全文获取类型
收费全文 | 13808篇 |
免费 | 32篇 |
国内免费 | 4篇 |
专业分类
教育 | 10617篇 |
科学研究 | 1399篇 |
各国文化 | 28篇 |
体育 | 529篇 |
综合类 | 12篇 |
文化理论 | 423篇 |
信息传播 | 836篇 |
出版年
2023年 | 10篇 |
2022年 | 38篇 |
2021年 | 56篇 |
2020年 | 68篇 |
2019年 | 130篇 |
2018年 | 2279篇 |
2017年 | 2199篇 |
2016年 | 1654篇 |
2015年 | 185篇 |
2014年 | 199篇 |
2013年 | 454篇 |
2012年 | 301篇 |
2011年 | 757篇 |
2010年 | 900篇 |
2009年 | 482篇 |
2008年 | 694篇 |
2007年 | 1208篇 |
2006年 | 119篇 |
2005年 | 466篇 |
2004年 | 526篇 |
2003年 | 462篇 |
2002年 | 208篇 |
2001年 | 70篇 |
2000年 | 57篇 |
1999年 | 24篇 |
1998年 | 9篇 |
1997年 | 21篇 |
1996年 | 11篇 |
1995年 | 20篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 19篇 |
1990年 | 8篇 |
1989年 | 16篇 |
1988年 | 5篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1967年 | 4篇 |
1966年 | 6篇 |
1963年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Test procedures and their accuracy in determining critical fall height (CFH) on sporting grounds are paramount to player safety.
The procedure currently adopted for synthetic turf in Australian football [1] consists of four consecutive drops at various drop heights at three test locations on the sample. The quantity and packing
of the infill in third-generation turf and the pooling effect of the rubber particles with consecutive drops suggests that
the current standard protocol may need re-assessment. Therefore, the purpose of this pilot study was to investigate whether
current methods of testing for CFH are appropriate for third-generation synthetic turf or whether an alternative or adapted
method needs to be developed. CFH was measured, using a HISUN Uniaxe-II Impact Tester, on 12 combinations of synthetic turf
samples (four different products with three shock pad options). Three conditions were investigated on each sample; the existing
protocol; an alternative 12 single-drop protocol and four single drops from the CFH determined from the existing protocol.
A significant difference was found for both absolute and percentage difference between the existing and 12 single-drop protocol,
with p = 0.001 and t = 4.33 and p < 0.001 and t = 6.03, respectively. There was also a significant difference between the CFH reached with and without a shock pad for both
the existing protocol and the 12 single-drop protocol. The results of this pilot study demonstrate that differences do occur
with alterations to the existing protocol and highlight the need for a more detailed characterisation of testing methods on
third-generation synthetic turf and the response of surfaces to them. 相似文献
992.
A number of recent studies have measured the extent and timing of segment rotation during the golf swing. A promising technique,
instantaneous screw axis (ISA) theory, could provide a better expression of segment rotation. In Part 1 of this two-part study,
the objectives are to identify the ISA of the pelvis, shoulders and left arm during the downswing, compute segment angular
velocity relative to that segment’s ISA and verify that ISA theory is a valid tool to analyse segment rotation during the
golf swing. Results indicate that for all subjects, at least 71% of marker velocity is a result of rotation about their respective
ISA, when averaging results over the duration of the downswing, confirming that motion is primarily rotational. Furthermore,
ISA position and orientation of each segment approaches, on average, the expected gross axis of rotation, confirming that
motion about the ISA is representative of joint motion. 相似文献
993.
Eduardo N. Borges Moisés G. de Carvalho Renata Galante Marcos André Gonçalves Alberto H.F. Laender 《Information processing & management》2011
Digital libraries of scientific articles contain collections of digital objects that are usually described by bibliographic metadata records. These records can be acquired from different sources and be represented using several metadata standards. These metadata standards may be heterogeneous in both, content and structure. All of this implies that many records may be duplicated in the repository, thus affecting the quality of services, such as searching and browsing. In this article we present an approach that identifies duplicated bibliographic metadata records in an efficient and effective way. We propose similarity functions especially designed for the digital library domain and experimentally evaluate them. Our results show that the proposed functions improve the quality of metadata deduplication up to 188% compared to four different baselines. We also show that our approach achieves statistical equivalent results when compared to a state-of-the-art method for replica identification based on genetic programming, without the burden and cost of any training process. 相似文献
994.
Kannan Vaidyanathan M. P. Narayanan D. M. Vasudevan 《Indian journal of clinical biochemistry : IJCB》2011,26(4):319-325
Organic acidurias are an important class of inherited metabolic disorders arising due to defect in intermediary metabolic
pathways of carbohydrate, amino acids and fatty acid oxidation. This review summarizes the current knowledge about the important
organic acidurias in the Indian population. Specifically, diagnosis and principles of treatment of organic acidurias are covered.
The salient features of common organic acidurias as well as their prevalence in various parts of the world are reviewed in
some detail. 相似文献
995.
