全文获取类型
收费全文 | 1046篇 |
免费 | 121篇 |
专业分类
1167篇 |
出版年
2022年 | 12篇 |
2021年 | 23篇 |
2020年 | 13篇 |
2019年 | 23篇 |
2018年 | 28篇 |
2017年 | 18篇 |
2016年 | 30篇 |
2015年 | 53篇 |
2014年 | 40篇 |
2013年 | 54篇 |
2012年 | 61篇 |
2011年 | 56篇 |
2010年 | 49篇 |
2009年 | 38篇 |
2008年 | 54篇 |
2007年 | 53篇 |
2006年 | 54篇 |
2005年 | 46篇 |
2004年 | 49篇 |
2003年 | 32篇 |
2002年 | 30篇 |
2001年 | 25篇 |
2000年 | 10篇 |
1999年 | 19篇 |
1998年 | 15篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 22篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 16篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1972年 | 4篇 |
1970年 | 5篇 |
排序方式: 共有1167条查询结果,搜索用时 0 毫秒
71.
Conserved loop I of U5 small nuclear RNA is dispensable for both catalytic steps of pre-mRNA splicing in HeLa nuclear extracts 下载免费PDF全文
Ségault V Will CL Polycarpou-Schwarz M Mattaj IW Branlant C Lührmann R 《Molecular and cellular biology》1999,19(4):2782-2790
The function of conserved regions of the metazoan U5 snRNA was investigated by reconstituting U5 small nuclear ribonucleoprotein particles (snRNPs) from purified snRNP proteins and HeLa or Xenopus U5 snRNA mutants and testing their ability to restore splicing to U5-depleted nuclear extracts. Substitution of conserved nucleotides comprising internal loop 2 or deletion of internal loop 1 had no significant effect on the ability of reconstituted U5 snRNPs to complement splicing. However, deletion of internal loop 2 abolished U5 activity in splicing and spliceosome formation. Surprisingly, substitution of the invariant loop 1 nucleotides with a GAGA tetraloop had no effect on U5 activity. Furthermore, U5 snRNPs reconstituted from an RNA formed by annealing the 5' and 3' halves of the U5 snRNA, which lacked all loop 1 nucleotides, complemented both steps of splicing. Thus, in contrast to yeast, loop 1 of the human U5 snRNA is dispensable for both steps of splicing in HeLa nuclear extracts. This suggests that its function can be compensated for in vitro by other spliceosomal components: for example, by proteins associated with the U5 snRNP. Consistent with this idea, immunoprecipitation studies indicated that several functionally important U5 proteins associate stably with U5 snRNPs containing a GAGA loop 1 substitution. 相似文献
72.
73.
Nazaré M Matter H Klingler O Al-Obeidi F Schreuder H Zoller G Czech J Lorenz M Dudda A Peyman A Nestler HP Urmann M Bauer A Laux V Wehner V Will DW 《Bioorganic & medicinal chemistry letters》2004,14(11):2801-2805
A series of novel, highly potent, achiral factor Xa inhibitors based on a benzoic acid scaffold and containing a chlorophenethyl moiety directed towards the protease S1 pocket is described. A number of structural features, such as the requirements of the P1, P4 and ester-binding pocket ligands were explored with respect to inhibition of factor Xa. Compound 46 was found to be the most potent compound in a series of antithrombotic secondary assays. 相似文献
74.
Nazaré M Essrich M Will DW Matter H Ritter K Urmann M Bauer A Schreuder H Dudda A Czech J Lorenz M Laux V Wehner V 《Bioorganic & medicinal chemistry letters》2004,14(16):4191-4195
A series of novel, highly potent 2-carboxyindole-based factor Xa inhibitors is described. Structural requirements for neutral ligands, which bind in the S1 pocket of factor Xa were investigated with the 2-carboxyindole scaffold. This privileged fragment assembly approach yielded a set of equipotent, selective inhibitors with structurally diverse neutral P1 substituents. 相似文献
75.
In the present investigation, -galactosidase was solubilized into Aerosol OT (AOT)/isooctane reverse micelles. Kinetic data for the hydrolysis of o-nitrophenyl--D-galactopyranoside (ONPG) at different pH values and molar ratios of water to AOT (Wo) were collected. It was observed that the usual kinetic model used for -galactosidase catalysis in aqueous systems failed to represent the experimental data. A bounded water model, however, showed a better correlation between enzymatic activity and Wo. In contrast to the aqueous system, controlling the water concentration in the reverse micelles allows the rate constants for the reaction between water molecules and glycosyl-enzyme complexes to be evaluated. 相似文献
76.
Growth of high quality crystals is often the most difficult step in the determination of protein structures by X-ray diffraction. Automation can improve the success of this process both by reducing the amount of protein required for each screen and by relieving the tedium of setting up crystallization experiments by hand. We have been using an automated system for the design and execution of hanging drop crystallization experiments for the last two years. The system includes robots for the preparation of solutions, setup of hanging drops, and automated imaging, as well as a new software package (RoCKS) for managing all phases of the crystallization process. Here, we review the fundamentals of automated protein crystallization and present results from our comparisons of various approaches to screening. 相似文献
77.
