全文获取类型
收费全文 | 1667篇 |
免费 | 218篇 |
出版年
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 20篇 |
2017年 | 19篇 |
2016年 | 35篇 |
2015年 | 43篇 |
2014年 | 63篇 |
2013年 | 66篇 |
2012年 | 96篇 |
2011年 | 101篇 |
2010年 | 59篇 |
2009年 | 54篇 |
2008年 | 83篇 |
2007年 | 67篇 |
2006年 | 77篇 |
2005年 | 49篇 |
2004年 | 59篇 |
2003年 | 55篇 |
2002年 | 63篇 |
2001年 | 60篇 |
2000年 | 52篇 |
1999年 | 49篇 |
1998年 | 18篇 |
1997年 | 29篇 |
1996年 | 14篇 |
1995年 | 28篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 39篇 |
1991年 | 29篇 |
1990年 | 45篇 |
1989年 | 42篇 |
1988年 | 41篇 |
1987年 | 37篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1978年 | 22篇 |
1977年 | 9篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 14篇 |
1972年 | 13篇 |
1971年 | 15篇 |
1968年 | 11篇 |
排序方式: 共有1885条查询结果,搜索用时 15 毫秒
61.
62.
Reovirus-induced apoptosis of MDCK cells is not linked to viral yield and is blocked by Bcl-2. 总被引:10,自引:10,他引:0
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
S E Rodgers E S Barton S M Oberhaus B Pike C A Gibson K L Tyler T S Dermody 《Journal of virology》1997,71(3):2540-2546
In this study, we investigated the relationship between reovirus-induced apoptosis and viral growth. Madin-Darby canine kidney (MDCK) epithelial cells infected with prototype reovirus strains type 1 Lang (T1L) or type 3 Dearing (T3D) were found to undergo apoptosis, and T3D induced apoptosis of MDCK cells to a substantially greater extent than T1L. By using T1L x T3D reassortant viruses, we found that differences in the capacities of these strains to induce apoptosis are determined by the viral S1 and M2 gene segments. These genes encode viral outer-capsid proteins that play important roles in viral entry into cells. T1L grew significantly better in MDCK cells than T3D, and these differences in growth segregated with the viral L1 and M1 gene segments. The L1 and M1 genes encode viral core proteins involved in viral RNA synthesis. Bcl-2 overexpression in MDCK cells inhibited reovirus-induced apoptosis but did not substantially affect reovirus growth. These findings indicate that differences in the capacities of reovirus strains to induce apoptosis and grow in MDCK cells are determined by different viral genes and that premature cell death by apoptosis does not limit reovirus growth in MDCK cells. 相似文献
63.
Determination of Effective Transport Coefficients for Bacterial Migration in Sand Columns 总被引:6,自引:1,他引:5
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A well-characterized experimental system was designed to evaluate the effect of porous media on macroscopic transport coefficients which are used to characterize the migration of bacterial populations. Bacterial density profiles of Pseudomonas putida PRS2000 were determined in the presence and absence of a chemical attractant (3-chlorobenzoate) gradient within sand columns having a narrow distribution of particle diameters. These experimental profiles were compared with theoretical predictions to evaluate the macroscopic transport coefficients. The effective random motility coefficient, used to quantify migration due to a random process in a porous medium, decreased nearly 20-fold as grain size in the columns decreased from 800 to 80 (mu)m. The effective random motility coefficient (mu)(infeff) was related to the random motility coefficient (mu), measured in a bulk aqueous system, according to (mu)(infeff) = ((epsilon)/(tau))(mu) with porosity (epsilon) and tortuosity (tau). Over the times and distances examined in these experiments, bacterial density profiles were unaffected by the presence of an attractant gradient. Theoretical profiles with the aqueous phase value of the chemotactic sensitivity coefficient (used to quantify migration due to a directed process) were consistent with this result and suggested that any chemotactic effect on bacterial migration was below the detection limits of our assay. 相似文献
64.
R. Fundele R. Krause S. C. Barton M. A. Surani B. Christ 《Development genes and evolution》1995,204(7-8):484-493
To asses the potential of androgenetic cells to participate in post-midgestation fetal development we have made use of an in situ detectable cell lineage marker in the analysis of chimeric mouse fetuses containing an androgenetic cell lineage. Our results show conclusively that androgenetic cells participate in the formation of derivatives of all lineages and in some tissues may contribute the majority of the total cell population. However, the allocation or persistence of androgenetic cells was non-random. High contribution of androgenetic cells was observed in brown adipose tissue, mesenchyme, smooth muscle, perichondrium, peripheral nerves and epithelia of the intestinal tract and the trachea. Thus, androgenetic cells were able to efficiently populate mesodermal, ectodermal and endodermal derivatives. In contrast, there was a clear prejudice against androgenetic cells in the brain. 相似文献
65.
