全文获取类型
收费全文 | 975篇 |
免费 | 118篇 |
国内免费 | 72篇 |
专业分类
化学 | 535篇 |
晶体学 | 3篇 |
力学 | 9篇 |
综合类 | 7篇 |
数学 | 65篇 |
物理学 | 167篇 |
无线电 | 379篇 |
出版年
2024年 | 6篇 |
2023年 | 18篇 |
2022年 | 54篇 |
2021年 | 53篇 |
2020年 | 51篇 |
2019年 | 37篇 |
2018年 | 30篇 |
2017年 | 46篇 |
2016年 | 51篇 |
2015年 | 40篇 |
2014年 | 57篇 |
2013年 | 61篇 |
2012年 | 74篇 |
2011年 | 71篇 |
2010年 | 49篇 |
2009年 | 45篇 |
2008年 | 56篇 |
2007年 | 63篇 |
2006年 | 50篇 |
2005年 | 32篇 |
2004年 | 42篇 |
2003年 | 39篇 |
2002年 | 21篇 |
2001年 | 20篇 |
2000年 | 20篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1987年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
排序方式: 共有1165条查询结果,搜索用时 15 毫秒
1.
Aditi Chatterjee Jayabrata Biswas Kiranmoy Das 《International Journal of Communication Systems》2020,33(9)
In recent years, Internet of Things (IoT) devices are used for remote health monitoring. For remotely monitoring a patient, only the health information at different time points are not sufficient; predicted values of biomarkers (for some future time points) are also important. In this article, we propose a powerful statistical model for an efficient dynamic patient monitoring using wireless sensor nodes through Bayesian Learning (BL). We consider the setting where a set of correlated biomarkers are measured from a patient through wireless sensors, but the sensors only report the ordinal outcomes (say, good, fair, high, or very high) to the sink based on some prefixed thresholds. The challenge is to use the ordinal outcomes for monitoring and predicting the health status of the patient under consideration. We propose a linear mixed model where interbiomarker correlations and intrabiomarker dependence are modeled simultaneously. The estimated and the predicted values of the biomarkers are transferred over the internet so that health care providers and the family members of the patient can remotely monitor the patient. Extensive simulation studies are performed to assess practical usefulness of our proposed joint model, and the performance of the proposed joint model is compared to that of some other traditional models used in the literature. 相似文献
2.
3.
4.
新颖外燃式湿空气燃气轮机循环及性能研究 总被引:2,自引:0,他引:2
本文首先提出一种新型的高效燃煤燃气轮机循环一外燃式湿空气透平循环动力系统。由于外燃的特点,作功工质为洁净湿空气,从而可以实现水的回收,是对常规HAT循环的突破;另外洁净湿空气排放不受通常烟气露点限制,从而可回收利用湿空气降温时的低温凝结潜热,提高了加湿能力,从而提高系统性能。揭示了新型循环的基本规律;推导出具有湿化特点的约束方程和系统性能简明表达式,指明影响系统性能的关键因素。在透平初温为850℃的工况下,系统热效率高达48.11%。基于能量品位梯级利用原理和系统集成方法论,通过探索充分而合理利用中低温余热的有效途径,开拓洁净煤燃气轮机总能系统的新方向。 相似文献
5.
6.
因子分析在企业竞争力评价中的应用 总被引:22,自引:1,他引:21
根据因子分析原理,建立了企业竞争力的规模因子、效益因子和成长因子得分模型。通过现实竞争力和潜在竞争力分析,实现了企业竞争力和可持续发展的评价。 相似文献
7.
8.
《Arabian Journal of Chemistry》2022,15(11):104272
Yinlan lipid regulatory capsule (YL) is a composite traditional Chinese medicine (TCM) new drug to alleviate hyperlipidemia, while its therapeutic mechanism in vivo was not clarified with nontargeted metabolomics investigation. An animal model was established in rats fed a high-fat diet, and their body weights, body mass index (BMI) and blood cholesterol levels were measured. Serum, liver and kidney tissue samples were also extracted for PXR-CYP3A4-ABCB1-FXR signaling pathway research using PCR and UHPLC–MS. The obtained plasma samples were analyzed by UHPLC-Q-TOF-MS metabolomic investigation, which revealed PXR-CYP3A4-related metabolites and changes induced by YL. Finally, the key metabolites were chosen as index components, and their levels in the serum, liver, small intestine and bile were used for simultaneous UHPLC–MS-MS determination. The results indicated that YL was effective in rebalancing blood TG and TC levels (compared to controls). With respect to the PXR-CYP3A4-ABCB1 pathway, as a result of YL’s effect, gene expression or activity of the two targets decreased significantly in both the liver and kidney. The same trend was observed in the serum samples mentioned above. Metabolomics screening and data revealed that 44 metabolites can be regarded as biomarkers related to hyperlipidemia, fatty acids synthesis, and body energy consumption, as well as synthesis, transportation and exertion of cholesterol. YL’s treatment focused on 26 of them, primarily bile acids, indicating that the antihyperlipidemic effect of this drug lies in its inhibitory activity of cholesterol metabolism. Subsequent analysis of those in vivo components revealed that significant increases (compared to the model group) occurred in the blood, liver, small intestine and bile in groups that received medium and high doses of YL (while the low dose was relatively unchanged). Those target components exhibit a close relationship with PXR and/or CYP3A4. The use of YL repressed PXR expression and subsequently decreased CYP3A4 activity. As a result, synthesis of related bile acids increased, while cholesterol levels decreased, consequently leading to the attenuation of hyperlipidemia. This study comprehensively investigated the antihyperlipidemia mechanism of YL based on its repression of PXR-CYP3A4 activity and related metabolite yield, establishing an accurate method for evaluating the therapeutic effect of YL. 相似文献
9.
In this study, local least squares (LLS) and principal component analysis (PCA) were applied to deal with the disturbances in a data set of chromatographic fingerprints after necessary data transformations. It has been demonstrated that PCA with standard normal variate (SNV) transformation of data led to meaningful classification of 33 different Erigeron breviscapus herbal samples. The result was also corroborated by variance squares discriminant method. The quality of herbal objects was further evaluated, and the causes of this fact have been explained from a chemical point of view. At the same time, it implied an idea for qualitative evaluation of the herbal objects with a common class pattern of chromatographic fingerprints. 相似文献
10.
Bonnie R. Hames Steven R. Thomas Amie D. Sluiter Christine J. Roth David W. Templeton 《Applied biochemistry and biotechnology》2003,105(1-3):5-16
New, rapid, and inexpensive methods that monitor the chemical composition of corn stover and corn stover-derived samples are
a key element to enabling the commercialization of processes that convert stover to fuels and chemicals. These new techniques
combine near infrared (NIR) spectroscopy and projection to latent structures (PLS) multivariate analysis to allow the compositional
analysis of hundreds of samples in 1 d at a cost of about $10 each. The new NIR/PLS rapid analysis methods can also be used
to support a variety of research projects that would have been too costly to pursue by traditional methods. 相似文献