全文获取类型
收费全文 | 3091篇 |
免费 | 236篇 |
国内免费 | 2篇 |
出版年
2023年 | 15篇 |
2022年 | 33篇 |
2021年 | 64篇 |
2020年 | 40篇 |
2019年 | 43篇 |
2018年 | 61篇 |
2017年 | 58篇 |
2016年 | 99篇 |
2015年 | 164篇 |
2014年 | 177篇 |
2013年 | 197篇 |
2012年 | 254篇 |
2011年 | 264篇 |
2010年 | 161篇 |
2009年 | 141篇 |
2008年 | 191篇 |
2007年 | 180篇 |
2006年 | 172篇 |
2005年 | 156篇 |
2004年 | 132篇 |
2003年 | 137篇 |
2002年 | 99篇 |
2001年 | 39篇 |
2000年 | 30篇 |
1999年 | 35篇 |
1998年 | 29篇 |
1997年 | 22篇 |
1996年 | 21篇 |
1995年 | 13篇 |
1994年 | 17篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 16篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1974年 | 10篇 |
1951年 | 9篇 |
排序方式: 共有3329条查询结果,搜索用时 734 毫秒
51.
Neurotensin is a tridacapeptide which has been isolated from bovine hypothalamus. The action of synthetic neurotensin was studied on gastric acid secretion in dogs provided with gastric pouches. Intravenously infused neurotensin, 50 ng × kg?1 × min?1, was found to produce a considerable inhibition of pentagastrin stimulated gastric acid secretion. On the other hand, there was no sign of inhibition of histamine induced gastric acid secretion. The experiments show that neurotensin, isolated from the central nervous system is a potent gastric secretory inhibitor and that it has a selective action in inhibiting gastric acid responses to pentagastrin but not to histamine. 相似文献
52.
Sven Erik Rognes 《Phytochemistry》1975,14(9):1975-1982
Asparagine synthetase (glutamine-hydrolyzing [l-aspartate: l-glutamine amido-ligase (AMP-forming), E.C. 6.3.5.4] was purified over 500-fold from cotyledon extracts of 1-week-old yellow lupin seedlings. The enzyme was labile and required protection by high levels of thiols; glycerol and the substrates also stabilized it. The reaction products were shown to be asparagine, AMP, PPi and glutamate. The limiting Km values were for aspartate 1·3 mM, for MgATP 0·14 mM and for glutamine 0·16 mM. Positive homotropic cooperativity was observed for MgATP only, and gel filtration studies indicated that the substrate-free enzyme (MW 160 000) associated to a dimer (MW 320 000 in the presence of MgCl2 and ATP. The purified enzyme, which had some glutaminase activity, catalyzed an aspartate- and glutamine-independent ATP-PPi exchange reaction at a rate 5–7-fold higher than the rate of asparagine synthesis. Initial velocity studies and exchange data indicated an overall ping-pong mechanism. Compared to similar enzymes isolated from mammalian tumor cells, the lupin enzyme appears to be unique with respect to MW, reaction mechanism and regulatory properties. The allosteric properties observed suggest an important role for this enzyme in the regulation of asparagine biosynthesis. 相似文献
53.
Recent studies have suggested that ribosomal protein S12 modulates 16S rRNA function and susceptibility to 2-deoxystreptamine aminoglycosides. To study whether the non-restrictive K42R mutation in RpsL affects 2-deoxystreptamine susceptibility in Mycobacterium smegmatis, we studied the drug susceptibility pattern of various mutants with genetic alterations in the 16S rRNA decoding A-site in the context of wild-type and mutant protein S12. RpsL K42R substitution was found not to affect the drug resistance pattern associated with mutational alterations in 16S rRNA H44. 相似文献
54.
55.
56.
Sven Hörstadius 《Development genes and evolution》1923,98(1-2):1-9
Ohne ZusammenfassungDie Untersuchungen wurden an der Zoologischen Station Kristineberg, Schweden, ausgeführt. Es ist mir eine angenehme Pflicht, dem Direktor, Herrn ProfessorHjalmar Théel, und dem Vorstand, Herrn Dr.Hjalmar Östergren, meinen besten Dank auszusprechen. Schließlich richte ich den herzlichsten Dank an Herrn Dr.John Runnström, Stockholm, der mir die Idee der Untersuchung gegeben und mit größtem Interesse und größter Freundlichkeit meine Arbeit geleitet hat. 相似文献
57.
58.
Sven Larsson 《Inorganica chimica acta》1996,250(1-2):189-193
In most quantum models for the four-site four-electron problem the lowest singlet state has two short and two long bonds in the absence of lattice polarization and is called the resonating valence bond (VB) state. It is shown here that if the lattice polarization is large, the ground state is a ‘negative U’ state with valence disproportionation (for example BaBiO3 with Bi(V) and Bi(III) sites). Furthermore the model shows that the coupling between the pairs on different sites is provided via the VB state. 相似文献
59.
Sven Kurbel 《BioEssays : news and reviews in molecular, cellular and developmental biology》2020,42(10):2000056
This paper discusses possible mechanisms that might lead to misinterpretations of collected data and makes new evidence-based medicine (EBM) recommendations to oppose the previously accepted preventive measures, or treatment options. It is focused on the danger of the “red meat” consumption, and the question whether eating pungent food is good or bad for our health and finally whether the “bad luck” concept of getting several cancer types is valid or not. These three topics got and still have significant media attention. Several mechanisms are proposed as possible causes of these apparent conflicts. Some of them have already been recognized but sadly remained less known to medical readers and also to the general population. Also see the video abstract here https://youtu.be/owjoRXrNShA . 相似文献
60.
Holcombe Sven A. Agnew Amanda M. Derstine Brian Wang Stewart C. 《Biomechanics and modeling in mechanobiology》2020,19(6):2227-2239
Biomechanics and Modeling in Mechanobiology - Finite element human body models (HBMs) are used to assess injury risk in a variety of impact scenarios. The ribs are a key structural component within... 相似文献