全文获取类型
收费全文 | 643771篇 |
免费 | 76730篇 |
国内免费 | 439篇 |
专业分类
720940篇 |
出版年
2018年 | 5405篇 |
2016年 | 7189篇 |
2015年 | 10193篇 |
2014年 | 11643篇 |
2013年 | 17213篇 |
2012年 | 18823篇 |
2011年 | 19346篇 |
2010年 | 12988篇 |
2009年 | 12075篇 |
2008年 | 17265篇 |
2007年 | 17816篇 |
2006年 | 16730篇 |
2005年 | 16068篇 |
2004年 | 15622篇 |
2003年 | 15397篇 |
2002年 | 14914篇 |
2001年 | 28615篇 |
2000年 | 28832篇 |
1999年 | 22847篇 |
1998年 | 8269篇 |
1997年 | 8943篇 |
1996年 | 8521篇 |
1995年 | 7833篇 |
1994年 | 7777篇 |
1993年 | 7843篇 |
1992年 | 19380篇 |
1991年 | 19230篇 |
1990年 | 18369篇 |
1989年 | 18175篇 |
1988年 | 16723篇 |
1987年 | 16153篇 |
1986年 | 14931篇 |
1985年 | 15091篇 |
1984年 | 12599篇 |
1983年 | 10871篇 |
1982年 | 8404篇 |
1981年 | 7663篇 |
1980年 | 7277篇 |
1979年 | 12048篇 |
1978年 | 9571篇 |
1977年 | 8904篇 |
1976年 | 8336篇 |
1975年 | 9168篇 |
1974年 | 9791篇 |
1973年 | 9557篇 |
1972年 | 8661篇 |
1971年 | 8013篇 |
1970年 | 6903篇 |
1969年 | 6656篇 |
1968年 | 6026篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Interleukin-1 from P388D1: effects upon neutrophils, plasma iron, and fibrinogen in rats, mice, and rabbits 总被引:1,自引:0,他引:1
R F Kampschmidt M Mesecher 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1985,179(2):197-200
Partially purified interleukin-1 was prepared from the murine cell line P388D1. This interleukin-1 produced fever in rabbits and the amount required to cause an increase of 1 degree C was determined. This dose of interleukin-1 produced neutrophilia when injected into rats and rabbits but not in mice, and increased plasma iron and fibrinogen in all three species. Although the mouse was a poor responder to murine interleukin-1 for neutrophilia, it responded unusually well for increasing plasma fibrinogen. 相似文献
972.
Dependence on blood acetate concentration of the metabolic effects of ethanol in perfused rat liver 总被引:3,自引:0,他引:3
D L Topping A M Snoswell G B Storer R C Fishlock R P Trimble 《Biochimica et biophysica acta》1984,800(1):103-105
Unprotected oligonucleotides and oligodeoxynucleotides terminated with an unhindered 5'-phosphate group react with nucleoside 5'- phosphorimidazolides in aqueous solution to give 'capped' pyrophosphates in at least 70% yield. If adenosine 5'- phosphorimidazolide is used as a substrate in the reaction, ligase intermediates are obtained as products. 相似文献
973.
Effects of atropine on respiratory heat loss in asthma 总被引:4,自引:0,他引:4
Breslin F. J.; McFadden E. R. Jr; Ingram R. H. Jr; Deal E. C. Jr 《Journal of applied physiology》1980,48(4):619-623
974.
Protection of iron-catalysed the radical damage to DNA and lipids by copper (II) bleomycin 总被引:3,自引:0,他引:3
J M Gutteridge F Xiao Change 《Biochemical and biophysical research communications》1981,99(4):1354-1360
The ability of Copper(II)-bleomycin to inhibit oxygen-free-radical damage to biomolecules has been assessed. This copper complex showed inhibitory properties towards iron-catalysed damage to phospholipid membranes and cell-free DNA. It was also able to prevent superoxide-dependent reduction of nitroblue tetrazolium (NBT). Unlike iron, copper-bleomycin does not damage DNA . This may result from a site-specific dismutation of superoxide radicals on the DNA molecule. 相似文献
975.
The role of O6-methylguanine-DNA methyltransferase in cell survival, mutagenesis and carcinogenesis 总被引:13,自引:0,他引:13
D B Yarosh 《Mutation research》1985,145(1-2):1-16
976.
F F Smith J R Mertz I Krebs L L Tres C B Chae Z Zakeri J Engelhardt D Hoover M Tenniswood A L Kierszenbaum 《Molecular reproduction and development》1992,33(4):363-372
We have previously reported that a heterodimeric protein secreted by rat Sertoli cells is antigenically related to a protein associated with outer dense fibers of the sperm tail. Therefore, we have explored the possibility that Sertoli and spermatogenic cells express a similar gene encoding a homologous protein. A Sertoli cell heterodimeric protein cDNA probe recognizes specific mRNA in pachytene and round spermatids fractionated by centrifugal elutriation; however, this specific mRNA was less prominent than in cultured Sertoli cells. In agreement with these observations, in situ hybridization experiments show that Sertoli cells are predominantly engaged in active heterodimeric protein mRNA synthesis, while meiotic prophase spermatocytes and spermatids also show significant but less abundant specific mRNA. Immunoblotting experiments demonstrate that, while Sertoli cells synthesize a heterodimeric protein consisting of two disulfide-linked components with molecular masses of 45 and 35 kD, both primary spermatocytes and round spermatids synthesize single 30 kD monomers not associated by disulfide linkage but recognized by antisera to Sertoli cell heterodimeric protein. Immunoblotting and immunogold electron microscopic studies show that antisera to Sertoli cell heterodimeric protein recognize a protein associated with outer dense fibers. This immunoreactivity was abolished by a 5-min pronase treatment, without affecting the integrity of outer dense fibers. Results of this study and previous studies demonstrate that both Sertoli and spermatogenic cells express a similar gene and that an antigenically related product encoded by this gene becomes associated with outer dense fibers during their assembly at spermiogenesis. 相似文献
977.
