全文获取类型
收费全文 | 880篇 |
免费 | 36篇 |
国内免费 | 2篇 |
专业分类
918篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 23篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 32篇 |
2014年 | 42篇 |
2013年 | 65篇 |
2012年 | 78篇 |
2011年 | 70篇 |
2010年 | 45篇 |
2009年 | 30篇 |
2008年 | 40篇 |
2007年 | 51篇 |
2006年 | 39篇 |
2005年 | 46篇 |
2004年 | 43篇 |
2003年 | 46篇 |
2002年 | 23篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 7篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1970年 | 2篇 |
1966年 | 2篇 |
1963年 | 3篇 |
排序方式: 共有918条查询结果,搜索用时 15 毫秒
811.
Dehydrins (DHNs) compose a family of intrinsically unstructured proteins that have high water solubility and accumulate during late seed development at low temperature or in water-deficit conditions. They are believed to play a protective role in freezing and drought-tolerance in plants. A full-length cDNA encoding DHN (designated as ClDhn) was isolated from an oriental medicinal plant Codonopsis lanceolata, which has been used widely in Asia for its anticancer and anti-inflammatory properties. The full-length cDNA of ClDhn was 813 bp and contained a 477 bp open reading frame (ORF) encoding a polypeptide of 159 amino acids. Deduced ClDhn protein had high similarities with other plant DHNs. RT-PCR analysis showed that different abiotic stresses such as salt, wounding, chilling and light, triggered a significant induction of ClDhn at different time points within 4-48 hrs post-treatment. This study revealed that ClDhn assisted C. lanceolata in becoming resistant to dehydration. 相似文献
812.
Mammalian gastric mucin, at high concentration, is known to form a gel at low pH, behavior essential to the protection of the stomach from auto-digestion. Atomic force microscopy (AFM) measurements of dilute solutions of porcine gastric mucin in an aqueous environment in the pH range 6-2 provide a direct visualization of extended fiberlike molecules at pH 6 that aggregate at pH 4 and below forming well-defined clusters at pH 2. The clusters consist of 10 or less molecules. AFM images of mucin at high concentration at pH 2 reveal clusters similar to those seen in the dilute solutions at low pH. We also imaged human gastric mucus revealing a network having a "pearl necklace" structure. The "pearls" are similar in size to the clusters found in the purified porcine gastric mucin gels. AFM images of deglycosylated mucin reveal that the deglycosylated portions of the molecule re-fold into compact, globular structures suggesting that the oligosaccharide chains are important in maintaining the extended conformation of mucin. However, the oligosaccharides do not appear to be directly involved in the aggregation at low pH, as clusters of similar size are observed at pH 2 in both native and deglycosylated mucin. 相似文献
813.
Role of oxidative stress in the ammonia-induced mitochondrial permeability transition in cultured astrocytes 总被引:4,自引:0,他引:4
Ammonia is a neurotoxin that has been strongly implicated in the pathogenesis of hepatic encephalopathy (HE) and other neurological disorders, and astrocytes are thought to be the principal target of ammonia toxicity. While the precise mechanisms of ammonia neurotoxicity remain to be more clearly defined, altered bioenergetics and oxidative stress appear to be critical factors in its pathogenesis. It has recently been demonstrated that pathophysiological concentrations of ammonia induce the mitochondrial permeability transition (MPT) in cultured astrocytes, a process associated with mitochondrial dysfunction, and frequently caused by oxidative stress. This study investigated the potential role of oxidative stress in the induction of the MPT by ammonia. Accordingly, the effect of various antioxidants on the induction of the MPT by ammonia in cultured astrocytes was examined. Astrocytes were subjected to NH4Cl (5 mM) treatment for 2 days with or without various antioxidants. The MPT was assessed by quantitative fluorescence imaging for the mitochondrial membrane potential (DeltaPsim), employing the potentiometric dye TMRE; by changes in mitochondrial calcein fluorescence and by 2-deoxyglucose-6-phosphate (2-DG-6-P) changes in mitochondrial permeability. Astrocytes treated with ammonia significantly dissipated the DeltaPsim, which was blocked by the MPT inhibitor, cyclosporin A, caused a decrease in mitochondrial calcein fluorescence and increased 2-DG-6-P permeability into mitochondria. All of these findings are consistent with induction of the MPT. Pretreatment with SOD, catalase, desferroxamine, Vitamin E, PBN and the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), completely blocked the ammonia-induced MPT. These data provide strong evidence that oxidative stress is involved in the induction of the MPT by ammonia, and suggest that oxidative stress and the subsequent induction of the MPT contribute to the pathogenesis of HE and other hyperammonemic disorders. 相似文献
814.
815.
Ranga RS Sowmyalakshmi S Burikhanov R Akbarsha MA Chendil D 《Molecular and cellular biochemistry》2005,280(1-2):125-133
Lung cancer is the leading cause of cancer-related deaths throughout the world. Extracts of medicinal plants are believed
to contain different chemopreventive or chemotherapeutic compounds. In this study, we determined the anti-cancer property
of one of the traditional Indian medicine Rasagenthi Lehyam (RL) for the treatment of lung cancer. Two lung cancer cell lines (A-549 and H-460) and one normal bronchial epithelial (BEAS-2B)
cell line were used to test the chemotherapeutic effect of RL. Out of five fractions of RL, chloroform fraction of RL (cRL)
demonstrated a significant inhibition of cell proliferation and induction of apoptosis in A-549 and H-460 cells but not in
normal BEAS-2B cells. The cRL fraction up-regulated the pro-apoptotic genes p53 and Bax and induced caspase-3 activation, and down-regulated the pro-survival gene Bcl-2 in both the lung cancer cell lines. Also, nuclear export of p53 was seen in cRL-treated lung cancer cells. In addition, cRL induced G2/M arrest of cell cycle and enhanced the radio-sensitivity of both the lung cancer cell lines. This study suggests that cRL
may prove to be a potent anti-cancer agent that may be used for the treatment of lung cancer. However, further studies are
required to bring cRL into the mainstream of medicine in the treatment of lung cancer. (Mol Cell Biochem xxx: 125–133, 2005) 相似文献
816.