Haruhiro Muratsubaki Akiko Yamaki 《Indian journal of clinical biochemistry : IJCB》2011,26(4):416-419
The effect of acute hypoxic hypoxia on the profile of plasma amino acids in rats was studied and compared to that resulting
from acute liver injury induced by giving carbon tetrachloride. In hypoxic rats exposed to 45% air in N2 for 5 h, the concentrations of branched chain amino acids, including valine, leucine and isoleucine, and aromatic amino acids
such as phenylalanine and tyrosine were significantly increased as compared to those in normoxic rats. The ratio of branched-chain
to aromatic amino acids (Fischer’s ratio) was significantly decreased. The levels of arginine and citrulline, which are related
to the urea cycle, were also depressed. Furthermore, plasma proline level was reduced in hypoxic rats. The activities of plasma
marker enzymes for tissue damage remained unchanged during hypoxia, indicating that tissue injury was not induced by exposure
to hypoxic conditions. We suggest that the characteristic profile of plasma amino acids and the Fischer ratio are valuable
tools for understanding the pathology of acute hypoxia in the absence of systemic tissue damage. 相似文献
996.
997.
Khan S Bhargava A Pathak N Maudar KK Varshney S Mishra PK 《Indian journal of clinical biochemistry : IJCB》2011,26(2):161-168
The present study evaluated the plausible role of circulating biomarkers in immune pathogenesis of chronic hepatitis considered
a priority in clinical hepatology. Total viral load of chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) patients
was quantified and correlation studies were performed with circulating levels of Th1/Th2 cytokines; C reactive protein and
circulating nucleosomes; glutathione reductase (GR) and superoxide dismutase. To our knowledge, the study is first among its
kind that validates strong positive correlation of viral load with IL-4, IL-6, GR in HBV and IL-6, IL-10, GR in HCV infections.
Although, multi-centric studies including large cohorts are required for translating our findings to clinical practice, however,
role of these biomarkers with potential diagnostic or prognostic significance might be helpful in clinical assessment of high-risk
individuals, thereby, designing interventional strategies, towards development of personalized medicare. The results of our
study also offer valuable insights of immune signaling mediators engaged in development of hepatocellular carcinoma. 相似文献
998.
999.
Nitric oxide (NO) a free radical having both cytoprotective as well as tumor promoting agent is formed from l-arginine by converting it to l-citrulline via nitric oxide synthase enzymes. The reaction product of nitric oxide with superoxide generates potent oxidizing
agent, peroxynitrite which is the main mediator of tissue and cellular injury. Peroxynitrite is reactive towards many biomolecules
which includes amino acids, nucleic acid bases; metal containing compounds, etc. NO metabolites may play a key role in mediating
many of the genotoxic/carcinogenic effects as DNA damage, protein or lipid modification, etc. The basic reactions of nitric
oxide can be divided as direct effect of the radical where it alone plays a role in either damaging or protecting the cell
milieu and an indirect effect in which the byproducts of nitric oxide formed by convergence of two independent radical generating
pathways play the role in biological reactions which mainly involve oxidative and nitrosative stress. Nitric oxide is also
capable of directly interacting with mitochondria through inhibition of respiration or by permeability transition. Reaction
of nitric oxide with metal ions include its direct interaction with the metals or with oxo complexes thereby reducing them
to lower valent state. Excessive production of nitric oxide can be studied by inhibiting the synthetic pathway of nitric oxide
using both selective or specific nitric oxide synthase inhibitor or non-selective nitric oxide synthase inhibitor with respect
to isoforms of nitric oxide. 相似文献
1000.
Franky D. Shah Rasheedunnisa Begum Bhairavi N. Vajaria Kinjal R. Patel Jayendra B. Patel Shilin N. Shukla Prabhudas S. Patel 《Indian journal of clinical biochemistry : IJCB》2011,26(4):326-334
Oral cancer has emerged as an alarming public health problem with increasing incidence and mortality rates all over the world.
Therefore, the implementation of newer screening and early detection approaches are of utmost importance which could reduce
the morbidity and mortality associated with this disease. Sensitive and specific biomarkers for oral cancer are likely to
be most effective for screening, diagnosis, staging and follow-up for this dreaded malignancy. Unlike other deep cancers,
oral cancer is located in oral cavity. Hence, the direct contact between saliva and oral cancer lesion makes the measurement
of tumor markers in saliva an attractive alternative to serum and tissue testing. The DNA, RNA and protein molecules derived
from the living cancer cells can be conveniently obtained from saliva. Thus, salivary biomarkers, a non-invasive alternative
to serum and tissue-based biomarkers may be an effective modality for early diagnosis, prognostication and monitoring post
therapy status. In the current post-genomic era, various technologies provide opportunities for high-throughput approaches
to genomics and proteomics; which have been used to evaluate altered expressions of gene and protein targets in saliva of
oral cancer patients. The emerging field of salivary biomarkers has great potentials to prove its clinical significance to
combat oral cancer. Hence, we have reviewed importance of several salivary genomics and proteomics biomarkers for oral cancer. 相似文献