全文获取类型
收费全文 | 3142篇 |
免费 | 263篇 |
国内免费 | 2篇 |
出版年
2023年 | 12篇 |
2022年 | 43篇 |
2021年 | 64篇 |
2020年 | 33篇 |
2019年 | 49篇 |
2018年 | 78篇 |
2017年 | 54篇 |
2016年 | 119篇 |
2015年 | 174篇 |
2014年 | 182篇 |
2013年 | 206篇 |
2012年 | 289篇 |
2011年 | 266篇 |
2010年 | 167篇 |
2009年 | 156篇 |
2008年 | 188篇 |
2007年 | 209篇 |
2006年 | 167篇 |
2005年 | 164篇 |
2004年 | 130篇 |
2003年 | 122篇 |
2002年 | 131篇 |
2001年 | 26篇 |
2000年 | 11篇 |
1999年 | 27篇 |
1998年 | 28篇 |
1997年 | 28篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1974年 | 6篇 |
1971年 | 4篇 |
1969年 | 4篇 |
1960年 | 4篇 |
1957年 | 5篇 |
1953年 | 4篇 |
1946年 | 4篇 |
排序方式: 共有3407条查询结果,搜索用时 15 毫秒
21.
22.
Esther Van de Vosse Paola Van der Bent Joris J. Heus Gert- Jan B. Van Ommen Johan T. Den Dunnen 《Mammalian genome》1997,8(7):497-501
The disease loci for X-linked Retinoschisis (RS), Keratosis follicularis spinulosa decalvans (KFSD), and Coffin-Lowry syndrome
(CLS) have been localized to the same, small region in Xp22 on the human X Chromosome (Chr). To generate a high-resolution
map of the available contig in this area, we have used the YAC fragmentation vectors pBP108/ADE2 and pBP109/ADE2 and generated fragmented YACs from a 2.5-Mb YAC (y939H7) spanning the mentioned disease gene candidate regions. Forty-seven
fragmented YACs were generated and analyzed, ranging in size from 170 kb to over 2400 kb. The resulting YAC fragmentation
panel was used to construct a detailed restriction map of the region and has been used to bin clones and markers. As a deletion
panel, it will present a valuable resource for further mapping.
Received: 31 December 1996 / Accepted: 22 February 1997 相似文献
23.
Esther M. Leise 《Zoomorphology》1984,104(6):337-343
Summary The larval integument and juvenile girdle integument of Mopalia muscosa (Mollusca: Polyplacophora) were studied by light microscopy. Within 24 h of settlement, eight distinctive changes occur that characterize metamorphosis: loss of the functional prototroch and apical tuft, secretion of a cuticle over the mantle field followed by the secretion of calcareous shell plates and the extrusion of spicules into the cuticle, a 20% decrease in length, secretion of chitinous hairs and the incorporation of the lateral ciliated bands into the pallial grooves. Similar changes which were often not recognized as metamorphic have been reported for other species. Evidence for metamorphosis being a common developmental feature of chitons is presented. 相似文献
24.
25.
26.
The role of transition metals in paraquat toxicity was studied in cultures of Plasmodium falciparum. We showed that addition of copper led to an enhancement of the plasmodium killing, whereas addition of chelating agents. such as desferrioxamine and diethylenetriamine pentaacetic acid markedly reduced the toxic effects. Parsitized G6PD deficient erythrocytes were more sensitive than parasitized normal eryth-rocytes to copper and to the combination of copper and paraquat. 相似文献
27.
Banasree Das Esther L. Sabban Edward J. Kilbourne Lloyd D. Fricker 《Journal of neurochemistry》1992,59(6):2263-2270
PC12 cells, a rat pheochromocytoma cell line, have been found to express carboxypeptidase E (CPE) enzymatic activity and CPE, furin, and peptidylglycine alpha-amidating monooxygenase (PAM) mRNAs. PC12 cells secrete CPE activity in response to depolarization induced by 50 mM KCl. Short-term (1- to 3-h) treatments of PC12 cells with KCl stimulates the secretion of CPE but does not appear to stimulate the synthesis of new CPE protein, based on the measurement of CPE activity and incorporation of [35S]-Met into CPE. Also, CPE mRNA is not altered by 2-h treatments with KCl. In contrast, prolonged treatment (24-48 h) of PC12 cells with 50 mM KCl continues to stimulate the secretion of CPE activity, without altering the cellular level of CPE. Levels of CPE mRNA are significantly elevated after long-term treatment of the cells with KCl, with increases of 35% after 5 h and 55-75% after 24 to 72 h of treatment. The level of PAM mRNA is also elevated approximately 70% after 24 h of stimulation with KCl. In contrast, the mRNA levels of furin and dopamine beta-hydroxylase (DBH) do not change on treatment of PC12 cells with KCl. These findings indicate that long-term depolarization, which leads to a prolonged stimulation of PC12 cells to secrete CPE, also stimulates the synthesis of CPE and PAM but not furin or DBH. 相似文献
28.
