全文获取类型
收费全文 | 4038篇 |
免费 | 329篇 |
国内免费 | 1篇 |
专业分类
4368篇 |
出版年
2023年 | 30篇 |
2022年 | 64篇 |
2021年 | 111篇 |
2020年 | 92篇 |
2019年 | 109篇 |
2018年 | 128篇 |
2017年 | 116篇 |
2016年 | 171篇 |
2015年 | 224篇 |
2014年 | 255篇 |
2013年 | 298篇 |
2012年 | 343篇 |
2011年 | 278篇 |
2010年 | 175篇 |
2009年 | 167篇 |
2008年 | 223篇 |
2007年 | 211篇 |
2006年 | 185篇 |
2005年 | 178篇 |
2004年 | 180篇 |
2003年 | 142篇 |
2002年 | 124篇 |
2001年 | 71篇 |
2000年 | 55篇 |
1999年 | 49篇 |
1998年 | 23篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 14篇 |
1994年 | 19篇 |
1993年 | 12篇 |
1992年 | 28篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1979年 | 6篇 |
1977年 | 7篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1971年 | 7篇 |
1970年 | 5篇 |
排序方式: 共有4368条查询结果,搜索用时 0 毫秒
31.
Luciane Mendes Hatadani James O. McInerney Hermes Fonseca de Medeiros Ana Carolina Martins Junqueira Ana Maria de Azeredo-Espin Louis Bernard Klaczko 《Molecular phylogenetics and evolution》2009,51(3):595-600
We suggest a new phylogenetic hypothesis for the tripunctata radiation based on sequences of mitochondrial genes. Phylogenetic trees were reconstructed by parsimony, maximum likelihood and Bayesian methods. We performed tests for hypotheses of monophyly for taxonomic groups and other specific hypotheses. Results reject the monophyly for the tripunctata group whereas monophyly is not rejected for the tripunctata radiation and other specific groups within the radiation. Although most of the basal nodes were unresolved we were able to identify four clusters within the tripunctata radiation. These results suggest the collection of additional data before a proper taxonomic revision could be proposed. 相似文献
32.
Charlene Cavalheiro de Menezes Aracélli Gnatta Dorneles Rita Leal Sperotto Marta Medeiros Frescura Duarte Maria Rosa Chitolina Schetinger Vania Lúcia Loro 《Neurochemical research》2009,34(7):1255-1260
This study aimed to determine whether patients with aseptic and bacterial meningitis presented alterations in oxidative stress
parameters of cerebrospinal fluid (CSF). A total of 30 patients were used in the research. The CSF oxidative stress status
has been evaluated through many parameters, such as lipid peroxidation through thiobarbituric acid reactive substances (TBARS)
and antioxidant defense systems such as superoxide dismutase (SOD), glutathione S-transferase (GST), reduced glutathione (GSH) and ascorbic acid. TBARS levels, SOD and GST activity increase in aseptic meningitis
and in bacterial meningitis. The ascorbic acid concentration increased significantly in patients with both meningitis types.
The reduced glutathione levels were reduced in CSF of patients with aseptic and bacterial meningitis. In present study we
may conclude that oxidative stress contributes at least in part to the severe neurological dysfunction found in meningitis. 相似文献
33.
Recently, we proposed a quantitative model to explain the molecular mechanism of action of the Tityus serrulatus Ts3 α-toxin on sodium channels. In this model, the toxin acts as a stop that prevents the segment S4 of domain IV from reaching
its outermost position, thus impairing the normal fast inactivation without affecting activation. In the present work, we
analyze the predictions of the proposed model with regard to the voltage-dependent transitions to and from inactivation. Our
results show that the recovery from inactivation was significantly faster in Ts3-bound channels and that there was no significant
voltage dependence. The transition to inactivated state from open state in Ts3-modified channels presented a small but significant
voltage dependence, which may derive from an intrinsic voltage dependence of inactivation or by a short movement of IVS4 in
the presence of bound Ts3. We also studied the thermodynamic parameters of the voltage-dependent displacement of Ts3 from
its binding site. We have observed that the activation energy to remove the toxin is 27 kJ/mol, part of which derives from
the imposed depolarizing potential and the movement of an equivalent electrical charge of 0.54 c
0. These results support the proposed model. 相似文献
34.
35.
