全文获取类型
收费全文 | 2589篇 |
免费 | 214篇 |
国内免费 | 1篇 |
出版年
2022年 | 21篇 |
2021年 | 52篇 |
2020年 | 27篇 |
2019年 | 39篇 |
2018年 | 53篇 |
2017年 | 44篇 |
2016年 | 76篇 |
2015年 | 90篇 |
2014年 | 114篇 |
2013年 | 145篇 |
2012年 | 178篇 |
2011年 | 158篇 |
2010年 | 95篇 |
2009年 | 97篇 |
2008年 | 118篇 |
2007年 | 104篇 |
2006年 | 93篇 |
2005年 | 83篇 |
2004年 | 89篇 |
2003年 | 63篇 |
2002年 | 72篇 |
2001年 | 63篇 |
2000年 | 58篇 |
1999年 | 47篇 |
1998年 | 18篇 |
1997年 | 28篇 |
1996年 | 20篇 |
1993年 | 18篇 |
1992年 | 54篇 |
1991年 | 27篇 |
1990年 | 30篇 |
1989年 | 29篇 |
1988年 | 40篇 |
1987年 | 31篇 |
1986年 | 27篇 |
1985年 | 48篇 |
1984年 | 27篇 |
1983年 | 34篇 |
1982年 | 19篇 |
1981年 | 30篇 |
1980年 | 20篇 |
1979年 | 30篇 |
1978年 | 30篇 |
1977年 | 21篇 |
1976年 | 19篇 |
1975年 | 29篇 |
1974年 | 16篇 |
1973年 | 23篇 |
1972年 | 22篇 |
1971年 | 19篇 |
排序方式: 共有2804条查询结果,搜索用时 15 毫秒
101.
S Ganguly D Sarkar D Sengupta S K Banerjee J J Ghosh 《Indian journal of experimental biology》1975,13(5):497-498
Hyaluronidase activity of human endometrial tissues and uterine fluids was investigated. Endometrial tissue and uterine fluid specimens were obtained from normal human subjects, and different cases of uterine dysfunction induced by steroidal contraceptives, copper IUD, lactational amenorrhea, and in early pregnancy. Hyaluronidase activity was found to increase from Cycle Days 8 to 10 and reach the maximum value during the secretory phase. Hyaluronidase activity was reduced in both endometrial tissue and uterine fluid during lactational amenorrhea and early pregnancy, and was drastically reduced in copper-IUD and steroidal contraceptive users. The low hyaluronidase activity in the early phase of the cycle may be due to rapid growth of endometrial tissue. In the secretory phase, the corresponding activities were found to increase because of high secretory activity and enhanced catabolic processes. In early pregnancy, the low lysosomal enzyme activity may also be explained on the basis of increased endometrium tissue growth. Low hyaluronidase activity of amenorrhic subjects may be due to the absence of ovarian steroids. 相似文献
102.
Peroxidase activity in rat intestine is stimulated two-fold after bilateral adrenalectomy and is reversed by dexamethasone (9-fluoro-11 beta,17,21-trihydroxy-16 alpha-methyl-1-4-pregnadiene-3,20-dione). The enzyme activity is inhibited on administration of various glucocorticoids of which dexamethasone acts as the most potent inhibitor of the enzyme in vivo. The change of enzyme activity results neither from alteration of the apparent Km of the enzyme nor from enzyme synthesis. Although a small amount of peroxidase is located in the intestinal epithelial cells, a large amount is present in the rest of the intestine. Histochemical studies indicate the presence of peroxidase in the lamina propria, the core of the intestinal villi which contains eosinophil. The peroxidase isolated from the epithelial cell-free intestine is similar to the peroxidase obtained from the pure eosinophil in terms of various physicochemical properties. Dexamethasone also inhibits the eosinophil peroxidase and decreases the number of both circulating and intestinal eosinophil. Studies indicate that a large part of the peroxidase of the intestine is contributed by invading eosinophil and dexamethasone inhibits the enzyme by sequestration of eosinophil both from intestine and blood possibly to the peripheral lymph nodes. 相似文献
103.
104.
