全文获取类型
收费全文 | 5410篇 |
免费 | 231篇 |
国内免费 | 15篇 |
专业分类
5656篇 |
出版年
2023年 | 57篇 |
2022年 | 155篇 |
2021年 | 311篇 |
2020年 | 128篇 |
2019年 | 181篇 |
2018年 | 202篇 |
2017年 | 159篇 |
2016年 | 224篇 |
2015年 | 267篇 |
2014年 | 306篇 |
2013年 | 427篇 |
2012年 | 384篇 |
2011年 | 390篇 |
2010年 | 220篇 |
2009年 | 180篇 |
2008年 | 211篇 |
2007年 | 204篇 |
2006年 | 189篇 |
2005年 | 161篇 |
2004年 | 126篇 |
2003年 | 98篇 |
2002年 | 105篇 |
2001年 | 57篇 |
2000年 | 67篇 |
1999年 | 50篇 |
1998年 | 31篇 |
1997年 | 19篇 |
1996年 | 25篇 |
1995年 | 20篇 |
1994年 | 23篇 |
1993年 | 26篇 |
1992年 | 36篇 |
1991年 | 51篇 |
1990年 | 45篇 |
1989年 | 38篇 |
1988年 | 33篇 |
1987年 | 45篇 |
1986年 | 33篇 |
1985年 | 37篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 23篇 |
1978年 | 25篇 |
1976年 | 13篇 |
1975年 | 16篇 |
1974年 | 15篇 |
1973年 | 20篇 |
排序方式: 共有5656条查询结果,搜索用时 15 毫秒
81.
82.
83.
Information about head orientation, position, and movement with respect to the trunk relies on the visual, vestibular, extensive muscular, and articular proprioceptive system of the neck. Various factors can affect proprioception since it is the function of afferent integration, and tuning of muscular and articular receptors. Pain, muscle fatigue, and joint position have been shown to affect proprioceptive capacity. Thus, it can be speculated that changes in body posture can alter the neck proprioception. This study was undertaken to investigate the effect of body posture on cervicocephalic kinesthetic sense in healthy subjects. Cervicocephalic kinesthetic sensibility was measured by the kinesthetic sensibility test in healthy young adults while in (a) habitual slouched sitting position with arms hanging by the side (SS), (b) habitual slouched sitting position with arms unloaded (supported) (SS-AS), and (c) upright sitting position with arms hanging by the side (US) during maximum and 30 degree right, left rotations, flexion, and extension. Thirty healthy male adults (mean age 27.83; SD 3.41) volunteered for this study. The least mean error was found for the SS-AS position (0.48; SD 0.24), followed by SS (0.60; SD 0.43) and US (0.96; SD 0.71), respectively. For all test conditions, there was significant difference in mean absolute error while head repositioning from maximum and 30 degree rotation during SS and SS-AS positions (p?0.05). In conclusion, body posture can affect the proprioception function of the neck. Supporting the upper extremities in such a way that their weight is unloaded, which leads to reduction in the tension between the neck and shoulder girdle, can improve cervicocephalic kinesthetic sense in both the horizontal and vertical planes. The findings of this study can be implemented in people who have to do repeated arm and neck movements, by using ergonomically effective chairs with proper arm supports. This might help in prevention and treatment of neck pain. 相似文献
84.
Triterpenoid CDDO-Me blocks the NF-kappaB pathway by direct inhibition of IKKbeta on Cys-179 总被引:3,自引:0,他引:3
Ahmad R Raina D Meyer C Kharbanda S Kufe D 《The Journal of biological chemistry》2006,281(47):35764-35769
The novel oleanane triterpenoid 2-cyano-3,12-dioxooleana-1,9,-dien-28-oic acid (CDDO) and the C-28 methyl ester (CDDO-Me) induce apoptosis of human tumor cells by disruption of redox balance and are currently in clinical trials. The present studies show that CDDO and CDDO-Me block tumor necrosis factoralpha-induced targeting of NF-kappaB p65 to the nucleus. CDDO-Me also blocked tumor necrosis factor alpha-induced phosphorylation of IkappaBalpha. In concert with these results, we found that CDDO-Me inhibits IkappaBalpha kinasebeta (IKKbeta) activity in cells. In support of a direct mechanism, CDDO-Me inhibited recombinant IKKbeta activity in vitro. The results also demonstrate that (i) CDDO and CDDO-Me form adducts with IKKbeta, but not IKKbeta with mutation of Cys-179 to Ala, and (ii) CDDO-Me inhibits IKKbeta by a mechanism dependent on oxidation of Cys-179. These findings indicate that CDDO and CDDO-Me directly block IKKbeta activity and thereby the NF-kappaB pathway by interacting with Cys-179 in the IKKbeta activation loop. 相似文献
85.
