全文获取类型
收费全文 | 21808篇 |
免费 | 309篇 |
国内免费 | 29篇 |
专业分类
教育 | 14974篇 |
科学研究 | 2599篇 |
各国文化 | 199篇 |
体育 | 1875篇 |
综合类 | 22篇 |
文化理论 | 252篇 |
信息传播 | 2225篇 |
出版年
2021年 | 200篇 |
2020年 | 312篇 |
2019年 | 434篇 |
2018年 | 613篇 |
2017年 | 648篇 |
2016年 | 565篇 |
2015年 | 385篇 |
2014年 | 551篇 |
2013年 | 3749篇 |
2012年 | 499篇 |
2011年 | 486篇 |
2010年 | 452篇 |
2009年 | 407篇 |
2008年 | 428篇 |
2007年 | 466篇 |
2006年 | 419篇 |
2005年 | 370篇 |
2004年 | 387篇 |
2003年 | 374篇 |
2002年 | 369篇 |
2001年 | 449篇 |
2000年 | 472篇 |
1999年 | 384篇 |
1998年 | 203篇 |
1997年 | 247篇 |
1996年 | 259篇 |
1995年 | 188篇 |
1994年 | 222篇 |
1993年 | 198篇 |
1992年 | 334篇 |
1991年 | 313篇 |
1990年 | 337篇 |
1989年 | 329篇 |
1988年 | 282篇 |
1987年 | 294篇 |
1986年 | 293篇 |
1985年 | 334篇 |
1984年 | 249篇 |
1983年 | 247篇 |
1982年 | 223篇 |
1981年 | 206篇 |
1980年 | 198篇 |
1979年 | 328篇 |
1978年 | 227篇 |
1977年 | 216篇 |
1976年 | 190篇 |
1975年 | 167篇 |
1974年 | 173篇 |
1973年 | 148篇 |
1971年 | 152篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ruth F.G. Williams 《普罗米修斯》2015,33(4):421-430
Dissent and assent contribute to new information and knowledge in that they foster ideas, avert errors and counter misplaced beliefs. Although intended to facilitate progress, innovation and creativity, dissent may be opposed by the closed mind and defensive mindset. Don Lamberton encountered a specific mindset in his own duties to scholarship in economics. Thus, the perspective of dissent is a fitting way to pay homage to his scholarship. However, this paper is also a lament. It gives an interpretation of Antigone from political philosophy which depicts Antigone rocking an ideological boat harboured by the polis. The silencing of Antigone’s voice results in unexpected losses in the oikos. This is the sort of tragedy threatening critical and innovative scholarship in the twenty-first century. 相似文献
992.
Michael C. Motal Daniel A. Klaus Diana Lebherz-Eichinger Bianca Tudor Thomas Hamp Marion Wiegele Rudolf Seemann Claus G. Krenn Georg A. Roth 《Biochemia medica : ?asopis Hrvatskoga dru?tva medicinskih biokemi?ara / HDMB》2015,25(1):90-96
Introduction
Vaspin (visceral adipose tissue-derived serpin) was first described as an insulin-sensitizing adipose tissue hormone. Recently its anti-inflammatory function has been demonstrated. Since no appropriate data is available yet, we sought to investigate the plasma concentrations of vaspin in sepsis.Materials and methods
57 patients in intensive care, fulfilling the ACCP/SCCM criteria for sepsis, were prospectively included in our exploratory study. The control group consisted of 48 critically ill patients, receiving intensive care after trauma or major surgery. Patients were matched by age, sex, weight and existence of diabetes before statistical analysis. Blood samples were collected on the day of diagnosis. Vaspin plasma concentrations were measured using a commercially available enzyme-linked immunosorbent assay.Results
Vaspin concentrations were significantly higher in septic patients compared to the control group (0.3 (0.1-0.4) ng/mL vs. 0.1 (0.0-0.3) ng/mL, respectively; P < 0.001). Vaspin concentration showed weak positive correlation with concentration of C-reactive protein (CRP) (r = 0.31, P = 0.002) as well as with SAPS II (r = 0.34, P = 0.002) and maximum of SOFA (r = 0.39, P < 0.001) scoring systems, as tested for the overall study population.Conclusion
In the sepsis group, vaspin plasma concentration was about three-fold as high as in the median surgical control group. We demonstrated a weak positive correlation between vaspin and CRP concentration, as well as with two scoring systems commonly used in intensive care settings. Although there seems to be some connection between vaspin and inflammation, its role in human sepsis needs to be evaluated further.Key words: adipocytokine, inflammation, vaspin, CRP, intensive care 相似文献993.
