全文获取类型
收费全文 | 18528篇 |
免费 | 3181篇 |
国内免费 | 1088篇 |
专业分类
化学 | 3157篇 |
晶体学 | 82篇 |
力学 | 1231篇 |
综合类 | 191篇 |
数学 | 5448篇 |
物理学 | 5176篇 |
无线电 | 7512篇 |
出版年
2024年 | 40篇 |
2023年 | 217篇 |
2022年 | 373篇 |
2021年 | 503篇 |
2020年 | 555篇 |
2019年 | 558篇 |
2018年 | 529篇 |
2017年 | 725篇 |
2016年 | 785篇 |
2015年 | 770篇 |
2014年 | 1058篇 |
2013年 | 1565篇 |
2012年 | 1244篇 |
2011年 | 1332篇 |
2010年 | 1078篇 |
2009年 | 1068篇 |
2008年 | 1132篇 |
2007年 | 1165篇 |
2006年 | 1055篇 |
2005年 | 918篇 |
2004年 | 828篇 |
2003年 | 801篇 |
2002年 | 681篇 |
2001年 | 588篇 |
2000年 | 513篇 |
1999年 | 456篇 |
1998年 | 335篇 |
1997年 | 332篇 |
1996年 | 259篇 |
1995年 | 220篇 |
1994年 | 174篇 |
1993年 | 134篇 |
1992年 | 107篇 |
1991年 | 103篇 |
1990年 | 66篇 |
1989年 | 66篇 |
1988年 | 45篇 |
1987年 | 48篇 |
1986年 | 42篇 |
1985年 | 71篇 |
1984年 | 41篇 |
1983年 | 26篇 |
1982年 | 37篇 |
1981年 | 31篇 |
1980年 | 16篇 |
1979年 | 32篇 |
1978年 | 16篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Mariusz Marć Marek Tobiszewski Bożena Zabiegała Miguel de la Guardia Jacek Namieśnik 《Analytica chimica acta》2015
This review summarizes the different tools and concepts that are commonly applied in air quality monitoring. The monitoring of atmosphere is extremely important as the air quality is an important problem for large communities. Main requirements for analytical devices used for monitoring include a long period of autonomic operation and portability. These instruments, however, are often characterized by poor analytical performance. Monitoring networks are the most common tools used for monitoring, so large-scale monitoring programmes are summarized here. Biomonitoring, as a cheap and convenient alternative to traditional sample collection, is becoming more and more popular, although its main drawback is the lack of standard procedures. Telemonitoring is another approach to air monitoring, which offers some interesting opportunities, such as ease of coverage of large or remote areas, constituting a complementary approach to traditional strategies; however, it requires huge costs. 相似文献
12.
Mourad Kainane Mezadek Mohamed Kainane Mezadek Michael Reissig 《Mathematical Methods in the Applied Sciences》2020,43(6):3117-3147
In this paper, we study the global (in time) existence of small data solutions to the Cauchy problem for the semilinear wave equation with friction, viscoelastic damping, and a power nonlinearity. We are interested in the connection between regularity assumptions for the data and the admissible range of exponents p in the power nonlinearity. 相似文献
13.
Azobenzene‐Functionalized Cage Silsesquioxanes as Inorganic–Organic Hybrid,Photoresponsive, Nanoscale,Building Blocks
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Hongzhi Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4731-4738
Mono‐ and octa‐azobenzene‐functionalized cage silsesquioxanes were easily synthesized by the reaction of 4‐bromoazobenzene with monovinyl‐substituted octasilsesquioxane and cubic octavinylsilsesquioxane through the Heck coupling reaction. Excited‐state energies obtained from time‐dependent density functional theory (TDDFT) and the CAM‐B3LYP functional correlate very well with experimental trans–cis photoisomerization results from UV/Vis spectroscopy. These azobenzene‐functionalized cages exhibit good thermal stability and are fluorescent with maximum emission at approximately 400 nm, making them potential materials for blue‐light emission. 相似文献
14.
异构分层无线网络中基于逗留时间的动态流量均衡算法研究 总被引:1,自引:1,他引:0
为使异构分层无线网络能服务更多的移动用户,提出了一种基于逗留时间的动态流量均衡算法.该算法首先根据用户移动模型计算其在小区内的逗留时间,然后基于小区呼叫到达率和重叠覆盖小区的流量状态来确定一个周期内呼叫转移的数量,最后依据逗留时间门限值将重负载小区中满足条件的呼叫转移到轻负载的重叠覆盖小区中.为降低切换呼叫掉线率,还对异构网间的呼叫切换策略做了改进.仿真实验结果表明,本算法在新呼叫阻塞率和切换呼叫掉线率等性能指标上比传统方法有显著的提高. 相似文献
15.
16.
Kicheon Kim 《ETRI Journal》2006,28(1):31-44
In a packet switching network, congestion is unavoidable and affects the quality of real‐time traffic with such problems as delay and packet loss. Packet fair queuing (PFQ) algorithms are well‐known solutions for quality‐of‐service (QoS) guarantee by packet scheduling. Our approach is different from previous algorithms in that it uses hardware time achieved by sampling a counter triggered by a periodic clock signal. This clock signal can be provided to all the modules of a routing system to get synchronization. In this architecture, a variant of the PFQ algorithm, called digitized delay queuing (DDQ), can be distributed on many line interface modules. We derive the delay bounds in a single processor system and in a distributed architecture. The definition of traffic contribution improves the simplicity of the mathematical models. The effect of different time between modules in a distributed architecture is the key idea for understanding the delay behavior of a routing system. The number of bins required for the DDQ algorithm is also derived to make the system configuration clear. The analytical models developed in this paper form the basis of improvement and application to a combined input and output queuing (CIOQ) router architecture for a higher speed QoS network. 相似文献
17.
串行和并行接口模式是A/D转换器诸多分类中的一种,但却是应用中器件选择的一个重要指标.在同样的转换分辨率及转换速度的前提下,不同的接口方式不但影响了电路结构,更重要的是将在高速数据采集的过程中对采样周期产生较大影响.本文通过12位串行ADC ADS7822和并行ADC ADS774与AT89C51的接口电路,给出二者采样时间的差异性. 相似文献
18.
叙述了二代近贴聚焦像增强器批量生产所用真空设备性能及特点,同时给出了管子工艺考核结果及管子纳秒时间响应特性。工艺考核结果表明,制管工艺可靠、性能稳定,管子批量生产合格率大于70%。 相似文献
19.
20.