全文获取类型
收费全文 | 4403篇 |
免费 | 292篇 |
国内免费 | 1篇 |
专业分类
4696篇 |
出版年
2022年 | 31篇 |
2021年 | 44篇 |
2020年 | 22篇 |
2019年 | 48篇 |
2018年 | 63篇 |
2017年 | 51篇 |
2016年 | 71篇 |
2015年 | 130篇 |
2014年 | 154篇 |
2013年 | 291篇 |
2012年 | 242篇 |
2011年 | 293篇 |
2010年 | 158篇 |
2009年 | 156篇 |
2008年 | 255篇 |
2007年 | 246篇 |
2006年 | 267篇 |
2005年 | 228篇 |
2004年 | 222篇 |
2003年 | 247篇 |
2002年 | 225篇 |
2001年 | 95篇 |
2000年 | 110篇 |
1999年 | 99篇 |
1998年 | 66篇 |
1997年 | 56篇 |
1996年 | 42篇 |
1995年 | 47篇 |
1994年 | 45篇 |
1993年 | 35篇 |
1992年 | 62篇 |
1991年 | 63篇 |
1990年 | 56篇 |
1989年 | 50篇 |
1988年 | 50篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 27篇 |
1984年 | 24篇 |
1983年 | 26篇 |
1982年 | 14篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1976年 | 19篇 |
1975年 | 17篇 |
1974年 | 15篇 |
1970年 | 10篇 |
1968年 | 16篇 |
排序方式: 共有4696条查询结果,搜索用时 0 毫秒
101.
Melanin inhibited rat liver phenylalanine hydroxylase, but activated tyrosine hydroxylase from rat brain (caudate nucleus), rat adrenal glands, and bovine adrenal medulla. Activation of tyrosine hydroxylase by melanin was demonstrated with the extensively dialyzed enzyme and in suboptimal concentrations of the substrate (tyrosine) and the cofactor (6-methyltetrahydropterin). Tyrosine hydroxylase from rat brain was activated by melanin more markedly than that from rat adrenal glands. Purified and extensively dialyzed bovine adrenal tyrosine hydroxylase had two Km values with 6-methyltetrahydropterin, depending upon its concentrations, but the melanin-activated tyrosine hydroxylase had a single Km value and showed the classical Michaelis-Menten kinetics. 相似文献
102.
103.
In situ hybridization of 3H-labelled ribosomal RNA to the chromosomes of rat bone marrow cells revealed that clusters of ribosomal cistrons (rDNA) are located in the secondary constrictions of chromosomes No. 3 and 12 and near the centromere of chromosome No. 11, both associated with the late DNA-replicating regions. They were not found in Nos. 1, 2, 13, 19, 20, and the Y chromosome. 相似文献
104.
Detection of Clostridium botulinum Toxin by Local Paralysis Elicited with Intramuscular Challenge 下载免费PDF全文
Clostridium botulinum toxin can be identified by a characteristic, acute local paralysis that follows its injection into the gastrocnemius ("calf" muscle) of mice. The local botulism can be elicited with slightly less than one-tenth the toxin amount that is needed to kill mice by the intraperitoneal (i.p.) challenge route. The practical sensitivities of the intramuscular (i.m.) versus i.p. tests are about equal, however, because maximum sample volume injectable i.m. is 0.1 ml as compared to the 0.5-ml range that can be given i.p. i.m. injection of 10 or more mouse i.p. mean lethal doses causes paralysis in about 1 h, and an i.m. injection of about 0.5 i.p. mean lethal doses causes paralysis in 3 to 4 h. Toxin neutralization by homologous type of antitoxin only can be demonstrated with an incubated mixture of toxin and antitoxin. Although not as convenient as the i.p. method for routine use to detect botulinum toxin, the i.m. method has characteristics which could make it a useful supplement to the presently accepted i.p. procedure. 相似文献
105.
106.
Yasuo Mukohata Takao Yagi Yasuo Sugiyama 《Journal of bioenergetics and biomembranes》1975,7(3):103-109
The effects of energy transfer inhibitors, electron transport inhibitors and uncouplers on the ADP-regulated and ADP-independent activity of ferricyanide reduction in isolated spinach chloroplasts were studied. Phlorizin and sulfate did not affect the ADP-independent ferricyanide reduction. In the ADP-regulated reduction, these reagents did not affect the ADP inhibition process but inhibited the activity restoration process due to phosphorylation. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea and linolenic acid depressed both ADP-regulated and ADP-independent activity of ferricyanide reduction. Gramicidin S and 2-amino-1-butanol depressed ADP-regulated activity and stimulated ADP-independent activity. The decrease in the ADP-regulated ferricyanide-reducing activity (restoration) due to (incomplete) uncoupling paralleled the decrease in phosphorylation activity (P/Δe=1). 相似文献
107.
