全文获取类型
收费全文 | 19143篇 |
免费 | 1410篇 |
国内免费 | 1237篇 |
出版年
2024年 | 42篇 |
2023年 | 259篇 |
2022年 | 560篇 |
2021年 | 943篇 |
2020年 | 575篇 |
2019年 | 815篇 |
2018年 | 808篇 |
2017年 | 568篇 |
2016年 | 842篇 |
2015年 | 1114篇 |
2014年 | 1362篇 |
2013年 | 1457篇 |
2012年 | 1693篇 |
2011年 | 1532篇 |
2010年 | 979篇 |
2009年 | 939篇 |
2008年 | 1050篇 |
2007年 | 981篇 |
2006年 | 800篇 |
2005年 | 684篇 |
2004年 | 532篇 |
2003年 | 519篇 |
2002年 | 439篇 |
2001年 | 343篇 |
2000年 | 299篇 |
1999年 | 289篇 |
1998年 | 165篇 |
1997年 | 160篇 |
1996年 | 155篇 |
1995年 | 117篇 |
1994年 | 84篇 |
1993年 | 70篇 |
1992年 | 113篇 |
1991年 | 85篇 |
1990年 | 68篇 |
1989年 | 52篇 |
1988年 | 44篇 |
1987年 | 44篇 |
1986年 | 39篇 |
1985年 | 54篇 |
1984年 | 8篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 5篇 |
1969年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Molecular cloning of the gene of a penicillin-binding protein supposed to cause high resistance to beta-lactam antibiotics in Staphylococcus aureus. 总被引:44,自引:10,他引:34 下载免费PDF全文
M Matsuhashi M D Song F Ishino M Wachi M Doi M Inoue K Ubukata N Yamashita M Konno 《Journal of bacteriology》1986,167(3):975-980
A novel penicillin-binding protein, PBP-2' (Mr about 75,000), is known to be induced in excessively large amount by most beta-lactam compounds in cells of a clinically isolated strain of Staphylococcus aureus, TK784, that is highly resistant to beta-lactams and also most other antibiotics. This protein has very low affinities to most beta-lactam compounds and has been supposed to be the cause of the resistance of the cells to beta-lactams. A 14-kilobase DNA fragment was isolated from the cells that carried the gene encoding this penicillin-binding protein and also a genetically linked marker that is responsible for the resistance to tobramycin. This DNA was cloned on plasmid pACYC184 and was shown to cause both production of PBP-2' and resistance to tobramycin in Escherichia coli cells. However, the formation of PBP-2' in E. coli was only moderate and was independent of normal inducer beta-lactams. The PBP-2' formed in the E. coli cells showed slow kinetics of binding to beta-lactams similar to that of PBP-2' formed in the original S. aureus cells and gave a similar pattern of peptides to the latter when digested with the proteolytic V8 enzyme of S. aureus. 相似文献
52.
互花米草、狐米草和大绳草的表皮均由长细胞、短细胞(栓质细胞和硅质细胞)、盐腺和气孔器组成。它们成纵行交互排列。盐腺的结构与大米草相似,但三个种的盐腺和气孔器的数目不同,尤其以大绳草最多。它们的内部结构是由气道、不同大小的维管束、基本组织以及厚壁组织组成。然而,维管束的数目及厚壁组织的发育各不相同。狐米草和大绳草有高度木质化的厚壁组织细胞,而互花米草的厚壁组织木质化较弱。大绳草的维管束多于其他两种。 相似文献
53.
Variations in ADP-ribosylation of nuclear scaffold proteins during the HeLa cell cycle 总被引:1,自引:0,他引:1
Cell cycle variations in ADP-ribosylation of nuclear scaffold proteins were determined. Nuclei of synchronized cells were isolated and labeled with [32P]NAD before nuclear scaffolds were obtained by digestion of DNA with DNase I and extraction of proteins with 2M NaCl. Autoradiograms revealed the three groups of "lamins" and a species identified as poly (ADP-ribose) polymerase to be the primary ADP-ribosylated proteins. The patterns of modification of nuclear scaffold proteins displayed similar features through the cell cycle. Radioactivity in the lamins increased from 20% in early-S phase to 40% in G1 phase of the next cell cycle. 相似文献
54.
Clostridium acetobutylicum NRRL B527 and ATCC 824 exhibited extracellular and cell-bound endoglucanase and cellobiase activities during growth in a chemically defined medium with cellobiose as the sole source of carbohydrate. For both strains, the endoglucanase was found to be mainly extracellular (70 to 90%) during growth in continuous or batch cultures with the pH maintained at 5.2, whereas the cellobiase was mainly cell associated (60 to 90%). During continuous cultivation of strain B527 with cellobiose as the limiting nutrient, maximum production of the endoglucanase and cellobiase occurred at pH values of 5.2 and 4.8, respectively. In the carbon-limited continuous cultures, strain 824 produced similar levels of endoglucanase, cellobiosidase, and cellobiase activities regardless of the carbon source used. However, in ammonium- or phosphate-limited cultures, with an excess of glucose, only 1/10 of the endoglucanase was produced, and neither cellobiosidase nor cellobiase activities were detectable. A crude extracellular enzyme preparation from strain B527 hydrolyzed carboxymethylcellulose and phosphoric acid-swollen cellulose readily and microcrystalline cellulose (A vicel) to a lesser extent. Glucose accounted for more than 90% of the reducing sugar produced by the hydrolysis of acid-swollen cellulose and Avicel. Strain B527 did not grow in medium with acid-swollen cellulose as the sole source of carbohydrate, although it grew readily on the products obtained by hydrolyzing the cellulose in vitro with a preparation of extracellular cellulase derived from the same organism. 相似文献
55.
