全文获取类型
收费全文 | 2867篇 |
免费 | 240篇 |
国内免费 | 2篇 |
出版年
2022年 | 19篇 |
2021年 | 40篇 |
2020年 | 17篇 |
2019年 | 28篇 |
2018年 | 33篇 |
2017年 | 30篇 |
2016年 | 79篇 |
2015年 | 125篇 |
2014年 | 144篇 |
2013年 | 145篇 |
2012年 | 193篇 |
2011年 | 172篇 |
2010年 | 137篇 |
2009年 | 87篇 |
2008年 | 184篇 |
2007年 | 145篇 |
2006年 | 146篇 |
2005年 | 129篇 |
2004年 | 140篇 |
2003年 | 122篇 |
2002年 | 131篇 |
2001年 | 67篇 |
2000年 | 71篇 |
1999年 | 53篇 |
1998年 | 45篇 |
1997年 | 26篇 |
1996年 | 29篇 |
1995年 | 31篇 |
1994年 | 16篇 |
1993年 | 23篇 |
1992年 | 38篇 |
1991年 | 51篇 |
1990年 | 39篇 |
1989年 | 32篇 |
1988年 | 33篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 29篇 |
1984年 | 27篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 14篇 |
1977年 | 16篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1972年 | 9篇 |
1971年 | 7篇 |
排序方式: 共有3109条查询结果,搜索用时 265 毫秒
81.
Lapeña David Olsen Pernille M. Arntzen Magnus Ø. Kosa Gergely Passoth Volkmar Eijsink Vincent G. H. Horn Svein J. 《Bioprocess and biosystems engineering》2020,43(4):723-736
Bioprocess and Biosystems Engineering - The production of microbial protein in the form of yeast grown on lignocellulosic sugars and nitrogen-rich industrial residues is an attractive approach for... 相似文献
82.
83.
Linda K. Petersson Daniel C. Dey Annika M. Felton Emile S. Gardiner Magnus Lf 《Ecology and evolution》2020,10(5):2626-2637
Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land‐use. We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low‐intensity surface fire (burn/no burn). Survival, relative height growth (RGRH), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGRH (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGRH (p = .058) and survival (p = .059). Burning reduced survival (p < .001), nonetheless, survival rates were relatively high across treatment combinations at the end of the experiment (54%–92%). Most oaks receiving fire were top‐killed and survived by producing new sprouts; therefore, RGRH in burned plots became strongly negative the first year. Thereafter, RGRH was greater in burned plots (p = .002). Burning altered the patterns of ungulate browsing frequency on oaks. Overall, browsing frequency was greater during winter; however, in recently burned plots summer browsing was prominent. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals (p < .001) and their heights (p < .001). Our results suggest that young, temperate European oaks may respond similarly to fire as their North American congeners. However, disturbance from a single low‐intensity fire may not be sufficient to ensure a persistent competitive advantage—multiple fires and canopy thinning to increase light availability may be needed. Further research investigating long‐term fire effects on oaks of various ages, species‐specific response of competitors and implications for biodiversity conservation is needed. 相似文献
84.
85.
Persson Joel Ford Scott Keophoxay Anousith Mertz Ole Nielsen Jonas Østergaard Vongvisouk Thoumthone Zörner Michael 《Human ecology: an interdisciplinary journal》2021,49(5):597-616
Human Ecology - Despite the popularity of integrated conservation and development approaches to protected area management, adjacent communities increasingly face livelihood dilemmas. Yet... 相似文献
86.
87.
In southern Brazil, we investigated shark and ray capture records in an integral protection marine protection area (MPA) that allows fishing in that area. We found 10 shark and nine ray species, of which 88.5% and 66.2%, respectively, are endangered. Female adults and neonates of both sexes are abundant in the area, with records of stranding of large specimens, postcapture abortions and ovigerous capsules with fresh embryos on the beach. We suggest the application of continuous fisheries monitoring and an increase in guidelines on the capture of endangered species. 相似文献
88.