105.
106.
Vibrio cholerae hemolysin (HlyA) is a 65?kDa pore-forming toxin which causes lysis of target eukaryotic cells by forming heptameric channels in the plasma membrane. Deletion of the 15?kDa C-terminus β-prism carbohydrate-binding domain generates a 50?kDa truncated variant (HlyA50) with 1000-fold-reduced pore-forming activity. Previously, we showed by cryo-electron microscopy that the two toxin oligomers have central channels, but the 65?kDa toxin oligomer is a seven-fold symmetric structure with bowl-, ring-, and arm-like domains, whereas the 50?kDa oligomer is an asymmetric jar-like heptamer. In the present study, we determined three-dimensional(3D) structures of HlyA and HlyA50 in presence of erythrocyte stroma and observed that interaction of the 65?kDa toxin with the stroma induced a significant decrease in the height of the β-barrel oligomer with a change in conformation of the ring- and arm-like domains of HlyA. These features were absent in interaction of HlyA50 with stroma. We propose that this conformational transition is critical for membrane-insertion of the toxin. 相似文献
107.
A new 3,7-dioxabicyclo[3,3,O]octane lignan, named justisolin, and a new lignan O-glucoside, named simplexoside, were isolated from the whole plant of Justicia simplex D. Don. (Acanthaceae), collected at fruiting. The structure of the free lignan was established as 2e-(3,4-methylenedioxy-6-hydroxy)-phenyl-6e- Piperonyl-3,7-dioxabicyclo[3,3,0]octane (1) and that of the glucoside as 2e-(3-methoxy-4-O-β-d- glucopyranosyl)-phenyl-6e-piperonyl-3,7-dioxabicyclo[3,3,0]octane (2) on the basis of chemical transformation and spectral evidence. The biological functions of these and related lignans are appraised. 相似文献
108.
Kumar Deepak Jain Ravikumar Shahjahan Banerjee Sabyasachi Prabhu Shriganesh S. Kumar Ranjan Azad Abul K. Roy Chowdhury Dibakar 《Plasmonics (Norwell, Mass.)》2020,15(6):1925-1934
Plasmonics - We present enhancement of operational bandwidths of planar terahertz metasurfaces by incorporating a complex unit cell that consists of a pair of concentric ring resonators. The inner... 相似文献
109.
110.
Achyut Kumar Banerjee Wuxia Guo Sitan Qiao Weixi Li Fen Xing Yuting Lin Zhuangwei Hou Sen Li Ying Liu Yelin Huang 《Ecology and evolution》2020,10(14):7349-7363
Phylogeographic forces driving evolution of sea‐dispersed plants are often influenced by regional and species characteristics, although not yet deciphered at a large spatial scale for many taxa like the mangrove species Heritiera littoralis. This study aimed to assess geographic distribution of genetic variation of this widespread mangrove in the Indo‐West Pacific region and identify the phylogeographic factors influencing its present‐day distribution. Analysis of five chloroplast DNA fragments’ sequences from 37 populations revealed low genetic diversity at the population level and strong genetic structure of H. littoralis in this region. The estimated divergence times between the major genetic lineages indicated that glacial level changes during the Pleistocene epoch induced strong genetic differentiation across the Indian and Pacific Oceans. In comparison to the strong genetic break imposed by the Sunda Shelf toward splitting the lineages of the Indian and Pacific Oceans, the genetic differentiation between Indo‐Malesia and Australasia was not so prominent. Long‐distance dispersal ability of H. littoralis propagules helped the species to attain transoceanic distribution not only across South East Asia and Australia, but also across the Indian Ocean to East Africa. However, oceanic circulation pattern in the South China Sea was found to act as a barrier creating further intraoceanic genetic differentiation. Overall, phylogeographic analysis in this study revealed that glacial vicariance had profound influence on population differentiation in H. littoralis and caused low genetic diversity except for the refugia populations near the equator which might have persisted through glacial maxima. With increasing loss of suitable habitats due to anthropogenic activities, these findings therefore emphasize the urgent need for conservation actions for all populations throughout the distribution range of H. littoralis. 相似文献