全文获取类型
收费全文 | 3090篇 |
免费 | 202篇 |
国内免费 | 3篇 |
出版年
2023年 | 18篇 |
2022年 | 42篇 |
2021年 | 90篇 |
2020年 | 47篇 |
2019年 | 75篇 |
2018年 | 63篇 |
2017年 | 60篇 |
2016年 | 77篇 |
2015年 | 144篇 |
2014年 | 169篇 |
2013年 | 251篇 |
2012年 | 280篇 |
2011年 | 230篇 |
2010年 | 151篇 |
2009年 | 138篇 |
2008年 | 164篇 |
2007年 | 200篇 |
2006年 | 144篇 |
2005年 | 153篇 |
2004年 | 138篇 |
2003年 | 115篇 |
2002年 | 93篇 |
2001年 | 20篇 |
2000年 | 38篇 |
1999年 | 18篇 |
1998年 | 22篇 |
1997年 | 17篇 |
1996年 | 27篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 35篇 |
1991年 | 26篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 20篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1979年 | 9篇 |
1976年 | 5篇 |
1974年 | 5篇 |
1971年 | 5篇 |
1970年 | 9篇 |
1969年 | 8篇 |
1968年 | 5篇 |
排序方式: 共有3295条查询结果,搜索用时 15 毫秒
1.
Background
Spidroins are a unique family of large, structural proteins that make up the bulk of spider silk fibers. Due to the highly variable nature of their repetitive sequences, spidroin evolutionary relationships have principally been determined from their non-repetitive carboxy (C)-terminal domains, though they offer limited character data. The few known spidroin amino (N)-terminal domains have been difficult to obtain, but potentially contain critical phylogenetic information for reconstructing the diversification of spider silks. Here we used silk gland expression data (ESTs) from highly divergent species to evaluate the functional significance and phylogenetic utility of spidroin N-terminal domains. 相似文献2.
The specificity of the syngeneic mixed leukocyte response, a primary anti-I region T cell proliferative response, is determined intrathymically 总被引:6,自引:0,他引:6
L H Glimcher R H Schwartz D L Longo A Singer 《Journal of immunology (Baltimore, Md. : 1950)》1982,129(3):987-991
In previous studies, the syngeneic MLR of peripheral T cells was shown to be predominantly an I region-restricted function. In this report we show that adult thymocytes are also capable of responding to syngeneic irradiated stimulator cells in a syngeneic MLR, provided that TCGF is added to the culture system. Using this assay, it was possible for the first time to examine the pattern of I region restriction within the thymus itself. Analysis of the thymocyte syngeneic MLR in thymuses from radiation-induced bone marrow chimeras demonstrated that the MHC preference seen in the peripheral T cell population also existed in cells resident within the thymus. Experiments utilizing congenitally athymic mice transplanted with allogeneic thymic grafts demonstrated that both peripheral T cells and thymocytes from such animals displayed a strong preferential proliferation toward stimulator cells bearing thymic-type MHC determinants. The results in the nude model thus demonstrate that the thymus by itself is sufficient to impart such restriction specificity on a developing T cell repertoire. These results are consistent with the notion that the thymus exerts selective pressure on maturing T cell populations that results in a skewing of the T cell repertoire toward the recognition of thymic-type I region products, and that this MHC preference exists before expansion of T cells in the periphery. 相似文献
3.
4.
Victoria Levterova Stefan Panaiotov Nadia Brankova Kristin Tankova 《Molecular biotechnology》2010,45(1):34-38
Identification of genetic markers involved in stress response to physical factors or chemical substances in organisms is a
challenging task. Typing of upregulated gene expression due to selective antibacterial pressure is a promising approach in
the search of molecular mechanisms responsible for development of resistance. cDNA-Fluorescent Amplified Fragment Length Polymorphism
(cDNA-FAFLP) strategy was developed and applied in the search of antimycotic drug resistance marker(s) in medically important
fungi as an alternative method to microarray analysis. We compared differential gene expression of two sensitive Candida albicans reference strains (ATCC 10231 and ATCC 60133) and two of their paired resistant to fluconazole and itraconazole mutants.
