全文获取类型
收费全文 | 94124篇 |
免费 | 7999篇 |
国内免费 | 6717篇 |
出版年
2024年 | 128篇 |
2023年 | 981篇 |
2022年 | 2251篇 |
2021年 | 4318篇 |
2020年 | 2863篇 |
2019年 | 3493篇 |
2018年 | 3536篇 |
2017年 | 2503篇 |
2016年 | 3473篇 |
2015年 | 5575篇 |
2014年 | 6486篇 |
2013年 | 7180篇 |
2012年 | 8428篇 |
2011年 | 7771篇 |
2010年 | 4719篇 |
2009年 | 4247篇 |
2008年 | 5047篇 |
2007年 | 4554篇 |
2006年 | 3901篇 |
2005年 | 3300篇 |
2004年 | 2835篇 |
2003年 | 2454篇 |
2002年 | 2143篇 |
2001年 | 1849篇 |
2000年 | 1844篇 |
1999年 | 1694篇 |
1998年 | 1020篇 |
1997年 | 945篇 |
1996年 | 935篇 |
1995年 | 822篇 |
1994年 | 793篇 |
1993年 | 593篇 |
1992年 | 895篇 |
1991年 | 717篇 |
1990年 | 657篇 |
1989年 | 565篇 |
1988年 | 449篇 |
1987年 | 382篇 |
1986年 | 349篇 |
1985年 | 323篇 |
1984年 | 232篇 |
1983年 | 212篇 |
1982年 | 126篇 |
1981年 | 121篇 |
1980年 | 90篇 |
1979年 | 149篇 |
1978年 | 89篇 |
1977年 | 97篇 |
1975年 | 112篇 |
1974年 | 119篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
61.
62.
It is still a difficult clinical issue to decide whether a patient is a suitable candidate for a cochlear implant and to plan postoperative rehabilitation, especially for some special cases, such as auditory neuropathy. A partial solution to these problems is to preoperatively evaluate the functional integrity of the auditory neural pathways. For evaluating the strength of phase-locking of auditory neurons, which was not reflected in previous methods using electrically evoked auditory brainstem response (EABR), a new method for recording phase-locking related auditory responses to electrical stimulation, called the electrically evoked frequency-following response (EFFR), was developed and evaluated using guinea pigs. The main objective was to assess feasibility of the method by testing whether the recorded signals reflected auditory neural responses or artifacts. The results showed the following: 1) the recorded signals were evoked by neuron responses rather than by artifact; 2) responses evoked by periodic signals were significantly higher than those evoked by the white noise; 3) the latency of the responses fell in the expected range; 4) the responses decreased significantly after death of the guinea pigs; and 5) the responses decreased significantly when the animal was replaced by an electrical resistance. All of these results suggest the method was valid. Recording obtained using complex tones with a missing fundamental component and using pure tones with various frequencies were consistent with those obtained using acoustic stimulation in previous studies. 相似文献
63.
64.
R H?kanson D Chen E Lindstr?m P Norlén M Bj?rkqvist D Lehto-Axtelius 《The Yale journal of biology and medicine》1998,71(3-4):163-171
The enterochromaffin-like (ECL) cells of the oxyntic mucosa (fundus) of the stomach produce, store and secrete histamine, chromogranin A-derived peptides such as pancreastatin, and an unanticipated but as yet unidentified peptide hormone. The cells are stimulated by gastrin and pituitary adenylate cyclase activating peptide and suppressed by somatostatin and galanin. Choline esters and histamine seem to be without effect on ECL cell secretion. The existence of a gastrin-ECL cell axis not only explains how gastrin stimulates acid secretion but also may help to explore the functional significance of the ECL cells with respect to the nature and bioactivity of its peptide hormone. From the results of studies of gastrectomized/fundectomized and gastrin-treated rats, it has been speculated that the anticipated ECL-cell peptide hormone acts on bone metabolism. 相似文献
65.
66.
67.
