全文获取类型
收费全文 | 6764篇 |
免费 | 1343篇 |
国内免费 | 548篇 |
专业分类
化学 | 3014篇 |
晶体学 | 74篇 |
力学 | 136篇 |
综合类 | 27篇 |
数学 | 559篇 |
物理学 | 3201篇 |
无线电 | 1644篇 |
出版年
2024年 | 23篇 |
2023年 | 105篇 |
2022年 | 187篇 |
2021年 | 283篇 |
2020年 | 365篇 |
2019年 | 263篇 |
2018年 | 218篇 |
2017年 | 278篇 |
2016年 | 288篇 |
2015年 | 249篇 |
2014年 | 376篇 |
2013年 | 521篇 |
2012年 | 427篇 |
2011年 | 490篇 |
2010年 | 379篇 |
2009年 | 407篇 |
2008年 | 395篇 |
2007年 | 420篇 |
2006年 | 460篇 |
2005年 | 319篇 |
2004年 | 307篇 |
2003年 | 251篇 |
2002年 | 219篇 |
2001年 | 180篇 |
2000年 | 186篇 |
1999年 | 113篇 |
1998年 | 135篇 |
1997年 | 132篇 |
1996年 | 117篇 |
1995年 | 86篇 |
1994年 | 84篇 |
1993年 | 80篇 |
1992年 | 74篇 |
1991年 | 44篇 |
1990年 | 44篇 |
1989年 | 44篇 |
1988年 | 21篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
排序方式: 共有8655条查询结果,搜索用时 15 毫秒
991.
Tsang‐Chi Lee Jui‐Yi Hung Yun Chi Yi‐Ming Cheng Gene‐Hsiang Lee Pi‐Tai Chou Chung‐Chia Chen Chih‐Hao Chang Chung‐Chih Wu 《Advanced functional materials》2009,19(16):2639-2647
A new series of charge neutral Os(II) isoquinolyl triazolate complexes ( 1 – 4 ) with both trans and cis arrangement of phosphine donors are synthesized, and their structural, electrochemical and photophysical properties are established. In sharp contrast to the cis‐arranged complexes 2 – 4 , the trans derivative 1 , which shows a planar arrangement of chromophoric N‐substituted chelates, offers the most effective extended π‐delocalization and hence the lowest excited state energy gap. These complexes exhibit phosphorescence with peak wavelengths ranging from 692–805 nm in degassed CH2Cl2 at room temperature. Near‐infrared (NIR)‐emitting electroluminescent devices employing 6 wt % of 1 (or 4 ) doped in Alq3 host material are successfully fabricated. The devices incorporating 1 as NIR phosphor exhibit fairly intense emission with a peak wavelength at 814 nm. Forward radiant emittance reaches as high as 65.02 µW cm?2, and a peak EQE of ~1.5% with devices employing Alq3, TPBi and/or TAZ as electron‐transporting/exciton‐blocking layers. Upon switching to phosphor 4 , the electroluminescence blue shifts to 718 nm, while the maximum EQE and radiance increase to 2.7% and 93.26 (μW cm?2) respectively. Their performances are optimized upon using TAZ as the electron transporting and exciton‐blocking material. The OLEDs characterized represent the only NIR‐emitting devices fabricated using charge‐neutral and volatile Os(II) phosphors via thermal vacuum deposition. 相似文献
992.
Zhi‐Gang Chen Jin Zou Dai‐Wei Wang Li‐Chang Yin Gang Liu Qingfeng Liu Cheng‐Hua Sun Xiangdong Yao Feng Li Xiao‐Li Yuan Takashi Sekiguchi Gao Qing Lu Hui‐Ming Cheng 《Advanced functional materials》2009,19(3):484-490
Single‐crystal hexagonal pyramids of zinc blende ZnS are fabricated by facile thermal evaporation in an ammonia atmosphere at 1150 °C. It is found that ZnS pyramids grow along the [111] crystal axis and possess a sharp tip with a diameter of ~10 nm and a micrometer‐sized base. The structural model and growth mechanism are proposed based on crystallographic characteristics. This unique ZnS pyramid structure exhibits a low turn‐on field (2.81 V µm?1), a high field‐enhancement factor (over 3000), a large field‐emission current density (20 mA cm?2), and good stability with very small fluctuation (0.9%). These superior field‐emission properties are clearly attributed to the pyramid morphology, with micrometer‐sized bases and nanotips, and high crystallinity. Moreover, a stable UV emission of 337 nm at room temperature is observed and can be ascribed to the band emission of the zinc blende phase. These results suggest that the ZnS hexagonal pyramids can be expected to find promising applications as field emitters and optoelectronic devices. 相似文献
993.