A Jans E F Ippel P F Dijkstra J B Bijlsma 《Genetic counseling (Geneva, Switzerland)》1992,3(3):139-143
We report two sisters with mental retardation, coarse facial features, telecanthus, flat malar region, prominent lower lip, kyphoscoliosis, and tapering fingers. Although these patients' phenotypes showed considerable overlap with the Coffin-Lowry and the Atkin-Flaitz syndromes, their overall picture makes these diagnoses controversial. 相似文献
978.
A Malassiné C Besse A Roche E Alsat R Rebourcet F Mondon L Cedard 《Histochemistry》1987,87(5):457-464
Low density lipoproteins (LDL) were conjugated to colloidal gold to visualize the route for internalization of LDL in the cultured cells of human term placenta. Cells were obtained from placental villi (caesarian section) by a standard trypsin-DNase dispersion method followed in some cases by a Percoll gradient centrifugation step. Employing electron microscopy it was observed that after 3 days of culture, cells obtained by trypsin-DNase dispersion were a mixture of macrophages, mononucleated cells and large multinucleated cells. When the cells were incubated for 3 days after the Percoll purification, essentially multinucleated cells identical to the syncytiotrophoblast were present. The number of LDL receptor was increased by preincubation in medium with lipoprotein depleted serum. In binding experiments cells incubated at 4 degrees C for 2 h with medium containing gold LDL conjugates showed gold LDL attached to the plasma membrane without characteristic localization. After incubation with gold LDL at 37 degrees C for various times, the three cellular types showed ligand internalization. Gold LDL endocytosis involved first coated pits but also uncoated plasmalemmal invaginations. Then gold LDL was further observed in coated and non coated vesicles, smooth walled endosomes, multivesicular bodies and tubular vesicles. Lastly free gold particles were observed in lysosome like dense bodies. These results prove the internalization of gold LDL conjugates by human cultured placental cells, particularly by syncytiotrophoblast like multinucleated cells. This accumulation of LDL (the major cholesterol carrying protein in humans) is recognised to be responsible for the exogenous cholesterol supply indispensable to the progesterone biosynthesis and cellular growth of the placenta. 相似文献
979.
980.
D A McMillen J J Volwerk J Ohishi M Erion J F Keana P C Jost O H Griffith 《Biochemistry》1986,25(1):182-193
A series of amine-specific reagents based on the benzaldehyde reactive group have been synthesized, characterized, and used to study beef heart cytochrome c oxidase reconstituted in phospholipid bilayers. The series contained three classes of reagents: lipid-soluble phosphodiesters having a single hydrocarbon chain, phospholipid analogues, and a water-soluble benzaldehyde. All reagents were either radiolabeled or spin-labeled or both. The Schiff bases formed by these benzaldehydes with amines were found to be reversible until the addition of the reducing agent sodium cyanoborohydride, whereas attachment of lipid-derived aliphatic aldehydes was not readily reversible in the absence of the reducing agent. The benzaldehyde group provides a convenient method of controlling and delaying permanent attachment to integral membrane proteins until after the reconstitution steps. This ensures that the lipid analogues are located properly to identify amine groups at the lipid-protein interface rather than reacting indiscriminately with amines of the hydrophilic domains of the protein. The benzaldehyde lipid labels attach to cytochrome c oxidase with high efficiency. Typically, 20% of the amount of lipid label present was covalently attached to the protein, and the number of moles of label incorporated per mole of protein ranged from 1 to 6, depending on the molar ratios of label, lipid, and protein. The efficiency of labeling by the water-soluble benzaldehyde was much less than that observed for any of the lipid labels because of dilution effects, but equivalent levels of incorporation were achieved by increasing the label concentration. Electron spin resonance spectra of a nitroxide-containing phospholipid analogue covalently attached to reconstituted cytochrome c oxidase exhibited a large motion-restricted component, which is characteristic of spin-labeled lipids in contact with the hydrophobic surfaces of membrane proteins. The line shape and splittings were similar for covalently attached label and label free to diffuse and contact the protein molecules in the bilayer, providing independent evidence that the coupling occurs at the protein-lipid interface. The distribution of the benzaldehyde reagents attached to the polypeptide components of cytochrome c oxidase was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The labeling pattern observed for the lipid analogues was not affected by the presence of the nitroxide moiety on the acyl chains but was dependent on the molar ratio of labeling reagent to protein.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献