全文获取类型
收费全文 | 57534篇 |
免费 | 4461篇 |
国内免费 | 4409篇 |
专业分类
化学 | 14504篇 |
晶体学 | 72篇 |
力学 | 2508篇 |
综合类 | 564篇 |
数学 | 14257篇 |
物理学 | 9822篇 |
综合类 | 24677篇 |
出版年
2024年 | 118篇 |
2023年 | 524篇 |
2022年 | 1042篇 |
2021年 | 981篇 |
2020年 | 1229篇 |
2019年 | 1196篇 |
2018年 | 1168篇 |
2017年 | 1469篇 |
2016年 | 1693篇 |
2015年 | 1687篇 |
2014年 | 2651篇 |
2013年 | 3022篇 |
2012年 | 3144篇 |
2011年 | 3533篇 |
2010年 | 2838篇 |
2009年 | 3526篇 |
2008年 | 3359篇 |
2007年 | 4040篇 |
2006年 | 3621篇 |
2005年 | 3245篇 |
2004年 | 2893篇 |
2003年 | 2580篇 |
2002年 | 2173篇 |
2001年 | 1941篇 |
2000年 | 1711篇 |
1999年 | 1447篇 |
1998年 | 1345篇 |
1997年 | 1194篇 |
1996年 | 1011篇 |
1995年 | 890篇 |
1994年 | 835篇 |
1993年 | 635篇 |
1992年 | 622篇 |
1991年 | 547篇 |
1990年 | 503篇 |
1989年 | 433篇 |
1988年 | 383篇 |
1987年 | 272篇 |
1986年 | 175篇 |
1985年 | 119篇 |
1984年 | 97篇 |
1983年 | 64篇 |
1982年 | 89篇 |
1981年 | 78篇 |
1980年 | 47篇 |
1979年 | 42篇 |
1978年 | 36篇 |
1977年 | 27篇 |
1976年 | 36篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Dr. Zaifa Shi Dr. Yihuang Jiang Dr. Jingxiong Yu Prof. Shanjun Chen Prof. Jun Chen Prof. Zichao Tang Prof. Lansun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(8):e202103546
At present, the reactivity of cyclic alkanes is estimated by comparison with acyclic hydrocarbons. Due to the difference in the structure of cycloalkanes and acycloalkanes, the thermodynamic data obtained by analogy are not applicable. In this study, a molecular beam sampling vacuum ultraviolet photoionization time-of-flight mass spectrometer (MB-VUV-PI-TOFMS) was applied to study the low-temperature oxidation of cyclopentane (CPT) at a total pressure range from 1–3 atm and low-temperature range between 500 and 800 K. Low-temperature reaction products including cyclic olefins, cyclic ethers, and highly oxygenated intermediates (e. g., ketohydroperoxide KHP, keto-dihydroperoxide KDHP, olefinic hydroperoxides OHP and ketone structure products) were observed. Further investigation of the oxidation of CPT – electronic structure calculations – were carried out at the UCCSD(T)-F12a/aug-cc-pVDZ//B3LYP/6-31+ G(d,p) level to explore the reactivity of O2 molecules adding sequentially to cyclopentyl radicals. Experimental and theoretical observations showed that the dominant product channel in the reaction of CPT radicals with O2 is HO2 elimination yielding cyclopentene. The pathways of second and third O2 addition – the dissociation of hydroperoxide – were further confirmed. The results of this study will develop the low-temperature oxidation mechanism of CPT, which can be used for future research on accurately simulating the combustion process of CPT. 相似文献
2.
4.
5.
利用初等方法研究了一个包含Smarandache Ceil函数Sk(n)的对偶函数-Sk(n),给出了当k=6时方程-S6(1)+-S6(2)+…+-S6(n)=6Ω(n)的具体正整数解。 相似文献
6.
《Wave Motion》2018
Large cable net structures have been widely applied in aerospace engineering due to the feature of light-weight, high packaging efficiency, and high thermal stability. Structural vibrations induced by a variety of disturbances are inevitable in the space environment, resulting in the requirement of effective vibration control strategies for large cable net structures. Since the large cable net structures have many closely spaced vibrational modes in the range of low frequencies, traditional modal based control may cause modal truncation and spillover problems. In this paper, a wave-based boundary control strategy is adopted and its effectiveness to control the vibration of cable net structures is investigated, by transfer function analysis and numerical methods. It is found that the structural vibration can be absolutely resisted by applying the wave-based boundary controllers onto all the exterior nodes, when disturbances come from the external boundaries of the cable net. Our results in this paper can provide a theoretical basis for the vibration control of large cable net structures. 相似文献
7.
若f∈PfT(R)∩C(R),则F(x)=∫axf(t)dt,x∈R与周期函数有何关系,具有哪些性质?本文将就这一问题进行研究,获得了一个关于周期函数一个重要的若干性质的定理,应用其便捷的处理了一大批与周期函数有关的问题,进而给出了关于映射周期性的若干性质及其应用的注记,这对经济周期性研究有一定的参考意义。 相似文献
8.
Antonio R. Montoro Bustos Marta Garcia-Cortes Hector González-Iglesias Jorge Ruiz Encinar José M. Costa-Fernández Miguel Coca-Prados Alfredo Sanz-Medel 《Analytica chimica acta》2015
A generic strategy based on the use of CdSe/ZnS Quantum Dots (QDs) as elemental labels for protein quantification, using immunoassays with elemental mass spectrometry (ICP-MS), detection is presented. In this strategy, streptavidin modified QDs (QDs-SA) are bioconjugated to a biotinylated secondary antibody (b-Ab2). After a multi-technique characterization of the synthesized generic platform (QDs-SA-b-Ab2) it was applied to the sequential quantification of five proteins (transferrin, complement C3, apolipoprotein A1, transthyretin and apolipoprotein A4) at different concentration levels in human serum samples. It is shown how this generic strategy does only require the appropriate unlabeled primary antibody for each protein to be detected. Therefore, it introduces a way out to the need for the cumbersome and specific bioconjugation of the QDs to the corresponding specific recognition antibody for every target analyte (protein). Results obtained were validated with those obtained using UV–vis spectrophotometry and commercial ELISA Kits. 相似文献
9.
Multi-sensor data fusion is an evolving technology whereby data from multiple sensor inputs are processed and combined. The data derived from multiple sensors can, however, be uncertain, imperfect, and conflicting. The present study is undertaken to help contribute to the continuous search for viable approaches to overcome the problems associated with data conflict and imperfection. Sensor readings, represented by belief functions, have to be fused according to their corresponding weights. Previous studies have often estimated the weights of sensor readings based on a single criterion. Mono-criteria approaches for the assessment of sensor reading weights are, however, often unreliable and inadequate for the reflection of reality. Accordingly, this work opts for the use of a multi-criteria decision aid. A modified Analytical Hierarchy Process (AHP) that incorporates several criteria is proposed to determine the weights of a sensor reading set. The approach relies on the automation of pairwise comparisons to eliminate subjectivity and reduce inconsistency. It assesses the weight of each sensor reading, and fuses the weighed readings obtained using a modified average combination rule. The efficiency of this approach is evaluated in a target recognition context. Several tests, sensitivity analysis, and comparisons with other approaches available in the literature are described. 相似文献
10.
考虑了线性回归模型中,在Fisherian和Mahalanobis损失函数下,几乎无偏刘估计对于最小二乘估计的不可容许性;结论表明:几乎无偏刘估计在Mahalanobis损失函数下是不可容的;最后进行了数值模拟来表明结果. 相似文献