全文获取类型
收费全文 | 5818篇 |
免费 | 443篇 |
国内免费 | 2篇 |
出版年
2023年 | 17篇 |
2022年 | 38篇 |
2021年 | 68篇 |
2020年 | 50篇 |
2019年 | 51篇 |
2018年 | 79篇 |
2017年 | 70篇 |
2016年 | 117篇 |
2015年 | 185篇 |
2014年 | 260篇 |
2013年 | 341篇 |
2012年 | 348篇 |
2011年 | 384篇 |
2010年 | 261篇 |
2009年 | 252篇 |
2008年 | 342篇 |
2007年 | 366篇 |
2006年 | 341篇 |
2005年 | 346篇 |
2004年 | 305篇 |
2003年 | 287篇 |
2002年 | 305篇 |
2001年 | 68篇 |
2000年 | 57篇 |
1999年 | 82篇 |
1998年 | 110篇 |
1997年 | 86篇 |
1996年 | 74篇 |
1995年 | 58篇 |
1994年 | 66篇 |
1993年 | 66篇 |
1992年 | 49篇 |
1991年 | 57篇 |
1990年 | 40篇 |
1989年 | 58篇 |
1988年 | 48篇 |
1987年 | 31篇 |
1986年 | 43篇 |
1985年 | 35篇 |
1984年 | 31篇 |
1983年 | 24篇 |
1982年 | 54篇 |
1981年 | 33篇 |
1980年 | 33篇 |
1979年 | 24篇 |
1978年 | 16篇 |
1977年 | 23篇 |
1976年 | 16篇 |
1975年 | 21篇 |
1974年 | 16篇 |
排序方式: 共有6263条查询结果,搜索用时 15 毫秒
971.
Homing of intravenously and intralymphatically injected human dendritic cells generated in vitro from CD34+ hematopoietic progenitor cells 总被引:6,自引:0,他引:6
Andreas Mackensen Thomas Krause Uli Blum Peter Uhrmeister Roland Mertelsmann Albrecht Lindemann 《Cancer immunology, immunotherapy : CII》1999,48(2-3):118-122
Dendritic cells (DC) are professional antigen-presenting cells that can be generated in vitro from CD34+ peripheral blood progenitor cells by recombinant cytokines. These cells have potential implications for immunotherapeutic
approaches in the treatment of cancer and other diseases. Physiologically, immature DC in the periphery capture and process
antigens, then mature to interdigitating DC and migrate to lymphoid organs, where they activate lymphocytes. However, it is
not known if DC generated in vitro have the capacity to traffic in vivo to the lymphoid tissues, such as spleen and lymph
nodes. We have investigated whether human radiolabeled DC differentiated in vitro migrate and localize to lymphoid tissues
after intravenous and intralymphatic injection. The distribution and localization of the DC were evaluated in five patients
with malignant melanoma using serial whole-body gamma camera imaging. Intravenously infused DC demonstrated transient lung
uptake followed by localization in the spleen and liver for at least 7 days. DC injected into a lymphatic vessel at the dorsal
foot were rapidly detected in the draining lymph nodes where they remained for more than 24 h. These data suggest that DC
differentiated in vitro localize preferentially to lymphoid tissue, where they could induce specific immune responses.
Received: 28 January 1999 / Accepted: 4 March 1999 相似文献
972.
Comparison of the nature, activity, and cellular localization of superoxide-dismutases (SOD) from soil and clinical isolates
of Streptomyces species was investigated to identify possible factors that could account for the pathological role of the strains isolated
from human lesions. Results showed that all of the studied strains possessed a cytoplasmic Ni-SOD. This particular SOD, found
in isolates from patients, could be a new taxonomic criterion to identify Streptomyces species with greater precision. A second minor SOD, assimilated to an Fe/Zn-SOD, was detected in some strains, but no relationship
was established between the presence of this enzyme and the clinical origin of the strains.
Received: 9 April 1999 / Accepted: 9 June 1999 相似文献
973.
