全文获取类型
收费全文 | 8717篇 |
免费 | 817篇 |
专业分类
9534篇 |
出版年
2021年 | 96篇 |
2020年 | 71篇 |
2019年 | 74篇 |
2018年 | 91篇 |
2017年 | 90篇 |
2016年 | 145篇 |
2015年 | 274篇 |
2014年 | 274篇 |
2013年 | 342篇 |
2012年 | 487篇 |
2011年 | 427篇 |
2010年 | 273篇 |
2009年 | 248篇 |
2008年 | 358篇 |
2007年 | 382篇 |
2006年 | 328篇 |
2005年 | 315篇 |
2004年 | 291篇 |
2003年 | 309篇 |
2002年 | 284篇 |
2001年 | 245篇 |
2000年 | 222篇 |
1999年 | 227篇 |
1998年 | 96篇 |
1997年 | 80篇 |
1996年 | 98篇 |
1995年 | 96篇 |
1994年 | 76篇 |
1993年 | 84篇 |
1992年 | 164篇 |
1991年 | 165篇 |
1990年 | 134篇 |
1989年 | 138篇 |
1988年 | 144篇 |
1987年 | 109篇 |
1986年 | 98篇 |
1985年 | 108篇 |
1984年 | 101篇 |
1983年 | 85篇 |
1982年 | 63篇 |
1981年 | 59篇 |
1979年 | 83篇 |
1978年 | 71篇 |
1977年 | 72篇 |
1976年 | 60篇 |
1975年 | 51篇 |
1974年 | 91篇 |
1973年 | 57篇 |
1972年 | 62篇 |
1970年 | 64篇 |
排序方式: 共有9534条查询结果,搜索用时 0 毫秒
941.
942.
Sabine Vogel Marieke Wottawa Katja Farhat Anke Zieseniss Moritz Schnelle Sinja Le-Huu Melanie von Ahlen Cordula Malz Gieri Camenisch D?rthe M. Katschinski 《The Journal of biological chemistry》2010,285(44):33756-33763
Cells are responding to hypoxia via prolyl-4-hydroxylase domain (PHD) enzymes, which are responsible for oxygen-dependent hydroxylation of the hypoxia-inducible factor (HIF)-1α subunit. To gain further insight into PHD function, we generated knockdown cell models for the PHD2 isoform, which is the main isoform regulating HIF-1α hydroxylation and thus stability in normoxia. Induction of a PHD2 knockdown in tetracycline-inducible HeLa PHD2 knockdown cells resulted in increased F-actin formation as detected by phalloidin staining. A similar effect could be observed in the stably transfected PHD2 knockdown cell clones 1B6 and 3B7. F-actin is at least in part responsible for shaping cell morphology as well as regulating cell migration. Cell migration was impaired significantly as a consequence of PHD2 knockdown in a scratch assay. Mechanistically, PHD2 knockdown resulted in activation of the RhoA (Ras homolog gene family member A)/Rho-associated kinase pathway with subsequent phosphorylation of cofilin. Because cofilin phosphorylation impairs its actin-severing function, this may explain the F-actin phenotype, thereby providing a functional link between PHD2-dependent signaling and cell motility. 相似文献
943.
Hosaka K Rayner SE von der Weid PY Zhao J Imtiaz MS van Helden DF 《American journal of physiology. Heart and circulatory physiology》2006,290(2):H813-H822
The effects of calcitonin gene-related peptide (CGRP) on constriction frequency, smooth muscle membrane potential (V(m)), and endothelial V(m) of guinea pig mesenteric lymphatics were examined in vitro. CGRP (1-100 nM) caused an endothelium-dependent decrease in the constriction frequency of perfused lymphatic vessels. The endothelium-dependent CGRP response was abolished by the CGRP-1 receptor antagonist CGRP-(8-37) (1 microM) and pertussis toxin (100 ng/ml). This action of CGRP was also blocked by the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine (L-NNA; 10 microM), an action that was reversed by the addition of L-arginine (100 microM). cGMP, adenylate cyclase, cAMP-dependent protein kinase (PKA), and ATP-sensitive K+ (K+(ATP)) channels were all implicated in the endothelium-dependent CGRP response because it was abolished by methylene blue (20 microM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 microM), dideoxyadenosine (10 microM), N-[2-(p-bromociannamylamino)-ethyl]-5-isoquinolinesulfonamide-dichloride (H89; 1 microM) and glibenclamide (10 microM). CGRP (100 nM), unlike acetylcholine, did not alter endothelial intracellular Ca2+ concentration or V(m). CGRP (100 nM) hyperpolarized the smooth muscle V(m), an effect inhibited by L-NNA, H89, or glibenclamide. CGRP (500 nM) also caused a decrease in constriction frequency. However, this was no longer blocked by CGRP-(8-37). CGRP (500 nM) also caused smooth muscle hyperpolarization, an action that was now not blocked by L-NNA (100 microM). It was most likely mediated by the activation of the cAMP/PKA pathway and the opening of K+(ATP) channels because it was abolished by H89 or glibenclamide. We conclude that CGRP, at low to moderate concentrations (i.e., 1-100 nM), decreases lymphatic constriction frequency primarily by the stimulation of CGRP-1 receptors coupled to pertussis toxin-sensitive G proteins and the release of NO from the endothelium or enhancement of the actions of endogenous NO. At high concentrations (i.e., 500 nM), CGRP also directly activates the smooth muscle independent of NO. Both mechanisms of activation ultimately cause the PKA-mediated opening of K+(ATP) channels and resultant hyperpolarization. 相似文献
944.
