全文获取类型
收费全文 | 17817篇 |
免费 | 1100篇 |
国内免费 | 507篇 |
专业分类
系统科学 | 1449篇 |
丛书文集 | 266篇 |
教育与普及 | 330篇 |
理论与方法论 | 322篇 |
现状及发展 | 946篇 |
研究方法 | 47篇 |
综合类 | 16059篇 |
自然研究 | 5篇 |
出版年
2024年 | 65篇 |
2023年 | 119篇 |
2022年 | 218篇 |
2021年 | 187篇 |
2020年 | 133篇 |
2019年 | 46篇 |
2018年 | 776篇 |
2017年 | 808篇 |
2016年 | 528篇 |
2015年 | 237篇 |
2014年 | 326篇 |
2013年 | 294篇 |
2012年 | 644篇 |
2011年 | 1357篇 |
2010年 | 1166篇 |
2009年 | 853篇 |
2008年 | 1005篇 |
2007年 | 1210篇 |
2006年 | 369篇 |
2005年 | 495篇 |
2004年 | 502篇 |
2003年 | 458篇 |
2002年 | 407篇 |
2001年 | 444篇 |
2000年 | 405篇 |
1999年 | 755篇 |
1998年 | 702篇 |
1997年 | 754篇 |
1996年 | 662篇 |
1995年 | 558篇 |
1994年 | 491篇 |
1993年 | 465篇 |
1992年 | 388篇 |
1991年 | 390篇 |
1990年 | 274篇 |
1989年 | 323篇 |
1988年 | 268篇 |
1987年 | 182篇 |
1986年 | 88篇 |
1985年 | 27篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1970年 | 3篇 |
1969年 | 4篇 |
1968年 | 2篇 |
1967年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
931.
This paper proposes a knowledge-scientific approach to evaluation of community service systems from the viewpoints of knowledge creation, consciousness reform, and value co-creation. A concrete example of the community service system treated here is an education program for old men to find their reason for living after the retirement. After introducing this program and the traditional evaluation methods for such a program, the paper emphasizes the necessity of developing new evaluation methods for such a community service system based on knowledge science. The paper proposes a new evaluation framework and reports an actual evaluation result using the interview data from participants in that program. 相似文献
932.
Nicole Note 《Foundations of Science》2016,21(2):311-314
This final comment provides, a theoretical framework on how to conceive the self as presented in the key-note paper ‘Meaningfulness, volunteering and being moved. The event of wit(h)nessing’. This is deemed requisite to achieve a full understanding of how depth in meaningfulness comes about. 相似文献
933.
Traditional processes for treating vanadium slag generate a huge volume of solid residue and a large amount of harmful gas, which cause serious environmental problems. In this study, a new process for the comprehensive utilization of vanadium slag was proposed, wherein zeolite A and a V2O5/TiO2 system were synthesized. The structural properties of the as-synthesized zeolite A and the V2O5/TiO2 system were characterized using various experimental techniques, including X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and infrared spectroscopy. The results reveal that zeolite A and the V2O5/TiO2 system are successfully obtained with high purity. The results of gas adsorption measurements indicate that the prepared zeolite A exhibits high selectivity for CO2 over N2 and is a candidate material for CO2 capture from flue-gas streams. 相似文献
934.
To reveal the impact of the composite agglomeration process (CAP) on the reduction disintegration properties of TiO2-rich ironmaking burden for a blast furnace, the reduction disintegration indices (RDIs), mineral constituents, and microstructure of the products prepared by the CAP and the traditional sintering process (TSP) were investigated. The results showed that, compared to the sinter with a basicity of 2.0 prepared by the TSP, the RDI+6.3 and the RDI+3.15 of the CAP product with the same basicity increased by 28.2wt% and 13.7wt%, respectively, whereas the RDI-0.5 decreased by 2.7wt%. The analysis of the mineral constituents and microstructure of the products indicated that the decreasing titanohematite content decreased the volume expansion during reduction. Meanwhile, the decreasing perovskite content decreased its detrimental effect on the reduction disintegration properties. In addition, the higher silicoferrite of calcium and aluminum (SFCA) content improved the strength of the CAP product. Together, these factors result in an improvement of the RDI of the CAP products. In addition, compared to the sinter, the reduced CAP products clearly contained fewer cracks, which also led to mitigation of reduction disintegration. 相似文献
935.
