteins provide essential functions for multicellular life. They enter the endoplasmic reticulum (ER) lumen co-translationally, where they mature and fold into their complex three-dimensional structures. The ER is populated with a host of molecular chaperones, associated co-factors, and enzymes that assist and stabilize folded states. Together, they ensure that nascent proteins mature properly or, if this process fails, target them for degradation. BiP, the ER HSP70 chaperone, interacts with unfolded client proteins in a nucleotide-dependent manner, which is tightly regulated by eight DnaJ-type proteins and two nucleotide exchange factors (NEFs), SIL1 and GRP170. Loss of SIL1′s function is the leading cause of Marinesco-Sjögren syndrome (MSS), an autosomal recessive, multisystem disorder. The development of animal models has provided insights into SIL1′s functions and MSS-associated pathologies. This review provides an in-depth update on the current understanding of the molecular mechanisms underlying SIL1′s NEF activity and its role in maintaining ER homeostasis and normal physiology. A precise understanding of the underlying molecular mechanisms associated with the loss of SIL1 may allow for the development of new pharmacological approaches to treat MSS. 相似文献
48.
The effect of the emergency perception of bystanders of cyberbullying victims on helping behaviors is often neglected in research on cyberbullying. In this study, we explored the influence of this cognitive factor on cyber-bystanders’ helping tendencies as well as elucidated possible underlying processes. The results of two studies were reported. In Study 1, 150 undergraduates read a true case of a girl experiencing cyberbullying. The results indicated that when the participants perceived the victim’s situation to be more critical (i.e., higher emergency perception), their helping tendencies were stronger, partly through increased state empathy followed by feelings of responsibility to help. In Study 2, we randomly assigned 300 undergraduates to two groups. The low emergency group read the same cyberbullying case as Study 1, whereas the cyberbullying case read by the high emergency group contained additional emergency information of the victim. The results indicated that the high emergency group expressed stronger helping tendencies than did the low emergency group. This effect was caused by a stronger perception that the victim was in an emergency situation, which not only strengthened the participants’ helping tendencies directly but also indirectly through increasing their state empathy and feelings of responsibility to help. 相似文献
49.
Narrow linewidth light source is a prerequisite for high-performance coherent optical communication and sensing.Waveguide-based external cavity narrow linewidth semiconductor lasers(WEC-NLSLs)have become a competitive and attractive candidate for many coherent applications due to their small size,volume,low energy consumption,low cost and the ability to integrate with other optical components.In this paper,we present an overview of WEC-NLSLs from their required technologies to the state-of-the-art progress.Moreover,we highlight the common problems occurring to current WEC-NLSLs and show the possible approaches to resolving the issues.Finally,we present the possible development directions for the next phase and hope this review will be beneficial to the advancements of WEC-NLSLs. 相似文献
50.