全文获取类型
收费全文 | 13352篇 |
免费 | 867篇 |
国内免费 | 2篇 |
专业分类
14221篇 |
出版年
2022年 | 81篇 |
2021年 | 138篇 |
2019年 | 92篇 |
2018年 | 126篇 |
2017年 | 107篇 |
2016年 | 195篇 |
2015年 | 312篇 |
2014年 | 341篇 |
2013年 | 778篇 |
2012年 | 636篇 |
2011年 | 593篇 |
2010年 | 325篇 |
2009年 | 369篇 |
2008年 | 575篇 |
2007年 | 563篇 |
2006年 | 567篇 |
2005年 | 570篇 |
2004年 | 601篇 |
2003年 | 578篇 |
2002年 | 534篇 |
2001年 | 542篇 |
2000年 | 528篇 |
1999年 | 436篇 |
1998年 | 167篇 |
1997年 | 154篇 |
1996年 | 139篇 |
1995年 | 108篇 |
1994年 | 123篇 |
1993年 | 125篇 |
1992年 | 328篇 |
1991年 | 305篇 |
1990年 | 308篇 |
1989年 | 282篇 |
1988年 | 238篇 |
1987年 | 238篇 |
1986年 | 211篇 |
1985年 | 181篇 |
1984年 | 136篇 |
1983年 | 131篇 |
1982年 | 114篇 |
1981年 | 107篇 |
1980年 | 89篇 |
1979年 | 113篇 |
1978年 | 91篇 |
1977年 | 80篇 |
1976年 | 81篇 |
1975年 | 71篇 |
1974年 | 86篇 |
1973年 | 93篇 |
1971年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Native oxymyoglobin (MbO2) was isolated from red muscle of G. japonicus by chromatographic separation from metmyoglobin (metMb) on DEAE-cellulose and the amino acid sequence of the major chain was determined with the aid of sequence homology with that of G. australis. It was shown to differ in amino acid sequence from that of G. australis by 10 replacements, to be acetylated at the amino terminus and to contain glutamine at the distal (E7) residue. It was also shown to have a spectrum very similar to that of mammalian MbO2. However, the pH-dependence for the autoxidation of MbO2 was seen to be quite different from that of sperm whale (Physeter catodon) MbO2. Although the sequence homology between sperm whale and G. japonicus myoglobins is about 40%, their hydropathy profiles were very similar, indicating that they have a similar geometry in their globin folding. 相似文献
72.
Purification and characterization of an inhibitor of the cysteine protease from the hemolymph of Sarcophaga peregrina larvae 总被引:2,自引:0,他引:2
The hemolymph of Sarcophaga peregrina (flesh fly) larvae was found to contain multiple inhibitors of hemocyte cysteine protease. One of them, named sarcocystatin A, was purified and found to be a mixture of the components sarcocystatin A alpha and A beta in a molar ratio of 2:1. These components can exist in either the associated or dissociated form. The apparent heterogeneity of the protease inhibitors in the hemolymph was found to be partly due to association of sarcocystatin A alpha and A beta. 相似文献
73.
74.
