全文获取类型
收费全文 | 15709篇 |
免费 | 1484篇 |
国内免费 | 4篇 |
出版年
2023年 | 81篇 |
2022年 | 195篇 |
2021年 | 439篇 |
2020年 | 268篇 |
2019年 | 300篇 |
2018年 | 353篇 |
2017年 | 305篇 |
2016年 | 497篇 |
2015年 | 855篇 |
2014年 | 919篇 |
2013年 | 1009篇 |
2012年 | 1353篇 |
2011年 | 1426篇 |
2010年 | 892篇 |
2009年 | 749篇 |
2008年 | 973篇 |
2007年 | 956篇 |
2006年 | 903篇 |
2005年 | 731篇 |
2004年 | 791篇 |
2003年 | 693篇 |
2002年 | 687篇 |
2001年 | 144篇 |
2000年 | 89篇 |
1999年 | 118篇 |
1998年 | 157篇 |
1997年 | 90篇 |
1996年 | 80篇 |
1995年 | 82篇 |
1994年 | 81篇 |
1993年 | 99篇 |
1992年 | 74篇 |
1991年 | 66篇 |
1990年 | 52篇 |
1989年 | 38篇 |
1988年 | 42篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 43篇 |
1984年 | 48篇 |
1983年 | 31篇 |
1982年 | 47篇 |
1981年 | 45篇 |
1980年 | 36篇 |
1979年 | 26篇 |
1978年 | 40篇 |
1977年 | 18篇 |
1976年 | 21篇 |
1975年 | 16篇 |
1974年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
HIF-1 expression in healing wounds: HIF-1alpha induction in primary inflammatory cells by TNF-alpha 总被引:12,自引:0,他引:12
4.
5.
Modern nutritional studies have found that diverse diets are linked to lower infant mortality rates and longer life expectancies in humans. This is primarily because humans require more than fifty essential nutrients for growth and cell maintenance and repair; most of these essential nutrients must come from outside food sources rather than being manufactured by the body itself; and a diversity of food types is required to consume the full suite of essential nutrients necessary for optimal human health. These principles and their related affects on human adaptations and demography are the hallmarks of a theoretical paradigm defined as nutritional ecology. This essay applies concepts derived from nutritional ecology to the study of human evolution. Principles of nutritional ecology are applied to the study of the Middle‐to‐Upper Paleolithic transition in order to broadly illustrate the interpretive ramifications of this approach. At any stage in human evolution, those hominid populations that chose to diversify their subsistence base may have had a selective advantage over competitors who restricted their diet principally to one food type, such as terrestrial mammals. 相似文献
6.
7.
Intrinsic sympathomimetic- and membrane activities of beta-adrenoceptor blocking agents are of little or no clinical significance. A selective blockade of cardiac receptors has important therapeutic consequences, especially in the treatment of patients with obstructive airways diseases. Profound depression of miocardial contractility can be deleterious in patients with cardiac muscle damage and the use of beta-adrenergic blockers with a quantitative selectivity towards chronotropism may become an important consideration. The effects of a number of beta-sympatholytics have been determined on isolated cardiac preparations (beta1-adrenergic receptors) and tracheal preparations (beta2-adrenergic receptors) of guinea-pigs. Results indicate that prindolol is the most selective blocker of the beta1 chronotropic receptors whilst atenolol could be classified as being the most cardioselective beta-adrenergic blocker investigated. Butoxamine, on the other hand, proved to be the most beta2-selective one. 相似文献
8.
Paul D. Bonnitcha Simon R. Bayly Mark B.M. Theobald Helen M. Betts Jason S. Lewis Jonathan R. Dilworth 《Journal of inorganic biochemistry》2010,104(2):126-9888
Combination agents comprising two different pharmacophores with the same biological target have the potential to show additive or synergistic activity. Bis(thiosemicarbazonato)copper(II) complexes (e.g. 64Cu-ATSM) and nitroimidazoles (e.g. 18F-MISO) are classes of tracer used for the delineation of tumor hypoxia by positron emission tomography (PET). Three nitroimidazole-bis(thiosemicarbazonato)copper(II) conjugates were produced in order to investigate their potential as combination hypoxia imaging agents. Two were derived from the known bifunctional bis(thiosemicarbazone) H2ATSM/A and the third from the new precursor diacetyl-2-(4-N-methyl-3-thiosemicarbazone)-3-(4-N-ethylamino-3-thiosemicarbazone) - H2ATSM/en. Oxygen-dependent uptake studies were performed using the 64Cu radiolabelled complexes in EMT6 carcinoma cells. All the complexes displayed appreciable hypoxia selectivity, with the nitroimidazole conjugates displaying greater selectivity than a simple propyl derivative used as a control. Participation of the nitroimidazole group in the trapping mechanism is indicated by the increased hypoxic uptake of the 2- vs. the 4-substituted 64Cu-ATSM/A derivatives. The 2-nitroimidazole derivative of 64Cu-ATSM/en demonstrated superior hypoxia selectivity to 64Cu-ATSM over the range of oxygen concentrations tested. Biodistribution of the radiolabelled 2-nitroimidazole conjugates was carried out in EMT6 tumor-bearing mice. The complexes showed significantly different uptake trends in comparison to each other and previously studied Cu-ATSM derivatives. Uptake of the Cu-ATSM/en conjugate in non-target organs was considerably lower than for derivatives based on Cu-ATSM/A. 相似文献
9.
10.
Jonathan D. Nickels Joseph E. Curtis Hugh O’Neill Alexei P. Sokolov 《Journal of biological physics》2012,38(3):497-505
Recent studies have discovered strong differences between the dynamics of nucleic acids (RNA and DNA) and proteins, especially at low hydration and low temperatures. This difference is caused primarily by dynamics of methyl groups that are abundant in proteins, but are absent or very rare in RNA and DNA. In this paper, we present a hypothesis regarding the role of methyl groups as intrinsic plasticizers in proteins and their evolutionary selection to facilitate protein dynamics and activity. We demonstrate the profound effect methyl groups have on protein dynamics relative to nucleic acid dynamics, and note the apparent correlation of methyl group content in protein classes and their need for molecular flexibility. Moreover, we note the fastest methyl groups of some enzymes appear around dynamical centers such as hinges or active sites. Methyl groups are also of tremendous importance from a hydrophobicity/folding/entropy perspective. These significant roles, however, complement our hypothesis rather than preclude the recognition of methyl groups in the dynamics and evolution of biomolecules. 相似文献