全文获取类型
收费全文 | 13624篇 |
免费 | 159篇 |
国内免费 | 122篇 |
专业分类
教育 | 8883篇 |
科学研究 | 1531篇 |
各国文化 | 145篇 |
体育 | 1954篇 |
综合类 | 21篇 |
文化理论 | 114篇 |
信息传播 | 1257篇 |
出版年
2021年 | 114篇 |
2020年 | 222篇 |
2019年 | 303篇 |
2018年 | 399篇 |
2017年 | 386篇 |
2016年 | 353篇 |
2015年 | 242篇 |
2014年 | 334篇 |
2013年 | 2371篇 |
2012年 | 291篇 |
2011年 | 312篇 |
2010年 | 264篇 |
2009年 | 281篇 |
2008年 | 266篇 |
2007年 | 250篇 |
2006年 | 280篇 |
2005年 | 248篇 |
2004年 | 449篇 |
2003年 | 416篇 |
2002年 | 387篇 |
2001年 | 447篇 |
2000年 | 294篇 |
1999年 | 208篇 |
1998年 | 161篇 |
1997年 | 140篇 |
1996年 | 132篇 |
1995年 | 141篇 |
1994年 | 133篇 |
1993年 | 112篇 |
1992年 | 184篇 |
1991年 | 154篇 |
1990年 | 175篇 |
1989年 | 187篇 |
1988年 | 155篇 |
1987年 | 171篇 |
1986年 | 155篇 |
1985年 | 166篇 |
1984年 | 155篇 |
1983年 | 161篇 |
1982年 | 125篇 |
1981年 | 101篇 |
1980年 | 115篇 |
1979年 | 176篇 |
1978年 | 123篇 |
1977年 | 102篇 |
1976年 | 119篇 |
1975年 | 82篇 |
1974年 | 95篇 |
1973年 | 93篇 |
1971年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Thomas K. Gaisser 《Journal of The Franklin Institute》2011,348(3):453-458
This award recognizes two specific discoveries that constitute the experimental discovery of neutrino oscillations. In 1998 the Super-Kamiokande group under the leadership of Yoji Totsuka published their paper, “Evidence for Oscillation of Atmospheric Neutrinos” in Physical Review Letters [1]. The paper describes a deficit of muon-type neutrinos from below the detector relative to those from above. It explains this “atmospheric neutrino anomaly” as a result of transformation of some of the muon neutrinos into another type of neutrino. Four years later, the group led by Arthur McDonald described “Direct Evidence for Neutrino Flavor Transformation from Neutral-Current Interactions in the Sudbury Neutrino Observatory” [2] in the same journal. This experiment detected lower energy neutrinos from deep inside the Sun. By measuring all flavors of neutrinos with large rates, the SNO collaboration showed definitively that the long-standing “solar neutrino puzzle” was another manifestation of neutrino oscillations. As a result of these two experiments, we now understand that neutrinos can change identities during propagation and that both the solar and atmospheric neutrino “problems” result from the same underlying phenomenon of oscillations. A consequence of neutrino oscillations is that neutrinos, previously thought to be massless, must have a non-zero rest mass. 相似文献
992.
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
993.
Wouter P.C. BoonAuthor Vitae Ellen H.M. Moors Author VitaeStefan Kuhlmann Author Vitae Ruud E.H.M. Smits Author Vitae 《Research Policy》2011,40(2):242-252
User involvement is assumed to be beneficial to innovation processes. Intermediary user organisations contribute to articulating societal demands for innovations. However, the learning processes inside these organisations are still not understood well. Therefore, this paper empirically investigates intermediaries using an event history approach. It yields characteristic learning mechanisms, e.g. concerning the management of expectations or actively building a case. If intermediaries overcome challenges regarding positioning, representation and the level of proactivity, they can play a precarious role in demand articulation in the context of new technologies. 相似文献
994.
T.P. Dweba M.A. MearnsAuthor vitae 《International Journal of Information Management》2011,31(6):564-571
Indigenous knowledge erodes rapidly. When the loss of this knowledge negatively affects the lives and health of traditionally living rural communities, a drive to conserve indigenous knowledge becomes vital. This article argues that the transfer of indigenous knowledge on traditional vegetables will ensure the availability and utilisation of this important food source for resource-poor rural communities. Data collected on the present use of traditional vegetables at a rural Xhosa village in the Eastern Cape Province of South Africa documented indigenous practices of traditional vegetable use and measured attitudes and perceptions of young women. Findings revealed that although traditional vegetables are readily available, there is a decline in the use of traditional vegetables in this village. Since the loss of associated indigenous knowledge is a reality, and in view of the negative attitude towards traditional vegetables, future use of this valuable food source is threatened. The transfer of the associated indigenous knowledge holds the key to the potential future use of traditional vegetables. Altered perceptions of traditional vegetables are crucial for the conservation of the associated indigenous knowledge. As a result awareness campaigns to promote the use of traditional vegetables, related nutritional education, including proper cooking and preservation techniques are necessary. 相似文献
995.
