全文获取类型
收费全文 | 133739篇 |
免费 | 7971篇 |
国内免费 | 17篇 |
专业分类
141727篇 |
出版年
2023年 | 794篇 |
2021年 | 1512篇 |
2020年 | 1443篇 |
2019年 | 1409篇 |
2018年 | 3693篇 |
2017年 | 3304篇 |
2016年 | 4444篇 |
2015年 | 5814篇 |
2014年 | 5910篇 |
2013年 | 7986篇 |
2012年 | 9313篇 |
2011年 | 8283篇 |
2010年 | 5361篇 |
2009年 | 3964篇 |
2008年 | 6669篇 |
2007年 | 6358篇 |
2006年 | 6203篇 |
2005年 | 5219篇 |
2004年 | 5195篇 |
2003年 | 4729篇 |
2002年 | 4305篇 |
2001年 | 3359篇 |
2000年 | 3298篇 |
1999年 | 2501篇 |
1998年 | 1064篇 |
1997年 | 770篇 |
1996年 | 791篇 |
1995年 | 738篇 |
1994年 | 665篇 |
1992年 | 1478篇 |
1991年 | 1341篇 |
1990年 | 1242篇 |
1989年 | 1324篇 |
1988年 | 1156篇 |
1987年 | 1143篇 |
1986年 | 1070篇 |
1985年 | 1098篇 |
1984年 | 947篇 |
1983年 | 793篇 |
1982年 | 668篇 |
1979年 | 948篇 |
1978年 | 696篇 |
1975年 | 785篇 |
1974年 | 867篇 |
1973年 | 843篇 |
1972年 | 767篇 |
1971年 | 688篇 |
1970年 | 745篇 |
1969年 | 788篇 |
1968年 | 751篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
The oscillations of the free fatty acid concentration in the serum and white (epididymal) adipose tissue, of triglycerides in the serum and liver, of total serum, liver and adrenal cholesterol and of serum phospholipids were studied at 3-hour intervals for a period of 24 hours in fed male Wistar rats and in animals fasted for 24 hours (both adapted to an illumination regimen of 12 hours' light and 12 hours' darkness. The rhythm--studied by means of the cosinor analysis--was present in most of the given parameters; it was not recorded in the liver triglycerides and serum phospholipids of fasted rats and in the adrenal cholesterol of fed animals. Apart from the circadian rhythm, many parameters distinctly displayed an ultradian rhythm, mainly an approximately 12-hour period. In general, one day's starvation did not significantly affect the course of the circadian oscillations of the given indicators of rat lipid metabolism. 相似文献
122.
123.
124.
A new class of Phycomyces behavioral mutants with enhanced tropic responses has been analyzed genetically to determine the number of genes involved and the nature of their expression. These hypertropic mutants carry pleiotropic nuclear mutations. Besides their effects on sensory behavior, they also affect morphology and meiotic processes. Behavioral analyses of heterokaryons containing hypertropic and wild-type nuclei in varying proportions show that the hypertropic mutations in strains L82, L84, L86, and L88 are strongly dominant. Conversely, the hypertropic mutations carried by the strains L83, L85, and L87 are strongly recessive. We performed recombination analyses between hypertropic mutants and mutants with diminished phototropism, affected in the seven genes madA to madG. We found no evidence of linkage between the hypertropic mutations and any of these mad mutations. From crosses, we isolated double mutants carrying hypertropic mutations together with madC (night blind) and madG (stiff) mutations. The behavioral phenotypes of the double mutants are intermediate between those of the parentals. Complementation analyses show that the three recessive hypertropic mutations affect the same gene, which we call madH. The expression of the recessive hypertropic allele becomes dominant in heterokaryons carrying madC and madH nuclei; the madC gene has been implicated separately with the photoreceptor at the input to the sensory pathway, while the madH gene is associated with the growth control output. This result suggests the physical interaction of both gene products, madH and madC, in a molecular complex for the photosensory transduction chain. 相似文献
125.
126.
Six peripheral blood lymphoid fractions (total lymphocytes, non-T, T, Tar (autologous rosette-forming T cells/precursor), T mu (helper), and T gamma (suppressor) lymphocytes) isolated through rosetting procedures were examined for the presence of ferritin by a direct immunofluorescence technique. Although ferritin was present in all lymphoid fractions studied, a significantly higher proportion of ferritin-containing cells were detected in the T-cell fraction than in the non-T-cell fraction, (mean +/- SD = 7.9 +/- 1.6% and 5.0 +/- 1.2%, respectively). T mu- and T gamma-cell fractions showed a twofold increase in the number of ferritin-positive cells (14.1 +/- 1.4% and 15.4 +/- 2.6%, respectively), as compared with Tar (7.0 +/- 0.9%)-and total lymphocyte (6.9 +/- 1.3%)-cell fractions. These results indicate that ferritin is preferentially distributed in T mu and T gamma lymphocytes and may constitute the basis for explaining some of the roles exercised by these cells in the control of other biological systems. 相似文献
127.
128.
129.
S. H. Habib S.-E. Ooi Ond?ej Novák Danu?e Tarkowská Jakub Rol?ík Karel Dole?al S. S. R. Syed-Alwee C.-L. Ho P. Namasivayam 《Plant Growth Regulation》2012,68(2):313-317
Comparative mineral and hormonal analyses were made on tissue culture derived truncated leaf syndrome and wild type oil palm seedlings. Mineral analysis confirmed that Boron, Zinc and chlorophyll levels were significantly lower in truncated leaf syndrome leaves than those of wild type. Hormonal analysis also revealed various cytokinin derivatives such as trans-zeatin, trans-zeatin riboside, trans-zeatin O-glucoside and trans-zeatin riboside 5??mono phosphate were significantly higher in truncated leaf syndrome leaves compared to wild type leaves. Brassinolide level was also significantly higher in truncated leaf syndrome leaves than those of the wild type. These observations suggest that the truncated leaf syndrome abnormality could be associated to high cytokinin and brassinosteroid production which affects the uptake of Boron and Zinc. 相似文献
130.