首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   696篇
  免费   32篇
  728篇
  2023年   4篇
  2022年   8篇
  2021年   12篇
  2020年   8篇
  2019年   8篇
  2018年   6篇
  2017年   15篇
  2016年   23篇
  2015年   31篇
  2014年   41篇
  2013年   45篇
  2012年   51篇
  2011年   58篇
  2010年   25篇
  2009年   19篇
  2008年   56篇
  2007年   48篇
  2006年   39篇
  2005年   38篇
  2004年   28篇
  2003年   38篇
  2002年   34篇
  2001年   7篇
  2000年   3篇
  1999年   10篇
  1998年   8篇
  1996年   4篇
  1995年   4篇
  1994年   9篇
  1993年   5篇
  1991年   2篇
  1990年   6篇
  1989年   3篇
  1987年   2篇
  1986年   1篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1981年   3篇
  1980年   2篇
  1978年   2篇
  1977年   1篇
  1976年   2篇
  1975年   2篇
  1974年   2篇
  1972年   2篇
  1971年   2篇
  1970年   2篇
  1968年   1篇
  1967年   1篇
排序方式: 共有728条查询结果,搜索用时 15 毫秒
101.
To examine the potential linkage between sex-biased growth and dispersal in demersal fish, we studied the movement distance and growth of tag-recaptured sablefish (Anoplopoma fimbria). Tagging was conducted by teams from Japan and the United States. From 1980 to 1984, 58,918 sablefish were captured by Japanese vessels and tagged with anchor tags, and between 1980 and 2007, 3319 sablefish were recaptured in the Bering Sea and northeastern Pacific. Of these 3319 fish, we analyzed data on 659 individuals for which we have reliable data on recapture location, sex and fork length at the time of release and recapture, and elapsed time longer than 10?days. Annual growth increments (mean±S.D.) were 2.5?±?6.5?cm (males) and 3.5?±?8.6?cm (females), and the movement distances (assumed to be straight) were 712?±?800?km (males) and 877?±?920?km (females). Females grew larger and moved longer distances than males. We calculated the growth increment deviation that accounted for the effects of elapsed time, curvilinear growth, and initial fork length at release using a von Bertalanffy growth model. The growth increment deviation increased significantly with the distance moved over elapsed time. In addition, the relationship between distance moved over elapsed time and the growth deviation differed significantly between sexes; females grew faster than males at a given movement distance. We suggest that female-biased dispersal is a factor generating female-biased growth in sablefish.  相似文献   
102.
Angelica keiskei (Ashitaba in Japanese), a traditional herb in Japan, contains abundant prenylated chalcones. It has been reported that the chalcones from A. keiskei showed such bioactivities as anti-bacterial, anti-cancer and anti-diabetic effects. Xanthoangelol, 4-hydroxyderricin and six new chalcones were isolated in this study from an ethanol extract of A. keiskei by octadecyl silyl (ODS) and silica gel chromatography, and identified by 1D- and 2D-nuclear magnetic resonance (NMR) and high-resolution mass spectrometric analyses. The chalcones from A. keiskei markedly increased the expression of the adiponectin gene and the production of adiponectin in 3T3-L1 adipocytes. These results suggest that the chalcones from A. keiskei might be useful for preventing the metabolic syndrome.  相似文献   
103.
104.

Background

The electrophysiological properties of the brain and influence of parental bonding in childhood irritable bowel syndrome (IBS) are unclear. We hypothesized that children with chronic gastrointestinal (GI) symptoms like IBS may show exaggerated brainstem auditory evoked potential (BAEP) responses and receive more inadequate parental bonding.

Methodology/Principal Findings

Children aged seven and their mothers (141 pairs) participated. BAEP was measured by summation of 1,000 waves of the electroencephalogram triggered by 75 dB click sounds. The mothers completed their Children''s Somatization Inventory (CSI) and Parental Bonding Instrument (PBI). CSI results revealed 66 (42%) children without GI symptoms (controls) and 75 (58%) children with one or more GI symptoms (GI group). The III wave in the GI group (median 4.10 interquartile range [3.95–4.24] ms right, 4.04 [3.90–4.18] ms left) had a significantly shorter peak latency than controls (4.18 [4.06–4.34] ms right, p = 0.032, 4.13 [4.02–4.24] ms left, p = 0.018). The female GI group showed a significantly shorter peak latency of the III wave (4.00 [3.90–4.18] ms) than controls (4.18 [3.97–4.31] ms, p = 0.034) in the right side. BAEP in the male GI group did not significantly differ from that in controls. GI scores showed a significant correlation with the peak latency of the III wave in the left side (rho = −0.192, p = 0.025). The maternal care PBI scores in the GI group (29 [26][33]) were significantly lower than controls (31 [28.5–33], p = 0.010), while the maternal over-protection PBI scores were significantly higher in the GI group (16 [12][17]) than controls (13 [10.5–16], p = 0.024). Multiple regression analysis in females also supported these findings.

