全文获取类型
收费全文 | 40446篇 |
免费 | 106篇 |
国内免费 | 183篇 |
专业分类
系统科学 | 219篇 |
丛书文集 | 722篇 |
教育与普及 | 66篇 |
理论与方法论 | 160篇 |
现状及发展 | 19287篇 |
研究方法 | 1556篇 |
综合类 | 18181篇 |
自然研究 | 544篇 |
出版年
2013年 | 322篇 |
2012年 | 509篇 |
2011年 | 1051篇 |
2010年 | 214篇 |
2008年 | 652篇 |
2007年 | 713篇 |
2006年 | 738篇 |
2005年 | 706篇 |
2004年 | 809篇 |
2003年 | 657篇 |
2002年 | 650篇 |
2001年 | 1172篇 |
2000年 | 1089篇 |
1999年 | 764篇 |
1992年 | 750篇 |
1991年 | 551篇 |
1990年 | 618篇 |
1989年 | 635篇 |
1988年 | 579篇 |
1987年 | 668篇 |
1986年 | 637篇 |
1985年 | 805篇 |
1984年 | 616篇 |
1983年 | 509篇 |
1982年 | 472篇 |
1981年 | 506篇 |
1980年 | 606篇 |
1979年 | 1293篇 |
1978年 | 1085篇 |
1977年 | 1031篇 |
1976年 | 832篇 |
1975年 | 933篇 |
1974年 | 1259篇 |
1973年 | 1085篇 |
1972年 | 1100篇 |
1971年 | 1273篇 |
1970年 | 1601篇 |
1969年 | 1223篇 |
1968年 | 1242篇 |
1967年 | 1213篇 |
1966年 | 1021篇 |
1965年 | 757篇 |
1964年 | 249篇 |
1959年 | 411篇 |
1958年 | 727篇 |
1957年 | 496篇 |
1956年 | 411篇 |
1955年 | 417篇 |
1954年 | 405篇 |
1948年 | 271篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The antifungal activity of two drimane sesquiterpene dialdehydes, polygodial (1) and warburganal (2), alone and in combination with several other substances, was examined against three fungi,Candida albicans, Saccharomyces cerevisiae andPityrosporum ovale employing a broth dilution method. Anethole significantly synergized the activity of the two sesquiterpenoids againstC. albicans andS. cerevisiae however, it had only an, additive effect againstP. ovale. By contrast, two antioxidants, ascorbic acid (vitamin C) and BHA (butylated hydroxyanisole), noticeably enhanced the activity of the sesquiterpenoids againstP. ovale, but had no, effect againstC. albicans andS. cerevisiae. 相似文献
62.
The murine Elo (eye lens obsolescence) mutation confers a dominant phenotype characterized by malformation of the eye lens. The mutation maps to chromosome 1, in close proximity to the gamma E-crystallin gene which is the 3'-most member of the gamma-crystallin gene cluster. We have analysed the sequence of this gene from the Elo mouse and identified a single nucleotide deletion which destroys the fourth and last "Greek key" motif of the protein. This mutation is tightly associated with the phenotype, as no recombination was detected in 274 meioses. In addition, the mutant mRNA is present in the affected lens, providing further support for our hypothesis that the deletion is responsible for the dominant Elo phenotype. 相似文献
63.
D. Porquet M. Appel T. Fournier O. Bertaux D. Biou J. Féger 《Cellular and molecular life sciences : CMLS》1992,48(3):257-261
Both in vivo and in vitro models have certain disadvantages for the study of the chronic hepatotoxicity of drugs. The aim of this work was to evaluate a new approach based on an in vivo/in vitro model. After chronic in vivo treatment of rats with Vincamine and Vindeburnol (an eburnamenine derivative which exhibits hepatotoxic properties in man) liver cells were isolated, and functional and metabolic disorders (metabolic utilization of fructose and protein biosynthesis) were studied to determine injury. The results showed no modification of blood parameters, but a direct relationship between the dose of Vindeburnol administered in vivo and the metabolic disorders observed in vitro, evidencing the high sensitivity and reliability of this model. 相似文献
64.
