全文获取类型
收费全文 | 11736篇 |
免费 | 7篇 |
专业分类
教育 | 9082篇 |
科学研究 | 1216篇 |
各国文化 | 6篇 |
体育 | 353篇 |
文化理论 | 385篇 |
信息传播 | 701篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 22篇 |
2018年 | 2191篇 |
2017年 | 2094篇 |
2016年 | 1582篇 |
2015年 | 118篇 |
2014年 | 126篇 |
2013年 | 129篇 |
2012年 | 224篇 |
2011年 | 690篇 |
2010年 | 833篇 |
2009年 | 432篇 |
2008年 | 644篇 |
2007年 | 1155篇 |
2006年 | 69篇 |
2005年 | 392篇 |
2004年 | 449篇 |
2003年 | 356篇 |
2002年 | 131篇 |
2001年 | 6篇 |
2000年 | 22篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 19篇 |
1996年 | 1篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1987年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
The flow in a finite diverging channel opening into a large space and resembling the experimental prototype of Putkaradze and Vorobieff (2006) was numerically investigated. The effects of the Reynolds number, initial condition, intersection angle, length of the wedge edges, and the outer boundary condition were examined. The numerical results showed that the flow in the wedge undergoes a change from symmetrical flow to unsymmetrical flow with a weak backflow, then a vortical (circulation) flow and finally an unsteady jet flow as the Reynolds number is increased for an intersection angle of 32° and a wedge edge of length 30 times the width of the inlet slit. For the unsteady flow, the jet attached to one side of the wedge constantly loses stability and rolls up into a mushroom-shaped vortex-pair near the outlet of the wedge. As the intersection angle is increased to 50°, a stable jet flow is observed as a new regime between the vortex and unsteady regimes. Both the intersection angle and the wedge length have negative effects on the stability of the flow, although the effect of the wedge length on the critical Reynolds number for the symmetry-breaking instability is not pronounced. The outer boundary condition was found not to affect the flow patterns inside the wedge significantly. At a certain Re regime above the onset of symmetry-breaking instability, the flows evolve into steady state very slowly except for the initial stage in the case of decreasing flow flux. Two different solutions can be observed within the normal observation time for the experiment, providing a possible explanation for the hysteresis phenomenon in the experiment. 相似文献
902.
Bülent 《浙江大学学报(A卷英文版)》2010,11(2):106-114
In this study, an electro-mechanical valve (EMV) system for the intake valve ofa fottr stroke, single cylinder, overhead valve and spark ignition (SI) engine was designed and constructed. An engine with the EMV system and a standard engine were tested to observe the effects of the EMV on engine performance and emissions at different speeds under full load. The EMV engine showed improved engine power, engine torque and break specific fuel consumption (BSFC). A 66% decrease in CO emissions was also obtained with the EMV system, but hydrocarbons (HC) and NOx emissions increased by 12% and 13% respectively. 相似文献
903.
Temporal variation of dynamical modal properties of a base-isolated building is investigated using earthquake records in the building. A batch processing least-squares estimation method is applied to segment-wise time-series data. To construct an input-output system, an auto-regressive model with exogenous input (ARX) of second-order including a forgetting coefficient as a weighting coefficient is used for the estimation of modal parameters. The fundamental and second natural frequencies and the damping ratios of the fundamental and second natural modes of the base-isolated building are identified in the time domain. The identified results are consistent with the results obtained from the micro-tremor vibration data, forced-vibration test data and earthquake records in the present base-isolated building in the case of taking into account the amplitude-dependency of the iso- lators and viscous dampers. It is finally pointed out that several factors, e.g., amplitude dependency of the isolator and damper system and special characteristics of the series-type viscous damper system, may be related complicatedly with the temporal variation in modal properties of the above-mentioned system. 相似文献
904.
Improved response surface method for anti-slide reliability analysis of gravity dam based on weighted regression 总被引:1,自引:0,他引:1
The aim of this study was to design and construct an improved response surface method (RSM) based on weighted regression for the anti-slide reliability analysis of concrete gravity dam. The limitation and lacuna of the traditional RSM were briefly analyzed. Firstly, based on small experimental points, research was devoted to an improved RSM with singular value decomposition techniques. Then, the method was used on the basis of weighted regression and deviation coefficient correction to reduce iteration times and experimental points and improve the calculation method of checking point. Finally, a test example was given to verify this method. Compared with other conventional algorithms, this method has some strong advantages: this algorithm not only saves the arithmetic operations but also greatly enhances the calculation efficiency and the storage efficiency. 相似文献
905.
