全文获取类型
收费全文 | 63243篇 |
免费 | 5289篇 |
国内免费 | 53篇 |
专业分类
68585篇 |
出版年
2023年 | 219篇 |
2022年 | 666篇 |
2021年 | 1127篇 |
2020年 | 641篇 |
2019年 | 846篇 |
2018年 | 1312篇 |
2017年 | 1043篇 |
2016年 | 1790篇 |
2015年 | 2925篇 |
2014年 | 3307篇 |
2013年 | 3797篇 |
2012年 | 4945篇 |
2011年 | 4715篇 |
2010年 | 3006篇 |
2009年 | 2642篇 |
2008年 | 3770篇 |
2007年 | 3464篇 |
2006年 | 3159篇 |
2005年 | 2885篇 |
2004年 | 2787篇 |
2003年 | 2488篇 |
2002年 | 2129篇 |
2001年 | 1811篇 |
2000年 | 1674篇 |
1999年 | 1317篇 |
1998年 | 589篇 |
1997年 | 509篇 |
1996年 | 428篇 |
1995年 | 432篇 |
1994年 | 346篇 |
1993年 | 325篇 |
1992年 | 690篇 |
1991年 | 567篇 |
1990年 | 536篇 |
1989年 | 523篇 |
1988年 | 442篇 |
1987年 | 421篇 |
1986年 | 348篇 |
1985年 | 368篇 |
1984年 | 299篇 |
1983年 | 252篇 |
1982年 | 209篇 |
1981年 | 186篇 |
1980年 | 172篇 |
1979年 | 241篇 |
1978年 | 210篇 |
1977年 | 195篇 |
1976年 | 182篇 |
1974年 | 213篇 |
1973年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Sung Ho Son Sung Mee Choi Kum Boo Choi Yun Hee Lee Dea Sook Lee Myung Suk Choi Young Goo Park 《Biotechnology and Bioprocess Engineering》1999,4(2):112-118
Calli were induced from 300,000 embryos isolated from immature to mature stage of seeds collected on late September from 14
elite trees. When the embryos were cultured onto plastic Petri-dish containing 20 mL of modified B5 basal medium supplemented
with 3% (w/v) sucrose, 500 mg/L casein hydrolysate, 250 mg/L myo-inositol, 0.5% (w/v) polyvinyl polypyrrolidon (PVPP), 2×MS
vitamins, 0.5 mg/L gibberellic acid, and 10 mg/L 2,4-D after 2 weeks of culture, yellowish-white calli were immediately formed
on the surfaces of embryos, and subcultured for 4 weeks in same culture medium. Because most of calli maintained for more
than 3 months were revealed differences in their colors, surface texture, and growth rate, visual selection was made for first
round screening. When the size of visually selected calli larger than 19 mm in their diameter were inoculated, persistent
proliferation was observed. Among the plating methods tested for the selection of rapid growing cell lines at single cell
and/or small cell aggregate level, 2-layer spread plating revealed as the best for single cell cloning. To enhance cell growth
and maintain high rate of viability for long-term culture of yew cells in bioreactor, final cell volume less than 50% in SCV
seemed to be the best. Time course study revealed that 30% of inoculum density was suitable for fed batch culture. Among the
tested conditional media, the rate of 1∶2 (old medium: fresh medium) was recorded at the best for cell growth. 相似文献
72.
The effect of overexpression of the heat shock chaperone genes dnaK and groESL on heterologous protein production in Escherichia coli was examined, using a set of related human procollagenase proteins. A diverse range of effects on protein solubility, secretion, and accumulation was observed, and these effects were highly dependent on the particular chaperone/procollagenase pairing involved. Both chaperones caused a large increase in the apparent solubility of a fusion of the LamB signal peptide to procollagenase. GroESL had no effect on the accumulation of mature (secreted) procollagenase, while DnaK suppressed secretion considerably. In the absence of a signal peptide, overexpression of either chaperone resulted in a dramatic increase in both solubility and accumulation of procollagenase. The 10-fold increase in accumulation was associated with an increase in in vivo protein half-life. 相似文献
73.
74.
75.
76.
77.
The 24-h time budget of a takh harem stallion (Equus ferus przewalskii) pre- and post-reintroduction
Lee Boyd 《Applied animal behaviour science》1998,60(4):291-299
Focal animal sampling was used to determine the 24-h time budget of a takh harem stallion (Equus ferus przewalskii) during the 2 weeks prior to, and the two weeks following, reintroduction into the Hustain Nuruu Steppe Reserve, Mongolia. Both before and after release, the stallion spent approximately 47% of his time grazing, 6% standing, and 5% in recumbent rest. The biggest changes to the time budget after release were a 4-fold increase in the amount of time spent moving, and a 50% decrease in the amount of time spent resting in a standing position. During the middle of the day when the temperatures were hottest, the stallion exhibited less grazing and more standing resting behaviour than in the morning or evening hours. Recumbent rest invariably occurred in the hours before dawn. 相似文献
78.
The CO-stretching mode of the carbon monoxide ligand in reduced cytochrome P450cam, in the absence or presence of camphor and in the presence of nine different camphor analogues, was measured at room temperature using Fourier transform infrared spectroscopy. Substrate-free cytochrome P450cam--CO reveals a broad, slightly structured band resulting from an overlap of several stretching mode signals. The multitude of the signals indicates that cytochrome P450 exists in a dynamic equilibrium of several conformational substates. Binding of camphor or camphor analogues strongly influences this equilibrium. For substrate analogues which are not able to form a hydrogen bond to the hydroxyl group of tyrosine 96, the CO-stretching band is rather broad and asymmetric. In contrast, substrate analogues with one quinone group which form a hydrogen bond to the Tyr96 OH induce a shift and a sharpening of the CO-stretching mode band. For substrate analogues with two hetero groups, the infrared spectrum is slightly asymmetric or a minor band appears. Sterical hindrance, substrate mobility, and protein flexibility finally determine the position and width of the CO-stretching mode signals. 相似文献
79.
80.