全文获取类型
收费全文 | 2387篇 |
免费 | 168篇 |
国内免费 | 128篇 |
出版年
2024年 | 5篇 |
2023年 | 28篇 |
2022年 | 67篇 |
2021年 | 127篇 |
2020年 | 89篇 |
2019年 | 84篇 |
2018年 | 78篇 |
2017年 | 67篇 |
2016年 | 113篇 |
2015年 | 142篇 |
2014年 | 161篇 |
2013年 | 201篇 |
2012年 | 203篇 |
2011年 | 184篇 |
2010年 | 121篇 |
2009年 | 96篇 |
2008年 | 121篇 |
2007年 | 109篇 |
2006年 | 92篇 |
2005年 | 69篇 |
2004年 | 64篇 |
2003年 | 57篇 |
2002年 | 61篇 |
2001年 | 39篇 |
2000年 | 37篇 |
1999年 | 30篇 |
1998年 | 13篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 24篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1980年 | 5篇 |
1975年 | 4篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有2683条查询结果,搜索用时 15 毫秒
131.
Young?Sik?Kim Chong?Ho?Lee Phillip?C.?Wankat Yoon?Mo?KooEmail author 《Biotechnology and Bioprocess Engineering》2004,9(5):362-368
A new one-column chromatography process, analogous to a four-zone simulated moving bed (SMB), was presented. The basic principle
of the process was identical to that of a four-zone SMB. The process consisted of one chromatographic column and four tanks,
instead of the four columns in the four-zone SMB (1-1-1-1), and has been used for the separation of two amino acids, phenylalanine
and tryptophan, using an ion exchange resin. The operating parameters for the one-column process and four-zone SMB were obtained
from equilibrium theory. Computer simulations were used to compare the performances of the new one column process to that
of the general four-zone SMB, using Aspen Chromatography™ v 11.1. The differences between the one-column and SMB processes in terms of the purities and yields of phenylalanine and
tryptophan were less than 4 and about 6%, respectively. The lower purities of the one-column process were due to the loss
of the developed concentration profiles in the column when the liquid was stored in tanks. The one-column process gave great
flexibility, and would be useful for reconstructing an existing conventional chromatography process to one of a SMB. 相似文献
132.
In?Seop?KimEmail author Yong?Woon?Choi Sung?Rae?Lee Hark?Mo?Sung 《Biotechnology and Bioprocess Engineering》2004,9(1):65-68
The purpose of the present study was to examine the efficacy and mechanism of fraction IV cold ethanol fractionation and pasteurization
(60°C heat treatment for 10h), involved in the manufacture of albumin from human plasma, in the removal and/or inactivation
of the hepatitis A virus (HAV). Samples from the relevant stages of the production process were spiked with HAV and the amount
of virus in each fraction then quantified using a 50% tissue culture infectious dose (TCID50). HAV was effectively partitioned from albumin during the fraction IV cold ethanol fractionation with a log reduction factor
of 3.43. Pasteurization was also found to be a robust and effective step in inactivating HAV, where the titers were reduced
from an initial titer of 7.60 log TCID50 to undetectable levels within 5 h of treatment. The log reduction factor achieved during pasteurization was≽4.76. Therefore,
the current results indicate that the production process for albumin has sufficient HAV reducing capacity to achieve a high
margin of virus safety. 相似文献
133.
134.
Koo BC Kwon MS Choi BR Lee HT Choi HJ Kim JH Kim NH Jeon I Chang W Kim T 《Molecular reproduction and development》2004,68(4):429-434
Here, we successfully demonstrate expression of the EGFP (enhanced green fluorescence protein) gene in chickens using replication-defective MLV (murine leukemia virus)-based retrovirus vectors encapsidated with VSV-G (vesicular stomatitis virus G glycoprotein). The recombinant retrovirus was injected beneath the blastoderm of non-incubated chicken embryos (stage X). After 12 days incubation, all of the eight living embryos assayed were found to express this vector-encoded EGFP gene, which was under the control of the RSV (Rous Sarcoma Virus) promoter, in diverse organ tissues, including head, beak, neck, wing, hock, tail, toes, heart, amnion, and yolk sac. Surprisingly, despite the presumed cytotoxicity of EGFP, some embryos hatched and survived and these had prominent green fluorescent spots, both in internal organs and externally. 相似文献
135.
Changes in structure and dynamics of the Fv fragment of a catalytic antibody upon binding of inhibitor 下载免费PDF全文
Kroon GJ Mo H Martinez-Yamout MA Dyson HJ Wright PE 《Protein science : a publication of the Protein Society》2003,12(7):1386-1394
Binding of the product inhibitor p-nitrophenol to the monoclonal esterolytic antibody NPN43C9 has been investigated by performing NMR spectroscopy of the heterodimeric variable-domain fragment (Fv) of the antibody in the presence and absence of inhibitor. Structural information from changes in chemical shift upon binding has been related to the changes in local dynamics in the active site of the catalytic antibody using NMR relaxation measurements. Significant changes in the chemical shifts of the backbone resonances upon binding extend beyond the immediate vicinity of the antigen binding site into the interface between the two associated polypeptides that form the Fv heterodimer, a possible indication that the binding of ligand causes a change in the relative orientations of the component light (V(L)) and heavy (V(H)) chain polypeptides. Significant differences in backbone dynamics were observed between the free Fv and the complex with p-nitrophenol. A number of resonances, including almost all of the third hypervariable loop of the light chain (L3), were greatly broadened in the free form of the protein. Other residues in the antigen-binding site showed less broadening of resonances, but still required exchange terms (R(ex)) in the model-free dynamics analysis, consistent with motion on a slow timescale in the active site region of the free Fv. Binding of p-nitrophenol caused these resonances to sharpen, but some R(ex) terms are still required in the analysis of the backbone dynamics. We conclude that the slow timescale motions in the antigen-binding site are very different in the bound and free forms of the Fv, presumably due to the damping of large-amplitude motions by the bound inhibitor. 相似文献
136.
