全文获取类型
收费全文 | 5950篇 |
免费 | 573篇 |
国内免费 | 2篇 |
出版年
2023年 | 20篇 |
2022年 | 58篇 |
2021年 | 136篇 |
2020年 | 80篇 |
2019年 | 95篇 |
2018年 | 103篇 |
2017年 | 86篇 |
2016年 | 164篇 |
2015年 | 270篇 |
2014年 | 295篇 |
2013年 | 333篇 |
2012年 | 473篇 |
2011年 | 470篇 |
2010年 | 288篇 |
2009年 | 219篇 |
2008年 | 372篇 |
2007年 | 376篇 |
2006年 | 296篇 |
2005年 | 331篇 |
2004年 | 303篇 |
2003年 | 262篇 |
2002年 | 276篇 |
2001年 | 65篇 |
2000年 | 72篇 |
1999年 | 85篇 |
1998年 | 68篇 |
1997年 | 45篇 |
1996年 | 37篇 |
1995年 | 41篇 |
1994年 | 31篇 |
1993年 | 25篇 |
1992年 | 33篇 |
1991年 | 41篇 |
1990年 | 39篇 |
1989年 | 40篇 |
1988年 | 31篇 |
1987年 | 31篇 |
1986年 | 34篇 |
1985年 | 28篇 |
1984年 | 21篇 |
1983年 | 32篇 |
1982年 | 24篇 |
1980年 | 19篇 |
1979年 | 26篇 |
1977年 | 20篇 |
1974年 | 27篇 |
1973年 | 20篇 |
1971年 | 20篇 |
1969年 | 22篇 |
1966年 | 20篇 |
排序方式: 共有6525条查询结果,搜索用时 15 毫秒
91.
Relationship between heterogeneous changes in airway morphometry and lung resistance and elastance 总被引:3,自引:0,他引:3
Lutchen, Kenneth R., and Heather Gillis. Relationshipbetween heterogeneous changes in airway morphometry and lung resistanceand elastance. J. Appl. Physiol.83(4): 1192-1201, 1997.We present a dog lung model to predictthe relation between inhomogeneous changes in airway morphometry andlung resistance (RL) andelastance (EL) for frequenciessurrounding typical breathing rates. TheRL andEL were sensitive in distinctways to two forms of peripheral constriction. First, when there is alarge and homogeneous constriction, theRL increases uniformly over thefrequency range. The EL israther unaffected below 1 Hz but then increases with frequencies up to5 Hz. This increase is caused by central airway wallshunting. Second, the RL andEL are extremely sensitive to mild inhomogeneous constriction in which a few highly constricted ornearly closed airways occur randomly throughout theperiphery. This results in extreme increases in the levelsand frequency dependence of RLand EL but predominantly attypical breathing rates (<1 Hz). Conversely, theRL andEL are insensitive to highly inhomogeneous airway constriction that does not produce any nearly closed airways. Similarly, alterations in theRL andEL due to central airway wallshunting are not likely until the preponderance of the peripheryconstricts substantially. The RLand EL spectra are far moresensitive to these two forms of peripheral constriction than toconstriction conditions known to occur in the central airways. On thebasis of these simulations, we derived a set of qualitative criteria toinfer airway constriction conditions from RL andEL spectra. 相似文献
92.
Thermoregulatory control during pregnancy and lactation in rats 总被引:1,自引:0,他引:1
Eliason, Heather L., and James E. Fewell.Thermoregulatory control during pregnancy and lactation in rats.J. Appl. Physiol. 83(3): 837-844, 1997.Although the mechanisms remain unknown, maternal coretemperature (Tc) decreases nearterm of pregnancy and is increased throughout lactation in rats. Thepurpose of our present experiments was to determine whether pregnancy and lactation shift the thermoneutral zone of rats and to investigate whether the changes in maternal Tcduring pregnancy and lactation result from "forced" or"regulated" thermoregulatory responses. Conscious, chronicallyinstrumented nonpregnant and pregnant and lactating rats were studiedboth in a thermocline (a chamber with a linear temperature gradientfrom 12 to 36°C) and in a metabolic chamber to determine theinfluence of pregnancy and lactation on selected ambient temperature aswell as the thermoregulatory response to changes in ambienttemperature. We found that selected ambient temperature, oxygenconsumption, and thermal conductance did not change in rats studied ina thermocline as Tc decreased nearterm of pregnancy. There was, however, a downward shift in thethermoneutral zone of rats studied in a metabolic chamber near term ofpregnancy. During lactation, selected ambient temperature decreased inrats studied in a thermocline as oxygen consumption andTc increased. The thermoneutralzone of lactating rats was not different from that of nonpregnantanimals. Thus our data provide evidence that the decrease inTc near term of pregnancy in ratsresults from a regulated thermoregulatory response,whereas the increase in Tc duringlactation results from a forced thermoregulatory response. 相似文献
93.
Characteristics of triplex-directed photoadduct formation by psoralen-linked oligodeoxynucleotides. 总被引:2,自引:2,他引:0
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
P J Bates V M Macaulay M J McLean T C Jenkins A P Reszka C A Laughton S Neidle 《Nucleic acids research》1995,23(21):4283-4289
A triplex-forming oligopyrimidine has been attached at its 5'-end to a photoreactive psoralen derivative and used to target a sequence which forms part of the coding region of the human aromatase gene. The 20 base pair sequence is not a perfect triplex target since it contains three pyrimidine interruptions within the purine-rich strand. Despite this, we have detected triplex-directed photoadduct formation at pH 7.0 between the psoralen-linked oligonucleotide and a 30mer duplex representing the aromatase target. Photoadduct formation was found to be sensitive to pH, temperature, cation concentration and the base composition of the third strand. By varying the base sequence of the target duplex around the psoralen intercalation site, we have characterised the site and mode of psoralen intercalation. The attached psoralen has been found to intercalate at the triplex-duplex junction with a strong preference for one orientation. We have shown that the psoralen will bind at the junction even when there is a preferred TpA step at an adjacent site. We have also compared the binding affinity and photoreactivity of oligodeoxyribonucleotides linked to two different psoralen derivatives and found differences in the rate of crosslinking and the extent of crosslink formation. Finally, we have examined oligodeoxyribonucleotides which are attached to psoralen by polymethylene linkers of different lengths. 相似文献
94.
