全文获取类型
收费全文 | 19033篇 |
免费 | 1628篇 |
国内免费 | 6篇 |
出版年
2021年 | 171篇 |
2020年 | 122篇 |
2019年 | 174篇 |
2018年 | 232篇 |
2017年 | 176篇 |
2016年 | 310篇 |
2015年 | 522篇 |
2014年 | 613篇 |
2013年 | 1047篇 |
2012年 | 995篇 |
2011年 | 972篇 |
2010年 | 667篇 |
2009年 | 602篇 |
2008年 | 967篇 |
2007年 | 968篇 |
2006年 | 922篇 |
2005年 | 982篇 |
2004年 | 977篇 |
2003年 | 902篇 |
2002年 | 953篇 |
2001年 | 391篇 |
2000年 | 410篇 |
1999年 | 407篇 |
1998年 | 271篇 |
1997年 | 179篇 |
1996年 | 160篇 |
1995年 | 206篇 |
1994年 | 187篇 |
1993年 | 174篇 |
1992年 | 276篇 |
1991年 | 311篇 |
1990年 | 266篇 |
1989年 | 251篇 |
1988年 | 275篇 |
1987年 | 250篇 |
1986年 | 224篇 |
1985年 | 249篇 |
1984年 | 246篇 |
1983年 | 193篇 |
1982年 | 195篇 |
1981年 | 209篇 |
1980年 | 197篇 |
1979年 | 153篇 |
1978年 | 162篇 |
1977年 | 129篇 |
1976年 | 110篇 |
1975年 | 116篇 |
1974年 | 132篇 |
1973年 | 127篇 |
1972年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
1.
Kenneth S. Ramos Kathryn K. McMahon Celestine Alipui Diane Demick 《Cell biology and toxicology》1991,7(2):111-128
Studies were conducted to determine if in vivo exposure to dinitrotoluenes (DNT), which is associated with circulatory disorders of atherosclerotic etiology in humans, is associated with alterations of vascular smooth muscle cells (SMC) consistent with the atherogenic process. Sprague-Dawley rats (150-180 g) were injected IP for 5 days/week for 8 weeks with 2,4- or 2,6-DNT (0.5, 5, or 10 mg/kg) or medium chain triglyceride (MCT) oil. Histopathologic evaluation of aortae from animals exposed to either isomer showed dysplasia and rearrangement of SMC at all doses tested. Reduced 3H-thymidine incorporation was observed in primary cultures of aortic SMC from DNT-exposed animals relative to vehicle controls. This inhibitory response was maintained for up to two passages in culture after which a significant increase in thymidine incorporation was observed. Exposure of SMC from naive animals to DNT in vitro (1–100 µM) did not alter the extent of thymidine incorporation in cycling or growth-arrested cultures. In contrast, exposure to 2,4- or 2,6-diaminotoluene (DAT) (1–100 µM), carcinogens which share toxic metabolic intermediates in common with DNT, inhibited replicative DNA synthesis and stimulated unscheduled DNA synthesis in cycling and growth-arrested cultures of SMC, respectively. Our results suggest that modulation of DNA synthesis in aortic SMC by DNT metabolites generated in vivo contribute to the development of vascular lesions.Abbreviation DAT
diaminotuluene
- tDNT
technical grade dinitrotoluene
- DNT
dinitrotoluenes
- HU
hydroxyurea
- IP
intraperitoneal
- LDH
lactate dehydrogenase
- MCT oil
medium chain triglyceride
- NPTC
non-protein thiol content
- RDS
replicative DNA synthesis
- SEM
standard error of the mean
- SMC
smooth muscle cells
- UDS
unscheduled DNA synthesis 相似文献
2.
Yufeng Qian Aashiq H. Kachroo Christopher M. Yellman Edward M. Marcotte Kenneth A. Johnson 《The Journal of biological chemistry》2014,289(9):5970-5985
Mutations in the human mitochondrial polymerase (polymerase-γ (Pol-γ)) are associated with various mitochondrial disorders, including mitochondrial DNA (mtDNA) depletion syndrome, Alpers syndrome, and progressive external opthamalplegia. To correlate biochemically quantifiable defects resulting from point mutations in Pol-γ with their physiological consequences, we created “humanized” yeast, replacing the yeast mtDNA polymerase (MIP1) with human Pol-γ. Despite differences in the replication and repair mechanism, we show that the human polymerase efficiently complements the yeast mip1 knockouts, suggesting common fundamental mechanisms of replication and conserved interactions between the human polymerase and other components of the replisome. We also examined the effects of four disease-related point mutations (S305R, H932Y, Y951N, and Y955C) and an exonuclease-deficient mutant (D198A/E200A). In haploid cells, each mutant results in rapid mtDNA depletion, increased mutation frequency, and mitochondrial dysfunction. Mutation frequencies measured in vivo equal those measured with purified enzyme in vitro. In heterozygous diploid cells, wild-type Pol-γ suppresses mutation-associated growth defects, but continuous growth eventually leads to aerobic respiration defects, reduced mtDNA content, and depolarized mitochondrial membranes. The severity of the Pol-γ mutant phenotype in heterozygous diploid humanized yeast correlates with the approximate age of disease onset and the severity of symptoms observed in humans. 相似文献
3.
