全文获取类型
收费全文 | 6613篇 |
免费 | 119篇 |
国内免费 | 20篇 |
专业分类
教育 | 4642篇 |
科学研究 | 722篇 |
各国文化 | 52篇 |
体育 | 482篇 |
综合类 | 6篇 |
文化理论 | 56篇 |
信息传播 | 792篇 |
出版年
2023年 | 46篇 |
2022年 | 69篇 |
2021年 | 75篇 |
2020年 | 142篇 |
2019年 | 216篇 |
2018年 | 278篇 |
2017年 | 305篇 |
2016年 | 253篇 |
2015年 | 188篇 |
2014年 | 251篇 |
2013年 | 1089篇 |
2012年 | 212篇 |
2011年 | 192篇 |
2010年 | 196篇 |
2009年 | 138篇 |
2008年 | 169篇 |
2007年 | 176篇 |
2006年 | 123篇 |
2005年 | 99篇 |
2004年 | 120篇 |
2003年 | 102篇 |
2002年 | 96篇 |
2001年 | 117篇 |
2000年 | 154篇 |
1999年 | 102篇 |
1998年 | 87篇 |
1997年 | 71篇 |
1996年 | 76篇 |
1995年 | 49篇 |
1994年 | 55篇 |
1993年 | 41篇 |
1992年 | 82篇 |
1991年 | 80篇 |
1990年 | 69篇 |
1989年 | 70篇 |
1988年 | 83篇 |
1987年 | 61篇 |
1986年 | 84篇 |
1985年 | 72篇 |
1984年 | 56篇 |
1983年 | 69篇 |
1982年 | 55篇 |
1981年 | 41篇 |
1980年 | 34篇 |
1979年 | 53篇 |
1978年 | 50篇 |
1977年 | 37篇 |
1976年 | 42篇 |
1974年 | 34篇 |
1973年 | 35篇 |
排序方式: 共有6752条查询结果,搜索用时 24 毫秒
981.
Jessica N. Byram Jason M. Organ Michael Yard Naomi A. Schmalz 《Anatomical sciences education》2020,13(2):149-157
The demand for upper-level undergraduate dissection-based anatomy courses is growing, as professional programs require more advanced anatomy training prior to matriculation. To address this need, Indiana University School of Medicine (IUSM) partnered with Indiana University-Purdue University Indianapolis—a large, urban, life science-focused campus nearby to IUSM—to offer an undergraduate, dissection-based course in regional gross anatomy. Because this is a new course, a deeper post-course evaluation of student perceptions was conducted using Q methodology. In this study, Q methodology was used to evaluate student views of the overall course structure, pre-laboratory materials and activities, assessments, and quality of instruction. Of the 15 students in the spring semester 2018 cohort, 80% (n = 12) participated in the evaluation, and 10 of those students followed up with written explanations for their rationale in selecting the four statements with which they most strongly agreed and disagreed. The Q methodology sorted the students into one of three statistically significant groups: Motivated Dissectors (n = 6), Traditional Students (n = 3), and Inspired Learners (n = 3). Motivated Dissectors and Inspired Learners felt strongly that the course did not encourage self-directed learning and that the pre-laboratory materials were not adequate to prepare them for quizzes. Traditional Students, however, disagreed, having a favorable opinion of the pre-laboratory materials, even though this group felt most strongly that the amount of material covered in the course was overwhelming. This study demonstrates the utility of Q methodology to evaluate courses to elucidate student perspectives and inform future course modifications. 相似文献
982.
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
983.
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
984.
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
985.
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
986.
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
987.
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
988.
The degree to which teachers' perceptions of a student can be distorted by characteristics indigenous to teachers, as well as students, were investigated to determine whether teachers would initiate a referral for special education. Sixty-five teachers volunteered for participation. Twenty-seven of them were experienced, having had their own classrooms in a public school. Thirty-eight were preservice student teachers who had not yet had their own classrooms. Teachers were evaluated to have had either an internal or external locus of control and were judged to have had either a high or low opinion of self according to either of two separate scales. After viewing two video tapes of two elementary-aged students (one student was severely emotionally disturbed [SED] and the other non-SED), teachers rated the children on several child characteristics and referral questions. Results revealed that the locus of control and self-esteem of teachers, in conjunction with teaching experience and a child's characteristics, can predict teachers' inclinations to refer children. Findings point to the need to place greater care in the initiation of referrals. © 1997 John Wiley & Sons, Inc. 相似文献
989.
990.
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