全文获取类型
收费全文 | 10895篇 |
免费 | 855篇 |
国内免费 | 5篇 |
专业分类
11755篇 |
出版年
2023年 | 51篇 |
2022年 | 109篇 |
2021年 | 177篇 |
2020年 | 131篇 |
2019年 | 141篇 |
2018年 | 173篇 |
2017年 | 203篇 |
2016年 | 272篇 |
2015年 | 514篇 |
2014年 | 636篇 |
2013年 | 728篇 |
2012年 | 961篇 |
2011年 | 851篇 |
2010年 | 542篇 |
2009年 | 470篇 |
2008年 | 629篇 |
2007年 | 667篇 |
2006年 | 632篇 |
2005年 | 552篇 |
2004年 | 513篇 |
2003年 | 503篇 |
2002年 | 494篇 |
2001年 | 103篇 |
2000年 | 88篇 |
1999年 | 110篇 |
1998年 | 125篇 |
1997年 | 85篇 |
1996年 | 92篇 |
1995年 | 93篇 |
1994年 | 76篇 |
1993年 | 84篇 |
1992年 | 88篇 |
1991年 | 58篇 |
1990年 | 66篇 |
1989年 | 54篇 |
1988年 | 42篇 |
1987年 | 48篇 |
1986年 | 39篇 |
1985年 | 44篇 |
1984年 | 59篇 |
1983年 | 50篇 |
1982年 | 48篇 |
1981年 | 43篇 |
1979年 | 24篇 |
1978年 | 29篇 |
1977年 | 32篇 |
1976年 | 26篇 |
1975年 | 23篇 |
1974年 | 34篇 |
1972年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Hypomorphic mutations in the gene encoding a key Fanconi anemia protein, FANCD2, sustain a significant group of FA-D2 patients with severe phenotype 下载免费PDF全文
Kalb R Neveling K Hoehn H Schneider H Linka Y Batish SD Hunt C Berwick M Callen E Surralles J Casado JA Bueren J Dasi A Soulier J Gluckman E Zwaan CM van Spaendonk R Pals G de Winter JP Joenje H Grompe M Auerbach AD Hanenberg H Schindler D 《American journal of human genetics》2007,80(5):895-910
FANCD2 is an evolutionarily conserved Fanconi anemia (FA) gene that plays a key role in DNA double-strand-type damage responses. Using complementation assays and immunoblotting, a consortium of American and European groups assigned 29 patients with FA from 23 families and 4 additional unrelated patients to complementation group FA-D2. This amounts to 3%-6% of FA-affected patients registered in various data sets. Malformations are frequent in FA-D2 patients, and hematological manifestations appear earlier and progress more rapidly when compared with all other patients combined (FA-non-D2) in the International Fanconi Anemia Registry. FANCD2 is flanked by two pseudogenes. Mutation analysis revealed the expected total of 66 mutated alleles, 34 of which result in aberrant splicing patterns. Many mutations are recurrent and have ethnic associations and shared allelic haplotypes. There were no biallelic null mutations; residual FANCD2 protein of both isotypes was observed in all available patient cell lines. These analyses suggest that, unlike the knockout mouse model, total absence of FANCD2 does not exist in FA-D2 patients, because of constraints on viable combinations of FANCD2 mutations. Although hypomorphic mutations arie involved, clinically, these patients have a relatively severe form of FA. 相似文献
52.
Facilitation in plant communities: the past, the present, and the future 总被引:24,自引:11,他引:24
Rob W. Brooker Fernando T. Maestre Ragan M. Callaway Christopher L. Lortie Lohengrin A. Cavieres Georges Kunstler Pierre Liancourt Katja Tielbörger Justin M. J. Travis Fabien Anthelme Cristina Armas Lluis Coll Emmanuel Corcket Sylvain Delzon Estelle Forey Zaal Kikvidze Johan Olofsson Francisco Pugnaire Constanza L. Quiroz Patrick Saccone Katja Schiffers Merav Seifan Blaize Touzard Richard Michalet 《Journal of Ecology》2008,96(1):18-34
53.
Demmel L Melak M Kotisch H Fendos J Reipert S Warren G 《Traffic (Copenhagen, Denmark)》2011,12(11):1575-1591
The Sec24 subunit of the coat protein complex II (COPII) has been implicated in selecting newly synthesized cargo from the endoplasmic reticulum (ER) for delivery to the Golgi. The protozoan parasite, Trypanosoma brucei, contains two paralogs, TbSec24.1 and TbSec24.2, which were depleted using RNA interference in the insect form of the parasite. Depletion of either TbSec24.1 or TbSec24.2 resulted in growth arrest and modest inhibition of anterograde transport of the putative Golgi enzyme, TbGntB, and the secretory marker, BiPNAVRG-HA9. In contrast, depletion of TbSec24.1, but not TbSec24.2, led to reversible mislocalization of the Golgi stack proteins, TbGRASP and TbGolgin63. The latter accumulated in the ER. The localization of the COPI coatomer subunit, TbεCOP, and the trans Golgi network (TGN) protein, TbGRIP70, was largely unaffected, although the latter was preferentially lost from those Golgi that were not associated with the bilobe, a structure previously implicated in Golgi biogenesis. Together, these data suggest that TbSec24 paralogs can differentiate among proteins destined for the Golgi. 相似文献
54.