Hongchi Yu Yang Shen Jingsi Jin Yingying Zhang Tang Feng 《Cell Adhesion & Migration》2018,12(1):56-68
Hepatocellular carcinoma (HCC) is a subtype of malignant liver cancer with poor prognosis and limited treatment options. It is noteworthy that mechanical forces in tumor microenvironment play a pivotal role in mediating the behaviors and functions of tumor cells. As an instrumental type of mechanical forces in vivo, fluid shear stress (FSS) has been reported having potent physiologic and pathologic effects on cancer progression. However, the time-dependent mechanochemical transduction in HCC induced by FSS remains unclear. In this study, hepatocellular carcinoma HepG2 cells were exposed to 1.4 dyn/cm2 FSS for transient duration (15s and 30s), short duration (5 min, 15 min and 30 min) and long duration (1h, 2h and 4h), respectively. The expression and translocation of Integrins induced FAK-Rho GTPases signaling events were examined. Our results showed that FSS endowed HepG2 cells with higher migration ability via reorganizing cellular F-actin and disrupting intercellular tight junctions. We further demonstrated that FSS regulated the expression and translocation of Integrins and their downstream signaling cascade in time-dependent patterns. The FSS downregulated focal adhesion components (Paxillin, Vinculin and Talin) while upregulated the expression of Rho GTPases (Cdc42, Rac1 and RhoA) in long durations. These results indicated that FSS enhanced tumor cell migration through Integrins-FAK-Rho GTPases signaling pathway in time-dependent manners. Our in vitro findings shed new light on the role of FSS acting in physiologic and pathological processes during tumor progression, which has emerged as a promising clinical strategy for liver carcinoma. 相似文献
68.
Lysine acetylation, one of the major types of post-translational modifications, plays critical roles in regulating gene expression and protein function. Histone deacetylases(HDACs) are responsible for removing acetyl groups from lysines of both histone and non-histone proteins. While tremendous progress has been made in understanding the function and mechanism of HDACs in animals in the past two decades, nearly half of the HDAC studies in plants were reported within the past five years. In this review,we summarize the major findings on plant HDACs, with a focus on the model plant Arabidopsis thaliana, and highlight the components, regulatory mechanisms, and biological functions of HDAC complexes. 相似文献
69.
Jian Xiao Dan Chen Xiu-Xian Lin Shi-Fang Peng Mei-Fang Xiao Wei-Hua Huang Yi-Cheng Wang Jing-Bo Peng Wei Zhang Dong-Sheng Ouyang Yao Chen 《PloS one》2016,11(2)
Ginsenoside compound K (CK), a rare ginsenoside originating from Panax Ginseng, has been found to possess unique pharmacological activities specifically as anti-cancers. However, the role of cytochrome P450s (CYPs) in the metabolism of CK is unclear. In this study, we screened the CYPs for the metabolism of CK in vitro using human liver microsomes (HLMs) or human recombinant CYPs. The results showed that CK inhibited the enzyme activities of CYP2C9 and CYP3A4 in the HLMs. The Km and Vmax values of CK were 84.20±21.92 μM and 0.28±0.04 nmol/mg protein/min, respectively, for the HLMs; 34.63±10.48 μM and 0.45±0.05 nmol/nmol P450/min, respectively, for CYP2C9; and 27.03±5.04 μM and 0.68±0.04 nmol/nmol P450/min, respectively, for CYP3A4. The IC50 values were 16.00 μM and 9.83 μM, and Ki values were 14.92 μM and 11.42μM for CYP2C9 and CYP3A4, respectively. Other human CYP isoforms, including CYP1A2, CYP2A6, CYP2D6, CYP2E1, and CYP2C19, showed minimal or no effect on CK metabolism. The results suggested that CK was a substrate and also inhibitors for both CYP2C9 and CYP3A4. Patients using CK in combination with therapeutic drugs that are substrates of CYP2C9 and CYP3A4 for different reasons should be careful, although the inhibiting potency of CK is much poorer than that of enzyme-specific inhibitors. 相似文献
70.