V. Ralevic P. Milner K. A. Kirkpatrick G. Burnstock 《Cellular and molecular life sciences : CMLS》1992,48(1):31-34
Adenosine 5-triphosphate (ATP) was released into the perfusate of rat isolated mesenteric arterial beds during each of two consecutive increases in flow. There was no significant difference between the amounts of ATP released on each occasion. Substance P was also released into the perfusate by increased flow, although its release was more variable. Removal of the endothelium of the mesenteric vessels with sodium deoxycholate led to a significant reduction (74%) in the amount of ATP released compared with the release before the endothelium had been removed. This suggests that the ATP released into the mesenteric arterial perfusate during increased flow arises from endothelial cells. 相似文献
65.
J. Y. Toullec M. Chikhi A. van Wormhoudt 《Cellular and molecular life sciences : CMLS》1992,48(3):272-277
In crustaceans, all the steps in the assimilation of food take place in the hepatopancreas. To facilitate the study of this organ, a method for the dissociation of cell types was developed. The hepatopancreas of the prawnPalaemon serratus was mechanically dissociated and the cells separated by Percoll density-gradient centrifugation. The E and R cells had similar densities of around 1.05 g/ml. The F cells were separated into two distinct fractions with densities of 1.075 and 1.082 g/ml. The B cells sedimented at a density of 1.12 g/ml. The ratio between the two populations of F cells was found to vary during the intermolt cycle while B cells disappeared after the molt. When the density gradient fractions were incubated with3H-leucine, incorporation was highest in the F cell fractions. Measurements of -amylase activity, indicated that the two populations of F cells may be derived from the same cell type. 相似文献
66.
G. L. Mendz C. R. Middlehurst P. W. Kuchel P. A. Crossie 《Cellular and molecular life sciences : CMLS》1986,42(9):1016-1018
Summary A technique to assay erythrocyte pyrimidine 5-nucleotidase activity in situ using31P nuclear magnetic resonance spectroscopy is presented. The assay is chemically specific, simple and applicable to untreated lysates. A comparison of enzyme levels in normal controls and in multiple sclerosis patients employing the assay yielded no significant differences between both groups. Difficulties encountered in the quantitative analysis of the assay using1H-NMR spectroscopy are briefly discussed. 相似文献
67.
S. Suzuki S. Kurasawa H. Kitai M. Oba S. Komatsu K. Yoda R. Iizuka 《Cellular and molecular life sciences : CMLS》1986,42(7):795-798
Summary Porcine or human follicular fluid inhibited the spontaneous maturation of isolated hamster oocytes in vitro during the first 1.5 h of culture. Moreover, the presence of 50% follicular fluid combined with 100 M dbcAMP cooperatively reduced the incidence of germinal vesicle breakdown. The addition of FSH also inhibited the resumption of meiosis, and the presence of LH did not overcome the inhibitory effects of follicular fluid and tended to impede isolated hamster oocyte maturation in vitro. 相似文献
68.
69.
New phytotoxic butenolides produced bySeiridium cardinale,the pathogen of cypress canker disease 总被引:1,自引:0,他引:1
L. Sparapano A. Evidente A. Ballio A. Graniti G. Randazzo 《Cellular and molecular life sciences : CMLS》1986,42(6):627-628
Summary Two new butenolides, seiridin andiso-seiridin, were isolated from culture filtrates ofSeiridium cardinale, the pathogen of cypress canker, a destructive disease ofCupressus and relatedConiferae These metabolites were characterized as 3-methyl-4-(2-hydroxyheptyl)-2(5H)-furanone and its 4-(3-hydroxyheptyl) isomer, respectively. Chlorotic, and necrotic symptoms were produced on leaves of either host or non-host test plants by absorption of 0.3 mg/ml solutions of either compound. These also showed antibacterial activity.This study was supported in part by the National Research Council, Rome (special ad hoc project Chimica fine e secondaria) and in part by the Ministry of Education, Rome. 相似文献
70.
R. S. Verma S. Thomas M. Coleman R. T. Silver H. Dosik 《Cellular and molecular life sciences : CMLS》1986,42(4):440-441
Summary A random distribution of the Y-chromosome at somatic metaphase was found in 50 patients with Ph' positive chronic myelogenous leukemia (CML). Thus, it is concluded that the positive of the Y-chromosome at somatic metaphase does not appear to influence the loss from bone marrow cells. 相似文献