Sara Brosh Oded Sperling Esther Dantziger Yechezkel Sidi 《Journal of neurochemistry》1992,58(4):1485-1490
The metabolic fate of guanine and of guanine ribonucleotides (GuRNs) in cultured rat neurons was studied using labeled guanine. 8-Aminoguanosine (8-AGuo), an inhibitor of purine nucleoside phosphorylase, was used to clarify the pathways of GMP degradation, and mycophenolic acid, an inhibitor of IMP dehydrogenase, was used to assess the flux from IMP to GMP and, indirectly, the activity of the guanine nucleotide cycle (GMP----IMP----XMP----GMP). The main metabolic fate of guanine in the neurons was deamination to xanthine, but significant incorporation of guanine into GuRNs, at a rate of approximately 8.5-13.1% of that of the deamination, was also demonstrated. The turnover rate of GuRNs was fast (loss of 80% of the radioactivity of the prelabeled pool in 22 h), reflecting synthesis of nucleic acids (32.8% of the loss in radioactivity) and degradation to xanthine, guanine, hypoxanthine, guanosine, and inosine (49.3, 4.3, 4.1, 1.1, and 0.5% of the loss, respectively). Of the radioactivity in GuRNs, 7.9% was shifted to adenine nucleotides. The accumulation of label in xanthine indicates (in the absence of xanthine oxidase) that the main degradative pathway from GMP is that to xanthine through guanosine and guanine. The use of 8-AGuo confirmed this pathway but indicated the operation of an additional, relatively slower degradative pathway, that from GMP through IMP to inosine and hypoxanthine. Hypoxanthine was incorporated mainly into adenine nucleotide (91.5%), but a significant proportion (6%) was found in GuRNs.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
29.
Esther Senn Erwin Scharrer Siegfried Wolffram 《Biological trace element research》1992,33(1-3):103-108
The influence of glutathione (1 mmol/L) (GSH) on in vitro mucosal uptake and in vivo absorption of75Se-labeled selenite (10 μmol/L) was investigated in rat jejunum. For comparison, the effect ofl-cysteine (1 mmol/L) on in vivo absorption of75Se-labeled selenite was also studied. In the in vitro, uptake experiments, only the mucosal surface was exposed to the incubation
medium for 3 min. For the in vivo experiments, a luminal perfusion technique was employed. GSH inhibited in vitro mucosal
Se uptake, whereas absorption in vivo was stimulated by GSH.l-Cysteine also stimulated in vivo Se absorption, confirming former in vitro mucosal uptake experiments. Thus, unlikel-cysteine, GSH affected in vitro and in vivo absorption of Se from selenite differently. Enzymatic cleavage of products of
the reaction of selenite with GSH occuring more efficiently under in vivo than in vitro conditions may be a prerequisite for
the stimulatory effect of GSH on Se absorption. This apparently does not apply to the stimulatory effect of cysteine. Since,
GSH occurs in the intestinal lumen under physiological conditions, it may contribute to the high bioavailability of Se from
selenite. 相似文献
30.
Erwin Scharrer Esther Senn Siegfried Wolffram 《Biological trace element research》1992,33(1-3):109-120
The influence of several thiols (conc. 1 mmol/L) on mucosal uptake of75Se from75Se-labeled selenite (conc. 10 μmol/L) across the brush border of rat jejunum and cecum was investigated in vitro using a short-term
uptake technique.l-Cysteine (l-Cys) stimulated75Se uptake in the mid- and distal jejunum and cecum, but not in the proximal jejunum. The effect was maximal in the distal
jejunum.d-Cys was less effective in the jejunum and similarly effective in the cecum.l-Leucine (l-Leu) andl-glutamic acid significantly reduced the stimulatory effect ofl-Cys on Se uptake in the distal jejunum, whereas the respective effect ofd-Cys was not diminished byl-Leu. Cysteamine stimulated mucosal75Se uptake at all intestinal sites tested, whereas the effect of mercaptopyruvate was restricted to the distal jejunum. Thioglycolate
also enhanced75Se uptake in the distal jejunum. The stimulatory effects ofl-Cys, mercaptopyruvate, and thiologlycolate were Na+-dependent, whereas the effect of cysteamine also occurred in the absence of Na+. Mercaptosuccinate,d-penicillamine, ergothioneine, and thiosulfate did not enhance mucosa75Se uptake. It is concluded from these findings that the reaction of some thiols with selenite results in Se compounds that
are rapidly absorbed by the intestinal epithelium through various Na+-dependent and Na+-independent, mechanisms. The high bioavailability of Se from selenite found by others might thus be the result of the presence
of thiols in the gastrointestinal tract. 相似文献