全文获取类型
收费全文 | 17589篇 |
免费 | 1086篇 |
国内免费 | 38篇 |
出版年
2023年 | 185篇 |
2022年 | 389篇 |
2021年 | 932篇 |
2020年 | 499篇 |
2019年 | 660篇 |
2018年 | 786篇 |
2017年 | 541篇 |
2016年 | 766篇 |
2015年 | 949篇 |
2014年 | 1054篇 |
2013年 | 1361篇 |
2012年 | 1377篇 |
2011年 | 1255篇 |
2010年 | 771篇 |
2009年 | 626篇 |
2008年 | 754篇 |
2007年 | 776篇 |
2006年 | 652篇 |
2005年 | 598篇 |
2004年 | 518篇 |
2003年 | 425篇 |
2002年 | 391篇 |
2001年 | 216篇 |
2000年 | 179篇 |
1999年 | 141篇 |
1998年 | 105篇 |
1997年 | 67篇 |
1996年 | 77篇 |
1995年 | 73篇 |
1994年 | 55篇 |
1993年 | 55篇 |
1992年 | 108篇 |
1991年 | 84篇 |
1990年 | 104篇 |
1989年 | 91篇 |
1988年 | 86篇 |
1987年 | 70篇 |
1986年 | 70篇 |
1985年 | 73篇 |
1984年 | 79篇 |
1983年 | 64篇 |
1982年 | 56篇 |
1981年 | 65篇 |
1980年 | 60篇 |
1979年 | 39篇 |
1978年 | 52篇 |
1977年 | 41篇 |
1976年 | 38篇 |
1974年 | 36篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Immunoaffinity purified Sm/RNP antigens from buffalo and goat liver were studied to determine the role of RNA and proteins
towards the antigenicity of Sm and RNP antigens. A more direct approach using enzyme-linked immunosorbent assay on nylon beads
has been utilized to look into the problem. The effect of enzyme treatment and the role of RNA and protein fractions in influencing
antigenicity have been described. RNA seems to be involved in the maintenance of RNP specific polypeptides in suitable conformation
so as to keep them in solution. Removal of RNA leads to insolubilization of RNP specific polypeptides. Antibodies to Sm and
RNP antigens have been shown to cross react with poly A containing heterogeneous nuclear ribonucleoprotein with no cross reactivity
with thymus RNA or DNA. 相似文献
102.
Abstract The determinants for a haemolysin from an extraintestinal isolate of Citrobacter freundii have been cloned and expressed in both Escherichia coli K12 and phylogenetically related bacteria. Compared with E. coli , where the haemolytic determinants are encoded in 7.5 kb, the hemolysin determinants of C. freundii are located on a 2.5-kb Hin dIII fragment in the recombinant plasmid PJP71. Chicken embryo tests indicate that this haemolysin does contribute to the pathogenicity of C. freundii . 相似文献
103.
Summary Our ultrastructural study of the retinal pigmented epithelium (RPE) of young, pigmented, and mature silver eels, (Anguilla anguilla), revealed the presence of retinomotor responses in the RPE of both growth stages. Furthermore, while the overall fine structure of the RPE is similar to that of other vertebrates, specific structures were also found. These include various forms of lipid droplets, intercellular membranous whorls, multitubular bodies, macrophages, melanolysosomes, and myeloid bodies (large and numerous in young eels). Structural variations in cellular organelles of the RPE according to different adaptive states (light, dark) and growth stages (young, mature) of the animal are discussed with respect to their significance in its complex life cycle. 相似文献
104.
A unique DR-related B cell differentiation antigen 总被引:2,自引:0,他引:2
M A Shipp B D Schwartz C C Kannapell R C Griffith M G Scott P Ahmed J M Davie M H Nahm 《Journal of immunology (Baltimore, Md. : 1950)》1983,131(5):2458-2467
The Ia or class II molecules in both mouse and man are the basis for the genetic control of the immune response. In addition to DR, other class II antigens have been described in man. We describe a new human Ia antigen K19, recognized by three monoclonal antibodies (HK-9, HK-19, and HK-20). This antigen has the general biochemical characteristics of an Ia antigen but is different from a DR antigen. Further, this antigen is found only on mature B lymphocytes and not on monocytes and activated T cells. Thus, this antigen may represent a new Ia-like molecule that is preferentially expressed on mature B cells. 相似文献
105.
