全文获取类型
收费全文 | 2521篇 |
免费 | 286篇 |
国内免费 | 3篇 |
出版年
2021年 | 27篇 |
2018年 | 25篇 |
2017年 | 21篇 |
2016年 | 27篇 |
2015年 | 52篇 |
2014年 | 71篇 |
2013年 | 77篇 |
2012年 | 95篇 |
2011年 | 123篇 |
2010年 | 68篇 |
2009年 | 66篇 |
2008年 | 85篇 |
2007年 | 91篇 |
2006年 | 67篇 |
2005年 | 84篇 |
2004年 | 83篇 |
2003年 | 77篇 |
2002年 | 77篇 |
2001年 | 82篇 |
2000年 | 74篇 |
1999年 | 75篇 |
1998年 | 43篇 |
1997年 | 37篇 |
1996年 | 39篇 |
1995年 | 28篇 |
1994年 | 29篇 |
1993年 | 39篇 |
1992年 | 57篇 |
1991年 | 63篇 |
1990年 | 64篇 |
1989年 | 63篇 |
1988年 | 44篇 |
1987年 | 52篇 |
1986年 | 31篇 |
1985年 | 46篇 |
1984年 | 31篇 |
1983年 | 39篇 |
1982年 | 31篇 |
1981年 | 28篇 |
1979年 | 45篇 |
1978年 | 34篇 |
1977年 | 33篇 |
1976年 | 36篇 |
1975年 | 20篇 |
1974年 | 34篇 |
1973年 | 33篇 |
1972年 | 32篇 |
1971年 | 25篇 |
1969年 | 22篇 |
1967年 | 24篇 |
排序方式: 共有2810条查询结果,搜索用时 15 毫秒
81.
A Rhodococcus sp. BPG-8 produces 1,2,4-benzenetriol during the transformation of resorcinol by phloroglucinol induced cell-free extract. The oxidation of 1,2,4-benzenetriol to 2-hydroxy-1,4-benzoquinone produces superoxide radicals that may have potential deleterious effects on cellular integrity. It has been shown that both superoxide dismutase (SOD) and catalase retard the autoxidation of 1,2,4-benzenetriol to 2-hydroxy-1,4-benzoquinone. Termination of the free radical chain reaction between superoxide radical and 1,2,4-benzenetriol seems to prevent this autoxidation. A NAD(P)H-dependent reductase appears to convert the 2-hydroxy-1,4-benzoquinone back to 1,2,4-benzenetriol. Both of these mechanisms appear to stabilize 1,2,4-benzenetriol so that it may be cleaved by meta cleavage enzymes. The enzymes responsible for the stabilization of 1,2,4-benzenetriol appear not to be inducible. 相似文献
82.
The emergence of structure-based drug design as a tool for drug discovery and development has focused increased attention on pharmacologically relevant proteins and the use of their three-dimensional structures to design novel pharmaceutical agents. This review describes recent structural studies of selected macromolecules that have been identified as targets for drug development. Several examples of the successful application of structure-based drug design techniques are also described. 相似文献
83.
84.
Daniel W. Armstrong Mary Gasper Sun Haing Lee Janusz Zukowski Nuran Ercal 《Chirality》1993,5(5):375-378
Plasma, urine, cerebrospinal fluid (CSF), and amniotic fluid were examined to determine whether free D-amino acids were present and if so at what levels. It was found that D-amino acids exist in all physiological fluids tested, but that their level varied, considerably. The lowest levels of D-amino acids were usually found in amniotic fluid or CSF (almost always <1% of the corresponding L-amino acid). The highest levels were found in urine (usually tenth percent to low percent levels). Pipecolic acid seemed to be different from the other amino acids tested in that it was excreted primarily as the D-enantiomer (often >90%). Correspondingly high levels of D-pipecolic acid were not found in plasma. Some of the trends found in this work seemed to be analogous to those found in a recent rodent study. © 1993 Wiley-Liss, Inc. 相似文献
85.
Doris Armstrong Goldman 《American journal of botany》1991,78(2):189-197
Because a male/female resource tradeoff is a basic assumption of many models of sex allocation in cosexual plants, statistical and manipulative methods were used to look for evidence of intersexual resource conflicts in Zizania palustris. In this monoecious grass, male and female investments overlap in time within each panicle and on successive panicles, and sex allocation quickly responds to environmental changes. Nevertheless, no negative correlations were found between the numbers of florets of each sex within panicles, on consecutive panicles, or on whole plants. Removing immature fruits or florets of either sex did not significantly increase subsequent investment in the other sex. The one significant tradeoff was slightly lower total fruit production on plants with exceptionally large male investment. Wild rice, therefore, fits the tradeoff assumption of sex allocation models at the population level but rarely at the individual level. 相似文献
86.
87.
Production of transgenic maize plants and progeny by bombardment of hi-II immature embryos 总被引:4,自引:0,他引:4
D. D. Songstad C. L. Armstrong W. L. Petersen B. Hairston M. A. W. Hinchee 《In vitro cellular & developmental biology. Plant》1996,32(3):179-183
Summary Production of transgenic maize (Zea mays L.) callus, plants, and progeny from microprojectile bombardment of 2–5-d cultured Hi-II immature embryos is described. Histological
evidence indicates that these tissues are amenable to transformation due to surface layer cell division of the scutellum.
