全文获取类型
收费全文 | 1659537篇 |
免费 | 157827篇 |
国内免费 | 1577篇 |
出版年
2021年 | 18244篇 |
2019年 | 16279篇 |
2018年 | 19591篇 |
2017年 | 18299篇 |
2016年 | 29499篇 |
2015年 | 43264篇 |
2014年 | 51395篇 |
2013年 | 77654篇 |
2012年 | 47020篇 |
2011年 | 38294篇 |
2010年 | 47641篇 |
2009年 | 47756篇 |
2008年 | 35298篇 |
2007年 | 34295篇 |
2006年 | 37107篇 |
2005年 | 38122篇 |
2004年 | 37028篇 |
2003年 | 34187篇 |
2002年 | 32186篇 |
2001年 | 52754篇 |
2000年 | 50559篇 |
1999年 | 45463篇 |
1998年 | 27573篇 |
1997年 | 27586篇 |
1996年 | 26564篇 |
1995年 | 24748篇 |
1994年 | 24375篇 |
1993年 | 23669篇 |
1992年 | 38382篇 |
1991年 | 36619篇 |
1990年 | 35184篇 |
1989年 | 35423篇 |
1988年 | 32674篇 |
1987年 | 30924篇 |
1986年 | 29237篇 |
1985年 | 30726篇 |
1984年 | 28581篇 |
1983年 | 25054篇 |
1982年 | 23372篇 |
1981年 | 22265篇 |
1980年 | 20914篇 |
1979年 | 24974篇 |
1978年 | 22092篇 |
1977年 | 20904篇 |
1976年 | 19724篇 |
1975年 | 19947篇 |
1974年 | 21077篇 |
1973年 | 21200篇 |
1972年 | 18570篇 |
1971年 | 16909篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Localization of cathepsin D in rat liver. Immunocytochemical study using post-embedding immunoenzyme and protein A-gold techniques 总被引:1,自引:0,他引:1
Light and electron microscopic localization of cathepsin D in rat liver was investigated by post-embedding immunoenzyme and protein A-gold techniques. By light microscopy, cytoplasmic granules of parenchymal cells and Kupffer cells were stained for cathepsin D. Weak staining was also noted in sinusoidal endothelial cells. In the parenchymal cells many of positive granules located around bile canaliculi. In the Kupffer cells and the endothelial cells, diffuse staining was noted in the cytoplasm in addition to granular staining. By electron microscopy, gold particles representing the antigenic sites for cathepsin D were seen in typical secondary lysosomes and some multivesicular bodies of the parenchymal cells and Kupffer cells. The lysosomes of the endothelial cells and fat-storing cells were weakly labeled. Quantitative analysis of the labeling density in the lysosomes of these three types of cells demonstrated that the lysosomes of parenchymal cells and Kupffer cells are main containers of cathepsin D in rat liver. The results suggest that cathepsin D functions in the intracellular digestive system of parenchymal cells and Kupffer cells but not so much in that of the endothelial cells. 相似文献
72.
The immunological analysis of 24 spontaneous Strr, Rifr and Kanr mutants of streptococcal strain IP, highly virulent for mice and capable of binding polyclonal human IgG (IgG FcR+), was made. The characteristic feature of all these mutants was decreased virulence, restored after their passage in vivo. 23 mutants were capable of binding polyclonal IgG; one Strr mutant had no such capacity, but acquired it, together with an increase in virulence, after its passage in vivo. When stored in meat-peptone agar without antibiotics, 5 out of 10 Strr mutants lost their capacity for binding polyclonal human IgG. After passage in vivo they regained this property simultaneously with virulence. 相似文献
73.
