全文获取类型
收费全文 | 2723篇 |
免费 | 226篇 |
国内免费 | 81篇 |
专业分类
3030篇 |
出版年
2021年 | 34篇 |
2019年 | 26篇 |
2018年 | 25篇 |
2017年 | 30篇 |
2016年 | 34篇 |
2015年 | 59篇 |
2014年 | 83篇 |
2013年 | 92篇 |
2012年 | 101篇 |
2011年 | 105篇 |
2010年 | 77篇 |
2009年 | 86篇 |
2008年 | 100篇 |
2007年 | 96篇 |
2006年 | 84篇 |
2005年 | 98篇 |
2004年 | 78篇 |
2003年 | 84篇 |
2002年 | 79篇 |
2001年 | 90篇 |
2000年 | 81篇 |
1999年 | 57篇 |
1998年 | 30篇 |
1997年 | 25篇 |
1996年 | 38篇 |
1995年 | 37篇 |
1992年 | 49篇 |
1991年 | 47篇 |
1990年 | 50篇 |
1989年 | 53篇 |
1988年 | 49篇 |
1987年 | 45篇 |
1986年 | 29篇 |
1985年 | 38篇 |
1984年 | 35篇 |
1983年 | 29篇 |
1981年 | 27篇 |
1980年 | 24篇 |
1977年 | 30篇 |
1975年 | 28篇 |
1974年 | 35篇 |
1973年 | 32篇 |
1972年 | 23篇 |
1971年 | 33篇 |
1970年 | 29篇 |
1969年 | 26篇 |
1959年 | 24篇 |
1958年 | 36篇 |
1955年 | 25篇 |
1953年 | 27篇 |
排序方式: 共有3030条查询结果,搜索用时 203 毫秒
121.
D L Maxwell R W Fuller C M Dixon F M Cuss P J Barnes 《Journal of applied physiology》1990,68(1):295-301
Animal studies suggest that the neuropeptides, substance P and vasoactive intestinal peptide (VIP), may influence carotid body chemoreceptor activity and that substance P may take part in the carotid body response to hypoxia. The effects of these peptides on resting ventilation and on ventilatory responses to hypoxia and to hypercapnia have been investigated in six normal humans. Infusions of substance P (1 pmol.kg-1.min-1) and of VIP (6 pmol.kg-1.min-1) were compared with placebo and with nitroprusside (5 micrograms.kg-1.min-1) as a control for the hypotensive action of the peptides. Both peptides caused significantly less hypotension than nitroprusside. Substance P and nitroprusside caused significantly greater increases in ventilation and in the hypoxic ventilatory response than VIP. No changes were seen in hypercapnic sensitivity. The stimulation of ventilation and the differential effects on ventilatory chemosensitivity that accompanied hypotension are consistent either with stimulation of carotid body chemoreceptor activity or with an interaction with peripheral chemoreceptor input to the respiratory center, as is seen in animals. The similar cardiovascular but different ventilatory effects of the peptides suggest that substance P may also stimulate the carotid body in a manner independent of the effect of hypotension. This is consistent with a role of substance P in the hypoxic ventilatory response in humans. 相似文献
122.
Barnes PJ 《Cytokine & growth factor reviews》2003,14(6):511-522
Multiple cytokines play a critical role in orchestrating and perpetuating inflammation in asthma and chronic obstructive pulmonary disease (COPD) and several specific cytokine and chemokine inhibitors now in development as future therapy for these diseases. Anti-IL-5 antibody markedly reduces peripheral blood and airway eosinophils, but does not appear to be effective in symptomatic asthma. Inhibition of IL-4 despite promising early results in asthma has been discontinued and blocking IL-13 might be more effective. Inhibitory cytokines, such as IL-10, interferons and IL-12 are less promising, as systemic delivery produces side effects. Inhibition of TNF-alpha may be useful in severe asthma and for treating severe COPD with systemic features. Many chemokines are involved in the inflammatory response of asthma and COPD and several small molecule inhibitors of chemokine receptors (CCR) are in development. CCR3 antagonists (which block eosinophil chemotaxis) and CXCR2 antagonists (which block neutrophil and monocyte chemotaxis) are in clinical development for asthma and COPD, respectively. Because so many cytokines are involved in asthma, drugs that inhibit the synthesis of multiple cytokines may prove to be more useful; several such classes of drug are now in clinical development and any risk of side effects with these non-specific inhibitors may be reduced by the inhaled route. 相似文献
123.
124.
Aggregation of granulocyte-colony stimulating factor in vitro involves a conformationally altered monomeric state 下载免费PDF全文
Raso SW Abel J Barnes JM Maloney KM Pipes G Treuheit MJ King J Brems DN 《Protein science : a publication of the Protein Society》2005,14(9):2246-2257
Aggregation of partially folded intermediates populated during protein folding processes has been described for many proteins. Likewise, partially unfolded chains, generated by perturbation of numerous proteins by heat or chemical denaturants, have also been shown to aggregate readily. However, the process of protein aggregation from native-state conditions is less well understood. Granulocyte-colony stimulating factor (G-CSF), a member of the four-helix bundle class of cytokines, is a therapeutically relevant protein involved in stimulating the growth and maturation of phagocytotic white blood cells. Under native-like conditions (37 degrees C [pH 7.0]), G-CSF shows a significant propensity to aggregate. Our data suggest that under these conditions, native G-CSF exists in equilibrium with an altered conformation, which is highly aggregation prone. This species is enriched in 1-2 M GdmCl, as determined by tryptophan fluorescence and increased aggregation kinetics. In particular, specific changes in Trp58 fluorescence report a local rearrangement in the large loop region between helices A and B. However, circular dichroism, reactivity toward cyanylation, and ANS binding demonstrate that this conformational change is subtle, having no substantial disruption of secondary and tertiary structure, reactivity of the free sulfhydryl at Cys17 or exposure of buried hydrophobic regions. There is no indication that this altered conformation is important to biological activity, making it an attractive target for rational protein stabilization. 相似文献
125.
