全文获取类型
收费全文 | 6106篇 |
免费 | 422篇 |
出版年
2021年 | 49篇 |
2019年 | 57篇 |
2018年 | 61篇 |
2017年 | 60篇 |
2016年 | 87篇 |
2015年 | 108篇 |
2014年 | 130篇 |
2013年 | 324篇 |
2012年 | 297篇 |
2011年 | 215篇 |
2010年 | 145篇 |
2009年 | 136篇 |
2008年 | 287篇 |
2007年 | 287篇 |
2006年 | 290篇 |
2005年 | 254篇 |
2004年 | 289篇 |
2003年 | 277篇 |
2002年 | 284篇 |
2001年 | 240篇 |
2000年 | 222篇 |
1999年 | 184篇 |
1998年 | 80篇 |
1997年 | 67篇 |
1996年 | 50篇 |
1995年 | 45篇 |
1994年 | 59篇 |
1993年 | 60篇 |
1992年 | 144篇 |
1991年 | 115篇 |
1990年 | 138篇 |
1989年 | 143篇 |
1988年 | 117篇 |
1987年 | 106篇 |
1986年 | 101篇 |
1985年 | 87篇 |
1984年 | 83篇 |
1983年 | 63篇 |
1982年 | 60篇 |
1981年 | 51篇 |
1980年 | 41篇 |
1979年 | 72篇 |
1978年 | 55篇 |
1977年 | 50篇 |
1976年 | 36篇 |
1975年 | 44篇 |
1974年 | 44篇 |
1973年 | 38篇 |
1972年 | 45篇 |
1970年 | 34篇 |
排序方式: 共有6528条查询结果,搜索用时 31 毫秒
951.
An enzyme in Pseudomonas diminuta showed hydrolyzing activity of a benzhydrylamide ( = diphenylmethylamide) bond in S-benzylcysteinylglycine benzhydrylamide. The enzyme was purified 225-fold by precipitation with ammonium sulfate, and column chromatography with ECTEOLA-cellulose, DEAE-cellulose and hydroxyapatite. It showed an optimum pH of 6 to 8 and it was markedly inhibited by Hg2 + or p-chloromercuribenzoate. The preparation was more specific against S-benzylcysteinylglycine benzhydrylamide than other substrates tested. 相似文献
952.
953.
Human observers perceive illusory rotations after the disappearance of circularly repeating patches containing dark-to-light luminance. This afterimage rotation is a very powerful phenomenon, but little is known about the mechanisms underlying it. Here, we use a computational model to show that the afterimage rotation can be explained by a combination of fast light adaptation and the physiological architecture of the early visual system, consisting of ON- and OFF-type visual pathways. In this retinal ON/OFF model, the afterimage rotation appeared as a rotation of focus lines of retinal ON/OFF responses. Focus lines rotated clockwise on a light background, but counterclockwise on a dark background. These findings were consistent with the results of psychophysical experiments, which were also performed by us. Additionally, the velocity of the afterimage rotation was comparable with that observed in our psychophysical experiments. These results suggest that the early visual system (including the retina) is responsible for the generation of the afterimage rotation, and that this illusory rotation may be systematically misinterpreted by our high-level visual system. 相似文献
954.
H. Furuya Yoh-ji Kukita Sukehisa Nagano Yasuyoshi Sakai Yoriaki Yamashita Hidenao Fukuyama Yuichiro Inatomi Yutaka Saito Ryoko Koike Shoji Tsuji Yasuyuki Fukumaki Kenshi Hayashi Takuro Kobayashi 《Human genetics》1997,100(3-4):450-456
We examined galactosylceramidase (GALC) cDNA in four Japanese patients with adult onset globoid cell leukodystrophy (Krabbe
disease; AO-GLD) by polymerase chain reaction/single-strand conformation polymorphism (PCR-SSCP) analysis, subsequent sequence
determination, and restriction enzyme digestion of PCR products. Initial symptoms were the onset of slowly progressive spastic
paraplegia from the middle of the second decade, and all patients had diminished GALC activity in their leukocytes. We identified
three missense mutations (I66M, G270D, L618S) and one exon-6 skipping (535– 573del). Two of the patients had only the I66M
mutant mRNA, and one only the G270D mutant mRNA. The fourth patient carried a compound heterozygous mutation of 535–573del
and L618S. To determine the enzymatic activities produced by these mutations, we constructed mutated GALC cDNAs and expressed
them in COS-1 cells. Three mutations, viz., G270D, L618S, and exon-6 skipping (535–573del), produced diminished GALC activity
as expected. The I66M mutation in the wild-type GALC cDNA(I289) had normal activity, but when this mutation and the V289 polymorphism
were introduced into the same allele, it had decreased activity. Thus, the combination of a unique mutation and polymorphism
causes conformational change in the GALC enzyme, resulting in low enzymatic activity. AO-GLD mutations, including those found
here, are located in the N-terminus (I66M, G270D, 535–573del) or C-terminus (L618S) of the GALC enzyme, whereas the reported
mutations in the infantile form (IF-GLD) are in the central domain. This difference in mutation sites may affect the clinical
features of GLD.
