全文获取类型
收费全文 | 2269篇 |
免费 | 125篇 |
专业分类
2394篇 |
出版年
2022年 | 14篇 |
2021年 | 37篇 |
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 30篇 |
2017年 | 35篇 |
2016年 | 49篇 |
2015年 | 86篇 |
2014年 | 81篇 |
2013年 | 149篇 |
2012年 | 144篇 |
2011年 | 123篇 |
2010年 | 74篇 |
2009年 | 103篇 |
2008年 | 120篇 |
2007年 | 128篇 |
2006年 | 148篇 |
2005年 | 118篇 |
2004年 | 131篇 |
2003年 | 110篇 |
2002年 | 117篇 |
2001年 | 35篇 |
2000年 | 37篇 |
1999年 | 38篇 |
1998年 | 20篇 |
1997年 | 22篇 |
1996年 | 19篇 |
1995年 | 9篇 |
1994年 | 22篇 |
1993年 | 12篇 |
1992年 | 26篇 |
1991年 | 23篇 |
1990年 | 24篇 |
1989年 | 18篇 |
1988年 | 18篇 |
1987年 | 20篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1976年 | 19篇 |
1975年 | 12篇 |
1974年 | 15篇 |
1973年 | 10篇 |
1972年 | 10篇 |
1970年 | 9篇 |
排序方式: 共有2394条查询结果,搜索用时 31 毫秒
21.
Adenosine deaminase (EC 3.5.4.4) was found to occur in the extract of Azotobacter vinelandii, strain 0, and purified by heating at 65°C, fractionation with ammonium sulfate, DEAE-cellulose chromatography and gel filtration on Sephadex G-150. Purified adenosine deaminase was effectively stabilized by the addition of ethylene glycol. The molecular weight of the enzyme was estimated to be 66,000 by gel filtration on Sephadex G-150. The enzyme specifically attacked adenosine and 2-deoxyadenosine to the same extent, and formycin A to a lesser extent. The pH optimum of the enzyme was observed at pH 7.2. Double reciprocal plot of initial velocity versus adenosine concentration was concave upward, and Hill interaction coefficient was calculated to be 1.5, suggesting the allosteric binding of the substrate. ATP inhibited adenosine deaminase in an allosteric manner, whereas other nucleotides were without effect. The physiological significance of the enzyme was discussed in relation to salvage pathway of purine nucleotides. 相似文献
22.
Treatment of rats with pyrazole elevated the hepatic microsomal dimethylnitrosamine demethylase activity (DMNd) by several fold. Methylethylnitrosamine demethylase activity was also increased by pyrazole, but some classical monooxygenase activities were not induced. The treatment induced a new protein species which has an apparent molecular weight of 52,000 dal and is believed to be a cytochrome P-450 isozyme. The involvement of a hemoprotein in the pyrazole-induced DMNd was demonstrated in an experiment with CoCl2 which decreased both the microsomal cytochrome P-450 content and DMNd. The induced enzyme with a single Km value of 0.061 mM and Vmax of 12.1 nmol/min/mg is probably the most efficient enzyme known to metabolize nitrosamines. NADPH-cytochrome P-450 reductase was also demonstrated to be an essential component enzyme of the DMNd. These results further substantiate the idea that the P-450-containing monooxygenase is responsible for the metabolism of dimethylnitrosamine in both the control and pyrazole induced microsomes. 相似文献
23.
The differential effects of polyamines on the activity of AMP deaminase isozyme A (from rat muscle) and isozyme B (from rat liver) are reported. Polyamines activate isozyme B but inhibit isozyme A. 相似文献
24.
25.
Nakagami H Nishikawa T Tamura N Maeda A Hibino H Mochizuki M Shimosato T Moriya T Morishita R Tamai K Tomono K Kaneda Y 《Journal of cellular and molecular medicine》2012,16(7):1629-1639
We previously identified a novel angiogenic peptide, AG30, with antibacterial effects that could serve as a foundation molecule for the design of wound-healing drugs. Toward clinical application, in this study we have developed a modified version of the AG30 peptide characterized by improved antibacterial and angiogenic action, thus establishing a lead compound for a feasibility study. Because AG30 has an α-helix structure with a number of hydrophobic and cationic amino acids, we designed a modified AG30 peptide by replacing several of the amino acids. The replacement of cationic amino acids (yielding a new molecule, AG30/5C), but not hydrophobic amino acids, increased both the angiogenic and the antimicrobial properties of the peptide. AG30/5C was also effective against methicillin-resistant Staphylococcus aureus (MRSA) and antibiotic-resistant Pseudomonas aeruginosa. In a diabetic mouse wound-healing model, the topical application of AG30/5C accelerated wound healing with increased angiogenesis and attenuated MRSA infection. To facilitate the eventual clinical investigation/application of these compounds, we developed a large-scale procedure for the synthesis of AG30/5C that employed the conventional solution method and met Good Manufacturing Practice guidelines. In the evaluation of stability of this peptide in saline solution, RP-HPLC analysis revealed that AG30/5C was fairly stable under 5°C for 12 months. Therefore, we propose the use of AG30/5C as a wound-healing drug with antibacterial and angiogenic actions. 相似文献
26.
