全文获取类型
收费全文 | 411篇 |
免费 | 60篇 |
出版年
2021年 | 5篇 |
2019年 | 4篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 14篇 |
2014年 | 14篇 |
2013年 | 12篇 |
2012年 | 13篇 |
2011年 | 18篇 |
2010年 | 5篇 |
2009年 | 12篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 8篇 |
2005年 | 12篇 |
2004年 | 17篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1992年 | 8篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1972年 | 4篇 |
1969年 | 3篇 |
1968年 | 6篇 |
1931年 | 3篇 |
排序方式: 共有471条查询结果,搜索用时 15 毫秒
101.
102.
103.
The objective of this study was to evaluate the effect of 2 independent formulation variables on the drug release from a novel doughnut-shaped minitablet (DSMT) in order to optimize formulations for intraocular drug delivery. Formulations were based on a 3(2) full-factorial design. The 2 independent variables were the concentration of Resomer (% wt/wt) and the type of Resomer grade (RG502, RG503, and RG504), respectively. The evaluated response was the drug release rate constant computed from a referenced marketed product and in vitro drug release data obtained at pH 7.4 in simulated vitreous humor. DSMT devices were prepared containing either of 2 model drugs, ganciclovir or foscarnet, using a Manesty F3 tableting press fitted with a novel central-rod, punch, and die setup. Dissolution data revealed biphasic drug release behavior with 55% to 60% drug released over 120 days. The inherent viscosity of the various Resomer grades and the concentration were significant to achieve optimum release rate constants. Using the resultant statistical relationships with the release rate constant as a response, the optimum formulation predicted for devices formulated with foscarnet was 70% wt/wt of Resomer RG504, while 92% wt/wt of Resomer RG503 was ideal for devices formulated with ganciclovir. The results of this study revealed that the full-factorial design was a suitable tool to predict an optimized formulation for prolonged intraocular drug delivery. 相似文献
104.
Shaw GM Carmichael SL Laurent C Louik C Finnell RH Lammer EJ;National Birth Defects Prevention Study 《Birth defects research. Part A, Clinical and molecular teratology》2007,79(10):708-713
BACKGROUND: There is a paucity of information about risk factors for the human eye anomalies anophthalmia and microphthalmia. In this population-based case-control study we investigated whether periconceptional intakes of supplemental folic acid, dietary folate, vitamin A, and several other nutrients were associated with these eye defects. METHODS: This study included data on deliveries that had estimated due dates from 1997-2002 and were part of the National Birth Defects Prevention Study (the National Birth Defects Prevention Study is a population-based case-control study of a wide spectrum of birth defects, incorporating data from 10 birth defects surveillance systems in the United States [Arkansas, California, Georgia/Centers for Disease Control and Prevention, Iowa, Massachusetts, New Jersey, New York, North Carolina, Texas, and Utah]). Cases were those infants or fetuses born with either anophthalmia or microphthalmia. Liveborn infants without major malformations were eligible as controls. Maternal interviews were conducted, primarily by telephone, in English or Spanish. Participation in the interview was 71% among case mothers and 68% among control mothers. Interviews were completed with 89 case mothers and 4,143 control mothers. A shortened version of the food frequency questionnaire from the Nurse's Health Study was used to assess frequency of intake of 58 food items during the year before pregnancy. RESULTS: Our results did not indicate reduced risks for these eye malformations associated with maternal intake of vitamin supplements containing folic acid. The data did not show an association between malformation risk and higher or lower intakes of vitamin A. We also did not observe strong evidence that an abundance or a lack of dietary intake of any other nutrient was associated with increased risk of the studied eye malformations. CONCLUSIONS: Our observations contribute to a limited body of findings on these rare eye defects. 相似文献
105.
106.
Arctic foxes are highly mobile arctic predators with a very weak population genetic structure over large parts of their range.
Less is, however, known about the more local genetic structure within regions. Here, we analyze genotypes at 12 microsatellite
loci for 561 arctic foxes trapped in the high-arctic archipelago Svalbard and investigate the genetic structure in three different
age classes. Significant linkage disequilibrium, deficit of heterozygotes, genetic differentiation, and a decrease in relatedness
with distance among animals trapped in their first winter suggested that some litter mates remain in proximity of each other
during the first winter. This pattern was stronger for females than for males, indicating male-biased juvenile dispersal,
and weaker for older animals. There was no genetic differentiation among adult foxes harvested in different hunting areas.
The foxes from the protected area around Hornsund were however more differentiated than expected based on geographic distance
alone, suggesting a possible disrupting effect of harvest on the spatial genetic structure in the rest of Svalbard. Our results
also indicated a possible kin structure among adult females, suggesting natal philopatry, but further investigations will
be needed to reach firm conclusions concerning kin structure in arctic foxes. 相似文献
107.
