全文获取类型
收费全文 | 5753篇 |
免费 | 100篇 |
国内免费 | 22篇 |
专业分类
教育 | 3956篇 |
科学研究 | 668篇 |
各国文化 | 41篇 |
体育 | 474篇 |
综合类 | 8篇 |
文化理论 | 46篇 |
信息传播 | 682篇 |
出版年
2022年 | 46篇 |
2021年 | 59篇 |
2020年 | 121篇 |
2019年 | 184篇 |
2018年 | 238篇 |
2017年 | 262篇 |
2016年 | 226篇 |
2015年 | 147篇 |
2014年 | 191篇 |
2013年 | 978篇 |
2012年 | 150篇 |
2011年 | 172篇 |
2010年 | 130篇 |
2009年 | 119篇 |
2008年 | 125篇 |
2007年 | 145篇 |
2006年 | 113篇 |
2005年 | 77篇 |
2004年 | 96篇 |
2003年 | 94篇 |
2002年 | 76篇 |
2001年 | 109篇 |
2000年 | 136篇 |
1999年 | 94篇 |
1998年 | 74篇 |
1997年 | 65篇 |
1996年 | 66篇 |
1995年 | 46篇 |
1994年 | 47篇 |
1993年 | 35篇 |
1992年 | 76篇 |
1991年 | 72篇 |
1990年 | 62篇 |
1989年 | 64篇 |
1988年 | 76篇 |
1987年 | 61篇 |
1986年 | 80篇 |
1985年 | 70篇 |
1984年 | 57篇 |
1983年 | 71篇 |
1982年 | 56篇 |
1981年 | 44篇 |
1980年 | 32篇 |
1979年 | 52篇 |
1978年 | 49篇 |
1977年 | 38篇 |
1976年 | 41篇 |
1975年 | 31篇 |
1974年 | 34篇 |
1973年 | 34篇 |
排序方式: 共有5875条查询结果,搜索用时 31 毫秒
861.
Electrospinning, a flexible jet-based fiber, scaffold, and membrane fabrication approach, has been elucidated as having significance to the heath sciences. Its capabilities have been most impressive as it possesses the ability to spin composite fibers ranging from the nanometer to the micrometer scale. Nonetheless, electrospinning has limitations and hazards, negating its wider exploration, for example, the inability to handle highly conducting suspensions, to its hazardous high voltage. Hence, to date electrospinning has undergone an exhaustive research regime to a point of cliché. Thus, in the work reported herein we unveil a competing technique to electrospinning, which has overcome the above limitations and hazards yet comparable in capabilities. The fiber preparation approach unearthed herein is referred to as “pressure driven spinning (PDS).” The driving mechanism exploited in this fiber spinning process is the pressurized by-pass flow. This mechanism allows the drawing of either micro- or nanosized fibers while processing polymeric suspensions containing a wide range of advanced materials spanning structural, functional, and biological entities. Similar to electrospinning if the collection time of these continuous formed fibers is varied, composite scaffolds and membranes are generated. In keeping with our interests, multicompositional structural entities such as these could have several applications in biology and medicine, for example, ranging from the development of three-dimensional cultures (including disease models) to the development of synthetic tissues and organ structures to advanced approaches for controlled and targeted therapeutics. 相似文献
862.
A class of hybrid multi-rate control models with time-delay and switching controllers are formulated based on combined remote control and local control strategies. The problem of robust dissipative control for this discrete system is investigated. An improved Lyapunov-Krasovskii functional is constructed and the subsequent analysis provides some new sufficient conditions in the form of LMIs for both nominal and uncertain representations. Several special cases of practical interests are derived. A numerical simulation example is given to illustrate the effectiveness of the theoretical result. 相似文献
863.
