全文获取类型
收费全文 | 9445篇 |
免费 | 722篇 |
国内免费 | 40篇 |
专业分类
10207篇 |
出版年
2024年 | 10篇 |
2023年 | 43篇 |
2022年 | 136篇 |
2021年 | 200篇 |
2020年 | 141篇 |
2019年 | 194篇 |
2018年 | 275篇 |
2017年 | 242篇 |
2016年 | 364篇 |
2015年 | 542篇 |
2014年 | 633篇 |
2013年 | 696篇 |
2012年 | 866篇 |
2011年 | 797篇 |
2010年 | 578篇 |
2009年 | 473篇 |
2008年 | 582篇 |
2007年 | 564篇 |
2006年 | 494篇 |
2005年 | 434篇 |
2004年 | 433篇 |
2003年 | 324篇 |
2002年 | 339篇 |
2001年 | 152篇 |
2000年 | 127篇 |
1999年 | 113篇 |
1998年 | 52篇 |
1997年 | 55篇 |
1996年 | 41篇 |
1995年 | 30篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 27篇 |
1991年 | 38篇 |
1990年 | 27篇 |
1989年 | 23篇 |
1988年 | 9篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1968年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Michael D. Jensen Ji?í Bajnárek Sang Yeoup Lee Soren Nielsen Christina Koutsari 《Journal of lipid research》2009,50(9):1863-1869
The relationship between overnight postabsorptive (fasting) respiratory exchange ratio (RER) and plasma FFA concentrations was addressed using data from three separate protocols, each of which involved careful control of the antecedent diet. Protocol 1 examined the relationship between fasting RER and the previous daytime RER. In Protocol 2 fasting, RER and plasma palmitate concentrations were measured in 29 women and 31 men (body mass index <30 kg·m−2). Protocol 3 analyzed data from Nielsen et al. (Nielsen, S., Z. K. Guo, J. B. Albu, S. Klein, P. C. O''Brien, M. D. Jensen. 2003. Energy expenditure, sex and endogenous fuel availability in humans. J. Clin. Invest. 111: 981-988.) to understand how fasting RER and palmitate concentrations relate within individuals during four consecutive measurements. The results were as follows: 1) Fasting RER was correlated (r = 0.74, P < 0.001) with the previous day''s average RER, and less so with RER variability. 2) Fasting RER was correlated (r = −0.39, P = 0.007) with fasting plasma palmitate concentrations. 3) The pattern of the RER/palmitate relationship was similar within individuals and between individuals; a negative slope was observed significantly more often than a positive slope (χ2 test; P < 0.001). Our findings suggest that, despite a fixed food quotient, the slight departures from energy equilibrium in a controlled General Clinical Research Center environment can effect plasma FFA concentrations. We suggest that including indirect calorimetry as part of FFA metabolism studies may aid in data interpretation. 相似文献
3.
Tyrosinase plays a pivotal role in the synthesis of melanin pigment synthesis on skin utilizing tyrosine as a substrate. Melanin is responsible for the protection against harmful ultraviolet irradiation, which can cause significant pathological conditions, such as skin cancers. However, it can also create esthetic problems when accumulated as hyperpigmented spots. Various skin-whitening ingredients which inhibit tyrosinase activity have been identified. Some of them, especially ones with natural product origins, possess phenolic moiety and have been employed in cosmetic products. Semi-synthetic and synthetic inhibitors have also been developed under inspiration of the natural inhibitors yet some of which have no phenolic groups. In this review, tyrosinase inhibitors with natural, semi-synthetic and synthetic origins are listed up with their structures, activities and characteristics. Further, a recent report on the adverse effect of a natural melanin synthesis inhibitor which was included in skin-whitening cosmetics is also briefly discussed. 相似文献
4.
5.
