全文获取类型
收费全文 | 2318篇 |
免费 | 195篇 |
国内免费 | 7篇 |
出版年
2023年 | 39篇 |
2022年 | 52篇 |
2021年 | 92篇 |
2020年 | 45篇 |
2019年 | 59篇 |
2018年 | 75篇 |
2017年 | 61篇 |
2016年 | 79篇 |
2015年 | 143篇 |
2014年 | 127篇 |
2013年 | 161篇 |
2012年 | 205篇 |
2011年 | 177篇 |
2010年 | 100篇 |
2009年 | 81篇 |
2008年 | 107篇 |
2007年 | 107篇 |
2006年 | 84篇 |
2005年 | 76篇 |
2004年 | 76篇 |
2003年 | 81篇 |
2002年 | 74篇 |
2001年 | 47篇 |
2000年 | 34篇 |
1999年 | 40篇 |
1998年 | 10篇 |
1997年 | 17篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 17篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 19篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1969年 | 4篇 |
排序方式: 共有2520条查询结果,搜索用时 15 毫秒
991.
A flow method is described for determination of the kinetics parameters (V-m and K-m) for enzymes that are bound to particles, to membranes, and to the interior surfaces of tubes. Substrate solution is pumped through Tygon tubing to a microvolume flow cell and back into the reaction mixture, the flow rate being adjusted to be faster than the rate of formation of product. To illustrate the technique, it is applied to the determination of the parameters for electric-eel acetylcholinesterase attached to particles, to membranes, and to the inner surface of nylon tubing. 相似文献
992.
J. Nguyen H. Anh 《Cell and tissue research》1972,131(2):187-198
Résumé Les corps myéloïdes de l'épithélium pigmentaire rétinien ont été observés après différentes techniques de fixation, déshydratation, inclusion et coloration. Après fixation classique par le glutaraldéhyde et l'osmium, l'espace intersacculaire apparaît réduit (jonctions) et une ligne dense est parfois observable dans l'espace intrasacculaire. La fixation par le permanganate met en évidence de façon permanente cette ligne dense qui correspondrait à la fusion des membranes. La coloration négative caractérise un constituant protéique entre les saccules. La déshydratation par le Durcupan hydrosoluble met en évidence un matériel lipidique intrasacculaire qui est extrait par le méthanol-chloroforme et partiellement par la déshydratation alcoolique classique.Les corps myéloïdes apparaissent plusieurs jours avant l'éclosion chez l'oiseau. Ils se forment à partir du réticulum granulaire. Ils ne peuvent être confondus avec les dictyosomes Golgiens : Ils ne contiennent pas de glycoprotéines.
Summary Myeloid bodies of the retinal pigment epithelium of different vertebrates were investigated by various techniques of fixation, dehydration, embedding and staining. After classical fixation with buffered glutaraldehyde and osmium, the intersaccular space is narrow (junction complexes) and a dense line is sometimes visible in the middle of the intrasaccular space. With permanganate fixative this dense line is always visible; it represents probably the fusion of the unit-membranes. The negative staining demonstrates the presence of proteins between the saccules. Dehydration by water soluble Durcupan shows a lipidic component in the intrasaccular space, which is removed by methanol-chloroform and partly by the classical ethanol dehydration.The existence of myeloid bodies is demonstrated in the bird-embryo a few days before birth. They originate from granular reticulum cisternae. They are not of Golgi origin: glycoprotein cannot been demonstrated at their level.
Chargé de Recherche à l'I.N.S.E.R.M. (contrat n° 711.152). Avec la collaboration technique de L. Salin et D. Joseph. 相似文献
993.
Plateau-phase V79 cells were exposed sequentially to fast neutrons and gamma rays. A dose-dependent reduction in the shoulder width of the gamma-ray survival curve was observed after preexposure of cells to neutrons. A similar effect was demonstrated on the neutron survival curve when cells were preirradiated with gamma rays. Treatment of cells with 150 microM beta-araA after either gamma or neutron irradiation reduced primarily the shoulder of the survival curve. When beta-araA was given to the cells after exposure to mixed radiation modalities, survival curves similar to those observed after exposure to a single radiation modality and treatment with beta-araA were obtained. The kinetics of loss of the interaction observed after exposure of cells to gamma rays following neutron irradiation was similar to the kinetics of loss of sensitivity to beta-araA (T1/2 = 1 h) measured by delaying drug administration after exposure to gamma rays. The results suggest that the PLD expressed by beta-araA is at least partly involved in the interactive effect observed after combined exposure of plateau-phase V79 cells to neutrons and gamma rays. 相似文献
994.
The ermE gene was cloned from Streptomyces erythraeus into Escherichia coli on a series of plasmids. When transcribed from the lac promoter, ermE conferred high-level resistance to erythromycin and other macrolide-lincosamide-streptogramin-B (MLS) antibiotics. A methylase activity capable of N6-mono- and N6,N6-dimethylation of adenine residues in E. coli rRNA was detected in extracts of MLS-resistant cells. In addition, rRNA extracted from MLS-resistant E. coli contained N6-mono- and N6,N6-dimethylated adenine residues. 相似文献
995.
