全文获取类型
收费全文 | 69151篇 |
免费 | 5513篇 |
国内免费 | 16篇 |
出版年
2023年 | 340篇 |
2022年 | 286篇 |
2021年 | 937篇 |
2020年 | 666篇 |
2019年 | 785篇 |
2018年 | 1478篇 |
2017年 | 1392篇 |
2016年 | 1830篇 |
2015年 | 2142篇 |
2014年 | 2429篇 |
2013年 | 3577篇 |
2012年 | 5015篇 |
2011年 | 5278篇 |
2010年 | 2942篇 |
2009年 | 2203篇 |
2008年 | 4162篇 |
2007年 | 4156篇 |
2006年 | 3852篇 |
2005年 | 3521篇 |
2004年 | 3342篇 |
2003年 | 3129篇 |
2002年 | 2958篇 |
2001年 | 1702篇 |
2000年 | 1889篇 |
1999年 | 1165篇 |
1998年 | 616篇 |
1997年 | 515篇 |
1996年 | 551篇 |
1995年 | 488篇 |
1994年 | 519篇 |
1993年 | 466篇 |
1992年 | 577篇 |
1991年 | 494篇 |
1990年 | 486篇 |
1989年 | 444篇 |
1988年 | 419篇 |
1987年 | 414篇 |
1986年 | 377篇 |
1985年 | 455篇 |
1984年 | 490篇 |
1983年 | 442篇 |
1982年 | 398篇 |
1981年 | 375篇 |
1980年 | 328篇 |
1979年 | 347篇 |
1978年 | 334篇 |
1977年 | 312篇 |
1976年 | 304篇 |
1975年 | 357篇 |
1974年 | 289篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
11.
12.
Georg Söderbom 《Ethnos》2013,78(1-2):95-100
Current debates over the concept of culture are examined, especially with regard to the relationship of culture to bounded collectivities, human nature, and individuality; present‐day views are seen against the background of back‐and‐forth swings in the history of anthropological thought. Recent theorizing about cultural acquisition is also considered. 相似文献
13.
R J Srám 《Molecular & general genetics : MGG》1970,106(3):286-288
Summary Ethylenimine, ethyl methanesulfonate and formaldehyde have been shown to produce a storage effect in dominant lethality in Drosophila melanogaster. 相似文献
14.
15.
Haems are the cofactors of cytochromes and important catalysts of biological electron transfer. They are composed of a planar porphyrin structure with iron coordinated at the centre. It is known from spectroscopy that ferric low-spin haem has one unpaired electron at the iron, and that this spin is paired as the haem receives an electron upon reduction (I. Bertini, C. Luchinat, NMR of Paramagnetic Molecules in Biological Systems, Benjamin/Cummins Publ. Co., Menlo Park, CA, 1986, pp. 165-170; H.M. Goff, in: A.B.P. Lever, H.B. Gray (Eds.), Iron Porphyrins, Part I, Addison-Wesley Publ. Co., Reading, MA, 1983, pp. 237-281; G. Palmer, in: A.B.P. Lever, H.B. Gray (Eds.), Iron Porphyrins, Part II, Addison-Wesley Publ. Co., Reading, MA, 1983, pp. 43-88). Here we show by quantum chemical calculations on a haem a model that upon reduction the spin pairing at the iron is accompanied by effective delocalisation of electrons from the iron towards the periphery of the porphyrin ring, including its substituents. The change of charge of the iron atom is only approx. 0.1 electrons, despite the unit difference in formal oxidation state. Extensive charge delocalisation on reduction is important in order for the haem to be accommodated in the low dielectric of a protein, and may have impact on the distance dependence of the rates of electron transfer. The lost individuality of the electron added to the haem on reduction is another example of the importance of quantum mechanical effects in biological systems. 相似文献
16.
The mechanisms controlling early adenovirus gene expression in vivo have been studied using inhibitors of protein synthesis. When inhibitors were added shortly before or at the onset of infection, viral mRNA from all early regions was transcribed, spliced and accumulated over a 7 hr period. After longer pretreatment, accumulation of several early mRNAs were suppressed. Addition of inhibitors 1 hr after infection enhanced the accumulation of viral mRNA in the cytoplasm. Translation of early mRNA selected on adenovirus DNA in a cell-free system reflected the amount of viral mRNA present. A viral coded product may therefore control accumulation of viral mRNA.A different pattern emerged when inhibitors of protein synthesis were removed at 5 hr postinfection and cells were pulse-labeled in vivo. If inhibitors were introduced at or before infection, early viral proteins were synthesized only after a lag of 1–3 hr. However, if treatment was introduced 1 hr post-infection, reversion of the protein synthesis block was instantaneous. It appears that protein synthesis inhibitors reveal an in vivo translational block for viral mRNA. This block could be overcome by preinfection with a related virus. Furthermore, no block was observed in a virus-transformed human embryonic kidney cell line (293) which expresses early region 1 of the viral genome. Viral gene product(s) encoded in early region 1 may control translation of early adenovirus messenger RNA in vivo. 相似文献
17.
18.
A total dosage up to 1 mg PGF2a as i.v. infusions of 10–40 μg/min. was investigated on patients with arrhythmias of several kinds. We found therapeutic effects in 5 of 6 patients with constant extrasystoles and in one patient with digitalis - induced partial AV-block respectively. In 3 of 4 patients with acute tachyarrhythmias the results were not convincing, probably due to a dosage not high enough. An increase of the diastolic stimulation threshold usually seen with other antiarrhythmics was not to be observed in 3 patients. The mechanism of action of PGF2a has not yet been clarified. 相似文献
19.
Reactions of cis-[PtCl(NH(3))(CyNH(2))(OH(2))](+) (Cy=cyclohexyl) with thione-containing single-stranded oligonucleotides d(T(8)XT(8)) and d(XT(16)) (X=(s6)I or (s4)U) and the mononucleotides 4-thiouridine ((s4)UMP) and 6-mercaptoinosine ((s6)IMP) have been studied in aqueous solution at pH 4.1. The reaction kinetics was followed using HPLC methodology as a function of ionic strength in the interval 5.0 mM相似文献
20.