Received: 4 February 1997 / Accepted: 28 April 1997 相似文献
955.
K Hirano M Fukuta T Adachi K Hayashi M Sugiura Y Mori K Toyoshi 《Biochemical and biophysical research communications》1985,129(1):89-94
The syntheses of copper, zinc-superoxide dismutase (Cu,Zn-SOD) and manganese-superoxide dismutase (Mn-SOD) in vitro were studied. Both Cu,Zn-SOD and Mn-SOD were preferentially synthesized by free polysomes. Mn-SOD was synthesized as a large precursor (26,000 daltons), which was processed to the mature size (22,500 daltons) by in vitro incubation with a rat liver mitochondrial fraction. On the other hand, Cu,Zn-SOD was synthesized as the mature size product. It was shown that Cu,Zn-SOD and Mn-SOD synthesized in vitro represented 0.018% and 0.016% of the total translation products of free polysomes, respectively. 相似文献
956.
Kazuya Hayashi Masaru Terada Koya Mogi 《Bioscience, biotechnology, and biochemistry》2013,77(4):627-637
Some enzymatic properties of purified alkaline proteinase from Aspergillus sojae were investigated. The optimum pH for casein digestion was 11.0. The enzyme activity was almost completely lost at 60°C within ten minutes. At low temperature, the enzyme was highly stable at the range of pH 4.5 to 10.0. At 50°C, the most stable pH was around 6.0. None of metallic ions tested promoted the activity, but Hg2+ showed a remarkable inhibition. The Hg2+-treatment seemed to cause a large unfolding of the enzyme molecule. The enzyme was inhibited by potato inhibitor and a number of animal sera. Metal chelating reagents and sulfhydryl reagents tested had no effect on the activity, but DFP caused a marked inhibition. The sensitivity to DFP of the enzyme was about 1/300 of that of α-chymotrypsin. The enzyme was inhibited neither by TPCK nor by TLCK. As the result it was assumed that the structure of the active site of the enzyme is fairly different from that of trypsin, or of chymotrypsin. 相似文献
957.
958.
The presence of a human hepatocyte growth factor (hHGF)-like DNA-synthesis promoter in platelet-poor serum of mice with liver injury was examined. Activity of the serum for stimulating DNA synthesis in cultured rat hepatocytes was low in untreated or vehicle-treated mice, but markedly increased 24 h after carbon tetrachloride administration and then dropped to normal levels prior to the peak of liver DNA synthesis. The effect of the serum was additive with the maximal effects of mouse and human epidermal growth factors, but not with that of hHGF. The growth-stimulating factor in the mouse serum, like hHGF, had affinity for heparin and was heat-labile. These results indicate that the level of a serum hHGF-like hepatocyte growth factor increased in mice treated with carbon tetrachloride prior to liver regeneration. 相似文献
959.
Gramicidin A (GA) in absolute ethanol (AE) at concentrations (c), below 0.01 g/100 ml, failed to sediment but sedimented normally in ethanol-water mixtures (EWM). The apparent partial specific volume, φ, increased on decreasing c in AE but no increase was observed in EWM, where it remained around φ=0.83. These results indicate that GA solutions consist of an equilibrium system containing species differing in volume. This behavior may help to explain the biological mechanism of action of GA. 相似文献
960.
Masuko Suzuki Yoshiro Hayashi Sumio Arai Katsuo Kumagai 《Microbiology and immunology》1976,20(3):191-196
Cells of Mycoplasma pneumoniae Mac strain were fractionated into acetone-soluble and insoluble fractions. Acetone-insoluble fractions were digested with pronase and further purified by chromatography on Sephadex G-75, yielding three water-soluble fractions which were free from lipid and consisted mainly of polysaccharide-protein complex. All these water-soluble fractions possessed eliciting antigenicity to delayed hypersensitivity for M. pneumoniae as measured by skin reactions and macrophage migration inhibition tests, but not to complement-fixing antibodies. In contrast, the acetone-soluble fraction was reactive with the complement-fixing antibodies but not for the delayed hypersensitivity. 相似文献