Genes related to sex and reproduction are known to evolve rapidly, however, the mechanism for rapid evolutionary change is
proving to be more complex than a simple relaxation of selective constraint. We compared the divergence between orthologous
human and mouse fertility genes according to their degree of dispensability as suggested by mouse knockout mutation phenotypes.
The dataset consisted of 161 orthologous genes affecting fertility and 803 orthologous genes affecting viability. We find
that essential fertility genes affecting both sexes evolve at a similar rate as essential viability genes, but that within
sexes the degree of dispensability is not an important factor affecting the rate of fertility gene evolution. We also find
no difference in the evolutionary rates of fertility genes that affect the male versus the female, however, there are a greater
number of sterility genes that affect the male. Generally there are a significantly greater number of fertility genes that
affect one sex rather than both, suggesting that fertility genes tend toward sex-specific functions, particularly in the male.
Our findings support the hypothesis that the rapid evolution of sex- and reproduction-related genes is facilitated through
an increased specialization of gene function and that dispensability is not a major factor determining their evolutionary
rate.
Electronic Supplementary Material Electronic Supplementary material is available for this article at
and accessible for authorised users.
[Reviewing Editor: Dr. Willie J. Swanson] 相似文献
817.
Signature for long-term vaccine-mediated control of a Simian and human immunodeficiency virus 89.6P challenge: stable low-breadth and low-frequency T-cell response capable of coproducing gamma interferon and interleukin-2 总被引:2,自引:0,他引:2 下载免费PDF全文
Sadagopal S Amara RR Montefiori DC Wyatt LS Staprans SI Kozyr NL McClure HM Moss B Robinson HL 《Journal of virology》2005,79(6):3243-3253
In 2001, we reported 20 weeks of control of challenge with the virulent 89.6P chimera of simian and human immunodeficiency viruses (SHIV-89.6P) by a Gag-Pol-Env vaccine consisting of DNA priming and modified vaccinia virus Ankara boosting. Here we report that 22 out of 23 of these animals successfully controlled their viremia until their time of euthanasia at 200 weeks postchallenge. At euthanasia, all animals had low to undetectable viral loads and normal CD4 counts. During the long period of viral control, gamma interferon (IFN-gamma)-producing antiviral T cells were present at unexpectedly low breadths and frequencies. Most animals recognized two CD8 and one CD4 epitope and had frequencies of IFN-gamma-responding T cells from 0.01 to 0.3% of total CD8 or CD4 T cells. T-cell responses were remarkably stable over time and, unlike responses in most immunodeficiency virus infections, maintained good functional characteristics, as evidenced by coproduction of IFN-gamma and interleukin-2. Overall, high titers of binding and neutralizing antibody persisted throughout the postchallenge period. Encouragingly, long-term control was effective in macaques of diverse histocompatibility types. 相似文献
818.
The radiosensitivities of three mouse strains (BALB/cLacY, C3H/SnY, and 101/HY) have been compared using the following parameters: survival after irradiation at a dose of 6-7 Gy, chromosome aberration frequency in bone marrow cells after irradiation at a dose of 1.5 Gy, and the change in testis weight and frequency of abnormal sperm heads (ASHs) after irradiation at doses from 0.5 to 4 Gy. Strain BALB/c is the most radiosensitive with respect to the survival and chromosome aberration frequency in the bone marrow but the most resistant with respect to the change in testis weight and the frequency of abnormal sperm heads. Strain 101/HY was the most resistant with respect to survival and chromosome aberration frequency in bone marrow after irradiation but the most radiosensitive with respect to testis damage. 相似文献
819.
Zhu YJ Crawford SE Stellmach V Dwivedi RS Rao MS Gonzalez FJ Qi C Reddy JK 《The Journal of biological chemistry》2003,278(3):1986-1990
820.
Ramaĭia LK Pomerantseva MD Malashenko AM 《Radiatsionnaia biologiia, radioecologiia / Rossi?skaia akademiia nauk》2002,42(2):169-172
The aim of the work was to study the possible protective effect of para-aminobenzoic acid (PABA) on the radiation lethality in mice of three inbred lines (BALB/cLacY, C3H/HeY, 101/Hy), stock YT1 and hybrids (C3H/He x 101/H)F1. The PABA solution was given to the mice intraperitoneally in single doses of 10, 50 and 100 mg/kg 40-50 min prior to irradiation with doses of 6 to 8 Gy depending on the line and sex of mice. The used doses of gamma-radiation were roughly LD75/30. The radioprotective effect of PABA was observed in all variants of the experiment but it was relatively low. The protection coefficient varied from 0 to 0.45. The protective effect depended on the line and sex of mice and on the dose of the injected substance. 相似文献