全文获取类型
收费全文 | 14181篇 |
免费 | 1109篇 |
出版年
2022年 | 100篇 |
2021年 | 176篇 |
2020年 | 122篇 |
2019年 | 156篇 |
2018年 | 222篇 |
2017年 | 166篇 |
2016年 | 337篇 |
2015年 | 557篇 |
2014年 | 553篇 |
2013年 | 816篇 |
2012年 | 991篇 |
2011年 | 947篇 |
2010年 | 664篇 |
2009年 | 521篇 |
2008年 | 782篇 |
2007年 | 854篇 |
2006年 | 850篇 |
2005年 | 820篇 |
2004年 | 798篇 |
2003年 | 732篇 |
2002年 | 744篇 |
2001年 | 163篇 |
2000年 | 113篇 |
1999年 | 163篇 |
1998年 | 217篇 |
1997年 | 151篇 |
1996年 | 131篇 |
1995年 | 140篇 |
1994年 | 122篇 |
1993年 | 118篇 |
1992年 | 139篇 |
1991年 | 96篇 |
1990年 | 79篇 |
1989年 | 99篇 |
1988年 | 90篇 |
1987年 | 79篇 |
1986年 | 83篇 |
1985年 | 96篇 |
1984年 | 128篇 |
1983年 | 102篇 |
1982年 | 113篇 |
1981年 | 109篇 |
1980年 | 98篇 |
1979年 | 65篇 |
1978年 | 68篇 |
1977年 | 62篇 |
1976年 | 58篇 |
1975年 | 50篇 |
1974年 | 57篇 |
1972年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
A biological ricefield in northern Italy, without periodic dry spells in its growing cycle and therefore more familiar to naturally humid zones, was studied for its heleoplankton community. The biocoenosis reached a greater level of complexity than reported in literature. In particular, the seasonal succession of Cladocerans, the dominant group throughout the study period, was analyzed. Wlassicsia pannonica (Daday, 1904; Anomopoda Macrothricidae), is new to Italy; its morphology is compared to that of other populations of the same species and its biological cycle is compared with that of other dominant Cladocerans. 相似文献
922.
G Protein β Subunit–null Mutants Are Impaired in Phagocytosis and Chemotaxis Due to Inappropriate Regulation of the Actin Cytoskeleton
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Barbara Peracino Jane Borleis Tian Jin Monika Westphal Jean-Marc Schwartz Lijun Wu Enrico Bracco Günther Gerisch Peter Devreotes Salvatore Bozzaro 《The Journal of cell biology》1998,141(7):1529-1537
Chemotaxis and phagocytosis are basically similar in cells of the immune system and in Dictyostelium amebae. Deletion of the unique G protein β subunit in D. discoideum impaired phagocytosis but had little effect on fluid-phase endocytosis, cytokinesis, or random motility. Constitutive expression of wild-type β subunit restored phagocytosis and normal development. Chemoattractants released by cells or bacteria trigger typical transient actin polymerization responses in wild-type cells. In β subunit–null cells, and in a series of β subunit point mutants, these responses were impaired to a degree that correlated with the defect in phagocytosis. Image analysis of green fluorescent protein–actin transfected cells showed that β subunit– null cells were defective in reshaping the actin network into a phagocytic cup, and eventually a phagosome, in response to particle attachment. Our results indicate that signaling through heterotrimeric G proteins is required for regulating the actin cytoskeleton during phagocytic uptake, as previously shown for chemotaxis. Inhibitors of phospholipase C and intracellular Ca2+ mobilization inhibited phagocytosis, suggesting the possible involvement of these effectors in the process. 相似文献
923.
Dieter Sültemeyer Barbara Klughammer Murray R. Badger G. Dean Price 《Plant physiology》1998,116(1):183-192
The induction of a high-affinity state of the CO2-concentration mechanism was investigated in two cyanobacterial species, Synechococcus sp. strain PCC7002 and Synechococcus sp. strain PCC7942. Cells grown at high CO2 concentrations were resuspended in low-CO2 buffer and illuminated in the presence of carbonic anhydrase for 4 to 10 min until the inorganic C compensation point was reached. Thereafter, more than 95% of a high-affinity CO2-concentration mechanism was induced in both species. Mass-spectrometric analysis of CO2 and HCO3− fluxes indicated that only the affinity of HCO3− transport increased during the fast-induction period, whereas maximum transport activities were not affected. The kinetic characteristics of CO2 uptake remained unchanged. Fast induction of high-affinity HCO3− transport was not inhibited by chloramphenicol, cantharidin, or okadaic acid. In contrast, fast induction of high-affinity HCO3− transport did not occur in the presence of K252a, staurosporine, or genistein, which are known inhibitors of protein kinases. These results show that induction of high-affinity HCO3− transport can occur within minutes of exposure to low-inorganic-C conditions and that fast induction may involve posttranslational phosphorylation of existing proteins rather than de novo synthesis of new protein components. 相似文献
924.