Lin Xiao Can Chen Zhendong Li Sumin Zhu Johan Ck Tay Xi Zhang Shijun Zha Jieming Zeng Wee Kiat Tan Xin Liu Wee Joo Chng Shu Wang 《Cytotherapy》2018,20(3):420-435
Vγ9Vδ2 T cells are a minor subset of lymphocytes in the peripheral blood that has been extensively investigated for their tolerability, safety and anticancer efficacy. A hindrance to the broad application of these cells for adoptive cellular immunotherapy has been attaining clinically appropriate numbers of Vγ9Vδ2 T cells. Furthermore, Vγ9Vδ2 T cells exist at low frequencies among cancer patients. We, therefore, sought to conceive an economical method that allows for a quick and robust large-scale expansion of Vγ9Vδ2 T cells. A two-step protocol was developed, in which peripheral blood mononuclear cells (PBMCs) from healthy donors or cancer patients were activated with Zometa and interleukin (IL)-2, followed by co-culturing with gamma-irradiated, CD64-, CD86- and CD137L-expressing K562 artificial antigen-presenting cells (aAPCs) in the presence of the anti-CD3 antibody OKT3. We optimized the co-culture ratio of K562 aAPCs to immune cells, and migrated this method to a G-Rex cell growth platform to derive clinically relevant cell numbers in a Good Manufacturing Practice (GMP)-compliant manner. We further include a depletion step to selectively remove αβ T lymphocytes. The method exhibited high expansion folds and a specific enrichment of Vγ9Vδ2 T cells. Expanded Vγ9Vδ2 T cells displayed an effector memory phenotype with a concomitant down-regulated expression of inhibitory immune checkpoint receptors. Finally, we ascertained the cytotoxic activity of these expanded cells by using nonmodified and chimeric antigen receptor (CAR)–engrafted Vγ9Vδ2 T cells against a panel of solid tumor cells. Overall, we report an efficient approach to generate highly functional Vγ9Vδ2 T cells in massive numbers suitable for clinical application in an allogeneic setting. 相似文献
55.
Rebholz H Panasyuk G Fenton T Nemazanyy I Valovka T Flajolet M Ronnstrand L Stephens L West A Gout IT 《The FEBS journal》2006,273(9):2023-2036
Ribosomal protein S6 kinase (S6K) is activated by an array of mitogenic stimuli and is a key player in the regulation of cell growth. The activation process of S6 kinase involves a complex and sequential series of multiple Ser/Thr phosphorylations and is mainly mediated via phosphatidylinositol 3-kinase (PI3K)-3-phosphoinositide-dependent protein kinase-1 (PDK1) and mTor-dependent pathways. Upstream regulators of S6K, such as PDK1 and protein kinase B (PKB/Akt), are recruited to the membrane via their pleckstrin homology (PH) or protein-protein interaction domains. However, the mechanism of integration of S6K into a multi-enzyme complex around activated receptor tyrosine kinases is not clear. In the present study, we describe a specific interaction between S6K with receptor tyrosine kinases, such as platelet-derived growth factor receptor (PDGFR). The interaction with PDGFR is mediated via the kinase or the kinase extension domain of S6K. Complex formation is inducible by growth factors and leads to S6K tyrosine phosphorylation. Using PDGFR mutants, we have shown that the phosphorylation is exerted via a PDGFR-src pathway. Furthermore, src kinase phosphorylates and coimmunoprecipitates with S6K in vivo. Inhibitors towards tyrosine kinases, such as genistein and PP1, or src-specific SU6656, but not PI3K and mTor inhibitors, lead to a reduction in tyrosine phosphorylation of S6K. In addition, we mapped the sites of tyrosine phosphorylation in S6K1 and S6K2 to Y39 and Y45, respectively. Mutational and immunofluorescent analysis indicated that phosphorylation of S6Ks at these sites does not affect their activity or subcellular localization. Our data indicate that S6 kinase is recruited into a complex with RTKs and src and becomes phosphorylated on tyrosine/s in response to PDGF or serum. 相似文献
56.
