全文获取类型
收费全文 | 3632篇 |
免费 | 274篇 |
国内免费 | 8篇 |
出版年
2022年 | 15篇 |
2021年 | 19篇 |
2020年 | 25篇 |
2019年 | 25篇 |
2018年 | 25篇 |
2017年 | 23篇 |
2016年 | 48篇 |
2015年 | 92篇 |
2014年 | 103篇 |
2013年 | 148篇 |
2012年 | 195篇 |
2011年 | 230篇 |
2010年 | 145篇 |
2009年 | 131篇 |
2008年 | 203篇 |
2007年 | 230篇 |
2006年 | 208篇 |
2005年 | 244篇 |
2004年 | 244篇 |
2003年 | 225篇 |
2002年 | 229篇 |
2001年 | 40篇 |
2000年 | 28篇 |
1999年 | 45篇 |
1998年 | 67篇 |
1997年 | 47篇 |
1996年 | 37篇 |
1995年 | 39篇 |
1994年 | 38篇 |
1993年 | 32篇 |
1992年 | 25篇 |
1991年 | 28篇 |
1990年 | 36篇 |
1989年 | 35篇 |
1988年 | 27篇 |
1987年 | 27篇 |
1986年 | 19篇 |
1985年 | 30篇 |
1984年 | 43篇 |
1983年 | 44篇 |
1982年 | 50篇 |
1981年 | 42篇 |
1980年 | 48篇 |
1979年 | 34篇 |
1978年 | 38篇 |
1977年 | 37篇 |
1976年 | 34篇 |
1975年 | 30篇 |
1974年 | 22篇 |
1973年 | 14篇 |
排序方式: 共有3914条查询结果,搜索用时 992 毫秒
101.
The morphology and distribution of a variety of types of nucleus in the apex, in young and mature gametangia, and in older regions of the Cymopolia cell were studied by light and electron microscopy. Spherical and convoluted nuclei 2–7μm in diameter were observed in apical regions of the vegetative siphon. Nuclei 4 μm in diameter were present in the young primary laterals and in developing gametangia. A single characteristic nucleus migrates from the siphon into the primary lateral of the second basipetal whorl. It is further transported into one of several possible secondary laterals and determines the development of gametangia which become multinucleate in the fourth or fifth whorls. Nuclei are characterized by size, shape, nucleolar morphology, nucleoplasmic inclusions and the ultrastructure of the perinuclear cytoplasm. Although no “primary nucleus” characteristic of the uninucleate genera, Acetabularia and Batophora was observed, some nuclei of Cymopolia have features in common with secondary nuclei of these genera. 相似文献
102.
Britta Swebilius Singer Larry Gold Sidney T. Shinedling Michelle Colkitt Lawrence R. Hunter David Pribnow Mary Anne Nelson 《Journal of molecular biology》1981,149(3):405-432
We have mapped the mutants isolated by Nelson et al. (1981) that reduce the amount of rIIB protein synthesized during bacteriophage T4 infection of Escherichia coli B and characterized their rIIB expression in vivo. These mutants fall into four distinct groups in terms of mapping and phenotype. We have located the probable site of each mutation on the DNA sequence. We have also analyzed a number of other mutations near the initiating AUG of rIIB with respect to their rIIB expression. In some of these mutants, ribosomal recognition of the wild-type initiating AUG is precluded and so initiation occurs at a different AUG, which, in some instances, we have identified. 相似文献
103.
Trachelomonas hispida var. coronata Lemm. has a fibrous, mucilaginous, ovoid, mineralized envelope (lorica), the ornamentation and coloration of which are capricious in culture. Cells exhibit a radial distribution of most organelles: (i) A cortical endoplasmic reticulum, (ii) parietal chloroplasts, and (iii) a median vacuolar region surrounded by several Golgi bodies and diverse vesicles. Associated with the emergent flagellum is a “paraflagellar complex” that consists of dense globules, cross-striated ribbon-like structures, a paraflagellar body, and an array of parallel striated filaments. The stigma consists of a single layer of pigmented granules that partially surrounds the canal/reservoir transition zone where microtubular bands intersect. A microtubular cytoskeleton consists of pellicular microtubules, peri-canal microtubules, stigma-associated microtubules and para-reservoir microtubules. The thickenings on the posterior, concave margins of the pellicular strips suggest that this pellicle is of intermediate complexity between those of Euglena spirogyra (Ehrenb. and Trachelomonas volvocina (Ehrenb.). 相似文献
104.
