全文获取类型
收费全文 | 16002篇 |
免费 | 1593篇 |
国内免费 | 3223篇 |
出版年
2024年 | 61篇 |
2023年 | 295篇 |
2022年 | 676篇 |
2021年 | 1005篇 |
2020年 | 801篇 |
2019年 | 925篇 |
2018年 | 781篇 |
2017年 | 655篇 |
2016年 | 803篇 |
2015年 | 1136篇 |
2014年 | 1429篇 |
2013年 | 1393篇 |
2012年 | 1753篇 |
2011年 | 1635篇 |
2010年 | 1019篇 |
2009年 | 917篇 |
2008年 | 1020篇 |
2007年 | 882篇 |
2006年 | 713篇 |
2005年 | 552篇 |
2004年 | 419篇 |
2003年 | 394篇 |
2002年 | 315篇 |
2001年 | 194篇 |
2000年 | 176篇 |
1999年 | 172篇 |
1998年 | 116篇 |
1997年 | 98篇 |
1996年 | 80篇 |
1995年 | 61篇 |
1994年 | 58篇 |
1993年 | 41篇 |
1992年 | 46篇 |
1991年 | 38篇 |
1990年 | 30篇 |
1989年 | 21篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 22篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1950年 | 3篇 |
1938年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
In this study we describe the contribution of matrilineal and patrilineal effects on the adiposity, body weight, and on the
weights of individual fat pads in F2 male mice derived from an SWR/J × AKR/J cross. AKR/J mice become obese after 12 weeks on a high-fat diet, whereas SWR/J mice
remain relatively lean. Here we report that mice with AKR maternal and AKR paternal grandmothers have significantly larger
epidydimal and retroperitoneal fat pads than those with SWR maternal and paternal grandmothers. However, grandparental strain
had no effect on the overall adiposity (AI) or the weights of the inguinal, subcutaneous or mesenteric fat pads. The strain
of the paternal grandparents had a small but significant effect on body weight. These effects can be attributed to in utero
effects, imprinting effects, cytoplasmic and/or Y chromosome transmission of factors controlling body fat. We also describe
the presence of a quantitative trait locus (QTL) on Chromosome X, close to DXMit174, which is linked to adiposity, body weight, and to the weights of the individual fat depots. However, this QTL is not responsible
for the grandparental strain effects described above.
Received: 3 March 1997 / Accepted: 5 May 1997 相似文献
102.
银川异伊螨新种记述(蜱螨亚纲:犹伊螨科) 总被引:1,自引:0,他引:1
本文记述一新种,即银川异伊螨。标本采自银川市日本埋葬虫体上,文中列表比较了相近种长沟异伊螨和玉溪异伊螨的区别。 相似文献
103.
角绥螨属在中国首次发现及一新种记述(蜱螨亚纲:囊螨科) 总被引:2,自引:1,他引:1
本文记述角绥螨属一新种,中华角绥螨Antennoseius sinicus sp.nov.,标本采自云南剑川县大绒鼠巢中。该属在中国尚系首次发现。 相似文献
104.
载脂蛋白E(ApoE)与迟发的家族性及孤发性阿尔茨海默(Alzheimer)病密切相关. 氯喹慢性中毒可诱发某些肌病理改变, 出现β淀粉样蛋白(βAP)与tau蛋白等的沉积, 与Alzheimer脑中见到的病理改变类似. 为分析这一改变的机制, 用逆转录结合多聚酶链反应技术(RT-PCR)对氯喹处理的大鼠肌肉中ApoE表达的改变进行了研究. 在PCR定量中采用了一种稳定表达的内源性甘油醛-3-磷酸脱氢酶mRNA作为内部参照. PCR扩增在很宽的循环数范围内成线性, 且靶mRNA与参照mRNA的扩增效率相当. 氯喹处理后大鼠肌肉中ApoE mRNA的表达从第6周开始增加, 第8周后超过对照组的20多倍. 结果提示, ApoE在氯喹慢性中毒所致的大鼠肌病理改变中发挥某些作用. 相似文献
105.
以细胞形态观察、细胞存活率、乳酸脱氢酶释放和前列环素测定等方面研究载脂蛋白AⅡ保护内皮细胞的作用.结果显示,载脂蛋白AⅡ可部分拮抗低密度脂蛋白对内皮细胞的损伤作用, 维持内皮细胞形态基本正常,乳酸脱氢酶释放减少,前列环素合成增加. 相似文献
106.
兔感觉神经特异蛋白的纯化及稳定性观察 总被引:2,自引:0,他引:2
以兔脊神经节及背根纤维为材料,通过制备匀浆,DEAE-Sephacel阴离子交换层析,高压液相凝胶过滤层析分离纯化了感觉神经特异蛋白29 ku,并进行了该蛋白的稳定性观察. 相似文献
107.
Expression of betaine aldehyde dehydrogenase gene and salinity tolerance in rice transgenic plants 总被引:9,自引:0,他引:9
Betaine as one of osmolytes plays an important role in osmoregulation of most high plants. Betaine aldehyde dehydrogenase C BADH) is the second enzyme involved in betaine biosynthesis. The BADH gene from a halophite, Atriplex hortensis, was transformed into rice cultivars by bombarment method. Totally 192 transgenic rice plants were obtained and most of them had higher salt tolerance than controls. Among transgenic plants transplanted in the saline pool containing 0.5% NaCl in a greenhouse, 22 survived, 13 of which set seeds, and the frequency of seed setting was very low, only 10% . But the controls could not grow under the same condition. The results of BADH ac-tivity assay and Northern blot showed that the BADH gene was integrated into chromosomes of transgenic plants and expressed. 相似文献
108.
宽寄螨属一新种:蜱螨亚纲:胭螨科 总被引:2,自引:1,他引:1
本文描述阔腹宽寄螨,新种Euryparasituslaxiventralissp.nvo.,并讨论了与近似促长安宽寄螨E.changanensisGuetHuang的鉴别要点,模式标本采自贵州省思南县褐家鼠RattusnorvegicusBerkenbout体上,存放在南京大学医学院寄生虫学教研究。 相似文献
109.
Limited proteolysis of glutamine synthetase from Escherichia coli has been studied under nondenaturing conditions (pH 7.6, 20 degrees C). Trypsin cleaves the polypeptide chain of glutamine synthetase into two principal fragments, Mr = about 32,000 and 18,000. The covalently bound AMP group is attached to the larger fragment and its presence does not affect cleavage. Although the cleaved polypeptide chain does not dissociate under nondenaturing conditions, catalytic activity is lost. Chymotrypsin and Staphylococcus aureus protease produce similar cleavages in glutamine synthetase. The substrate L-glutamate retards tryptic as well as chymotryptic digestion. Tryptic digestion is also retarded by some of the feedback inhibitors of glutamine synthetase including CTP, L-alanine, L-serine, L-histidine, and glucosamine 6-phosphate. An implication of these findings is that there is a region of the glutamine synthetase polypeptide chain that is particularly susceptible to proteolysis. Either the glutamate and inhibitor sites are formed partly by this suceptible peptide or the binding of glutamate and some inhibitors induces conformational changes within the E. coli glutamine synthetase molecule in the region of the susceptible peptide. 相似文献
110.