Michael J. Sheriff Melanie M. Richter C. Loren Buck Brian M. Barnes 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2013,368(1624)
Many studies have addressed the effects of climate change on species as a whole; however, few have examined the possibility of sex-specific differences. To understand better the impact that changing patterns of snow-cover have on an important resident Arctic mammal, we investigated the long-term (13 years) phenology of hibernating male arctic ground squirrels living at two nearby sites in northern Alaska that experience significantly different snow-cover regimes. Previously, we demonstrated that snow-cover influences the timing of phenological events in females. Our results here suggest that the end of heterothermy in males is influenced by soil temperature and an endogenous circannual clock, but timing of male emergence from hibernation is influenced by the timing of female emergence. Males at both sites, Atigun and Toolik, end heterothermy on the same date in spring, but remain in their burrows while undergoing reproductive maturation. However, at Atigun, where snowmelt and female emergence occur relatively early, males emerge 8 days earlier than those at Toolik, maintaining a 12-day period between male and female emergence found at each site, but reducing the pre-emergence euthermic period that is critical for reproductive maturation. This sensitivity in timing of male emergence to female emergence will need to be matched by phase shifts in the circannual clock and responsiveness to environmental factors that time the end of heterothermy, if synchrony in reproductive readiness between the sexes is to be preserved in a rapidly changing climate. 相似文献
126.
127.
Selenium reduction by a denitrifying consortium 总被引:1,自引:0,他引:1
Rege MA Yonge DR Mendoza DP Petersen JN Bereded-Samuel Y Johnstone DL Apel WA Barnes JM 《Biotechnology and bioengineering》1999,62(4):479-484
A denitrifying bacterial consortium obtained from the Pullman, Washington wastewater treatment facility was enriched under denitrifying conditions and its ability to reduce selenite and selenate was studied. Replicate experiments at two different experimental conditions were performed. All experiments were performed under electron-acceptor limiting conditions, with acetate as the carbon source and nitrate the electron acceptor. In the first set of experiments, selenite was present, whereas, in the second set, selenate was added. A significant lag period of approximately 150 h was necessary before selenite or selenate reduction was observed. During this lag period, nitrate and nitrite use was observed. Once selenite or selenate reduction had started, nitrate and nitrite reduction was concomitant with selenium species reduction. Trace amounts of selenite were detected during the selenate reduction study. Analysis of the data indicates that, once selenium species reduction was induced, the rate of reduction was proportional to the selenium species concentration and to the biomass concentration. Furthermore, at similar biomass and contaminant concentrations, selenite reduction is approximately four times faster than selenate reduction. Copyright 1999 John Wiley & Sons, Inc. 相似文献
128.
129.
QTL analysis of an intervarietal set of substitution lines in Brassica napus: (i) Seed oil content and fatty acid composition 总被引:14,自引:0,他引:14
Backcross breeding with marker-assisted selection was used to construct an intervarietal set of part chromosome substitution lines in Brassica napus, formed from a cross between two winter varieties of oilseed rape: Tapidor and Victor. A total of 22 lines from this substitution library were examined over a 3-year period, in a total of nine field trials, for seed oil fatty acid composition and seed oil content. Trialing of the substitution lines gave evidence for the existence of 13 quantitative trait loci (QTL). All 13 QTL affected fatty acid composition of the seed, and were distributed among linkage groups 1, 3, 6, 7, 8, 11, 13, 14, 18, and 19. Seven of these QTL, on linkage groups 3, 6, 8, 13, 14, 18, and 19, also affected total seed oil content. The positions of these QTL are compared to those in the published literature and with respect to erucic acid QTL previously identified in a backcross population of the same cross. The substitution line approach gives increased precision and sensitivity for QTL mapping compared to other methods. 相似文献
130.
Fracture healing as a post-natal developmental process: molecular,spatial, and temporal aspects of its regulation 总被引:30,自引:0,他引:30
Gerstenfeld LC Cullinane DM Barnes GL Graves DT Einhorn TA 《Journal of cellular biochemistry》2003,88(5):873-884
Fracture healing is a specialized post-natal repair process that recapitulates aspects of embryological skeletal development. While many of the molecular mechanisms that control cellular differentiation and growth during embryogenesis recur during fracture healing, these processes take place in a post-natal environment that is unique and distinct from those which exist during embryogenesis. This Prospect Article will highlight a number of central biological processes that are believed to be crucial in the embryonic differentiation and growth of skeletal tissues and review the functional role of these processes during fracture healing. Specific aspects of fracture healing that will be considered in relation to embryological development are: (1) the anatomic structure of the fracture callus as it evolves during healing; (2) the origins of stem cells and morphogenetic signals that facilitate the repair process; (3) the role of the biomechanical environment in controlling cellular differentiation during repair; (4) the role of three key groups of soluble factors, pro-inflammatory cytokines, the TGF-beta superfamily, and angiogenic factors, during repair; and (5) the relationship of the genetic components that control bone mass and remodeling to the mechanisms that control skeletal tissue repair in response to fracture. 相似文献