全文获取类型
收费全文 | 262篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
儿科学 | 15篇 |
妇产科学 | 5篇 |
基础医学 | 17篇 |
口腔科学 | 5篇 |
临床医学 | 53篇 |
内科学 | 77篇 |
皮肤病学 | 4篇 |
神经病学 | 15篇 |
特种医学 | 23篇 |
外科学 | 19篇 |
综合类 | 7篇 |
预防医学 | 28篇 |
眼科学 | 1篇 |
药学 | 8篇 |
肿瘤学 | 7篇 |
出版年
2021年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2013年 | 4篇 |
2012年 | 3篇 |
2011年 | 5篇 |
2010年 | 6篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2000年 | 4篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 16篇 |
1993年 | 10篇 |
1991年 | 2篇 |
1989年 | 5篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 5篇 |
1969年 | 3篇 |
1965年 | 3篇 |
1963年 | 4篇 |
1962年 | 2篇 |
1956年 | 2篇 |
1955年 | 2篇 |
1939年 | 1篇 |
1938年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有284条查询结果,搜索用时 15 毫秒
231.
232.
Stephanie A. Richard Benjamin J. J. McCormick Laura E. MurrayKolb Crystal L. Patil Ram K. Chandyo Cloupas Mahopo Bruna L. Maciel Anuradha Bose Mustafa Mahfuz Ramya Ambikapathi Maribel Paredes Olortegui Laura E. Caulfield the MALED Network Investigators 《Maternal & child nutrition》2021,17(3)
The WHO recommends exclusive breastfeeding for the first 6 months of life. However, the transition of the infants'' diet to partial breastfeeding with the addition of animal milks and/or solids typically occurs earlier than this. Here, we explored factors associated with the timing of an early transition to partial breastfeeding across seven sites of a birth cohort study in which twice weekly information on infant feeding practices was collected. Infant (size, sex, illness and temperament), maternal (age, education, parity and depressive symptoms), breastfeeding initiation practices (time of initiation, colostrum and pre‐lacteal feeding) and household factors (food security, crowding, assets, income and resources) were considered. Three consecutive caregiver reports of feeding animal milks and/or solids (over a 10‐day period) were characterized as a transition to partial breastfeeding, and Cox proportional hazard models with time (in days) to partial breastfeeding were used to evaluate associations with both fixed and time‐varying characteristics. Overall, 1470 infants were included in this analysis. Median age of transition to partial breastfeeding ranged from 59 days (South Africa and Tanzania) to 178 days (Bangladesh). Overall, higher weight‐for‐length z‐scores were associated with later transitions to partial breastfeeding, as were food insecurity, and infant cough in the past 30 days. Maternal depressive symptoms (evaluated amongst 1227 infants from six sites) were associated with an earlier transition to partial breastfeeding. Relative thinness or heaviness within each site was related to breastfeeding transitions, as opposed to absolute z‐scores. Further research is needed to understand relationships between local perceptions of infant body size and decisions about breastfeeding. 相似文献
233.
234.
ED. S. MOOBERRY JERRY L. DALLAS TED T. SAKAI JERRY D. GLICKSON 《Chemical biology & drug design》1980,15(4):365-376
The acid-base titration of bleomycin-A2 in D2O solution at 35 ± 5° has been monitored by 13C n.m.r. spectroscopy at 67.89 MHz. The following pKDa values were obtained: 3.68 ± 0.05 (secondary amine), 5.29 ± 0.03 (imidazole), and 8.23 ± 0.19 (primary amine), where KDa is the dissociation constant in D2O solution. The equilibrium isotope effects (pKDa -pKa in H2O) are: 0.70 ± 0.06 (secondary amine), 0.28 ± 0.04 (imidazole), and 0.85 ± 0.19 (primary amine). Titration of the imidazole group of Bleo-A2 occurs at Nπ, i.e. only Nπ is protonated in basic solution. Significant protonation shifts are almost completely limited to carbons of the N-terminal tetrapeptide, suggesting that the C-terminal tripeptide extends into the solvent and interacts to a minimal extent with the rest of the molecule. Long range protonation shifts associated with titration of the imidazole and secondary amine groups indicate that protonation of one or both of these sites is probably accompanied by significant conformational changes. The observed protonation shifts generally fail to correlate with Zn(II) complexation shifts reported by Dabrowiak et al. (1973, Biochemistry 17, 4090) indicating that ligation sites cannot unambiguously be determined from these complexation shifts. The complexation shifts previously attributed to coordination of the imidazole and carbamoyl groups probably result from conformational changes. 相似文献
235.
