全文获取类型
收费全文 | 22148篇 |
免费 | 2122篇 |
国内免费 | 11篇 |
出版年
2022年 | 120篇 |
2021年 | 227篇 |
2020年 | 184篇 |
2019年 | 299篇 |
2018年 | 351篇 |
2017年 | 382篇 |
2016年 | 508篇 |
2015年 | 844篇 |
2014年 | 871篇 |
2013年 | 1187篇 |
2012年 | 1281篇 |
2011年 | 1249篇 |
2010年 | 928篇 |
2009年 | 864篇 |
2008年 | 1122篇 |
2007年 | 1223篇 |
2006年 | 1173篇 |
2005年 | 1208篇 |
2004年 | 1162篇 |
2003年 | 1201篇 |
2002年 | 1204篇 |
2001年 | 257篇 |
2000年 | 235篇 |
1999年 | 321篇 |
1998年 | 409篇 |
1997年 | 299篇 |
1996年 | 274篇 |
1995年 | 268篇 |
1994年 | 243篇 |
1993年 | 242篇 |
1992年 | 290篇 |
1991年 | 227篇 |
1990年 | 230篇 |
1989年 | 204篇 |
1988年 | 163篇 |
1987年 | 176篇 |
1986年 | 142篇 |
1985年 | 207篇 |
1984年 | 198篇 |
1983年 | 160篇 |
1982年 | 202篇 |
1981年 | 197篇 |
1980年 | 156篇 |
1979年 | 164篇 |
1978年 | 146篇 |
1977年 | 150篇 |
1976年 | 148篇 |
1975年 | 98篇 |
1974年 | 117篇 |
1973年 | 115篇 |
排序方式: 共有10000条查询结果,搜索用时 782 毫秒
11.
Corine Vialas Geneviève Pratviel Jean Bernadou Bernard Meunier 《Nucleosides, nucleotides & nucleic acids》2013,32(4-5):1061-1063
Abstract Mn TMPyP in the presence of sulfite/O2 catalyses the oxidation of dG into dIz as selectively but slower and less efficiently than in the presence of KHSO5. 相似文献
12.
13.
The effects on olfaction of N-ethylmaleimide (NEM), a specificreagent of free sulfhydryl groups, were studied in the mothMamestra brassicae. The antennae of male M.brassicae bear twotypes of specialist receptor neurons involved in pheromone communication.One type is tuned to (Z)-11-hexadecenyl acetate (Z11-16:Ac),the main pheromone component; the second type is tuned to (Z)-9-tetradecenylacetate (Z9-14:Ac), an interspecific inhibitor not producedby the females of this species. Vapours of NEM irreversiblyinhibited the electro-antennographic (EAG) responses to Z11-16:Acand Z9-14:Ac. When Zll-16:Ac was applied before and during NEMtreatment, the responses to Z9-14:Ac were preserved and someprotection was observed in the responses to Zll-16:Ac. In return,Z9-14:Ac partially prevented the disappearance of responsesto Zll-16:Ac but not to Z9-14:Ac. A third compound, hexadecylacetate (16:Ac), found in the pheromone gland, but not detectedby the antennal receptors, did not prevent the inhibition causedby NEM. 相似文献
14.
15.
16.
17.
Pierre Kerner Elena Simionato Martine Le Gouar Michel Vervoort 《Evolution & development》2009,11(5):513-524
SUMMARY The molecular mechanisms underlying the formation and patterning of the nervous system are relatively poorly understood for lophotrochozoans (like annelids) as compared with ecdysozoans (especially Drosophila ) and deuterostomes (especially vertebrates). Therefore, we have undertaken a candidate gene approach to study aspects of neurogenesis in a polychaete annelid Platynereis dumerilii . We determined the spatiotemporal expression for Platynereis orthologs of four genes ( SoxB, Churchill, prospero / Prox , and SoxC) known to play key roles in vertebrate neurogenesis. During Platynereis development, SoxB is expressed in the neuroectoderm and its expression switches off when committed neural precursors are formed. Subsequently, Prox is expressed in all differentiating neural precursors in the central and peripheral nervous systems. Finally, SoxC and Churchill are transcribed in patterns consistent with their involvement in neural differentiation. The expression patterns of Platynereis SoxB and Prox closely resemble those in Drosophila and vertebrates—this suggests that orthologs of these genes play similar neurogenic roles in all bilaterians. Whereas Platynereis SoxC , like its vertebrate orthologs, plays a role in neural cell differentiation, related genes in Drosophila do not appear to be involved in neurogenesis. Finally, conversely to Churchill in Platynereis , vertebrate orthologs of this gene are expressed during neuroectoderm formation, but not later during nerve cell differentiation; in the insect lineage, homologs of these genes have been secondarily lost. In spite of such instances of functional divergence or loss, the present study shows conspicuous similarities in the genetic control of neurogenesis among bilaterians. These commonalities suggest that key features of the genetic program for neurogenesis are ancestral to bilaterians. 相似文献
18.
Household‐level correlates of children's physical activity levels in and across 12 countries
下载免费PDF全文
![点击此处可从《Obesity (Silver Spring, Md.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Deirdre M. Harrington Fiona Gillison Stephanie T. Broyles Jean‐Philippe Chaput Mikael Fogelholm Gang Hu Rebecca Kuriyan Anura Kurpad Allana G. LeBlanc Carol Maher Jose Maia Victor Matsudo Timothy Olds Vincent Onywera Olga L. Sarmiento Martyn Standage Mark S. Tremblay Catrine Tudor‐Locke Pei Zhao Peter T. Katzmarzyk for the ISCOLE Research Group 《Obesity (Silver Spring, Md.)》2016,24(10):2150-2157
19.
20.
Location within a tree was analyzed as a source of variation in Sequoia sempervirens leaf monoterpenes. No differences were found for quantitative composition or total yield/dry wt among lower, middle and upper canopy positions. The awlshaped, spirally arranged leaves of vigorous upper shoots showed small quantitative compositional differences, but not differences in total yield. The intermediate leaf form of young sprouts had the most different monoterpene quantitative composition and about three times the total yield of the above two leaf forms. Analysis of a clonal ring of 17 adult trees resulted in coefficients of variation similar to those for samples collected from different canopy levels of the same shoot. Results revealed the sources and magnitudes of experimental error in comparative studies of this species' leaf monoterpenes, and did not support the concept that somatic mutation provides an important source of variation in a large, long-lived organism such as coast redwood. 相似文献