全文获取类型
收费全文 | 390884篇 |
免费 | 35179篇 |
国内免费 | 298篇 |
专业分类
426361篇 |
出版年
2018年 | 3951篇 |
2017年 | 3787篇 |
2016年 | 5103篇 |
2015年 | 5458篇 |
2014年 | 6916篇 |
2013年 | 9956篇 |
2012年 | 11075篇 |
2011年 | 12012篇 |
2010年 | 8265篇 |
2009年 | 7417篇 |
2008年 | 10641篇 |
2007年 | 11079篇 |
2006年 | 10498篇 |
2005年 | 9970篇 |
2004年 | 9936篇 |
2003年 | 9625篇 |
2002年 | 9546篇 |
2001年 | 18648篇 |
2000年 | 18870篇 |
1999年 | 14248篇 |
1998年 | 4394篇 |
1997年 | 4533篇 |
1996年 | 4300篇 |
1995年 | 3969篇 |
1994年 | 3828篇 |
1992年 | 11449篇 |
1991年 | 11290篇 |
1990年 | 11171篇 |
1989年 | 10938篇 |
1988年 | 10154篇 |
1987年 | 9587篇 |
1986年 | 8653篇 |
1985年 | 9056篇 |
1984年 | 7267篇 |
1983年 | 6235篇 |
1982年 | 4316篇 |
1981年 | 3952篇 |
1980年 | 3779篇 |
1979年 | 6819篇 |
1978年 | 5247篇 |
1977年 | 4778篇 |
1976年 | 4607篇 |
1975年 | 5331篇 |
1974年 | 5899篇 |
1973年 | 5832篇 |
1972年 | 5302篇 |
1971年 | 4835篇 |
1970年 | 4316篇 |
1969年 | 3999篇 |
1968年 | 3824篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Convenient extraction and radioimmunoassay methods for measurement of leukotrienes C4 and D4 (LTC4 and LTD4) in biological fluids are described. LTC4 or LTD4 in plasma was extracted with acetonitrile, and the extract was washed with dichloromethane then adjusted to pH 3.5 or 6.0, respectively. Each leukotriene was partially purified by using a C18-bonded silica cartridge and quantitated by radioimmunoassay. Amounts of LTC4 and LTD4 in the range of 0.025-1.6 ng could be assayed in plasma. This procedure was employed to examine the increase in plasma LTC4 (0.249 +/- 0.036 ng/ml) and LTD4 (1.399 +/- 0.235 ng/ml) of guinea pigs during intravenous challenge-induced anaphylactic bronchoconstriction, and the suppression of the increase of bronchoconstriction and leukotrienes by the administration of 5-lipoxygenase inhibitors such as E6080 (6-hydroxy-2-(4-sulfamoylbenzyl-amino)- 4,5,7-trimethylbenzothiazole hydrochloride), AA861 (2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone ) and phenidone. On the other hand, LTC4 and LTD4 were not detected in plasma after an inhaled challenge, though significant bronchoconstriction was provoked. It was concluded that the present study validates a new technique for quantitating plasma leukotrienes on the basis of pH and a suitable method for evaluating the pharmacological efficacy of 5-lipoxygenase inhibitors. 相似文献
92.
93.
94.
Hugo R. Permingeat Maria V. Romagnoli Juliana I. Sesma Ruben H. Vallejos 《Plant Molecular Biology Reporter》1998,16(1):89-89
An easy, reproducible and fast procedure to isolate DNA from cotton leaves is described. The addition of 0.5 M glucose in the extraction buffer avoids browning by polyphenolic compounds and improves the quality of DNA for molecular analysis. The DNA yield ranged between 150–400 mg per gram of fresh tissue. The DNA was suitable for digestion by restriction enzymes and amplificatiion by Taq DNA polymerase. 相似文献
95.
A rational attempt to prepare FmocHis(piTrt)OH regiospecifically gave in fact the well-known tau-trityl isomer, and experiments with model systems indicate that the prospects for access to pi-trityl histidine derivatives, which would be of great value for the racemization-free synthesis of histidine-containing peptides, are poor. 相似文献
96.
97.
N. P. Todaria 《Biologia Plantarum》1986,28(4):280-287
A comparative study of dark respiration and effects of high and low temperature on dark respiration in five greenhouse cultivated tropical and sub-tropical species was made. The respiration rates determined manometrically were low in all species. Respiration rates increased with increasing temperature. Low temperature treatment accelerated the rate of respiration at 25 °G except in two species. An attempt has been made to determine the critical and optimum temperature for these species. The respiratory behaviour of these species has been discussed with respect to their original habitats and prevailing environmental conditions. 相似文献
98.
99.
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100.
G. Franz M. Reindl S. C. Patel R. Beer I. Unterrichter T. Berger E. Schmutzhard W. Poewe & A. Kampfl 《Journal of neurochemistry》1999,73(4):1615-1625
Increasing evidence suggests that apolipoprotein D (apoD) could play a major role in mediating neuronal degeneration and regeneration in the CNS and the PNS. To investigate further the temporal pattern of apoD expression after experimental traumatic brain injury in the rat, male Sprague-Dawley rats were subjected to unilateral cortical impact injury. The animals were killed and examined for apoD mRNA and protein expression and for immunohistological analysis at intervals from 15 min to 14 days after injury. Increased apoD mRNA and protein levels were seen in the cortex and hippocampus ipsilateral to the injury site from 48 h to 14 days after the trauma. Immunohistological investigation demonstrated a differential pattern of apoD expression in the cortex and hippocampus, respectively: Increased apoD immunoreactivity in glial cells was detected from 2 to 3 days after the injury in cortex and hippocampus. In contrast, increased expression of apoD was seen in cortical and hippocampal neurons at later time points following impact injury. Concurrent histopathological examination using hematoxylin and eosin demonstrated dark, shrunken neurons in the cortex ipsilateral to the injury site. In contrast, no evidence of cell death was observed in the hippocampus ipsilateral to the injury site up to 14 days after the trauma. No evidence of increased apoD mRNA or protein expression or neuronal pathology by hematoxylin and eosin staining was detected in the contralateral cortex and hippocampus. Our results reveal induction of apoD expression in the cortex and hippocampus following traumatic brain injury in the rat. Our data also suggest that increased apoD expression may play an important role in cortical neuronal degeneration after brain injury in vivo. However, increased expression of apoD in the hippocampus may not necessarily be indicative of neuronal death. 相似文献