Critical role of the alpha 4 integrin/VCAM-1 pathway in cerebral leukocyte trafficking in lupus-prone MRL/fas(lpr) mice 总被引:1,自引:0,他引:1
MRL/fas(lpr) mice are affected by a systemic autoimmune disease that results in leukocyte recruitment to a wide range of vascular beds, including the cerebral microvasculature. The mechanisms responsible for the leukocyte trafficking to the brain in these animals are not known. Therefore, the aim of this study was to directly examine the cerebral microvasculature in MRL/fas(lpr) mice and determine the molecular mechanisms responsible for this leukocyte recruitment. Intravital microscopy was used to assess leukocyte-endothelial cell interactions (rolling, adhesion) in the pial microcirculation of MRL(+/+) (control) and MRL/fas(lpr) mice at 8, 12, and 16 wk of age. Leukocyte rolling and adhesion were rarely observed in MRL(+/+) mice of any age. MRL/fas(lpr) mice displayed similar results at 8 and 12 wk. However, at 16 wk, significant increases in leukocyte rolling and adhesion were observed in these mice. Histological analysis revealed that the interacting cells were exclusively mononuclear. Leukocyte rolling was reduced, but not eliminated in P-selectin(-/-)-MRL/fas(lpr) mice. However, leukocyte adhesion was not reduced in these mice, indicating that P-selectin-dependent rolling was not required for leukocyte recruitment to the cerebral vasculature in this model of systemic inflammation. E-selectin blockade also had no effect on leukocyte rolling. In contrast, blockade of either the alpha4 integrin or VCAM-1 eliminated P-selectin-independent leukocyte rolling. alpha4 Integrin blockade also significantly inhibited leukocyte adhesion. These studies demonstrate that the systemic inflammatory response that affects MRL/fas(lpr) mice results in leukocyte rolling and adhesion in the cerebral microcirculation, and that the alpha4 integrin/VCAM-1 pathway plays a central role in mediating these interactions. 相似文献
78.
Mass spectrometry was used to identify novel proteins associated with the human 17S U2 snRNP and one of its stable subunits, SF3b. Several additional proteins were identified, demonstrating that 17S U2 snRNPs are significantly more complex than previously thought. Two of the newly identified proteins, namely the DEAD-box proteins SF3b125 and hPrp5 (a homologue of Saccharomyces cerevisiae Prp5p) were characterized further. Immunodepletion experiments with HeLa nuclear extract indicated that hPrp5p plays an important role in pre-mRNA splicing, acting during or prior to prespliceosome assembly. The SF3b-associated protein SF3b125 dissociates at the time of 17S U2 formation, raising the interesting possibility that it might facilitate the assembly of the 17S U2 snRNP. Finally, immunofluorescence/FISH studies revealed a differential subnuclear distribution of U2 snRNA, hPrp5p and SF3b125, which were enriched in Cajal bodies, versus SF3b155 and SF3a120, which were not; a model for 17S U2 snRNP assembly based on these findings is presented. Taken together, these studies provide new insight into the composition of the 17S U2 snRNP and the potential function of several of its proteins. 相似文献
79.
Coort SL Willems J Coumans WA van der Vusse GJ Bonen A Glatz JF Luiken JJ 《Molecular and cellular biochemistry》2002,239(1-2):213-219
Sulfo-N-succinimidyl esters of LCFAs are a powerful tool to investigate the functional significance of plasmalemmal proteins in the LCFA uptake process. This notion is based on the following observations. First, sulfo-N-succinimidyl oleate (SSO) was found to inhibit the bulk of LCFA uptake into various cell types, i.e. rat adipocytes, type II pneumocytes and cardiac myocytes. Second, using cardiac giant membrane vesicles, in which LCFA uptake can be investigated in the absence of mitochondrial -oxidation, SSO retained the ability to largely inhibit LCFA uptake, indicating that inhibition of LCFA transsarcolemmal transport is its primary action. Third, SSO has no inhibitory effect on glucose and octanoate uptake into giant membrane vesicles derived from heart and skeletal muscle, indicating that its action is specific for LCFA uptake. Finally, SSO specifically binds to the 88 kDa plasmalemmal fatty acid transporter FAT, a rat homologue of human CD36, resulting in an arrest of the transport function of this protein.In addition to its inhibitory action at the plasma membrane level, evidence is presented for the lack of a direct inhibitory effect on subsequent LCFA metabolism. First, the relative contribution of oxidation and esterification to LCFA uptake is not altered in the presence of SSO. Second, isoproterenol-mediated channeling of LCFAs into oxidative pathways is not affected by sulfo-N-succinimidyl palmitate (SSP). As an example of its application we used SSP to study the role of FAT/CD36 in contraction- and insulin-stimulated LCFA uptake by cardiac myocytes , showing that this transporter is a primary site of regulation of cellular LCFA utilization. 相似文献
80.
Ivie MA Pollock DA Gustafson DL Ivie LL Rasolomandimby J Swearingen WD 《Journal of economic entomology》2002,95(4):651-660
A community of 225 species of Coleoptera was used as a surrogate to evaluate nontarget effects of entomopathogenic fungi under development as biopesticides for use against the Malagasy migratory locust Locusta migratoria capito Saussure (Orthoptera: Acrididae). Evaluation of a standard chemical treatment of fenitrothion + esfenvalerate, two indigenous isolates of Metarhiziumflavoviride Gams & Roszsypol (SP3 and SP9), and an indigenous isolate of Beauveria bassiana (Balsamo) Vuillemin (SP16) against an untreated control in a replicated field trial in southern Madagascar showed that one of the isolates of M. flavoviride (SP3) and fenitrothion + esfenvalerate had distinct effects on nontarget beetle communities that were similar to each other. The other two isolates had no detectable effects compared with the untreated control. Based on an evaluation of the species affected, the similar effects of SP3 and the chemical pesticide are hypothesized to be the result of a perturbation of predator-prey relationships, with a distinct tendency to be manifested via predators. The data indicate that use of SP9 and SP16 would have minimal detrimental effects on the biodiversity of nontarget beetles, but that SP3 needs further testing. 相似文献