全文获取类型
收费全文 | 2970篇 |
免费 | 192篇 |
出版年
2022年 | 13篇 |
2021年 | 39篇 |
2020年 | 22篇 |
2019年 | 12篇 |
2018年 | 35篇 |
2017年 | 25篇 |
2016年 | 57篇 |
2015年 | 95篇 |
2014年 | 112篇 |
2013年 | 145篇 |
2012年 | 201篇 |
2011年 | 185篇 |
2010年 | 119篇 |
2009年 | 122篇 |
2008年 | 165篇 |
2007年 | 173篇 |
2006年 | 167篇 |
2005年 | 169篇 |
2004年 | 164篇 |
2003年 | 159篇 |
2002年 | 139篇 |
2001年 | 39篇 |
2000年 | 38篇 |
1999年 | 28篇 |
1998年 | 68篇 |
1997年 | 28篇 |
1996年 | 35篇 |
1995年 | 31篇 |
1994年 | 37篇 |
1993年 | 32篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 21篇 |
1989年 | 24篇 |
1988年 | 25篇 |
1987年 | 11篇 |
1986年 | 29篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 26篇 |
1981年 | 29篇 |
1980年 | 23篇 |
1979年 | 22篇 |
1978年 | 25篇 |
1977年 | 12篇 |
1976年 | 17篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1969年 | 10篇 |
排序方式: 共有3162条查询结果,搜索用时 185 毫秒
111.
Multi-species compartment epidemic models, such as the multi-species susceptible–infectious–recovered (SIR) model, are extensions of the classic SIR models, which are used to explore the transient dynamics of pathogens that infect multiple hosts in a large population. In this article, we propose a dynamical Bayesian hierarchical SIR (HSIR) model, to capture the stochastic or random nature of an epidemic process in a multi-species SIR (with recovered becoming susceptible again) dynamical setting, under hidden mass balance constraints. We call this a Bayesian hierarchical multi-species SIR (MSIRB) model. Different from a classic multi-species SIR model (which we call MSIRC), our approach imposes mass balance on the underlying true counts rather than, improperly, on the noisy observations. Moreover, the MSIRB model can capture the discrete nature of, as well as uncertainties in, the epidemic process. 相似文献
112.
Vincent Daien Isabelle Carriere Ryo Kawasaki Jean-Paul Cristol Max Villain Pierre Fesler Karen Ritchie Cecile Delcourt 《PloS one》2013,8(7)
Purpose
Retinal vascular caliber has been linked with increased cardiovascular risk and is predictive of cardiovascular pathology, including stroke and coronary heart disease. Oxidative stress, as well as inflammatory mechanisms, plays a major role in the pathogenesis and progression of atherosclerosis, plaque rupture and vascular thrombotic propensity. The purpose of this study is to explore the relationship between retinal vascular calibers and biomarkers of oxidative stress and inflammation, in subjects free of cardiovascular pathology.Patients and Methods
Cross-sectional analysis from a community-dwelling cohort comprising 1224 individuals aged 60 years and over, without a history of coronary or peripheral artery disease or stroke. Retinal vascular caliber was measured from fundus photographs using semi-automated standardized imaging software. Oxidative stress was evaluated using plasma superoxide dismutase 2 and glutathione peroxidase (GPx-3) activities, and inflammatory state was assessed using plasma high sensitivity C-reactive protein (hsCRP) and orosomucoid.Results
In a multivariate model controlling for cardiovascular risk factors, larger retinal arteriolar caliber was independently related to higher level of GPx-3 activity (p = 0.003) whereas larger venular caliber was associated with higher levels of hsCRP (p = 0.0001) and orosomucoid (p = 0.01).Conclusion
In the present study, biomarkers of oxidative stress regulation and inflammation were independently associated with retinal vascular calibers. This suggests that an assessment of retinal vessels may offer early and non-invasive detection of subclinical vascular pathology. 相似文献113.
Léa Leuzinger Lionel Cavin Adriana López-Arbarello Jean-Paul Billon-Bruyat 《Palaeontology》2020,63(1):117-129
Tooth replacement in vertebrates is extremely diverse, and its study in extinct taxa gives insights into the evolution of the different dental renewal modes. Based on μ-CT scans of a left lower jaw of the extinct fish †Scheenstia (Actinopterygii, Lepisosteiformes), we describe in detail a peculiar tooth replacement mode that is, as far as we could ascertain from the literature, unique among vertebrates. The formation of the replacement teeth comprises a 180° rotation of their acrodin cap that occurs intraosseously within bony crypts, and their setting up appears to be synchronous. We propose a model for the dental renewal process and identify complementary anatomical features visible in the tomography such as the junction between the different tooth-bearing bones (prearticular–coronoid and dentary), as well as cavities corresponding to intraosseous crypts, nervous and/or vascular canals. The location of the cavities and their subsequent identification (e.g. Meckel's cavity, mandibular sensory canal) help us to identify the function of pores visible on the bone surface and understand their relation to internal anatomical features. Finally, recognition of this tooth replacement mode raises the question of whether it is specific to †Scheenstia or related to a particular dentition type and thus potentially occurs in other lineages. 相似文献
114.
115.
