全文获取类型
收费全文 | 723篇 |
免费 | 59篇 |
国内免费 | 10篇 |
出版年
2023年 | 16篇 |
2022年 | 11篇 |
2021年 | 16篇 |
2020年 | 17篇 |
2019年 | 18篇 |
2018年 | 15篇 |
2017年 | 19篇 |
2016年 | 18篇 |
2015年 | 24篇 |
2014年 | 38篇 |
2013年 | 33篇 |
2012年 | 28篇 |
2011年 | 26篇 |
2010年 | 22篇 |
2009年 | 34篇 |
2008年 | 25篇 |
2007年 | 49篇 |
2006年 | 44篇 |
2005年 | 35篇 |
2004年 | 24篇 |
2003年 | 26篇 |
2002年 | 26篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 16篇 |
1998年 | 16篇 |
1997年 | 16篇 |
1996年 | 12篇 |
1995年 | 13篇 |
1994年 | 12篇 |
1993年 | 4篇 |
1992年 | 12篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
排序方式: 共有792条查询结果,搜索用时 31 毫秒
141.
Benjamin Buemann Marie-Claude Vohl Monique Chagnon Yvon C. Chagnon Jacques Gagnon Louis Prusse France Dionne Jean-Pierre Desprs Angelo Tremblay Andr Nadeau Claude Bouchard 《Obesity (Silver Spring, Md.)》1997,5(3):186-192
Several investigations have suggested that body fat distribution is influenced by nonpathologic variations in the responsiveness to Cortisol. Genetic variations in the glucocorticoid receptor (GRL) could therefore potentially have an impact on the level of abdominal fat. A restriction fragment length polymorphism (RFLP) has previously been detected with the BelI restriction enzyme in the GRL gene identifying two alleles with fragment lengths of 4.5 and 2.3 kb. This study investigates whether abdominal fat areas measured by computerized tomography (CT) are associated with this polymorphism in 152 middle-aged men and women. The less frequent 4.5-kb allele was found to be associated with a higher abdominal visceral fat (A VF) area independently of total body fat mass (4.5/4.5 vs. 2.3/2.3 kb genotype; men: 190.7 ± 30.1 vs. 150.7 ± 33.3 cm2, p=0.04; women: 132.7 ± 37.3 vs. 101.3 ± 34.5 cm2, p=0.06). However, the association with AVF was seen only in subjects of the lower tertile of the percent body fat level. In these subjects, the polymorphism was found to account for 41% (p=0.003) and 35% (p=0.007), in men and women, respectively, of the total variance in AVF area. The consistent association between the GRL polymorphism detected with BelI and AVF area suggests that this gene or a locus in linkage disequilibrium with the BelI restriction site may contribute to the accumulation of AVF. 相似文献
142.
Fabio Armellini Mauro Zamboni Tamara Harris Rocco Micciolo Ottavio Bosello 《Obesity (Silver Spring, Md.)》1997,5(4):315-320
ARMELLINI FABIO, MAURO ZAMBONI, TAMARA HARRIS, ROCCO MICCIOLO, OTTAVIO BOSELLO. Sagittal diameter minus subcutaneous thickness. An easy-to-obtain parameter that improves visceral fat prediction. Two groups of 99 and 98 women were studied to test if correcting sagittal diameter by subtracting the thickness of subcutaneous abdominal adipose tissue improves its degree of association with visceral adipose tissue. The first group (age, 40 ± 14 years; body mass index [BMI], 36 ± 6 kg/m2) was used to calculate the predictive equations for visceral adipose tissue. The second group (age, 43 ± 14 years; BMI, 37 ± 6 kg/m2) was used for cross-validation. Various anthropometric parameters were measured by ultrasound and computed tomography. Correlation coefficients with single-slice visceral adipose tissue area, after sagittal diameter was corrected by subtracting subcutaneous thickness, rose from 0.63 to 0.72 in the first group and from 0.64 to 0.71 in the second group. The standard error of residuals of the regression formula for visceral adipose tissue area was 10% lower with modified sagittal diameter than with sagittal diameter alone. During cross-validation, the standard error of differences was 5% lower with modified sagittal diameter. The visceral adipose tissue estimate was also less biased by the size of the area when sagittal diameter minus subcutaneous thickness was used. Results show that subtracting the thickness of abdominal subcutaneous adipose tissue from sagittal diameter significantly improves the predictive power of sagittal diameter for visceral adipose tissue and could be a useful tool for epidemiological studies. 相似文献
143.