Generation of activated killer (AK) cells by recombinant interleukin 2 (rIL 2) in collaboration with interferon-gamma (IFN-gamma) 总被引:12,自引:0,他引:12
K Itoh K Shiiba Y Shimizu R Suzuki K Kumagai 《Journal of immunology (Baltimore, Md. : 1950)》1985,134(5):3124-3129
Activation of human peripheral blood mononuclear cells (PBMC) by interleukin 2 (IL 2) and the role of interferon-gamma (IFN-gamma) in the IL 2-induced activation were investigated. Activated killer (AK) cells against NK-resistant tumor cell lines were induced in the medium containing recombinant IL 2 (rIL 2) and autologous serum without any other stimulating agents. AK activity was induced by doses of rIL 2 as low as 3 U/ml, and reached a maximum at 10(3) U/ml. Incubation of PBMC with rIL 2 resulted in IFN-gamma production and augmented NK activity after 1 day of culture, and in induction of AK cells and proliferative response after 2 days of culture. These results suggested that endogenous IFN-gamma was required for rIL 2-induction of AK cells and proliferative response. To prove this, PBMC were cultured with rIL 2 and rIFN-gamma or were pretreated with rIFN-gamma before culture with rIL 2. Both rIFN-gamma treatments of PBMC augmented rIL 2-induced AK activity and proliferative response. rIL 2-induced IFN-gamma production was also enhanced by the rIFN-gamma pretreatment of PBMC. The addition of anti-IFN-gamma antibody to rIL 2 cultures abrogated the rIL 2-induced NK augmentation, AK generation, and proliferative response in proportion to the decreased amounts of endogenous IFN-gamma detectable in culture. rIFN-gamma and/or rIL 2 cultures of PBMC increased Tac antigen expression on cell surfaces as measured by flow cytometry. Enhanced Tac expression by rIL 2 was abrogated by adding anti-IFN-gamma antibody. These data indicate that: 1) AK generation and IFN-gamma production are mediated by IL 2, and 2) IFN-gamma production may be required for IL 2 induction of AK cells and proliferative response. These finding are consistent with the hypothesis that AK generation involves a collaboration between IL 2 and IFN-gamma, in which IL 2 stimulates PBMC to produce IFN-gamma, which in turn acts as a differentiation signal that may be involved in the IL 2-initiated AK generation and proliferative response. 相似文献
75.
On the Role of Stored mRNA in Protein Synthesis in Embryonic Axes of Germinating Vigna unguiculata Seeds 总被引:1,自引:1,他引:0 下载免费PDF全文
Polyadenylated (poly A+) RNAs were prepared from both dry and incubated embryonic axes of Vigna unguiculata seeds and were translated by a wheat germ translation system. Analysis with gel electrophoresis and fluorography showed that translation products of poly A+ RNA from dry embryonic axes were nearly the same as those from 2-hour incubated axes but somewhat different from those of 4- to 24-hour incubated axes, and that translation products remained almost unchanged between the 4- and 24-hour stages of postimbibition. The results indicate the possibility that the stored mRNA (poly A+ RNA from dry embryonic axes) directs the protein synthesis required for early stages of germination. This is supported by comparison of the in vitro translation products of poly A+ RNAs with those of polysomal RNAs. Experiments with α-amanitin, a specific inhibitor of RNA polymerase II (J. Jendrisak 1980 J Biol Chem 255: 8529-8533), suggested that the synthesis of some of the stored mRNA species is resumed as early as 4 hours after the onset of imbibition. 相似文献
76.
Identification of the active site in penicillin-binding protein 3 of Escherichia coli. 总被引:5,自引:5,他引:0 下载免费PDF全文
We report the sequence of the active site tryptic peptide of penicillin-binding protein 3 from Escherichia coli. Purified penicillin-binding protein 3 was labeled with [14C]penicillin G and digested with trypsin, and the resulting radioactive peptides were isolated by a combination of gel filtration and high-pressure liquid chromatography. The major radioactive peak from high-pressure liquid chromatography was sequenced, and the peptide Thr-Ile-Thr-Asp-Val-Phe-Glu-Pro-Gly-Ser-Thr-Val-Lys, which comprises residues 298 to 310 in the amino acid sequence, was identified. This sequence is compared with the active site sequences from other penicillin-binding proteins and beta-lactamases. 相似文献
77.
Fimbriae from the oral anaerobe Bacteroides gingivalis: physical, chemical, and immunological properties. 总被引:15,自引:3,他引:12 下载免费PDF全文
F Yoshimura T Takasawa M Yoneyama T Yamaguchi H Shiokawa T Suzuki 《Journal of bacteriology》1985,163(2):730-734
Circular dichroism spectra indicated the predominance of beta-sheet structure in Bacteroides gingivalis fimbriae regardless of the presence of sodium dodecyl sulfate. By using a computer program, the alpha-helix, beta-sheet, and beta-turn contents and the remainder were estimated to be 0, 55, 18, and 27%, respectively, judging from the circular dichroism spectra of the fimbriae. Heating for 5 min at 100 degrees C in sodium dodecyl sulfate was necessary to denature the fimbriae into their constituent protein (fimbrilin) monomers with a reduced content of beta-sheet structure. The amino-terminal amino acid sequence of the fimbrilin was different from partial or complete amino acid sequences of fimbrilins so far determined from Bacteroides nodosus, which falls into the same nonfermentative species of the genus Bacteroides as B. gingivalis, and from various other bacteria. Fimbrilin monomers had an isoelectric point of 6.0. Examination of antibodies against fimbriae and sodium dodecyl sulfate-denatured fimbrilin by enzyme-linked immunosorbent assay reinforced a previous notion (F. Yoshimura, K. Takahashi, Y. Nodasaka, and T. Suzuki, J. Bacteriol. 160:949-957, 1984) that different sets of antigenic determinants seemed to be exposed on their surfaces. 相似文献
78.
