全文获取类型
收费全文 | 139655篇 |
免费 | 15782篇 |
国内免费 | 10477篇 |
专业分类
电工技术 | 11982篇 |
技术理论 | 2篇 |
综合类 | 14262篇 |
化学工业 | 18386篇 |
金属工艺 | 8958篇 |
机械仪表 | 10165篇 |
建筑科学 | 10997篇 |
矿业工程 | 5594篇 |
能源动力 | 3657篇 |
轻工业 | 15084篇 |
水利工程 | 4119篇 |
石油天然气 | 5068篇 |
武器工业 | 2088篇 |
无线电 | 15052篇 |
一般工业技术 | 12338篇 |
冶金工业 | 5736篇 |
原子能技术 | 2120篇 |
自动化技术 | 20306篇 |
出版年
2024年 | 914篇 |
2023年 | 2565篇 |
2022年 | 5657篇 |
2021年 | 7363篇 |
2020年 | 5315篇 |
2019年 | 3703篇 |
2018年 | 4067篇 |
2017年 | 4794篇 |
2016年 | 4151篇 |
2015年 | 6463篇 |
2014年 | 8221篇 |
2013年 | 9526篇 |
2012年 | 11612篇 |
2011年 | 11942篇 |
2010年 | 11264篇 |
2009年 | 10510篇 |
2008年 | 10601篇 |
2007年 | 10311篇 |
2006年 | 8766篇 |
2005年 | 7065篇 |
2004年 | 5041篇 |
2003年 | 3463篇 |
2002年 | 3250篇 |
2001年 | 2766篇 |
2000年 | 2429篇 |
1999年 | 1258篇 |
1998年 | 517篇 |
1997年 | 463篇 |
1996年 | 410篇 |
1995年 | 312篇 |
1994年 | 230篇 |
1993年 | 198篇 |
1992年 | 145篇 |
1991年 | 114篇 |
1990年 | 84篇 |
1989年 | 102篇 |
1988年 | 62篇 |
1987年 | 33篇 |
1986年 | 28篇 |
1985年 | 18篇 |
1984年 | 30篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 22篇 |
1980年 | 38篇 |
1979年 | 21篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1959年 | 19篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
对天津及其滨海新区生态城市水利建设进行了分析。研究了在淡水资源极度匮乏的条件下,有效开发利用非常规水资源的必要性、重要性和现实性。认为天津市对水资源应遵循节水、治污、高效配置,妥善处理生活、生产、生态之间的关系,力求平衡调配。供水水源应是多元的,增加非常规水资源(污水、海/咸水、雨/洪水)的利用,同时增加可用地下水,外调来水等,逐步进入可持续发展配置。 相似文献
22.
A powerful concept to cope with resource limitations and information redundancy in wireless sensor networks is the use of collaboration groups to distill information within the network and suppress unnecessary activities. When the phenomena to be monitored have large geographical extents, it is not obvious how to define these collaboration groups. This article presents the application of geometric duality to form such groups for sensor selection and non-local phenomena tracking. Using a dual-space transformation, which maps a non-local phenomenon (e.g., the edge of a half-plane shadow) to a single point in the dual space and maps locations of distributed sensor nodes to a set of lines that partitions the dual space, one can turn off the majority of the sensors to achieve resource preservation without losing detection and tracking accuracy. Since the group so defined may consist of nodes that are far away in physical space, we propose a hierarchical architecture that uses a small number of computationally powerful nodes and a massive number of power constrained motes. By taking advantage of the continuity of physical phenomena and the duality principle, we can greatly reduce the power consumption in non-local phenomena tracking and extend the lifetime of the network. 相似文献
23.
本文通过测定甲酸铀酰[UO_2(HCOO)_2·H_2O]在290K-10K的红外光谱,确定了该化合物铀酰基团(O-U-O)v_(as)振动峰位,研究了温度对峰宽、峰位的影响,并采用差减及峰内标法估算了甲酸铀酰在290K-10K的同位素位移值。测得290K,77K及10K时~(238)U的v_(as)值分别为931.90cm~(-1),930.82cm~(-1)和930.74cm~(-1),~(235)U-~(238)U同位素位移△v分别为0.63cm~(-1),0.67±0.18cm~(-1)和0.71±0.21cm~(-1),位移值与理论计算值接近。 相似文献
24.
加强电炉钢短流程生产工艺研究与技术开发的建议 总被引:1,自引:0,他引:1
论述了加强电炉钢短流程生产工艺研究与技术开发的必要性和主要课题,并提出关于组织合金钢短流程生产工艺研究与技术开发“九五”国家科技攻关及提高高研究开发投资强度的建议。 相似文献
25.
人类聚居环境学对于居住区规划设计的启示 总被引:1,自引:0,他引:1
以人类聚居环境学的研究方法从若干方面对目前的居住区规划设计进行了一定的探讨,分析规划设计及建设方面目前存在的主要问题,提出以人类聚居环境学为指导的居住区规划设计理念。 相似文献
26.
27.
A simple method has been devised for immobilization of acetylcholinesterase (AChE) covalent bonding to a multiwall carbon
nanotube (MWNT)-cross-linked cellulose acetate composite on a screen-printed carbon electrode (SPCE) and a sensitive and disposable
amperometric sensor for rapid determination of carbaryl pesticide is proposed. The immobilized enzyme was preserved on this
film because of the excellent biocompatibility and non-toxicity of cellulose acetate. Based on the inherent conductive properties
of the MWNT, the immobilized AChE had greater affinity for ATCl and excellent catalytic effect in the hydrolysis of ATCl.
MWNT improved the interface enzymatic hydrolysis reaction and increased the amperometric response of the sensor. Under optimum
conditions, the inhibition of carbaryl on AChE increased linearly with the increasing concentration of carbaryl in two ranges,
from 0.01 to 0.5 μg mL−1 and from 2 to 20 μg mL−1, with the correlation coefficients of 0.9985 and 0.9977, respectively. The detection limit was 0.004 μg mL−1 taken as the concentration equivalent to 10% decrease in signal. The sensor showed acceptable stability, accuracy and could
be fabricated in batches, thus it is economic and portable. This type of disposable enzyme-based amperometric sensor has extensive
application potential in environmental monitoring of pesticides. 相似文献
28.
Ching‐Nan Chuang Liang Chao Ying‐Jie Huang Tar‐Hwa Hsieh Hung‐Yi Chuang Shu‐Chi Lin Ko‐Shan Ho 《应用聚合物科学杂志》2008,107(6):3917-3924
The synthesis of a p‐toluidine/formaldehyde (PTF) resin was performed, and the effects of the molar ratio of the individual monomers and the polymerization conditions on the structure of the PTF resin were studied. Fourier transform infrared and 13C‐NMR spectra were used to characterize the PTF. Wide‐angle X‐ray diffraction patterns revealed the crystalline structures of various PTFs. Polarized optical microscopy revealed that the molar ratio of the monomers had a strong effect on the crystalline morphologies. A longer polymerization time turned out a polymer with a higher intrinsic viscosity and molecular weight, which led to differences in the proton conductivity. All of the PTFs showed a higher proton conductivity than a commercial Nafion membrane at 90–100°C and 0% relative humidity. The proton conductivity of the PTF series could be improved by sulfonation with sulfuric acid and could be maintained after blending with polyurethane. Pure methanol could be used as a fuel source because of the insolubility and nonwetting properties of PTF in methanol to increase the output current density for a PTF membrane electrode assembly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
29.
30.