Roshanida Abd Rahman Rosli Md. Illias Mohd Ghazali Mohd Nawawi Ahmad Fauzi Ismail Osman Hassan Kamarulzaman Kamaruddin 《Process Biochemistry》2004,39(12):2053-2060
Cyclodextrin glucanotransferase (CGTase) activity was observed when the bacterium was grown in the medium at various initial pH values, containing carbon, nitrogen, phosphorus and mineral salt sources at 50 °C for 24 h in the shake flasks. The optimisation of this growth medium was carried out using response surface methodology. The design contains a total of 32 experimental trials involving 10 star points and 6 replicates at the centre points. The design was employed by selecting sago starch, peptone from casein, K2HPO4, CaCl2 and initial pH as five independent variables in this study. The optimal calculated values of tested variables for maximal production of CGTase were found to be comprised of: sago starch, 16.02 g/l; peptone from casein, 20 g/l; K2HPO4, 1.4 g/l; CaCl2, 0.2 g/l and initial pH, 7.54 with a predicted CGTase activity of 14.20 U/ml. These predicted optimal parameters were tested in the laboratory and the final CGTase activity obtained was very close to the predicted value at 14.80 U/ml. 相似文献
86.
In the present study, the newly synthesized TRH analog (l-pGlu-(2-propyl)-l-His-l-ProNH2; NP-647) was evaluated for its effects in in vitro (oxygen glucose deprivation (OGD)-, glutamate- and H2O2-induced injury in PC-12 cells) and in vivo (transient global ischemia) models of cerebral ischemic injury. PC-12 cells were subjected to oxygen and glucose deprivation for 6 h. Exposure of NP-647 was given before and during OGD. In glutamate and H2O2 induced injury, exposure of NP-647 was given 1, 6 and 24 h prior to exposure of glutamate and H2O2 exposure. NP-647, per se found to be non-toxic in 1-100 μM concentrations. NP-647 showed protection against OGD at the 1 and 10 μM. The concentration-dependent protection was observed in H2O2- and glutamate-induced cellular injury. In in vivo studies, NP-647 treatment showed protection of hippocampal (CA1) neuronal damage in transient global ischemia in mice and subsequent improvement in memory retention was observed using passive avoidance retention test. Moreover, administration of NP-647 resulted in decrease in inflammatory cytokines TNF-α and IL-6 as well as lipid peroxidation. These results suggest potential of NP-647 in the treatment of cerebral ischemia and its neuroprotective effect may be attributed to reduction of excitotoxicity, oxidative stress and inflammation. 相似文献
87.
Hemayatkar M Mahboudi F Majidzadeh-A K Davami F Vaziri B Barkhordari F Adeli A Mahdian R Davoudi N 《Biotechnology journal》2010,5(11):1198-1206
Recombinant tissue plasminogen activator (rt-PA) is one of the most important thrombolytic agents for treating cardiovascular obstructions such as stroke. Glycoprotein rt-PA is a serine protease, consisting of 527 amino acids of which 35 are cysteine residues. A variety of recombinant protein expression systems have been developed for heterologous gene expression in prokaryotic and eukaryotic hosts. In recent years, Leishmania tarentolae has been considered because of its safety aspects and special attributes in expression of complex proteins. In this study, two expression cassettes, each one including two copies of t-PA cDNA, were used for integration into the L. tarentolae genome by electroporation. Transformed clones were selected in the presence of appropriate antibiotics. Expression of active rt-PA was confirmed by Western blot and Zymography tests. Real-time PCR analysis was applied to investigate the presence of multiple t-PA gene copies in the parasite genome. Correlation of t-PA gene dosage and production rate was confirmed with real-time PCR. It was shown that the expression level of rt-PA in L. tarentolae is at least 480 IU/mL of culture media. This concentration of rt-PA is seven times higher than what was reported in previous studies in L. tarentolae and some other eukaryotic systems. 相似文献
88.
