全文获取类型
收费全文 | 13550篇 |
免费 | 1242篇 |
国内免费 | 3篇 |
出版年
2021年 | 156篇 |
2020年 | 116篇 |
2019年 | 118篇 |
2018年 | 148篇 |
2017年 | 157篇 |
2016年 | 248篇 |
2015年 | 399篇 |
2014年 | 482篇 |
2013年 | 648篇 |
2012年 | 807篇 |
2011年 | 710篇 |
2010年 | 521篇 |
2009年 | 449篇 |
2008年 | 648篇 |
2007年 | 703篇 |
2006年 | 649篇 |
2005年 | 605篇 |
2004年 | 640篇 |
2003年 | 602篇 |
2002年 | 611篇 |
2001年 | 262篇 |
2000年 | 250篇 |
1999年 | 270篇 |
1998年 | 202篇 |
1997年 | 178篇 |
1996年 | 142篇 |
1995年 | 172篇 |
1994年 | 176篇 |
1993年 | 143篇 |
1992年 | 213篇 |
1991年 | 197篇 |
1990年 | 159篇 |
1989年 | 162篇 |
1988年 | 155篇 |
1987年 | 161篇 |
1986年 | 146篇 |
1985年 | 141篇 |
1984年 | 148篇 |
1983年 | 116篇 |
1982年 | 154篇 |
1981年 | 132篇 |
1980年 | 101篇 |
1979年 | 117篇 |
1978年 | 119篇 |
1977年 | 95篇 |
1976年 | 91篇 |
1975年 | 107篇 |
1974年 | 107篇 |
1973年 | 89篇 |
1972年 | 79篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Regulation of intracellular pH by a neuronal homolog of the erythrocyte anion exchanger 总被引:23,自引:0,他引:23
We have isolated AE3, a novel gene expressed primarily in brain neurons and in heart. The predicted AE3 polypeptide shares a high degree of identity with the anion exchange and cytoskeletal binding domains of the erythrocyte band 3 protein. Expression of AE3 cDNA in COS cells leads to chronic cytoplasmic acidification and to chloride- and bicarbonate-dependent changes in intracellular pH, confirming that this gene product is an anion exchanger. Characterization of an AE3 mutant lacking the NH2-terminal 645 amino acids demonstrates that the COOH-terminal half of the polypeptide is both necessary and sufficient for correct insertion into the plasma membrane and for anion exchange activity. The NH2-terminal domain may play a role in regulating the activity of the exchanger and may be involved in the structural organization of the cytoskeleton in neurons. 相似文献
62.
63.
James AP Zahab DM Mahmourides G Maleszka R Schneider H 《Applied and environmental microbiology》1989,55(11):2871-2876
Induced mutants, selected for their defective growth on d-xylose while retaining the ability to grow normally on d-glucose, were studied in Pachysolen tannophilus, a yeast capable of converting d-xylose to ethanol. Fourteen of the mutations were found to occur at nine distinct loci, and data indicated that many more loci remain to be detected. Most of the mutations were pleiotropic in character, and the expression of some of them was much affected by nutritional conditions and by genetic background. Mutations at several loci resulted in poor growth on at least one compound that was either an intermediate of the tricarboxylic acid cycle, succinate or alpha-ketoglutarate, or on compounds metabolizable via this cycle, ethanol or glycerol. An initial biochemical characterization of the mutants was undertaken. Analysis for xylose reductase, xylitol dehydrogenase, and xylulose kinase activity showed that one or more of these activities was affected in 12 of 13 mutants. However, drastic reduction in activity of a single enzyme was confined to that of xylitol dehydrogenase by mutations at three different loci and to that of d-xylose reductase by mutation at another locus. Growth of these latter four mutants was normal on all carbon sources tested that were not five-carbon sugars. 相似文献
64.
Klaus Rohde 《Systematic parasitology》1989,14(2):79-91
The following gill monogeneans are described, based on a survey of 240 Rastrelliger kanagurta, 12 R. faughni and 185 R. brachysoma (Scombridae) from many geographical areas: Eyelavera typica from R. kanagurta, R. faughni and R. brachysoma, Indomazocraes jagannath from R. kanagurta and R. faughni, Kuhnia sprostonae from R. kanagurta and R. brachysoma, and Kuhnia scombercolias from R. kanagurta and R. brachysoma. Eyelavera parukhini Lebedev, 1980 is synonymised with E. typica, Scomberocotyle eyela Unnithan, 1964 with Indomazocraes jagannath, Kuhnia microlepidotusi Gupta & Krishna, 1977 and K. kanagurta Mamaev & Parukhin, 1986 with K. sprostonae, K. arabica Mamaev & Parukhin, 1986 with K. scombercolias Nasir & Fuentes Zambrano, 1983. It is emphasized that populations of Monogenea from the same host species or genus in different geographical areas are likely to be conspecific, and should not be described as different species, if they differ only slightly from each other. Monogenea that differ from insufficiently described species in minor detail should not be described as new species unless material of the original species has been examined. 相似文献
65.
