全文获取类型
收费全文 | 20938篇 |
免费 | 2026篇 |
国内免费 | 14篇 |
出版年
2022年 | 132篇 |
2021年 | 312篇 |
2020年 | 179篇 |
2019年 | 210篇 |
2018年 | 305篇 |
2017年 | 274篇 |
2016年 | 434篇 |
2015年 | 759篇 |
2014年 | 888篇 |
2013年 | 1115篇 |
2012年 | 1428篇 |
2011年 | 1452篇 |
2010年 | 969篇 |
2009年 | 857篇 |
2008年 | 1219篇 |
2007年 | 1203篇 |
2006年 | 1109篇 |
2005年 | 1097篇 |
2004年 | 1117篇 |
2003年 | 1078篇 |
2002年 | 1044篇 |
2001年 | 219篇 |
2000年 | 182篇 |
1999年 | 279篇 |
1998年 | 310篇 |
1997年 | 199篇 |
1996年 | 186篇 |
1995年 | 166篇 |
1994年 | 202篇 |
1993年 | 191篇 |
1992年 | 194篇 |
1991年 | 168篇 |
1990年 | 159篇 |
1989年 | 145篇 |
1988年 | 124篇 |
1987年 | 130篇 |
1986年 | 122篇 |
1985年 | 145篇 |
1984年 | 198篇 |
1983年 | 135篇 |
1982年 | 193篇 |
1981年 | 158篇 |
1980年 | 168篇 |
1979年 | 126篇 |
1978年 | 140篇 |
1977年 | 122篇 |
1976年 | 121篇 |
1975年 | 110篇 |
1974年 | 117篇 |
1973年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Jeffrey Pomerance Richard Johnson Shoba Kagal Philip Brooks Malcolm Margolin Arthur Allen 《The Western journal of medicine》1980,133(4):289-291
Recently, there has been increased interest in the influence of maternal prenatal nutrition on the course and outcome of pregnancy. Evidence has accumulated that a woman''s weight before pregnancy and the weight gained during pregnancy directly affect infant birth weight, incidence of neonatal mortality, and growth and development of the infant during the first year of life. Although recent recommendations for weight gain in pregnancy have been liberalized, a survey of 195 pregnant women who had prenatal visits in both clinic and private offices showed deficiencies in their understanding of the subject. Some 37 percent of women believed they should gain 20 pounds (9 kg) or less during pregnancy. Eight percent admitted to dieting before at least one antenatal visit and 54 percent thought their doctor would not be concerned about too little weight gained during pregnancy. This suggests that many women and some doctors are still ignorant of current concepts of proper nutrition during pregnancy. Apparently, increased lay and professional educational efforts are needed. 相似文献
23.
Tobias Gerlach Dennis Sprenger Nico K. Michiels 《Proceedings. Biological sciences / The Royal Society》2014,281(1787)
Fluorescence enables the display of wavelengths that are absent in the natural environment, offering the potential to generate conspicuous colour contrasts. The marine fairy wrasse Cirrhilabrus solorensis displays prominent fluorescence in the deep red range (650–700 nm). This is remarkable because marine fishes are generally assumed to have poor sensitivity in this part of the visual spectrum. Here, we investigated whether C. solorensis males can perceive the fluorescence featured in this species by testing whether the presence or absence of red fluorescence affects male–male interactions under exclusive blue illumination. Given that males respond aggressively towards mirror-image stimuli, we quantified agonistic behaviour against mirrors covered with filters that did or did not absorb long (i.e. red) wavelengths. Males showed significantly fewer agonistic responses when their fluorescent signal was masked, independent of brightness differences. Our results unequivocally show that C. solorensis can see its deep red fluorescent coloration and that this pattern affects male–male interactions. This is the first study to demonstrate that deep red fluorescent body coloration can be perceived and has behavioural significance in a reef fish. 相似文献
24.
Olivia Sackett Katherina Petrou Brian Reedy Ross Hill Martina Doblin John Beardall Peter Ralph Philip Heraud 《The ISME journal》2016,10(2):416-426
Diatoms, an important group of phytoplankton, bloom annually in the Southern Ocean, covering thousands of square kilometers and dominating the region''s phytoplankton communities. In their role as the major food source to marine grazers, diatoms supply carbon, nutrients and energy to the Southern Ocean food web. Prevailing environmental conditions influence diatom phenotypic traits (for example, photophysiology, macromolecular composition and morphology), which in turn affect the transfer of energy, carbon and nutrients to grazers and higher trophic levels, as well as oceanic biogeochemical cycles. The paucity of phenotypic data on Southern Ocean phytoplankton limits our understanding of the ecosystem and how it may respond to future environmental change. Here we used a novel approach to create a ‘snapshot'' of cell phenotype. Using mass spectrometry, we measured nitrogen (a proxy for protein), total carbon and carbon-13 enrichment (carbon productivity), then used this data to build spectroscopy-based predictive models. The models were used to provide phenotypic data for samples from a third sample set. Importantly, this approach enabled the first ever rate determination of carbon productivity from a single time point, circumventing the need for time-series measurements. This study showed that Chaetoceros simplex was less productive and had lower protein and carbon content during short-term periods of high salinity. Applying this new phenomics approach to natural phytoplankton samples could provide valuable insight into understanding phytoplankton productivity and function in the marine system. 相似文献
25.
26.
27.
28.
29.
30.
Dennis W. Jung Gerald P. Brierley 《Biochemical and biophysical research communications》1982,106(4):1372-1377
Heart mitochondria respiring in the presence of Pi release endogenous K+ to a sucrose medium when an uncoupler is added. The uncoupled mitochondria retain K+, however, if the oxidation of NAD(P)H is prevented by the addition of rotenone or antimycin. Addition of rotenone, once the uncoupler-dependent K+-efflux has been initiated, results in a rapid reduction of NAD(P) and a simultaneous decrease in permeability to K+. These changes are independent of respiration. The results suggest that a latent pathway for K+-permeability is present in the membrane, that it can be opened and closed reversibly, and that it reflects, either directly or indirectly, the redox status of mitochondrial pyridine nucleotides. The possible relationship of this putative pathway to those available for Ca2+ uptake and release is considered. 相似文献