Casikar V Mujica E Mongelli M Aliaga J Lopez N Smith C Bartholomew F 《Indian journal of clinical biochemistry : IJCB》2010,25(3):311-314
Andean Indians have used coca leaves (Erythroxylon coca and related species) for centuries to enhance physical performance. The benefits and disadvantages of using coca leaf have
been a subject of many political debates. The aim of this study was to investigate the effects of chewing coca leaves on biochemical
and physiological parameters. Cutaneous microdialysis catheters were used to estimate systemic biochemical changes. We subjected
10 healthy adult males (local residents) in Cajamarca (Peru, altitude 2700 m) to a standardised exercise routine on a stationary
cycle ergometer. The blood pressure, oxygen saturation (digital), pulse, VO2 max and ECG (Holter monitor) were recorded before
the exercise. Cutaneous microdialysis catheters were introduced in the forearm. The subjects were given to chew 8 g of coca
leaves with a small amount of lime. They were then placed on the cycle ergometer for 20 min. Blood pressure, oxygen saturation,
pulse, ECG and VO2 max were recorded. Pyruvate, glucose, lactate, glycerol and glutamate levels were estimated. Oxygen saturation,
blood pressure, and pulse rate did not show any significant changes between the two groups. Glucose levels showed hyperglycaemic
response. Glycerol, Lactate and Pyruvate increased. Glutamate remained unchanged. Similar changes were not seen in the controls.
These results suggest that coca leaves have blocked the glycolytic pathway of glucose oxidation resulting in accumulation
of glucose and pyruvate. The energy requirement for exercise is being met with beta-oxidation of fatty acids. The glycerol
released was also getting accumulated since its pathway for oxidation was blocked. These experimental findings suggest that
chewing coca leaves is beneficial during exercise and that the effects are felt over a prolonged period of sustained physical
activity. 相似文献
864.
Raviraja A Vishal Babu GN Sehgal A Saper RB Jayawardene I Amarasiriwardena CJ Venkatesh T 《Indian journal of clinical biochemistry : IJCB》2010,25(3):326-329
Ayurveda is a traditional form of medicine used by majority of the Indians. Here we report three cases of lead toxicity, following
intake of Ayurvedic medicines. Three patients presented with blood lead levels (BLLs) of 122.4, 115 and 42.8 μg/dl respectively
at the time of hospitalization. The first case was chelated with D- penicillamine, the second with calcium disodium ethylene
diamino tetra acetate (EDTA) and the third with environmental intervention and education. Associated Ayurvedic products were
collected from patients and analyzed for metallic concentration. Cessation of Ayurvedic medication along with chelation, nutritional
intervention and education, reduced the BLL to 27.4 μg/dl in the first case after 1 year, 21.1 μg/dl after 9 months in the
second and 18.2 μg/dl after 6 months in the third case. 相似文献
865.
Kadam DP Suryakar AN Ankush RD Kadam CY Deshpande KH 《Indian journal of clinical biochemistry : IJCB》2010,25(4):388-392
Psoriasis is a chronic inflammatory, proliferative skin disease characterized by pathological skin lesions due to various
exogenous and endogenous factors. It is associated with a number of biochemical and immunological disturbances. Recently,
it has been suggested that increased reactive oxygen species (ROS) production and compromised function of antioxidant system
may be involved in the pathogenesis of this disease. In the present study, 90 psoriasis patients were selected. Disease severity
was assessed by psoriasis area severity index score and grouped as mild, moderate and severe (each group consists of 30 subjects)
and compared with 30 healthy controls. Serum levels of malondialdehyde, nitric oxide end products and the activities of antioxidant
enzymes such as erythrocyte-superoxide dismutase, catalase and total antioxidant status were investigated in these groups/subjects.
As compared to controls, we found severitywise significantly increased serum malondialdehyde, nitric oxide end products with
decrease in erythrocyte-superoxide dismutase activity, catalase activity and total antioxidant status in patients with psoriasis
suggesting worsening of the disease. It seems to be linked with the enhancement of Reactive Oxygen Species production and
decreased antioxidant potential in psoriasis. 相似文献
866.
