全文获取类型
收费全文 | 8576篇 |
免费 | 685篇 |
国内免费 | 2篇 |
出版年
2023年 | 60篇 |
2022年 | 91篇 |
2021年 | 195篇 |
2020年 | 158篇 |
2019年 | 173篇 |
2018年 | 220篇 |
2017年 | 213篇 |
2016年 | 317篇 |
2015年 | 483篇 |
2014年 | 481篇 |
2013年 | 636篇 |
2012年 | 761篇 |
2011年 | 636篇 |
2010年 | 448篇 |
2009年 | 406篇 |
2008年 | 486篇 |
2007年 | 520篇 |
2006年 | 460篇 |
2005年 | 405篇 |
2004年 | 391篇 |
2003年 | 341篇 |
2002年 | 350篇 |
2001年 | 106篇 |
2000年 | 71篇 |
1999年 | 81篇 |
1998年 | 85篇 |
1997年 | 69篇 |
1996年 | 56篇 |
1995年 | 62篇 |
1994年 | 54篇 |
1993年 | 46篇 |
1992年 | 51篇 |
1991年 | 50篇 |
1990年 | 25篇 |
1989年 | 32篇 |
1988年 | 39篇 |
1987年 | 18篇 |
1986年 | 23篇 |
1985年 | 15篇 |
1984年 | 21篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 8篇 |
1973年 | 4篇 |
排序方式: 共有9263条查询结果,搜索用时 31 毫秒
991.
992.
Over the past two decades, research scientists have been involved in the investigation of thermophilic and hyperthermophilic microorganisms owing to the unique features of their enzymic systems. Such in-depth investigations are now on their way to mastering the cloning and industrial exploitation of a broad variety of genes encoding enzymes involved in starch hydrolysis, amino acid biosynthesis, protein hydrolysis, etc. In this work, we review the state of the art and future perspectives of industrial applications of enzymes from hyperthermophilic and extreme thermophilic microorganisms, special attention being paid to the biotechnological methods involved in their industrial exploitation. 相似文献
993.
Casas J Gijón MA Vigo AG Crespo MS Balsinde J Balboa MA 《The Journal of biological chemistry》2006,281(9):6106-6116
The calcium ionophore ionomycin induces apoptosis-like events in the human embryonic kidney cell line at early times. Plasma membrane blebbing, mitochondrial depolarization, externalization of phosphatidylserine, and nuclear permeability changes can all be observed within 15 min of treatment. However, there is no activation of caspases or chromatin condensation. Expression of a fusion protein containing the enhanced green fluorescent protein (EGFP) and human cytosolic Group IVA phospholipase A(2)alpha (EGFP-cPLA(2)alpha) in these cells prevents ionomycin-induced phosphatidylserine externalization and death. Cells expressing the cPLA(2)alpha mutant D43N, which does not bind calcium, retain their susceptibility to ionomycin-induced cell death. Both nonexpressing and EGFP-D43N-cPLA(2)alpha-expressing human embryonic kidney cells can be spared from ionomycin-induced cell death by pretreating them with exogenous arachidonic acid. Moreover, during calcium overload, mitochondrial depolarization is significantly lower in the EGFP-cPLA(2)alpha-expressing cells than in cells expressing normal amounts of cPLA(2)alpha. These results suggest that early cell death events promoted by an overload of calcium can be prevented by the presence of high levels of arachidonic acid. 相似文献
994.