The problems of intellectualization in the process development of integrated expert systems on the basis of the task-oriented methodology and the AT-TECHNOLOGY instrumental software complex are considered. The experience from carrying out intellectual planning for the synthesis of architectural layouts of prototypes in integrated expert systems, a usage-based intelligent scheduler, reusable components, typical project procedures, and other components of the intellectual software environment in the AT-TECHNOLOGY complex is described. 相似文献
994.
M. G. Belyaev 《Scientific and Technical Information Processing》2015,42(5):328-339
We consider the problem of multidimensional approximation according to samples with a factorial experimental design (full or incomplete). Universal approximation methods do not take this peculiarity of a sample into account. In the present work, a structural approximation method is developed: the function class and the regularization are chosen in a special way and efficient methods for finding an optimal solution in this class are proposed. 相似文献
995.
Biomimetic scaffolds approaching physiological scale, whose size and large cellular load far exceed the limits of diffusion, require incorporation of a fluidic means to achieve adequate nutrient/metabolite exchange. This need has driven the extension of microfluidic technologies into the area of biomaterials. While construction of perfusable scaffolds is essentially a problem of microfluidic device fabrication, functional implementation of free-standing, thick-tissue constructs depends upon successful integration of external pumping mechanisms through optimized connective assemblies. However, a critical analysis to identify optimal materials/assembly components for hydrogel substrates has received little focus to date. This investigation addresses this issue directly by evaluating the efficacy of a range of adhesive and mechanical fluidic connection methods to gelatin hydrogel constructs based upon both mechanical property analysis and cell compatibility. Results identify a novel bioadhesive, comprised of two enzymatically modified gelatin compounds, for connecting tubing to hydrogel constructs that is both structurally robust and non-cytotoxic. Furthermore, outcomes from this study provide clear evidence that fluidic interconnect success varies with substrate composition (specifically hydrogel versus polydimethylsiloxane), highlighting not only the importance of selecting the appropriately tailored components for fluidic hydrogel systems but also that of encouraging ongoing, targeted exploration of this issue. The optimization of such interconnect systems will ultimately promote exciting scientific and therapeutic developments provided by microfluidic, cell-laden scaffolds. 相似文献
996.
The flow focusing is a fundamental prior step in order to sort, analyze, and detect particles or cells. The standard hydrodynamic approach requires two fluids to be injected into the microfluidic device: one containing the sample and the other one, called the sheath fluid, allows squeezing the sample fluid into a narrow stream. The major drawback of this approach is the high complexity of the layout for microfluidic devices when parallel streams are required. In this work, we present a novel parallelized microfluidic device that enables hydrodynamic focusing in each microchannel using a single feed flow. At each of the parallel channels, a cross-filter region is present that allows removing fluid from the sample fluid. This fluid is used to create local sheath fluids that hydrodynamically pinch the sample fluid. The great advantage of the proposed device is that, since only one inlet is needed, multiple parallel micro-channels can be easily introduced into the design. In the paper, the design method is described and the numerical simulations performed to define the optimal design are summarized. Moreover, the operational functionality of devices tested by using both polystyrene beads and Acute Lymphoid Leukemia cells are shown. 相似文献
997.
