全文获取类型
收费全文 | 890篇 |
免费 | 93篇 |
出版年
2022年 | 8篇 |
2021年 | 9篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 16篇 |
2015年 | 28篇 |
2014年 | 34篇 |
2013年 | 44篇 |
2012年 | 60篇 |
2011年 | 45篇 |
2010年 | 32篇 |
2009年 | 30篇 |
2008年 | 41篇 |
2007年 | 33篇 |
2006年 | 35篇 |
2005年 | 33篇 |
2004年 | 27篇 |
2003年 | 37篇 |
2002年 | 25篇 |
2001年 | 24篇 |
2000年 | 29篇 |
1999年 | 26篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 7篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 7篇 |
1971年 | 6篇 |
1970年 | 9篇 |
排序方式: 共有983条查询结果,搜索用时 15 毫秒
121.
Travins JM Ali F Huang H Ballentine SK Khalil E Hufnagel HR Pan W Gushue J Leonard K Bone RF Soll RM DesJarlais RL Crysler CS Ninan N Kirkpatrick J Cummings MD Huebert N Molloy CJ Gaul M Tomczuk BE Subasinghe NL 《Bioorganic & medicinal chemistry letters》2008,18(5):1603-1606
Complement activation has been implicated in disease states such as hereditary angioedema, ischemia-reperfusion injury, acute respiratory distress syndrome, and acute transplant rejection. Even though the complement cascade provides several protein targets for potential therapeutic intervention only two complement inhibitors have been approved so far for clinical use including anti-C5 antibodies for the treatment of paroxysmal nocturnal hemoglobinuria and purified C1-esterase inhibitor replacement therapy for the control of hereditary angioedema flares. In the present study, optimization of potency and physicochemical properties of a series of thiophene amidine-based C1s inhibitors with potential utility as intravenous agents for the inhibition of the classical pathway of complement is described. 相似文献
122.
Farrand S Hotze E Friese P Hollingshead SK Smith DF Cummings RD Dale GL Tweten RK 《Biochemistry》2008,47(27):7097-7107
The cholesterol-dependent cytolysins (CDCs) are a large family of pore-forming toxins that often exhibit distinct structural changes that modify their pore-forming activity. A soluble platelet aggregation factor from Streptococcus mitis (Sm-hPAF) was characterized and shown to be a functional CDC with an amino-terminal fucose-binding lectin domain. Sm-hPAF, or lectinolysin (LLY) as renamed herein, is most closely related to CDCs from Streptococcus intermedius (ILY) and Streptococcus pneumoniae (pneumolysin or PLY). The LLY gene was identified in strains of S. mitis, S. pneumoniae, and Streptococcus pseudopneumoniae. LLY induces pore-dependent changes in the light scattering properties of the platelets that mimic those induced by platelet aggregation but does not induce platelet aggregation. LLY monomers form the typical large homooligomeric membrane pore complex observed for the CDCs. The pore-forming activity of LLY on platelets is modulated by the amino-terminal lectin domain, a structure that is not present in other CDCs. Glycan microarray analysis showed the lectin domain is specific for difucosylated glycans within Lewis b (Le (b)) and Lewis y (Le (y)) antigens. The glycan-binding site is occluded in the soluble monomer of LLY but is apparently exposed after cell binding, since it significantly increases LLY pore-forming activity in a glycan-dependent manner. Hence, LLY represents a new class of CDC whose pore-forming mechanism is modulated by a glycan-binding domain. 相似文献
123.
High rates of deforestation in the Brazilian Amazon have the potential to alter the storage and cycling of carbon (C) and nitrogen (N) across this region. To investigate the impacts of deforestation, we quantified total aboveground biomass (TAGB), aboveground and soil pools of C and N, and soil N availability along a land-use gradient in Rondônia, Brazil, that included standing primary forest, slashed primary and secondary forest, shifting cultivation, and pasture sites. TAGB decreased substantially with increasing land use, ranging from 311 and 399 Mg ha–1 (primary forests) to 63 Mg ha–1 (pasture). Aboveground C and N pools declined in patterns and magnitudes similar to those of TAGB. Unlike aboveground pools, soil C and N concentrations and pools did not show consistent declines in response to land use. Instead, C and N concentrations were strongly related to percent clay content of soils. Concentrations of NO3-N and NH4-N generally increased in soils following slash-and-burn events along the land-use gradient and decreased with increasing land use. Increasing land use resulted in marked declines in NO3-N pools relative to NH4-N pools. Rates of net nitrification and N-mineralization were also generally higher in postfire treatments relative to prefire treatments along the land-use gradient and declined with increasing land use. Results demonstrate the linked responses of aboveground C and N pools and soil N availability to land use in the Brazilian Amazon; steady reductions in aboveground pools along the land-use gradient were accompanied by declines in inorganic soil N pools and transformation rates. 相似文献
124.