Specific immunolabeling of brain macrophages and microglial cells in the developing and mature chick central nervous system. 总被引:1,自引:0,他引:1
Miguel A Cuadros Ana M Santos David Martín-Oliva Ruth Calvente Mohamed Tassi José Luis Marín-Teva Julio Navascués 《The journal of histochemistry and cytochemistry》2006,54(6):727-738
The present study showed that the HIS-C7 monoclonal antibody, which recognizes the chick form of CD45, is a specific marker for macrophages/microglial cells in the developing and mature chick central nervous system (CNS). HIS-C7-positive cells were characterized according to their morphological features and chronotopographical distribution patterns within developing and adult CNS, similar to those of macrophages/microglial cells in the quail CNS and confirmed by their histochemical labeling with Ricinus communis agglutinin I, a lectin that recognizes chick microglial cells. Therefore, the HIS-C7 antibody is a valuable tool to identify brain macrophage and microglial cells in studies of the function, development, and pathology of the chick brain. CD45 expression differed between chick microglia (as revealed with HIS-C7 antibody) and mouse microglial cells (as revealed with an antibody against mouse form of CD45). Thus, a discontinuous label was seen on mouse microglial cells with the anti-mouse CD45 immunostaining, whereas the entire surface of chick microglial cells was labeled with the anti-chick CD45 staining. The functional relevance of these differences between species has yet to be determined. 相似文献
995.
996.
Varaldi J Ravallec M Labrosse C Lopez-Ferber M Boulétreau M Fleury F 《Journal of insect physiology》2006,52(11-12):1202-1212
In parasitoids, the adaptive significance of superparasitism (laying of egg(s) in already parasitized hosts) has been the subject of strong controversy. The current view is to interpret this behaviour as an adaptation to increased competition for hosts, because the supernumerary egg still has a chance to win possession for the host. However, we recently discovered that in the solitary parasitoid Leptopilina boulardi, superparasitism is rather caused by an unknown infectious element: stable non superparasitizing lineages (NS) are transformed into stable superparasitizing lineages (S) after eggs from both lineages have competed inside the same host (superparasitism). In this report, we investigate the nature and location of the causative agent. Involvement of bacteria is unlikely because antibiotic treatments do not affect wasp phenotype and because bacterial 16S ribosomal DNA was not detected using PCR. We report successful injection experiments showing that the causative agents are located in wasp poison gland and ovaries and are stably inherited. Electron microscopic studies demonstrate that long filamentous virus particles located in wasp oviducts are strongly associated with superparasitism behaviour, leading to reconsider the adaptive significance of this behaviour in parasitoids. Interestingly, parasitoids are often infected with similar viruses for which no phenotypic effect has been documented. This raises the possibility that they could induce the same behavioural manipulation. 相似文献
997.
Brizuela L Rábano M Peña A Gangoiti P Macarulla JM Trueba M Gómez-Muñoz A 《Journal of lipid research》2006,47(6):1238-1249
Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid capable of regulating critical physiological and pathological functions. Here, we report for the first time that S1P stimulates aldosterone secretion in cells of the zona glomerulosa of the adrenal gland. Regulation of aldosterone secretion is important because this hormone controls electrolyte and fluid balance and is implicated in cardiovascular homeostasis. S1P-stimulated aldosterone secretion was dependent upon the protein kinase C (PKC) isoforms alpha and delta and extracellular Ca2+, and it was inhibited by pertussis toxin (PTX). S1P activated phospholipase D (PLD) through a PTX-sensitive mechanism, also involving PKC alpha and delta and extracellular Ca2+. Primary alcohols, which attenuate the formation of phosphatidic acid (the product of PLD), and cell-permeable ceramides, which inhibit PLD activity, blocked S1P-stimulated aldosterone secretion. Furthermore, propranolol, chlorpromazine, and sphingosine, which are potent inhibitors of phosphatidate phosphohydrolase (PAP) (the enzyme that produces diacylglycerol from phosphatidate), also blocked aldosterone secretion. These data suggest that the PLD/PAP pathway plays a crucial role in the regulation of aldosterone secretion by S1P and that Gi protein-coupled receptors, extracellular Ca2+, and the PKC isoforms alpha and delta are all important components in the cascade of events controlling this process. 相似文献
998.
