全文获取类型
收费全文 | 6709篇 |
免费 | 581篇 |
国内免费 | 6篇 |
出版年
2023年 | 19篇 |
2022年 | 102篇 |
2021年 | 165篇 |
2020年 | 85篇 |
2019年 | 95篇 |
2018年 | 160篇 |
2017年 | 125篇 |
2016年 | 216篇 |
2015年 | 360篇 |
2014年 | 408篇 |
2013年 | 466篇 |
2012年 | 586篇 |
2011年 | 526篇 |
2010年 | 318篇 |
2009年 | 252篇 |
2008年 | 403篇 |
2007年 | 394篇 |
2006年 | 315篇 |
2005年 | 314篇 |
2004年 | 305篇 |
2003年 | 211篇 |
2002年 | 221篇 |
2001年 | 208篇 |
2000年 | 144篇 |
1999年 | 113篇 |
1998年 | 52篇 |
1997年 | 35篇 |
1996年 | 45篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 23篇 |
1992年 | 56篇 |
1991年 | 36篇 |
1990年 | 39篇 |
1989年 | 34篇 |
1988年 | 31篇 |
1987年 | 37篇 |
1986年 | 24篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 22篇 |
1980年 | 16篇 |
1979年 | 21篇 |
1978年 | 20篇 |
1977年 | 22篇 |
1976年 | 20篇 |
1974年 | 17篇 |
1969年 | 13篇 |
排序方式: 共有7296条查询结果,搜索用时 15 毫秒
991.
Rebecca M. Rose Michael St. J. Warne Richard P. Lim 《Journal of Aquatic Ecosystem Stress and Recovery (Formerly Journal of Aquatic Ecosystem Health)》2002,9(3):205-211
One of the acknowledged limitations ofconventional toxicity tests is their inabilityto evaluate the impact of toxicants onsubsequent generations. Given their relativelyshort lifespan, cladocerans in the field may beexposed to toxicants for several generations.However, it is unclear what effect such anexposure regime could have on the cladoceranfitness after removal of the toxicant. Thispaper aimed to determine the offspring fitnessof juveniles produced by adult Ceriodaphnia cf. dubia exposed toresidual levels of 3,4-dichloroaniline overfour generations. Mass cultures of Ceriodaphnia cf. dubia were maintainedfor several generations in variousconcentrations of 3,4-dichoroaniline (0, 2.5,5, 10, 15 and 20 µg/L). The mass cultureswere re-established every generation using4th brood neonates <24 h old. Eachgeneration, 4th brood neonates <24 h oldwere also transferred individually intotoxicant-free water and examined until theproduction of their 3rd brood. F1offspring of mothers exposed to 15 and20 µg/L 3,4-dichloroaniline showedsignificantly (p < 0.05) reducedreproduction compared to the controls. Nosignificant (p > 0.05) changes inreproduction due to 3,4-dichloroaniline wereobserved for the F2 and F3 offspring. However,F4 offspring of mothers exposed to all3,4-dichloroaniline concentrations showedsignificantly (p < 0.05) increasedreproduction compared to the controls. Possibleexplanations for the varying influence ofmaternal 3,4-dichloroaniline exposure on thereproductive output of the offspring arediscussed. 相似文献
992.
The phylogenetic relationship of the thecate PSP-toxin producing dinoflagellate Alexandrium tamiyavanichii Balech to other species of Alexandrium was studied based on nucleotide sequences of the ITS1, ITS2, 5.8S, 18S and 28S subunits of the ribosomal RNA gene. These are the first such sequences available for A. tamiyavanichii, which is one of the producers of paralytic shellfish poisoning toxins in tropical waters. Based on the nucleotide sequences of the 28S, 18S and 5.8S subunits of the rRNA gene, A. tamiyavanichii grouped together with A. tamarense, A. catenella and A. fundyense. More interestingly, A. tamiyavanichii was most closely affiliated to A. tamarense isolates from Thailand. This result reaffirmed conclusions from previous studies that, for the A. tamarense/fundyense/catenella species complex, geographical origin rather than morphology seems to determine genetic relatedness. Results of this study also suggest that A. tamiyavanichii most probably belongs to the same species complex. Ribosomal RNA gene sequences do not separate the PSP toxin producing from the non-producing species of Alexandrium. 相似文献
993.
994.
