全文获取类型
收费全文 | 1904篇 |
免费 | 186篇 |
国内免费 | 135篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 46篇 |
2021年 | 85篇 |
2020年 | 57篇 |
2019年 | 72篇 |
2018年 | 77篇 |
2017年 | 69篇 |
2016年 | 93篇 |
2015年 | 140篇 |
2014年 | 134篇 |
2013年 | 150篇 |
2012年 | 167篇 |
2011年 | 149篇 |
2010年 | 95篇 |
2009年 | 77篇 |
2008年 | 96篇 |
2007年 | 83篇 |
2006年 | 81篇 |
2005年 | 53篇 |
2004年 | 68篇 |
2003年 | 50篇 |
2002年 | 57篇 |
2001年 | 30篇 |
2000年 | 30篇 |
1999年 | 40篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 26篇 |
1991年 | 12篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 14篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有2225条查询结果,搜索用时 7 毫秒
1.
2.
3.
Novel Method for Detection of Butanolides in Streptomyces coelicolor Culture Broth, Using a His-Tagged Receptor (ScbR) and Mass Spectrometry 总被引:1,自引:0,他引:1 下载免费PDF全文
Yung-Hun Yang Hwang-Soo Joo Kwangwon Lee Kwang-Kyung Liou Hei-Chan Lee Jae-Kyung Sohng Byung-Gee Kim 《Applied microbiology》2005,71(9):5050-5055
γ-Butyrolactone derivative molecules in Streptomyces play a crucial role in cell density control, secondary metabolism, and cell differentiation. As their synthesis level in the cell is very low compared to those of similar N-acyl homoserine lactone molecules from gram-negative bacteria, it is very hard to analyze them even with several hundredfold concentration of the culture broth. We have developed a very quick and easy detection method using an affinity capture technique with His-tagged receptor proteins and electrospray tandem mass spectrometry. Using Streptomyces coelicolor as a model system, SCB1 was detected from only 100 ml of the culture broth after solvent extraction. This method can be further applied to detection and quantitative analysis of butanolides and inhibitor screening of the receptor molecules. 相似文献
4.
The mechanism of mass collaboration in risk management was studied during the Sichuan earthquake under a Web-based “PeopleFinder” project, where information is contributed and shared among mass contributors. The case study is provided by a great earthquake that happened in Wenchuan County, Sichuan Province, of southwestern China at 2:28 p.m. on May 12, 2008. We witnessed and experienced the rescue and relief efforts for the great earthquake. In this article, two fundamental frameworks are developed to study the mechanism of mass collaboration. Mass collaboration is proven to be effective in a big public crisis such as the Sichuan earthquake. 相似文献
5.
K B Choo K Y Chong H F Chou L N Liew C C Liou 《Biochemical and biophysical research communications》1989,158(1):334-340
The structure of the c-myc oncogene in 17 cervical tumors and patient-matched nontumor tissues from Chinese patients residing in Taiwan was analysed. In contrast to recent reports on Mexican patients, none of the samples showed rearrangements and sequence amplification in the c-myc gene. The discrepancy may be explained by different carcinogenesis mechanisms being in operation in different geographic regions. Although no structural alterations in the c-myc gene were found in seven cervical carcinoma cell lines analysed, Northern blot analysis indicated different levels of c-myc gene expression which may be related to the presence of human papillomavirus (HPV) sequence in the cell and suggests a possible c-myc-hpv interaction in some stages of the transformation process. 相似文献
6.
A G Chuchalin V A Babushkina V Ia Arion R D Aspetov T B Sha?khinova 《Biulleten' eksperimental'no? biologii i meditsiny》1984,98(7):76-78
A study was made of the effect of T-activin on the biosynthesis of immune gamma-interferon. It was shown that in 27% of patients with chronic nonspecific pulmonary diseases, production of gamma-interferon by lymphocytes was substantially reduced during exacerbation of inflammatory process in the lungs. It was discovered that T-activin was not an interferon inductor but enhanced its synthesis in patients with a low capacity of producing immune interferon even at small doses of interferon inductor. The preparation does not produce any effect on this process in normal subjects and in patients showing the normal level of gamma-interferon. Thus T-activin can be used for stimulation of interferonogenesis. 相似文献
7.
8.
Testosterone inhibits cAMP-induced de Novo synthesis of Leydig cell cytochrome P-450(17 alpha) by an androgen receptor-mediated mechanism 总被引:4,自引:0,他引:4
The regulation of the novo synthesis of the microsomal cytochrome P-450 enzyme, P-450(17 alpha), was studied in mouse Leydig cell cultures. Chronic treatment with 0.05 mM 8-Br-cAMP (cAMP) caused a time-dependent increase in 17 alpha-hydroxylase activity and in the amount of P-450(17 alpha), quantitated by immunoblotting. This increase in both activity and amount was enhanced by inhibiting testosterone production with aminoglutethimide, an inhibitor of cholesterol side-chain cleavage or SU 10603, an inhibitor of 17 alpha-hydroxylase. To examine the mechanism by which cAMP or cAMP plus inhibitors of testosterone production increased the activity and amount of P-450(17 alpha), changes in the rate of de novo synthesis were studied by measuring [35S]methionine incorporation into newly synthesized protein. Treatment with cAMP plus aminoglutethimide or SU 10603 caused a 2-fold or greater increase in the rate of de novo synthesis of P-450(17 alpha) compared to treatment with cAMP only. The addition of exogenous testosterone reversed this increase in the rate of synthesis, indicating that testosterone modulates the extent of cAMP-stimulated induction of P-450(17 alpha). This negative effect of testosterone could be mimicked by the addition of the androgen agonist, mibolerone, and prevented by the addition of the antiandrogen, hydroxyflutamide. Neither estradiol nor dexamethasone had any effect on the synthesis of P-450(17 alpha). Studies on the degradation of newly synthesized P-450(17 alpha) demonstrated that testosterone had no effect on the decay of P-450(17 alpha) during the first 24 h but caused a significant increase in the rate of decay between 24 and 48 h. These data indicate that testosterone produced during cAMP induction of P-450(17 alpha) negatively regulates the amount of this cytochrome P-450 enzyme by two distinct mechanisms: by repressing cAMP-induced synthesis of P-450(17 alpha) by an androgen receptor-mediated mechanism and by increasing the rate of degradation of P-450(17 alpha). A model is proposed for the regulation of P-450(17 alpha) in Leydig cells. 相似文献
9.
10.