Pello OM Duthey B García-Bernal D Rodríguez-Frade JM Stein JV Teixido J Martínez C Mellado M 《Journal of immunology (Baltimore, Md. : 1950)》2006,176(3):1675-1685
Inflammatory reactions involve a network of chemical and molecular signals that initiate and maintain host response. In inflamed tissue, immune system cells generate opioid peptides that contribute to potent analgesia by acting on specific peripheral sensory neurons. In this study, we show that opioids also modulate immune cell function in vitro and in vivo. By binding to its specific receptor, the opioid receptor-specific ligand DPDPE triggers monocyte adhesion. Integrins have a key role in this process, as adhesion is abrogated in cells treated with specific neutralizing anti-alpha5beta1 integrin mAb. We found that DPDPE-triggered monocyte adhesion requires PI3Kgamma activation and involves Src kinases, the guanine nucleotide exchange factor Vav-1, and the small GTPase Rac1. DPDPE also induces adhesion of pertussis toxin-treated cells, indicating involvement of G proteins other than Gi. These data show that opioids have important implications in regulating leukocyte trafficking, adding a new function to their known effects as immune response modulators. 相似文献
999.
Kan-Mitchell J Bajcz M Schaubert KL Price DA Brenchley JM Asher TE Douek DC Ng HL Yang OO Rinaldo CR Benito JM Bisikirska B Hegde R Marincola FM Boggiano C Wilson D Abrams J Blondelle SE Wilson DB 《Journal of immunology (Baltimore, Md. : 1950)》2006,176(11):6690-6701
CD8+ CTL responses are important for the control of HIV-1 infection. The immunodominant HLA-A2-restricted Gag epitope, SLYNTVATL (SL9), is considered to be a poor immunogen because reactivity to it is rare in acute infection despite its paradoxical dominance in patients with chronic infection. We have previously reported SL9 to be a help-independent epitope in that it primes highly activated CTLs ex vivo from CD8+ T cells of seronegative healthy donors. These CTLs produce sufficient cytokines for extended autocrine proliferation but are sensitive to activation-induced cell death, which may cause them to be eliminated by a proinflammatory cytokine storm. Here we identified an agonist variant of the SL9 peptide, p41 (SLYNTVAAL), by screening a large synthetic combinatorial nonapeptide library with ex vivo-primed SL9-specific T cells. p41 invariably immunized SL9-cross-reactive CTLs from other donors ex vivo and H-2Db beta2m double knockout mice expressing a chimeric HLA-A*0201/H2-Db MHC class I molecule. Parallel human T cell cultures showed p41-specific CTLs to be less fastidious than SL9-CTLs in the level of costimulation required from APCs and the need for exogenous IL-2 to proliferate (help dependent). TCR sequencing revealed that the same clonotype can develop into either help-independent or help-dependent CTLs depending on the peptide used to activate the precursor CD8+ T cells. Although Ag-experienced SL9-T cells from two patients were also sensitive to IL-2-mediated cell death upon restimulation in vitro, the loss of SL9 T cells was minimized with p41. This study suggests that agonist sequences can replace aberrantly immunogenic native epitopes for the rational design of vaccines targeting HIV-1. 相似文献
1000.
Migliaccio M Alves PM Romero P Rufer N 《Journal of immunology (Baltimore, Md. : 1950)》2006,176(4):2173-2182
Human Ag-specific CD8(+) T lymphocytes are heterogeneous and include functionally distinct populations. In this study, we report that at least two distinct mechanisms control the expansion of circulating naive, memory, and effector CD8(+) T lymphocytes when exposed to mitogen or Ag stimulation. The first one leads to apoptosis and occurs shortly after in vitro stimulation. Susceptibility to cell death is prominent among primed T cell subsets, and it is inversely correlated with the size of the ex vivo Bcl-2(high) population within these subsets. Importantly, the Bcl-2(high) phenotype is associated to the proportion of responsive CD8(+) T cells, independently of their differentiation stage. The second one depends on the expression of newly synthesized cyclin-dependent kinase inhibitor p16(INK4a) that occurs in a significant fraction of T cells that had been actively cycling, leading to their cell cycle arrest upon stimulation. Strikingly, accumulation of p16(INK4a) protein preferentially occurs in naive as opposed to primed derived T lymphocytes and is not related to apoptosis. Significant levels of p16 are readily detectable in a small number of ex vivo CD8(+) T cells. Our observations reveal that activation-induced p16 expression represents an alternative process to apoptosis, limiting the proliferation potential of activated naive derived T lymphocytes. 相似文献