全文获取类型
收费全文 | 201164篇 |
免费 | 16017篇 |
国内免费 | 106篇 |
出版年
2018年 | 2042篇 |
2017年 | 1947篇 |
2016年 | 2578篇 |
2015年 | 2742篇 |
2014年 | 3587篇 |
2013年 | 5184篇 |
2012年 | 5873篇 |
2011年 | 6423篇 |
2010年 | 4411篇 |
2009年 | 4003篇 |
2008年 | 5884篇 |
2007年 | 6184篇 |
2006年 | 5800篇 |
2005年 | 5508篇 |
2004年 | 5606篇 |
2003年 | 5498篇 |
2002年 | 5447篇 |
2001年 | 8594篇 |
2000年 | 8745篇 |
1999年 | 6562篇 |
1998年 | 2241篇 |
1997年 | 2219篇 |
1996年 | 2008篇 |
1995年 | 1851篇 |
1993年 | 1834篇 |
1992年 | 5372篇 |
1991年 | 5527篇 |
1990年 | 5278篇 |
1989年 | 5266篇 |
1988年 | 4899篇 |
1987年 | 4642篇 |
1986年 | 4222篇 |
1985年 | 4412篇 |
1984年 | 3601篇 |
1983年 | 3094篇 |
1982年 | 2127篇 |
1981年 | 1962篇 |
1980年 | 1922篇 |
1979年 | 3369篇 |
1978年 | 2733篇 |
1977年 | 2445篇 |
1976年 | 2221篇 |
1975年 | 2689篇 |
1974年 | 3046篇 |
1973年 | 2963篇 |
1972年 | 2738篇 |
1971年 | 2512篇 |
1970年 | 2195篇 |
1969年 | 2122篇 |
1968年 | 2016篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Organelles such as endosomes and the Golgi apparatus play a critical role in regulating signal transmission to the nucleus. Recent experiments have shown that appropriate positioning of these organelles within the intracellular space is critical for effective signal regulation. To understand the mechanism behind this observation, we consider a reaction-diffusion model of an intracellular signaling cascade and investigate the effect on the signaling of intracellular regulation in the form of a small release of phosphorylated signaling protein, kinase, and/or phosphatase. Variational analysis is applied to characterize the most effective regions for the localization of this intracellular regulation. The results demonstrate that signals reaching the nucleus are most effectively regulated by localizing the release of phosphorylated substrate protein and kinase near the nucleus. Phosphatase release, on the other hand, is nearly equally effective throughout the intracellular space. The effectiveness of the intracellular regulation is affected strongly by the characteristics of signal propagation through the cascade. For signals that are amplified as they propagate through the cascade, reactions in the upstream levels of the cascade exhibit much larger sensitivities to regulation by release of phosphorylated substrate protein and kinase than downstream reactions. On the other hand, for signals that decay through the cascade, downstream reactions exhibit larger sensitivity than upstream reactions. For regulation by phosphatase release, all reactions within the cascade show large sensitivity for amplified signals but lose this sensitivity for decaying signals. We use the analysis to develop a simple model of endosome-mediated regulation of cell signaling. The results demonstrate that signal regulation by the modeled endosome is most effective when the endosome is positioned in the vicinity of the nucleus. The present findings may explain at least in part why endosomes in many cell types localize near the nucleus. 相似文献
992.
We performed a comparative analysis of different classes of algorithms for computer-assisted cardiological diagnostics. The concepts of an “internal” and “external” image of myocardial ischemia were formulated. We also discussed the biophysical aspects for the basic indices of spatial heterogeneity of the repolarization process in the myocardium, as well as the problems of measurement of the corresponding parameters. The experimental part was performed on two groups of patients. Both experimental and control groups included two sets of 12-lead electrocardiograms of real patients: “Normal” and “Ischemia” (with lateral localization). The experimental group consisted of 202 and 143 electrocardiograms, while the control group consisted of 200 and 91 electrocardiograms, respectively. The electrocardiograms were verified according to the Minnesota Code criteria. 相似文献
993.
Protective effects of manganese, cobalt, nickel, and barium against a calcium paradox in the isolated frog heart 总被引:1,自引:0,他引:1
The effect of inorganic slow channel blockers on the calcium paradox in the frog heart was examined. Addition of the divalent cations of manganese, cobalt, nickel, or barium during calcium depletion protected the frog heart against a calcium paradox. This protective effect was indicated by reduced protein release, maintenance of electrical activity, and recovery of mechanical activity during reperfusion. Tissue calcium determination results showed that in the control paradox in the absence of divalent cations, there is an efflux of calcium from myocardial cells during calcium depletion and a massive influx of calcium during the following reperfusion, leading to a calcium overload. Divalent cations protected frog myocardial cells, when present in the calcium-free perfusion medium, by reducing both calcium efflux during calcium depletion and the massive calcium influx during reperfusion. The effectiveness of the added divalent cations showed a strong dependence upon their ionic radius. The most potent inhibitors of the calcium paradox in the frog heart were the divalent cations having an ionic radius closer to the ionic radius of calcium. These results are discussed in terms of the possible mechanism involved in the protective effect of manganese, cobalt, nickel, and barium. 相似文献
994.