994.
医院药品对保质期和服务水平有非常高的要求,同时,药品的库存空间在医药库存中也有重要影响。首先针对快速失效的医药药品考虑了医药库存的合同保质期以及库存空间约束,同时考虑医院库存以及制造商库存,基于经济订货批量模型和经济生产批量模型建立了二级供应链的医药库存模型,然后用MATLAB软件求解了模型最优解,并对一些重要参数进行了敏感性分析。研究发现,合同保质期对医院订购批量、制造商生产批量和总库存成本有一定的影响,其中对于制造商的生产批量以及医院的库存成本影响较大。如果不考虑合同保质期的约束,将会对总库存成本带来更大损失。 相似文献
995.
考虑消费者具有低碳产品偏好的情况,研究需求随机且受减排影响的期权契约,建立了由单个制造商和单个零售商组成的供应链模型。该模型中制造商处主导地位,零售商处追随地位,制造商首先提出期权契约,零售商购买期权。求解发现,由于传统双重边际化效应的存在,只有当零售价格等于期权执行价格时,才能达到供应链的协调,这时零售商利润为负,不满足参与约束。为此,从降低期权执行价格的角度,对期权契约进行补充,增加了成本共担条款。研究表明,减排成本共担的期权契约能够实现供应链的协调。最后利用算例验证了结论,计算了制造商和零售商利润及零售商分担的减排成本比例随期权价格和期权执行价格的变化情况,并对减排难度系数的敏感性做了分析。 相似文献
996.
997.
Alain Bensoussan Sonny Skaaning Janos Turi 《Journal of Applied Analysis & Computation》2018,8(3):805-835
We continue to study the problem of inventory control, with simultaneous pricing optimization in continuous time. In our previous paper [8], we considered the case without set up cost, and established the optimality of the base stock-list price (BSLP) policy. In this paper we consider the situation of fixed price. We prove that the discrete time optimal strategy (see [11]), i.e., the (s, S, p) policy can be extended to the continuous time case using the framework of quasi-variational inequalities (QVIs) involving the value function. In the process we show that an associated second order, nonlinear two-point boundary value problem for the value function has a unique solution yielding the triplet (s, S, p). For application purposes the explicit knowledge of this solution is needed to specify the optimal inventory and pricing strategy. Se- lecting a particular demand function we are able to formulate and implement a numerical algorithm to obtain good approximations for the optimal strategy. 相似文献
998.
This paper shows how a manufacturer may use an incentive contract with a distributor under a VMI arrangement to gain market share. The manufacturer promises a distributor lower inventory levels in exchange for efforts by the distributor to convert potential lost sales due to stockouts to backorders. Data gathered from a third party provider of information services are then used to illustrate that this incentive arrangement may, at least implicitly, be employed in industry. Our data estimations show that when a manufacturer and distributor are operating under a VMI arrangement, lower inventory at the distributor is associated with a higher conversion rate of lost sales stockouts to backorders. 相似文献
999.
In this paper we presented an extended version of the Ng-modelg [W.L. Ng, A simple classifier for multiple criteria ABC analysis, European Journal of Operational Research 177 (2007) 344–353] for multi-criteria inventory classification. The proposed model is a nonlinear programming model which determines a common set of weights for all the items. Our model not only incorporates multiple criteria for ABC classification, but also maintains the effects of weights in the final solution, an improvement over the model proposed by Ng. An illustrative example is presented to compare our model and the Ng-model. 相似文献
1000.
探讨了需求对时间和价格敏感产品的最优动态定价和订购策略,建立了使零售商利润最大化的库存模型.然后对模型的性质进行了分析,给出了一个寻找最优价格调整次数的算法和数值例子,得到一些有意义的管理经验. 相似文献