Cerebellar granule and glial cells were cultured from 7 day-old rat pups after pre- and post-natal nicotine treatment. Ten days later, the basal release of glutamate in the granule cells prepared from the pre- and post-natally nicotine-exposed pups was higher and lower than the controls, respectively. The N-methyl-D-aspartate-induced release of glutamate was higher in the granule cells of post-natal nicotine exposed rats. However, the nicotine-induced glutamate release was either unchanged or was lower in the granule cells of all nicotine-treated pups. The basal glutamate uptake was higher in the glial cells from those exposed pre-natally and lower in the continuously nicotine-exposed pups. The sensitivities of L-trans-pyrrolidine-2,4-dicarboxylic acid on glutamate uptake were higher in all nicotine treated groups. There was a higher number of specific [3H]dizocilpine binding sites in the pre- or continuously nicotine-exposed group. These results suggest that the cerebellar cell properties are altered after perinatal nicotine exposure and that the development of an excitatory amino acid system might be affected differently depending on the nicotine exposure time. 相似文献
995.
Treatment with a copper-zinc chelator markedly and rapidly inhibits beta-amyloid accumulation in Alzheimer's disease transgenic mice. 总被引:34,自引:0,他引:34
R A Cherny C S Atwood M E Xilinas D N Gray W D Jones C A McLean K J Barnham I Volitakis F W Fraser Y Kim X Huang L E Goldstein R D Moir J T Lim K Beyreuther H Zheng R E Tanzi C L Masters A I Bush 《Neuron》2001,30(3):665-676
Inhibition of neocortical beta-amyloid (Abeta) accumulation may be essential in an effective therapeutic intervention for Alzheimer's disease (AD). Cu and Zn are enriched in Abeta deposits in AD, which are solubilized by Cu/Zn-selective chelators in vitro. Here we report a 49% decrease in brain Abeta deposition (-375 microg/g wet weight, p = 0.0001) in a blinded study of APP2576 transgenic mice treated orally for 9 weeks with clioquinol, an antibiotic and bioavailable Cu/Zn chelator. This was accompanied by a modest increase in soluble Abeta (1.45% of total cerebral Abeta); APP, synaptophysin, and GFAP levels were unaffected. General health and body weight parameters were significantly more stable in the treated animals. These results support targeting the interactions of Cu and Zn with Abeta as a novel therapy for the prevention and treatment of AD. 相似文献
996.
A new method to calculate the optimal feed rate profile for fedbatch culture is proposed. Instead of the usual singular control approach of taking the feed rate as the control variable, the substrate concentration profile is used as the transformed control variable to avoid the computational difficulty associated with the singular control. Thus, the problem is converted into a nonsingular optimization problem of determining the optimal substrate concentration profile subject to a constraint. The equivalent feed rate profile to match the optimal substrate concentration profile is then generated. With this method the computational difficulty associated with singular controls for high-order systems is circumvented. The proposed method is illustrated by a number of examples. 相似文献
997.
Ji Young Kim Hun-Young Park Jisu Kim Kiwon Lim 《Journal of Exercise Nutrition & Biochemistry》2021,25(2):26
[Purpose]This study aimed to analyze the prevalence of hypertension according to the body mass index (BMI) and relative handgrip strength (RHGS) among elderly individuals in Korea. [Methods]We analyzed the data of 44,183 Korean elderly individuals over 65 years old (men: n = 15,798, age = 73.31 ± 5.04 years, women: n = 28,385, age = 72.14 ± 5.04 years) obtained from the Korean National Fitness Assessment in 2019. All the participants were categorized into three groups according to the BMI and RHGS; additionally, one-way ANOVA and logistic regression analysis were performed. [Results]Overweight (men: 1.16 odds ratio [OR] 1.06–1.26, 95% confidence interval [CI]; women: 1.15 OR, 1.07–1.23 95% CI) and obese (men: 1.54 OR, 1.42–1.66 95% CI; women: 1.44 OR, 1.36–1.53 95% CI) elderly individuals showed a higher prevalence of hypertension than elderly individuals with normal weight, after controlling for age. In men, a lower RHGS was associated with a higher prevalence of hypertension after controlling for age (weak RHGS: 1.09 OR, 1.00–1.17 95% CI; middle RHGS: 1.21 OR, 1.12–1.31 95% CI vs. strong RHGS). [Conclusion]A higher BMI was associated with the prevalence of hypertension in the elderly Korean population. In addition, a lower RHGS was associated with the prevalence of hypertension in elderly Korean men. 相似文献
998.
Wan Yun Ho Jer-Cherng Chang Kenneth Lim Amaury Cazenave-Gassiot Aivi T. Nguyen Juat Chin Foo Sneha Muralidharan Ashley Viera-Ortiz Sarah J.M. Ong Jin Hui Hor Ira Agrawal Shawn Hoon Olubankole Aladesuyi Arogundade Maria J. Rodriguez Su Min Lim Seung Hyun Kim John Ravits Shi-Yan Ng Markus R. Wenk Edward B. Lee Greg Tucker-Kellogg Shuo-Chien Ling 《The Journal of cell biology》2021,220(9)
999.
1000.