在胰岛细胞株 H I T 细胞中,用瞬时转染法观察高 K+ 导致的膜去极化与c A M P对 C B P C端片段转录活性的影响.发现二者均可诱导 C B P C端片段的转录活性增强,并有协同效应; C B P C端片段的突变体( Ser 1 772 突变为 Ala)表现相同的诱导特性,但其基本转录活性降低.说明膜去极化和 c A M P对 C B P C 端片段转录活性的诱导作用与 P K A 磷酸化位点 Ser 1 772 无关,而该位点的磷酸化对调节 C B P C 端片段的基本转录活性起重要作用.蛋白激酶 C 通路对 C B P Ti的转录活性无影响. 相似文献
974.
John G. Day Erica E. Benson Roland A. Fleck 《In vitro cellular & developmental biology. Plant》1999,35(2):127-136
Summary Microalgae are a highly diverse group of unicellular organisms comprising the eukaryotic protists and the prokaryotic cyanobacteria
or blue-green algae. The microalgae have a unique environmental status; being virtually ubiquitous in euphotic aquatic niches,
they can occupy extreme habitats ranging from tropical coral reefs to the polar regions, and they contribute to half of the
globe’s photosynthetic activity. Furthermore, they form the basis of the food chain for more than 70% of the world’s biomass.
Microalgae are a valuable environmental and biotechnological resource, and the aim of this review is to explore the use of
in vitro technologies in the conservation and sustainable exploitation of this remarkable group of organisms. The first part
of the review evaluates the importance of in vitro methods in the maintenance and conservation of microalgae and describes
the central role of culture collections in applied algal research. The second part explores the application of microalgal
in vitro technologies, particularly in the context of the aquaculture and biotechnology industries. Emphasis is placed upon
the exploitation of economically important algal products including aquaculture feed, biomass production for the health care
sector, green fertilizers, pigments, vitamins, antioxidants, and antimicrobial agents. The contribution that microalgae can
make to environmental research is also appraised; for example, they have an important role as indicator organisms in environmental
impact assessments. Similarly, designated culture collection strains of microalgae are used for ecotoxicity testing. Throughout
the review, emphasis is placed on the application of in vitro techniques for the continued advancement of microalgal research.
The paper concludes by assessing future perspectives for the novel application of microalgae and their products. 相似文献
975.
Factors Affecting the Terminal Resolution Site Endonuclease, Helicase, and ATPase Activities of Adeno-Associated Virus Type 2 Rep Proteins
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)
The Rep68 and Rep78 proteins (Rep68/78) of adeno-associated virus type 2 (AAV) are critical for AAV replication and site-specific integration. They bind specifically to the AAV inverted terminal repeats (ITRs) and possess ATPase, helicase, and strand-specific/site-specific endonuclease activities. In the present study, we further characterized the AAV Rep68/78 helicase, ATPase, and endonuclease activities by using a maltose binding protein-Rep68 fusion (MBP-Rep68Delta) produced in Escherichia coli cells and Rep78 produced in vitro in a rabbit reticulocyte lysate system. We found that the minimal length of single-stranded DNA capable of stimulating the ATPase activity of MBP-Rep68Delta is 100 to 200 bases. The degree of stimulation correlated positively with the length of single-stranded DNA added to the reaction mixture. We then determined the ATP concentration needed for optimal MBP-Rep68Delta helicase activity and showed that the helicase is active over a wide range of ATP concentrations. We determined the directionality of MBP-Rep68Delta helicase activity and found that it appears to move in a 3' to 5' direction, which is consistent with a model in which AAV Rep68/78 participates in AAV DNA replication by unwinding DNA ahead of a cellular DNA polymerase. In this report, we also demonstrate that single-stranded DNA is capable of inhibiting the MBP-Rep68Delta or Rep78 endonuclease activity greater than 10-fold. In addition, we show that removal of the secondary Rep68/78 binding site, which is found only in the hairpin form of the AAV ITR, causes a three- to eightfold reduction in the ability of the ITR to be used as a substrate for the Rep78 or MBP-Rep68Delta endonuclease activity. This suggests that contact between Rep68/78 and this secondary element may play an important role in the Rep-mediated endonuclease activity. 相似文献
976.