DM Woolley 《The Journal of cell biology》1977,75(3):851-865
Motile spermatozoa from the golden hamster have been arrested by rapid freezing and then fixed with glutaraldehyde at low temperature after substitution with ethylene glycol. As far as can be judged, the flagellar waveforms thus stabilized are similar to those seen in living sperm; in contrast, fixation in glutaraldehyde, without prior freezing, induces agonal changes in flagellar conformation. The characteristics waveform after freeze substitution contains three bends. Approx. half of these flagella are entirely planar. The rest are three dimensional, with the third bend displaced in a regular way from the plane containing the proximal two bends. From the geometry of these flagella, it is concluded that the plane of action of a given bending cycle undergoes a clockwise twist (from a forward viewpoint) as the cycle is succeeded by new bending cycles. This "twisted plane" undulation is quite different from helical movement. The twisting seems to occur abruptly, between cycles, as if each bending cycle has a preferred plane of action. The mechanism underlying the twisting is uncertain. However, on the basis of the angular displacements between the preferred planes, and the findings from electron microscopy, the following idea is presented as a working hypothesis: that, if the most proximal plane of bending is topographically determined by peripheral doublet 1, then successive distal planes of action are influenced predominantly by doublets 2, 3, etc., in clockwise sequence. The merits and weaknesses of this hypothesis are discussed. 相似文献
66.
Accessibility of sialo components in a murine tumor cell to extracellular glycohydrolase (sialidase)
Lipid-bound sialic acid in the murine melanoma cell is not totally inaccessible to an exogenous macromolecular probe, as formerly believed. Roughly 30% of the sialic acid bound to lipid, and an equal proportion of the sialic acid bound to protein is cleaved by the action of Clostridium perfringens glycohydrolase (neuraminidase, sialidase) when the purified enzyme is added to the suspension medium of intact murine melanoma cells freshly derived from the tumor. Cleavage of lipid-bound sialic acid is indifferent to the presence of Ca2+ in the medium. However, maximum release from protein requires a physiological concentration of this divalent cation. Variation in ionic strength has no effect on release of sialic acid. These findings show that a restricted portion of the bound sialic acid may be released from the intact murine melanama cell by the extracellularly supplied enzyme acting topographically. 相似文献
67.
Measurement of carboxypeptidase A, one of the pancreatic proteolytic enzymes, in human serum is made possible by a combination of affinity chromatography to isolate and concentrate the enzyme followed by monitoring activity spectrophotometrically with a high-turnover peptide substrate. Concentrations of enzyme in the nanogram-per-milliliter range can be determined with high precision and reliability. Initial clinical application of this method demonstrates no detectable activity in serum from normal individuals, but the enzyme is present in the sera of individuals with pancreatitis. 相似文献
68.
R M Cerda-Flores G K Kshatriya S A Barton C H Leal-Garza R Garza-Chapa W J Schull R Chakraborty 《Human biology; an international record of research》1991,63(3):309-327
The Mexicans residing in the Monterrey metropolitan area in Nuevo León, Mexico, were grouped by generation and birthplace [Monterrey Metropolitan Area (MMA), San Luis Potosi (SLP), and Zacatecas (ZAC)] of the four grandparents to determine the extent of genetic variation within this population and the genetic differences, if any, between the natives living in the MMA and the immigrant populations from SLP and ZAC. Nine genetic marker systems were analyzed. The genetic distance analysis indicates that SLP and ZAC are similar to the MMA, irrespective of birthplace and generation. Gene diversity analysis (GST) suggests that more than 96% of the total gene diversity (HT) can be attributed to individual variation within the population. The genetic admixture analysis suggests that the Mexicans of the MMA, SLP, and ZAC, stratified by birthplace and generation, have received a predominantly Spanish contribution (78.5%), followed by a Mexican Indian contribution (21.5%). Similarly, admixture analysis, conducted on the population of Nuevo León and stratified by generation, indicates a substantial contribution from the MMA (64.6%), followed by ZAC (22.1%) and SLP (13.3%). Finally, we demonstrate that there is no nonrandom association of alleles among the genetic marker systems (i.e., no evidence of gametic disequilibrium) despite the Mestizo origin of this population. 相似文献
69.
The programme pscan has been developed to distribute proteindatabank scans over a network of computers that share a commonfilesystem. pscan may be used in conjunction with most conventionalsequence comparison programmes with few modifications. In testruns using the Smith Waterman dynamic programming algorithm,the time required to scan a 6858 sequence databank using a querysequence 740 residues long was reduced from 50 min for a singleprocessor, to 11 minutes for five processors. Accordingly, pscanprovides a low-cost, portable alternative to dedicated parallelprocessing computers.
Received on August 27, 1990; accepted on September 25, 1990 相似文献
70.
Conservation analysis and structure prediction of the SH2 family of phosphotyrosine binding domains.
Src homology 2 (SH2) regions are short (approximately 100 amino acids), non-catalytic domains conserved among a wide variety of proteins involved in cytoplasmic signaling induced by growth factors. It is thought that SH2 domains play an important role in the intracellular response to growth factor stimulation by binding to phosphotyrosine containing proteins. In this paper we apply the techniques of multiple sequence alignment, secondary structure prediction and conservation analysis to 67 SH2 domain amino acid sequences. This combined approach predicts seven core secondary structure regions with the pattern beta-alpha-beta-beta-beta-beta-alpha, identifies those residues most likely to be buried in the hydrophobic core of the native SH2 domain, and highlights patterns of conservation indicative of secondary structural elements. Residues likely to be involved in phosphotyrosine binding are shown and orientations of the predicted secondary structures suggested which could enable such residues to cooperate in phosphate binding. We propose a consensus pattern that encapsulates the principal conserved features of the SH2 domains. Comparison of the proposed SH2 domain of akt to this pattern shows only 12/40 matches, suggesting that this domain may not exhibit SH2-like properties. 相似文献