C S Song J H Yu D H Bai P Y Hester K H Kim 《Journal of immunology (Baltimore, Md. : 1950)》1985,135(5):3354-3359
Simple methods for the generation, purification, and assay of antibodies to the alpha-subunit of insulin receptor from eggs of immunized hens have been described. Chicken antibodies against the alpha-subunit inhibit insulin binding to the receptor and stimulate glucose oxidation as well as autophosphorylation of the beta-subunit. Thus the properties of chicken antibodies are very similar to those of antibodies found in human autoimmune diseases and different from rabbit antibodies obtained against the same antigen. 相似文献
56.
Actively cycling human lymphocytes were treated with mitomycin C for 1 h (1.4 μg/ml) and then grown in medium containing 10 μg/ml bromodeoxyuridine. Serial 5-h colcemid accumulation samples were taken up to 35 h and the air-dried methaphase spreads stained for replication banding. A complete cell-cycle subphasing analysis was made, and classified cells scored for all categories of chromatid-type aberrations and their location.
Inspite of the high dose which produced massive delay and cycle perturbation, there was no evidence for selectively lethality of early-S cells, in fact such cells were in excess. Extreme localization of aberrations to late-replicating (mostly centromeric) regions was found at all subphases and in pre-S cells. This rules out ‘localization by default’ as an explanation for the observed preferential occurence of ‘break points’ in these regions.
The frequency of incomplete intrachanges, low in late S, rises dramaticallyin early S to become maximal in pre-S cells. 相似文献
57.
M K Song H Krutzsch W D Hankins W L Richards S S Thorgeirsson 《Experimental cell research》1985,156(1):271-276
A specific, rapid, and economical method for measuring the extent of DNA synthesis in adherent rat hepatoma H4-II-E cells grown in 96-well microtiter plates is described. The adherent cells were pulsed for 1 h with [methyl-3H]thymidine, released from the substratum by trypsinization, and collected on fiberglass filters with a MASH II cell harvester. The amount of radioactivity incorporated was directly proportional to the number of cells per well. Growth curves generated by measuring [methyl-3H]thymidine incorporation and counting the number of cells per well were identical. Experiments with inhibitors of DNA, protein, and RNA synthesis demonstrated that this method selectively measured DNA synthesis. In addition, [3H]thymidine uptake showed excellent correlation with autoradiographic assessment of DNA synthesis. This specific and sensitive method for determining DNA synthesis in microtiter cultures should facilitate studies of effects of various growth-controlling agents on epithelial, fibroblastic, and other cells which grow as adherent cells in culture. 相似文献
58.
Epitope-relatedness and phenotyping of hepatic cytochromes P-450 with monoclonal antibodies. 总被引:1,自引:1,他引:0 下载免费PDF全文
The epitope-specific cytochrome P-450 content of animal livers was analysed by radioimmunoassay using a panel of seven monoclonal antibodies (MAbs) made to a 3-methylcholanthrene-induced rat liver cytochrome P-450. Competitive radioimmunoassays utilizing a reference radiolabelled MAb and a series of unlabelled MAbs indicated that there are at least three distinct classes of MAbs to different epitopes on cytochrome P-450. In addition, a direct radioimmunoassay employing a radiolabelled second antibody detected MAb-specific cytochromes P-450 in livers from different animals. This radioimmunoassay detected large elevations in the levels of these cytochromes P-450 in the livers of 3-methylcholanthrene-treated rats and C57BL/6 mice compared with untreated rats, 3-methylcholanthrene-treated DBA/2 mice or guinea pigs. The two complementary radioimmunoassay methods are sensitive, efficient, and easily applicable for screening large number of tissue samples for MAb-defined cytochrome P-450 phenotype. 相似文献
59.
新城疫病毒单克隆抗体的特性及应用 总被引:2,自引:0,他引:2
建立了8个分泌抗新城疫病毒(NDV)特异性单克隆抗体(McAb)的杂交瘤细胞株,根据它们的免疫生物学特性可以分为三种类型:(1)具有FA和ELISA特性(FN1、FN4、FN29、FN30、FN35、FNl22);(2)具有FA、ELISA和HI特性(FN7);(3)具有ELISA、HI特性和中和能力(FN106),根据FN30和FN106的ELISA试验,可将11个NDV毒株分为二种不同的抗原群,应用FN4-FITC,FN7-FITC和FN29-HRP试剂,对人工感染NDV和野外送检病例检测结果表明,单抗试剂的DFA阳性率(92.3%)高于病毒分离阳性率(87.2%),两种方法的符合率89.7%,这些单抗试剂用于临床诊断敏感性和特异性高,且方法快速、简便。 相似文献
60.