Carmichael MD Davis JM Murphy EA Brown AS Carson JA Mayer EP Ghaffar A 《American journal of physiology. Regulatory, integrative and comparative physiology》2006,291(5):R1344-R1348
Brain cytokines, induced by various inflammatory challenges, have been linked to sickness behaviors, including fatigue. However, the relationship between brain cytokines and fatigue after exercise is not well understood. Delayed recovery of running performance after muscle-damaging downhill running is associated with increased brain IL-1beta concentration compared with uphill running. However, there has been no systematic evaluation of the direct effect of brain IL-1beta on running performance after exercise-induced muscle damage. This study examined the specific role of brain IL-1beta on running performance (either treadmill or wheel running) after uphill and downhill running by manipulating brain IL-1beta activity via intracerebroventricular injection of either IL-1 receptor antagonist (ra; downhill runners) or IL-1beta (uphill runners). Male C57BL/6 mice were assigned to the following groups: uphill-saline, uphill-IL-1beta, downhill-saline, or downhill-IL-1ra. Mice initially ran on a motor-driven treadmill at 22 m/min and -14% or +14% grade for 150 min. After the run, at 8 h (wheel cage) or 22 h (treadmill), uphill mice received intracerebroventricular injections of IL-1beta (900 pg in 2 microl saline) or saline (2 microl), whereas downhill runners received IL-1ra (1.8 microg in 2 microl saline) or saline (2 microl). Later (2 h), running performance was measured (wheel running activity and treadmill run to fatigue). Injection of IL-1beta significantly decreased wheel running activity in uphill runners (P<0.01), whereas IL-1ra improved wheel running in downhill runners (P<0.05). Similarly, IL-1beta decreased and Il-1ra increased run time to fatigue in the uphill and downhill runners, respectively (P<0.01). These results support the hypothesis that increased brain IL-1beta plays an important role in fatigue after muscle-damaging exercise. 相似文献
108.
R. Ranga Rao Ashok K. Tiwari P. Prabhakar Reddy K. Suresh Babu Amtul Z. Ali K. Madhusudana J. Madhusudana Rao 《Bioorganic & medicinal chemistry》2009,17(14):5170-5175
A bioassay-guided fractionation and chemical examination of antihyperglycemic root extract of Derris indica resulted in isolation and characterization of two new furanoflavanoids (1, 2) along with thirteen known compounds (3–15). Their structures were determined on the basis of extensive spectroscopic (IR, MS, 1D and 2D NMR) data analysis and by comparison with the literature data. All the compounds were tested in vitro for intestinal α-glucosidase inhibitory and DPPH radical activity. New compounds (1, 2) displayed moderate intestinal α-glucosidase inhibitory as well as free radical scavenging activity. Other compounds also displayed varying degrees of moderate intestinal α-glucosidase inhibitory activity. Pongamol (6) displayed potent intestinal α-glucosidase inhibition. 相似文献
109.
P. Prabhakar Reddy Ashok K. Tiwari R. Ranga Rao K. Madhusudhana V. Rama Subba Rao Amtul Z. Ali K. Suresh Babu J. Madhusudana Rao 《Bioorganic & medicinal chemistry letters》2009,19(9):2562-2565
Phytochemical investigation of antihyperglycemic extract of rhizomes of Hedychium spicatum led to the isolation of two new labdane type diterpenes 2, 3 along with seven known compounds (1, 4–9). Their structures were established on the basis of NMR (1D and 2D) and mass spectroscopic analysis. The new compound 2 displayed strong intestinal α-glucosidase inhibitory activity. Other compounds also displayed varying degree of intestinal α-glucosidase inhibitory potential. 相似文献
110.
Wenhui Zhang Hongqiu Zhao Ian Carmichael Anthony S. Serianni 《Carbohydrate research》2009,344(12):1582-9509
Methyl α-cellobioside (methyl β-d-glucopyranosyl-(1→4)-α-d-glucopyranoside) was labeled with 13C at C4′ for use in NMR studies in DMSO-d6 solvent to attempt the detection of a trans-H-bond J-coupling (3hJCCOH) between C4′ and OH3. Analysis of the OH3 signal at 600 MHz revealed only the presence of two homonuclear J-couplings: 3JH3,OH3 and a smaller, longer range JHH. No evidence for 3hJC4′,OH3 was found. The longer range JHH was traced to 4JH4,OH3 based on 2D 1H–1H COSY data and inspection of the H2 and H4 signal lineshapes. A limited set of DFT calculations was performed on a methyl cellobioside mimic to evaluate the structural dependencies of 4JH2,O3H and 4JH4,O3H on the H3–C3–O3–H torsion angle. Computed couplings range from about −0.7 to about +1.1 Hz, with maximal values observed when the C–H and O–H bonds are roughly diaxial. 相似文献