Summary OH mouse 10 T1/2 cells showing strong inhibition of growth at confluency were grown under daily refeeding in the presence of BrdUrd (from 0 to 1 µM) and exposed to-rays either while exponentially growing or in the plateau phase. An increase in radiosensitivity was observed in both growth conditions mainly reflected by a reduction in Dq. Greater radiosensitization was observed in exponentially growing than in plateau-phase cells, and 3–4 times higher BrdUrd concentrations were required in plateau-phase cells for similar potentiation in killing. This effect could not be entirely attributed to a reduction in BrdUrd incorporation since measurements with3H-BrdUrd showed reductions in incorporation between only 17–47% in plateau-phase cells. The rate of repair of potentially lethal damage (PLD) as demonstrated by delayed plating was not affected by the incorporation of BrdUrd, but the amount of repair (measured as the relative increase in cell survival) was higher for BrdUrd-containing cells. Post-irradiation treatment of cells in the plateau-phase (no BrdUrd) with 9--d-arabinofuranosyladenine (araA) caused fixation of radiation-induced PLD. AraA treatment of cells grown in the presence of various amounts of BrdUrd also caused fixation of PLD, but resulted in survival levels similar to those observed with cells growing in BrdUrd-free medium. This result indicates that BrdUrd mediated radiosensitization cannot be observed when cells are prevented from repairing PLD by postirradiation incubation with araA. Based on these findings we propose that the mechanism of radiosensitization by BrdUrd incorporation might be, by increasing probability of fixation, mediated by the postirradiation progression of cells through the cycle, of a sector of PLD also sensitive to post-irradiation treatment with araA. For this sector of PLD the term -PLD has been proposed.This investigation was partly supported by PHS grants CA33951, CA39938 and CA42026 awarded by NCI, DHHS 相似文献
996.
A simple method was devised for the maintenance of the chorioallantoic membrane (CAM) of chick embryos in organ culture. Explants of CAM survived for up to 5 days in this system and retained the characteristic three-layered morphology (ectoderm, mesoderm, and endoderm). Induction of the CAM calcium-binding protein (CaBP) by effectors of calcium metabolism was studied in these organ cultures. Vitamin K was found to elicit a seven- to eightfold increase in CaBP, whereas no increase in CaBP activity occurred on supplementation with vitamin A, parathyroid hormone, an analogue of vitamin D, vitamin D and its hydroxylated metabolites, or with elevated calcium levels. The vitamin K-mediated induction of CaBP was dose-dependent, inhibited by the vitamin K antagonists warfarin and dicoumarol, selective for vitamin K5, and maximal at the developmental stage (13-15 days of incubation) corresponding to the onset of calcium transport by the CAM in vivo. CaBP levels increased after 60-70 h in cultures of 13-15 day CAM supplemented with vitamin K and reached maximal levels around 80-90 h of culture. The CAM ectoderm underwent extensive proliferation and often assumed a villuslike morphology in the vitamin K cultures. 相似文献
997.
The investigation of three South American Wedelia species affords besides known acetylenes several new kaurenic acid derivatives, which have been isolated as their methyl esters. Their structures are elucidated by spectroscopic methods. Chemotaxonomic aspects are discussed. 相似文献
998.
999.
This study investigated odor-category organization in threecultures by evaluating (i) the relationship between linguisticand perceptual categorization and (ii) the existence of an internalstructure of odor categories. In the first experiment, threegroups of 30 participants from American, French and Vietnamesecultures performed a sorting task. The first group sorted 40odorants on the basis of odor similarity, the second group sorted40 odor names on the basis of name similarity and the last groupsorted 40 odor names on the basis of imagined odor similarity.Results showed that odor categorization was based on perceptualor conceptual similarity and was in part independent of wordand imagined categorizations. In the second experiment, anothergroup of 30 participants from each culture rated the typicalityof the odorants for 11 odor categories. Results showed thatsome odorants were rated as more typical than others. Moreover,the typicality gradient predicted the odor space obtained inthe odor sorting task in a consensual way among the three cultures.These results suggest that, as for other categories, odor categoriesare based on perceptual similarities rather than on semanticcues. Moreover odor-category structure might have a core representationwhich might be common to different cultures with boundarieswhich might be more culturally dependent. 相似文献
1000.
Molecular epidemiology of adenovirus infection among pediatric population with diarrhea in Asia 总被引:7,自引:0,他引:7
Li L Phan TG Nguyen TA Kim KS Seo JK Shimizu H Suzuki E Okitsu S Ushijima H 《Microbiology and immunology》2005,49(2):121-128
A total of 3,577 fecal specimens from infants and children with acute gastroenteritis in Japan, Korea and Vietnam during 1998 and 2001 were tested for adenovirus by the ELISA method. Of these, adenovirus was detected in 158 (4.4%). The detection rate of adenovirus was highest in Korea (8.7%, 20/231) followed by 5.0% (100/1,991) in Japan and 2.8% (38/1,355) in Vietnam. All adenoviruses were further serotyped by PCR-RFLP. The diversity of adenovirus serotypes including Ad2, 3, 5, 8, 31, 40 and 41 was demonstrated. Worth of note was a decrease in the rate of isolation of Ad40 (7.6%, 12/158) and a concomitant increase of Ad41 (63.9%, 101/158) to become the predominant serotype. Another interesting feature of the study was the presence of Ad3 (4.0% and 30%) and Ad8 (8.0% and 20%) in Japan and Korea, respectively, which is mainly associated with keratoconjunctivitis worldwide. Our result underscored the importance of adenovirus in association with acute gastroenteritis in Asian countries. 相似文献