全文获取类型
收费全文 | 7018篇 |
免费 | 1130篇 |
国内免费 | 3篇 |
专业分类
8151篇 |
出版年
2021年 | 89篇 |
2016年 | 93篇 |
2015年 | 179篇 |
2014年 | 197篇 |
2013年 | 200篇 |
2012年 | 276篇 |
2011年 | 265篇 |
2010年 | 207篇 |
2009年 | 173篇 |
2008年 | 234篇 |
2007年 | 247篇 |
2006年 | 201篇 |
2005年 | 222篇 |
2004年 | 268篇 |
2003年 | 222篇 |
2002年 | 249篇 |
2001年 | 194篇 |
2000年 | 219篇 |
1999年 | 214篇 |
1998年 | 92篇 |
1997年 | 103篇 |
1996年 | 97篇 |
1994年 | 81篇 |
1993年 | 75篇 |
1992年 | 190篇 |
1991年 | 181篇 |
1990年 | 180篇 |
1989年 | 175篇 |
1988年 | 161篇 |
1987年 | 165篇 |
1986年 | 161篇 |
1985年 | 155篇 |
1984年 | 150篇 |
1983年 | 130篇 |
1982年 | 101篇 |
1981年 | 100篇 |
1980年 | 106篇 |
1979年 | 144篇 |
1978年 | 116篇 |
1977年 | 97篇 |
1976年 | 100篇 |
1975年 | 99篇 |
1974年 | 91篇 |
1973年 | 115篇 |
1972年 | 96篇 |
1971年 | 92篇 |
1970年 | 71篇 |
1969年 | 82篇 |
1968年 | 70篇 |
1966年 | 64篇 |
排序方式: 共有8151条查询结果,搜索用时 15 毫秒
71.
Three-dimensional structure of the regular surface glycoprotein layer of Halobacterium volcanii from the Dead Sea 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A three-dimensional reconstruction from electron micrographs of negatively stained cell envelopes of Halobacterium volcanii has revealed the structure of the surface glycoprotein to a resolution of 2 nm. The glycoprotein is arranged on a p6 lattice with a lattice constant of 16.8 nm. It forms 4.5 nm high, dome-shaped, morphological complexes with a narrow pore at the apex opening into a `funnel' towards the cell membrane. The polarity of the structure was derived from freeze-etching experiments and `edge' views. Six radial protrusions emanate from each morphological complex and join around the 3-fold axis to provide lateral connectivity. Using the primary structure of the surface glycoprotein of the closely related species Halobacterium halobium (Lechner and Sumper, 1987) and the cell envelope profile from a previous X-ray analysis of the same species (Blaurock et al., 1976) we have integrated our reconstruction into a model of halobacterial cell envelope. 相似文献
72.
73.
74.
75.
Adam Slivka Mary Beth Spina Harold I. Calvin Gerald Cohen 《Journal of neurochemistry》1988,50(5):1391-1393
Previous studies indicated that DL-buthionine sulfoximine (DL-BSO), an agent that inhibits the biosynthesis of GSH in liver and other peripheral organs, fails to suppress levels of GSH in the CNS. In the current study, preweanling mice responded to repeated injections of L-BSO with marked declines (79.6-86.5%) of GSH content in brain and spinal cord. In adult mice, the same treatment schedule produced only modest declines (17.8-29.2%) of GSH content in brain and a 55.9% decline in spinal cord. Pretreatment of preweanling mice with L-BSO represents a tool for studying the role of GSH in the CNS. 相似文献
76.
Polyacrylamide gel analysis of the structural polypeptides of purified group C virions allowed six major proteins to be identified. Of these, two (52,000- and 39,000-molecular-weight polypeptides) were shown to be in the outer virion shell as judged by the ability to strip them from virions by treatment with EDTA. Treatment of purified particles with endo-beta-N-acetylglucosaminidase F showed that the 39,000-molecular-weight outer shell polypeptide is probably posttranslationally glycosylated. Serological cross-comparison of groups A and C by using Western blotting (immunoblotting) extended the previously demonstrated lack of cross-reaction for the group antigen to show that none of the structural polypeptides cross-reacted. Possible implications of these findings for the epidemiology of rotaviruses are discussed. 相似文献
77.
Antigenic analysis of a major neutralization site of herpes simplex virus glycoprotein D, using deletion mutants and monoclonal antibody-resistant mutants. 总被引:15,自引:14,他引:1
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)
M I Muggeridge V J Isola R A Byrn T J Tucker A C Minson J C Glorioso G H Cohen R J Eisenberg 《Journal of virology》1988,62(9):3274-3280
Herpes simplex virus glycoprotein D is a component of the virion envelope and appears to be involved in attachment, penetration, and cell fusion. Monoclonal antibodies against this protein can be arranged in groups on the basis of a number of biological and biochemical properties. Group I antibodies are type common, have high complement-independent neutralization titers, and recognize discontinuous (conformational) epitopes; they are currently being used in several laboratories to study the functions of glycoprotein D. We have used a panel of neutralization-resistant mutants to examine the relationships between these antibodies in detail. We found that they can be divided into two subgroups, Ia and Ib, such that mutations selected with Ia antibodies have little or no effect on binding and neutralization by Ib antibodies and vice versa. In addition, Ia antibodies are able to bind deletion and truncation mutants of glycoprotein D that Ib antibodies do not recognize, suggesting that their epitopes are physically distinct. However, with one exception, Ia and Ib antibodies block each other strongly in binding assays with purified glycoprotein D, whereas antibodies from other groups have no effect. We have therefore defined the sum of the Ia and Ib epitopes as antigenic site 1. 相似文献
78.