Nucleotide sequence of the extracellular glucoamylase gene STA1 in the yeast Saccharomyces diastaticus. 总被引:13,自引:6,他引:7 下载免费PDF全文
The complete nucleotide sequence of the extracellular glucoamylase gene STA1 from the yeast Saccharomyces diastaticus has been determined. A single open reading frame codes for a 778-amino-acid protein which contains 13 potential N-glycosylation sites. In the 5'- and 3'-flanking regions of the gene, there are striking sequence homologies to the corresponding regions of ADH1 for alcohol dehydrogenase and MAT alpha 2 for mating type control in the yeast Saccharomyces cerevisiae. The putative precursor begins with a hydrophobic segment that presumably acts as a signal sequence for secretion. The presumptive signal sequence showed a significant homology to that of Bacillus subtilis alpha-amylase precursor. The next segment, of ca. 320 amino acids, contains a threonine-rich tract in which direct repeat sequences of 35 amino acids exist, and is bordered by a pair of basic amino acid residues (Lys-Lys) which may be a proteolytic processing signal. The carboxy-terminal half of the precursor is a presumptive glucoamylase which contains several peptide segments showing a high degree of homology with alpha-amylases from widely diverse organisms including a procaryote (B. subtilis) and eucaryotes (Aspergillus oryzae and mouse). Analysis of both the nucleotide sequence of the STA1 gene and the amino acid composition of the purified glucoamylase suggested that the putative precursor is processed to yield subunits H and Y of mature enzyme by both trypsin-like and chymotrypsin-like cleavages. 相似文献
79.
Amino acid sequence of polypeptide chain IIB of extracellular hemoglobin from the polychaete Tylorrhynchus heterochaetus 总被引:1,自引:0,他引:1
T Suzuki H Yasunaga T Furukohri K Nakamura T Gotoh 《The Journal of biological chemistry》1985,260(21):11481-11487
The giant extracellular hemoglobin from the polychaete Tylorrhynchus heterochaetus consists of two types of subunits: a "monomeric" chain (chain I) and a disulfide-bonded trimer of chains IIA, IIB, and IIC. The complete amino acid sequence of chain IIB was determined. This chain has 148 amino acid residues and a molecular weight of 17,236 including a heme group. Of the residues in chain IIB, 74 (50%) and 34 (30%) were found to be identical with those in the corresponding positions in Tylorrhynchus chains IIC and I, respectively (Suzuki, T., Furukohri, T., and Gotoh, T. (1985) J. Biol. Chem. 260, 3145-3154). Marked differences were found between the chains of Tylorrhynchus and Lumbricus in the COOH-terminal regions. Significant differences were predicted between the monomeric chain I and the "trimeric" chains (IIB and IIC) in the hydropathy profiles and alpha-helical contents. 相似文献
80.
Dr. Shintaro Suzuki 《Cell and tissue research》1985,241(3):539-543
Summary In the thyroid follicles of species of cyclostomes, a hagfish and a lamprey, the distribution of stable iodine was examined by electron-probe X-ray microanalysis. A high concentration of stable iodine, heterogeneously distributed, was observed in the follicular cells of hagfish thyroid follicles. In the lamprey a low concentration of iodine was seen in the follicular lumina. The relative values for stable iodine determined in this way corresponded to values obtained by a chemical analytical method. 相似文献