In recent years,bank credit business is booming with the increasing borrowing intention of China’s listed companies,and debt financing has become the major approach among listed companies’financing strategies.As a series of institutional arrangements about rights,responsibilities and benefits between different shareholders,corporate governance mechanism has a significant influence on the cost of debt financing.This paper employs variable coefficient panel data model to investigate the relationship of the listed company’s debt financing costs and corporate governance mechanism in terms of structural characteristics and time series characteristics.The results show that optimizing the structure of both Board of Directors and Board of Supervisors,establishing a reasonable management incentive system and reducing the concentration of ownership properly can directly contribute to a lower company’s debt financing costs.Meanwhile,property rights have an interactive influence on corporate governance from four aspects,which indirectly effect in company’s debt financing costs. 相似文献
936.
Takayuki Fujita Masanari Umemura Utako Yokoyama Satoshi Okumura Yoshihiro Ishikawa 《Cellular and molecular life sciences : CMLS》2017,74(4):591-606
As one of the most important second messengers, 3′,5′-cyclic adenosine monophosphate (cAMP) mediates various extracellular signals including hormones and neurotransmitters, and induces appropriate responses in diverse types of cells. Since cAMP was formerly believed to transmit signals through only two direct target molecules, protein kinase A and the cyclic nucleotide-gated channel, the sensational discovery in 1998 of another novel direct effecter of cAMP [exchange proteins directly activated by cAMP (Epac)] attracted a great deal of scientific interest in cAMP signaling. Numerous studies on Epac have since disclosed its important functions in various tissues in the body. Recently, observations of genetically manipulated mice in various pathogenic models have begun to reveal the in vivo significance of previous in vitro or cellular-level findings. Here, we focused on the function of Epac in the heart. Accumulating evidence has revealed that both Epac1 and Epac2 play important roles in the structure and function of the heart under physiological and pathological conditions. Accordingly, developing the ability to regulate cAMP-mediated signaling through Epac may lead to remarkable new therapies for the treatment of cardiac diseases. 相似文献
937.
938.
Isothermal fatigue (IF) tests were performed on H13 tool steel subjected to three different mechanical strain amplitudes at a constant temperature to determine the effects of mechanical strain amplitude on the microstructure of the steel samples. The samples' extent of damage after IF tests was compared by observation of their cracks and calculation of their damage parameters. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to observe the microstructure of the samples. Cracks were observed to initiate at the surface because the strains and stresses there were the largest during thermal cycling. Mechanical strain accelerated the damage and softening of the steel. A larger mechanical strain caused greater deformation of the steel, which made the precipitated carbides easier to gather and grow along the deformation direction, possibly resulting in softening of the material or the initiation of cracks. 相似文献
939.
Ecological compensation is becoming one of key and multidiscipline issues in the field of resources and environmental management. Considering the change relation between gross domestic product (GDP) and ecological capital (EC) based on remote sensing estimation, we construct a new quantitative estimate model for ecological compensation, using county as study unit, and determine standard value so as to evaluate ecological compensation from 2001 to 2004 in Zhejiang Province, China. Spatial differences of the ecological compensation were significant among all the counties or districts. This model fills up the gap in the field of quantitative evaluation of regional ecological compensation and provides a feasible way to reconcile the conflicts among benefits in the economic, social, and ecological sectors. 相似文献
940.
本文从职务侵占犯罪的概念入手,分析其基本特征与该犯罪行为的主观,客观,主体,客体等四大要素。阐述了此类犯罪的构成,通过与其他相关犯罪的比较,使读者能正确把握此类犯罪。 相似文献