Mo RR Eisenbraun JK Sonstein J Craig RA Curtis JL Stoolman LM Chen J Yung RL 《Journal of immunology (Baltimore, Md. : 1950)》2003,171(2):745-753
D10.G4.1 (D10) cells, a murine conalbumin-reactive Th2 cell line, made to overexpress the beta(2) integrin LFA-1 by pharmacological manipulation or by transfection become autoreactive and are capable of inducing in vivo autoimmunity. However, whether this is specific to LFA-1 and whether overexpression of other T cell integrin molecules has the same effect are unknown. We examined the functional consequences of T cell CD49d (alpha(4) integrin) overexpression by transfecting murine CD49d cDNA into D10 cells. Similar to the LFA-1-transfected cells, the CD49d-overexpressing T cells are autoreactive and proliferate in response to APCs in an MHC class II-dependent manner in the absence of nominal Ag. Additionally, CD49d overexpression is associated with increased in vitro adhesion to endothelial cells and increased in vivo splenic homing. However, in contrast to LFA-1 overexpression, increased T cell CD49d expression is not associated with autoreactive cytotoxicity or the ability to induce in vivo autoimmunity. In addition to the novel observation that CD49d overexpression is sufficient to induce T cell autoreactivity, our results also support the hypothesis that the ability to induce in vivo autoimmunity is related to T cell cytotoxicity and not to T cell proliferation function in the D10 murine adoptive transfer model of autoimmunity. 相似文献
137.
138.
Yang J Si T Ling Y Ruan Y Han Y Wang X Zhou M Zhang D Zhang H Kong Q Liu C Li X Yu Y Liu S Shu L Ma D Wei J Zhang D 《Life sciences》2003,72(26):3017-3021
An increasing amount of evidence suggests that the pathophysiology of schizophrenia is associated with the abnormal immune system, and cytokines may be important in schizophrenia. Among these cytokines, interleukin-1beta may play a role in the pathogenesis of the disease. In the present study, we investigated the genetic association between a TaqI polymorphism in interleukin-1beta gene (IL-1beta) and schizophrenia by restriction fragment length polymorphism (RFLP) analysis among 132 Chinese families of Han descent. The transmission disequilibrium test (TDT) did not demonstrate an allelic association with schizophrenia. Our results suggested that the TaqI polymorphism in IL-1beta gene might not confer increased susceptibility for schizophrenia. 相似文献
139.
Moënne-Loccoz Y Tichy HV O'Donnell A Simon R O'Gara F 《Applied and environmental microbiology》2001,67(8):3418-3425
The impact of the 2,4-diacetylphloroglucinol-producing biocontrol agent Pseudomonas fluorescens F113Rif on the diversity of the resident community of culturable fluorescent pseudomonads associated with the roots of field-grown sugar beet seedlings was evaluated. At 19 days after sowing, the seed inoculant F113Rif had replaced some of the resident culturable fluorescent pseudomonads at the rhizoplane but had no effect on the number of these bacteria in the rhizosphere. A total of 498 isolates of resident fluorescent pseudomonads were obtained and characterized by molecular means at the level of broad phylogenetic groups (by amplified ribosomal DNA restriction analysis) and at the strain level (with random amplified polymorphic DNA markers) as well as phenotypically (55 physiological tests). The introduced pseudomonad induced a major shift in the composition of the resident culturable fluorescent Pseudomonas community, as the percentage of rhizoplane isolates capable of growing on three carbon substrates (erythritol, adonitol, and L-tryptophan) not assimilated by the inoculant was increased from less than 10% to more than 40%. However, the pseudomonads selected did not display enhanced resistance to 2,4-diacetylphloroglucinol. The shift in the resident populations, which was spatially limited to the surface of the root (i.e., the rhizoplane), took place without affecting the relative proportions of phylogenetic groups or the high level of strain diversity of the resident culturable fluorescent Pseudomonas community. These results suggest that the root-associated Pseudomonas community of sugar beet seedlings is resilient to the perturbation that may be caused by a taxonomically related inoculant. 相似文献
140.
Many biocontrol fluorescent pseudomonads can protect plants from soilborne fungal pathogens through production of the antifungal secondary metabolite 2,4-diacetylphloroglucinol (Phl). One of the phl biosynthetic genes, phlD, encodes a polyketide synthase similar to plant chalcone synthases. Here, restriction analysis of phlD from 39 Phl+ biocontrol fluorescent pseudomonads yielded seven different banding patterns. The gene was sequenced in seven strains, representing the different restriction patterns. Cluster analysis of phlD restriction data or phlD sequences indicated that phlD polymorphism was high, and two main clusters were obtained when predicted PhlD sequences were compared. When the seven PhlD sequences were studied with those of other procaryotic polyketide synthases (gram-positive bacteria) and plant chalcone synthases, however, Phl+ pseudomonads, gram-positive bacteria, and plants clustered separately. Yet, sequence analysis of active site regions for PhlD and plant chalcone synthases revealed that PhlD can be considered a member of the chalcone synthase family, which may be interpreted as convergent evolution of key enzymes involved in secondary metabolism. For the 39 Phl+ pseudomonads, a relationship was found among phlD restriction patterns, phylogenetic groups defined by 16S rDNA restriction analysis (confirmed by 16S rDNA sequencing), and production levels of Phl in vitro. 相似文献