Daniel R. McCulloch Carine Le Goff Sumantha Bhatt Laura J. Dixon John D. Sandy Suneel S. Apte 《Gene expression patterns : GEP》2009,9(5):314-323
The secreted metalloprotease ADAMTS5 is implicated in destruction of the cartilage proteoglycan aggrecan in arthritis, but its physiological functions are unknown. Its expression profile during embryogenesis and in adult tissues is therefore of considerable interest. β-Galactosidase (β-gal) histochemistry, enabled by a LacZ cassette inserted in the Adamts5 locus, and validated by in situ hybridization with an Adamts5 cRNA probe and ADAMTS5 immunohistochemistry, was used to profile Adamts5 expression during mouse embryogenesis and in adult mouse tissues. Embryonic expression was scarce prior to 11.5 days of gestation (E11.5) and noted only in the floor plate of the developing brain at E9.5. After E11.5 there was continued expression in brain, especially in the choroid plexus, peripheral nerves, dorsal root ganglia, cranial nerve ganglia, spinal and cranial nerves, and neural plexuses of the gut. In addition to nerves, developing limbs have Adamts5 expression in skeletal muscle (from E13.5), tendons (from E16.5), and inter-digital mesenchyme of the developing autopod (E13.5–15.5). In adult tissues, there is constitutive Adamts5 expression in arterial smooth muscle cells, mesothelium lining the peritoneal, pericardial and pleural cavities, smooth muscle cells in bronchi and pancreatic ducts, glomerular mesangial cells in the kidney, dorsal root ganglia, and in Schwann cells of the peripheral and autonomic nervous system. Expression of Adamts5 during neuromuscular development and in smooth muscle cells coincides with the broadly distributed proteoglycan versican, an ADAMTS5 substrate. These observations suggest the major contexts in which developmental and physiological roles could be sought for this protease. 相似文献
36.
Fine needle aspiration of retroperitoneal human dirofilariasis with a pseudotumoral presentation 总被引:1,自引:0,他引:1
The accidental finding of a pseudotumoral para-aortic mass in a 60-year-old woman led to the performance of a fine needle aspiration (FNA) biopsy under ultrasonographic guidance. The milky aspirate was centrifuged and processed as a cell block. The examination of sections confirmed the lymphatic origin of the sample, but also revealed some unexpected parasitic structures. While a complete identification could not be made on a few sections, the morphologic and epidemiologic evidence suggested Dirofilaria repens. The mass was surgically removed and identified as an adenolymphocele, which appears to be a new localization of dirofilariasis in humans. This case emphasizes the utility of FNA in diagnosing such unexpected findings without the use for exploratory surgery. 相似文献
37.
Cervical cancer stem‐like cells: systematic review and identification of reference genes for gene expression 下载免费PDF全文
38.
El Ashry el SH Awad LF Rashed N Abdelrahman A Rasheed HA 《Nucleosides, nucleotides & nucleic acids》2008,27(3):309-317
Selective alkylation of dyphylline (1) with (2-acetoxyethoxy)methyl bromide (2a) or 4-acetoxybutyl bromide (2b) afforded 3'-O-[(acetoxyethoxy)methyl]dyphylline (3a) and 3'-O-(4-acetoxybutyl)-dyphylline (3b), respectively. A trans esterification process rather than alkylation of the dihydroxy-propyl side chain in 1 had taken place during the reaction with 2-p-toluoyloxy)ethyl chloride (5) to afford the respective 3'-toluoyloxy derivative 7 and not the anticipated 3'-O-[(p-toluoyloxy)ethyl]-dyphylline (6). Deacylation of 3a,b and 7 afforded 4a,b and 1, respectively. Viral screening of selected compounds against HBV has been investigated. 相似文献
39.
The tomato mutant ars1 (altered response to salt stress 1) identifies an R1‐type MYB transcription factor involved in stomatal closure under salt acclimation 下载免费PDF全文
40.
L H Faccioli A I Medeiros A Malheiro R C Pietro A Januário B B Vargaftig 《Mediators of inflammation》1998,7(1):41-47
Serum and BALF (bronchoalveolar lavage fluid) IL-8 levels and serum levels were investigated in Toxocara canis infected guinea-pigs and the role of IL-5 as a modulator of cytokine secretion was studied. Serum levels increased early in infected animals, exceeding control levels 4 h after infection, peaked between days 6 and 18, and continued to exceed control levels after 48 days of infection. Serum and BALF IL-8 levels showed the same profile as blood eosinophilia, increasing 6 days post-infection and peaking between days 18 and 24. Treatment of infected animals with anti-IL-5 Ab suppressed eosinophilia with a parallel increase in blood IL-8 levels, whereas no change was found in levels. To support our in vivo observation we carried out experiments in vitro using guinea-pig LPS-stimulated adherent peritoneal cells which release large amounts of IL-8 into the supernatants. When rIL-5 was added to LPS-stimulated cells, 65% inhibition of IL-8 release into the supernatants was observed. Pre-incubation of cells with anti-IL-5 Ab prevented the inhibition of IL-8 release into the supernatants induced by rIL-5. Our results demonstrate for the first time that TNF-alpha and IL-8 are released concomitant with or after IL-5 in the eosinophilic inflammation induced by T. canis. Moreover, in addition to showing that IL-5 is fundamental for the induction of blood eosinophilia, the present results suggest that this cytokine may play a new biological role by acting as modulator of IL-8 secretion. 相似文献