全文获取类型
收费全文 | 20060篇 |
免费 | 1518篇 |
国内免费 | 482篇 |
出版年
2023年 | 119篇 |
2022年 | 240篇 |
2021年 | 446篇 |
2020年 | 311篇 |
2019年 | 366篇 |
2018年 | 434篇 |
2017年 | 364篇 |
2016年 | 498篇 |
2015年 | 767篇 |
2014年 | 864篇 |
2013年 | 1159篇 |
2012年 | 1296篇 |
2011年 | 1217篇 |
2010年 | 754篇 |
2009年 | 629篇 |
2008年 | 876篇 |
2007年 | 882篇 |
2006年 | 821篇 |
2005年 | 750篇 |
2004年 | 672篇 |
2003年 | 675篇 |
2002年 | 620篇 |
2001年 | 517篇 |
2000年 | 522篇 |
1999年 | 444篇 |
1998年 | 198篇 |
1997年 | 174篇 |
1996年 | 152篇 |
1995年 | 133篇 |
1994年 | 160篇 |
1993年 | 131篇 |
1992年 | 338篇 |
1991年 | 305篇 |
1990年 | 290篇 |
1989年 | 297篇 |
1988年 | 244篇 |
1987年 | 254篇 |
1986年 | 228篇 |
1985年 | 253篇 |
1984年 | 213篇 |
1983年 | 218篇 |
1982年 | 155篇 |
1981年 | 127篇 |
1979年 | 188篇 |
1978年 | 125篇 |
1977年 | 175篇 |
1976年 | 123篇 |
1975年 | 133篇 |
1974年 | 147篇 |
1973年 | 126篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Stage-dependent changes in localization of a germ cell-specific lamin during mammalian spermatogenesis 总被引:1,自引:0,他引:1
We had earlier identified a 110/120-kDa protein specific to nuclear matrix of rat pachytene spermatocytes (Behal, A., Prakash, K., and Rao, M.R.S. (1987) J. Biol. Chem. 262, 10898-10902). This protein is now shown to be a disulfide-linked homodimer of a 60-kDa polypeptide. Indirect immunofluorescence and Western blot analyses using anti-120-kDa polyclonal antibodies have shown that this protein is a component of the pore-complex lamina structure of spermatogonia. As germ cells enter meiotic prophase and the lamina structure disassembles, this polypeptide is redistributed in the nucleus and can be isolated as a component of synaptonemal complexes. Following meiotic division, this 60-kDa protein is relocalized in the lamina, then representing the sole major component of the lamina structure of round spermatids. The identity of the 60-kDa protein in the pore-complex lamina fraction and synaptonemal complexes was further confirmed by two-dimensional analysis of iodinated tryptic peptides. Such an analysis has also shown that the germ cell-specific 60-kDa protein is related but not identical to somatic lamin B. 相似文献
52.
Spectroscopic data and conformational energy calculations are reported for eight oligosaccharides from ovarian cyst mucins and from human milk, the nonreducing terminals of which have fucose (α1 → 2)galactose linked either (β1 → 3) (type I) or (β1 → 4)(type II) to N-acetylglucosamine or in (β1 → 3) linkage to galactosaminitol. The fully assigned proton nmr spectra are reported along with nuclear Overhauser enhancement (NOE) data. Amide proton coupling constants and vacuum-uv CD spectra provide information on the amide plane orientation and amide environment. Our results imply that the fucosidic dihedral angles are similar for all three cases and that the substantial differences in the chemical shifts of the fucosyl protons of type I, type II, and 3-ol chains result from different perturbations by the amide group of the residue to which the β-galactose is linked. Stereopair diagrams of conformational models for both type I and II H chains are presented that are consistent with NOE, coupling constants, conformational energy calculations, and the CD data. While the temperature dependence of the observed NOE of penta- and hexasaccharides indicates that their rotational correlation times are strongly temperature dependent, we conclude that the conformations are essentially independent of temperature. 相似文献
53.
54.
55.
56.
A retrovirus carrying the polyomavirus middle T gene induces acute thrombocythemic myeloproliferative disease in mice. 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A Fusco G Portella M Grieco G Tajana G Di Minno N Polli A Pinto 《Journal of virology》1988,62(1):361-365
Mice inoculated with an artificially constructed retrovirus carrying the middle T gene of polyomavirus develop acute myeloproliferative disease with severe thrombotic and hemorrhagic disorder and impaired platelet function. The megakaryocytic lineage appears to be a target for polyoma-murine leukemia virus infection and middle T gene expression. This newly described disease represents a unique model system for studying disorders of the megakaryocytic lineage. 相似文献
57.
58.
A. Negeswara Rao 《Nordic Journal of Botany》1990,10(2):161-162
A new species of Sarcoglyphis, S. arunachalensis, from Arunachal Pradesh, India is described. 相似文献
59.
Sudha Rao Gopalakrishna Kamath Gururaj Maralihalli Anil S. Bhagwat 《Photosynthesis research》1987,12(2):155-164
The -aminolevulinic acid dehydratase activity was irreversibly inactivated by irradiation of the enzyme in presence of flavin mononucleotide. The loss of enzyme activity was dependent on time of irradiation, concentration of FMN and intensity of irradiance. It required oxygen and was markedly enhanced in heavy water. The presence of levulinic acid (a competitive inhibitor of -ALAD) during irradiation prevented the inactivation considerably indicating photooxidative damage at or near the active site. Superoxide dismutase, sodium benzoate and sodium formate offered no protection, but singlet oxygen quenchers like azide and tryptophan were effective. NADH, electron donor to excited flavins, also prevented the loss of enzyme activity. These results indicate that singlet oxygen produced by light absorption of FMN was responsible for the photooxidative inhibition of the enzyme.Abbreviations ALAD
-aminolevulinic acid dehydratase
- FMN
flavin mononucleotide
- O2
-
superoxide
- H2O2
hydrogen peroxide
- 102
singlet oxygen
- LA
levulinic acid
- PBG
porphobilinogen
- BSA
bovine serum albumin
- BME
2-mercaptoethanol
- SOD
superoxide dismutase
- pHMB
para-hydroxymercuribenzoate
- DTT
dithiothreitol
- FAD
flavin adenine dinucleotide
- NADH
nicotinamide adenine dinucleotide 相似文献
60.
Proteolytic cleavage of IgG and other protein substrates by Dirofilaria immitis microfilarial enzymes 总被引:1,自引:0,他引:1
Proteases were detected in aqueous extracts of Dirofilaria immitis microfilariae. Enzymes within the extract were capable of hydrolyzing Azocoll, a general protease substrate, at pH's 7, 8, and 9. Sensitivities to a variety of protease inhibitors indicated that multiple azocollytic enzymes were present in the extract, most prominent of which appear to belong to the serine class of proteases. By incorporating various substrates into the matrices of polyacrylamide gels, 2 SDS-resistant, mercaptoethanol-sensitive proteases in the MF extract were identified at 22 and 76 kDa. These proteases showed differential abilities to digest casein, fibrinogen, hemoglobin, and IgG. The MF extract hydrolyzed radiolabeled IgG into 8-10-kDa fragments following a 20-hr incubation. A similar degree of digestion was observed in 2 hr when viable microfilariae were used. The potential significance of these proteases in the evasion of host effector mechanisms is discussed. 相似文献