全文获取类型
收费全文 | 223968篇 |
免费 | 14991篇 |
国内免费 | 45篇 |
出版年
2021年 | 1774篇 |
2018年 | 3125篇 |
2017年 | 3023篇 |
2016年 | 3667篇 |
2015年 | 3202篇 |
2014年 | 4437篇 |
2013年 | 6321篇 |
2012年 | 7544篇 |
2011年 | 8065篇 |
2010年 | 5721篇 |
2009年 | 4876篇 |
2008年 | 7197篇 |
2007年 | 7478篇 |
2006年 | 7178篇 |
2005年 | 6704篇 |
2004年 | 6848篇 |
2003年 | 6567篇 |
2002年 | 6524篇 |
2001年 | 9274篇 |
2000年 | 8953篇 |
1999年 | 6988篇 |
1998年 | 2122篇 |
1997年 | 1953篇 |
1996年 | 1820篇 |
1992年 | 5467篇 |
1991年 | 5678篇 |
1990年 | 5650篇 |
1989年 | 5620篇 |
1988年 | 5212篇 |
1987年 | 4862篇 |
1986年 | 4442篇 |
1985年 | 4678篇 |
1984年 | 3696篇 |
1983年 | 3025篇 |
1982年 | 2013篇 |
1981年 | 1722篇 |
1980年 | 1726篇 |
1979年 | 3338篇 |
1978年 | 2577篇 |
1977年 | 2376篇 |
1976年 | 2330篇 |
1975年 | 2826篇 |
1974年 | 3117篇 |
1973年 | 3084篇 |
1972年 | 2746篇 |
1971年 | 2604篇 |
1970年 | 2213篇 |
1969年 | 2158篇 |
1968年 | 2032篇 |
1967年 | 1797篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
A Sh Byshevski? G S Solov'ev S L Galian V G Solov'ev S V Solov'ev 《Biulleten' eksperimental'no? biologii i meditsiny》1992,114(9):262-265
In experiment on white rats it was shown that preventive 12-day administration of vitamins A, E, C, P decreases the death rate of animals with exogenous thromboplastinemia and reduces hemocoagulative changes, microcirculation disorders, destructive changes of functionally active elements of inner organs. The protective effect of the above vitamins combination in thromboplastinemia is promoted by hypoactivity of platelet aggregation, by low thromboplastic activity of erythrocytes, by limited destruction of vascular endothelium. 相似文献
952.
Construction of isogenic gonococci with variable porin structure: effects on susceptibility to human serum and antibiotics 总被引:11,自引:2,他引:9
Protein I (PI) is the most abundant protein on the gonococcal cell surface and besides its porin function it may have important properties contributing to pathogenicity. By allelic exchange using cloned PI genes from FA19 (PIA) and MS11 (PIB) and a selectable marker introduced closely downstream of these genes, we constructed sets of isogenic gonococcal strains that differ only in their PI gene. Analysis revealed that PI has a major effect on stable resistance to normal human serum, and a slight effect on low-level resistance to antibiotics. All PIA/B hybrids were hypersusceptible to serum, suggesting a possible explanation for why such hybrids do not occur in nature. 相似文献
953.
954.
G G Ivanov V A Vostrikov M S Bogushevich O S Medvedev Zh D Bespalova 《Biulleten' eksperimental'no? biologii i meditsiny》1992,113(5):463-464
Results of the study of taurine and dipeptide Tyr-Tyr effect on the threshold values of functional lesions of the myocardium and heart defibrillation are reported. The experiments were carried out on 27 narcotized mongrel dogs weighing 12-30 kg. Defibrillation was performed using Lifepak-7 defibrillator (USA). Lesion threshold (LT), defibrillation threshold (DT) and electrotherapeutic index (ETI) as a LT:DT ratio were determined. In 14 experiments (control group) these parameters were evaluated during 3 h. In group 1 (6 experiments) taurine (100 mg/kg) was infused intravenously by the end of the 1st hour, in group 2--Tyr-Tyr (25 mg/kg). It was shown that infusion of taurine did not have a noticeable effect of the LT, DT and ETI values. Infusion of Tyr-Tyr resulted in an increase in LT and DT. The possibility to use dipeptide Tyr-Tyr in the complex of measures aimed at ceasing ventricular fibrillation is discussed. 相似文献
955.
A L Rakhmilevich M A Shne?derova S S Obernikhin E V Klychkova R D Altynbaeva B B Fuks 《Biulleten' eksperimental'no? biologii i meditsiny》1990,110(7):80-83
We studied some possible mechanisms of action of immunosuppressor factors (ISF) produced by tumor cells on lymphocyte proliferation. ISF of murine tumor cell lines inhibited the mitogen induced proliferation of murine splenocytes as well as human mononuclear blood cells. Normal human mononuclear blood cells or concanavalin A-activated murine spleen cells preincubated with phytohemagglutinin (PHA) or interleukin 2 (IL-2) respectively, were strongly suppressed by ISF in response to these activators. When preincubated with splenocytes or blood cells for 2 h at 4 degrees C following washing, ISF suppressed the lymphocyte proliferation as effectively as when being with cells during all period of cultivation. ISF inhibited mitogen-induced lymphocyte proliferation at low dilutions. There was no competition for lymphocyte membrane receptors between these functionally heterogenic kinds of ISF. Collectively, these results show that ISF acted when being attached to some lymphocyte membrane receptors. 相似文献
956.