Keiichiro Morisawa Tetsuro Sugisaki Tomoyuki Kanamatsu Tsugutoshi Aoki Dr. Tetsuya Noguchi 《Neurochemical research》1989,14(2):173-177
We attempted to delineate the events leading to hypomyelination in the brain of thelittle mouse, a promising murine model of isolated growth hormone deficiency. At 20 days of age, the mutant mouse brain weighed less than its normal counterpart, and this difference in brain weight persisted. Increase in CNPase activity was found to be suppressed in the cerebrum throughout the developmental stage, but not in the other parts of the brain. Differences in cerebral DNA content between thelittle and normal mice first became apparent on the 10th day of age. Thereafter, the rate of increase in thelittle brain consistently lagged behind the normal. [3H]Thymidine incorporation into the DNA fraction in vivo on the 7th day of age, when glial cell proliferation in the normal cerebrum is most active, was approximately half that of the controls in all parts of thelittle brain. These findings indicate that the hypomyelination of the mutant cerebrum might result from reduced oligodendroglial proliferation due to growth hormone deficiency. 相似文献
27.
28.
Nakagawa T Ikehata R Uchino M Miyaji T Takano K Tomizuka N 《Microbiological research》2006,161(1):75-79
In the present study, psychrophilic yeasts, which grow on lactose as a sole carbon source at low temperature and under acidic conditions, were isolated from soil from Hokkaido, Japan. The phenotypes and sequences of 28S rDNA of the isolated strains indicated a taxonomic affiliation to Guehomyces pullulans. The isolated strains were able to grow on lactose at below 5 degrees C, and showed cold-active acid beta-galactosidase activity even at 0 degrees C and pH 4.0 in the extracellular fractions. Moreover, K(m) of beta-galactosidase activity for lactose in the extracellular fraction from strain R1 was found to be 50.5 mM at 10 degrees C, and the activity could hydrolyze lactose in milk at 10 degrees C. The findings in this study indicate the possibility that the isolated strains produce novel acid beta-galactosidases that are able to hydrolyze lactose at low temperature. 相似文献
29.
Expression, purification, and crystallization of endopolygalacturonase from a pathogenic fungus, Stereum purpureum, in Escherichia coli 总被引:1,自引:0,他引:1
Shimizu T Shibata H Araya T Nakatsu T Miyairi K Okuno T Kato H 《Protein expression and purification》2005,44(2):558-135
Endopolygalacturonases (EC 3.2.1.15) catalyze random hydrolysis of the alpha-1,4 glycosidic linkages in polygalacturonic acid, a component of pectin. Previously, we reported crystal structures of endogenously produced Stereum purprureum endopolygalacturonase I (endoPG I), both in its native form and complexed with its product, galacturonate. However, the substrate-binding mechanism of endoPG I is still unclear, because crystals have not yet been obtained with a substrate analog, or with mutant enzymes that can bind substrates. We describe here an expression system using Escherichia coli and a purification method to prepare functionally active endoPG I for such mutation and crystallographic studies. Expression in E. coli strain Origami (DE3) provided a soluble and active enzyme with proper disulfide bond formation, whereas the enzyme expressed in BL21 (DE3) was localized in inclusion bodies. A sufficient amount of recombinant endoPG I produced by Origami (DE3) was purified by a single-step procedure using cation exchange chromatography. The specific activity of recombinant endoPG I was equivalent to that of the enzyme produced by S. purpureum. Recombinant endoPG I was crystallized under the same conditions as those used for the native enzyme produced by S. purpureum. The crystals diffracted beyond 1.0 A resolution with synchrotron radiation. 相似文献
30.
The longnose filefish,Oxymonacanthus longirostris, usually lives in heterosexual pairs, the male and female swimming together and sharing the same territory. Pair territoriality
in the species was examined in detail in relation to sexual differences in territorial defense activities. Rigorous pair territoriality
was maintained only during the breeding season, although pairs used their home ranges exclusively to a certain extent, during
the non-breeding season. The frequency of aggression against other conspecific pairs in the breeding season was higher than
in the non-breeding season. Agonistic interactions appear to be over both mates and food resources, the strict pair territoriality
in the breeding season possibly being due to mutual mate guarding. In intraspecific aggressive interactions, males usually
led their partner females when attacking intruders. The feeding frequency of males was much lower than that of females in
the breeding season. Mate removal experiments indicated that females could not defend their original territories solitarily
and their feeding frequency decreased. Conversely, males could defend territories solitarily without a decrease in feeding
frequency. These results suggest that males contribute most to the defense of the pair territory, with females benefiting
from territorial pair-swimming with their partner males. 相似文献