K Schneider W Kausler D Tripier K Jouvenal G Spiteller 《Biological chemistry Hoppe-Seyler》1989,370(4):353-356
Two previously unknown peptides with a high amount of polar amino acids were isolated from human seminal plasma by a combination of dialysis, gel filtration, ion-exchange chromatography, and RP-HPLC. Their structures were determined by gas-phase sequencing simultaneously considering the different peak intensities. 相似文献
66.
Wolfgang Witt Peter Hampel Klaus Böcker Angelika Mertsching 《Archives of microbiology》1989,151(2):154-158
Divalent cations activate the lysophospholipase and transacylase reactions catalyzed by the same enzymes in the yeast Saccharomyces cerevisiae. The activation was observed at neutral pH, but not at the pH optimum of lysophospholipase/transacylase, near 3.5. Adenine nucleotides, especially AMP and ADP, are strong inhibitors of the same group of enzymes. Half maximal inhibition by AMP was found at a concentration of about 20 M. The inhibition by nucleotides in low concentrations is enhanced by divalent cations. 相似文献
67.
Freshly prepared human red blood cells incubated with 5 mM ferricyanide, 0.2 mM iodoacetate and 2 mM adenosine in the presence of 5 mM EGTA demonstrate comparable increases in Na+ and K+ permeability (ferricyanide effect). This effect is unrelated to the Ca2+-activated K+ channel (Gardos effect) since influx of Ca2+ from outside the cell is excluded. Also this effect is different from the non-specific Na+ and K+ permeability change elicited by PCMBS. These differences become obvious by using various reagents. For example, A23187 and quinidine exert opposite effects in Gardos and ferricyanide experiments, where A23187 and atebrin react oppositely in the latter and in PCMBS experiments. The ferricyanide effect described here does not involve formation of nonspecific channels. The change in Na+ permeability separately from K+ permeability under certain circumstances suggests a more specific effect. 相似文献
68.
Temperature jump study of charge translocation during the bacteriorhodopsin photocycle 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Temperature jump experiments were carried out on purple membranes oriented and fixed in polyacrylamide gel. With green background illumination a relaxation of the photocurrent after an infrared laser pulse could be observed. To simulate the temperature jump signals different models of the bacteriorhodopsin photocycle were tested. The parameters of these models were obtained by measuring absorbance changes and photocurrent after excitation with a 575-nm laser flash.
A model with a temperature-dependent branching before the M state turned out to be satisfying. Other models, especially those with a late branching or without branching, could not reproduce the temperature jump measurements.
相似文献69.
N J Holbrook R K Chopra M T McCoy J E Nagel D C Powers W H Adler E L Schneider 《Cellular immunology》1989,120(1):1-9
Lymphocytes of aged animals exhibit a marked decrease in proliferative capacity in response to mitogen stimulation when compared to those of younger animals. In humans and mice the decreased proliferation is due at least in part (i) to the inability of lymphocytes to synthesize sufficient interleukin 2 (IL-2) and (ii) to decreased expression of IL-2 receptors (IL-2R) on the surface of aged lymphocytes. We compared proliferative abilities, IL-2 production, and IL-2R expression in splenocyte cultures of 4- to 5- and 22- to 24-month-old Fischer 344 rats stimulated with either concanavalin A (Con A) or A23187 and phorbol myristate acetate (PMA). Proliferation was significantly decreased in aged lymphocytes (30-50%) with both treatment protocols. However, unlike mice and humans we observed no difference in IL-2 activity, IL-2 mRNA levels, or IL-2R cell surface expression of lymphocytes from young and aged rats stimulated with either Con A or A23187 and PMA. These results indicate that factors other than decreased expression of IL-2 and IL-2R are responsible for the diminished proliferative capacity of aged rat lymphocytes following mitogen stimulation. 相似文献
70.