全文获取类型
收费全文 | 3316篇 |
免费 | 223篇 |
国内免费 | 1篇 |
出版年
2021年 | 27篇 |
2019年 | 22篇 |
2018年 | 29篇 |
2016年 | 50篇 |
2015年 | 71篇 |
2014年 | 83篇 |
2013年 | 146篇 |
2012年 | 167篇 |
2011年 | 157篇 |
2010年 | 97篇 |
2009年 | 86篇 |
2008年 | 172篇 |
2007年 | 151篇 |
2006年 | 151篇 |
2005年 | 127篇 |
2004年 | 129篇 |
2003年 | 137篇 |
2002年 | 130篇 |
2001年 | 32篇 |
2000年 | 27篇 |
1999年 | 35篇 |
1998年 | 38篇 |
1997年 | 39篇 |
1996年 | 32篇 |
1995年 | 54篇 |
1994年 | 31篇 |
1993年 | 45篇 |
1992年 | 22篇 |
1991年 | 20篇 |
1990年 | 24篇 |
1989年 | 24篇 |
1988年 | 24篇 |
1987年 | 25篇 |
1985年 | 16篇 |
1984年 | 30篇 |
1983年 | 26篇 |
1982年 | 21篇 |
1981年 | 37篇 |
1980年 | 24篇 |
1979年 | 23篇 |
1978年 | 41篇 |
1974年 | 15篇 |
1973年 | 27篇 |
1971年 | 15篇 |
1966年 | 22篇 |
1965年 | 18篇 |
1964年 | 19篇 |
1960年 | 16篇 |
1956年 | 24篇 |
1939年 | 18篇 |
排序方式: 共有3540条查询结果,搜索用时 15 毫秒
151.
152.
Marco La Rosa Carl H. Schiesser Alfred Uhlherr Calum J. Drummond Keith Moody Robert Bohun 《Molecular simulation》2013,39(8-9):791-806
A coarse-grained model for simulation of interfacial phenomena in aqueous systems has been developed. The model captures the hydrophobic effect by only considering the structure and cohesiveness of water. Monte Carlo (MC) simulations of water-oil mixtures show that low concentrations of oil are solvated with little perturbation of the hydrogen bonding network structure of the water, while high concentrations of oil are excluded altogether. Analysis of the water structure in the simulations indicates that the water molecules maintain close to four coordination in the presence of solutes and the distribution of bond angles is not markedly affected by the presence of solutes. MC simulations of an alkane oligomer in water and a poly(ethylene oxide) (PEO) oligomer in water indicate that the chains are quite flexible and also do not perturb the network structure of the water phase. 相似文献
153.
Alfred J. Lewy MD. PhD Jonathan S. Emens Bryan J. Lefler Krista Yuhas Angela R. Jackman 《Chronobiology international》2013,30(6):1093-1106
The specific circadian role proposed for endogenous melatonin production was based on a study of sighted people who took low pharmacological doses (500 µg) of this chemical signal for the “biological night”: the magnitude and direction of the induced phase shifts were dependent on what time of day exogenous melatonin was administered and were described by a phase‐response curve that turned out to be the opposite of that for light. We now report that lower (physiological) doses of up to 300 µg can entrain (synchronize) free‐running circadian rhythms of 10 totally blind subjects that would otherwise drift later each day. The resulting log‐linear dose‐response curve in the physiological range adds support for a circadian function of endogenous melatonin in humans. Efficacy of exogenous doses in the physiological range are of clinical significance for totally blind people who will need to take melatonin daily over their entire lifetimes in order to remain entrained to the 24 h day. Left untreated, their free‐running endocrine, metabolic, behavioral, and sleep/wake cycles can be almost as burdensome as not having vision. 相似文献
154.
