全文获取类型
收费全文 | 10671篇 |
免费 | 788篇 |
国内免费 | 743篇 |
出版年
2024年 | 11篇 |
2023年 | 130篇 |
2022年 | 263篇 |
2021年 | 657篇 |
2020年 | 380篇 |
2019年 | 471篇 |
2018年 | 417篇 |
2017年 | 310篇 |
2016年 | 458篇 |
2015年 | 719篇 |
2014年 | 823篇 |
2013年 | 806篇 |
2012年 | 1030篇 |
2011年 | 820篇 |
2010年 | 495篇 |
2009年 | 469篇 |
2008年 | 508篇 |
2007年 | 477篇 |
2006年 | 389篇 |
2005年 | 368篇 |
2004年 | 286篇 |
2003年 | 257篇 |
2002年 | 191篇 |
2001年 | 208篇 |
2000年 | 150篇 |
1999年 | 163篇 |
1998年 | 96篇 |
1997年 | 109篇 |
1996年 | 110篇 |
1995年 | 100篇 |
1994年 | 106篇 |
1993年 | 65篇 |
1992年 | 64篇 |
1991年 | 84篇 |
1990年 | 53篇 |
1989年 | 44篇 |
1988年 | 25篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1984年 | 14篇 |
1983年 | 17篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
11.
Biosynthesis of fusarochromanone and its monoacetyl derivative by Fusarium equiseti. 总被引:3,自引:3,他引:0 下载免费PDF全文
One fluorescent compound previously named TDP-2 was isolated and purified from a rice culture of Fusarium equiseti (Alaska 2-2). Mass spectral and nuclear magnetic resonance data indicated that it is a C-3'-N-acetyl derivative of fusarochromanone, a newly discovered mycotoxin. Time course studies of synthesis of these two compounds on autoclaved rice and Czapek-Dox medium enriched with soybean peptone indicated that fusarochromanone was converted to TDP-2 in the cultures. A high concentration of peptone in the liquid medium may stimulate both fusarochromanone synthesis and its conversion to TDP-2. 相似文献
12.
A study has been made of the efficacy of nicardipine as a Ca2+ channel blocker by determining the magnitude of its effect on the stimulatory response of the ouabain-insensitive Na+ efflux in single barnacle muscle fibers to 100 mM external K+. The results show that nicardipine (at pH 6.5) is a potent inhibitor, the minimal effective concentration being approx. 10(-7) M and the IC(50) about 5.10(-6) M. Nicardipine, however, is not as potent as verapamil (at pH 6.5) on an equimolar basis. This is explained by assuming that the number of dihydropyridine receptors in the t-tubule membranes of barnacle fibers is not high or that verapamil is able to block the sarcoplasmic reticulum Ca2+ release channel in addition to the voltage-dependent Ca2+ channels. 相似文献
13.
14.
本文记述斯氏蚤属Smitipsylla Lewis,1971一新种,方突斯氏蚤S. quadrata sp. nov.。本新种的发现,是斯氏蚤属在中国的首次纪录。本文对其属征作了概述。 相似文献
15.
本研究旨在探讨福建荔枝最重要品种兰竹的叶片营养元素适宜含量。统计分析表明,不同地点、年份对同一品种叶片元素含量存在明显的差异;荔枝叶片含氮量变异系数最小,并按磷、镁、钙、钾依次增大。本研究初步提出的丰产兰竹荔枝秋梢叶片营养元素适宜含量为:氮1.5—2.2%,磷0.12—0.18%,钾0.7—1.4%,钙0.3—0.8%,及镁0.18一0.88%;其叶片氮、磷、钾、钙、镁的适宜比例是1:0.08:0.57:0.30:0.12。上列指标可供荔枝营养诊断指导施肥之参考。 相似文献
16.
17.
鳗鲡幼鱼耳石日轮的研究 总被引:16,自引:1,他引:15
本文报道采自辽东半岛沿岸鳗鲡(Anguilla japonica)的白仔鳗和经人工培育的当年幼鳗耳石日轮生长的观察结果。白仔鳗和幼鳗耳石平均直径均与体全长成直线相关。12尾白仔鳗耳石的平均日轮数146.3,据此推测其产卵期为11—12月。观察证实从咸淡水转人到淡水生活的幼鳗耳石的环纹有过渡带存在。 相似文献
18.
The Rex proteins of human T-cell leukemia virus type II differ by serine phosphorylation. 总被引:7,自引:6,他引:1 下载免费PDF全文
The Rex proteins of human T-cell leukemia virus types I and II (HTLV-I and HTLV-II) induce cytoplasmic expression of unspliced gag-pol mRNA and singly spliced env mRNA and are critical for virus replication. Two rex gene products, p27rex and p21rex of HTLV-I and p26rex and p24rex of HTLV-II, have been detected in HTLV-infected cells; however, the structural and biological relationship of the proteins has not been clearly elucidated. Endoproteinase digestion and phosphoamino acid analysis of HTLV-II Rex indicated that p24rex has the same amino acid backbone as p26rex and that the larger apparent molecular size of p26rex is attributable to serine phosphorylation. 相似文献
19.
In order to evaluate the involvement of the type II collagen regulatory sequences in development, we have injected a construct containing a toxin gene under the control of the rat type II collagen promoter and enhancer. The construct, pDAS10-DTA, contained the diphtheria toxin A chain gene under the control of type II collagen sequences which had been used previously to target cartilagenous tissues in transgenics. Inspection of developing fetuses at various stages of gestation revealed a high number of aborted implants as well as abnormally developing fetuses. These abnormal fetuses were of small size, had shortened and underdeveloped limbs, cleft palates, and generally resembled a phenotype similar to chondrodystrophic mice. Histological comparisons of normal and abnormal fetuses indicated a reduced amount of extracellular matrix surrounding chondrocytes, and a disorganized appearance of the tissue. These results suggest that the expression of the toxin has occurred in chondrocytes and altered the survival and development of the transgenic mice. These results also indicate that the promoter and enhancer sequences contained in the transgene controlled the developmental expression of the type II collagen gene expression. 相似文献
20.