Cell-free processing and segregation of insulin precursors 总被引:3,自引:0,他引:3
The biosynthesis, segregation, and processing of preproinsulin (116 amino acids) was investigated to determine the mechanism(s) by which it is translocated across the endoplasmic reticulum membrane. Islet mRNA was translated in the wheat germ cell-free system, and at various times during preproinsulin synthesis, puromycin was added, followed by addition of microsomal membranes. Neither processing of preproinsulin nor translocation of proinsulin into microsomal membranes occurred in the presence of puromycin. Synchronization of preproinsulin translation by addition of 7-methylguanosine 5'-phosphate enabled the timing of preproinsulin synthesis and proinsulin (91 amino acids) segregation into microsomal membranes to be determined. Membrane binding occurs when about 60 amino acids have been polymerized, i.e. prior to the completion of the polypeptide chain. The binding of signal recognition particle to the nascent signal is demonstrated to be an absolute requirement for translocation and processing of preproinsulin. The results indicate that segregation and processing of preproinsulin are co-translational events; no evidence for a post-translational mechanism was found. Furthermore, this work, together with similar studies, suggests that presecretory polypeptides must be synthesized as part of a precursor with a minimum size of 60-80 amino acids in order to effect membrane binding and translocation of the polypeptide chain within the intracisternal space of the endoplasmic reticulum. 相似文献
74.
R. A. Mueller M. J. Rosner J. N. Ghia S. K. Powers E. R. Kafer R. D. Hunt 《Cellular and molecular neurobiology》1988,8(2):235-243
1. Examination of the cerebrospinal fluid (CSF) of head-injured patients reveals that the concentration of intraventricular xanthine is elevated and that of uridine is decreased relative to those of adult lumbar CSF. 2. No correlations were observed between CSF lactate and CSF hypoxanthine, xanthine, or uridine, suggesting that changes in purine metabolites and the pyrimidine nucleoside do not index similar cellular events as does lactic acid production. 3. Ventricular CSF from hydrocephalic infants had uridine and hypoxanthine concentrations not significantly different from those of normal adult lumbar CSF, but xanthine was significantly elevated. 4. Since uridine has anticonvulsant properties and is a crucial substrate for cerebral metabolism, it may be useful to evaluate this pyrimidine for use in the management of patients with head injury. 相似文献
75.
Experiments on conscious rabbits were made to elaborate motor conditioned reflexes through pairing stimuli with electrocutaneous reinforcement applied every 30 s. Neuronal activity in the sensorimotor cortex and putamen was recorded during formation and reproduction of the conditioned reflexes before and after haloperidol injection (0.2 mg/kg i. v.). In the putamen, haloperidol increased the number of neurons exhibiting trace conditioned activity and made the intensity and duration of these processes rise. The changes seen in the sensorimotor cortex were opposite in nature. Inhibition of trace conditioned activity in the sensorimotor cortex depended mainly on the decreased amplitude of the reaction conditioned component. The role of the dopaminergic system in the interaction of the neostriatum and sensorimotor cortex and in formation and reproduction of trace conditioned activity of both the structures is discussed. 相似文献
76.
77.
78.
79.
80.
Comparison of statistics for candidate-gene association studies using cases and parents. 总被引:17,自引:5,他引:12
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Studies of association between candidate genes and disease can be designed to use cases with disease, and in place of nonrelated controls, their parents. The advantage of this design is the elimination of spurious differences due to ethnic differences between cases and nonrelated controls. However, several statistical methods of analysis have been proposed in the literature, and the choice of analysis is not always clear. We review some of the statistical methods currently developed and present two new statistical methods aimed at specific genetic hypotheses of dominance and recessivity of the candidate gene. These new methods can be more powerful than other current methods, as demonstrated by simulations. The basis of these new statistical methods is a likelihood approach. The advantage of the likelihood framework is that regression models can be developed to assess genotype-environment interactions, as well as the relative contribution that alleles at the candidate-gene locus make to the relative risk (RR) of disease. This latter development allows testing of (1) whether interactions between alleles exist, on the scale of log RR, and (2) whether alleles originating from the mother or father of a case impart different risks, i.e., genomic imprinting. 相似文献