全文获取类型
收费全文 | 1443411篇 |
免费 | 121755篇 |
国内免费 | 3006篇 |
出版年
2021年 | 18819篇 |
2019年 | 16999篇 |
2018年 | 24256篇 |
2017年 | 22735篇 |
2016年 | 32674篇 |
2015年 | 43826篇 |
2014年 | 51824篇 |
2013年 | 78340篇 |
2012年 | 40331篇 |
2011年 | 33262篇 |
2010年 | 50100篇 |
2009年 | 51157篇 |
2008年 | 30144篇 |
2007年 | 29591篇 |
2006年 | 28178篇 |
2005年 | 29977篇 |
2004年 | 28777篇 |
2003年 | 26512篇 |
2002年 | 24639篇 |
2001年 | 33993篇 |
2000年 | 31307篇 |
1999年 | 31617篇 |
1998年 | 25625篇 |
1997年 | 25453篇 |
1996年 | 25052篇 |
1995年 | 23118篇 |
1994年 | 22950篇 |
1993年 | 21994篇 |
1992年 | 27883篇 |
1991年 | 26327篇 |
1990年 | 25320篇 |
1989年 | 26132篇 |
1988年 | 24163篇 |
1987年 | 22744篇 |
1986年 | 21731篇 |
1985年 | 23813篇 |
1984年 | 23466篇 |
1983年 | 20762篇 |
1982年 | 20991篇 |
1981年 | 20149篇 |
1980年 | 18765篇 |
1979年 | 19551篇 |
1978年 | 18229篇 |
1977年 | 17586篇 |
1976年 | 16894篇 |
1975年 | 16380篇 |
1974年 | 16994篇 |
1973年 | 17325篇 |
1972年 | 15082篇 |
1971年 | 13799篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
201.
202.
203.
N. V. Ozolina E. V. Kolesnikova V. N. Nurminsky I. S. Nesterkina L. V. Dudareva L. I. Donskaya R. K. Salyaev 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2010,4(3):297-301
The changes in transport activity of tonoplast proton pumps under the influence of exogenous NO donator and modulation of
Ca2+ concentration jointly and separately were investigated at different stages of ontogenesis and under hyperosmotic stress.
The results suggest that both exogenous NO donator and Ca2+ ions can influence the activity of transport processes related to tonoplast and this influence is especially evident in the
period of growth and accumulation of metabolites. Under hyperosmotic stress, H+-pyrophosphatase plays a more important role than H+-ATPase: the activity of the former increases 2.3-fold compared to the control osmotic conditions, whereas the activity of
H+-ATPase is practically unchanged. H+-pyrophosphatase was more responsive to the presence of exogenous NO donator and to variations in Ca2+ concentration. The effects of exogenous NO donator on tonoplast proton pumps depended on the concentration of Ca2+, which apparently can mediate NO action. 相似文献
204.
K. Ferrazzoli Devienne M.S. Gonalves Raddi R. Gomes Coelho W. Vilegas 《Phytomedicine》2005,12(5):378-381
Three naturally occurring isocoumarins (paepalantine, paepalantine 9-O-beta-D-glucopyranoside and paepalantine 9-O-beta-D-allopyranosyl(1 --> 6) glucopyranoside) and two semi-synthetic analogues, 9,10-acylated compound and 9-OH-10-methylated compound, structurally similar to paepalantine, were evaluated for antimicrobial activity using a spectrophotometric microdilution technique. The paepalantine was active against S. aureus, S. epidermidis, and E. faecalis while the other four compounds proved ineffective against all microorganisms tested at concentrations of 500 microg/ml. Variations in phenolic substitution at OH-9 and/or OH-10 in the paepalantine molecule resulted in compounds without antimicrobial activity. A combination of structural features, two phenolic groups as cathecolic system, forms an oxygenated system arrangement that may reflect the potentially antimicrobial properties of paepalantine. 相似文献
205.
R Blomhoff W Eskild G M Kindberg K Prydz T Berg 《The Journal of biological chemistry》1985,260(25):13566-13570
The intracellular transport of chylomicron remnants labeled with [3H]retinyl ester was studied in rat liver parenchymal cells by means of subcellular fractionation in Nycodenz and sucrose density gradients. The data presented indicate that endocytosed chylomicron remnant [3H]retinyl ester initially is located in low density endosomes. Radioactivity is subsequently transferred to a denser vesicle. Equilibrium as well as rate zonal centrifugation suggest that this denser [3H] retinoid-containing vesicle may represent endoplasmic reticulum. We have compared the intracellular transport of chylomicron remnant [3H]retinyl ester and 125I-asialofetuin. The receptor-mediated endocytosis of asialoglycoproteins in rat liver parenchymal cells is a thoroughly studied system. Our results suggest that the [3H] retinoid and 125I-asialofetuin follow the same path initially to the endosomes. After transit in endosomes, the intracellular transport differs. While asialofetuin is transported to the lysosomes, the retinoid is probably transferred to the endoplasmic reticulum. 相似文献
206.
Summary A stream-breeding race of small-mouthed salamanders (Ambystoma texanum) in central Kentucky produces ova that are twice as large as those of a pond-breeding race found nearby. Embryos of stream-breeders also hatch at a more advanced developmental stage than those of pond-breeders. Morphological evidence indicates that stream-breeders were derived from pond-breeding stock. Assuming that differences between stream and pond-breeders reflect evolutionary change, and that the ancestral pond stock that invaded streams was similar to extant pond-breeders, we examined three hypotheses that might explain changes in ovum size and stage at hatching following the invasion of streams. (1) Larger ovum size evolved indirectly as a consequence of selection for rapid development which minimizes mortality risk from stream drying. (2) Increased ovum (hatchling) size and stage at hatching of stream-breeders are adaptations to resist stream current. (3) Increased ovum (hatchling) size and stage at hatching are adaptations to reduce predation on hatchlings from stream invertebrates. The results of field and laboratory studies only support hypotheses (2) and (3). Hatchlings that were relatively large or at a more advanced developmental stage had slower drift rates and were less vulnerable to predation by Phagocata gracilis, a flatworm abundant in streams in central Kentucky. Developmental and growth parameters were not correlated significantly with ovum size in populations of either geographic race. Differences in degree of parental care among races also cannot explain variation in ovum size since both races abandon their eggs immediately after oviposition. 相似文献
207.
208.
The effects on respiration of an analogue of adenosine, L-2-N6-(phenylisopropyl)adenosine (PIA), and of the methylxanthine, theophylline, were determined in 19 vagotomized glomectomized cats whose end-tidal PCO2 was kept constant by means of a servo-controlled ventilator. Integrated phrenic nerve activity was used to represent respiratory output. Our results show that PIA, whether given systemically or into the third cerebral ventricle, depressed respiration. Systemically administered theophylline stimulated respiration. Theophylline given intravenously, or into the third ventricle not only reversed the depressive effects of previously administered PIA but caused further increases of respiration above the control level. Prior systemic administration of theophylline blocked both respiratory and hypotensive effects of subsequently administered PIA. Effects of either agent on medullary extracellular fluid pH did not explain the results. We conclude that the adenosine analogue PIA, acts to inhibit neurons in the brain that are involved in the control of respiration and that its effects are blocked by theophylline. We suggest that adenosine acts as a tonic modulator of respiration and that theophylline stimulates breathing by competitive antagonism of adenosine at neuronal receptor sites. 相似文献
209.
210.