全文获取类型
收费全文 | 217647篇 |
免费 | 8354篇 |
国内免费 | 848篇 |
专业分类
226849篇 |
出版年
2021年 | 960篇 |
2018年 | 15100篇 |
2017年 | 14079篇 |
2016年 | 10444篇 |
2015年 | 2658篇 |
2014年 | 2611篇 |
2013年 | 3577篇 |
2012年 | 8768篇 |
2011年 | 19103篇 |
2010年 | 17102篇 |
2009年 | 12897篇 |
2008年 | 15470篇 |
2007年 | 17703篇 |
2006年 | 3385篇 |
2005年 | 4372篇 |
2004年 | 4229篇 |
2003年 | 4363篇 |
2002年 | 3908篇 |
2001年 | 4773篇 |
2000年 | 4480篇 |
1999年 | 3300篇 |
1998年 | 1106篇 |
1997年 | 1105篇 |
1996年 | 960篇 |
1995年 | 870篇 |
1994年 | 863篇 |
1993年 | 897篇 |
1992年 | 2499篇 |
1991年 | 2529篇 |
1990年 | 2490篇 |
1989年 | 2241篇 |
1988年 | 2098篇 |
1987年 | 2007篇 |
1986年 | 1836篇 |
1985年 | 1836篇 |
1984年 | 1521篇 |
1983年 | 1332篇 |
1982年 | 961篇 |
1981年 | 886篇 |
1979年 | 1442篇 |
1978年 | 1131篇 |
1977年 | 1023篇 |
1976年 | 986篇 |
1975年 | 1177篇 |
1974年 | 1257篇 |
1973年 | 1347篇 |
1972年 | 1882篇 |
1971年 | 1692篇 |
1970年 | 935篇 |
1969年 | 961篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
We studied the impulse activity of neurons of the basal and lateral amygdalar nuclei generated when experimental animals (rats) performed fast stereotyped food-procuring movements by the forelimb. Within the basolateral amygdala, there are neurons whose activity is related to different stages of getting off the food, and according to the characteristics of their spiking these neurons should be divided into a number of subpopulations. Activation forestalling the movement initiation by 0.5-1.0 sec was observed in most neurons of the basolateral amygdala; this is considered a manifestation of excitation related to a motivation component of the food-procuring behavior. Activation of amygdalar neurons following movement initiation can result from generation in this structure of additional excitation necessary for successful performance of a complete food-procuring motor cycle. 相似文献
43.
44.
45.
Background
Substituted catechols are important precursors for large-scale synthesis of pharmaceuticals and other industrial products. Most of the reported chemical synthesis methods are expensive and insufficient at industrial level. However, biological processes for production of substituted catechols could be highly selective and suitable for industrial purposes. 相似文献46.
Coordinate regulation of ribosomal protein mRNA level in regenerating rat liver. Study with the corresponding mouse cloned cDNAs. 总被引:17,自引:6,他引:11 下载免费PDF全文
Cloned mouse ribosomal protein (rp) cDNAs exhibit extensive homology with the corresponding rat sequences. The size of the rp-mRNAs and complexity of the rp-genes are very similar in the two species. Using the mouse rp-recombinant DNAs we find that the relative abundance of rat L7, L13, L18, L30, L32/33 and S16 mRNAs increases after partial hepatectomy. Their maximal level is about twice that of normal rat liver, and is achieved 12-18 h after the operation, while the relative abundance of albumin mRNA decreases to half the normal values 12 h after partial hepatectomy. This concomitant increase in the relative content of these rp-mRNAs indicates coordinate regulation of their level in the rat. The dissimilar behavior of L10 and L19 rp-mRNA suggests additional control mechanisms of rp-mRNA levels in the regenerating rat liver. 相似文献
47.
The amino acid composition, N- and C-terminal amino acid sequences, and the basic physicochemical and immunochemical properties of the recently discovered pregnancy-associated molecular variant of human transcortin (Strel'chyonok, O.A., Avvakumov, G.V. and Akhrem, A.A. (1984) Carbohydr. Res. 134, 133-140) have been found to be identical to those of transcortin from normal donor serum. This suggests the identity of polypeptide moieties of the two glycoproteins. The transcortin variant has a lower isoelectric point (3.5-4.1) than normal transcortin (3.6-4.2), and different electrophoretic mobility in low-porosity polyacrylamide gel (one band versus two for normal transcortin). These differences can be reasonably explained by different organization of the carbohydrate moieties of these glycoproteins due to diverse post-translational modification of a single polypeptide chain. The levels of transcortin variant in the maternal venous serum throughout normal gestation (447 donors in all) and on the fifth day after delivery, as well as in umbilical cord serum and extracts of term placenta, have been measured by a radioimmune assay. Analysis of the data obtained allowed us to conclude that the biosynthesis of pregnancy-associated transcortin variant occurs in some organ of the maternal organism rather than in the feto-placental system, and it is a characteristic of pregnancy as a unique physiological state of the female organism rather than a phenomenon caused by individual features of certain women. We assume that the transcortin variant takes part in the guided transport of corticosteroids and/or progestins into some tissues that develop in the course of gestation. 相似文献
48.
49.
The review summarizes the authors’ and literature data on accumulation of DNA breaks in differentiating cells. Large 50-kb free DNA fragments were observed by several research teams in non-apoptotic insect, mammal, and plant cells. More intense DNA breakage was observed during maturation of spermatides, embryo development, and differentiation of myotubes, epidermal cells, lymphocytes, and neutrophils. In general, accumulation of DNA breaks in differentiating cells cannot be attributed to a decrease in the DNA repair efficiency. Poly(ADP)ribose synthesis often follows the DNA breakage in differentiating cells. We hypothesize that DNA fragmentation is an epigenetic tool for regulating the differentiation process. Scarce data on localization of the differentiation-associated DNA breaks indicate their preferable accumulation in specific DNA sequences including the nuclear matrix attachment sites. The same sites are degraded at early stages of apoptosis. Recent data on non-apoptotic function of caspases provide more evidence for possible existence of a DNA breakage mechanism in differentiating cells, resembling the initial stage of apoptosis. Excision of methylated cytosine and recombination are other possible explanations of the phenomenon. Elucidation of mechanisms of differentiation-induced DNA breaks appears to be a prospective research direction. 相似文献
50.