全文获取类型
收费全文 | 73913篇 |
免费 | 7330篇 |
国内免费 | 1511篇 |
出版年
2022年 | 743篇 |
2021年 | 1427篇 |
2020年 | 961篇 |
2019年 | 1197篇 |
2018年 | 1471篇 |
2017年 | 1210篇 |
2016年 | 1685篇 |
2015年 | 2121篇 |
2014年 | 2663篇 |
2013年 | 3030篇 |
2012年 | 3321篇 |
2011年 | 3346篇 |
2010年 | 2090篇 |
2009年 | 1999篇 |
2008年 | 2514篇 |
2007年 | 2389篇 |
2006年 | 2247篇 |
2005年 | 1946篇 |
2004年 | 1802篇 |
2003年 | 1707篇 |
2002年 | 1573篇 |
2001年 | 4930篇 |
2000年 | 4459篇 |
1999年 | 3320篇 |
1998年 | 1118篇 |
1997年 | 1062篇 |
1996年 | 928篇 |
1995年 | 829篇 |
1994年 | 723篇 |
1993年 | 639篇 |
1992年 | 2028篇 |
1991年 | 1774篇 |
1990年 | 1587篇 |
1989年 | 1431篇 |
1988年 | 1218篇 |
1987年 | 1153篇 |
1986年 | 972篇 |
1985年 | 929篇 |
1984年 | 667篇 |
1983年 | 588篇 |
1979年 | 663篇 |
1978年 | 478篇 |
1975年 | 509篇 |
1974年 | 599篇 |
1973年 | 583篇 |
1972年 | 594篇 |
1971年 | 558篇 |
1970年 | 544篇 |
1969年 | 544篇 |
1968年 | 446篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Z V Gorbach S S Maglysh V L Kubyshin Iu M Ostrovski? 《Biokhimii?a (Moscow, Russia)》1985,50(8):1261-1268
Thiamine deficiency in rats induced by oxythiamine is accompanied by an increase in the free NADP+/NADPH ratio in liver tissue, which results in multifold stimulation of the metabolite flux in the oxidation branch of the pentose cycle. The increase in the intracellular concentrations of isocitrate and alpha-ketoglutarate with a simultaneous decrease of malate in the liver of vitamin-deficient rats points to the inhibition of alpha-ketoglutarate dehydrogenase responsible for the anomalous metabolism under conditions of thiamine deficiency. The decrease of the functional activity of the tricarboxylic acid cycle is concomitant with the activation of conversions in the oxidation branch of the pentose cycle, glucuronate and glycolytic pathways of carbohydrate metabolism, which is directed at eliminating the energy deficiency in rats with B1-hypovitaminosis. 相似文献
92.
The electrochemical oxidation of a number of N-methylated uric acids at the pyrolytic graphite and gold electrodes has been compared to their enzymic oxidation with type VIII peroxidase and H2O2. Spectral, electroanalytical and kinetic evidence supports the conclusion that for all compounds the electrochemical and enzymic reactions proceed by identical mechanisms. 相似文献
93.
An explicit high-order, symplectic, finite-difference time-domain (SFDTD) scheme is applied to a bioelectromagnetic simulation using a simple model of a pregnant woman and her fetus. Compared to the traditional FDTD scheme, this scheme maintains the inherent nature of the Hamilton system and ensures energy conservation numerically and a high precision. The SFDTD scheme is used to predict the specific absorption rate (SAR) for a simple model of a pregnant female woman (month 9) using radio frequency (RF) fields from 1.5 T and 3 T MRI systems (operating at approximately 64 and 128 MHz, respectively). The results suggest that by using a plasma protective layer under the 1.5 T MRI system, the SAR values for the pregnant woman and her fetus are significantly reduced. Additionally, for a 90 degree plasma protective layer, the SAR values are approximately equal to the 120 degree layer and the 180 degree layer, and it is reduced relative to the 60 degree layer. This proves that using a 90 degree plasma protective layer is the most effective and economical angle to use. 相似文献
94.
Six peripheral blood lymphoid fractions (total lymphocytes, non-T, T, Tar (autologous rosette-forming T cells/precursor), T mu (helper), and T gamma (suppressor) lymphocytes) isolated through rosetting procedures were examined for the presence of ferritin by a direct immunofluorescence technique. Although ferritin was present in all lymphoid fractions studied, a significantly higher proportion of ferritin-containing cells were detected in the T-cell fraction than in the non-T-cell fraction, (mean +/- SD = 7.9 +/- 1.6% and 5.0 +/- 1.2%, respectively). T mu- and T gamma-cell fractions showed a twofold increase in the number of ferritin-positive cells (14.1 +/- 1.4% and 15.4 +/- 2.6%, respectively), as compared with Tar (7.0 +/- 0.9%)-and total lymphocyte (6.9 +/- 1.3%)-cell fractions. These results indicate that ferritin is preferentially distributed in T mu and T gamma lymphocytes and may constitute the basis for explaining some of the roles exercised by these cells in the control of other biological systems. 相似文献
95.
Zhenzhen Zhang Changjiu He Yu Gao Lu Zhang Yukun Song Tianqi Zhu Kuanfeng Zhu Dongying Lv Jing Wang Xiuzhi Tian Teng Ma Pengyun Ji Wei Cui Guoshi Liu 《Aging cell》2021,20(2)
The fecundity reduction with aging is referred as the reproductive aging which comes earlier than that of chronological aging. Since humans have postponed their childbearing age, to prolong the reproductive age becomes urgent agenda for reproductive biologists. In the current study, we examined the potential associations of α‐ketoglutarate (α‐KG) and reproductive aging in mammals including mice, swine, and humans. There is a clear tendency of reduced α‐KG level with aging in the follicle fluids of human. To explore the mechanisms, mice were selected as the convenient animal model. It is observed that a long term of α‐KG administration preserves the ovarian function, the quality and quantity of oocytes as well as the telomere maintaining system in mice. α‐KG suppresses ATP synthase and alterations of the energy metabolism trigger the nutritional sensors to down‐regulate mTOR pathway. These events not only benefit the general aging process but also maintain ovarian function and delay the reproductive decline. Considering the safety of the α‐KG as a naturally occurring molecule in energy metabolism, its utility in reproduction of large mammals including humans deserves further investigation. 相似文献
96.
97.
98.
99.
Z Rondio 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1966,21(42):1593-1595
100.
The family of flaviviruses is one of the most medically important groups of emerging arthropod-borne viruses. Host cell cytoskeletons have been reported to have close contact with flaviviruses during virus entry, intracellular transport, replication, and egress process, although many detailed mechanisms are still unclear. This article provides a brief overview of the function of the most prominent flaviviruses-induced or-hijacked cytoskeletal structures including actin, microtubules and intermediate filaments, mainly focus on infection by dengue virus, Zika virus and West Nile virus. We suggest that virus interaction with host cytoskeleton to be an interesting area of future research. 相似文献