Niels C. Taubert 《Minerva》2012,50(3):261-275
This article analyzes the transformation of Minerva from an intellectual towards a scholarly journal by making use of bibliometric methods. The aim is to provide some empirical insights that help to understand what properties of the journal changed in the course of this transformation process. Minerva was one of the first journals that reflected on science and its role in society and science policy in particular. Analyzing the development of the journal sheds light on the emergence of science (policy) studies and on Minerva’s role as a forerunner in this field. In a first step, the methods will be described. The second section provides some empirical results of the publication output of Minerva and its relations to other journals in the field. The empirical findings are put into a broader perspective in the concluding third section. 相似文献
906.
Elena Aronova 《Minerva》2012,50(3):307-337
The Congress for Cultural Freedom is remembered as a paramount example of the “cultural cold wars.” In this paper, I discuss the ways in which this powerful transnational organization sought to promote “science studies” as a distinct – and politically relevant – area of expertise, and part of the CCF broader agenda to offer a renewed framework for liberalism. By means of its Study Groups, international conferences and its periodicals, such as Minerva, the Congress developed into an influential forum for examining the ways Big Science impacted the relations between science, society, and politics, thus constituting a semi-institutional niche for Science Studies before its professionalization within academia during the 1970s. I argue that the Congress contributed to the construction of public space in which the relations between science, society and politics were debated, and science was reconceptualized as a social activity. The vision of “science studies” the CCF-associated intellectuals promulgated was different from the science studies we know today. Yet, this alternative vision, in which the issues of science politics appeared inseparable from those of science policy, science organization, and science governance, constituted the “pre-history” of science studies today. 相似文献
907.
908.
Lang AJ Laffaye C Satz LE McQuaid JR Malcarne VL Dresselhaus TR Stein MB 《Child abuse & neglect》2006,30(11):1281-1292
OBJECTIVE: Women with histories of childhood maltreatment (CM) have higher rates of physical health problems and greater medical utilization compared to women without abuse histories. This study examined whether current post-traumatic stress disorder (PTSD) symptoms mediate the relationship between CM and indicators of physical health and medical utilization in female veterans. METHOD: Respondents were 221 female veterans (56% of the potential sample), who received medical care from the San Diego VA Healthcare System during a 12-month period. Respondents provided self-report information about CM, PTSD symptoms, use of pain medication, and physical symptoms and functioning. Additional information about medical utilization was extracted from respondents' medical charts. Regression-based models were conducted to test whether PTSD symptoms mediate the relationships between CM and physical symptoms and between CM and medical utilization. RESULTS: Emotional abuse was associated with poorer role-physical functioning, increased bodily pain and greater odds of using pain medication in the past 6 months. Physical abuse was associated with poorer general health. Contrary to prediction, emotional neglect was associated with better role-physical functioning, and CM was not associated with increased healthcare utilization. PTSD was shown to mediate the relationship between emotional and physical abuse and health outcomes. CONCLUSIONS: PTSD, or psychopathology more generally, appears to be an important factor in the negative health impact of CM. Given that several empirically supported interventions are available for PTSD, there may be physical health benefits in early identification and treatment of psychopathology related to CM. 相似文献
909.
Bill Kennedy 《Publishing Research Quarterly》2010,26(3):187-192
A concise review is presented of the essential elements of the book publishing and bookselling business in a complex and diverse
market. Demographics create the diversity while Arabic is the one language spoken across a multitude of different countries.
Three features are common to all of these countries and they are: the dominance of English as the second language, education
has and will remain to be a priority, and economic pressures cause price sensitivity to be a major challenge especially in
the educational market segments. It is the price sensitivity as a key factor for the lack of respect for intellectual property
and copyright regulations. A review of distribution and retail stores is a very important topic in relation to this complex
collection of countries. The emergence of e-books is discussed especially in the educational, professional and reference market
segments. Finally, there is a review of the Arabic language publishers and local book fairs to bring this article to closure. 相似文献
910.