全文获取类型
收费全文 | 419800篇 |
免费 | 43926篇 |
国内免费 | 216篇 |
专业分类
463942篇 |
出版年
2018年 | 4061篇 |
2017年 | 3809篇 |
2016年 | 5373篇 |
2015年 | 6985篇 |
2014年 | 8209篇 |
2013年 | 11605篇 |
2012年 | 13105篇 |
2011年 | 13058篇 |
2010年 | 9140篇 |
2009年 | 8133篇 |
2008年 | 11690篇 |
2007年 | 12098篇 |
2006年 | 11278篇 |
2005年 | 10776篇 |
2004年 | 10523篇 |
2003年 | 10149篇 |
2002年 | 10005篇 |
2001年 | 21680篇 |
2000年 | 21742篇 |
1999年 | 16676篇 |
1998年 | 5124篇 |
1997年 | 5393篇 |
1996年 | 5068篇 |
1995年 | 4720篇 |
1994年 | 4671篇 |
1993年 | 4492篇 |
1992年 | 13505篇 |
1991年 | 13126篇 |
1990年 | 12722篇 |
1989年 | 12105篇 |
1988年 | 11247篇 |
1987年 | 10537篇 |
1986年 | 9625篇 |
1985年 | 9539篇 |
1984年 | 7666篇 |
1983年 | 6670篇 |
1982年 | 4896篇 |
1981年 | 4355篇 |
1980年 | 4053篇 |
1979年 | 7354篇 |
1978年 | 5563篇 |
1977年 | 5015篇 |
1976年 | 4631篇 |
1975年 | 5339篇 |
1974年 | 5613篇 |
1973年 | 5593篇 |
1972年 | 5124篇 |
1971年 | 4422篇 |
1970年 | 3988篇 |
1969年 | 3826篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Y Wattanagoon R E Phillips D A Warrell K Silamut S Looareesuwan B Nagachinta D J Back 《BMJ (Clinical research ed.)》1986,293(6538):11-13
In a study of intramuscular injection of quinine eight adults with moderately severe falciparum malaria resistant to chloroquine were treated with quinine dihydrochloride, being given a loading dose of 20 mg salt (16.7 mg base)/kg followed by three or four eight hourly maintenance doses of 10 mg salt (8.3 mg base)/kg injected into the anterior thigh. All patients responded to treatment. Fever and parasite clearance times (mean (SD) 60 (23) h and 53 (22) h respectively) were comparable with those obtained with intravenous quinine. The mean peak plasma quinine concentration of 11.0 mg/l (34.4 mu mol/l) [corrected] was reached a median of five hours after administration of the loading dose. In all patients plasma quinine concentrations exceeded the high minimum inhibitory concentration for Plasmodium falciparum malaria prevalent in Thailand within four hours of the start of treatment but did not cause toxicity other than mild cinchonism. When intravenous infusion is not possible an intramuscular quinine loading dose is an effective means of starting treatment in patients with moderately severe falciparum malaria who cannot swallow tablets. 相似文献
112.
113.
Growth of cell-free subacute sclerosing panencephalitis (SSPE) virus was compared with that of measles virus in three human neural cell lines; neuroblastoma, oligodendroglioma, and glioblastoma. The Edmonston strain of measles virus replicated in these neural cells as efficiently as in Vero cells. In contrast, the growth of the Mantooth strain of SSPE virus was suppressed moderately in neuroblastoma cells and markedly in oligodendroglioma and glioblastoma cells in spite of the induction of apparent cytopathic effects in these cells. Virus adsorption, defective interfering particles, interferon, and temperature sensitivity were not responsible for this low yield of SSPE virus in neural cell lines. Synthesis of viral proteins of SSPE virus was slower than that of measles virus in oligodendroglioma and glioblastoma cells. These results suggest that the slow rate of synthesis of viral proteins may be relevant to the low yield of SSPE virus in neural cells. 相似文献
114.
Recombinant human insulin. 总被引:1,自引:0,他引:1
Insulin is a well-characterized peptide that can be produced by recombinant DNA technology for human therapeutic use. A brief overview of insulin production from both traditional mammalian pancreatic extraction and recombinant bacterial and yeast systems is presented, and detection techniques, including electrophoresis, are reviewed. Analytical systems for insulin separation are principally based on reversed-phase chromatography, which resolves the deamidation product(s) (desamido insulin) of insulin, proinsulin, and insulin. Process-scale separation is a multistep process and includes ion exchange, reversed-phase, and size exclusion chromatography. Advantages and/or disadvantages of various separation approaches, as described by the numerous literature references on insulin purification, are presented. 相似文献
115.
116.
