全文获取类型
收费全文 | 3372篇 |
免费 | 291篇 |
国内免费 | 2篇 |
出版年
2023年 | 12篇 |
2022年 | 34篇 |
2021年 | 69篇 |
2020年 | 38篇 |
2019年 | 52篇 |
2018年 | 79篇 |
2017年 | 57篇 |
2016年 | 126篇 |
2015年 | 181篇 |
2014年 | 187篇 |
2013年 | 214篇 |
2012年 | 298篇 |
2011年 | 278篇 |
2010年 | 173篇 |
2009年 | 165篇 |
2008年 | 200篇 |
2007年 | 215篇 |
2006年 | 172篇 |
2005年 | 166篇 |
2004年 | 140篇 |
2003年 | 128篇 |
2002年 | 135篇 |
2001年 | 30篇 |
2000年 | 20篇 |
1999年 | 36篇 |
1998年 | 32篇 |
1997年 | 35篇 |
1996年 | 20篇 |
1995年 | 16篇 |
1994年 | 20篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 22篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1969年 | 7篇 |
排序方式: 共有3665条查询结果,搜索用时 15 毫秒
1.
2.
Changes in the duration and size of the vulnerable period of the myocardium in the presence of respiratory changes were studied in acute experiments on rats. The limits of the vulnerable period were determined by directly stimulating the heart during ventilation via the enlarged respiratory dead space, during hyperventilation and during heart failure. In the control group (normal ventilation without enlargement of the dead space), the vulnerable period lasted 5.7 +/- 0.76 ms. During ventilation via the enlarged dead space, hypercapnic hypoxaemia developed and the vulnerable period was markedly prolonged (18.55 +/- 5.29 ms) by a shift of its inner limit to the left. Hyperventilation caused normoxic to hyperoxic hypocapnia and markedly reduced the duration of the vulnerable period (8.17 +/- 2.21 and 9.31 +/- 2.38 ms respectively). The vulnerable period lengthened the most in heart failure (25.46 +/- 3.93), mainly as a result of a shift of its outer limit. In all the experimental groups there was a shift of the vulnerable period to the right, which was fastest in hypercapnic hypoxaemia and slowest in hyperoxic hypocapnia. The administration of Inderal (3 mg/kg i.p.) or Arfonad (50 mg/kg i.p.) markedly shortened the vulnerable period during hypercapnic hypoxaemia (9.87 +/- 2.78 and 9.32 +/- 2.16 ms respectively), but did not block the shift. Lengthening of the vulnerable period during hypercapnic hypoxaemia was probably due to activation of sympathetic nerves via beta-adrenergic receptors. 相似文献
3.
4.
5.
zge Karayel Francesca Tonelli Sebastian Virreira Winter Phillip E. Geyer Ying Fan Esther M. Sammler Dario R. Alessi Martin Steger Matthias Mann 《Molecular & cellular proteomics : MCP》2020,19(9):1546-1560
- Download : Download high-res image (63KB)
- Download : Download full-size image
- •MS-based clinical assay that accurately determines phospho Rab10 occupancy.
- •Stable isotope labeled phosphopeptide injected as a standard with endogenous tryptic phospho Rab peptide for accurate ratio determination.
- •Determination of pRab levels in neutrophils of Parkinson disease patients.
- •Relevance of pRab levels as marker of PD.
6.
7.
Food subsidies have the potential to modify ecosystems and affect the provision of goods and services. Predictable Anthropogenic Food Subsidies (PAFS) modify ecosystems by altering ecological processes and food webs. The global concern over the effects of PAFS in ecosystems has led to development of environmental policies aimed at curbing the production or ultimately banning of PAFS. However, the effects of reducing or banning PAFS are not known. We explore the consequences of PAFS removal in a marine ecosystem under two scenarios: 1) gradual reduction, or 2) an abrupt ban, using a mass balance model to test these hypotheses–The reduction or loss of PAFS will: i) modify trophic levels and food webs through effects on foraging by opportunistic species, ii) increase the resilience of opportunistic species to food shortages, and iii) modify predator–prey interactions through shifts in prey consumption. We found that PAFS lower the trophic levels of opportunistic scavengers and increase their food pathways. Scavengers are able to switch prey when PAFS are reduced gradually but they decline when PAFS are abruptly banned. PAFS reduction to a certain minimal level causes a drop in the ecosystem’s stability. We recommend gradual reduction of PAFS to a minimal level that would maintain the ecosystem’s stability and allow species exploiting PAFS to habituate to the food subsidy reduction. 相似文献
8.
9.
"In solution" synthesis and separation of diastereoisomers of 5'-O-(4,4'-dimethoxytriphenylmethyl)dithymidyl (3',5') 4,4'-dimethoxytriphenylmethanephosphonate (DMTTDMTT) is described. One of diastereoisomers was successfully crystallized and characterized by means of HPLC. 相似文献
10.
W Niewiarowski Z J Le?nikowski A Wilk P Guga A Okruszek B Uznański W Stec 《Acta biochimica Polonica》1987,34(2):217-231
Diastereomers of the title compound were obtained and absolute configuration was assigned by means of stereochemical correlation. Their reaction with 3'-O-methoxyacetylthymidine in the presence of triisopropylbenzenesulphonyl (4-nitro) triazole is neither chemo- nor stereo-selective and leads to diastereomeric pairs of dithymidyl (3',5')methanephosphonate and -methanephosphonothioate. Obtained results are discussed in terms of mechanism of activation of phosphodiesters under conditions known as "phosphotriester approach to oligonucleotide synthesis". 相似文献