995.
996.
997.
A new kinetic model of the xanthophyll cycle is proposed. The model is based on the assumption that the light-dependent interconversion of the so-called available and unavailable violaxanthin constitutes the rate-limiting process of the cycle at intermediate, non-saturating light intensities. This assumption, together with the known properties of violaxanthin de-epoxidase, explains all specific features of the experimental facts. 相似文献
998.
Rearrangement of Fusarium oxysporum retro- transposon skippy was induced by growth in the presence of potassium chlorate. Three fungal strains, one sensitive to chlorate (Co60) and two resistant to chlorate and deficient for nitrate reductase (Co65 and Co94), were studied by Southern analysis of their genomic DNA. Polymorphism was detected in their hybridization banding pattern, relative to the wild type grown in the absence of chlorate, using various enzymes with or without restriction sites within the retrotransposon. Results were consistent with the assumption that three different events had occurred in strain Co60: genomic amplification of skippy yielding tandem arrays of the element, generation of new skippy sequences, and deletion of skippy sequences. Amplification of Co60 genomic DNA using the polymerase chain reaction and divergent primers derived from the retrotransposon generated a new band, corresponding to one long terminal repeat plus flanking sequences, that was not present in the wild-type strain. Molecular analysis of nitrate reductase-deficient mutants showed that generation and deletion of skippy sequences, but not genomic amplification in tandem repeats, had occurred in their genomes. 相似文献
999.
I A Tarakanov V A Safonov G A Semkina E A Golovatiuk 《Biulleten' eksperimental'no? biologii i meditsiny》1992,114(7):24-27
In experiments on sodium pentobarbital (40 mg/kg, i. p.) anesthetized mongrel cats of either sex weighting from 2.0 to 4.0 kg, it was stated, that sodium or lithium hydroxybutyrate (HOB) (200 mg/kg, i. v.) effectively slowed down breathing with inspiratory holdings. Thus 3-5 minutes after HOB administration, eupneic pattern of respiration was changed firstly to inspiratory apneustic one (100% of cats), and then to periodic one (80% of cats). This pattern persisted for 60-90 minutes, and after that the respiratory pattern usually changed its direction to the opposite one. In these conditions alterations of arterial blood composition (pH, pO2, pCO2, SO2) and hemodynamic variables (heart rate, arterial pressure) can not be considered as the cause of apneustic pattern of respiration. It is suggested, that HOB can be used for simulating such terminal respiratory patterns as apneustic and periodic ones. 相似文献
1000.
Beneficial effects of n-hexane bark extract of Onosma echioides L. on diabetic peripheral neuropathy
Ambreen Shoaib Badruddeen Rakesh Kumar Dixit Magdah Ganash George Barreto Ghulam Md Ashraf Hefazat Hussain Siddiqui 《Journal of cellular biochemistry》2019,120(10):16524-16532
Onosma echioides Linn (Boraginaceae) is the most frequently used curative herb widely used for kidney obstruction, sciatic pain, and gout. The present study was designed to investigate the therapeutic effects of n-hexane bark extract of O. echioides (OE) L. root in vivo against Streptozotocin-induced diabetic neuropathy in SD rats. For in vivo activity, the experiment was categorized into five different groups (n = 5). Group-I was considered as nondiabetic/normal control (NC) treated with 0.5% carboxymethyl cellulose (CMC), Group II as diabetic control, Group-III, IV, and V served as diabetic treated with OE 50, OE 100, and pregabalin at a dose of 50, 100, and 10 mg/kg body weight, orally, respectively. Body weight, blood glucose, oral glucose tolerance test, behavioral studies (motor coordination test, thermal hyperalgesia, cold allodynia, locomotor activity, oxidative biomarkers (thio barbituric acid reactive substances [TBARS], superoxide dismutase [SOD], glutathione [GSH], and catalase), and histopathology of the sciatic nerve were performed. Treatment with OE showed a dose-dependent increase in neuroprotective activity by improving the myelination and decreasing the axonal swelling of nerve fibers. The verdicts of behavioral activities showed a remarkable effect on animals after the treatment of extract and standard drug pregabalin. In conclusion, our findings supported the traditional application of OE and explored its importance in the management of diabetic neuropathy. Additional clinical experiments may provide novel therapeutic drugs for diabetes and its complications. 相似文献