The ontogeny of the axial skeleton, in particular the caudal skeleton, is described from embryos to adult specimens in common wolffish, Anarhichas lupus. The eggs were incubated at constant temperatures of 7.0, 11.0 and 13.0 °C. High egg mortality and structural changes in skeletal development (fusion of parts, absence of distal radials and most of dorsal and anal fin rays, abnormal neural arches and dorsal fin rays) were observed at 13 °C. The frequencies of some anomalies were lower at 11 °C than at 13 °C. The main reason of structural changes of the skeleton at high temperature is the breaking of normal correlations between developmental rates of some cartilaginous structures and other tissues and organs of the embryo. These data suggest an epigenetic mechanism of skeletal evolution. 相似文献
144.
P. Vandewalle† G. Germeau P. Besancenet‡ E. Parmentier E. Baras§ 《Journal of fish biology》2005,66(4):996-1024
At hatching (15 h post fertilization), Brycon moorei possesses no skeletal structure. Thereafter, development is very rapid. The first oral teeth appear no later than 3 h post‐hatching, but they remain covered with epithelium until c . 45 h. At 7 h, the trabecular bars and part of the cartilaginous visceral arches are visible and at 15 h, the dentaries and premaxillaries are present. At 25 h, i.e . the onset of piscivory and cannibalism (the yolk sac is only fully resorbed after 36 h), the oral teeth are fully developed, the first pharyngeal teeth are formed, and some head movements already appear synchronized, but the mouth cavity is not completely isolated from the neurocranium by bony structures. Thereafter, no new buccal or pharyngeal bony structure is visible until 45 h, when the maxilla and opercula appear, along with a new type of cannibalistic behaviour. Cartilage resorptions also start at 45 h, but with no concomitant replacement by formation of calcified structures. Later, development gradually becomes similar to that of many previously studied teleosts. The developmental pattern of B. moorei is thus extremely rapid in comparison with other teleosts, i.e . it prioritizes feeding structures that permit the expression of piscivory at a very early age. The uniqueness of this pattern is discussed in relation to ecological constraints on early feeding and fast growth. 相似文献
145.
Synchrotron analysis of a ‘mummified’ salamander (Vertebrata: Caudata) from the Eocene of Quercy,France
下载免费PDF全文
![点击此处可从《Zoological Journal of the Linnean Society》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jérémy Tissier Jean‐Claude Rage Renaud Boistel Vincent Fernandez Nicolas Pollet Géraldine Garcia Michel Laurin 《Zoological Journal of the Linnean Society》2016,177(1):147-164
An incomplete ‘mummy’ from the Phosphorites du Quercy (presumed Eocene) was identified as a salamander during the 19th century. The specimen has now been computed tomography (CT) scanned, and this revealed the incomplete skeleton (with perfectly preserved bones) and soft tissues (lung). The fossil represents a new, well‐characterized taxon. Despite the absence of the skull, several features allow a phylogenetic analysis. The fossil belongs to pseudosaurian caudates; it is tentatively assigned to the Salamandridae, although affinities with Plethodontidae cannot be definitely ruled out. 相似文献
146.
Priscilla A. Erickson Andrew M. Glazer Emily E. Killingbeck Rachel M. Agoglia Jiyeon Baek Sara M. Carsanaro Anthony M. Lee Phillip A. Cleves Dolph Schluter Craig T. Miller 《Evolution; international journal of organic evolution》2016,70(4):887-902
The extent to which convergent adaptation to similar ecological niches occurs by a predictable genetic basis remains a fundamental question in biology. Threespine stickleback fish have undergone an adaptive radiation in which ancestral oceanic populations repeatedly colonized and adapted to freshwater habitats. In multiple lakes in British Columbia, two different freshwater ecotypes have evolved: a deep‐bodied benthic form adapted to forage near the lake substrate, and a narrow‐bodied limnetic form adapted to forage in open water. Here, we use genome‐wide linkage mapping in marine × benthic F2 genetic crosses to test the extent of shared genomic regions underlying benthic adaptation in three benthic populations. We identify at least 100 Quantitative Trait Loci (QTL) harboring genes influencing skeletal morphology. The majority of QTL (57%) are unique to one cross. However, four genomic regions affecting eight craniofacial and armor phenotypes are found in all three benthic populations. We find that QTL are clustered in the genome and overlapping QTL regions are enriched for genomic signatures of natural selection. These findings suggest that benthic adaptation has occurred via both parallel and nonparallel genetic changes. 相似文献
147.