Conclusions

It is suggested that children with chronic GI symptoms have exaggerated brainstem responses to environmental stimuli and inadequate parental behaviors aggravate these symptoms.  相似文献   
105.
Sirenomelia, also known as mermaid syndrome, is a developmental malformation of the caudal body characterized by leg fusion and associated anomalies of pelvic/urogenital organs including bladder, kidney, rectum and external genitalia. Most affected infants are stillborn, and the few born alive rarely survive beyond the neonatal period. Despite the many clinical studies of sirenomelia in humans, little is known about the pathogenic developmental mechanisms that cause the complex array of phenotypes observed. Here, we provide new evidences that reduced BMP (Bone Morphogenetic Protein) signaling disrupts caudal body formation in mice and phenocopies sirenomelia. Bmp4 is strongly expressed in the developing caudal body structures including the peri-cloacal region and hindlimb field. In order to address the function of Bmp4 in caudal body formation, we utilized a conditional Bmp4 mouse allele (Bmp4flox/flox) and the Isl1 (Islet1)-Cre mouse line. Isl1-Cre is expressed in the peri-cloacal region and the developing hindimb field. Isl1Cre;Bmp4flox/flox conditional mutant mice displayed sirenomelia phenotypes including hindlimb fusion and pelvic/urogenital organ dysgenesis. Genetic lineage analyses indicate that Isl1-expressing cells contribute to both the aPCM (anterior Peri-Cloacal Mesenchyme) and the hindlimb bud. We show Bmp4 is essential for the aPCM formation independently with Shh signaling. Furthermore, we show Bmp4 is a major BMP ligand for caudal body formation as shown by compound genetic analyses of Bmp4 and Bmp7. Taken together, this study reveals coordinated development of caudal body structures including pelvic/urogenital organs and hindlimb orchestrated by BMP signaling in Isl1-expressing cells. Our study offers new insights into the pathogenesis of sirenomelia.  相似文献   
106.

Background

Type 2 diabetes mellitus (T2DM) patients are at increased risk of developing cardiovascular events. Unfortunately traditional risk assessment scores, including the Framingham Risk Score (FRS), have only modest accuracy in cardiovascular risk prediction in these patients.

Methods

We sought to determine the prognostic values of different non-invasive markers of atherosclerosis, including brachial artery endothelial function, carotid artery atheroma burden, ankle-brachial index, arterial stiffness and computed tomography coronary artery calcium score (CACS) in 151 T2DM Chinese patients that were identified low-intermediate risk from the FRS recalibrated for Chinese (<20% risk in 10?years). Patients were prospectively followed-up and presence of atherosclerotic events documented for a mean duration of 61?±?16?months.

Results

A total of 17 atherosclerotic events in 16 patients (11%) occurred during the follow-up period. The mean FRS of the study population was 5.0?±?4.6% and area under curve (AUC) from receiver operating characteristic curve analysis for prediction of atherosclerotic events was 0.59?±?0.07 (P?=?0.21). Among different vascular assessments, CACS?>?40 had the best prognostic value (AUC 0.81?±?0.06, P?<?0.01) and offered significantly better accuracy in prediction compared with FRS (P?=?0.038 for AUC comparisons). Combination of FRS with CACS or other surrogate vascular markers did not further improve the prognostic values over CACS alone. Multivariate Cox regression analysis identified CACS?>?40 as an independent predictor of atherosclerotic events in T2DM patients (Hazards Ratio 27.11, 95% Confidence Interval 3.36-218.81, P?=?0.002).

Conclusions

In T2DM patients identified as low-intermediate risk by the FRS, a raised CACS?>?40 was an independent predictor for atherosclerotic events.  相似文献   
107.
Genetic divergence among three morphs of a goby, Acentrogobius pflaumii, was investigated on the basis of sequence variations in a partial section of the mitochondrial cytochrome oxidase subunit?I gene. A total of 95 specimens, representing the three morphs, collected almost sympatrically from three sites around the Japanese archipelago, were sequenced, the sequence divergences between the morphs (8.62–15.50%) being much greater than within each morph (0.44–0.57%). In addition, each morph formed a distinct cluster in a neighbor-joining tree. Together with an earlier morphological study, such evidence indicated that each morph clearly represented a distinct species. Based on the determined gene sequences, three morph-specific primers were designed for multiplex haplotype-specific polymerase chain reaction (PCR) to enable quick and easy identification of each morph in future studies, especially for early life ecology given morphological similarities at these stages.  相似文献   
108.
A heat-labile phenolic acid decarboxylase from Candida guilliermondii (an anamorph of Pichia guilliermondii) was purified to homogeneity by simple successive column chromatography within 3 days. The molecular mass was 20 kDa by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and 36 kDa by gel-filtration chromatography, suggesting that the purified enzyme is a homodimer. The optimal pH and temperature were approximately 6.0 and 25°C. Characteristically, more than 50% of the optimal activity was observed at 0°C, suggesting that this enzyme is cold-adapted. The enzyme converted p-coumaric acid, ferulic acid, and caffeic acid to corresponding products with high specific activities of approximately 600, 530, and 46 U/mg, respectively. The activity was stimulated by Mg2+ ions, whereas it was completely inhibited by Fe2+, Ni2+, Cu2+, Hg2+, 4-chloromericuribenzoate, N-bromosuccinimide, and diethyl pyrocarbonate. The enzyme was inducible and expressed inside the cells moderately by ferulic acid and p-coumaric acid and significantly by non-metabolizable 6-hydroxy-2-naphthoic acid.  相似文献   
109.

Background

Advances in medical science have enabled many children with chronic diseases to survive to adulthood. The transition of adult patients with childhood-onset chronic diseases from pediatric to adult healthcare systems has received attention in Europe and the United States. We conducted a questionnaire survey among 41 pediatricians at pediatric hospitals and 24 nurses specializing in adolescent care to compare the perception of transition of care from pediatric to adult healthcare services for such patients.

Findings

Three-fourths of the pediatricians and all of the nurses reported that transition programs were necessary. A higher proportion of the nurses realized the necessity of transition and had already developed such programs. Both pediatricians and nurses reported that a network covering the transition from pediatric to adult healthcare services has not been established to date.

Conclusions

It has been suggested that spreading the importance of a transition program among pediatricians and developing a pediatric-adult healthcare network would contribute to the biopsychosocial well-being of adult patients with childhood-onset chronic disease.  相似文献   
110.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号