Amino acids are widely used waterborne olfactory stimuli proposed to serve as cues in the search for food. In natural waters the main source of amino acids is the decomposition of proteins. But this process also produces a variety of small peptides as intermediate cleavage products. In the present study we tested whether amino acids actually are the natural and adequate stimuli for the olfactory receptors they bind to. Alternatively, these olfactory receptors could be peptide receptors which also bind amino acids though at lower affinity. Employing calcium imaging in acute slices of the main olfactory epithelium of the fully aquatic larvae of Xenopus laevis we show that amino acids, and not peptides, are more effective waterborne odorants. 相似文献
57.
Procópio L Alvarez VM Jurelevicius DA Hansen L Sørensen SJ Cardoso JS Pádula M Leitão AC Seldin L van Elsas JD 《Antonie van Leeuwenhoek》2012,101(2):289-302
The draft genome of Dietzia cinnamea strain P4 was determined using pyrosequencing. In total, 428 supercontigs were obtained and analyzed. We here describe and
interpret the main features of the draft genome. The genome contained a total of 3,555,295 bp, arranged in a single replicon
with an average G+C percentage of 70.9%. It revealed the presence of complete pathways for basically all central metabolic
routes. Also present were complete sets of genes for the glyoxalate and reductive carboxylate cycles. Autotrophic growth was
suggested to occur by the presence of genes for aerobic CO oxidation, formate/formaldehyde oxidation, the reverse tricarboxylic
acid cycle and the 3-hydropropionate cycle for CO2 fixation. Secondary metabolism was evidenced by the presence of genes for the biosynthesis of terpene compounds, frenolicin,
nanaomycin and avilamycin A antibiotics. Furthermore, a probable role in azinomycin B synthesis, an important product with
antitumor activity, was indicated. The complete alk operon for the degradation of n-alkanes was found to be present, as were clusters of genes for biphenyl ring dihydroxylation. This study brings new insights
in the genetics and physiology of D. cinnamea P4, which is useful in biotechnology and bioremediation. 相似文献
58.
Fractions of three trypsin-like proteinases, TL I, TL II, and TL III, a chymotrypsin-like proteinase, CL, two carboxypeptidase A enzymes, CPA I and CPA II and two carboxypeptidase B enzymes, CPB I and CPB II, from Antarctic krill (Euphausia superba) have been characterized with respect to purity by the means of capillary electrophoresis, CE, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The masses of the trypsin-like and chymotrypsin-like proteinases were determined to be 25,020, 25,070, 25,060, and 26,260Da for TL I, TL II, TL III, and CL, respectively. The masses of the CPA enzymes are likely 23,170 and 23,260Da, whereas the CPB enzyme masses likely are 33,730 and 33,900Da. The degradation efficiency and cleavage pattern of the trypsin-like proteinases were studied with native myoglobin as a model substrate using CE, MALDI-TOF-MS, and nanoelectrospray mass spectrometry (nESI-MS). The degradation efficiency of the trypsin-like proteinases was found to be approximately 12 and 60 times higher compared to bovine trypsin at 37 degrees C and 1-3 degrees C, respectively. All three fractions of trypsin-like proteinases showed a carboxypeptidase activity in combination with their trypsin activity. 相似文献
59.
60.
Johan Larsbrink Atsushi Izumi Glyn R. Hemsworth Gideon J. Davies Harry Brumer 《The Journal of biological chemistry》2012,287(52):43288-43299
The metabolism of the storage polysaccharides glycogen and starch is of vital importance to organisms from all domains of life. In bacteria, utilization of these α-glucans requires the concerted action of a variety of enzymes, including glycoside hydrolases, glycoside phosphorylases, and transglycosylases. In particular, transglycosylases from glycoside hydrolase family 13 (GH13) and GH77 play well established roles in α-glucan side chain (de)branching, regulation of oligo- and polysaccharide chain length, and formation of cyclic dextrans. Here, we present the biochemical and tertiary structural characterization of a new type of bacterial 1,4-α-glucan 4-α-glucosyltransferase from GH31. Distinct from 1,4-α-glucan 6-α-glucosyltransferases (EC 2.4.1.24) and 4-α-glucanotransferases (EC 2.4.1.25), this enzyme strictly transferred one glucosyl residue from α(1→4)-glucans in disproportionation reactions. Substrate hydrolysis was undetectable for a series of malto-oligosaccharides except maltose for which transglycosylation nonetheless dominated across a range of substrate concentrations. Crystallographic analysis of the enzyme in free, acarbose-complexed, and trapped 5-fluoro-β-glucosyl-enzyme intermediate forms revealed extended substrate interactions across one negative and up to three positive subsites, thus providing structural rationalization for the unique, single monosaccharide transferase activity of the enzyme. 相似文献