E. Schreuders M. van Buuren R. J. Walsh H. Sijtsma M. Hollarek N. C. Lee L. Krabbendam 《Child development》2024,95(2):368-390
Longitudinal changes in trusting behavior across adolescence and their neural correlates were examined. Neural regions of interest (ROIs) included the medial prefrontal cortex (mPFC), dorsal anterior cingulate cortex (dACC), left anterior insula (AI), bilateral ventral striatum (VS), and right dorsal striatum (DS). Participants (wave 1 age: M = 12.90) played the investor in a Trust Game with an uncooperative trustee three times (1-year interval). Analyses included 77 primarily Dutch participants (33 females). Participants decreased their investments with wave. Furthermore, activity was heightened in mPFC, dACC, and DS during investment and repayment, and in right VS (investment) and AI (repayment). Finally, DS activity during repayment increased with wave. These findings highlight early–middle adolescence as an important period for developing sensitivity to uncooperative behavior. 相似文献
867.
In this paper, we address the problem of tracking DOA of multiple moving targets with known signal source waveforms and unknown gains in the presence of Gaussian noise using a nonuniform linear array. Herein, we make use of the fact that the output of each sensor can be described as a linear regression model whose coefficients each contain a pair of DOA and gain information corresponding to one target. These coefficients are determined by solving a linear least squares (LS) problem and then updated recursively based on a block QR decomposition recursive least squares (QRD-RLS) technique or a block regularized LS technique. Since the coefficients from different sensors have the same amplitude but variable phase information for the same signal, along with simple algebraic manipulations the well-known generalized least squares (GLS) are used to obtain an asymptotically-optimal DOA estimate without requiring a search over a large region of the parameter space. Computer simulations show that the proposed DOA tracking techniques when applied to a sparse antenna array can provide a better tracking performance than some of the existing methods do. 相似文献
868.
Susan Dickerson Mayes Susan L. Calhoun Edward O. Bixler Dennis N. Zimmerman 《Learning and individual differences》2009,19(2):238-241
Word reading and math computation scores were predicted from Wechsler Abbreviated Scale of Intelligence Full Scale IQ, 10 neuropsychological tests, and parent attention deficit hyperactivity disorder (ADHD) ratings in 214 general population elementary school children. IQ was the best single predictor of achievement. In addition, Digit Span contributed significantly to reading prediction, and the Developmental Test of Visual-Motor Integration (VMI) and Coding contributed to math prediction. The remaining neuropsychological test scores did not significantly improve achievement prediction. Exploratory factor analysis yielded a general ability factor (comprising the four IQ subtests, Digit Span, VMI, reading, and math), five factors made up solely of subtests from single measures (Wisconsin Card Sorting Test, Stroop Color and Word Test, Gordon Diagnostic System, California Verbal Learning Test, and ADHD ratings), a factor consisting of Grooved Pegboard Test and Coding, and a factor consisting of Symbol Search and Animal Naming Test. 相似文献
869.
Educational programs for young children emerged reasonably early in the history of the United States of America. The movements
of Child-Centered Education, the Nursery School, the Project Method, Curriculum Reform, and contemporary research have all
influenced mathematics in early childhood education. The Froebelian kindergarten and the Montessori Casa die Bambini (Children’s House) included approaches to teaching mathematics. This article reviews the history of mathematics education
in relation to the history of early childhood education from the turn of the twentieth century. It also discusses how research
in mathematics education attempted to gain its own identity. Throughout history, researchers have identified mathematics issues
and addressed them, defining the field, and generating a cadre of mathematics researchers. 相似文献
870.
A. S. Bugaev E. L. Loginov A. N. Raikov V. N. Saraev 《Scientific and Technical Information Processing》2009,36(1):68-72
The information problems of management in an information and electronic society are considered and the technologies for carrying out statistical analysis with the use of various types of information are evaluated. 相似文献