Journal of Ichthyology - The paper considers the effect of the Sea of Azov salinization on the food supply to anchovy Engraulis encrasicolus maeoticus as the level of salinity was rising from 12.7... 相似文献
957.
Sergio M. Villordo Claudia V. Filomatori Irma Sánchez-Vargas Carol D. Blair Andrea V. Gamarnik 《PLoS pathogens》2015,11(1)
Many viral pathogens cycle between humans and insects. These viruses must have evolved strategies for rapid adaptation to different host environments. However, the mechanistic basis for the adaptation process remains poorly understood. To study the mosquito-human adaptation cycle, we examined changes in RNA structures of the dengue virus genome during host adaptation. Deep sequencing and RNA structure analysis, together with fitness evaluation, revealed a process of host specialization of RNA elements of the viral 3’UTR. Adaptation to mosquito or mammalian cells involved selection of different viral populations harvesting mutations in a single stem-loop structure. The host specialization of the identified RNA structure resulted in a significant viral fitness cost in the non-specialized host, posing a constraint during host switching. Sequence conservation analysis indicated that the identified host adaptable stem loop structure is duplicated in dengue and other mosquito-borne viruses. Interestingly, functional studies using recombinant viruses with single or double stem loops revealed that duplication of the RNA structure allows the virus to accommodate mutations beneficial in one host and deleterious in the other. Our findings reveal new concepts in adaptation of RNA viruses, in which host specialization of RNA structures results in high fitness in the adapted host, while RNA duplication confers robustness during host switching. 相似文献
958.
G N Kryzhanovski? V G Kucherianu L S Godlevski? A D Mazarati 《Biulleten' eksperimental'no? biologii i meditsiny》1992,113(1):16-19
The effect of intranasal substance P injection on parkinsonian syndrome and the generator of pathologically enhanced excitation (GPEE) in caudate nuclei (CN) was investigated. MPTP or reserpine administration in old rats induced oligokinesia, rigidity and tremor followed by the high amplitude slow and rapid waves in both CN. The bilateral intranasal injection of substance P (25 micrograms/kg) resulted in an increase in motor activity and almost completely abolished the rigidity and tremor. The reduction of extrapyramidal symptoms was considered as a result of the inhibition of GPEE in CN. The possibility of substance P entry from nasal cavity into the brain was discussed. The changes of the substance P balance in nigrostriatal system was suggested to be on of the pathogenetic links of parkinsonian syndrome. 相似文献
959.
At the level of DNA organization into chromatin, there are mechanisms that define gene expression profiles in specialized cell types. Genes within chromatin regions that are located at the nuclear periphery are generally expressed at lower levels; however, the nature of this phenomenon remains unclear. These parts of chromatin interact with nuclear lamina proteins like Lamin B1 and, therefore, can be identified in a given cell type by chromatin profiling of these proteins. In this study, we created and tested a Dam Identification (DamID) system induced by Cre recombinase using Lamin B1 and mouse embryonic fibroblasts. This inducible system will help to generate genome-wide profiles of chromatin proteins in given cell types and tissues with no need to dissect tissues from organs or separate cells from tissues, which is achieved by using specific regulatory DNA elements and due to the high sensitivity of the method. 相似文献
960.
B N Kholodenko O V Demin G Moehren J B Hoek 《The Journal of biological chemistry》1999,274(42):30169-30181
During the past decade, our knowledge of molecular mechanisms involved in growth factor signaling has proliferated almost explosively. However, the kinetics and control of information transfer through signaling networks remain poorly understood. This paper combines experimental kinetic analysis and computational modeling of the short term pattern of cellular responses to epidermal growth factor (EGF) in isolated hepatocytes. The experimental data show transient tyrosine phosphorylation of the EGF receptor (EGFR) and transient or sustained response patterns in multiple signaling proteins targeted by EGFR. Transient responses exhibit pronounced maxima, reached within 15-30 s of EGF stimulation and followed by a decline to relatively low (quasi-steady-state) levels. In contrast to earlier suggestions, we demonstrate that the experimentally observed transients can be accounted for without requiring receptor-mediated activation of specific tyrosine phosphatases, following EGF stimulation. The kinetic model predicts how the cellular response is controlled by the relative levels and activity states of signaling proteins and under what conditions activation patterns are transient or sustained. EGFR signaling patterns appear to be robust with respect to variations in many elemental rate constants within the range of experimentally measured values. On the other hand, we specify which changes in the kinetic scheme, rate constants, and total amounts of molecular factors involved are incompatible with the experimentally observed kinetics of signal transfer. Quantitation of signaling network responses to growth factors allows us to assess how cells process information controlling their growth and differentiation. 相似文献