105.
106.
The spin labels, 5-doxylstearate, 12-doxylstearate, 16-doxylstearate and 1-oxyl-2,2,6,6-tetramethyl-4-dodecylphospiperidine, have been incorporated into dodecylphospocholine micelles and mixed dodecylphosphocholine/ glucagon micelles. The EPR spectral parameters for the different spin labels and the 1H- and 13C-NMR relaxation rates for nuclei of the detergent molecules indicated that inclusion of up to one spin label molecule per micelle had little influence on the spatial organization of the micelles. Furthermore, the location and environment of the spin labels in the dodecylphosphocholine micelles were not noticeably affected by the addition of glucagon and the 1H-NMR spectra observed for glucagon in mixed spin label/deuterated dodecylphosphocholine/glucagon micelles showed that the different spin labels had essentially no effect on the conformation of glucagon. Approximate spatial locations within the micelle for the nitroxide moieties of the different spin labels were determined from the NMR relaxation rates observed for different nuclei of dodecylphosphocholine. On this basis, the line broadening of individually assigned glucagon 1H-NMR lines by the different spin labels was used to determine the approximate orientation of the polypeptide chain with respect to the micelle surface. Overall, the data indicate that the glucagon backbone runs roughly parallel to the micelle surface, with the depth of immersion adjusted so that polar and apolar side chains can be oriented towards the surface or interior of the micelle, respectively. 相似文献
107.
C.Stuart Baxter Larry A. Fish 《Biochemical and biophysical research communications》1981,103(1):168-174
Linear saturated fatty acid methyl esters were comitogenic with lectins for mouse lymphocytes, the degree of comitogenicity being strongly dependent on the length of the acyl group, and maximal for methyl tetradecanoate. Lesser effects were found for analogs with 10, 12 or 16 acyl carbon atoms, whereas those with fewer than 10 or more than 16 were inactive. Analogous structure-function relationships have been described for various membrane-active and tumor-promoting phorbol diesters, where there is a similar dependence on ester acyl group length for many activities. The fatty acid esters may therefore represent simple model compounds for studying mechanistic aspects of phorbol diester activity. 相似文献
108.
Heart development in the Mexican salamander, Ambystoma mexicanum has been studied using two-dimensional gel electrophoresis and electron microscopy. At the preheart beat stage two forms of action, α and β, are present in the heart in approximately equal quantity, however, very few definitive thin filaments can be distinguished at this stage. Once the heart beat is initiated and heart development progresses α-actin increases relative to β-actin. This increase in muscle-specific actin is coincidental with the appearance of numerous thin filaments in the myocyte. 相似文献
109.
110.
Professor Shoji Matsushima Yuko Morisawa Larry J. Petterborg Jeannette W. Zeagler Russel J. Reiter 《Cell and tissue research》1979,204(3):407-416
Summary Fine structural features of pinealocytes of cotton rats (Sigmodon hispidus) were examined. Golgi complexes, mitochondria, endoplasmic reticulum and polysomes are usual organelles seen in the perikaryonal cytoplasm of pinealocytes. Many non-granulated vesicles (40 to 80 nm in diameter) and a few granulated vesicles (about 100 nm in diameter) are associated with the Golgi cisternae. Occasionally, the cisternae contain granular materials. The perikaryonal cytoplasm of pinealocytes is characterized by the presence of inclusion bodies. These bodies are usually round in shape, not bounded by a limiting membrane and composed of fine granular or filamentous materials of high electron-opacity, which are similar in appearance to the substance seen in the nucleolonema. Pinealocyte processes, filled with abundant non-granulated vesicles and some granulated vesicles, are mainly found within the parenchyma and occasionally in perivascular spaces.Supported in part by NSF grant no. PCM 77-05734 and NIH grant no. HD-10202 (Morphology Core) 相似文献