Scaffolding proteins are involved in the incorporation, anchoring, maintenance, and removal of AMPA receptors (AMPARs) at synapses, either through a direct interaction with AMPARs or via indirect association through auxiliary subunits of transmembrane AMPAR regulatory proteins (TARPs). Synaptic scaffolding molecule (S-SCAM) is a newly characterized member of the scaffolding proteins critical for the regulation and maintenance of AMPAR levels at synapses, and directly binds to TARPs through a PDZ interaction. However, the functional significance of S-SCAM–TARP interaction in the regulation of AMPARs has not been tested. Here we show that overexpression of the C-terminal peptide of TARP-γ2 fused to EGFP abolished the S-SCAM-mediated enhancement of surface GluA2 expression. Conversely, the deletion of the PDZ-5 domain of S-SCAM that binds TARPs greatly attenuated the S-SCAM-induced increase of surface GluA2 expression. In contrast, the deletion of the guanylate kinase domain of S-SCAM did not show a significant effect on the regulation of AMPARs. Together, these results suggest that S-SCAM is regulating AMPARs through TARPs. 相似文献
6.
7.
8.
Distinct effects of climate warming on populations of silver fir (Abies alba) across Europe 下载免费PDF全文
9.
Effect of limited homology on gene conversion in a Saccharomyces cerevisiae plasmid recombination system. 总被引:19,自引:10,他引:9 下载免费PDF全文
B Y Ahn K J Dornfeld T J Fagrelius D M Livingston 《Molecular and cellular biology》1988,8(6):2442-2448
Plasmids containing heteroallelic copies of the Saccharomyces cerevisiae HIS3 gene undergo intramolecular gene conversion in mitotically dividing S. cerevisiae cells. We have used this plasmid system to determine the minimum amount of homology required for gene conversion, to examine how conversion tract lengths are affected by limited homology, and to analyze the role of flanking DNA sequences on the pattern of exchange. Plasmids with homologous sequences greater than 2 kilobases have mitotic exchange rates as high as 2 x 10(-3) events per cell per generation. As the homology is reduced, the exchange rate decreases dramatically. A plasmid with 26 base pairs (bp) of homology undergoes gene conversion at a rate of approximately 1 x 10(-10) events per cell per generation. These studies have also shown that an 8-bp insertion mutation 13 bp from a border between homologous and nonhomologous sequences undergoes conversion, but that a similar 8-bp insertion 5 bp from a border does not. Examination of independent conversion events which occurred in plasmids with heteroallelic copies of the HIS3 gene shows that markers within 280 bp of a border between homologous and nonhomologous sequences undergo conversion less frequently than the same markers within a more extensive homologous sequence. Thus, proximity to a border between homologous and nonhomologous sequences shortens the conversion tract length. 相似文献
10.
H Y Ahn L F Sue J K Ma C A Pinkstaff R S Pore D O Overman C J Malanga 《Biochimica et biophysica acta》1988,966(1):122-132
The ability of the isolated gill epithelium of Mytilus edulis to incorporate [14C]glucosamine as a precursor in the biosynthesis and secretion of mucous glycoproteins was investigated. Localization of mucous cells in the gill filament was achieved using histochemical staining techniques. Mucus cells containing neutral and acidic mucins were found in the lateral region, whereas mucus cells containing primarily neutral or sulfated mucins were found in the abfrontal region. Autoradiographic results showed that in both regions, the mucous cells were rich in content of the incorporated radiolabel. The secreted glycoproteins containing the incorporated radiolabel were analyzed by column chromatography using Bio-Gel P-2 and P-6. Two populations of the glycoproteins differing in molecular size were isolated. Upon alkaline reductive borohydride cleavage of the O-glycosidic linkages of the high molecular weight protein, about 70% of the radiolabel and 85% of the carbohydrate content were removed from the protein. The alkaline borohydride cleavage resulted in the formation of at least six oligosaccharide chains of various lengths of sugar units. Gas chromatographic analysis of the carbohydrate composition shows that the glycoproteins contain N-acetylglucosamine, N-acetylgalactosamine, and galactose, fucose, and mannose as the neutral monosaccharides. The above results indicate that the isolated gill epithelium of M. edulis is capable of incorporating [14C]glucosamine in the synthesis of secretable mucin-type glycoproteins. 相似文献