Bertil Persson Anders Andersson Björn Hultberg Christer Hansson 《Free radical research》2013,47(2):151-156
Glutathione, the most abundant low-molecular weight thiol in the skin, has been shown to protect the skin from both photobiological and chemical injury. The thiols, glutathione in particular, have also been shown to be crucially involved in defence against contact allergens. Since the levels of extracellular thiol concentrations are important determinants of intracellular thiol status, we have compared the normal concentrations and the redox status of the main low-molecular weight thiol components in the extracellular fluid at the dermo-epidermal junction with the corresponding plasma levels. In their sulfhydryl form, all three thiols, i.e. glutathione, cysteine and homocysteine, were more abundant in experimental skin blister fluid than in plasma, as were the free disulfides of glutathione and homocysteine, whereas the free disulfides of cysteine were about the same in blister fluid and in plasma. Protein mixed disulfide levels were higher in plasma than in blister fluid. The present results provide information concerning the extracellular defence in the skin. 相似文献
89.
α1-Microglobulin is a 26 kDa plasma and tissue glycoprotein that belongs to the lipocalin protein superfamily. Recent reports show that it is a reductase and radical scavenger and that it binds heme and has heme-degrading properties. This study has investigated the protective effects of α1-microglobulin against oxidation by heme and reactive oxygen species in the human erythroid cell line, K562. The results show that α1-microglobulin prevents intracellular oxidation and up-regulation of heme oxygenase-1 induced by heme, hydrogen peroxide and Fenton reaction-generated hydroxyl radicals in the culture medium. It also reduces the cytosol of non-oxidized cells. Endogeneous expression of α1-microglobulin was up-regulated by these oxidants and silencing of the α1-microglobulin expression increased the cytosol oxidation. α1-microglobulin also inhibited cell death caused by heme and cleared cells from bound heme. Binding of heme to α1-microglobulin increased the radical reductase activity of the protein as compared to the apo-protein. Finally, α1-microglobulin was localized mainly at the cell surface both when administered exogeneously and in non-treated cells. The results suggest that α1-microglobulin is involved in the defence against oxidative cellular injury caused by haemoglobin and heme and that the protein may employ both heme-scavenging and one-electron reduction of radicals to achieve this. 相似文献
90.
Shahinaz M. Gadalla Ruth M. Pfeiffer Sigurdur Y. Kristinsson Magnus Bj?rkholm James E. Hilbert Richard T. Moxley III Ola Landgren Mark H. Greene 《PloS one》2013,8(11)
Recent studies show that patients with myotonic dystrophy (DM) have an increased risk of specific malignancies, but estimates of absolute cancer risk accounting for competing events are lacking. Using the Swedish Patient Registry, we identified 1,081 patients with an inpatient and/or outpatient diagnosis of DM between 1987 and 2007. Date and cause of death and date of cancer diagnosis were extracted from the Swedish Cause of Death and Cancer Registries. We calculated non-parametric estimates of absolute cancer risk and cancer mortality accounting for the high non-cancer competing mortality associated with DM. Absolute cancer risk after DM diagnosis was 1.6% (95% CI=0.4-4%), 5% (95% CI=3-9%) and 9% (95% CI=6-13%) at ages 40, 50 and 60 years, respectively. Females had a higher absolute risk of all cancers combined than males: 9% (95% CI=4-14), and 13% (95% CI=9-20) vs. 2% (95%CI= 0.7-6) and 4% (95%CI=2-8) by ages 50 and 60 years, respectively) and developed cancer at younger ages (median age =51 years, range=22-74 vs. 57, range=43-84, respectively, p=0.02). Cancer deaths accounted for 10% of all deaths, with an absolute cancer mortality risk of 2% (95%CI=1-4.5%), 4% (95%CI=2-6%), and 6% (95%CI=4-9%) by ages 50, 60, and 70 years, respectively. No gender difference in cancer-specific mortality was observed (p=0.6). In conclusion, cancer significantly contributes to morbidity and mortality in DM patients, even after accounting for high competing DM mortality from non-neoplastic causes. It is important to apply population-appropriate, validated cancer screening strategies in DM patients. 相似文献