Two out of every 100 bombarded embryos produced transgenic callus and R0 transgenic plants were both male and female fertile. Expected segregation of transgenes was observed in progeny. The primary
advantage of bombarding these tissues is increased male and female fertility of transgenic plants compared with those produced
using long-term callus or suspension cultures. 相似文献
88.
Differential recruitment of B and T cells in coxsackievirus B4-induced pancreatitis is influenced by a capsid protein. 总被引:2,自引:2,他引:0
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Two genetically similar variants of coxsackievirus B4, CB4-P and CB4-V, cause distinct disease syndromes in mice. A multidisciplinary approach was used to examine the events occurring in situ. The CB4-P variant induced acute pancreatitis, followed by repair of the exocrine tissues, while the CB4-V variant induced chronic pancreatitis, characterized by extensive destruction of the exocrine tissues. Since CB4-V replicated more efficiently than CB4-P in vivo, the more extensive tissue injury associated with CB4-V infection could be explained as the result of a higher level of viral replication. However, the fact that CB4-V replicated more efficiently in a mouse strain that survives infection than in a strain that succumbs to infection suggests that immune-mediated mechanisms as well as viral cytolysis may contribute to pancreatic tissue injury. To address the role of the immune system in virus-induced pancreatitis, the cell types within the inflammatory infiltrate were analyzed by flow cytometry. B cells (34 to 75%) were the most abundant, followed by T cells (10 to 30%), natural killer cells (4 to 8%), and macrophages (0 to 6%). Recruitment (and perhaps proliferation) of B and T cells to the pancreatic tissues was influenced by viral strain. Differential recruitment of T and B cells may reflect altered antigenic sites between CB4-P and CB4-V. The viral sequence that affected T- and B-cell recruitment was identified as a threonine residue at position 129 of the VP1 capsid protein. 相似文献
89.
Castellani John W.; Maresh Carl M.; Armstrong Lawrence E.; Kenefick Robert W.; Riebe Deborah; Echegaray Marcos; Casa Douglas; Castracane V. Daniel 《Journal of applied physiology》1997,82(3):799-806
Castellani, John W., Carl M. Maresh, Lawrence E. Armstrong,Robert W. Kenefick, Deborah Riebe, Marcos Echegaray, Douglas Casa, andV. Daniel Castracane. Intravenous vs. oral rehydration: effects onsubsequent exercise-heat stress. J. Appl.Physiol. 82(3): 799-806, 1997.This studycompared the influence of intravenous vs. oral rehydration afterexercise-induced dehydration during a subsequent 90-min exercisebout. It was hypothesized that cardiovascular, thermoregulatory, and hormonal variables would be the same between intravenous and oral rehydration because of similar restoration ofplasma volume (PV) and osmolality (Osmo). Eight non-heat-acclimated menreceived three experimental treatments (counterbalanced design) immediately after exercise-induced dehydration (33°C) to 4%body weight loss. Treatments were intravenous 0.45% NaCl (iv; 25 ml/kg), no fluid (NF), and oral saline (Oral; 25 ml/kg).After rehydration and rest (2 h total), subjects walked at 50% maximalO2 consumption for up to 90 min at36°C. The following observations were made: 1) heart rate was higher(P < 0.05) in Oral vs. ivat minutes 45, 60, and75 of exercise;2) rectal temperature, sweat rate, percent change in PV, and change in plasma Osmo were similar between ivand Oral; 3) change in plasmanorepinephrine decreased less (P < 0.05) in Oral compared with iv at minute45; 4) changes in plasma adrenocorticotropic hormone and cortisol were similar between ivand Oral after exercise was initiated; and5) exercise time was similar betweeniv (77.4 ± 5.4 min) and Oral (84.2 ± 2.3 min). These datasuggest that after exercise-induced dehydration, iv and Oral wereequally effective as rehydration treatments. Thermoregulation, changein adrenocorticotropic hormone, and change in cortisol were notdifferent between iv and Oral after exercise began; this is likely dueto similar percent change in PV and change in Osmo. 相似文献
90.
Identification of Possible Artifacts in the Association of Official Analytical Chemists Sporicidal Test 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
N. A. Miner G. K. Mulberry A. N. Starks A. Powers-Prather M. Entrup M. Armstrong B. Maida 《Applied microbiology》1995,61(4):1658-1660
Two laboratories tested four different brands of alkaline 2% glutaraldehyde sterilants by the Association of Official Analytical Chemists sporicidal test. Each laboratory found survival of Clostridium sporogenes spores on spore-labeled unglazed porcelain penicylinders (cylinders) to vary from test to test, and survival did not always correlate with increasing sterilant exposure time. These results were consistent with a theory that there may be random conditions within the test that prevent the sterilant from contacting all spores. Further studies indicated that the prior history of the unglazed porcelain cylinders and whether the C. sporogenes culture grown in egg-meat media had been processed (homogenized) to eliminate visible pieces of egg-meat media were important factors affecting the results and repeatability of this test. 相似文献