全文获取类型
收费全文 | 11951篇 |
免费 | 1058篇 |
国内免费 | 489篇 |
专业分类
化学 | 1131篇 |
晶体学 | 34篇 |
力学 | 333篇 |
综合类 | 107篇 |
数学 | 343篇 |
物理学 | 1517篇 |
无线电 | 10033篇 |
出版年
2024年 | 47篇 |
2023年 | 112篇 |
2022年 | 285篇 |
2021年 | 514篇 |
2020年 | 470篇 |
2019年 | 164篇 |
2018年 | 163篇 |
2017年 | 469篇 |
2016年 | 557篇 |
2015年 | 507篇 |
2014年 | 831篇 |
2013年 | 735篇 |
2012年 | 801篇 |
2011年 | 772篇 |
2010年 | 608篇 |
2009年 | 631篇 |
2008年 | 754篇 |
2007年 | 819篇 |
2006年 | 794篇 |
2005年 | 653篇 |
2004年 | 603篇 |
2003年 | 526篇 |
2002年 | 386篇 |
2001年 | 294篇 |
2000年 | 200篇 |
1999年 | 151篇 |
1998年 | 123篇 |
1997年 | 82篇 |
1996年 | 72篇 |
1995年 | 103篇 |
1994年 | 76篇 |
1993年 | 43篇 |
1992年 | 35篇 |
1991年 | 41篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 4篇 |
1986年 | 10篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
171.
CaO和NaCl焙烧混合稀土精矿过程中的分解反应 总被引:5,自引:0,他引:5
用XRD和TG-DTA热分析技术, 研究了含独居石和氟碳铈镧矿的混合稀土精矿在100~1000 ℃焙烧过程中, 添加CaO, NaCl时, REPO4和REFCO3的分解反应. 研究结果表明: 不添加CaO和NaCl时, 仅在377~450 ℃范围内存在REFCO3的分解反应, 其产物是REOF, RE2O3, 以及Ce2O3进一步的氧化产物CeO2, 而REPO4不分解; 添加CaO后在660~750 ℃之间, CaO有3种分解作用: (1) CaO分解REPO4, 其产物是RE2O3和Ca3(PO4)2. (2) CaO分解REOF, 其产物是RE2O3和CaF2. (3) CaO和REOF的分解产物CaF2共同作用分解REPO4, 其分解产物为RE2O3, Ca5F(PO4)3; 添加CaO, NaCl后, 混合精矿的分解率明显提高, NaCl的作用是为反应体系提供了液相, 促进了固相反应物间的传质过程, 加快了反应速度. 与此同时NaCl还可能参加了CaO分解REPO4的反应. 相似文献
172.
Guryca V Pacáková V Tlust'áková M Stulík K Michálek J 《Journal of separation science》2004,27(13):1121-1129
Topography and thickness of hydrophilic polymer coatings of fused-silica capillaries for capillary electrophoresis (CE) were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), and profilometry. Three hydrogels, poly(2-hydroxyethyl methacrylate) [poly(HEMA)], poly(diethylene glycol monomethacrylate) [poly(DEGMA)], and poly(triethylene glycol monomethacrylate) [poly(TEGMA)], were deposited using two procedures, either by simple physical sorption of the polymers, or by derivatization of the capillary wall surface with glycidyl methacrylate (EPMA) followed by polymerization of the appropriate monomers. The performance of the modified capillaries was tested under CE conditions (decrease in the electroosmotic flow, EOF dependence on pH, separation of milk and standard proteins). It has been found that the most important property of the polymer coating is its thickness, whereas its topography and the degree of its hydrophobicity are less significant. Film deposition by physical adsorption is preferable to polymerization on the derivatized surface. 相似文献
173.
A laboratory information management system (LIMS) can make a major contribution to the quality and therefore to the efficiency
and competitiveness of a laboratory. Since it can impact all aspects of a laboratory's organization it must be the key if
not the principal player of the laboratory's quality system. It should support the laboratory in establishing, maintaining
and applying quality procedures thereby enabling the laboratory to achieve its quality goals. As a tool, LIMS permits the
laboratory to input and use its own know-how and experience to optimize the total organization (internal and external) and
workflow of generated information. However, perceived "quality" in the context of an LIMS, can be viewed as being made up
of different facets such as the security, reliability and accessibility of information as well as its turn around time and
production cost. This paper reviews the role of a LIMS in the laboratory and the contribution that both system design and
functionality can have on "building quality ".