The recently extinct large-bodied New World monkey Protopithecus brasiliensis Lund 1836 was named based on a distal humerus and proximal femur found in the Lagoa Santa cave system in the southeastern Brazilian state of Minas Gerais. These bones are from an animal about twice the size of the largest extant platyrrhines. One hundred and seventy-five years later, a nearly complete skeleton was discovered in the Toca da Boa Vista caves in the neighboring state of Bahia and was allocated to the same taxon as it was the first platyrrhine fossil of comparable size found since the originals. Our detailed study of the equivalent elements, however, reveals important morphological differences that do not correspond to intraspecific variation as we know it in related platyrrhine taxa. The presence of both an expanded brachioradialis flange on the humerus and gluteal tuberosity on the femur of the Bahian skeleton distinguishes it from the Lagoa Santa fossil as well as from all other platyrrhines. Further cranial and postcranial evidence suggests a closer relationship of the former with the alouattine Alouatta, while the limited Lund material fits more comfortably with the ateline clade. Therefore, we propose to limit P. brasiliensis Lund to the distal humerus and proximal femur from Lagoa Santa and erect a new genus and species for the skeleton from Toca da Boa Vista. Cartelles coimbrafilhoi was a large-bodied frugivore with a relatively small brain and diverse locomotor repertoire including both suspension and climbing that expands the range of platyrrhine biodiversity beyond the dimensions of the living neotropical primates. 相似文献
155.
Alfred N. Fonteh Jiarong Chiang Matthew Cipolla Jack Hale Fatimatou Diallo Alejandra Chirino Xianghong Arakaki Michael G. Harrington 《Journal of lipid research》2013,54(10):2884-2897
Our aim is to study selected cerebrospinal fluid (CSF) glycerophospholipids (GP) that are important in brain pathophysiology. We recruited cognitively healthy (CH), minimally cognitively impaired (MCI), and late onset Alzheimer''s disease (LOAD) study participants and collected their CSF. After fractionation into nanometer particles (NP) and supernatant fluids (SF), we studied the lipid composition of these compartments. LC-MS/MS studies reveal that both CSF fractions from CH subjects have N-acyl phosphatidylethanolamine, 1-radyl-2-acyl-sn-glycerophosphoethanolamine (PE), 1-radyl-2-acyl-sn-glycerophosphocholine (PC), 1,2-diacyl-sn-glycerophosphoserine (PS), platelet-activating factor-like lipids, and lysophosphatidylcholine (LPC). In the NP fraction, GPs are enriched with a mixture of saturated, monounsaturated, and polyunsaturated fatty acid species, while PE and PS in the SF fractions are enriched with PUFA-containing molecular species. PC, PE, and PS levels in CSF fractions decrease progressively in participants from CH to MCI, and then to LOAD. Whereas most PC species decrease equally in LOAD, plasmalogen species account for most of the decrease in PE. A significant increase in the LPC-to-PC ratio and PLA2 activity accompanies the GP decrease in LOAD. These studies reveal that CSF supernatant fluid and nanometer particles have different GP composition, and that PLA2 activity accounts for altered GPs in these fractions as neurodegeneration progresses. 相似文献
156.
157.
158.
159.
Daniel Wibberg Jochen Blom Christian Rückert Anika Winkler Andreas Albersmeier Alfred Pühler Andreas Schlüter Birgit E. Scharf 《Journal of biotechnology》2013
Sinorhizobium meliloti of the order Rhizobiales is a symbiotic nitrogen-fixing bacterium nodulating plants of the genera Medicago, Trigonella and Melilotus and hence is of great agricultural importance. In its free-living state it is motile and capable of modulating its movement patterns in response to chemical attractants. Here, the draft genome consisting of a circular chromosome, the megaplasmids pSymA and pSymB and three accessory plasmids of Sinorhizobium meliloti RU11/001, a model organism for flagellum structure, motility and chemotaxis, is reported. 相似文献
160.
Irena Maus Daniel Wibberg Robbin Stantscheff Katharina Cibis Felix-Gregor Eikmeyer Helmut König Alfred Pühler Andreas Schlüter 《Journal of biotechnology》2013
Methanobacterium sp. Mb1, a hydrogenotrophic methanogenic Archaeon, was isolated from a rural biogas plant producing methane-rich biogas from maize silage and cattle manure in Germany. Here we report the complete genome sequence of the novel methanogenic isolate Methanobacterium sp. Mb1 harboring a 2,029,766 bp circular chromosome featuring a GC content of 39.74%. The genome encodes two rRNA operons, 41 tRNA genes and 2021 coding sequences and represents the smallest genome currently known within the genus Methanobacterium. 相似文献