Michaela Ecker Hervé Bocherens Marie-Anne Julien Florent Rivals Jean-Paul Raynal Marie-Hélène Moncel 《Journal of human evolution》2013
The Middle Palaeolithic site of Payre in southeastern France yields abundant archaeological material associated with fossil hominid remains. With its long sequence of Middle Pleistocene deposits, Payre is a key site to study the Middle Palaeolithic chronology of this region. This study is the first to investigate carbon and oxygen isotope contents of Neanderthal tooth enamel bioapatite, together with a wide range of herbivorous and carnivorous species. The aim is to contribute to the understanding of hunting behaviour, resource partitioning, diet and habitat use of animals and Neanderthals through a palaeoecological reconstruction. 相似文献
116.
The miniaturized wireless inertial measurement unit (IMU) technology and algorithms presented herein promote rapid and accurate predictions of the center-of-rotation (CoR) for ball/spherical joints. The algorithm improves upon existing IMU-based methods by directly utilizing the measured acceleration and angular velocity provided by the IMU to deduce the CoR in lieu of relying on error-prone velocity and position estimates. Results demonstrate that this new method resolves the position of the CoR to within a 3 mm sphere of the true CoR determined by a precision coordinate measuring machine. Such accuracy may render this method attractive for broad use in field, laboratory and clinical settings requiring non-invasive and rapid estimates of joint CoR. 相似文献
117.
William E. Schrank Blanca Skoda Paul Parsons Noel Roy 《Ocean Development & International Law》2013,44(4):357-390
The commercial fishery for northern cod off Newfoundland has been closed since 1992. Since then, the recreational “food fishery”; has also been closed, as have the fisheries for many additional cod and other groundfish stocks. The Newfoundland fisheries had been commercially unviable for many years before the closures. This article records the federal and provincial governments’ financial outlays (expenditures, transfer payments to individuals, subsidies, net equity purchases, and net loans) on the fishery during the decade following 1981. Special emphasis is placed on the cost of the financial restructuring of the industry in the mid‐1980s, net unemployment insurance payments, and social overhead capital expenditures. 相似文献
118.
Constanze Hartmann Fabienne Mayenzet Jean-Paul Larcinese Olivier P. Haefliger Andrea Buettner Christian Starkenmann 《Steroids》2013,78(2):156-160
A method was developed for the quantification of 5-α-androst-16-en-3-one in human breast milk based on application of a stable isotope dilution assay using 5α-androst-16-en-3-one-6, 6-d2. The procedure includes extraction of the human milk by hexane with subsequent clean-up of the obtained extract by gel permeation and silica gel column chromatography. The extracted samples were analyzed by gas chromatography–mass spectrometry. Using this method 5-α-androst-16-en-3-one could be identified and for the first time quantified in a concentration range of 26–155 ng/kg in human milk. 相似文献
119.
Cleoni Alves Mendes de Lima Harrison Magdinier Gomes Maraníbia Aparecida Cardoso Oelemann Jesus Pais Ramos Paulo Cezar Caldas Carlos Eduardo Dias Campos Márcia Aparecida da Silva Pereira Fátima Fandinho Onofre Montes Maria do Socorro Calixto de Oliveira Philip Noel Suffys Maria Manuela da Fonseca Moura 《Memórias do Instituto Oswaldo Cruz》2013,108(4):457-462
The main cause of pulmonary tuberculosis (TB) is infection with
Mycobacterium tuberculosis (MTB). We aimed to evaluate the
contribution of nontuberculous mycobacteria (NTM) to pulmonary disease in
patients from the state of Rondônia using respiratory samples and
epidemiological data from TB cases. Mycobacterium isolates were identified using
a combination of conventional tests, polymerase chain reaction-based restriction
enzyme analysis of hsp65 gene and hsp65 gene
sequencing. Among the 1,812 cases suspected of having pulmonary TB, 444 yielded
bacterial cultures, including 369 cases positive for MTB and 75 cases positive
for NTM. Within the latter group, 14 species were identified as
Mycobacterium abscessus, Mycobacterium
avium, Mycobacterium fortuitum,
Mycobacterium intracellulare, Mycobacterium
gilvum, Mycobacterium gordonae,
Mycobacterium asiaticum, Mycobacterium
tusciae, Mycobacterium porcinum,
Mycobacterium novocastrense, Mycobacterium
simiae, Mycobacterium szulgai,
Mycobacterium phlei and Mycobacterium
holsaticum and 13 isolates could not be identified at the species
level. The majority of NTM cases were observed in Porto Velho and the relative
frequency of NTM compared with MTB was highest in Ji-Paraná. In approximately
half of the TB subjects with NTM, a second sample containing NTM was obtained,
confirming this as the disease-causing agent. The most frequently observed NTM
species were M. abscessus and M. avium and
because the former species is resistant to many antibiotics and displays
unsatisfactory cure rates, the implementation of rapid identification of
mycobacterium species is of considerable importance. 相似文献
120.
Jean-Paul Comet Mathilde Noual Adrien Richard Julio Aracena Laurence Calzone Jacques Demongeot Marcelle Kaufman Aurélien Naldi El Houssine Snoussi Denis Thieffry 《Bulletin of mathematical biology》2013,75(6):906-919
It has been proved, for several classes of continuous and discrete dynamical systems, that the presence of a positive (resp. negative) circuit in the interaction graph of a system is a necessary condition for the presence of multiple stable states (resp. a cyclic attractor). A positive (resp. negative) circuit is said to be functional when it “generates” several stable states (resp. a cyclic attractor). However, there are no definite mathematical frameworks translating the underlying meaning of “generates.” Focusing on Boolean networks, we recall and propose some definitions concerning the notion of functionality along with associated mathematical results. 相似文献