全文获取类型
收费全文 | 4613篇 |
免费 | 121篇 |
国内免费 | 203篇 |
专业分类
系统科学 | 154篇 |
丛书文集 | 157篇 |
教育与普及 | 149篇 |
理论与方法论 | 17篇 |
现状及发展 | 20篇 |
研究方法 | 25篇 |
综合类 | 4414篇 |
自然研究 | 1篇 |
出版年
2024年 | 32篇 |
2023年 | 73篇 |
2022年 | 82篇 |
2021年 | 99篇 |
2020年 | 66篇 |
2019年 | 25篇 |
2018年 | 43篇 |
2017年 | 38篇 |
2016年 | 57篇 |
2015年 | 109篇 |
2014年 | 143篇 |
2013年 | 140篇 |
2012年 | 149篇 |
2011年 | 168篇 |
2010年 | 169篇 |
2009年 | 184篇 |
2008年 | 210篇 |
2007年 | 217篇 |
2006年 | 160篇 |
2005年 | 160篇 |
2004年 | 121篇 |
2003年 | 98篇 |
2002年 | 88篇 |
2001年 | 123篇 |
2000年 | 106篇 |
1999年 | 218篇 |
1998年 | 233篇 |
1997年 | 250篇 |
1996年 | 242篇 |
1995年 | 188篇 |
1994年 | 193篇 |
1993年 | 122篇 |
1992年 | 135篇 |
1991年 | 113篇 |
1990年 | 82篇 |
1989年 | 97篇 |
1988年 | 98篇 |
1987年 | 52篇 |
1986年 | 37篇 |
1985年 | 13篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有4937条查询结果,搜索用时 15 毫秒
991.
LIU ChenMing CAO HongBin LI YuPing ZHANG Yi 《科学通报(英文版)》2007,52(20):2771-2774
A novel quantitative electroanalysis method, triple potential step amperometry (TPSA), was developed and explained with an example of nitrobenzene analyzing in water. The selectivity of TPSA was im- proved by controlling the potential step within a narrow interval and using enzyme-modified electrode, the narrow potential step makes the method avoid most interferents, and enzyme-modified electrode can enhance the response of target substance selectively. The peak area was investigated for quanti- tative calibration, such as nitrobenzene concentration showing a linear relation with the peak area, with the correlation coefficients being 0.9995. The t-test and F-test were applied to evaluating the reliability of TPSA, the results showed that there was no evidence of systematic error for TPSA, and the method was of no significant difference from CV. The merit of fast detecting and few potential changing times make the TPSA suitably applicable to low-cost automatic monitoring equipments. 相似文献
992.
This paper investigates the semi-online scheduling problem with the known largest size on two uniform machines. The objective is to maximize the minimum machine completion time. Both lower bounds and algorithms are given. Algorithms are optimal for the majority values of s≥1, where s is the speed ratio of the two machines. The largest gap between the competitive ratio and the lower bound is about 0.064. Moreover, the overall competitive ratio 2 matches the overall lower bound. 相似文献
993.
It is an urgent project to realize online and overall condition monitoring and timely fault diagnosis for large-scale mobile and complex equipment. Moreover, most of the existing large-scale complex equipment has quite insufficient accessibility of examination, although it still has quite a long service life. The decentralized and overall condition monitoring, as a new concept, is proposed from the point of view of the whole system. A set of complex equipment is divided into several parts in terms of concrete equipment. Every part is processed via one detecting unit, and the main detecting unit is connected with other units. The management work and communications with the remote monitoring center have been taken on by it. Consequently, the difficulty of realizing a condition monitoring system and the complexity of processing information is reduced greatly. Furthermore, excellent maintainability of the condition monitoring system is obtained because of the modularization design. Through an application example, the design and realization of the decentralized and overall condition monitoring system is introduced specifically. Some advanced technologies, such as, micro control unit (MCU), advanced RISC machines (ARM), and control area network (CAN), have been adopted in the system. The system's applicability for the existing large-scale mobile and complex equipment is tested. 相似文献
994.
价格测算模型解的存在性定理曹国钧,王健(重庆医药设计院630000)(渝州大学数学系)ATheoremforExistenceoftheSolutiononPriceEstimateModelCaoGuojunWangJian(ChongQingPh... 相似文献
995.
Fe_2O_3型固体超强酸在酯化反应中显示出与浓硫酸相近的催化活性,但具有易与产物分离、腐蚀作用小、污染程度轻和可重复使用的优点。本文考察了Fe_2O_3型固体超强酸在乙酸异戊酯合成反应中的摧化活性,结果表明,最佳催化剂用量为Fe_2O_3型固体超强酸占总投料量的2%,最优反应时间为2h,此时异戊醇的转化率可达94%。 相似文献
996.
本文分析了用SAP5P进行轮式装载机结构件强度分析与可靠性分析的条件,讨论了计算中可能出现的问题,对计算模型的建立,各类部件单元的选取,计算结果的数据处理、应力分布和强度分布函数的确定和选择等提出了一套可行的方法,有很高的实用价值。 相似文献
997.
998.
曹建国 《上海理工大学学报》1986,(1)
本文分析了三维效应对平面光弹技术测量精度的影响,并以阿朋(Aben)的偏振光在光弹性体中传播的三维理论为基础,提出了平面光弹的“准平面”特征以及平面光弹的“准平面”点测法。此方法消除了三维效应所导致的测量误差,提高了测量精度。实验证明新方法是可行的。 相似文献
999.
用表面增强拉曼散射技术研究单晶硅表面键合光敏染料,可获得信噪比强的SERS图。因染料分子中含有孤对电子的氮原子和起增强作用的银离子相互作用,使Ag+成为连结染料分子间的锁,增加染料分子极化率,使拉曼散射截面积增大,从而起到增强效果的作用。 相似文献
1000.
应用X射线单晶衍射法测定了α-邻卤(F,Cl)代苯基二茂铁甲醇C_5H_5FeC_5H_4CH(OH)C_6H_4X(X=F,Cl)(Ⅰ)及其与丙烯腈的氰乙基化反应产物:α-二茂铁基邻卤(F,Cl)苄基-β-氰乙基醚C_5H_5FeC_5H_4CH(OCH_2CH_2CN)C_6H_4X(X=F,Cl)(Ⅱ)的晶体结构。描述并讨论了(Ⅰ)和(Ⅱ),氟原子和氯原子的变更所引起的分子结构变化,结果表明,取代卤原子(F,Cl)的不同,导致后一种化合物出现两种分子构型。 相似文献