全文获取类型
收费全文 | 2993篇 |
免费 | 179篇 |
专业分类
3172篇 |
出版年
2023年 | 14篇 |
2022年 | 39篇 |
2021年 | 56篇 |
2020年 | 35篇 |
2019年 | 75篇 |
2018年 | 69篇 |
2017年 | 53篇 |
2016年 | 89篇 |
2015年 | 164篇 |
2014年 | 140篇 |
2013年 | 211篇 |
2012年 | 244篇 |
2011年 | 211篇 |
2010年 | 136篇 |
2009年 | 101篇 |
2008年 | 175篇 |
2007年 | 180篇 |
2006年 | 170篇 |
2005年 | 162篇 |
2004年 | 161篇 |
2003年 | 133篇 |
2002年 | 152篇 |
2001年 | 23篇 |
2000年 | 18篇 |
1999年 | 29篇 |
1998年 | 21篇 |
1997年 | 19篇 |
1996年 | 24篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 11篇 |
1991年 | 19篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 23篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有3172条查询结果,搜索用时 15 毫秒
1.
2.
Roberta L. Millstein 《Journal of the history of biology》2008,41(2):339-367
Biologists and philosophers have been extremely pessimistic about the possibility of demonstrating random drift in nature,
particularly when it comes to distinguishing random drift from natural selection. However, examination of a historical case
– Maxime Lamotte’s study of natural populations of the land snail, Cepaea nemoralis in the 1950s – shows that while some pessimism is warranted, it has been overstated. Indeed, by describing a unique signature
for drift and showing that this signature obtained in the populations under study, Lamotte was able to make a good case for
a significant role for␣drift. It may be difficult to disentangle the causes of drift and selection acting in a population,
but it is not (always) impossible. 相似文献
3.
Francesca Passaretta Domenico Bosco Lucia Centurione Maria Antonietta Centurione Fabio Marongiu Roberta Di Pietro 《Journal of cellular and molecular medicine》2020,24(7):4350-4355
Human Amniotic Epithelial Cells (hAEC) isolated from term placenta are a promising source for regenerative medicine. However, it has long been debated whether the hAEC population consists of heterogeneous or homogeneous cells. In a previous study, we investigated the characteristics of hAEC isolated from four different regions of the amniotic membrane finding significant heterogeneity. The aim of this study was to evaluate the hepatic differentiation capability of hAEC isolated from these four regions. Human term placentae were collected after caesarean section and hAEC were isolated from four regions of the amniotic membrane (R1-R4, according to their relative distance from the umbilical cord) and treated in hepatic differentiation conditions for 14 days. hAEC-derived hepatocyte-like cells showed marked differences in the expression of hepatic markers: R4 showed higher levels of Albumin and Hepatocyte Nuclear Factor (HNF) 4α whereas R1 expressed higher Cytochrome P450 enzymes, both at the gene and protein level. These preliminary results suggest that hAEC isolated from R1 and R4 of the amniotic membrane are more prone to hepatic differentiation. Therefore, the use of hAEC from a specific region of the amniotic membrane should be taken into consideration as it could have an impact on the outcome of therapeutic applications. 相似文献
4.
K P Ossenkopp M Kavaliers F S Prato G C Teskey E Sestini M Hirst 《Life sciences》1985,37(16):1507-1514
Adult male mice exposed to a Nuclear Magnetic Resonance Imaging (NMRI) procedure during the mid-dark period and injected with morphine (10 mg/kg) failed to exhibit the normal nocturnally enhanced morphine analgesia response to a thermal stimulus that was displayed by mice exposed to a sham imaging procedure and treated with morphine (p less than .01). When tested during the mid-light period, animals exposed to the NMRI procedure and given morphine displayed attenuated analgesia levels relative to sham exposed mice (p less than .01) treated with morphine. However, the morphine induced analgesia was not totally abolished since the imaged mice still exhibited analgesia relative to saline treated mice (p less than .01). These results suggest that the magnetic and/or radio-frequency fields associated with the NMRI procedure alter both day- and night-time responses to morphine. These results may reflect magnetic field induced alterations in neuronal calcium binding and/or alterations in nocturnal pineal gland activity. 相似文献
5.
6.
7.
8.
9.
10.
At inflammatory sites neutrophils are stimulated to produce a variety of toxic agents, yet rarely harm the endothelium across which they migrate. We have recently found that endothelium releases adenosine which, acting via receptors on the surface of human neutrophils, inhibits generation of toxic metabolites by stimulated neutrophils but, paradoxically, promotes chemotaxis. Agents which diminish plasma membrane viscosity affect neutrophil function similarly, possibly by modulating chemoattractant receptor number or affinity. We therefore determined whether adenosine receptor agonists modulate neutrophil function by decreasing membrane viscosity and/or chaning the affinity of chemoattractant (N-fMet-Leu-Phe, FMLP) receptors. Surprisingly, 5′-(N-ethylcar☐amido)adenosine (NECA, 10 μM), the most potent agonist at neutrophil adenosine receptors, increased plasma membrane viscosity, as measured by fluorescence anisotropy of the plasma membrane specific probe 1-(4-trimethylaminophenyl)-6-diphenyl-1,3,5-hexatriene (TMA-DPH), in unstimulated neutrophils from a mean microviscosity of 1.67 ± 0.02 (S.E.) to 1.80 ± 0.02 (p < 0.001) while inosine (10 μM), a poor adenosine receptor agonist, had no effect (1.73 ± 0.04, p =n.s. vs. control, p < 0.01 vs. NECA). Adenosine receptor agonists increased plasma membrane viscosity in neutrophils with the same order of potency previously seen for inhibition of superoxide anion generation and enhancement of chemotaxis (NECA > adenosine = N6-phenylisopropyladenosine). The adenosine receptor antagonist 8-(p-sulfophenyl)theophylline reversed the effect of NECA on plasma membrane viscosity. Unlike other agents which modulate plasma membrane viscosity, NECA (10 μM) did not significantly change the number or affinity of [3H]FMLP binding sites on neutrophils. In contrast to the hypothesis of Yuli et al. these results indicate that occupancy of adenosine receptors on neutrophils increases plasma membrane viscosity without affecting chemoattractant receptor display. 相似文献