The basal pole of a cone photoreceptor is in close contact with hundreds of bipolar cell dendrites. The function and properties of these unconventional junctions are a long-standing mystery. In this issue of Neuron, DeVries and colleagues provide compelling evidence that glutamate release from a single quanta can diffuse to distant AMPA/KA receptors on these basal junctions to generate slow mEPSCs. 相似文献
945.
Zhu Y Marchal CC Casbon AJ Stull N von Löhneysen K Knaus UG Jesaitis AJ McCormick S Nauseef WM Dinauer MC 《The Journal of biological chemistry》2006,281(41):30336-30346
The heterodimeric flavocytochrome b558, comprised of the two integral membrane proteins p22phox and gp91phox, mediates the transfer of electrons from NADPH to molecular oxygen in the phagocyte NADPH oxidase to generate the superoxide precursor of microbicidal oxidants. This study uses deletion mutagenesis to identify regions of p22phox required for maturation of gp91phox and for NADPH oxidase activity. N-terminal, C-terminal, or internal deletions of human p22phox were generated and expressed in Chinese hamster ovary cells with transgenes for gp91phox and two other NADPH oxidase subunits, p47phox, and p67phox. The results demonstrate that p22phox-dependent maturation of gp91phox carbohydrate, cell surface expression of gp91phox, and the enzymatic function of flavocytochrome b558 are closely correlated. Whereas the 5 N-terminal and 25 C-terminal amino acids are dispensable for these functions, the N-terminal 11 amino acids of p22phox are required, as is a hydrophilic region between amino acids 65 and 90. Upon deletion of 54 residues at the C terminus of p22phox (amino acids 142-195), maturation and cell surface expression of gp91phox was still preserved, although NADPH oxidase activity was absent, as expected, due to removal of a proline-rich domain between amino acids 151-160 that is required for recruitment of p47phox. Antibody binding studies indicate that the extreme N terminus of p22phox is inaccessible in the absence of cell permeabilization, supporting a model in which both the N- and C-terminal domains of p22phox extend into the cytoplasm, anchored by two membrane-embedded regions. 相似文献
946.
The forward and reverse rate constants involved in carbamylation, activation, carboxylation, and inhibition of D-ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) have been estimated by a new technique of simultaneous non-linear regression of a differential equation kinetic model to multiple experimental data. Parameters predicted by the model fitted to data from purified spinach enzyme in vitro included binding affinity constants for non-substrate CO2 and Mg2+ of 200+/-80 microM and 700+/-200 microM, respectively, as well as a turnover number (k(cat)) of 3.3+/-0.5 s(-1), a Michaelis half-saturation constant for carboxylation (K(M,C)) of 10+/-4 microM and a Michaelis constant for RuBP binding (K(M,RuBP)) of 1.5+/-0.5 microM. These and other constants agree well with previously measured values where they exist. The model is then used to show that slow inactivation of RuBisCO (fallover) in oxygen-free conditions at low concentrations of CO2 and Mg2+ is due to decarbamylation and binding of RuBP to uncarbamylated enzyme. In spite of RuBP binding more tightly to uncarbamylated enzyme than to the activated form, RuBisCO is activated at high concentrations of CO2 and Mg2+. This apparent paradox is resolved by considering activation kinetics and the fact that while RuBP binds tightly but slowly to uncarbamylated enzyme, it binds fast and loosely to activated enzyme. This modelling technique is presented as a new method for determining multiple kinetic data simultaneously from a limited experimental data set. The method can be used to compare the properties of RuBisCO from different species quickly and easily. 相似文献
947.
