全文获取类型
收费全文 | 11744篇 |
免费 | 45篇 |
国内免费 | 72篇 |
专业分类
系统科学 | 63篇 |
丛书文集 | 29篇 |
教育与普及 | 22篇 |
理论与方法论 | 33篇 |
现状及发展 | 5477篇 |
研究方法 | 604篇 |
综合类 | 5501篇 |
自然研究 | 132篇 |
出版年
2012年 | 208篇 |
2011年 | 308篇 |
2010年 | 77篇 |
2009年 | 76篇 |
2008年 | 211篇 |
2007年 | 247篇 |
2006年 | 253篇 |
2005年 | 239篇 |
2004年 | 211篇 |
2003年 | 204篇 |
2002年 | 249篇 |
2001年 | 437篇 |
2000年 | 427篇 |
1999年 | 290篇 |
1992年 | 237篇 |
1991年 | 195篇 |
1990年 | 217篇 |
1989年 | 192篇 |
1988年 | 201篇 |
1987年 | 219篇 |
1986年 | 191篇 |
1985年 | 252篇 |
1984年 | 228篇 |
1983年 | 171篇 |
1982年 | 177篇 |
1981年 | 180篇 |
1980年 | 171篇 |
1979年 | 403篇 |
1978年 | 341篇 |
1977年 | 255篇 |
1976年 | 292篇 |
1975年 | 262篇 |
1974年 | 273篇 |
1973年 | 229篇 |
1972年 | 244篇 |
1971年 | 308篇 |
1970年 | 376篇 |
1969年 | 254篇 |
1968年 | 308篇 |
1967年 | 295篇 |
1966年 | 249篇 |
1965年 | 178篇 |
1964年 | 99篇 |
1959年 | 88篇 |
1958年 | 162篇 |
1957年 | 101篇 |
1956年 | 91篇 |
1955年 | 85篇 |
1954年 | 77篇 |
1948年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
1.
Prasad Parash Ghosh Sampurna Roy Sib Sankar 《Cellular and molecular life sciences : CMLS》2021,78(10):4821-4845
Cellular and Molecular Life Sciences - Glutamine is essential for maintaining the TCA cycle in cancer cells yet they undergo glutamine starvation in the core of tumors. Cancer stem cells (CSCs),... 相似文献
2.
3.
4.
5.
Vitamin B12 (methylcobalamin) was administered orally (3 mg/day) to 9 healthy subjects for 4 weeks. Nocturnal melatonin levels after exposure to bright light (ca. 2500 lx) were determined, as well as the levels of plasma melatonin over 24 h. The timing of sleep was also recorded. Vitamin B12 was given blind to the subjects and crossed over with placebo. We found that the 24-h melatonin rhythm was significantly phase-advanced (1.1 h) in the vitamin B12 trial as compared with that in the placebo trial. In addition, the 24-h mean of plasma melatonin level was much lower in the vitamin B12 trial than with the placebo. Furthermore, the nocturnal melatonin levels during bright light exposure were significantly lower in the vitamin B12 trial than with the placebo. On the other hand, vitamin B12 did not affect the timing of sleep. These findings raise the possibility that vitamin B12 phase-advances the human circadian rhythm by increasing the light sensitivity of the circadian clock. 相似文献
6.
Shiga toxin and some other protein toxins that act on targets in the cytosol have previously been shown to enter the trans-Golgi network. Transport by this route may be necessary for translocation of the toxin to the cytosol and for intoxication, but it is not known whether the enzymatically active part of the toxins actually enters the cytosol from the trans-Golgi network. It has been suggested that such toxins are transported in a retrograde manner to the endoplasmic reticulum and that translocation occurs in this organelle, but retrograde transport of endocytosed material beyond the trans-Golgi network has never been demonstrated. Here we show that in butyric acid-treated A431 cells endocytosed Shiga toxin is not only transported to the trans-Golgi network, but also to all Golgi stacks, to the endoplasmic reticulum and to the nuclear envelope. Furthermore, butyric acid sensitizes the cells to Shiga toxin, which is consistent with the possibility that retrograde transport is required for translocation of the toxin to the cytosol. 相似文献
7.
8.
A fast and accurate method based on FTIR is developed for determining the lignin content and its characteristic bands in alkali solutions. The work consisted of two main parts: 1) establishing a predictive model and 2) determination of the accuracy of the model. The model was derived by applying the partial least squares algorithm for multivariate analyses to a set of spectrum data obtained from selected IR absorption regions in the range of 1600 - 900 cm-1. The model was tested with spent liquors obtained from commercial pulp mills.The accuracy of the predictive model is extremely high suitable for commercial applications,particularly for monitoring the dynamic response of modern kraft pulping processes. 相似文献
9.
10.
The timing of sleep and sleep EEG parameters in 10 healthy male subjects were investigated in four seasons under controlled conditions. The phase of nocturnal sleep was delayed about one and a half hours in winter as compared to that in summer. The duration of stage 4 sleep decreased and REM sleep increased significantly in winter compared with summer. The seasonality in the timing of sleep can be explained by photoperiodic time cues, but the changes in sleep EEG parameters are difficult to explain in terms of photoperiod. 相似文献