Miguel-Ángel Gómez Otavio Battaglia Alberto Lorenzo Jorge Lorenzo Sergio Jiménez Jaime Sampaio 《Journal of sports sciences》2015,33(17):1844-1852
Ball screens are one of the most frequently used tactical behaviour in elite basketball games. The aim of the present study was to identify their predictors of success related to time, space, players, and tasks performed. The sample was composed of 818 ball screens corresponding to 20 close games (mean differences in score of 3.1 ± 0.8 points) randomly selected from the playoff games of the Spanish Basketball League (2008–2011). Classification tree analysis (CHAID) was used to analyse which variable or combination of variables, better predicts effectiveness during ball screens. The main results allowed identifying interactions with dribbler actions after the screen and the orientation of the screen on the ball. The results showed no interaction with game quarter and quarter minute temporal-related variables in both analyses. The present findings allow improving coaches’ strategic plans that involve selecting the most appropriate offensive approach when performing ball screens. 相似文献
998.
Irene R. Faber Maria W. G. Nijhuis-Van Der Sanden Marije T. Elferink-Gemser Frits G. J. Oosterveld 《Journal of sports sciences》2015,33(11):1149-1158
A motor skills assessment could be helpful in talent development by estimating essential perceptuo-motor skills of young players, which are considered requisite to develop excellent technical and tactical qualities. The Netherlands Table Tennis Association uses a motor skills assessment in their talent development programme consisting of eight items measuring perceptuo-motor skills specific to table tennis under varying conditions. This study aimed to investigate this assessment regarding its reproducibility, internal consistency, underlying dimensions and concurrent validity in 113 young table tennis players (6–10 years). Intraclass correlation coefficients of six test items met the criteria of 0.7 with coefficients of variation between 3% and 8%. Cronbach’s alpha valued 0.853 for internal consistency. The principal components analysis distinguished two conceptually meaningful factors: “ball control” and “gross motor function.” Concurrent validity analyses demonstrated moderate associations between the motor skills assessment’s results and national ranking; boys r = ?0.53 (P < 0.001) and girls r = ?0.45 (P = 0.015). In conclusion, this evaluation demonstrated six test items with acceptable reproducibility, good internal consistency and good prospects for validity. Two test items need revision to upgrade reproducibility. Since the motor skills assessment seems to be a reproducible, objective part of a talent development programme, more longitudinal studies are required to investigate its predictive validity. 相似文献
999.
The ankle joint’s role in shock absorption during landing has been researched in many studies, which have found that landing with higher amounts of plantarflexion (PF) results in lower peak vertical ground reaction forces and loading rates. However, there has not yet been a study that compares drop landings within participants along a quantitative continuum of PF angles. Using a custom-written real-time feedback program, participants adjusted their ankles to an instructed PF angle and dropped onto two force platforms. For increasing PF, peak ground reaction force and peak loading rate during weight acceptance decreased significantly. The hip’s contribution to peak support moment decreased as PF at initial contact increased up to 30°. The ankle and knee contributions increased over this same continuum of PF angles. There appears to be no optimal PF angle based on peak ground reaction force and loading rate measurements, but there may be an optimum where joint contributions to peak support moment converge and the hip moment’s contribution is minimised. 相似文献
1000.
Paul T. Cutrufello Stephen J. Gadomski Gerald S. Zavorsky 《Journal of sports sciences》2015,33(14):1459-1466
Citrulline has been proposed as an ergogenic aid, leading to an interest in watermelon given its high citrulline concentration. The aim of this study was to determine the effects of a single, pre-exercise dose of l-citrulline, watermelon juice, or a placebo on the total maximum number of repetitions completed over 5 sets, time to exhaustion, maximal oxygen consumption (VO2max), anaerobic threshold, and flow-mediated vasodilation. A randomised double-blind within-participants study design was used to examine these effects among 22 participants (n = 11 males). Supplementation included either a 7.5% sucrose drink containing 6 g of l-citrulline, 710 mL of watermelon juice (~1.0 g citrulline), or a 7.5% sucrose placebo drink. Supplementation was administered 1 or 2 h before exercise testing to investigate a timing effect. There was no significant effect between the three supplements for the total number of repetitions, time to exhaustion, VO2max, anaerobic threshold, or flow-mediated vasodilation. There was also no interaction observed relative to gender or supplement timing (P > 0.05). A single dose of l-citrulline or watermelon juice as a pre-exercise supplement appears to be ineffective in improving exercise performance; however, greater doses of l-citrulline have been shown to be safe and are currently left unexamined. 相似文献