Shunsuke Yaguchi Atsuko Yamazaki Wakana Wada Yasutaka Tsuchiya Toshihiko Sato Hideo Shinagawa Yutaro Yamada Junko Yaguchi 《Development, growth & differentiation》2015,57(3):242-250
Sea urchins are model non‐chordate deuterostomes, and studying the nervous system of their embryos can aid in the understanding of the universal mechanisms of neurogenesis. However, despite the long history of sea urchin embryology research, the molecular mechanisms of their neurogenesis have not been well investigated, in part because neurons appear relatively late during embryogenesis. In this study, we used the species Temnopleurus reevesii as a new sea urchin model and investigated the detail of its development and neurogenesis during early embryogenesis. We found that the embryos of T. reevesii were tolerant of high temperatures and could be cultured successfully at 15–30°C during early embryogenesis. At 30°C, the embryos developed rapidly enough that the neurons appeared at just after 24 h. This is faster than the development of other model urchins, such as Hemicentrotus pulcherrimus or Strongylocentrotus purpuratus. In addition, the body of the embryo was highly transparent, allowing the details of the neural network to be easily captured by ordinary epifluorescent and confocal microscopy without any additional treatments. Because of its rapid development and high transparency during embryogenesis, T. reevesii may be a suitable sea urchin model for studying neurogenesis. Moreover, the males and females are easily distinguishable, and the style of early cleavages is intriguingly unusual, suggesting that this sea urchin might be a good candidate for addressing not only neurology but also cell and developmental biology. 相似文献
4.
Y. Yamada 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(4):655-658
Conclusions The comparison of different selection indices is justified only if the indices are constrated to achieve the same profit function, even when each index is not optimized with respect to that profit function.When a profit function is known and is non-linear, the desired gains index may be more efficient than the economic index. The optimum desired gains index should be determined by iterative techniques over several generations to compare the genetic progress with the economic index, because gains by the economic index are not linear and the changes observed in the initial generations of selection are not the same rates in future generations, although those changes are linear in the case of the desired gains index. 相似文献
5.
6.
Mohammed Mamdani Vernell Williamson Gowon O. McMichael Tana Blevins Fazil Aliev Amy Adkins Laura Hack Tim Bigdeli Andrew D. van der Vaart Bradley Todd Web Silviu-Alin Bacanu Gursharan Kalsi COGA Consortium Kenneth S. Kendler Michael F. Miles Danielle Dick Brien P. Riley Catherine Dumur Vladimir I. Vladimirov 《PloS one》2015,10(9)
7.
Abstract: Bovine adrenal chromaffin cells (BCC) were used to compare histamine- and angiotensin II-induced changes of inositol mono-, bis-, and trisphosphate (InsP1, InsP2, and InsP3, respectively) isomers, intracellular free Ca2+ ([Ca2+]i), and the pathways of inositol phosphate metabolism. Both agonists elevated [Ca2+]i by 200 nM 3–4 s after addition, but afterwards the histamine response was much more prolonged. Histamine and angiotensin II also produced similar four- to fivefold increases of Ins(1,4,5)P3 that peaked within 5 s. Over the first minute of stimulation, however, Ins(1,4,5)P3 formation was monophasic after angiotensin II, but biphasic after histamine, evidence supporting differential regulation of angiotensin II- and histamine-stimulated signal transduction. The metabolism of Ins(1,4,5)P3 by BCC homogenates was found to proceed via (a) sequential dephosphorylation to Ins(1,4)P2 and Ins(4)P, and (b) phosphorylation to inositol 1,3,4,5-tetrakisphosphate, followed by dephosphorylation to Ins(1,3,4)P3, Ins(1,3)P2, and Ins(3,4)P2, and finally to Ins(1 or 3)P. In whole cells, Ins(1 or 3)P only increased after histamine treatment. Additionally, Ins(1,3)P2 was the only other InsP2 besides Ins(1,4)P2 to accumulate within 1 min of agonist treatment [Ins(3,4)P2 did not increase]. These results support a correlation between the time course of Ins(1,4,5)P3 formation and the time course of [Ca2+]i transients and illustrate that Ca2+-mobilizing agonists can produce distinguishable patterns of inositol phosphate formation and [Ca2+], changes in BCC. Different patterns of second-messenger formation are likely to be important in signal recognition and may encode agonist-specific information. 相似文献
8.
9.
10.
The XbaI-BlnI-CeuI genomic cleavage map of Salmonella enteritidis shows an inversion relative to Salmonella typhimurium LT2 总被引:10,自引:0,他引:10
We have established the genomic cleavage map of Salmonella enteritidis strain SSU7998 using pulsed-field gel electrophoresis. The chromosome of 4600kb was analysed by XbaI (16 fragments), I-CeuI (7 fragments) and BlnI (12 fragments); the genome also contains a plasmid of 60 kb. Cleavage sites of I-CeuI, in the large subunit ribosomal RNA gene, are conserved from Salmonella typhimurium and Escherichia coli K-12, and the XbaI and BinI sites in glt-tRNA are also conserved, but other sites are less conserved. Transposon Tn10, located at 60 different positions in the chromosome of S. typhimurium, was transduced by bacteriophage P22 into S. enteritidis and the insertion mapped using the XbaI and BlnI sites on Tn10. Gene order in S. enteritidis is identical to S. typhimurium LT2 and similar to E. coli K-12 except for an inversion of 815 kb, which covers the terminus region including T1 and T2. Endpoints are in the NDZs, or non-divisible zones, in which inversion endpoints were not detected in experiments in E. coli K-12 and S. typhimurium LT2. This inversion resembles the inversion between S. typhimurium and E. coli, but is longer at both ends. 相似文献