Peter Cummings Barbara McKnight Frederick P Rivara David C Grossman 《BMJ (Clinical research ed.)》2002,324(7346):1119-1122
ObjectiveTo estimate the association of driver air bag presence with driver fatality in road traffic crashes.DesignMatched pair cohort study.SettingAll passenger vehicle crashes in the United States during 1990-2000 inclusive.Subjects51 031 driver-passenger pairs in the same vehicle.ResultsDrivers with an air bag were less likely to die than drivers without an air bag (adjusted relative risk 0.92 (95% confidence interval 0.88 to 0.96)). This estimate was nearly the same whether drivers wore a seat belt (adjusted relative risk 0.93) or not (0.91). Air bags were associated with more protection for women (0.88 (0.82 to 0.93)), than for men (0.94 (0.90 to 0.99)). Drivers wearing a seat belt were less likely to die than unbelted drivers (0.35 (0.33 to 0.36)). Belted drivers with an air bag were less likely to die than unbelted drivers without an air bag (0.32 (0.30 to 0.34)).ConclusionsIf the associations are causal the average risk of driver death was reduced 8% (95% confidence interval 4% to 12%) by an air bag. Benefit was similar for belted and unbelted drivers and was slightly greater for women. However, seat belts offered much more protection than air bags.
What is already known on this topic
Studies have estimated that driver air bags reduce the risk of death in a road vehicle crash by 10-14%These studies disagree as to whether benefit is greater for drivers wearing a seat belt or for unbelted driversWhat this study adds
Having an air bag was associated with an 8% reduction in the risk of death, whether the driver was belted or notThe reduction in risk was greater for women (12%) than for men (6%)Seat belts provided much greater protection, with seat belt use reducing the risk of death by 65% (or by 68% in combination with an air bag) 相似文献125.
Caroline L. Willis John H. Cummings Graham Neale Glenn R. Gibson 《Current microbiology》1997,35(5):294-298
In contrast to other anaerobic ecosystems, such as marine and estuarine sediments, there is a lack of information on the
nutritional requirements of human gut sulfate-reducing bacteria (SRB). Various substrates stimulated sulfate reduction in
mixed culture, including short-chain fatty acids and other organic acids, alcohols, and amino acids (but not sugars or aromatic
compounds). However, the use of sodium molybdate as a specific inhibitor of sulfate reduction caused an accumulation of ethanol
and malonate only, and reduced the rate of utilization of lactate. This indicates the importance of these electron donors
for sulfate reduction. Since ethanol and lactate are primarily utilized by members of the Desulfovibrio genus, the results suggest a physiologically important role for this group. Experiments with two strains of Desulfovibrio desulfuricans isolated from human feces demonstrated that both were able to reduce sulfite, thiosulfate or nitrate in the absence of sulfate.
In addition, one strain (DsvUC1) was able to grow by fermentative metabolism, although the second strain (DsvFD1) showed more
restricted fermentative growth. The data indicate that desulfovibrios are ecologically the most significant group of SRB in
the human colon, and that colonic isolates belonging to this genus are versatile, in terms of both the electron acceptors
and donors that they are able to utilize.
Received: 24 March 1997 / Accepted: 10 June 1997 相似文献
126.
127.
128.
Synchronization of E. coli K 12 by membrane selection 总被引:2,自引:0,他引:2
D J Cummings 《Biochemical and biophysical research communications》1970,41(2):471-476
129.
130.
Horned beetles are emerging models in the study of coevolution between novel morphologies and behavior. In Onthophagus beetles, large males use horns to fight other males in brood tunnels while small males with higher mobility sneak around the large males to gain access to females. Mating tactics have rarely been described in other dung beetle genera. We studied the horned dung beetle Sulcophanaeus velutinus that exhibits two parallel horns on the prothorax and one on the head. We put two males of different horn lengths, but similar mass, in observation chambers and found that the large male with longer horns won access to the female in physical competition. Speed tests in artificial tunnels show that locomotion is impeded in large males, suggesting an advantage in mobility for males with small horns. This work contributes to the limited existing evidence on the function of alternative morphologies in horned dung beetles taxa. 相似文献