Gowtham Kankanala MS MCh Amar Singh Jain FRCS ED 《The Journal of foot and ankle surgery》2007,46(4):213-217
A retrospective study was carried out on 48 patients to correlate preoperative ultrasound findings with postoperative histopathology findings and to assess the sensitivity, specificity, positive predictive values, and negative predictive values of ultrasound in the diagnosis of Morton's interdigital neuroma. All case sheets of 48 patients operated on between 1997 and 2005 were reviewed in the medical record section of Ninewells Hospital, Dundee, Scotland, so that preoperative ultrasound reports were compared with the postoperative histopathological reports. A statistical analysis of the results was performed. Ultrasonography showed 43 true-positive cases, 1 true-negative case, and 4 false-negative cases out of 48 cases. Histopathology showed 47 true-positive cases and 1 true-negative case; statistical analysis performed on the results showed a sensitivity of 91.48%, a specificity of 100%, and 100% positive and 20% negative predictive values, respectively. In our analysis, the probability that ultrasound will confirm the presence of plantar intermetatarsal neuroma is 91.67%. 相似文献
236.
Use of monoclonal antihapten antibodies for immunolocalisation of tissue antigens 总被引:4,自引:2,他引:2 下载免费PDF全文
The applicability of a hapten-antihapten sandwich technique incorporating a monoclonal antihapten bridge antibody to localisation of tissue antigen is described. The results show that the method is both versatile and selective and has the potential of being even more sensitive than currently used immunoperoxidase methods. 相似文献
237.
238.
Neural dynamics in a model of the thalamocortical system. II. The role of neural synchrony tested through perturbations of spike timing 总被引:1,自引:1,他引:0
Activity in the mammalian thalamocortical system is often accompanied by a
synchronous discharge of cortical and thalamic neurons. Although many
functions have been attributed to such synchronous firing, it is not known
whether or how synchrony of firing per se affects thalamocortical
operations. Direct experimental tests of the consequences of neuronal
synchronization in vivo are hard to carry out, whereas theoretical studies
based on single-neuron models cannot reveal the effects of synchrony at the
system level. To overcome these limitations, we have used a perturbational
approach to test the causal efficacy of synchrony per se in large-scale
simulations of the thalamocortical system. The test consists of selectively
disrupting firing synchrony by 'jittering' the timing of action potentials
in the simulations and determining whether firing rates are modified by
this perturbation. The simulations are based in detail on the known anatomy
and physiology of the thalamocortical-visual system of the cat, and have
been shown in a companion paper to produce episodes of fast synchronous
activity at multiple levels. By carrying out the perturbation analysis, we
established that neurons can have long membrane time constants (8-16 ms)
and balanced synaptic activations, and yet function collectively in such a
way that synchrony within a time window of 4 ms significantly affects the
rates and selectivity of the responses to visual stimuli. The simulations
also revealed a complex interplay, at the network level, between synchrony
of firing and rate of firing. The dynamic consequences of firing synchrony
were most evident when spike jittering was applied to specific polysynaptic
loops involving corticocortical and corticothalamic connections. These
results support the view that firing synchrony within thalamocortical and
corticocortical loops plays a causal role in the cooperative and
competitive neural interactions that produce pattern-selective responses in
the cortex.
相似文献
239.
240.