全文获取类型
收费全文 | 4411篇 |
免费 | 429篇 |
国内免费 | 2篇 |
出版年
2022年 | 28篇 |
2021年 | 62篇 |
2020年 | 40篇 |
2019年 | 46篇 |
2018年 | 36篇 |
2017年 | 34篇 |
2016年 | 86篇 |
2015年 | 155篇 |
2014年 | 157篇 |
2013年 | 198篇 |
2012年 | 297篇 |
2011年 | 272篇 |
2010年 | 206篇 |
2009年 | 160篇 |
2008年 | 243篇 |
2007年 | 292篇 |
2006年 | 240篇 |
2005年 | 239篇 |
2004年 | 209篇 |
2003年 | 194篇 |
2002年 | 186篇 |
2001年 | 54篇 |
2000年 | 46篇 |
1999年 | 57篇 |
1998年 | 53篇 |
1997年 | 41篇 |
1996年 | 46篇 |
1995年 | 33篇 |
1994年 | 51篇 |
1993年 | 40篇 |
1992年 | 41篇 |
1991年 | 51篇 |
1990年 | 43篇 |
1989年 | 32篇 |
1988年 | 34篇 |
1987年 | 23篇 |
1986年 | 45篇 |
1985年 | 45篇 |
1984年 | 50篇 |
1983年 | 38篇 |
1982年 | 47篇 |
1981年 | 43篇 |
1980年 | 44篇 |
1979年 | 33篇 |
1978年 | 33篇 |
1977年 | 29篇 |
1976年 | 24篇 |
1975年 | 33篇 |
1974年 | 32篇 |
1973年 | 33篇 |
排序方式: 共有4842条查询结果,搜索用时 20 毫秒
991.
992.
Brian W. Fitzsimmons Alan Hume Leslie F. Larkworthy Michael H. Turnbull Ahmad Yavari 《Inorganica chimica acta》1985,106(2):109-114
The following complexes of iron(II) with the amino acids glycine, alanine, phenylglycine, phenylalanine, leucine, serine, aspartic acid, glutamic acid, glutamine, tryptophan, histidine, methionine, S-methylcysteine, cystine, and glycylglycine have been isolated: Fe(Gly)2, Fe(Ala)2, Fe(Phegly)2, Fe(Phe)2·2H20, Fe(Leu)2·2H20, Fe(Ser)2, Fe(Asp)·2H20, Fe(Glu)·2H20, Fe(Gln)2, Fe(Trp)2, Fe(His)2·H20 and 2H20, Fe(Met)2, Fe(MeCys)2, Fe(CysCys) and Fe(GlyGly)2. Their magnetic behaviour, reflectance spectra, and Mössbauer parameters are consistent with high spin, hexacoordinate iron(II), and imply extended structures involving carboxylate bridges. 相似文献
993.
994.
995.
996.
A long‐standing macroecological hypothesis posits that species range limits are primarily determined by abiotic factors (e.g. climate) at poleward boundaries and biotic factors (e.g. competition) at equatorward boundaries. Using correlative environmental niche models we test this hypothesis for 214 amphibian and reptile species endemic to the United States (U.S.). As predicted, we find a closer association between climate and northern (poleward) range limits than at southern (equatorward) boundaries. However when we separately analyze amphibians and reptiles, only reptiles show the predicted pattern; amphibians show the opposite pattern. We also find more unoccupied, but climatically habitable, area beyond species’ southern range limits for reptiles but not amphibians. This suggests that factors other than climate limit distributions at southern boundaries for reptiles and at northern boundaries for amphibians. These contrasting results suggest that even in the same biogeographic regions, this macroecological hypothesis does not hold. Further studies should investigate, preferably via experimental approaches, the proximate and ultimate mechanisms responsible for range limits. 相似文献
997.
998.
Francesca Bertolini Barbara Gandolfi Eui Soo Kim Bianca Haase Leslie A. Lyons Max F. Rothschild 《Mammalian genome》2016,27(3-4):144-155
The Persian cat is mainly characterized by an extremely brachycephalic face as part of the standard body conformation. Despite the popularity, world-wide distribution, and economic importance of the Persian cat as a fancy breed, little is known about the genetics of their hallmark morphology, brachycephaly. Over 800 cats from different breeds including Persian, non-Persian breeds (Abyssinian, Cornish Rex, Bengal, La Perm, Norwegian Forest, Maine Coon, Manx, Oriental, and Siamese), and Persian-derived breeds (British Shorthair, Scottish Fold, Selkirk Rex) were genotyped with the Illumina 63 K feline DNA array. The experimental strategy was composed of three main steps: (i) the Persian dataset was screened for runs of homozygosity to find and select highly homozygous regions; (ii) selected Persian homozygous regions were evaluated for the difference of homozygosity between Persians and those considered non-Persian breeds, and, (iii) the Persian homozygous regions most divergent from the non-Persian breeds were investigated by haplotype analysis in the Persian-derived breeds. Four regions with high homozygosity (H > 0.7) were detected, each with an average length of 1 Mb. Three regions can be considered unique to the Persian breed, with a less conservative haplotype pattern in the Persian-derived breeds. Moreover, two genes, CHL1 and CNTN6 known to determine face shape modification in humans, reside in one of the identified regions and therefore are positional candidates for the brachycephalic face in Persians. In total, the homozygous regions contained several neuronal genes that could be involved in the Persian cat behavior and can provide new insights into cat domestication. 相似文献
999.
Leslie A. Parsels Daria M. Tanska Joshua D. Parsels Sonya D. Zabludoff Kyle C. Cuneo Theodore S. Lawrence 《Cell cycle (Georgetown, Tex.)》2016,15(5):730-739
In order to determine the relative contribution of checkpoint abrogation and subsequent aberrant mitotic entry to gemcitabine chemosensitization by CHK1 inhibition, we established a model utilizing the CDK inhibitors roscovitine or purvalanol A to re-establish cell cycle arrest and prevent aberrant mitotic entry in pancreatic cancer cells treated with gemcitabine and the CHK inhibitor AZD7762. In this study, we report that the extent of aberrant mitotic entry, as determined by flow cytometry for the mitotic marker phospho-Histone H3 (Ser10), did not reflect the relative sensitivities of pancreatic cancer cell lines to gemcitabine chemosensitization by AZD7762. In addition, re-establishing gemcitabine-induced cell cycle arrest either pharmacologically, with roscovitine or purvalanol A, or genetically, with cyclin B1 siRNA, did not inhibit chemosensitization uniformly across the cell lines. Furthermore, we found that AZD7762 augmented high-intensity γH2AX signaling in gemcitabine-treated cells, suggesting the presence of replication stress when CHK1 is inhibited. Finally, the ability of roscovitine to prevent chemosensitization correlated with its ability to inhibit AZD7762-induced high-intensity γH2AX, but not aberrant pHH3, suggesting that the effects of AZD7762 on DNA replication or repair rather than aberrant mitotic entry determine gemcitabine chemosensitization in pancreatic cancer cells. 相似文献
1000.