Tobias Riede Chad M. Eliason Edward H. Miller Franz Goller Julia A. Clarke 《Evolution; international journal of organic evolution》2016,70(8):1734-1746
Most birds vocalize with an open beak, but vocalization with a closed beak into an inflating cavity occurs in territorial or courtship displays in disparate species throughout birds. Closed‐mouth vocalizations generate resonance conditions that favor low‐frequency sounds. By contrast, open‐mouth vocalizations cover a wider frequency range. Here we describe closed‐mouth vocalizations of birds from functional and morphological perspectives and assess the distribution of closed‐mouth vocalizations in birds and related outgroups. Ancestral‐state optimizations of body size and vocal behavior indicate that closed‐mouth vocalizations are unlikely to be ancestral in birds and have evolved independently at least 16 times within Aves, predominantly in large‐bodied lineages. Closed‐mouth vocalizations are rare in the small‐bodied passerines. In light of these results and body size trends in nonavian dinosaurs, we suggest that the capacity for closed‐mouth vocalization was present in at least some extinct nonavian dinosaurs. As in birds, this behavior may have been limited to sexually selected vocal displays, and hence would have co‐occurred with open‐mouthed vocalizations. 相似文献
148.
149.
Mauro Maciel de Arruda Fabiano Borges Figueiredo Andreza Pain Marcelino José Ronaldo Barbosa Guilherme Loureiro Werneck Elza Ferreira Noronha Gustavo Adolfo Sierra Romero 《Memórias do Instituto Oswaldo Cruz》2016,111(3):168-173
In Brazil, human and canine visceral leishmaniasis (CVL) caused byLeishmania
infantum has undergone urbanisation since 1980, constituting a public
health problem, and serological tests are tools of choice for identifying infected
dogs. Until recently, the Brazilian zoonoses control program recommended
enzyme-linked immunosorbent assays (ELISA) and indirect immunofluorescence assays
(IFA) as the screening and confirmatory methods, respectively, for the detection of
canine infection. The purpose of this study was to estimate the accuracy of ELISA and
IFA in parallel or serial combinations. The reference standard comprised the results
of direct visualisation of parasites in histological sections, immunohistochemical
test, or isolation of the parasite in culture. Samples from 98 cases and 1,327
noncases were included. Individually, both tests presented sensitivity of 91.8% and
90.8%, and specificity of 83.4 and 53.4%, for the ELISA and IFA, respectively. When
tests were used in parallel combination, sensitivity attained 99.2%, while
specificity dropped to 44.8%. When used in serial combination (ELISA followed by
IFA), decreased sensitivity (83.3%) and increased specificity (92.5%) were observed.
Serial testing approach improved specificity with moderate loss in sensitivity. This
strategy could partially fulfill the needs of public health and dog owners for a more
accurate diagnosis of CVL. 相似文献
150.
刺激左侧内脏大神经,同时记录肋间神经反射放电(VSR)及脊髓灰质单位电活动。由于 VSR 的阈值相当于内脏神经中 A-delta 纤维的阈值,故以诱发放电阈值等于或略高于 VSR的阈值的单位为 A-delta 单位。阈值等于或高于 VSR 中 C 突起的阈值的单位为 C-单位。我们所观察到的90个 A-delta 单位广泛分布在 Rexed 第Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ、Ⅵ、Ⅶ层,这和Pomeranz 等报道脊髓灰质中对内脏神经的 A-delta 纤维传入起反应的神经元仅分布在第Ⅴ层有所不同。我们记录到的30个 C 单位分布在第Ⅰ、Ⅳ、Ⅴ、Ⅶ、Ⅶ等层。在64个单位中有62个可观察到内脏大神经和肋间神经传入的会聚。在本工作中,我们还观察到自发放电受刺激内脏大神经抑制的单位。有许多单位的诱发放电出现在 VSR 时程以外,显然不可能参与 VSR 的反射弧。 相似文献