Stphanie Sherpa Jordan Tutagata Thierry Gaude Frdric Laporte Shinji Kasai Intan H. Ishak Xiang Guo Jiyeong Shin Sbastien Boyer Sbastien Marcombe Theeraphap Chareonviriyaphap Jean-Philippe David Xiao-Guang Chen Xiaohong Zhou Laurence Desprs 《Molecular biology and evolution》2022,39(5)
Climatic variation is a key driver of genetic differentiation and phenotypic traits evolution, and local adaptation to temperature is expected in widespread species. We investigated phenotypic and genomic changes in the native range of the Asian tiger mosquito, Aedes albopictus. We first refine the phylogeographic structure based on genome-wide regions (1,901 double-digest restriction-site associated DNA single nucleotide polymophisms [ddRAD SNPs]) from 41 populations. We then explore the patterns of cold adaptation using phenotypic traits measured in common garden (wing size and cold tolerance) and genotype–temperature associations at targeted candidate regions (51,706 exon-capture SNPs) from nine populations. We confirm the existence of three evolutionary lineages including clades A (Malaysia, Thailand, Cambodia, and Laos), B (China and Okinawa), and C (South Korea and Japan). We identified temperature-associated differentiation in 15 out of 221 candidate regions but none in ddRAD regions, supporting the role of directional selection in detected genes. These include genes involved in lipid metabolism and a circadian clock gene. Most outlier SNPs are differently fixed between clades A and C, whereas clade B has an intermediate pattern. Females are larger at higher latitude yet produce no more eggs, which might favor the storage of energetic reserves in colder climate. Nondiapausing eggs from temperate populations survive better to cold exposure than those from tropical populations, suggesting they are protected from freezing damages but this cold tolerance has a fitness cost in terms of egg viability. Altogether, our results provide strong evidence for the thermal adaptation of A. albopictus across its wide temperature range. 相似文献
108.
109.
Mahabub Alam Hiroki Shima Yoshitaka Matsuo Nguyen Chi Long Mitsuyo Matsumoto Yusho Ishii Nichika Sato Takato Sugiyama Risa Nobuta Satoshi Hashimoto Liang Liu Mika K. Kaneko Yukinari Kato Toshifumi Inada Kazuhiko Igarashi 《The Journal of biological chemistry》2022,298(7)
Methionine adenosyltransferase (MAT) catalyzes the synthesis of S-adenosylmethionine (SAM). As the sole methyl-donor for methylation of DNA, RNA, and proteins, SAM levels affect gene expression by changing methylation patterns. Expression of MAT2A, the catalytic subunit of isozyme MAT2, is positively correlated with proliferation of cancer cells; however, how MAT2A promotes cell proliferation is largely unknown. Given that the protein synthesis is induced in proliferating cells and that RNA and protein components of translation machinery are methylated, we tested here whether MAT2 and SAM are coupled with protein synthesis. By measuring ongoing protein translation via puromycin labeling, we revealed that MAT2A depletion or chemical inhibition reduced protein synthesis in HeLa and Hepa1 cells. Furthermore, overexpression of MAT2A enhanced protein synthesis, indicating that SAM is limiting under normal culture conditions. In addition, MAT2 inhibition did not accompany reduction in mechanistic target of rapamycin complex 1 activity but nevertheless reduced polysome formation. Polysome-bound RNA sequencing revealed that MAT2 inhibition decreased translation efficiency of some fraction of mRNAs. MAT2A was also found to interact with the proteins involved in rRNA processing and ribosome biogenesis; depletion or inhibition of MAT2 reduced 18S rRNA processing. Finally, quantitative mass spectrometry revealed that some translation factors were dynamically methylated in response to the activity of MAT2A. These observations suggest that cells possess an mTOR-independent regulatory mechanism that tunes translation in response to the levels of SAM. Such a system may acclimate cells for survival when SAM synthesis is reduced, whereas it may support proliferation when SAM is sufficient. 相似文献