Decidual NK cells alter in vitro first trimester extravillous cytotrophoblast migration: a role for IFN-gamma 总被引:3,自引:0,他引:3
Hu Y Dutz JP MacCalman CD Yong P Tan R von Dadelszen P 《Journal of immunology (Baltimore, Md. : 1950)》2006,177(12):8522-8530
Abnormal placentation results in either inadequate (consequences: recurrent miscarriage, intrauterine growth restriction, and preeclampsia) or overzealous (consequences: placenta accreta, increta, and percreta) placentation. NK cells dominate in first trimester decidua and probably control extravillous cytotrophoblast (EVT) invasion. We examined this interaction in a novel way, using NK cells and villous explants from concordant first trimester pregnancies cocultured using a new collagen (two-dimensional) model of placentation. Decidual NK (dNK) cells exerted contact-independent inhibition of normal cytotrophoblast migration, associated with changes in the cytotrophoblast expression of metalloproteases-2 and -9, and plasminogen activator inhibitor-1. dNK cells did not affect EVT proliferation and apoptosis, and cell column formation. dNK cell effects were partially reversed by neutralizing Abs against IFN-gamma. We provide ex vivo human evidence of a direct role for dNK in modulating EVT differentiation as they form columns and then migrate from anchoring villi. 相似文献
948.
Molecular chaperones are important components of mitochondrial protein biogenesis and are required to maintain the organellar function under normal and stress conditions. We addressed the functional role of the Hsp100/ClpB homolog Hsp78 during aggregation reactions and its functional cooperation with the main mitochondrial Hsp70, Ssc1, in mitochondria of the yeast Saccharomyces cerevisiae. By establishing an aggregation/disaggregation assay in intact mitochondria we demonstrated that Hsp78 is indispensable for the resolubilization of protein aggregates generated by heat stress under in vivo conditions. The ATP-dependent disaggregation activity of Hsp78 was capable of reversing the preprotein import defect of a destabilized mutant form of Ssc1. This role in disaggregation of Ssc1 is unique for Hsp78, since the recently identified, Hsp70-specific chaperone Zim17 had no effect on the resolubilization reaction. We observed only a minor effect of the second mitochondrial Hsp100 family member Mcx1 on protein disaggregation. A "holding" activity of the mitochondrial Hsp70 system was a prerequisite for a successful resolubilization of aggregated proteins. We conclude that the protective role of Hsp78 in thermotolerance is mainly based on maintaining the molecular chaperone Ssc1 in a soluble and functional state. 相似文献
949.
Koduru S Vegiraju SR Nadimpalli SK von Figura K Pohlmann R Dennes A 《Development genes and evolution》2006,216(3):133-143
Mannose-6-phosphate receptors (MPRs) have been identified in a wide range of species from humans to invertebrates such as
molluscs. A characteristic of all MPRs is their common property to recognize mannose-6-phosphate residues that are labelling
lysosomal enzymes and to mediate their targeting to lysosomes in mammalian cells by the corresponding receptor proteins. We
present here the analysis of full-length sequences for MPR 46 from zebrafish (Danio rerio) and its functional analysis. This is the first non-mammalian MPR 46 to be characterised. The amino acid sequences of the
zebrafish MPR 46 displays 70% similarity to the human MPR 46 protein. In particular, all essential cysteine residues, the
transmembrane domain as well as the cytoplasmic tail residues harbouring the signals for endocytosis and Golgi-localizing,
γ-ear-containing, ARF-binding protein (GGA)-mediated sorting at the trans-Golgi network, are highly conserved. The zebrafish
MPR 46 has the arginine residue known to be essential for mannose-6-phosphate binding and other additional characteristic
residues of the mannose-6-phosphate ligand-binding pocket. Like the mammalian MPR 46, zebrafish MPR 46 binds to the multimeric
mannose-6-phosphate ligand phosphomannan and can rescue the missorting of lysosomal enzymes in mammalian MPR-deficient cells.
The conserved C-terminal acidic dileucine motif (DxxLL) in the cytoplasmic domain of zebrafish MPR 46 essential for the interaction
of the GGAs with the receptor domains interacts with the human GGA1-VHS domain. Interestingly, the serine residue suggested
to regulate the interaction between the tail and the GGAs in a phosphorylation-dependent manner is substituted by a proline
residue in fish.
Electronic Supplementary Material Supplementary material is available for this article at .
The zebrafish MPR 46 sequence data have been submitted to the GenBank database under accession no. DQ089037. 相似文献
950.
von Scheven G Alvares LE Mootoosamy RC Dietrich S 《Development (Cambridge, England)》2006,133(14):2731-2745
Recent knockout experiments in the mouse generated amazing craniofacial skeletal muscle phenotypes. Yet none of the genes could be placed into a molecular network, because the programme to control the development of muscles in the head is not known. Here we show that antagonistic signals from the neural tube and the branchial arches specify extraocular versus branchiomeric muscles. Moreover, we identified Fgf8 as the branchial arch derived signal. However, this molecule has an additional function in supporting the proliferative state of myoblasts, suppressing their differentiation, while a further branchial arch derived signal, namely Bmp7, is an overall negative regulator of head myogenesis. 相似文献