Thomas Gould 《Publishing Research Quarterly》2011,27(1):36-53
Perhaps nothing strikes more fear into the hearts of all tenure-track professors than the process itself. Are four papers in this journal good enough? Are eight papers in another okay? What if someone doesn’t like me or my area of research? These issues have plagued academia since the first essay was penned by the first researcher hundreds of years ago. While personal bias and journal preference continue to infect honest tenure reviews, solutions exist. This does not mean we have a magic bullet to solve issues of bullying or elitism. However, if we are honest in our desire to improve the Academy, we should avail ourselves of every possible tool for improvement. This essay is based on a survey sent to 2,500 mass communication educators. Of the almost 500 respondents, roughly 10% took the time to express emotions that ranged from fear and confusion to outright rage and anger, all because what ought to be clear is not. The author offers 10 ideas of how academia can improve its evaluation of new faculty, as well as a few suggestions regarding the unnecessary inclusion of personal issues in a process that ought to be about creating better researchers and teachers. 相似文献
996.
Thomas W. Simpson 《Ethics and Information Technology》2011,13(1):29-38
Trust online can be a hazardous affair; many are trustworthy, but some people use the anonymity of the web to behave very badly indeed. So how can we improve the quality of evidence for trustworthiness provided online? I focus on one of the devices we use to secure others’ trustworthiness: tracking past conduct through online reputation systems. Yet existing reputation systems face problems. I analyse these, and in the light of this develop some principles for system design, towards overcoming these challenges. In providing better evidence for trustworthiness online, so we can also encourage people actually to be trustworthy more often, which is an ethically welcome outcome. 相似文献
997.
Dimov N Muñoz L Carot-Sans G Verhoeven ML Bula WP Kocer G Guerrero A Gardeniers HJ 《Biomicrofluidics》2011,5(3):34102-3410212
To prepare a biosynthetic module in an infochemical communication project, we designed a silicon/glass microreactor with anti-adsorption polyelectrolyte multilayer coating and immobilized alcohol acetyl transferase (atf), one of the key biosynthetic enzymes of the pheromone of Spodoptera littoralis, on agarose beads inside. The system reproduces the last step of the biosynthesis in which the precursor diene alcohol (Z,E)-9,11-tetradecadienol is transformed into the major component (Z,E)-9,11-tetradecadienyl acetate. The scope of this study was to analyze and implement a multilayer, anti-adsorption coating based on layer-by-layer deposition of polyethylenimine/dextransulfate sodium salt (PEI/DSS). The multilayers were composed of two PEI with molecular weights 750 and 1.2 kDa at pH 9.2 or 6.0. Growth, morphology, and stability of the layers were analyzed by ellipsometry and atomic force microscopy (AFM). The anti-adsorption functionality of the multilayer inside the microreactor was validated. The activity of His(6)-(atf) was measured by gas chromatography coupled to mass spectrometer (GC-MS). 相似文献
998.
Found in all eukaryotic cells, linker histones H1 are known to bind to and rearrange nucleosomal linker DNA. In vitro, the fundamental nature of H1∕DNA interactions has attracted wide interest among research communities-from biologists to physicists. Hence, H1∕DNA binding processes and structural and dynamical information about these self-assemblies are of broad importance. Targeting a quantitative understanding of H1 induced DNA compaction mechanisms, our strategy is based on using small-angle x-ray microdiffraction in combination with microfluidics. The usage of microfluidic hydrodynamic focusing devices facilitates a microscale control of these self-assembly processes, which cannot be achieved using conventional bulk setups. In addition, the method enables time-resolved access to structure formation in situ, in particular, to transient intermediate states. The observed time dependent structure evolution shows that the H1∕DNA interaction can be described as a two-step process: an initial unspecific binding of H1 to DNA is followed by a rearrangement of molecules within the formed assemblies. The second step is most likely induced by interactions between the DNA and the H1's charged side chains. This leads to an increase in lattice spacing within the DNA∕protein assembly and induces a decrease in the correlation length of the mesophases, probably due to a local bending of the DNA. 相似文献
999.
We examined differences in anthropometry and training between 64 Triple Iron ultra-triathletes competing over 11.4 km swimming, 540 km cycling, and 126.6 km running, and 71 Ironman triathletes competing over 3.8 km swimming, 180 km cycling, and 42.2 km running. The association of anthropometry and training with race time was investigated using multiple linear regression analysis. The Triple Iron ultra-triathletes were smaller (P < 0.05), had shorter limbs (P < 0.05), a higher body mass index (P < 0.05), and larger limb circumferences (P < 0.01) than the Ironman triathletes. The Triple Iron ultra-triathletes trained for more hours (P < 0.01) and covered more kilometres (P < 0.01), but speed in running during training was slower compared with the Ironman triathletes (P < 0.01). For Triple Iron ultra-triathletes, percent body fat (P = 0.022), training volume per week (P < 0.0001), and weekly kilometres in both cycling (P < 0.0001) and running (P < 0.0001) were related to race time. For Ironman triathletes, percent body fat (P < 0.0001), circumference of upper arm (P = 0.006), and speed in cycling training (P = 0.012) were associated with total race time. We conclude that both Triple Iron ultra-triathletes and Ironman triathletes appeared to profit from low body fat. Triple Iron ultra-triathletes relied more on training volume in cycling and running, whereas speed in cycling training was related to race time in Ironman triathletes. 相似文献
1000.
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