S-Protein/vitronectin is a serum glycoprotein that inhibits the lytic activity of the membrane attack complex of complement, i.e., of the complex including the proteins C5b, C6, C7, C8, and C9n. We show that intact S-protein/vitronectin or its cyanogen bromide generated fragments also inhibit the hemolysis mediated by perforin from cytotoxic T-cells at 45 and 11 microM, respectively. The glycosaminoglycan binding site of S-protein/vitronectin is responsible for the inhibition, since a synthetic peptide corresponding to a part of this highly basic domain (amino acid residues 348-360) inhibits complement- as well as perforin-mediated cytolysis. In the case of C9, the synthetic peptide binds to the acidic residues occurring in its N-terminal cysteine-rich domain (residues 101-111). Antibodies raised against this particular segment react 25-fold better with the polymerized form of C9 as compared with its monomeric form, indicating that this site becomes exposed only upon the hydrophilic-amphiphilic transition of C9. Since the cysteine-rich domain of C9 has been shown to be highly conserved in C6, C7, and C8 as well as in perforin, the inhibition of the lytic activities of these molecules by S-protein/vitronectin or by peptides corresponding to its heparin binding site may be explained by a similar mechanism. 相似文献
117.
The oxidative half-reaction of phenol hydroxylase has been studied by stopped-flow spectrophotometry. Three flavin-oxygen intermediates can be detected when the substrate is thiophenol, or m-NH2, m-OH, m-CH3, m-Cl, or p-OH phenol. Intermediate I, the flavin C(4a)-hydroperoxide, has an absorbance maximum at 380-390 nm and an extinction coefficient approximately 10,000 M-1 cm-1. Intermediate III, the flavin C(4a)-hydroxide, has an absorbance maximum at 365-375 nm and an extinction coefficient approximately 10,000 M-1 cm-1. Intermediate II has absorbance maxima of 350-390 nm and extinction coefficients of 10,000-16,000 M-1 cm-1 depending on the substrate. A Hammett plot of the logarithm of the rates of the oxygen transfer step, the conversion of intermediate I to intermediate II, gives a straight line with a slope -0.5. Fluoride ion is a product of the enzymatic reaction when 2,3,5,6-tetrafluorophenol is the substrate. These results are consistent with an electrophilic substitution mechanism for oxygen transfer. The conversions of I to II and II to III are acid-catalyzed. A kinetic isotope effect of 8 was measured for the conversion of II to III using deuterated resorcinol as substrate. The conversion of III to oxidized enzyme is base-catalyzed, suggesting that the reaction depends on the removal of the flavin N(5) proton. Product release occurs at the same time as the formation of intermediate III, or rapidly thereafter. The results are interpreted according to the ring-opened model of Entsch et al. (Entsch, B., Ballou, D. P., and Massey, V. (1976) J. Biol. Chem. 251, 2550-2563). 相似文献
118.
Concentration factor and biological half-life of 54Mn were determined in three species representing an ecologically and economically important food chain. Green algae (Chlorella spp.), Daphnia magna and yellow perch (Perca flavescens) were exposed to 54Mn in water and assayed for 54Mn uptake. Steady state concentration factors computed from the laboratory data for algae, Daphnia and perch were 4230, 17 000 and 11, respectively. Respective biological half-lives were 1.6, 1.2 and 8.3 days. 相似文献
119.
Coordinate regulation of ribosomal protein mRNA level in regenerating rat liver. Study with the corresponding mouse cloned cDNAs. 总被引:17,自引:6,他引:11
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cloned mouse ribosomal protein (rp) cDNAs exhibit extensive homology with the corresponding rat sequences. The size of the rp-mRNAs and complexity of the rp-genes are very similar in the two species. Using the mouse rp-recombinant DNAs we find that the relative abundance of rat L7, L13, L18, L30, L32/33 and S16 mRNAs increases after partial hepatectomy. Their maximal level is about twice that of normal rat liver, and is achieved 12-18 h after the operation, while the relative abundance of albumin mRNA decreases to half the normal values 12 h after partial hepatectomy. This concomitant increase in the relative content of these rp-mRNAs indicates coordinate regulation of their level in the rat. The dissimilar behavior of L10 and L19 rp-mRNA suggests additional control mechanisms of rp-mRNA levels in the regenerating rat liver. 相似文献
120.
The amino acid composition, N- and C-terminal amino acid sequences, and the basic physicochemical and immunochemical properties of the recently discovered pregnancy-associated molecular variant of human transcortin (Strel'chyonok, O.A., Avvakumov, G.V. and Akhrem, A.A. (1984) Carbohydr. Res. 134, 133-140) have been found to be identical to those of transcortin from normal donor serum. This suggests the identity of polypeptide moieties of the two glycoproteins. The transcortin variant has a lower isoelectric point (3.5-4.1) than normal transcortin (3.6-4.2), and different electrophoretic mobility in low-porosity polyacrylamide gel (one band versus two for normal transcortin). These differences can be reasonably explained by different organization of the carbohydrate moieties of these glycoproteins due to diverse post-translational modification of a single polypeptide chain. The levels of transcortin variant in the maternal venous serum throughout normal gestation (447 donors in all) and on the fifth day after delivery, as well as in umbilical cord serum and extracts of term placenta, have been measured by a radioimmune assay. Analysis of the data obtained allowed us to conclude that the biosynthesis of pregnancy-associated transcortin variant occurs in some organ of the maternal organism rather than in the feto-placental system, and it is a characteristic of pregnancy as a unique physiological state of the female organism rather than a phenomenon caused by individual features of certain women. We assume that the transcortin variant takes part in the guided transport of corticosteroids and/or progestins into some tissues that develop in the course of gestation. 相似文献