全文获取类型
收费全文 | 13269篇 |
免费 | 207篇 |
国内免费 | 11篇 |
专业分类
教育 | 9154篇 |
科学研究 | 1675篇 |
各国文化 | 113篇 |
体育 | 984篇 |
综合类 | 17篇 |
文化理论 | 160篇 |
信息传播 | 1384篇 |
出版年
2022年 | 93篇 |
2021年 | 134篇 |
2020年 | 203篇 |
2019年 | 270篇 |
2018年 | 390篇 |
2017年 | 413篇 |
2016年 | 376篇 |
2015年 | 249篇 |
2014年 | 363篇 |
2013年 | 2149篇 |
2012年 | 322篇 |
2011年 | 304篇 |
2010年 | 296篇 |
2009年 | 257篇 |
2008年 | 276篇 |
2007年 | 285篇 |
2006年 | 269篇 |
2005年 | 229篇 |
2004年 | 256篇 |
2003年 | 223篇 |
2002年 | 235篇 |
2001年 | 312篇 |
2000年 | 332篇 |
1999年 | 252篇 |
1998年 | 138篇 |
1997年 | 179篇 |
1996年 | 174篇 |
1995年 | 118篇 |
1994年 | 130篇 |
1993年 | 115篇 |
1992年 | 196篇 |
1991年 | 182篇 |
1990年 | 213篇 |
1989年 | 210篇 |
1988年 | 180篇 |
1987年 | 192篇 |
1986年 | 172篇 |
1985年 | 207篇 |
1984年 | 150篇 |
1983年 | 131篇 |
1982年 | 124篇 |
1981年 | 109篇 |
1980年 | 112篇 |
1979年 | 174篇 |
1978年 | 130篇 |
1977年 | 113篇 |
1976年 | 89篇 |
1975年 | 92篇 |
1974年 | 94篇 |
1973年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
Analytical expressions are derived from a single symmetrical relay feedback test for the identification of open loop stable and unstable non-minimum phase processes. The second derivative of the limit cycle output helps in finding the time delay of the process. The derived expressions can be used to identify the process models with up to five unknowns. The effectiveness of the proposed identification method is verified through different simulation results. 相似文献
952.
This paper studies bounded input bounded output (BIBO) stability for a class of neutral systems with time-varying delays. Based on Lyapunov method and linear matrix inequalities, some new BIBO stability criteria are established. The numerical simulation is made to demonstrate the effectiveness of the theoretical results obtained in this paper. 相似文献
953.
A simple design method for the cosine-modulated filter banks using weighted constrained least square technique 总被引:1,自引:0,他引:1
This paper presents a simple and efficient design method for cosine-modulated filter banks with prescribed stopband attenuation, passband ripple, and channel overlap. The method casts the design problem as a linear minimization of filter coefficients such that their value at ω=π/2M is 0.707, which results in a simpler, more direct design procedure. The weighted constrained least squares technique is exploited for designing the prototype filter for cosine modulation (CM) filter banks. Several design examples are included to show the increased efficiency and flexibility of the proposed method over the exiting methods. An application of the proposed method is considered in the area of sub-band coding of the ECG and speech signals. 相似文献
954.
Michael S. Moss 《Archival Science》2011,11(3-4):409-425
Trust is an overused concept in our contemporary world. This paper explores the complex relationship of trust, efficiency, accountability, transparency and responsibility and their relationship to recordkeeping in our globalizing culture. It focuses on the profound changes that have taken place in the meaning and practice of audit within neo-liberal societies and how the ??rituals of verification?? and the ??managerialism?? may pervert the resulting record. It challenges the unthinking use of much of the rhetoric surrounding these concepts by archivists to justify their existence. It reflects on why the archival voice often remains silent or at best goes unheard in much of the discussion about these questions that have profound consequences for democratic societies. It is easy to lay the blame at the door of a perceived breakdown of trust rather than to consider whether the root of the problem lies with archivists and records managers themselves. This paper draws on my experience in directing the Information Management and Preservation MSC programme at the University of Glasgow and wide and serendipitous reading, which has sometimes been brought to my notice by students. 相似文献
955.
956.
957.
