全文获取类型
收费全文 | 3334篇 |
免费 | 206篇 |
专业分类
3540篇 |
出版年
2022年 | 30篇 |
2021年 | 48篇 |
2020年 | 22篇 |
2019年 | 41篇 |
2018年 | 62篇 |
2017年 | 47篇 |
2016年 | 73篇 |
2015年 | 94篇 |
2014年 | 118篇 |
2013年 | 216篇 |
2012年 | 206篇 |
2011年 | 199篇 |
2010年 | 124篇 |
2009年 | 120篇 |
2008年 | 197篇 |
2007年 | 185篇 |
2006年 | 168篇 |
2005年 | 183篇 |
2004年 | 175篇 |
2003年 | 147篇 |
2002年 | 145篇 |
2001年 | 90篇 |
2000年 | 77篇 |
1999年 | 74篇 |
1998年 | 42篇 |
1997年 | 23篇 |
1996年 | 30篇 |
1995年 | 34篇 |
1994年 | 26篇 |
1993年 | 28篇 |
1992年 | 42篇 |
1991年 | 52篇 |
1990年 | 44篇 |
1989年 | 54篇 |
1988年 | 39篇 |
1987年 | 35篇 |
1986年 | 21篇 |
1985年 | 31篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1975年 | 10篇 |
1974年 | 10篇 |
1969年 | 9篇 |
排序方式: 共有3540条查询结果,搜索用时 0 毫秒
81.
82.
Expression of major myelin glycoprotein P0 by P0 cDNA transfection into C6 glioma cells promoted homophilic cell adhesion of the cells. After the dissociated cells were incubated for various times, the number of particles at each time point was measured. The total number of particles decreased to 24% in 60 min for transformant (C6P0) cells, in contrast to only 68% for control (C6P0') cells. To confirm the homophilic mechanism of adhesion, mixed-cell aggregation experiments were performed. Among the four synthetic peptides corresponding to a part of the P0 sequence used, only peptide 3 (residues 90-96), which contained a carbohydrate attaching site, caused considerable inhibition of cell aggregation (approximately 50%). In addition, the glycopeptide (residues 91-95) obtained from bovine P0 markedly inhibited cell aggregation (by approximately 85%). 相似文献
83.
A Yamamoto T Kaji K Tomoo T Ishida M Inoue M Murata K Kitamura 《Journal of molecular biology》1992,227(3):942-944
Cathepsin B from bovine spleen has been purified and crystallized as a complex with a specific inhibitor CA074 [N-(L-3-trans-propylcarbamoyloxirane-2-carbonyl)-L- isoleucyl-L-proline], using the hanging-drop method. The complex crystals obtained from 50 mM-citrate buffer (pH 3.5) belong to the tetragonal space group P4(1) (or P4(3)) with a = 73.06 A and c = 141.59 A, and diffract beyond 2.2 A resolution. There are two complex molecules per asymmetric unit giving a packing density of 3.37 A3/Da and indicating a high solvent content of 63.5%. 相似文献
84.
A Naito Y Kitamura H Yoshikura 《Biochemical and biophysical research communications》1991,174(1):305-312
Relative orientation of recombination substrates, neo gene, strongly influenced homologous recombination events in a bovine papillomavirus shuttle vector. Between direct repeats, recombination occurred at a high frequency while between inverted repeats, it was rare. Double strand break near the mutation site increased the recombination frequency between inverted repeats but not between direct repeats. Formation of long heteroduplex as a recombination intermediate may explain this apparently paradoxical phenomenon. 相似文献
85.
Dissociation of hydroxylase and lyase activities by site-directed mutagenesis of the rat P45017 alpha. 总被引:1,自引:0,他引:1
Site-directed mutagenesis of the arginine-rich region within the putative active site of the rat testicular P45017 alpha (17 alpha-hydroxylase cytochrome P-450, the product of P450XVII gene) was performed to identify specific amino acids that contribute to either the hydroxylase or lyase activities catalyzed by this enzyme. The conversion of Arg346 to alanine differentially abolished lyase activity without affecting hydroxylase activity, resulting in an accumulation of the 17 alpha-hydroxylated intermediate, and partial lyase activity was recovered by conversion of this mutant to Lys346. Similar results were obtained with the conversion of Arg357 to alanine, although this mutant also diminished hydroxylase activity, and full lyase and hydroxylase activities were recovered with a lysine in this position. Major reductions in hydroxylase activity were apparent with the conversion of Arg363 to Ala, and this inhibition was reversed by a lysine at position 363. In contrast, differential effects were not observed with the mutants Arg361 Ala, Arg361 Lys, or Tyr334Phe. Both mutations at the Arg361 position resulted in a total loss of hydroxylase and lyase activities, and mutation at the Tyr334 position had no effect on either activity. The identification of specific amino acids that are essential for either the hydroxylase or lyase reaction indicates that the steroid substrate-protein interaction changes during the course of the two consecutive reactions and reveals the potential for separation of the two activities by chemical and biological modulators within the active site region of the P45017 alpha. 相似文献
86.
87.
88.
J S Allen K Matsunaga T Nakamura F Kitamura T Furukawa S S Hacisalihzade V M Sarich L Stark 《Human biology; an international record of research》1990,62(3):337-352
Smooth-pursuit eye-tracking dysfunction is a putative genetic trait marker for schizophrenia. In this study 88 Japanese schizophrenics from Kyushu and Okinawa were examined for the marker using precise high-resolution instrumentation: 76% of the schizophrenics from Kyushu and 89% of those from Okinawa had pursuit dysfunction. The presence of the culture-neutral smooth-pursuit marker for schizophrenia in Japan demonstrates that the etic concept "schizophrenia" is cross-culturally valid. Furthermore, the ubiquity of the marker in biologically and culturally diverse populations may indicate a limit on the extent of meaningful heterogeneity likely to be discovered within the condition. 相似文献
89.
Some common properties of lectins from marine algae 总被引:10,自引:1,他引:9
Twelve kinds of lectins isolated from four species of marine algae, Boodlea coacta (Chlorophyta) and Hypnea japonica, Carpopeltis flabellata and Solieria robusta (Rhodophyta), were compared for their chemical and biological properties. These lectins were proteins or glycoproteins, similar to terrestrial plant lectins. However, unlike most terrestrial plant lectins, they had a small molecular size (4,200 to 25,000 daltons), were mostly monomeric, and had no affinity for monosaccharides. They strongly agglutinated trypsin-treated rabbit erythrocytes, and their activities commonly were inhibited by glycoproteins bearing N-glycans. From hemagglutination-inhibition tests with various glycoproteins and related compounds, it was found that B. coacta lectins recognize high-mannose N-glycans; H. japonica lectins complex N-glycans, and C. flabellata and S. robusta lectins recognize both types of N-glycans. 相似文献
90.
H Shimizu H Tsuchie H Honma K Yoshida T Tsuruoka H Ushijima T Kitamura 《Japanese journal of medical science & biology》1990,43(3):75-87
The effect of N-(3-phenyl-2-propenyl)-1-deoxynojirimycin (ppDNM) on the lectin binding to HIV-1 glycoprotein was analyzed by using biotinylated lectins of various sugar specificities as probes. ppDNM potentially inhibited HIV-1-induced syncytium formation and viral infectivity of HIV-1 without cytotoxicity. The lectin binding assay showed that ppDNM treatment reduced Con A binding to gp120 of HIV-1. 相似文献