全文获取类型
收费全文 | 771225篇 |
免费 | 97724篇 |
国内免费 | 454篇 |
出版年
2019年 | 7720篇 |
2018年 | 10169篇 |
2017年 | 9964篇 |
2016年 | 12549篇 |
2015年 | 15072篇 |
2014年 | 17151篇 |
2013年 | 23687篇 |
2012年 | 24114篇 |
2011年 | 24361篇 |
2010年 | 18046篇 |
2009年 | 16035篇 |
2008年 | 20991篇 |
2007年 | 21321篇 |
2006年 | 20182篇 |
2005年 | 19505篇 |
2004年 | 19211篇 |
2003年 | 18509篇 |
2002年 | 17897篇 |
2001年 | 39492篇 |
2000年 | 39608篇 |
1999年 | 30698篇 |
1998年 | 9597篇 |
1997年 | 10253篇 |
1996年 | 9508篇 |
1995年 | 8776篇 |
1994年 | 8538篇 |
1993年 | 8600篇 |
1992年 | 24332篇 |
1991年 | 23507篇 |
1990年 | 22661篇 |
1989年 | 22047篇 |
1988年 | 20461篇 |
1987年 | 19046篇 |
1986年 | 17590篇 |
1985年 | 17333篇 |
1984年 | 14095篇 |
1983年 | 11951篇 |
1982年 | 8784篇 |
1981年 | 7883篇 |
1980年 | 7542篇 |
1979年 | 13087篇 |
1978年 | 10076篇 |
1977年 | 9295篇 |
1976年 | 8318篇 |
1975年 | 9288篇 |
1974年 | 10045篇 |
1973年 | 9748篇 |
1972年 | 8786篇 |
1971年 | 8048篇 |
1970年 | 7010篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
M Soler-López L Malinina J Liu T Huynh-Dinh J A Subirana 《The Journal of biological chemistry》1999,274(34):23683-23686
A detailed picture of hydration and counterion location in the B-DNA duplex d(GCGAATTCG) is presented. Detailed data have been obtained by single crystal x-ray diffraction at atomic resolution (0.89 A) in the presence of Mg(2+). The latter is the highest resolution ever obtained for a B-DNA oligonucleotide. Minor groove hydration is compared with that found in the Na(+) and Ca(2+) crystal forms of the related dodecamer d(CGCGAATTCGCG). High resolution data (1.45 A) of the Ca(2+) form obtained in our laboratory are used for that purpose. The central GAATTC has a very stable hydration spine identical in all cases, independent of duplex length and crystallization conditions (counterions, space group). However, the organization of the water molecules (tertiary and quaternary layers) associated with the central spine vary in each case. 相似文献
993.
QIAN‐WAN MENG YI‐BO LUO 《Botanical journal of the Linnean Society. Linnean Society of London》2008,158(4):689-695
A new species, Galearis huanglongensis Q.W.Meng & Y.B.Luo, is described and illustrated. It is similar to Galearis cyclochila (Franch. & Sav.) Soó and Galearis diantha (Schltr.) P.F.Hunt, but differs in having a short spur, two elliptical lateral stigma lobes and distinctly separated bursicles. This new species is known only from the type locality, the Huanglong Valley, Songpan County, western Sichuan, China, growing amongst mosses under alpine shrubs at an elevation of about 3000 m. Based on two years of observations of its population size, the species was categorized as critically endangered CR (B1a, B2a) according to the World Conservation Union (IUCN) Red List Categories and Criteria, Version 3.1. The micromorphology of pollinia and seeds was observed by scanning electron microscopy and compared with that of G. cyclochila and G. diantha. The results supported G. huanglongensis Q.W.Meng & Y.B.Luo as a new species. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 689–695. 相似文献
994.
The Capricorn silvereye (Zosterops lateralis chlorocephalus) is ideally suited to investigating the genetic basis of body size evolution. We have isolated and characterized a set of microsatellite markers for this species. Seven out of 11 loci were polymorphic. The number of alleles detected ranged from two to five and observed heterozygosities between 0.12 and 0.67. One locus, ZL49, was found to be sex‐linked. This moderate level of diversity is consistent with that expected in an isolated, island population. 相似文献
995.
996.
Nimra Khan Dylan Pelletier Thomas S. McAlear Nathalie Croteau Simon Veyron Andrew N. Bayne Corbin Black Muneyoshi Ichikawa Ahmad Abdelzaher Zaki Khalifa Sami Chaaban Igor Kurinov Gary Brouhard Susanne Bechstedt Khanh Huy Bui Jean-François Trempe 《Structure (London, England : 1993)》2021,29(6):572-586.e6
- Download : Download high-res image (220KB)
- Download : Download full-size image
997.
998.
In an ultrastructural study of the hepatopancreas of Porcellio scaber, an obligate intracellular parasite, Chlamydia, was noted in the epithelial cells. Although the infection was found to extend the entire length of the hepatopancreas, it was most extensive in the glandular region. Indirect immunofluorescence testing revealed no cross-reactivity with either lymphogranuloma venereum or psittacosis antisera. 相似文献
999.
Flash-induced absorption changes at 820 nm were studied as a function of redox potential in Tris-extracted Photosystem II oxygen-evolving particles and Triton subchloroplast fraction II particles. The rereduction kinetics of P-680+ in both preparations showed biphasic recovery phases with half-times of 42 and 625 microseconds at pH 4.5. The magnitude of the 42 microseconds phase of P-680+ rereduction was strongly dependent on the redox potential of the medium. This absorption transient, attributed to electron donation from D1 (the secondary electron donor in oxygen-inhibited chloroplasts), titrated as a single redox component with a midpoint potential of +240 +/- 35 mV. The experimentally determined midpoint potential was found to be independent of pH over the tested range 4.5-6.0. In contrast, the magnitude of the 625 microseconds phase of P-680+ rereduction was independent of redox potential between +350 and +100 mV. These results are interpreted in terms of a model in which an alternate electron donor with Em approximately equal to 240 mV, termed D0, serves as a rapid donor (t 1/2 less than or equal to 2 microseconds) to P-680+ in Tris-extracted and Triton-treated Photosystem-II preparations. According to this model, the slower electron donor, D1, is functional only when D0 becomes oxidized. 相似文献
1000.
Summary Responses of lentil in unsterile soils at low, medium and high levels of plant available soil P toGlomus fasciculatum inoculation were evaluated. It was observed that growth, dry matter accumulation, nodulation, and nitrogen fixation were considerably improved in VAM inoculated plants over uninoculated control at low and medium levels of plant available soil P. 相似文献