In this work a disposable, parallel microbioreactor (MBR) suitable for screening in batch or continuous mode is presented. The reactor consists of five parallel microchambers made of poly(dimethylsiloxane) bonded to a glass substrate. A grid structure is engraved on each chamber, allowing subsequent morphology imaging. Measurements are recorded over the entire cultivation period with constant parameters, namely, position and focus in the z-axis. The microdevice may be used for either parallel, uni- or multiparametric screening, and overcomes the drawback of gridless microwell plates which require expensive equipment such as an inverted microscope with an automatic stage. To validate the scalability from laboratory scale to microscale, and thus the cultivation protocol in the MBR, the germination of fungal spores (A. ochraceus) is evaluated for two different key magnitudes (pH and temperature) and compared to the results obtained from conventional laboratory scale systems (flasks and agar plates). Information on germination capacity with regard to interspecies' variability allows for optimization of industrial processes as optimal pH and temperature matched to the mesoscopic cultivation systems. The germination conditions therefore remain unaffected inside the MBR, while providing the following advantages: (i) dramatic reduction of medium consumption, (ii) submerged cultivation with constant oxygen supply, (iii) assured low cost and disposability, and (iv) possibility of a continuous cultivation mode. 相似文献
958.
A simple experimental setup to study the impact and coalescence of deposited droplets is described. Droplet impact and coalescence have been investigated by high-speed particle image velocimetry. Velocity fields near the liquid-substrate interface have been observed for the impact and coalescence of 2.4 mm diameter droplets of glycerol∕water striking a flat transparent substrate in air. The experimental arrangement images the internal flow in the droplets from below the substrate with a high-speed camera and continuous laser illumination. Experimental results are in the form of digital images that are processed by particle image velocimetry and image processing algorithms to obtain velocity fields, droplet geometries, and contact line positions. Experimental results are compared with numerical simulations by the lattice Boltzmann method. 相似文献
959.
Greene NP Greene ES Carbuhn AF Green JS Crouse SF 《Research quarterly for exercise and sport》2011,82(2):264-273
We compared cardiorespiratory responses to exercise on an underwater treadmill (UTM) and land treadmill (LTM) and derived an equation to estimate oxygen consumption (VO2) during UTM exercise. Fifty-five men and women completed one LTM and five UTM exercise sessions on separate days. The UTM sessions consisted of chest-deep immersion, with 0, 25, 50, 75, and 100% water-jet resistance. All session treadmill velocities increased every 3 min from 53.6 to 187.8 m x min(-1). Cardiorespiratory responses were similar between LTM and UTM when jet resistance for UTM was 50%. Using multiple regression analysis, weight-relative VO2 could be estimated as: VO2 (mLO2 c kg(-1) x min(-1)) = 0.19248 x height (cm) + 0.17422 x jet resistance (% max) + 0.14092 x velocity (m x min(-1)) -0.12794 x weight (kg)-27.82849, R2 = .82. Our data indicate that similar LTM and UTM cardiorespiratory responses are achievable, and we provide a reasonable estimate of UTM VO2. 相似文献
960.
The aim of this study was to assess the effects of a single session of cold or thermoneutral water immersion after a one-off match on muscular dysfunction and damage in soccer players. Twenty-male soccer players completed one match and were randomly divided into cryotherapy (10 min cold water immersion, 10°C, n = 10) and thermoneutral (10 min thermoneutral water immersion, 35°C, n = 10) groups. Muscle damage (creatine kinase, myoglobin), inflammation (C-reactive protein), neuromuscular function (jump and sprint abilities and maximal isometric quadriceps strength), and delayed-onset muscle soreness were evaluated before, within 30 min of the end, and 24 and 48 h after the match. After the match, the players in both groups showed increased plasma creatine kinase activity (30 min, 24 h, 48 h), myoglobin (30 min) and C-reactive protein (30 min, 24 h) concentrations. Peak jump ability and maximal strength were decreased and delayed-onset muscle soreness increased in both groups. However, differential alterations were observed between thermoneutral water and cold water immersion groups in creatine kinase (30 min, 24 h, 48 h), myoglobin (30 min), C-reactive protein (30 min, 24 h, 48 h), quadriceps strength (24 h), and quadriceps (24 h), calf (24 h) and adductor (30 min) delayed-onset muscle soreness. The results suggest that cold water immersion immediately after a one-off soccer match reduces muscle damage and discomfort, possibly contributing to a faster recovery of neuromuscular function. 相似文献