Received: 5 October 1998 · Accepted: 20 October 1998 相似文献
174.
Photocatalysis has been extensively studied due to its potential ability to avoid the excessive use of chemical reagents and reduce the energy consumption by employing solar energy. Moreover, to alleviate the reduction in the membrane permeation selectivity, separation efficiency, and membrane service life caused by the emerging micro-pollutants and membrane fouling, membrane technology is often coupled with microbial, electrochemical, and catalytic processes. However, although physical/chemical cleaning and membrane module replacement can overcome the inherent limitations caused by membrane fouling and other membrane separation processes, high operating costs limit their practical applications. In this review, common preparation methods for TiO2 photocatalytic membranes are described in detail, and the main approaches to enhancing their photocatalytic performance are discussed. More importantly, the mechanism of the TiO2 photocatalytic membrane antifouling process is elucidated, and some applications of photocatalytic membranes in other areas are described. This review systematically outlines future research directions in the field of photocatalytic membrane modification, including metal and non-metal doping, fabrication of heterojunction structures, control over reaction conditions, increase in hydrophilicity, and increase in membrane porosity. 相似文献
175.
本文首先运用考虑非期望产出的SBM-SupSBM模型估计我国各省市绿色技术创新效率并进行分类:稳定上升类、平稳类、大幅度波动类以及下降类。之后从企业内部和外部两方面对绿色技术创新效率提升的影响因素提出假设,着重考虑大幅度波动类别省份的效率提升。运用面板数据模型各影响因素进行验证,结论显示:企业规模对绿色技术创新效率波动较大的省份起到显著的抑制作用,环境规制和技术进步对绿色技术创新效率波动较大的省份作用不明显。针对分析结果,提出结论:在提升绿色技术创新效率的过程中,应注重企业规模和技术进步的协同作用,以及技术的开放程度。 相似文献
176.
The single machine group scheduling problem is considered. Jobs are classified into several groups on the basis of group technology, i.e. jobs of the same group have to be processed jointly. A machine set-up time independent of the group sequence is needed between each two consecutive groups. A schedule specifies the sequence of groups and the sequence of jobs in each group. The quality of a schedule is measured by the criteriaF
1, ...,F
m ordered by their relative importance. The objective is to minimize the least important criterionF
m subject to the schedule being optimal with respect to the more important criterionF
m–1 which is minimized on the set of schedules minimizing criterionF
m–2 and so on. The most important criterion isF
1, which is minimized on the set of all feasible schedules. An approach to solve this multicriterion problem in polynomial time is presented if functionsF
1, ...,F
m have special properties. The total weighted completion time and the total weighted exponential time are the examples of functionsF
1, ...,F
m–1 and the maximum cost is an example of functionF
m for which our approach can be applied.The research of the authors was partially supported by a KBN Grant No. 3 P 406 003 05, the Fundamental Research Fund of Belarus, Project N 60-242, and the Deutsche Forschungsgemeinschaft, Project Schema, respectively. The paper was completed while the first author was visiting the University of Melbourne. 相似文献
177.
针对全球定位系统(Global Positioning System,GPS)接收机传统捕获算法计算复杂度高、捕获灵敏度低等缺点,提出了一种可降噪的简化并行码相位捕获(Noise Reduction for Simplified Parallel Code Phase Acquisition,NR-SPCA)算法。该算法通过对信号降采样,利用小波变换对二次采样信号作降噪处理,提高了捕获灵敏度;利用GPS信号和C/A码互相关的稀疏性,并行计算降噪后的信号的相关值,提高了运算效率。仿真结果表明,在90%概率捕获成功的前提下,NR-SPCA算法比传统的PCA算法信噪比低1 dB,运算效率提升了100%。该算法还可应用于航天探测、自动驾驶等领域。 相似文献
178.
179.
高校新工科人才培养的要求是培养一大批多样化、创新型卓越工程科技人才。针对培养要求切实做出积极的改革,首先重构EDA技术课程的教学时间,由线上和线下两部分组成。线上课要求完成课程视频学习、单元测验、讨论和期末测试;线下课堂要求完成见面课项目设计、实验课和期末考试。通过线上线下课堂教学的结合,加强过程性考核手段,完善学生学习评价机制。 相似文献
180.