Zhiping Ye Teresa Liu Daniel P. Offringa Jonathan McInnis Roland A. Levandowski 《Journal of virology》1999,73(9):7467-7473
To characterize the sites and nature of binding of influenza A virus matrix protein (M1) to ribonucleoprotein (RNP), M1 of A/WSN/33 was altered by deletion or site-directed mutagenesis, expressed in vitro, and allowed to attach to RNP under a variety of conditions. Approximately 70% of the wild-type (Wt) M1 bound to RNP at pH 7.0, but less than 5% of M1 associated with RNP at pH 5.0. Increasing the concentration of NaCl reduced M1 binding, but even at a high salt concentration (0.6 M NaCl), approximately 20% of the input M1 was capable of binding to RNP. Mutations altering potential M1 RNA-binding regions (basic amino acids 101RKLKR105 and the zinc finger motif at amino acids 148 to 162) had varied effect: mutations of amino acids 101 to 105 reduced RNP binding compared to the Wt M1, but mutations of zinc finger motif did not. Treatment of RNP with RNase reduced M1 binding by approximately half, but even M1 mutants lacking RNA-binding regions had residual binding to RNase-treated RNP provided that the N-terminal 76 amino acids of M1 (containing two hydrophobic domains) were intact. Addition of detergent to the reaction mixture further reduced binding related to the N-terminal 76 amino acids and showed the greatest effect for mutations affecting the RNA-binding regions of basic amino acids. The data suggest that M1 interacts with both the RNA and protein components of RNP in assembly and disassembly of influenza A viruses. 相似文献
977.
The innervation‐induced down‐regulation of fetal‐type acetylcholine receptor (AChR) expression in developing muscle fibers has largely been attributed to nerve‐evoked muscle activity; however, there is increasing evidence that a neural trophic factor also contributes to this receptor down‐regulation. Previous studies from this laboratory have shown that neural extracts contain a factor which decreases fetal‐type AChR expression in skeletal muscle cell lines and therefore may account for the proposed inhibitory neurotrophic influence. The current study investigated possible intracellular signaling molecules involved in this receptor down‐regulation and demonstrated that activation of protein kinase C and p70S6k appeared to be important in receptor down‐regulation. Decreases in AChR density were independent of myogenin. In addition, the receptor down‐regulation was independent of neuregulin, which also induces p70S6k activity. These studies demonstrate that neural extracts contain an inhibitory factor which can down‐regulate fetal‐type AChR expression independently of nerve‐evoked muscle activity through intracellular signaling molecules which are known to regulate AChR expression. © 2000 John Wiley & Sons, Inc. J Neurobiol 42: 190–201, 2000 相似文献
978.
In order to elucidate the chiral recognition mechanisms of the enzyme cellobiohydrolase I (CBH I), its carboxylic groups were covalently modified. The synthetic modification was carried out either in the presence or absence of cellobiose, which has proven to inhibit the enzymatic activity and if present in the mobile phase impairs enantioselectivity of amino alcohols. Compared to the reference CSP (unmodified CBH-I silica and CBH-I core silica), the synthetically modified phases show differences both in enantioselectivity and retention. The enzymatic differences between the CSPs were also in line with the chromatographic results. The selectivity factors of propranolol are almost unchanged during the reaction periods in the presence of cellobiose, while they decreased rapidly without the inhibitor. In one case, even a slight improvement in enantioselectivity was obtained, indicating that non-stereospecific carboxylic groups were ruled out. Chirality 10:760–769, 1998. © 1998 Wiley-Liss, Inc. 相似文献
979.
Agnes Billecocq William C. Horne Munmun Chakraborty Kunio Takeyasu Robert Levenson Roland Baron 《Journal of cellular physiology》1997,172(2):221-229
Treatment of avian myelomonocytic cells with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) results in an approximately two fold increase in levels of Na,K-ATPase β1 subunit mRNA and protein (both total and plasma membrane-associated). The changes in β1 subunit expression occur in the absence of a detectable increase in expression of any of the three α subunit isoforms or in Na,K-ATPase activity. The selective induction of the expression of the β subunit in avian myelomonocytic cells by 1,25(OH)2D3 reveals a previously unobserved feature of the regulation of Na,K-ATPase expression, while the targeting of β subunit polypeptides to the plasma membrane in the absence of a corresponding increase in active Na,K-ATPase suggests that, in these cells, transport of the β subunit to the plasma membrane may be independent of its binding to the α subunit. J. Cell. Physiol. 172:221–229, 1997. © 1997 Wiley-Liss, Inc. 相似文献
980.