Delineation of the viral products of recombination in vaccinia virus-infected cells. 总被引:7,自引:5,他引:2
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)
Plasmids containing the vaccinia virus thymidine kinase gene, its flanking DNA sequences, and the Escherichia coli beta-galactosidase gene were used in conjunction with a thymidine kinase-deficient virus to examine the viral products of recombination. Progeny derived from single-crossover events could be distinguished from those generated by gene conversion or double-crossover events when the beta-galactosidase gene was separated from the thymidine kinase gene by the flanking sequences. Using methotrexate to select for recombinant virus and a chromogenic indicator to detect beta-galactosidase, the generation of viral recombinants was measured over a 48-h period. Recombinant progeny were first observed at 12 h and increased to a maximum of 2.5% at 48 h. Single-crossover products, as determined by beta-galactosidase expression, reached a maximum of 57% of the recombinant population at 24 h and thereafter declined. DNA hybridization analysis was used to examine genomic structures of the progeny of the initial viral plaques, plaques purified three times, and those subject to a 10(4)-fold amplification. These analyses confirmed that single-crossover events within either the 5'- or 3'-homologous flanking sequences generated unstable recombinant structures. These structures were shown to contain a single copy of the intact thymidine kinase gene within the corresponding copy of the duplicated thymidine kinase flanking sequences, separated by the beta-galactosidase gene and plasmid DNA. Significantly, these duplicated structures could undergo further recombination to produce repeats of either the intact or the deleted thymidine kinase sequences. These intermediate structures ultimately degenerated to produce either the parental thymidine kinase-deleted or the wild-type genome. The wild-type genome was also shown to be generated directly by gene conversion or double-crossover events. 相似文献
79.
Mutant LF-1 of the green alga Scenedesmus obliquus has been described by Metz and co-workers (Metz, J. G., Pakrasi, H., Seibert, M., and Arntzen, C. J. (1986) FEBS Lett. 205, 269-274) to be inactive for light-driven oxygen evolution, despite a functional Photo-system II reaction center. A polypeptide, D1, implicated in the ligation of the primary photoreactants of photosystem II, was shown to migrate with an apparent higher molecular mass on LDS-PAGE in the mutant than in the wild-type (WT) strain. We show here that polypeptide D1 is synthesized in a precursor form in Scenedesmus WT. Following synthesis and insertion into the thylakoid membrane, a 1.5-2-kDa oligopeptide is clipped off with a half-time of 1-2 min, yielding the mature 34-kDa form of the polypeptide. No processing of polypeptide D1 from mutant LF-1 was observed to take place. We show here that polypeptide D1 of LF-1 displays an identical proteolytic fingerprint pattern to the precursor D1 polypeptide of the wild-type strain. These both have molecular masses about 1.5-2 kDa higher than that of the mature WT polypeptide. A polyclonal antibody elicited by a synthetic oligopeptide (14-mer), predicted from the psbA gene nucleotide sequence to be homologous to the COOH terminus of the precursor D1 of spinach, cross-reacts only with D1 of mutant LF-1 and not with mature D1 of spinach, Chlamydomonas, or of Scenedesmus WT. This observation demonstrates that the greater molecular mass of polypeptide D1 from mutant LF-1 and of Scenedesmus WT precursor D1 is derived from a COOH-terminal extension. We conclude that the LF-1 mutant lacks the appropriate nuclear-encoded protease which processes polypeptide D1 at its COOH terminus from the precursor to the mature form. Such processing would appear to be a necessary step toward the stable incorporation of manganese into the oxygen-evolving site. 相似文献
80.
In vitro fusion of newt macrophages 总被引:1,自引:0,他引:1
Spontaneous formation of multinucleate giant cells is often observed in in vitro cultures of peritoneal adherent macrophages from the newts, Notophthalmus viridescens and Taricha granulosa (urodele amphibians). The frequency of such giant cells in these cultures is increased by the addition of phorbol myristic acetate at the initiation of the cultures. This high frequency of multinucleate cells permitted us to evaluate whether multinucleate giant cells arise by cell fusion and/or by repeated nuclear division without cytokinesis. Cell fusion is readily detectable by scanning electron microscopy. To determine whether nuclear division without cytokinesis also occurs, some cultures were treated with colchicine to arrest mitotic figures; others were pulsed with tritiated thymidine to detect DNA synthesis. Mitotic figures were not seen in acridine orange-stained samples. In monolayers that were processed for autoradiography, only a few nuclei were marked with tritium. These observations suggest that nuclear division does not contribute significantly, if at all, to the formation of multinucleate giant cells from cultured newt peritoneal macrophages. 相似文献