Ursula Schulze-Gahmen Jeroen Brandsen Heather D. Jones David O. Morgan Laurent Meijer Jaroslav Vesely Sung-Hou Kim 《Proteins》1995,22(4):378-391
Cyclin-dependent kinases (CDKs) are conserved regulators of the eukaryotic cell cycle with different isoforms controlling specific phases of the cell cycle. Mitogenic or growth inhibitory signals are mediated, respectively, by activation or inhibition of CDKs which phosphorylate proteins associated with the cell cycle. The central role of CDKs in cell cycle regulation makes them a potential new target for inhibitory molecules with anti-proliferative and/or anti-neoplastic effects. We describe the crystal structures of the complexes of CDK2 with a weakly specific CDK inhibitor, N6-(δ2-isopentenyl)adenine, and a strongly specific inhibitor, olomoucine. Both inhibitors are adenine derivatives and bind in the adenine binding pocket of CDK2, but in an unexpected and different orientation from the adenine of the authentic ligand ATP. The N6-benzyl substituent in olomoucine binds outside the conserved binding pocket and is most likely responsible for its specificity. The structural information from the CDK2-olomoucine complex will be useful in directing the search for the next generation inhibitors with improved properties. © 1995 Wiley-Liss, Inc. 相似文献
95.
96.
Fructose 2,6-bisphosphate, sugar phosphates and adenine nucleotides in the regulation of glucose metabolism in the lactating rat mammary gland 总被引:2,自引:0,他引:2
Fructose 2,6-bisphosphate is present in the rat mammary gland, rising from a value of 1.4 nmol/g in pregnancy to 4.3 nmol/g tissue at 14 days lactation; the equivalent values calculated/ml intracellular water are 5.2 and 11.6 nmol, respectively. The tissue content of fructose 6-phosphate, fructose 1,6-bisphosphate, ATP and phosphoenolpyruvate remain relatively constant in the transition from pregnancy to the height of lactation. The changes in AMP, cyclic AMP, and citrate content of the mammary gland during lactation are such as to promote an increase in fructose 2,6-bisphosphate formation and flux through phosphofructokinase. 相似文献
97.
Radiolabeled oxindole-3-acetic acid was metabolized by roots, shoots, and caryopses of dark grown Zea mays seedlings to 2,3-dihydro-7-hydroxy-2-oxo-1H indole-3-acetic acid-7′-O-β-d-glycopyranoside with the simpler name of 7-hydroxyoxindole-3-acetic acid-glucoside. This compound was also formed from labeled indole-3-acetic acid supplied to intact seedlings and root segments. The glucoside of 7-hydroxyoxindole-3-acetic acid was also isolated as an endogenous compound in the caryopses and shoots of 4-day-old seedlings. It accumulates to a level of 4.8 nanomoles per plant in the kernel, more than 10 times the amount of oxindole-3-acetic acid. In the shoot it is present at levels comparable to that of oxindole-3-acetic acid and indole-3-acetic acid (62 picomoles per shoot). We conclude that 7-hydroxyoxindole-3-acetic acid-glucoside is a natural metabolite of indole-3-acetic acid in Z. mays seedlings. From the data presented in this paper and in previous work, we propose the following route as the principal catabolic pathway for indole-3-acetic acid in Zea seedlings: Indole-3-acetic acid → Oxindole-3-acetic acid → 7-Hydroxyoxindole-3-acetic acid → 7-Hydroxyoxindole-3-acetic acid-glucoside. 相似文献
98.
99.
Summary Twenty-one suppressor gene mutations which suppress the met-5.1 missense mutation of Coprinus were separated into six groups (A-F) on the basis of dominance or recessiveness, linkage to the met-5 locus, comlementation in heterozygous cells and growth behaviour. The actual number of suppressor loci could not be determined because crosses between suppressed mutants were inviable. The allele specificity of group A, C, D and F suppressors was confirmed by appropriate crosses. Group B and E suppressors were not tested because of close linkage to the met-5 locus. No evidence for functional suppression of met-5 mutations was obtained thus it is likely that all the suppressors cause translational corelation of met-5.1. Suppressors in four groups (C-F) have properties expected of tRNA structural gene mutations: the group C mutation is dominant, the other mutations are recessive but do not complement in heterozygous cells. The relative efficiencies of the tRNA species involved was assessed by comparing the degree to which the different sup
+ mutations depressed the growth rate on methionine supplemented medium. The dominant mutation depressed growth to the greatest extent and is, therefore, the most efficient suppressor. The least efficient suppressors did not depress growth at all. When growth was compared on minimal medium it was found that the more efficient the suppressor the less well it restored growth. The mutations in groups A and B depressed growth more than the tRNA mutations but affect some other component in translation because they are recessive and complement normally. It is suggested that they may act to alter tRNA modifying enzymes. 相似文献
100.
Heather Windle 《BMJ (Clinical research ed.)》1977,1(6065):891-892