The irreversible binding of [2,3-14C]acrylonitrile (VCN) to proteins, RNA and DNA of various tissues of male Sprague-Dawley rats after a single oral dose of 46.5 mg/kg (0.5 LD50) has been studied. Proteins were isolated by chloroform-isoamyl alcohol-phenol extraction. RNA and DNA were separated by hydroxyapatite chromatography. Binding of VCN to proteins was extensive and was time dependent. Radioactivity in nucleic acids was registered in the liver and the target organs, stomach and brain. DNA alkylation, which increased by time, was significantly higher in the target organs, brain and stomach (119 and 81 pmol/mg, respectively, at 24 h) than that in the liver. The covalent binding indices for the liver, stomach and brain at 24 h after dosing were, 5.9, 51.9 and 65.3, respectively. These results suggest that VCN is able to act as a multipotent carcinogen by alkylation of DNA in the extrahepatic target tissues, stomach and brain. 相似文献
106.
107.
Water-soluble chromatin from rat submandibular gland nuclei was isolated, and had a DNA: RNA:protein ratio of 8:1:20. The spectral properties of this preparation were similar to those described for chromatins from other tissues. The rat submandibular gland chromatin possessed protein phosphokinase activity. It was able to incorporate 32P from [γ-32P]-ATP into chromatin proteins, and into dephospho-phosvitin. The chromatin-associated protein phosphokinase activity (measured with dephospho-phosvitin as substrate) required Mg2+, Na+ or K+ and dithiothreitol for optimal activity. A single injection of isoproterenol influenced the activity of this enzyme system, so that it was decreased at 2 h, showed a transient increase at 4 h, and a large increase at 10–16 h after the injection. This event appears to precede the increase in ribosomal RNA induced by Ipr [13]. By 48 h the chromatin-associated protein kinase returned to the normal control levels. These changes appeared to be commensurate with the corresponding alterations in the non-histone acidic protein complement of these chromatins. Actinomycin D or cycloheximide, when administered 30 min prior to isoproterenol, blocked the increase in chromatin-associated protein kinase at 4 as well as 10 h after the injection of isoproterenol. Injection of pilocarpine did not influence the chromatin-associated protein phosphokinase activity. Dichloroisoproterenol appeared to be antagonistic to the influence of isoproterenol in mediating changes in chromatin-associated protein kinase. The results suggest that the isoproterenol-induced increase in chromatin-bound protein phosphokinase which precedes the increase in RNA synthesis is related to the eventual onset of DNA synthesis in rat submandibular gland stimulated by isoproterenol. The chromatin-bound protein phosphokinase activity (or activities) may have a regulatory role on gene action, mediated through the control of phosphorylation of nuclear non-histone acidic proteins [26]. 相似文献
108.
Shahid Ali A. Sitaramayya K. Sree Kumar Padmanabhan S. Krishnan 《The Biochemical journal》1974,137(1):85-92
1. An inhibitor of cytoplasmic guanine deaminase of rat liver was isolated from liver ;heavy mitochondrial' fraction after freezing and thawing and treatment with Triton X-100. 2. Submitochondrial fractionation revealed that the inhibitor was localized in the outer-membrane fraction. 3. The method of purification of inhibitor, involving precipitation with (NH(4))(2)SO(4) and chromatography on DEAE-cellulose, its precipitability by trichloroacetic acid and the pattern of absorption in the u.v. indicated that the inhibitor was a protein. In confirmation, tryptic digestion of the isolated material resulted in destruction of the inhibitor activity. The inhibitor was stable to acid, but labile to heat. 4. The isolated inhibitor required phosphatidylcholine (lecithin) for activity. Phosphatidylcholine also partially protected the inhibitor against heat inactivation. 5. When detergent treatment was omitted, the inhibitor activity of frozen mitochondria was precipitated by (NH(4))(2)SO(4) in a fully active form without supplementation with phosphatidylcholine, indicating that Triton X-100 ruptured the linkage between inhibitor and lipid. 6. A reconstituted sample of inhibitor-phosphatidylcholine complex was precipitated in a fully active form by dialysis against 2-mercaptoethanol, but treatment of the precipitate with NaCl yielded an extract which was inactive unless supplemented with fresh phosphatidylcholine. 7. We interpret the results as evidence that the inhibitor was present in vivo as a lipoprotein and that once the complex was dissociated by the action of detergent and the protein precipitated, there was an absolute need for exogenous phosphatidylcholine for its activity. The manner in which inhibitor associated with the outer membrane of rat liver mitochondria might regulate the activity of the enzyme in the supernatant has been suggested. 相似文献
109.
110.
Ali H. Qizilbash 《CMAJ》1974,110(2):185-186
A case of early bilateral serous papillary adenocarcinoma of the ovaries in an asymptomatic 58-year-old woman was diagnosed by the discovery of psammoma bodies in routine cervicovaginal and endometrial smears. Multiple small foci of carcinoma in-situ involving both fallopian tubes were also present. The significance of psammoma bodies in the cervicovaginal smear is discussed and the literature on the subject briefly reviewed. 相似文献