全文获取类型
收费全文 | 10002篇 |
免费 | 739篇 |
国内免费 | 1352篇 |
出版年
2024年 | 20篇 |
2023年 | 206篇 |
2022年 | 219篇 |
2021年 | 315篇 |
2020年 | 393篇 |
2019年 | 447篇 |
2018年 | 350篇 |
2017年 | 376篇 |
2016年 | 400篇 |
2015年 | 435篇 |
2014年 | 506篇 |
2013年 | 699篇 |
2012年 | 419篇 |
2011年 | 485篇 |
2010年 | 357篇 |
2009年 | 514篇 |
2008年 | 547篇 |
2007年 | 581篇 |
2006年 | 541篇 |
2005年 | 421篇 |
2004年 | 388篇 |
2003年 | 396篇 |
2002年 | 313篇 |
2001年 | 275篇 |
2000年 | 247篇 |
1999年 | 184篇 |
1998年 | 198篇 |
1997年 | 193篇 |
1996年 | 144篇 |
1995年 | 134篇 |
1994年 | 148篇 |
1993年 | 140篇 |
1992年 | 136篇 |
1991年 | 105篇 |
1990年 | 104篇 |
1989年 | 86篇 |
1988年 | 73篇 |
1987年 | 66篇 |
1986年 | 60篇 |
1985年 | 99篇 |
1984年 | 59篇 |
1983年 | 45篇 |
1982年 | 63篇 |
1981年 | 52篇 |
1980年 | 29篇 |
1979年 | 31篇 |
1978年 | 20篇 |
1977年 | 26篇 |
1976年 | 10篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Copper- and arsenate-induced oxidative stress in Holcus lanatus L. clones with differential sensitivity 总被引:5,自引:0,他引:5
The biochemical responses of Holcus lanatus L. to copper and arsenate exposure were investigated in arsenate‐tolerant and ‐non‐tolerant plants from uncontaminated and arsenic/copper‐contaminated sites. Increases in lipid peroxidation, superoxide dismutase (SOD) activity and phytochelatin (PC) production were correlated with increasing copper and arsenate exposure. In addition, significant differences in biochemical responses were observed between arsenate‐tolerant and ‐non‐tolerant plants. Copper and arsenate exposure led to the production of reactive oxygen species, resulting in significant lipid peroxidation in non‐tolerant plants. However, SOD activity was suppressed upon metal exposure, possibly due to interference with metallo‐enzymes. It was concluded that in non‐tolerant plants, rapid arsenate influx resulted in PC production, glutathione depletion and lipid peroxidation. This process would also occur in tolerant plants, but by decreasing the rate of influx, they were able to maintain their constitutive functions, detoxify the metals though PC production and quench reactive oxygen species by SOD activity. 相似文献
2.
N. L. Biddington P. A. Brocklehurst A. S. Dearman Jane Dearman 《Physiologia plantarum》1982,55(4):407-410
Celery seeds ( Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion. 相似文献
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion. 相似文献
3.
Diego Sustaita Patty Finfrock Quickert Laura Patterson Laureen Barthman-Thompson Sarah Estrella 《The Journal of wildlife management》2011,75(6):1498-1507
We undertook a 2-year (2002–2004) mark–recapture study to investigate demographic performance and habitat use of salt marsh harvest mice (Reithrodontomys raviventris halicoetes) in the Suisun Marsh. We examined the effects of different wetland types and microhabitats on 3 demographic variables: density, reproductive potential, and persistence. Our results indicate that microhabitats dominated by mixed vegetation or pickleweed (Salicornia spp.) supported similar salt marsh harvest mouse densities, reproductive potential, and persistence throughout much of the year, whereas few salt marsh harvest mice inhabited upland grass-dominated microhabitats. We found that densities were higher in diked wetlands, whereas post-winter persistence was higher in tidal wetlands, and reproductive potential did not differ statistically between wetland types. Our results emphasize the importance of mixed vegetation for providing adequate salt marsh harvest mouse habitat and suggest that, despite their physiognomic and hydrological differences, both diked and tidal wetlands support salt marsh harvest mouse populations by promoting different demographic attributes. We recommend that habitat management, restoration, and enhancement efforts include areas containing mixed vegetation in addition to pickleweed in both diked and tidal wetlands. © 2011 The Wildlife Society. 相似文献
4.
In order to evaluate the effectiveness and selectivity of various reagents in the solubilization of bacterial membranes, membranes of Micrococcus lysodeikticus were treated with detergents and chaotropic agents. The composition of the extracts so obtained was analyzed by rocket and two-dimensional immunoelectrophoretic techniques. Recovery of succinate-, malate-, and reduced nicotinamide adenine dinucleotide- (NADH) dehydrogenases, ATPase, succinylated lipomannan and cytochromes in the extracts was measured. Treatment with a variety of non-denaturing detergents produced extracts that were generally qualitatively uniform although quantitative differences were observed. The degree of extraction of various components was correlated with the hydrophile-lipophile balance. Several chaotropic agents were also evaluated as reagents for membrane solubilization. These agents were less effective in extraction of bulk protein, but produced extracts enriched in some membrane components. 相似文献
5.
6.
7.
8.
A simple method is described for picomole determinations of fatty acid metal salts. Fatty acid salts are directly labeled with 4-bromomethyl-7-methoxycoumarin in the presence of excess ethylenediaminetetraacetic acid tripotassium salt without any solvent extractions. The fluorescence derivatives of fatty acids are separated by reverse-phase high-performance liquid chromatography followed by fluorometric detection. The response of each fatty acid (C8-C18) calcium salt is linear from 1 to 50 micrograms/ml of samples. The detection limit is about 7 pmol. Good recoveries are obtained for the calcium salts of myrystic acid and soap (C8-C18, C18:1,2). The new method is successfully applied to the study on biodegradation of fatty acids in river water. 相似文献
9.
Genetic and spatial structure within a swift fox population 总被引:1,自引:0,他引:1
10.
Georg Steinhauser Johannes H. Sterba Karin Poljanc Max Bichler Karl Buchtela 《Journal of trace elements in medicine and biology》2006,20(3):119-153
In this study, 18 partly commercially available samples of rock salt from Austria, Germany, Pakistan, Poland, Switzerland, and Ukraine were investigated with respect to their content of trace elements using instrumental neutron activation analysis. Elements detected were Al, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Eu, Fe, Hf, La, Mn, Na, Rb, Sb, Sc, Sm, Sr, Ta, Tb, Th, and Zn, some of them only in individual cases. An estimation of the bioavailability of these trace elements was performed by dissolving an equivalent of the sodium chloride samples in diluted hydrochloric acid (simulating stomach acid), filtering off the insoluble components, and analyzing the evaporated filtrate. It could be shown that in most cases bioactive trace elements like Fe can be found in rock salt in the form of almost insoluble compounds and are therefore not significantly bioavailable, whereas thorium, for example, was partly bioavailable in two cases. A significant contribution to the recommended daily intake of metal trace elements by using rock salt for nutrition can be excluded. 相似文献