Dominique Delforge Barbara Gillon Muriel Art Janique Dewelle Martine Raes José Remacle 《Letters in Peptide Science》1998,5(2-3):87-91
A synthetic adhesion protein was designed by chemical grafting of the RGD tailed cyclic peptide cyclo[-d-Val-Arg-Gly-Asp-Glu(-Ahx-Tyr-Cys-NH2)-] on the carrier protein bovine serum albumin (BSA). The cyclic conformation of the RGD motif grafted on the protein mimics the conformation of the motif displayed in native adhesion proteins such as fibronectin. The adhesion of the cells on polystyrene coated with the conjugate BSA–peptide was similar or even better than the one obtained when the proadhesive protein fibronectin was coated on the plates. Results also indicated that covalent coupling of the peptide on BSA is not absolutely required, since simple adsorption of the peptide on the protein coated on plates was efficient for enhancing cell adhesion. These results show that polystyrene support can be reconditioned with conformationally constrained RGD peptides to enhance cell adhesion on solid supports. The same methodology can be adapted for the development of new biomaterials based on the recognition of specific peptides. 相似文献
925.
926.
Barbara S Bregman 《Current opinion in neurobiology》1998,8(6):800-807
Important advances have been made in our understanding of conditions that influence the intrinsic capacity of mature CNS neurons to initiate and maintain a regrowth response. The combination of exogenous neurotrophic support with strategies to alter the terrain at the injury site itself suggests that there are important interactions between them that lead to increased axonal regeneration. The ability of chronically injured neurons to initiate a regeneration response is unexpected. Our view of the role that inhibitors play in restricting axonal growth has also expanded. The findings indicate that the windows of opportunity for enhancing growth after spinal cord injury may be more numerous than previously thought. 相似文献
927.
Christopher S. Cobbett Mike J. May Ross Howden Barbara Rolls 《The Plant journal : for cell and molecular biology》1998,16(1):73-78
This paper reports that the glutathione (GSH)-deficient mutant, cad2–1 , of Arabidopsis is deficient in the first enzyme in the pathway of GSH biosynthesis, γ-glutamylcysteine synthetase (GCS). The mutant accumulates a substrate of GCS, cysteine, and is deficient in the product, γ-glutamylcysteine. In vitro enzyme assays showed that the cad2–1 mutant has 40% of wild-type levels of GCS activity but is unchanged in the activity of the second enzyme in the pathway, GSH synthetase. The CAD2 locus maps to chromosome 4 and is tightly linked to a gene, GSHA , identified by a previously isolated cDNA. A genomic clone of GSHA complements both the phenotypic and biochemical deficiencies of the cad2–1 mutant. The nucleotide sequence of the gene has been determined and, in the mutant, this gene contains a 6 bp deletion within an exon. These data demonstrate that the CAD2 gene encodes GCS. The cad2–1 mutation is close to the conserved cysteine which is believed to bind the substrate glutamate and the specific inhibitor L-buthionine-[S,R] sulfoximine (BSO). Both root growth and GCS activity of the cad2–1 mutant was less sensitive than the wild-type to inhibition by BSO, indicating that the mutation may alter the affinity of the inhibitor binding site. 相似文献
928.
Regulation of Adherence and Virulence by the Entamoeba histolytica Lectin Cytoplasmic Domain, Which Contains a β2 Integrin Motif
下载免费PDF全文
![点击此处可从《Molecular biology of the cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Richard R. Vines Girija Ramakrishnan Joshua B. Rogers Lauren A. Lockhart Barbara J. Mann William A. Petri Jr. 《Molecular biology of the cell》1998,9(8):2069-2079
Killing of human cells by the parasite Entamoeba histolytica requires adherence via an amebic cell surface lectin. Lectin activity in the parasite is regulated by inside-out signaling. The lectin cytoplasmic domain has sequence identity with a region of the β2 integrin cytoplasmic tail implicated in regulation of integrin-mediated adhesion. Intracellular expression of a fusion protein containing the cytoplasmic domain of the lectin has a dominant negative effect on extracellular lectin-mediated cell adherence. Mutation of the integrin-like sequence abrogates the dominant negative effect. Amebae expressing the dominant negative mutant are less virulent in an animal model of amebiasis. These results suggest that inside-out signaling via the lectin cytoplasmic domain may control the extracellular adhesive activity of the amebic lectin and provide in vivo demonstration of the lectin’s role in virulence. 相似文献
929.
930.
John M. Andersland David C. Dixon Robert W. Seagull Barbara A. Triplett 《In vitro cellular & developmental biology. Plant》1998,34(3):173-180
Summary Over the last 25 yr, success in characterizing the individual protein components of animal cytoskeletons was possible, in
part, due to technical advances in the isolation and purification of anucleate cytoskeletons from animal cells. As a step
towards characterizing protein components of the plant cytoskeleton, we have isolated cytoskeletons from cytoplasts (anucleate
protoplasts) prepared from cotton fiber cells grown in ovule culture. Cytoplasts isolated into a hypertonic, Ca2+-free medium at pH 6.8 retained internal structures after extraction with the detergent, Triton X-100. These structures were
shown to include microtubule and microfilament arrays by immunofluorescence and electron microscopy. Actin and tubulin were
the only abundant proteins in these preparations, suggesting that microfilaments and microtubules were the major cytoskeleta
elements in the isolated cytoskeletons. The absence of additional, relatively abundant proteins suggests that (a) other cytoskeletal
arrays potentially present in fiber cells (e.g., intermediate filaments) were either lost during detergent extraction or were
minor components of the fiber cell cytoskeleton; and (b) high ratios of individual cytoskeletal-associated proteins relative
to actin and tubulin were not required to maintain microtubules and microfilaments in organized structures. 相似文献