Resistant mutants Candida albicans
FLC-R, resistant to fluconazole (MIC > 128 μg/ml) and Candida albicans ICZ-R, resistant to itraconazole (MIC > 4 μg/ml) were obtained in subcultures with gradual increase of the antifungal in the culture
medium. cDNA-AFLP profile in both itraconazole resistant mutants showed specific spectrophotometric peaks with 5–6-fold RNA
overexpression product of 500 bp length compared to the sensitive strains. Fluconazole mutants do not reveal RNA level changes
under tested by us typing conditions. These results indicate that the cDNA-FAFLP strategy is a relatively rapid, simple, and
reliable method for simultaneous typing of both constitutive and induced differences in expression of host genes providing
insight into the biological processes involved in response to drugs in bacteria and fungi. Moreover, this methodology could
be tested for typing of the genome response of any organism to physical or chemical stress factors. 相似文献
5.
The red-striped soft scale insect Pulvinaria tenuivalvata (Newstead) (Hemiptera: Coccidae) started to infest sugarcane plants (Saccharum officinarum L.) in different districts in Egypt during the last decade. The percentage of infestation was recorded in El-Wakf area, Qena Governorate (Naghhamadi mill zone) Upper Egypt in some fields. There are three levels of infestation, low, intermediate and high. From these fields, samples were selected for physical and chemical studies. The results obtained show that the stalks of infested plants decreased in weight, the sugar content (glucose and sucrose) drastically reduced and as the percentage of infestation increased the percentage of glucose and sucrose content significantly decreased. The primary and secondary humidity and the cellulose content also increased in the healthy plants compared to the infested ones. All the physical character of the infested plants was significantly affected in comparison with the healthy ones. 相似文献
6.
7.
8.
9.
Kristel Van Steen Nadia Tahri Geert Molenberghs 《Biometrical journal. Biometrische Zeitschrift》2004,46(2):187-202
Until recently, the most common parametric approaches to study the combined effects of several genetic polymorphisms located within a gene or in a small genomic region are, at the genotype level, logistic regressions and at the haplotype level, haplotype analyses. An alternative modeling approach, based on the case/control principle, is to regard exposures (e.g., genetic data such as derived from Single Nucleotide Polymorphisms – SNPs) as random and disease status as fixed and to use a marginal multivariate model that accounts for inter‐relationships between exposures. One such model is the multivariate Dale model. This model is based on multiple logistic regressions. That is why the model, applied in a case/control setting, leads to straightforward interpretations that are similar to those drawn in a classical logistic modeling framework. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
Basic proteins of the perinuclear theca of mammalian spermatozoa and spermatids: a novel class of cytoskeletal elements 总被引:8,自引:1,他引:7
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The nuclei of bovine spermatids and spermatozoa are surrounded by dense cytoplasmic webs sandwiched between the nuclear envelope and the acrosome and plasma membrane, respectively, filling most of the cytoplasmic space of the sperm head. This web contains a complex structure, the perinuclear theca, which is characterized by resistance to extractions in nondenaturing detergents and high salt buffers, and can be divided into two major subcomponents, the subacrosomal layer and the postacrosomal calyx. Using calyces isolated from bull and rat spermatozoa we have identified two kinds of basic proteins as major constituents of the thecal structure and have localized them by specific antibodies at the light and electron microscopic level. These are an Mr 60,000 protein, termed calicin, localized almost exclusively to the calyx, and a group of multiple-band polypeptides (MBP; Mr 56,000-74,000), which occur in both the calyx and the subacrosomal layer. The polypeptides of the MBP group are immunologically related to each other, but unrelated, by antibody reactions and peptide maps, to calicin. We show that these basic cytoskeletal proteins are first detectable in the round spermatid stage. As we have not detected any intermediate filament proteins and proteins related to nuclear lamins of somatic cells in sperm heads, we conclude that the perinuclear theca and its constituents, calicin and MBP proteins, are the predominant cytoskeletal elements of the sperm head. Immunologically cross-reacting polypeptides with similar properties have been identified in the heads of rat and human spermatozoa. We speculate that these insoluble basic proteins contribute, during spermiogenesis, to the formation of the perinuclear theca as an architectural element involved in the shape changes and the intimate association of the nucleus with the acrosome and the plasma membrane. 相似文献