Singh S Ahmad R Mathur D Sagar RK Krishana B 《Indian journal of experimental biology》2006,44(9):699-704
Brain derived neurotrophic factor (BDNF) has been shown to exert trophic effects on dopaminergic neurons against 6-hydroxydopamine (6-OHDA) in young rat. Since the degeneration of substantia nigra dopaminergic neurons that occurs in Parkinson's disease is more often than not confined to elderly individuals, it is of interest to determine whether the effects of BDNF against 6 hydroxydopamine (6-OHDA) in young rats can be extended to aged animals. 6-hydroxydopamine was stereotaxically injected into the striatum of young (3-months) and aged (24-months) rats, which were treated two hours earlier with BDNF. 6-OHDA results in almost complete destruction of substantia nigra pars compacta dopaminergic neurons. BDNF injection significantly changed apomorphine induced rotations from 132 +/- 15 to 181 +/- 10, staircase test from 73 +/- 2% to 61 +/- 3%, initiation time from 7 +/- 2 to 12 +/- 1 sec, and disengage time from 80 +/- 7 to 90 +/- 5 sec in young and aged animals, respectively. It is concluded that BDNF causes the limited behavior recovery of striatal DA systems from 6-OHDA toxicity in aged animals. 相似文献
89.
Salt stress-induced changes in antioxidant enzymes, lipid peroxidation, proline and glycine betaine contents, and proline-metabolizing
enzymes were examined in the leaves of two mulberry cultivars (Local and Sujanpuri). With increasing salinity up to 150 mM
NaCl, superoxide dismutase, catalase, ascor-bate peroxidase, guaiacol peroxidase, glutathione reductase, and monodehydroascorbate
reductase activities were increased in both cultivars as compared to control, but more pronounced increase was observed in
cv. Local. Salt stress enhanced the rate of lipid peroxidation (as indicated by increasing MDA content) in both cultivars.
Under NaCl stress, cv. Local showed less change in the MDA content than cv. Sujanpuri. Salt stress resulted in a significant
accumulation of free proline in mulberry leaves, and more accumulation was detected in cv. Local than cv. Sujanpuri. The leaves
of cv. Local showed 9-fold accumulation of glycine betaine in comparision with cv. Sujanpuri after 20 days at 150 mM NaCl.
A decrease in proline oxidase activity and an increase in γ-glutamyl kinase activity were observed with increasing NaClconcentration.
The relative water content and electrolyte leakage also decreased after increasing the NaCl concentration, but a decrease
was more pronounced in cv. Sujanpuri than in cv. Local. The results indicate that oxidative stress may play an important role
in salt-stressed mulberry plants and cv. Local have more efficient antioxidant characteristics, which could provide for a
better protection against oxidative stress. 相似文献
90.
Sabrina Florent-Béchard Cédric Desbène Pierre Garcia Ahmad Allouche Ihsen Youssef Marie-Christine Escanyé Violette Koziel Marine Hanse Catherine Malaplate-Armand Christophe Stenger Badreddine Kriem Frances T. Yen-Potin Jean Luc Olivier Thierry Pillot Thierry Oster 《Biochimie》2009
In the absence of efficient diagnostic and therapeutic tools, Alzheimer's disease (AD) is a major public health concern due to longer life expectancy in the Western countries. Although the precise cause of AD is still unknown, soluble β-amyloid (Aβ) oligomers are considered the proximate effectors of the synaptic injury and neuronal death occurring in the early stages of AD. Aβ oligomers may directly interact with the synaptic membrane, leading to impairment of synaptic functions and subsequent signalling pathways triggering neurodegeneration. Therefore, membrane structure and lipid status should be considered determinant factors in Aβ-oligomer-induced synaptic and cell injuries, and therefore AD progression. Numerous epidemiological studies have highlighted close relationships between AD incidence and dietary patterns. Among the nutritional factors involved, lipids significantly influence AD pathogenesis. It is likely that maintenance of adequate membrane lipid content could prevent the production of Aβ peptide as well as its deleterious effects upon its interaction with synaptic membrane, thereby protecting neurons from Aβ-induced neurodegeneration. As major constituents of neuronal lipids, n-3 polyunsaturated fatty acids are of particular interest in the prevention of AD valuable diet ingredients whose neuroprotective properties could be essential for designing preventive nutrition-based strategies. In this review, we discuss the functional relevance of neuronal membrane features with respect to susceptibility to Aβ oligomers and AD pathogenesis, as well as the prospective capacities of lipids to prevent or to delay the disease. 相似文献